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ASME Conference Presenter Attendance Policy and Archival Proceedings

2011;():i. doi:10.1115/IMECE2011-NS7.
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This online compilation of papers from the ASME 2011 International Mechanical Engineering Congress and Exposition (IMECE2011) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in the ASME Digital Library and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Dynamic Systems and Control

2011;():1-14. doi:10.1115/IMECE2011-62030.

Damage detection and localization allow for automated real-time monitoring of engineered systems. The benefits of such a system include improved safety, lower maintenance costs, and higher reliability. Many of the early works focus almost exclusively on numerical simulations of real systems, with very little experimentally acquired data used in detection. Introducing real world data complicates the analysis significantly by requiring noise reducing techniques to acquire legitimate results. Further, the cost of obtaining enough data to fully define a damaged system can quickly become prohibitive. This paper focuses on damage detection schemes carried out through empirical means. First a concept proving scheme is used by which data about the system is collected through accelerometer data. The damage detection scheme requires the reduction of a large set of data to one or two descriptive eigen parameters. Second, the scheme is repeated using optically gathered data through use of a high speed camera and software image manipulation tools. Damage detection is shown to be possible under the same conditions and initial parameters. Localization of the damage, however, is shown to require sensor information from multiple locations. Further still the optically based method is shown to supplement a failed detection by other means.

Commentary by Dr. Valentin Fuster
2011;():15-23. doi:10.1115/IMECE2011-62271.

Sliding mode controller for trajectory tracking of a surface vessel is designed based on a 3DOF dynamic model. The model has six unknown parameters. For parameter identification, four special test scenarios are defined to isolate and identify one of the six parameters at a time. The identification tests are performed on a robotic boat which has an onboard PC104 computer and a navigation sensor providing vessel’s dynamic states in real-time. The data from experiments are used to determine the model parameters. A sliding mode controller is designed based on the identified model, and is implemented and tested on a real robotic boat. The experiments show the excellent performance of the controller.

Commentary by Dr. Valentin Fuster
2011;():25-31. doi:10.1115/IMECE2011-62608.

Chilled water systems used in the industry and on board ships are critical for safe and reliable operation. It is hence important to understand the fundamental physics of these systems. This paper focuses in particular on a critical part of the automation system, namely, actuators and valves that are used in so-called “smart valve” systems. The system is strongly nonlinear, and necessitates a nonlinear dynamic analysis to be able to predict all critical phenomena that affect effective operation and efficient design. The derived mathematical model includes electromagnetics, fluid mechanics, and mechanical dynamics. Nondimensionalization has been carried out in order to reduce the large number of parameters to a few critical independent sets to help carry out a broad parametric analysis. The system stability analysis is then carried out by the aid of the tools from nonlinear dynamic analysis. This reveals that the system is unstable in a certain region of the parameter space. The system is also shown to exhibit crisis and chaotic responses; this is characterized using Lyapunov exponents and power spectra. Knowledge and avoidance of these dangerous regimes is necessary for successful and safe operation.

Topics: Actuators , Valves , Solenoids
Commentary by Dr. Valentin Fuster
2011;():33-43. doi:10.1115/IMECE2011-62944.

Nonlinear dynamical behaviors of a train suspension system with impacts are investigated. The suspension system is described through an impact model with possible stick between a bolster and two wedges. The analytical conditions that reflect the motion mechanisms for the complex motion are given. The mapping structures for periodic and chaotic motions of such a system can be described. The analytical prediction of the complex motions can be conducted from the mapping structure, and numerical simulations for periodic and chaotic motions can be carried out in sequel.

Commentary by Dr. Valentin Fuster
2011;():45-53. doi:10.1115/IMECE2011-62947.

In this paper, switchability and bifurcation of motions in a double excited Fermi acceleration oscillator is discussed using the theory of discontinuous dynamical systems. The two oscillators are chosen to have different excitation and parameters. The analytical conditions for motion switching in such a Fermi-oscillator are presented. Bifurcation scenario for periodic and chaotic motions is presented, and the analytical predictions of periodic motions are presented. Finally, different motions in such an oscillator are illustrated.

Topics: Bifurcation
Commentary by Dr. Valentin Fuster
2011;():55-61. doi:10.1115/IMECE2011-62949.

In this paper, the analytical, approximate solutions of period-1 motions in the nonlinear damping, periodically forced, Duffing oscillator is obtained. The corresponding stability and bifurcation analysis of the HB2 approximate solution of period-1 motions in the forced Duffing oscillator is carried out. Numerical illustrations of period-1 motions are presented.

Commentary by Dr. Valentin Fuster
2011;():63-71. doi:10.1115/IMECE2011-62955.

In this paper, chaotic synchronization of a controlled, noised gyroscope system with an expected gyroscope system is investigated. From the theory of discontinuous dynamical systems, the necessary and sufficient conditions of such synchronization are presented. Numerical simulations for non-synchronization, partial and full chaotic synchronizations of two gyroscope systems are carried out.

Topics: Synchronization
Commentary by Dr. Valentin Fuster
2011;():73-82. doi:10.1115/IMECE2011-63153.

Synchronization of coupled, self-excited oscillators in complex systems is a common occurance. This report examines the effects of thermal coupling through the walls of a building on temperature oscillations due to hysteretic thermostatic control. The specific case of three rooms is studied. A system of differential equations models the dynamics of each room temperature, accounting for on-off heating, heat loss to the environment, and heat exchange between rooms. Three types of solutions are observed: one in which all room temperatures oscillate in phase, another with the oscillations equidistant in phase, and a third that is time-independent. The existence and linear stability of each solution type is investigated as a function of a parameter k that represents the thermal interaction between neighboring rooms. The in-phase behavior exists and is linearly stable for all k, the out-of-phase oscillations exist in a band of k and are stable in a smaller band, and the time-independent solution exists above a certain k where they are stable.

Commentary by Dr. Valentin Fuster
2011;():83-92. doi:10.1115/IMECE2011-63564.

Control of fluid flow is an important, and quite underutilized process possessing significant potential benefits ranging from avoidance of separation and stall on aircraft wings and reduction of friction factors in oil and gas pipelines to mitigation of noise from wind turbines. But the Navier–Stokes (N.–S.) equations governing fluid flow consist of a system of time-dependent, multi-dimensional, non-linear partial differential equations (PDEs) which cannot be solved in real time using current, or near-term foreseeable, computing hardware. The poor man’s Navier–Stokes (PMNS) equations comprise a discrete dynamical system that is algebraic—hence, easily (and rapidly) solved—and yet which retains many (possibly all) of the temporal behaviors of the full (PDE) N.–S. system at specific spatial locations. In this paper we outline derivation of these equations and present a short discussion of their basic properties. We then consider application of these equations to the problem of control by adding a control force. We examine the range of PMNS equation behaviors that can be achieved by changing values of this control force, and, in particular, consider controllability of this (non-linear) system via numerical experiments. Moreover, we observe that the derivation leading to the PMNS equations is very general, and, at least in principle, it can be applied to a wide variety of problems governed by PDEs and (possibly) time-delay ordinary differential equations such as, for example, models of machining processes.

Commentary by Dr. Valentin Fuster
2011;():93-106. doi:10.1115/IMECE2011-63967.

Cylindrical shells under a moving internal pressure has wide applications such as oil, gas, and water transmission and distribution pipelines, gun tubes, pressured aircraft fuselages, rocket casings, space station modules, and pulse detonation engines. As a moving load produces larger deformations and higher stresses than does an equivalent static load, the study of this kind of problems has significant importance in design and optimization of such structures. The problem of a cylindrical shell subjected detonation loading has been studied by many researchers, but there are still some problems that need to be further investigated, especially in the application aspect. In this work, analytical solutions for cylindrical shells under detonation loading are developed. The analytical solutions include static state and transient state. For transient state, three analytical models are presented. Numerical results show these analytical solutions are reliable and stable.

Topics: Explosions , Pipes
Commentary by Dr. Valentin Fuster
2011;():107-113. doi:10.1115/IMECE2011-64140.

Damage detection is important for sensing and analyzing the degradation of structures, and can effectively avoid potential catastrophic failures. Among the numerous studies in literature, most emphasis was given to the damage detection based on vibration response signals for simple beam structures. In this paper, the feasibility of roughness method for plates was investigated using both vibration-based data and static deformation data. Two detection methods, namely, roughness method and fractal dimension method, were used to analyze the data. Both types of data were obtained for aluminum plates using finite element simulation. It was found that both methods were able to detect the damage and locate its position precisely with the two types of signals. The effectiveness of damage detection using static deformation data was further demonstrated by experimenting with a cracked cantilever beam. A computer vision camera efficiently and automatically collected the static deformation data, and this approach showed great potential compared with the expensive and time-consuming collection process for vibration response data such as mode shapes.

Commentary by Dr. Valentin Fuster
2011;():115-125. doi:10.1115/IMECE2011-64773.

This work concerns the implementation of nonlinear modal reduction to flexible multi-body dynamics. Linear elastic theory will lead to instability issues with rotating beamlike structures, due to the neglecting of the membrane-bending coupling on the beam cross-section. During the past decade, considerable efforts have been focused on the derivation of geometric nonlinear formulation based on nodal coordinates. In this work, in order to improve the convergence characteristic and also to reduce the computation time in flexible multi-body dynamics, which is extremely important for complicated large systems, a standard modal reduction procedure based on matrix operation is developed with essential geometric stiffening nonlinearities retained in the equation of motion. The example used in this work is a rotating Euler-Bernoulli beam, two nonlinear reduced models were established based on modal coordinates, the first reduced model created from theoretical bending and axial mode shapes by Galerkin method; the second reduced model is derived by the standard matrix operator from a full finite element model. Transient simulation results of lower degrees of freedom from above two reduced models are compared with those obtained from full nonlinear finite element model.

Commentary by Dr. Valentin Fuster
2011;():127-136. doi:10.1115/IMECE2011-62105.

This paper proposes a leader-following formation control strategy for a group of mobile robots. The nonholonomic constraints of the mobile robots, instead of the usual point-mass assumption, are taken into account in the design of the formation control. The proposed formation control computes desired driving force and steering torque, instead of desired translational and angular velocities, for each robot. The proposed control consists of a formation control scheme and a kinematic trajectory generation scheme for the leader of a group. In the design of the proposed control schemes, the Lyapunov stability theorem is used as a mathematical tool. The leader follows its desired trajectory while the rest of robots are following the leader in a specified formation. Under certain conditions, the proposed formation control guarantees asymptotic stability while keeping all internal signals bounded. The effectiveness of the proposed control has been shown with realistic computer simulations.

Topics: Mobile robots
Commentary by Dr. Valentin Fuster
2011;():137-144. doi:10.1115/IMECE2011-62270.

A control system for the walking of a redundant biped robot in the swing phase is considered. The biped is a humanoid with 6DOF per leg and 3DOF per arm. The controller will be based on a full kinematic model of the robot to depict a more accurate behavior of the robot. The arms of the robot are used to compensate for disturbances the robot may experience during walking. Instead of controlling the robots ZMP, keeping it within the support polygon, all six foot support reaction components are controlled. First, a “shoe” with force sensors detect the forces and moments on the foot for feedback. The feedback from the joint servos provide position and velocity information. The support reaction and the joint position/velocities are fedback to a sliding mode controller, which makes adjustments to the arm links’ acceleration to compensate the shift in the reaction components. Simulations show the comparison of the ZMP shift when disturbances are applied with and without controlling the reaction forces to prove the effectiveness of the approach.

Commentary by Dr. Valentin Fuster
2011;():145-153. doi:10.1115/IMECE2011-62328.

A challenge for cylinder-slider parallel manipulators is their limited workspace and singularity-free path generation. In this paper, the linkage feasibility conditions are derived based on the elimination of dead point position within the workspace. The workspace is generated using the curve-enveloping theory. The singularity-free path generation capability is analyzed. The performance index contours within the workspace are produced using the condition number of the manipulator Jacobian matrix. This paper shows that five-bar cylinder-slider parallel manipulators can be used as effective singularity-free path generators if properly designed. The results of this paper provide a useful map for designing this type of parallel manipulator.

Commentary by Dr. Valentin Fuster
2011;():155-165. doi:10.1115/IMECE2011-62329.

The design domain of a synthesized compliant mechanism is discretized into quadrilateral design cells in both hybrid and quadrilateral discretization models. However, quadrilateral discretization model allows for point connection between two diagonal design cells. Hybrid discretization model completely eliminates point connection by subdividing each quadrilateral design cell into triangular analysis cells and connecting any two contiguous quadrilateral design cells using four triangular analysis cells. When point connection is detected and suppressed in quadrilateral discretization, the local topology search space is dramatically reduced and slant structural members are serrated. In hybrid discretization, all potential local connection directions are utilized for topology optimization and any structural members can be smooth whether they are in the horizontal, vertical or diagonal direction. To compare the performance of hybrid and quadrilateral discretizations, the same design and analysis cells, genetic algorithm parameters, constraint violation penalties are employed for both discretization models. The advantages of hybrid discretization over quadrilateral discretization are obvious from the results of two classical synthesis examples of compliant mechanisms.

Commentary by Dr. Valentin Fuster
2011;():167-172. doi:10.1115/IMECE2011-62613.

Automated equipment is used for the ship fabrication process for higher productivity. However, in final assembly stage of ship structures, automatic welding system has the constraints for application because of inclination and curvature of the hull block. In order to solve these problems, an automatic welding system which has special mechanism to travel on the flexible rail has been studied. This paper describes the essential characteristics of the new automatic welding system equipped with the proper mechanism for flexible rail and continuously adjustable welding torch slider.

Topics: Welding
Commentary by Dr. Valentin Fuster
2011;():173-181. doi:10.1115/IMECE2011-62852.

Due to the nonlinear dynamics of hydraulic systems, applying high performance closed-loop controllers is complicated. In this paper, a single-rod hydraulic actuator is considered in which load displacement (for positioning purposes) is controlled via manipulation of the input voltage to the servo-valve. Dynamics of the servo-valve is described by first and second order transfer functions (named as Models 1 and 2). Through linearization of the system around its operating points, dynamics of the hydraulic actuator is represented in the state space. A full-order observer is designed for on-line states estimation. Then, feedback control system is designed for both regulation and tracking objectives through pole-placement approach based on general canonical control form (GCCF). For tracking of the desired commands, a modified integral control is required (since the plant has not integrator). Results show that the regulation, states estimation, desired tracking and final tracking accuracy are achieved after applying the controller. Required input voltage and load positioning are compared for the two distinct dynamics of the servo-valve (Model 1 and 2).

Commentary by Dr. Valentin Fuster
2011;():183-190. doi:10.1115/IMECE2011-63106.

In this work, size optimization of a single link flexible robotic manipulator is carried out by considering the link as an Euler-Bernoulli beam. Finite element method is used for obtaining the natural frequencies and time response. Sequential quadratic programming method is used to maximize fundamental frequencies of the manipulator for different designs. A comparative study of the optimized designs is carried out to find out their suitability for real world situation. Based on the numerical experimentation, suggestion for formulating optimization problem for varying tip loads is provided.

Commentary by Dr. Valentin Fuster
2011;():191-198. doi:10.1115/IMECE2011-63482.

Inspired by the octopus and snakes, we designed and built a wire-driven serpentine robot arm. The robot arm is made of a number of rigid nodes connected by two sets of wires. The rigid nodes act as the backbone while the wires work as the muscle, which enables the 2 DOF bending. The forward kinematics is derived using D-H method, while the inverse kinematics and its workspace can be solved by geometric analysis. To validate the design, a prototype is built. It is found that the positioning error of the robot arm is generally less than 2%. The advantage of this robot arm is that with several nodes fixed the rest nodes are still controllable. The positioning error is smaller when the fixed node is closer to the end effector.

Topics: Robots , Wire , Design , Biomimetics
Commentary by Dr. Valentin Fuster
2011;():199-205. doi:10.1115/IMECE2011-63960.

A novel three-dimensional robotic surface is devised and implemented using triangular modules. Each module is connected by a passive sixbar mechanism that mimics the constraints of a spherical joint at each triangle intersection. The finite element method (FEM) is applied to the static loading of this device using linear three dimensional (6 degrees of freedom) beam elements to calculate the cartesian displacement and force and the angular displacement and torque at each joint. In this way, the traditional methods of finding joint forces and torques are completely bypassed. An effiecient algorithm is developed to linearly combine local stiffness matrices into a full structural stiffness matrix for the easy application of loads. This is then decomposed back into the local matrices to easily obtain joint variables used in the design and open-loop control of the surface.

Commentary by Dr. Valentin Fuster
2011;():207-214. doi:10.1115/IMECE2011-64050.

Mobile robots face great challenges in terms of mobility when traversing rough terrain, especially obstacle filled environments. Current terrestrial locomotion mechanisms such as wheels, tracks, and legs, face difficulties surmounting obstacles equal to or greater than their own height. This is especially true for smaller robots. In this respect, bioinspired approaches offer some solutions. Some insects in particular tackle rough terrain locomotion by performing high powered jumps. Their morphology has evolved to create specialized energy storage structures, and their hind legs have adapted to provide improved mechanical leverage. This paper investigates jumping as employed by insects and develops principles pertinent for the design of a jumping robotic system. A mathematical model depicting bipedal jumping is presented. The model includes mechanical energy storage elements in the form of springs for the purpose of assessing jumping locomotion for robotic applications. This model will assist in analyzing jumping locomotion and presenting some insights, as well as rough dimensioning of system parameters to achieve desired jumping performance.

Commentary by Dr. Valentin Fuster
2011;():215-222. doi:10.1115/IMECE2011-64055.

An approach to concurrent type and dimensional synthesis of planar mechanisms is presented. Using graph-theoretic enumeration of mechanisms and determination of loops, automatic loop closure equations are generated. Using constrained optimization routines based on descent methods, and given an appropriate goal function, optimal mechanism designs can be determined. These are not limited to traditional problems such as rigid-body guidance and path generation, but can be more flexibly expressed according to designer needs. This method can be effective at finding mechanism solutions when topology has not been determined a priori and may also be extensible to synthesis of spatial mechanisms. This paper presents the data flow and algorithm outline, simulation results, and examples of nonstandard synthesis problems solvable with this method.

Commentary by Dr. Valentin Fuster
2011;():223-232. doi:10.1115/IMECE2011-64137.

This paper presents the analysis of a 2 DOF end-effector that carries out a haptic tool consisting in a developable servo-actuated plastic strip. To overcome some drawbacks of conventional systems related to the use of point based force-feedback, tactile and glove devices we have developed the triangular mesh approach in the developable haptic interface. The developable haptic strip, has evolved as a result of this research. The haptic interface of our system consists of a haptic strip that is inspired by the deformable tape that designers use for creating and modifying aesthetic shapes. The first step for designing the end effector and the haptic strip mechanism has been the assignment of both the total length of the haptic strip and the number of tessellation triangles required to control the strip as a developable surface. The strip is aimed at haptically rendering medium sized design objects (vases, lamps, household appliances, etc.). Thus, the total length of the strip has been set to be 160 mm. This length value also ensures the possibility to easily manipulate the strip. Seven triangles have been assigned in order to maintain the haptic strip symmetric; this consideration is particularly important because guarantees an adequate balancing of weight in the mechanism. The device is based on a modular architecture of elements that deform a plastic tape.

Commentary by Dr. Valentin Fuster
2011;():233-239. doi:10.1115/IMECE2011-64278.

Straight-line motion, albeit simple, manifest itself in numerous applications, from running steam engines and oil wells to manufacturing parts with straight edges and sides. The drive to maximize production creates a need for continuously running assembly-line manufacturing comprised of precise, individually optimized components. While there are many so-called straight-line generating mechanisms, few actually produce a true straight-line, most generate only approximate straight-line. Featured an eight-link rhomboidal system with length constraints, the Peaucellier mechanism is one that actually produces a true straight line intrinsically. This paper presents a study on the dimension synthesis of the Peaucellier mechanism, namely by identifying the correct ratio of linkage lengths to produce the longest straight line stroke. In addition to designing for stroke, another objective of interest is to attain a desired velocity profile along the path. Kinematic analysis of the velocity profile on the mechanism will render the creation of input angular velocity standards based on desired stroke speed. Given the stroke and velocity specifications, specific steps to size the dimensions of the mechanism developed as result of this study will be presented.

Commentary by Dr. Valentin Fuster
2011;():241-257. doi:10.1115/IMECE2011-64527.

Robotic manipulators are complex mechanisms due to which their kinematics and dynamics are nonlinear in nature and computationally intensive. Fuzzy logic based approach provides an alternative for modeling and control of non-linear systems and hence has been extensively applied in the field of robotics. This paper presents a review of fuzzy logic based techniques for modeling and control of robotic manipulators. The survey is reported in terms of objectives, types of robotic manipulators, types and structures of fuzzy systems employed. A summary of quantitative results is presented as performance indicators of fuzzy modeling and control of robotic manipulators.

Commentary by Dr. Valentin Fuster
2011;():259-268. doi:10.1115/IMECE2011-64699.

In many applications, it is required that heterogeneous multi-robots are grouped to work on multi-targets simultaneously. Therefore, this paper proposes a control method for a single-master multi-slave (SMMS) teleoperator to cooperatively control a team of mobile robots for a multi-target mission. The major components of the proposed control method are the compensation for contact forces, modified potential field based leader-follower formation, and robot-task-target pairing method. The robot-task-target paring method is derived from the proven auction algorithm for a single target and is extended for multi-robot multi-target cases, which optimizes effect-based robot-task-target pairs based on heuristic and sensory data. The robot-task-target pairing method can produce a weighted attack guidance table (WAGT), which contains benefits of different robot-task-target pairs. With the robot-task-target pairing method, subteams are formed by paired robots. The subteams perform their own paired tasks on assigned targets in the modified potential field based leader-follower formation while avoiding sensed obstacles. Simulation studies illustrate system efficacy with the proposed control method.

Commentary by Dr. Valentin Fuster
2011;():269-276. doi:10.1115/IMECE2011-64762.

A novel piezoelectric energy harvester with multi-mode dynamic magnifier is proposed and investigated in this paper, which is capable of significantly increasing the bandwidth and the energy harvested from the ambient vibration. The design comprises of an multi-mode intermediate beam with a tip mass, called “dynamic magnifier”, and an “energy harvesting beam with a tip mass. The piezoelectric film is adhered to the harvesting beam to harvest the vibration energy. By properly designing the parameters, such as the length, width and thickness of the two beams and the weight of the two tip masses, we can virtually magnify the motion in all the resonance frequencies of the energy harvesting beam, in a similar way as designing a new beam-type tuned mass damper (TMD) to damp the resonance frequencies of all the modes of the primary beam. Theoretical analysis, finite element simulation, and the experiment study are carried out. The results show that voltage produced by the harvesting beam is amplified for efficient energy harvesting over a broader frequency range, while the peaks of the first three modes of the primary beam can be effectively mitigated simultaneously. The experiment demonstrates 25.5 times more energy harvesting capacity than the conventional cantilever type harvester in broadband frequency 3–300Hz, and over 1000 times more energy close to the first three resonances of harvesting beam.

Topics: Dampers , Vibration
Commentary by Dr. Valentin Fuster
2011;():277-284. doi:10.1115/IMECE2011-65471.

The kinematics design of a new mobile robot suspension for unstructured environments is presented in this paper. This design incorporates an adaptable-passive mechanism that compensates for irregularities of terrain. The new mechanism comprises two pairs of bogies joined by a crank-slider mechanism. The kinematic analysis and numerical simulations of the robot have been carried out and are presented. Two performance indexes based on the tilt angle of the payload platform and velocity of the front wheel are proposed and used as a mean of performance evaluation. From a comparative analysis of reported mobile robots in the specialized literature several advantages of the new system are identified. Moreover the results have shown that the system is able to overcome most types of obstacles with a minimum variation of the tilt angle of the payload platform.

Commentary by Dr. Valentin Fuster
2011;():285-293. doi:10.1115/IMECE2011-65613.

This paper presents the modeling and analysis of an electromagnetic harvester for potential applications in large-scale vibration energy harvesting such as from vehicle suspensions or civil structures. The kinematics and dynamics of a motion mechanism and generator are considered, including backlash and friction. In this study, a dynamic model for a rack-pinion type regenerative shock absorber has been derived and analyzed based on differential equations. To understand the influence of the friction and backlash on the system, nonlinear models have been created. Simulations are carried out to study the features of the design. The validation of the models is demonstrated by comparing the simulation results with experimental measurements. Guidelines are given for the design of this type of regenerative shock absorbers.

Topics: Motion , Modeling , Vibration
Commentary by Dr. Valentin Fuster
2011;():295-300. doi:10.1115/IMECE2011-65649.

The Clock-Torqued Spring-Loaded Inverted Pendulum (CT-SLIP) model is extended to predict both leg revolution and oscillation behaviors. With this model we demonstrate that the center-of-mass locomotion dynamics of both leg revolution and oscillation cases have identical local stability with respect to small perturbations, while global stability (with respect to large perturbations) shows differences. This extension of the CT-SLIP model and comparative analysis has potential benefits in robot path planning where there may be a choice between a leg revolution or oscillation. Further, this analysis helps relate mathematical models and physical models based on leg revolution to animal locomotion that is dependent on leg retraction and oscillation.

Topics: Oscillations , Robots
Commentary by Dr. Valentin Fuster
2011;():301-306. doi:10.1115/IMECE2011-65652.

A reduced model of legged locomotion, called the Spring Loaded Inverted Pendulum (SLIP) has previously been developed to predict the dynamics of locomotion. However, due to energy conservation, the SLIP model can only be partially asymptotically stable in the center-of-mass velocity. The more recently developed Clock-Torqued Spring Loaded Inverted Pendulum (CT-SLIP) model is fully asymptotically stable, and has a significantly larger stability basin than SLIP, but requires more than twice as many parameters. To more completely explore the parameter space and understand the reason for improved stability, we develop and analyze a further reduced model called the Forced-Damped Spring Loaded Inverted Pendulum (FD-SLIP) model.

Topics: Stability , Springs
Commentary by Dr. Valentin Fuster
2011;():307-316. doi:10.1115/IMECE2011-62153.

This paper demonstrates the use of two feed-forward control algorithms in order to mitigate crack propagation in a simply supported beam with a pre-existing crack. The main objective of the control algorithms is to minimize or reduce transverse deflection at the crack location so as to contain the damage resulting from the pre-existing crack and, thereby, reduce the rate of crack propagation. A point-load sinusoidal excitation, from a known disturbance, is used as the input load acting on the beam. Two control algorithms are used — the first control algorithm computes a control force to eliminate transverse displacement at the crack location resulting from the excitation force, and the second control algorithm minimizes the mean square transverse displacement over a section of the beam that contains the crack. Both the control algorithms are a-causal and assume that the excitation input is completely known a-priori. Simulation results for a simply supported beam are presented and discussed in detail. It is observed that the rate of crack propagation can be significantly reduced by implementing the proposed feed-forward control algorithms, increasing the useful life of the damaged beam. Also, it is found that the transverse displacement over a significant length of the beam can be substantially reduced when the beam response is dominated by a specific mode.

Commentary by Dr. Valentin Fuster
2011;():317-323. doi:10.1115/IMECE2011-62635.

The aim of this work is the reduction of the steady state amplitude of harmonically forced simply supported beams using mass dampers. The considered system consists of a mass damper attached to a simply supported beam with a harmonic force applied at a given point along its span. Traditionally, passive vibration devices such as mass spring dampers or mass dampers were attached to beams and carefully designed to minimize the maximum amplitude at a given point along their span. Since minimizing the amplitude at one point of the beam might increase it at another point, in this work the maximum amplitude along the entire beam span is minimized. The problem is solved first using an approximate method. For a given mass ratio, the optimal location of the mass damper is determined first, and then the optimal damping constant is calculated. Fixed-lines of the amplitude of the entire span of the beam which are independent of the damping constant are determined. The optimal placement of the mass damper is chosen such that the maximum of these lines is minimized. Then, the optimal damping constant is obtained analytically from an average of two damping ratios corresponding each to one of the peaks of the amplitude of the entire beam span to coincide with one of the two equally leveled maxima of the fixed-lines. The optimal placement and damping constant are calculated for all possible positions of the point force on the beam. These results are compared to those obtained from an exact numerical optimization procedure. The results are written in dimensionless form and can be applied to a system with any material and geometric properties.

Topics: Dampers
Commentary by Dr. Valentin Fuster
2011;():325-334. doi:10.1115/IMECE2011-62651.

In roll balancing the behaviour of the roll can be studied either experimentally with trial weights or, if the roll dimensions are known, analytically by forming a model of the roll to solve response to imbalance. Essential focus in roll balancing is to find the correct amount and placing for the balancing mass or masses. If this selection is done analytically the roll model used in calculations has significant effect to the balancing result. In this paper three different analytic methods are compared. In first method the mode shapes of the roll are defined piece wisely. The roll is divided in to five parts having different cross sections, two shafts, two roll ends and a shell tube of the roll. Two boundary conditions are found for both supports of the roll and four combining equations are written to the interfaces of different roll parts. Totally 20 equations are established to solve the natural frequencies and to form the mode shapes of the non-uniform roll. In second model the flexibility of shafts and the stiffness of the roll ends are added to the support stiffness as serial springs and the roll is modelled as a one flexibly supported beam having constant cross section. Finally the responses to imbalance of previous models are compared to finite element model using beam elements. Benefits and limitations of each three model are then discussed.

Commentary by Dr. Valentin Fuster
2011;():335-344. doi:10.1115/IMECE2011-62704.

There are many approaches to simulating and visualizing a dynamic system. Our focus is on developing/understanding and trading-off three different approaches that are relatively easy to implement with inexpensive, commonly available software using combinations of MATLAB, Simulink, Simulink 3D Animation, SolidWorks (basic), SolidWorks (Motion Manager) in addition to several common animation players such as Windows (Live) Movie Maker or the resident animation capability within MATLAB. The “SolidWorks Design Table” approach entails creating MATLAB/Simulink driven time-dependent assembly configurations, associated graphics files (e.g. JPG, TIFF) and then effectively “playing” them sequentially with animation software. The “SolidWorks Motor” approach utilizes SolidWorks’ Motion Manager capability (an add-on), whereby each spatially time-dependent geometric system variable is driven by a “motor” based on MATLAB/Simulink time-dependent data and an animation file can be generated from within Motion Manager. Lastly, in the “Simulink 3D Animation” approach, SolidWorks data is brought into the MATLAB environment and modified with V-Realm Builder (VRML Editor) supplied within the Simulink 3D Animation toolbox to define geometric constraints prior to inclusion as an animation VR Sink block within the Simulink model of the dynamic system. In each case, detailed procedures are provided. To exercise these three different approaches and permit comparisons, a benchmark problem was posed: parallel-parking of a four-wheeled vehicle possessing front wheel steering. Comparisons were then made and the recommended approach depends on such issues as the software background of the developer, the animation quality standard (e.g. framerate), and relative ease of implementation.

Commentary by Dr. Valentin Fuster
2011;():345-351. doi:10.1115/IMECE2011-62882.

In this paper, a method is proposed for integrated design of mechatronics systems. The integrated design problem is formulated as a semi-definite programming optimization problem. However, this is an infinite dimensional convex optimization problem, which is hard to solve. In this paper, it is shown that a vertex enumeration method can be used to transform the infinite dimensional optimization problem into a finite dimensional problem, which under the assumptions that the state space matrices are affine function of structural variables and that the structural variables belong to a polytope, can be solved efficiently. To show the effectiveness of the method, the method is applied to a mechatronics system.

Commentary by Dr. Valentin Fuster
2011;():353-360. doi:10.1115/IMECE2011-63045.

Stability of the magnetorheological rotational flow in presence of magnetic excitation in the axial direction is examined. The Galerkin projection method is used to derive a low-order dynamical system from the conservation of mass and momentum equations while mixed boundary conditions are assumed. In absence of magnetic excitation, the base flow loses its radial flow stability to the vortex structure at a critical Taylor number. The emergence of the vortices corresponds to the onset of a supercritical bifurcation. The Taylor vortices, in turn, lose their stability as the Taylor number reaches a second critical number corresponding to the onset of a Hopf bifurcation. The axial magnetic field turns out to be a controlling parameter as it alters the critical points throughout the bifurcation diagram.

Topics: Rotational flow
Commentary by Dr. Valentin Fuster
2011;():361-369. doi:10.1115/IMECE2011-63214.

Although the spring is an integral component of most any cam follower system, its design is often ignored in studies aimed at minimizing energy loss. This study makes an initial assessment of the possible energy savings that can be achieved by using a spring designed with a variable pitch. Using a simple spring model that accounts for coil contacts, the pitch is optimized in numerical experiments and the energy savings are calculated. The experiments show that savings in energy are promising enough to warrant further investigation.

Commentary by Dr. Valentin Fuster
2011;():371-381. doi:10.1115/IMECE2011-63260.

A new approach to understand factors that affect self-balancing devices is proposed. Experimentation was conducted to determine the influence of different factors on the performance of an automatic washing machine hydraulic balance ring fluid during transient and steady states. Two different optical techniques were used: one for visualization (high-speed photography) and another for velocity field measurement (Particle Image Velocimetry, PIV). Results were used to build a new balancer design and compared with previous findings. Important factors in balancer design were deducted.

Topics: Design
Commentary by Dr. Valentin Fuster
2011;():383-392. doi:10.1115/IMECE2011-63264.

An automatic landing system for an unmanned aerial vehicle (UAV) is presented in the following paper. The nonlinear aircraft model with thrust, elevator, rudder and aileron deflections as control inputs is established using the appropriate aerodynamic data. The flight trajectory the airplane is expected to travel during landing is then defined. A nonlinear control law, using feedback linearization method, is designed to develop the automatic landing controller for the UAV aircraft. A linear state-feedback control law is also designed for means of comparison with the nonlinear controller. The elevator is employed for longitudinal control whereas the rudder and aileron aid in lateral control. Thrust is the control input for velocity control, which is held constant during landing. A nonlinear simulation, incorporating wind shear and ground effects, is run using MATLAB/Simulink to assess the controllers’ integrity. The auto-landing system designed in this paper is meant to increase the autonomy of the UAV to eventually reach a fully autonomous system. Simulation results show the importance of designing the controller considering such effects. Landing trajectory tracking performance by the nonlinear controller is of great tone.

Commentary by Dr. Valentin Fuster
2011;():393-404. doi:10.1115/IMECE2011-63370.

Pneumatic servo positioning systems have been in use for long time and subject to wide spectrum of studies due to their numerous advantages: inexpensive, clean, safe and high ratio of power to weight. However, the compressibility of air and the inherent non-linearity of these systems continue to make achieving accurate position control a real challenge. Conventional pneumatic servo systems are based on cylinder actuators that are difficult to control precisely due to the aforementioned nonlinearities as well as the nonlinear behavior of the air flow through the valve, the friction between the cylinder and the piston, and the stick slip effect at the low velocity of the system. In this paper, a position servo control system using a pneumatic muscle actuator is studied. Pneumatic muscle actuator is a novel type of actuator which has even higher force to weight ratio than the cylinder. In addition, muscle actuator introduces a stick slip free operation giving an interesting option for positioning systems. However, significant hysteresis and position dependant force result in a highly nonlinear system, a real challenge for good control performance. In this paper, pneumatic muscle actuator is controlled by a low-cost on/off valve with PWM-strategy instead of costly servo or proportional valve. The main processes of the system, including flow dynamics, pressure dynamics, force dynamics and load dynamics are derived to provide a full nonlinear model that captures all the major nonlinearities of the system. This model is used for analyzing and tuning the controller performances by simulations before implementing in the real system. In addition, a recently introduced method of using bipolynomial functions to model the valve flow rate is utilized to provide a continuous and invertible description of flow for controller designs. A proportional plus velocity plus acceleration controller with feed-forward component (PVA+FF) is designed based on the linearized system model. For a comparison, a sliding mode controller (SMC) based on linear as well as non-linear system model are designed. The performance of the designed controllers is studied by simulations. The stability and performance analysis includes the effects of friction modeling error and valve modeling error. The robustness of the controllers is tested by varying the payload mass of the system.

Commentary by Dr. Valentin Fuster
2011;():405-412. doi:10.1115/IMECE2011-63495.

Friction damping devices such as under platform dampers are installed for modern turbine blades to suppress dynamic vibrations of the blades. In order to secure the reliability of the blades, it is important to predict the dynamic response and friction damping characteristics accurately. In this present paper, the dynamic response and friction damping characteristics of a last stage blade (LSB) of a steam turbine with contact surfaces at the cover, tie-boss and blade root was investigated. Especially, it is focused on the effect of the non-uniform normal contact forces at the contact surface. To investigate the effect of non-uniform normal contact forces, an analysis method was developed. Analysis model of the LSB with contact surfaces was discretized by finite elements. Tangential forces at the contact surfaces were modeled by multi-DOF macro-slip modeling. The non-linear frequency responses of the LSB were obtained by using the harmonic balance method. Using this analysis method, the relationship between the contact surface behavior and the dynamic response was studied.

Commentary by Dr. Valentin Fuster
2011;():413-422. doi:10.1115/IMECE2011-63519.

Final machining operations, such as surface grinding, play a crucial role in manufacturing of paper machine rolls. Due to developing new web-tension-measuring systems and due to demand on reduction of roll masses, a grinding operation of thin-walled rolls is required. In this paper first, delay differential equations describing the dynamics of the grinding system are introduced. The dynamic model consists of a rotating thin-walled roll and its drive and a rotating grinding stone with its drive attached to an axially moving sledge. The derivation of the cutting forces is based on wear theory. The roll is modelled in two ways for later comparison: (1) as a flexible simply supported rotor using Euler-Bernoulli beam theory and (2) as a simply supported flexible shell using Love’s equations. In both cases, a method of eigenfunctions expansion is employed for obtaining the responses. The effect of the time delay, shape error, overlapping and the PD-controller are included. The set of the delay differential equations is solved numerically. Finally, the dynamic response of the roll to the cutting forces is presented. An influence of different wall-thicknesses on the dynamic behaviour of the roll during the grinding process is studied as well. Lastly, a comparison of results obtained by using the beam theory and the shell theory are discussed.

Commentary by Dr. Valentin Fuster
2011;():423-433. doi:10.1115/IMECE2011-64010.

The real-time prediction of bearing wear for roller cone bits using the Intelligent Drilling Advisory system (IDAs) may result in better performance in oil and gas drilling operations and reduce total drilling cost. IDAs is a real time engineering software and being developed for the oil and gas industry to enhance the performance of complex drilling processes providing meaningful analysis of drilling operational data. The prediction of bearing wear for roller cone bits is one of the most important engineering modules included into IDAs to analyze the drilling data in real time environment. The ‘Bearing Wear Prediction’ module in IDAs uses a newly developed wear model considering drilling parameters such as, weight on bit (WOB), revolution per minute (RPM), diameter of bit and hours drilled as a function of IADC (International Association of Drilling Contractors) bit bearing wear. The drilling engineers can evaluate bearing wear status including cumulative wear of roller cone bit in real time while drilling, using this intelligent system and make a decision on when to pull out the bit in time to avoid bearing failure. The wear prediction module, as well as the intelligent system has been successfully tested and verified with field data from different wells drilled in Western Canada. The estimated cumulative wears from the analysis match close with the corresponding field values.

Topics: Wear , Drilling , Bearings
Commentary by Dr. Valentin Fuster
2011;():435-440. doi:10.1115/IMECE2011-64277.

In this paper an adaptive supervisory controller is designed to control the superheat temperature of a supermarket refrigeration system. The adaptive controller utilizes a switching algorithm with a forgetting factor. At each time step, the switching algorithm selects the best model among multi models using a supervisory monitoring signal. Each model corresponds to a controller; hence the corresponding controller to the selected model generates the required signal to determine the opening degree of an expansion valve. Simulations results of the proposed controller on a model of superheat of a supermarket refrigeration system for different operating point, show very satisfactory performance.

Commentary by Dr. Valentin Fuster
2011;():441-447. doi:10.1115/IMECE2011-64459.

One of the most dangerous phenomena associated with chainsaw use is kickback. This occurs when the upper quadrant of the chainsaw bar’s tip catches on the work-piece, accelerating the saw toward the user. Safety devices currently installed on chainsaws rely on the rotational acceleration of the saw to move a difficult-to-design mechanical linkage and activate a band brake. Even with a well-designed braking linkage, the saw must rotate through a large angle (approximately 45°) before actuating the brake. A more effective kickback detection and chain-braking system is needed—one that is capable of (i) early detection of the kickback event and (ii) rapid braking of the moving chain. This paper deals with a method of detecting such a kickback event. The approach taken in this work determines the key kinematic parameters associated with kickback using an electronics package of accelerometers and a gyroscope attached to a typical chainsaw. Testing consisted of (i) performing a series of normal cuts through wooden poles, and (ii) purposely initiating kickback via several common scenarios. Data analysis consisted of comparing magnitude, duration, and frequency of sensor output between normal cutting and kickback scenarios. After data filtering, a method of scaling factor variation was used to extract the optimum detection algorithm of a single gyroscope with appropriate signal conditioning, Kickback is detected within 30 milliseconds, before the saw loses contact with the work-piece. The gyroscope magnifies the signal corresponding to the kickback event while attenuating signals corresponding to normal use. This method presents the possibility of a significantly improved chainsaw kickback control system.

Topics: Chain saws
Commentary by Dr. Valentin Fuster
2011;():449-454. doi:10.1115/IMECE2011-64539.

Finishing processes such as deburring are performed on a wide variety of products in various quantities by workers on a piece-by-piece basis. Accordingly, the accuracy of the product depends on the worker’s skill. The aim of this research is to develop a finish machining support system. The machining is supported by using a haptic device and controlled by a bilateral control system. Here, we propose a original bilateral controller which have the gain components on the line used to transfer the force signal between master and slave robot. These gains change the binding force between master and slave robot to change the construct of the system. The effectiveness of this system is shown in simulations using haptic device and virtual model of slave robot.

Topics: Machining , Finishes
Commentary by Dr. Valentin Fuster
2011;():455-461. doi:10.1115/IMECE2011-65108.

In this investigation, formulations of sliding joint constraints for flexible bodies modeled using the absolute nodal coordinate formulation are developed using intermediate coordinates. Since modeling of prismatic and cylindrical joints for flexible bodies requires solutions to moving boundary problems in which joint definition points are moving on flexible bodies, arc-length coordinates are introduced for defining time-variant constraint definition points on flexible bodies. While this leads to a systematic modeling procedure for sliding joints, specialized formulations and implementations are required in general multibody dynamics computer algorithms. For this reason, intermediate coordinates are introduced to derive a mapping between the generalized gradient coordinates used in the absolute nodal coordinate formulation and the intermediate rotational coordinates used for defining the orientation constraints with rigid bodies. With this mapping, existing joint constraint libraries formulated for rigid bodies can be employed for the absolute nodal coordinate formulation without significant modifications. It is also demonstrated that the intermediate coordinates and arc-length coordinates introduced for modeling sliding joint constraints can be systematically eliminated from the equations of motion and standard differential algebraic equations used in general multibody dynamics computer algorithms can be obtained. Several numerical examples are presented in order to demonstrate the use of the formulation developed in this investigation.

Commentary by Dr. Valentin Fuster
2011;():463-470. doi:10.1115/IMECE2011-65123.

Flexoelectricity, an electromechanical coupling effect, exhibits two opposite electromechanical properties. One is the direct flexoelectric effect that mechanical strain gradient induces an electric polarization (or electric field); the other is the inverse flexoelectric effect that polarization (or electric field) gradient induces internal stress (or strain). The later can serve as an actuation mechanism to control the static deformation of flexible structures. This study focuses on an application of the inverse flexoelectric effect to the static displacement control of a cantilever beam. The flexoelectric layer is covered with an electrode layer on the bottom surface and an AFM probe tip on the top surface in order to generate an inhomogeneous electric field when powered. The control force induced by the inverse flexoelectric effect is evaluated and its spatial distribution resembles a Dirac delta function. Therefore, a “buckling” characteristic happens at the contact point of the beam under the inverse flexoelectric control. The deflection results of the cantilever beam with respect to the AFM probe tip radius indicate that a smaller AFM probe tip achieves a more effective control effect. To evaluate the control effectiveness, the flexoelectric deflections are also compared with those resulting from the converse piezoelectric effect. It is evident that the inverse flexoelectric effect provides much better localized static deflection control of.flexible beams.

Commentary by Dr. Valentin Fuster
2011;():471-476. doi:10.1115/IMECE2011-65446.

The paper presents an inverse method for control of temperature distribution in thick cylindrical shells. Since the thickness is large enough, three-dimensional heat diffusion equations must be considered. To control the temperature distribution, the heat fluxes at the boundary surfaces of the cylindrical shell are assigned values such that the desired temperature distribution, which satisfies the steady state heat conduction equation, will be achieved. Furthermore, a Lyapunov-based method for identification of the conductivity of the cylinder is presented, and the estimated conductivity is updated such that it converges to the exact value. The numerical results are obtained by the finite element method (FEM), which include the heat flux at the surfaces of the cylinder. These results are shown to be in excellent agreement with the analytical solution.

Commentary by Dr. Valentin Fuster
2011;():477-483. doi:10.1115/IMECE2011-65637.

The accuracy of multi dimensional simulation of vehicle dynamics has been significantly increased for both passive and active vehicles which are equipped with advanced electronic components. Recently, one of the subjects that has been considered is increasing the car safety in design. Therefore, many efforts have been done to increase vehicle stability especially during the turn. It is also very important in three wheel car. One of the most important efforts is adjusting the camber angle in the car suspension system. Camber angle as well as the vehicle stability has major effects on the wheel slip, reducing rubber abrasion, acceleration and braking. Since the increase or decrease in the camber angle impacts on the stability of three wheel vehicles, in this paper, a car suspension system mechanism is introduced by which camber angle could be adjusted furthermore the mechanism is user friendly applicable and also economic. Actually, a passive double wishbone suspension system with variable camber angle has been designed, analyzed and subsequently manufactured. This mechanism was modeled in Visual Nastran software and kinematic analysis was presented. It can change camber angle from −5.5 to 5 degrees. In this work, two different modeling is presented, active geometry system (variable camber) and passive (conventional suspension system) then the rate of Roll and Yaw angle were discussed to investigate and compare models stability in same condition. Simulation and test results have shown that vehicle stability in active geometry model is sustained more than conventional models.

Commentary by Dr. Valentin Fuster
2011;():485-495. doi:10.1115/IMECE2011-62441.

Constrained layer frictional interfaces, such as joints, are prevalent in engineering applications. Because these interfaces are often used in built-up structures, reduced order modeling techniques are utilized for developing simulations of them. One limitation of the existing reduced order modeling techniques, though, is the loss of the local kinematics due to regularization of the frictional interfaces. This paper aims to avoid the use of regularization in the modeling of constrained layer frictional interfaces by utilizing a new technique, the discontinuous basis function method. This method supplements the linear mode shapes of the system with a series of discontinuous basis functions that are used to account for nonlinear forces acting on the system. A symmetric, constrained layer frictional interface is modeled as a continuous system connected to two rigid planes by a series of Iwan elements. This symmetric model is used to test the hypothesis that symmetric problems are not subjected to the range of variability seen in physical structures, which have non-uniform pressure and friction distributions. Insights from solving the symmetric problem are used to consider the case where a non-uniform distribution of friction and pressure exists.

Topics: Modeling , Functions
Commentary by Dr. Valentin Fuster
2011;():497-510. doi:10.1115/IMECE2011-64939.

Two major challenges associated with a vibration-based damage detection method using changes in natural frequencies are addressed: accurate modeling of structures and the development of a robust inverse algorithm to detect damage, which are defined as the forward and inverse problems, respectively. To resolve the forward problem, new physics-based finite element modeling techniques are developed for fillets in thin-walled beams and for bolted joints, so that complex structures can be accurately modeled with a reasonable model size. To resolve the inverse problem, a logistic function transformation is introduced to convert the constrained optimization problem to an unconstrained one, and a robust iterative algorithm using the Levenberg-Marquardt method is developed to accurately detect the locations and extent of damage. The new methodology can ensure global convergence of the iterative algorithm in solving under-determined system equations and deal with damage detection problems with relatively large modeling error and measurement noise. It is applied to various engineering structures including lightning masts, a space frame structure and one of its components, and a pipeline. The exact locations and extent of damage can be detected in the numerical simulation, and the locations and extent of damage can be successfully detected in experimental damage detection.

Topics: Structures , Vibration
Commentary by Dr. Valentin Fuster
2011;():511-516. doi:10.1115/IMECE2011-65190.

Reduction of structural vibrations is of major interest in mechanical engineering for lowering sound emission of vibrating structures, improving accuracy of machines and increasing structure durability. Besides optimization of the mechanical design or various types of passive damping treatments, active structural vibration control concepts are efficient means to reduce unwanted vibrations. In this contribution, two different semi-active control concepts for vibration reduction are proposed that adapt the normal force of attached friction dampers. Thereby, semi-active control concepts generally possess the advantage over active control that the closed loop is intrinsically stable and that less energy is required for the actuation than in active control. In the chosen experimental implementation, a piezoelectric stack actuators is used to apply adjustable normal forces between a structure and an attached friction damper. Simulation and experimental results of a benchmark structure with passive and semi-actively controlled friction dampers are compared for stationary narrow-band excitation.

Topics: Friction , Vibration
Commentary by Dr. Valentin Fuster
2011;():517-518. doi:10.1115/IMECE2011-65193.

In engineering practice frictional resistance is considered on a macroscopic scale: All the physical processes resulting in resistance against sliding are subsumed under a single friction coefficient, though there is no real evidence for this separation of scales. A feasible way to bring multiscale modelling to frictional problems can be the consideration of friction on a mesoscale on which the roughness of apparently smooth surfaces appears. Although surface roughness has always been connected with friction, recently experiments and models revealed that dynamic processes in the rough interface determine the frictional behaviour.

Commentary by Dr. Valentin Fuster
2011;():519-526. doi:10.1115/IMECE2011-62109.

By introducing a statistical hypothesis to Periodicity Ratio, the efficiency and accuracy of diagnosing the nonlinear characteristics of dynamic systems are improved. Overlapping points in a Poincare map are verified on a statistically sound basis. The characteristics of nonlinear systems are investigated by using the present approach. The numerical results generated by the approach are compared with that of the conventional approaches.

Commentary by Dr. Valentin Fuster
2011;():527-532. doi:10.1115/IMECE2011-62110.

This research focuses on quantitative analysis of elastic space waves propagating porous media saturated with fluid. Compressive wave propagations are described in three dimensional (3-D) spherical coordinates in terms of displacements of the fluid and solid of the porous media. The wave superposition properties under multiple energy resources are investigated. Relative displacements between the fluid and solid of a porous medium in 3-D domain are quantified with consideration of the wave propagations excited by multiple point energy sources. Numerical analyses are performed and practically sound results are obtained.

Commentary by Dr. Valentin Fuster
2011;():533-538. doi:10.1115/IMECE2011-62124.

In this article, based on the Euler-Bernoulli hypothesis and the Galerkin method, ananalysis of the nonlinear dynamic stability for a clamped-guided piezoelectric laminated microbeam under both a periodic axial force and a symmetric electrostatic load is presented. By using the incremental harmonic balanced method (IHBM), the boundary of the principal region of instability is got. In the numerical calculation, the effect of the environmental damping, geometric nonlinear, piezoelectric effect and the symmetric electrostatic load on the principal region of instability is discussed.

Commentary by Dr. Valentin Fuster
2011;():539-545. doi:10.1115/IMECE2011-62898.

In this paper, the nonlinear vibration characteristics of the micro-beam structure acting by multi-couplings factors are investigated. Taking the nonlinear air damping force, alternating voltage excitation as well as the geometric nonlinearity of the micro-beam into account, the nonlinear vibration governing equations of the micro-beam are derived on the basis of the Euler-Bernoulli beam theory. The Galerkin method and harmonic balance method are adopted to obtain the amplitude-frequency response characteristic and phase-frequency response characteristic of the micro-beam structure. Then the effects of the nonlinear air damping force and the geometric nonlinearity on the resonance frequency and stiffness of micro-beam structure are analyzed.

Commentary by Dr. Valentin Fuster
2011;():547-554. doi:10.1115/IMECE2011-62900.

In this paper, based on Euler-Bernoulli assumptions and piezoelectric theory, taken electric excitation loads generated by AC and DC’s interactions, control voltage of piezoelectric layer and geometric nonlinearity into consideration, the nonlinear differential governing equation of piezoelectric laminated microbeam is established. The equation is solved by Galerkin method and mathematical tools. Making use of P-R criterion method, the analysis of single parameter bifurcation is carried on firstly to understand the characteristics of system, and the effects of multiple parameters variation on nonlinear dynamic characteristics of system are discussed in detail. The results can be used for the design of such micro-structures.

Commentary by Dr. Valentin Fuster
2011;():555-561. doi:10.1115/IMECE2011-63003.

A known problem in classical hydraulic engine mount is that because of the density mismatch between the decoupler and surrounding fluid, the decoupler might float, or stick to the cage bounds, assuming static conditions. The problem appears in the transient response of a bottomed up floating decoupler hydraulic engine mount. To overcome the bottomed up problem, a suspended decoupler design for improved decoupler control is introduced. The new design does not noticeably effect the mechanisms steady state behavior, but improves start up and transient response. Additionally, the decoupler mechanism is incorporated into a smaller, lighter, yet more tunable and hence more effective hydraulic mount design. Ususally the elastomechanical components in a hydraulic engine mount are assumed lumped and linear. To have a more realistic modeling, utilizing nonlinear finite elements in conjunction with a lumped parameter modeling approach, we evaluate the resorting characteristics of the components and implement them in the equations of motion. The steady state response of a dimensionless model of the mount is examined utilizing the averaging perturbation method applied to a set of second order nonlinear ordinary differential equations. It is shown that the frequency responses of the floating and suspended decoupled designs are similar and functional.

Commentary by Dr. Valentin Fuster
2011;():563-569. doi:10.1115/IMECE2011-63007.

The time derivative of vectors depends on the coordinate frame in which the vector is expresses and the coordinate frame in which the derivative is taken. By redefining and expanding the Euler’s derivative transformation formula, we introduce the general theory of derivative and coordinate frames using a proper notation method. Introducing three coordinate frames, we show that the Coriolis acceleration is actually the addition of two different accelerations. Furthermore, a new acceleration term appears that we call it Razi acceleration.

Commentary by Dr. Valentin Fuster
2011;():571-577. doi:10.1115/IMECE2011-63398.

This paper provides a method for optimal synthesis of the passenger cars suspension system to obtain the best road-holding as well as ride-comfort characteristics. The longitudinal vehicle model consists of sprung and unsprung masses, tire-ground interaction model, and suspension system kinematics. Defining the non-dimensional parameters the equations of motion of the system are derived in the non-dimensional form. Several objective functions are defined for the optimization of road-holding and ride comfort characteristics based on the transient and steady-state response of the sprung mass, respectively. The optimization variables are position of instant centers of rotation of the wheels with respect to the sprung mass. Bee’s algorithm is used to obtain the solutions of the problem. The best position for the instant centers of front and rear suspension linkages are obtained and compared with 100% anti-squat line.

Commentary by Dr. Valentin Fuster
2011;():579-592. doi:10.1115/IMECE2011-63803.

In this paper, an efficient method is proposed for modelling and simulation of multi-body dynamic problems. The method employs symbolic computational abilities of Maple as well as graphical environment of Matlab-Simulink to obtain and solve the equations of motion of a multi-body system accurately and rapidly. Considering a typical multi-body dynamical system the governing equations of system including second order equations of motion, first order nonholonomic and holonomic algebraic constraint equations are derived in Maple software. The state variables of the system are defined based on the systems degrees of freedom or generalized velocities. Converting the system’s equations to an algebraic form and combining them together by using a few Maple commands, the simplest form of the system’s equations of motion are obtained in the canonical standard state space form. This form is suitable when an explicit numerical method of integration is used. Then using a few toolboxes of Simulink, the equations are solved and can be studied. To procedural illustration of the method a lateral vehicle dynamic problem having thirty equations is considered. Beside the present method, Maple as well as Matlab is used to solve the problem. The results show the distinction of the method from the points of execution CPU time, accuracy and longer simulation. This method is suitable when investigation of long term behavior of multi-body dynamical systems is needed.

Topics: Simulation
Commentary by Dr. Valentin Fuster
2011;():593-598. doi:10.1115/IMECE2011-64152.

Fibre Reinforced Plastics (FRPs) generally have greater advantages over conventional materials for their structural properties. However, the service life can significantly be shortened if the fibre reinforced plastics are exposed to adverse environmental conditions especially acid vapour, humidity and high temperature. In many chemical industrial plants in Australia and elsewhere fibre reinforced plastic gratings are used as structural components of stairs and passages where they are subjected to varying degrees of fluosilicic acid, a byproduct of the industrial manufacturing process. As currently no experimental data on the effects of fluosilicic acid on FRPs is available in the public domain, it is difficult to predict the service life of FRPs with some certainty. In order to understand the structural strength of fluosilicic acid exposed FRPs, an experimental study was undertaken. A series of specimens from various locations of a chemical plan in Australia were acquired and studied. Some new specimens (not exposed to acid, humidity and high temperature) were also studied to provide a benchmark for the comparison. The results indicated that the long time exposure to harsh environment and acid vapour can significantly deteriorate the flexural strength and service life of FRPs.

Commentary by Dr. Valentin Fuster
2011;():599-605. doi:10.1115/IMECE2011-64389.

The topology optimization method is extended for the optimization of geometrically nonlinear, time-dependent multibody dynamics systems undergoing nonlinear responses. In particular, this paper focuses on sensitivity analysis methods for topology optimization of general multibody dynamics systems, which include large displacements and rotations and dynamic loading. The generalized-α method is employed to solve the multibody dynamics system equations of motion. The developed time integration incorporated sensitivity analysis method is based on a linear approximation of two consecutive time steps, such that the generalized-α method is only applied once in the time integration of the equations of motion. This approach significantly reduces the computational costs associated with sensitivity analysis. To show the effectiveness of the developed procedures, topology optimization of a ground structure embedded in a planar multibody dynamics system under dynamic loading is presented.

Commentary by Dr. Valentin Fuster
2011;():607-616. doi:10.1115/IMECE2011-62702.

A mechanical acceleration switch has been developed to synchronize instrumentation during a destructive acceleration test. The tests are of short durations and involve very high velocities and accelerations, and a destructive impact. Therefore, accurately synchronized instrumentation is critical. When the switch detects a desired acceleration time history, the switch closes to complete a circuit for instrument activation. Preliminary tests on the proposed switch have shown that switch-to-switch variations exist due to fabrication and assembly tolerances, and that combinations of variations may lead to a switch that does not respond properly. If the switch does not close at the proper time, improper data may be collected; or, at worst, no data may be collected before destructive impact. In this paper, a nonlinear model of the switch closing dynamics is developed in order to investigate the effect of uncertainty on its operation. In particular, the propagation of uncertainty from the switch parameters to the switch dynamics is quantified, and then the design is optimized such that the operation of the switch is insensitive to the variation and uncertainty. The results of the analysis elucidate the parameters that significantly impact switch operation, quantify the reliability of the existing switch design, and ultimately are used to recommend a design that could significantly improve reliability.

Commentary by Dr. Valentin Fuster
2011;():617-625. doi:10.1115/IMECE2011-63207.

In this article, the effects of noise on a base-excited cantilever structure with nonlinear tip force interactions are studied by using experimental, numerical, and analytical methods. The focus of the study is on the enhancement of the cantilever response, when Gaussian white noise is added to the harmonic base input. The experimental arrangement consists of a base-excited elastic cantilever with a magnet attached to its free end. An attractive force is generated at the cantilever tip magnet through another magnet of opposite polarity, which is fixed to a translatory stage. The second magnet is covered by a thin compliant material, with which the tip magnet makes intermittent contact when the cantilever is subjected to a base excitation. For a purely harmonic excitation, it is observed that the tip magnet of the cantilever sticks to the base magnet due to the attractive force. Starting from a situation where the cantilever tip is sticking to the surface, band-limited white Gaussian noise is added to the excitation and the strength of noise is gradually increased. The cantilever tip resumes its periodic motion when the strength of added noise reaches a sufficient signal to noise ratio. This phenomenon is explored by using a reduced-order numerical model and an analytical framework involving the application of a moment-evolution approximation derived from the associated Fokker Planck equation for the system. Since the macro-scale experimental system qualitatively replicates the micro-scale attractive-repulsive force interaction experienced by an atomic force microscope cantilever operated in tapping mode, this study sheds light on the possible use of white noise to control the sticking of such micro-scale cantilevers with sample surfaces.

Commentary by Dr. Valentin Fuster
2011;():627-633. doi:10.1115/IMECE2011-63798.

This paper deals with electrostatically actuated micro and nano-electromechanical (MEMS/NEMS) circular plates. The system under investigation consists of two bodies, a deformable and conductive circular plate placed above a fixed, rigid and conductive ground plate. The deformable circular plate is electrostatically actuated by applying an AC voltage between the two plates. Nonlinear parametric resonance and pull-in occur at certain frequencies and relatively large AC voltage, respectively. Such phenomena are useful for applications such as sensors, actuators, switches, micro-pumps, micro-tweezers, chemical and mass sensing, and micro-mirrors. A mathematical model of clamped circular MEMS/NEMS electrostatically actuated plates has been developed. Since the model is in the micro- and nano-scale, surface forces, van der Waals and/or Casimir, acting on the plate are included. A perturbation method, the Method of Multiple Scales (MMS), is used for investigating the case of weakly nonlinear MEMS/NEMS circular plates. Two time scales, fast and slow, are considered in this work. The amplitude-frequency and phase-frequency response of the plate in the case of primary resonance are obtained and discussed.

Commentary by Dr. Valentin Fuster
2011;():635-642. doi:10.1115/IMECE2011-64000.

In this paper, the dynamics of a micro-machined structure with three parallel cantilevers is investigated. The cantilevers are electrically charged and apply electrostatic force to each other. The governing equations of motion are derived using Euler-Bernoulli beam theory and considering structural modal damping. The stability condition of the beams for various electric charges is also studied. In addition, the equations of motion are integrated to obtain the response of the beams in time-domain for a range of initial conditions. This response is used to study the behavior of the beams at the stability margin. The end application of the structure under investigation is in the device characterization. The dynamic stability condition and time-domain responses are used to investigate the reliability of the characterization. Once translated back to physical quantities, these results can be used for improving the measurements.

Commentary by Dr. Valentin Fuster
2011;():643-646. doi:10.1115/IMECE2011-64722.

In this paper, nonlinear vibration of a micro cantilever exposed to a constant velocity flow is studied. In order to obtain vibration frequency and time response of the micro beam the variational iteration method is used as a novel tool for solving nonlinear differential equations. Results of the analytical solution are compared with those obtained by Runge-Kutta method which shows very good agreement between them. Results confirm that frequency of vibration depends on the flow velocity. Also, the high sensitivity of the vibration frequency to the flow velocity means that it can be an effective indicator of velocity.

Commentary by Dr. Valentin Fuster
2011;():647-654. doi:10.1115/IMECE2011-64822.

Chaotic vibrations of functionally graded doubly curved shells subjected to concentrated harmonic load are investigated. It is assumed that the shell is simply supported and the edges can move freely in in-plane directions. Donnell’s nonlinear shallow shell theory is used and the governing partial differential equations are obtained in terms of shell’s transverse displacement and Airy’s stress function. By using Galerkin’s technique, the equations of motion are reduced to a set of infinite nonlinear ordinary differential equations with cubic and quadratic nonlinearities. A bifurcation analysis is carried out and the discretized equations are integrated at (i) fixed excitation frequencies and variable excitation amplitudes and (ii) fixed excitation amplitudes and variable excitation frequencies. In particular, Gear’s backward differentiation formula is used to obtain bifurcation diagrams, Poincaré maps and time histories. Furthermore, maximum Lyapunov exponent and Lyapunov spectrum are obtained to classify the rich dynamics. It is revealed that the shell may exhibit complex behaviour including sub-harmonic, quasi-periodic and chaotic response when subjected to large harmonic excitations.

Topics: Resonance , Vibration , Shells
Commentary by Dr. Valentin Fuster
2011;():655-659. doi:10.1115/IMECE2011-64835.

Biomimetics is one of the most important paradigms as researchers seek to invent better engineering designs over human history. However, the observation of insect flight is a relatively recent work. Several researchers have tried to address the aerodynamic performance of flapping creatures and other natural properties of insects, although there are still many unsolved questions. In this study, we have attempted to investigate the structural dynamic characteristic of an artificial wing that mimicked the wing shape and main venation structure of a beetle hind wing using a non contact measurement method. The structural dynamic characteristic of the artificial wing was measured and compared to the real beetle hind wing by determining the natural frequencies and damping factor. The artificial wing was glued with the cyanoacrylate adhesive at the wing base onto the acrylic stand which was attached to the base of a shaker. The shaker produces the translation motion in the lateral direction of the wing plane. A non-contact laser sensor was used to measure the displacement history of the painted spots on the hind wing. A Brüel & Kjær FFT analyzer was adopted to calculate the frequency response functions where the natural frequencies of the wing structure can be extracted. The fundamental natural frequency of artificial wing is 51.3 Hz while the natural frequency of the beetle hind wing is 48.8 Hz. In addition, the wing structures were lightly damped with damping factor around 3.1% that is close to the one of beetle hind wing. We found that, in terms of the wing elasticity, the plastic wing frame of artificial wing was suitable for beetle-like flight.

Topics: Wings
Commentary by Dr. Valentin Fuster
2011;():661-668. doi:10.1115/IMECE2011-64850.

An efficient O(N) algorithm has been developed on the basis of the proper integration between an internal coordinate method (ICM) and a multibody molecular method. The method has been implemented for virtual prototyping of molecular systems with a simple chain structure and the results showed O(N) computational performance. This paper results the application of O(N) procedure to a large molecular chain and show the linear computational load relationship with the number of subsets. Initially, a brief introduction to O(N) procedure and the theoretical development of the algorithm is presented. Later focus will be turned to the implementation of the algorithm on the molecular structure. Finally, the motion behavior and the simulation time are analyzed for different computer systems.

Commentary by Dr. Valentin Fuster
2011;():669-673. doi:10.1115/IMECE2011-64854.

The nonlinear response of an electrostatically actuated cantilever beam microresonator sensor for mass detection is investigated. The excitation is near the natural frequency. A first order fringe correction of the electrostatic force, viscous damping, and Casimir effect are included in the model. The dynamics of the resonator is investigated using the Reduced Order Model (ROM) method, based on Galerkin procedure. Steady-state motions are found. Numerical results for uniform microresonators with mass deposition and without are reported.

Commentary by Dr. Valentin Fuster
2011;():675-684. doi:10.1115/IMECE2011-64910.

It is the purpose of this study to investigate the principal nonlinear dynamic phenomena associated with the dynamic behavior of elastic suspended pipelines transporting fuels for refueling of aircrafts. The pipe is modeled as a slender beam that obtains a catenary configuration between the end points, i.e. the connections between the tanker and the refueled aircraft. In the specific arrangement the excitation is mainly induced due to the 3D motions of the connected aircrafts and is imposed in both ends of the pipeline. A characteristic feature of the investigated operation is the lack of a large damping component that could cancel potential instabilities. In the present study, the pipeline is considered as a continuous media and its dynamic problem is expressed through the complete nonlinear system of partial differential equations which are derived following a Newtonian derivation. The model adopted for describing the inner flow is the so called “plug-flow model”. The system is treated as a two point boundary value problem and it is solved in the time domain to trace all possible nonlinearities. To tackle the details of the nonlinear modes of motion the output signals of the dynamic response, that provide all governing dynamic components, namely, motions, inner loading terms, bending moments and angles of rotation, are further elaborated by the POD method. The POD Transform provides insight into the reduced order dynamics of this geometrically nonlinear exact coupled dynamical system.

Commentary by Dr. Valentin Fuster
2011;():685-695. doi:10.1115/IMECE2011-62436.

This paper presents a new formulation for elastic-plastic contact in the normal direction between two round surfaces that is solely based on material properties and contact geometries. The problem is formulated as three separate domains: the elastic regime, mixed elastic-plastic behavior, and unconstrained (fully plastic) flow. Solutions for the force-displacement relationship in the elastic regime follow from Hertz’s classical solution. In the fully plastic regime, two assumptions are made: that there is a uniform pressure distribution and that there is conservation of volume. The force-displacement relationship in the intermediate, mixed elastic-plastic regime is approximated by enforcing continuity between the elastic and fully plastic regimes. Transitions between the three regimes are determined based on empirical quantities: the von Mises yield criterion is used to determine the initiation of mixed elastic-plastic deformation, and Brinell’s hardness for the onset of unconstrained flow. Unloading from each of these three regimes is modeled as an elastic process with different radii of curvature based on the regime in which the maximum force occurred. Simulation results explore the relationship between the impact velocity and coefficient of restitution. Further comparisons are made between the model, experimental results found in the literature, and other existing elastic-plastic models.

Commentary by Dr. Valentin Fuster
2011;():697-705. doi:10.1115/IMECE2011-62537.

Roadside guard systems such as concrete and wire barriers and steel guard rails are mainly developed to protect occupants of the errant cars or trucks. Yet motorcycle riders are vulnerable to these barriers and guard systems, and impact on these barriers may result in major injuries. The objective of this study is to examine the major factors causing injuries in motorcycle-barriers accidents. A mathematical multi-body motorcycle model with a motorcycle anthropometric test device, MATD, is developed in the MADYMO 7.2 for this purpose. The motorcycle model as well as the motorcycle and rider model are validated using full-scale crash test data available in the literature. The simulations results are found to be in a reasonable agreement with the experimental data. A parametric study using the design of experiment (DOE) is then conducted to investigate the nature of crash injuries for various impact speeds, impact angles, different bike and rider positions to assess the rider kinematics and potential injuries. The results from this study can help in designing road barriers and guard systems in order to protect the motorcycle riders.

Topics: Design , Modeling
Commentary by Dr. Valentin Fuster
2011;():707-715. doi:10.1115/IMECE2011-62914.

A study of the feasibility of using a curved Hopkinson bar for the measurement of impact load and energy transmission is presented. The length requirements of straight prismatic bars commonly used to measure long wavelength impact events are often prohibitive, and the use of curved bars can result in a significant increase in wavelength capabilities while reducing the overall size of the measurement apparatus. The ABAQUS/Explicit finite element analysis (FEA) program is used to model steel bars of circular cross section bent with various bend radii and at various bend angles ranging from 15 to 180 degrees. A uniform compressive pressure pulse of known amplitude and wavelength is applied to the FEA models and the wave propagation behavior predicted by ABAQUS/Explicit is then compared to the response predicted by the theory of wave propagation in curved bars and experiments performed using curved bars. The numerical results show good agreement with the theoretical and experimental results. Significant distortion of the incident wave as it travels around the bend results in a transmitted pulse that is not characteristic of the input pulse, particularly at larger bend angles and long wavelengths. The energy transmitted around the bend radius contains only a fraction of the initial impact energy due to large reflections that develop at the bend radius, and this loss increases significantly at larger bend angles and smaller bend radii. However, the transmitted energy can be used to predict the incident energy at a variety of bend angles and bend radii. A curved carbon steel Hopkinson bar is fabricated with a bend angle of 180 degrees and instrumented with strain gauges to monitor the wave propagation within the bar at several locations resulting from a compressive impact pulse. The experimental results agree well with the results predicted using explicit dynamic FEA. The results of this study indicate that a curved Hopkinson bar can be used to predict the impact energy applied to the incident end of the bar using the measurement of the energy transmitted around the bend in the bar. The overall length of the curved Hopkinson bar apparatus can be significantly less than a comparable straight bar apparatus.

Topics: Wavelength
Commentary by Dr. Valentin Fuster
2011;():717-724. doi:10.1115/IMECE2011-63790.

This paper deals with linear elastic structures exposed to impact and contact phenomena. Within a time stepping integration scheme contact forces are computed with a Lagrangian multiplier approach. The main focus is turned on a simplified solving method of the linear complementarity problem for the frictionless contact. Numerical effort is reduced by applying a Craig-Bampton transformation to the structural equations of motion.

Commentary by Dr. Valentin Fuster
2011;():725-731. doi:10.1115/IMECE2011-64353.

Space frames are usually used to enhance the structural strength of a vehicle while reducing its overall weight. Impact loading is a critical factor when assessing the functionality of these frames. In order to properly design the space frame structure, it is important to predict the shocks moving through the members of the space frame. While performance of space frame structures under static loads in well-understood, research on space frame structures subjected to impact loading is minimal. In this research, a lab-scale space frame structure, comprising of hollow square members that are connected together through bolted joints which allow for quick assembly/disassembly of a particular section, is manufactured. Non-destructive impact tests are carried out on this space frame structure and the resulting acceleration signals at various locations are recorded. A finite element (FE) model of the lab-scale structure is created and simulated for the experimental impact loads. Acceleration signals from the FE model are compared with the experimental data. The natural frequencies of the structure are also compared with the results of the FE model. The results show a good match between the model and the experimental setup.

Commentary by Dr. Valentin Fuster
2011;():733-744. doi:10.1115/IMECE2011-65736.

In many engineered structures and components, impact events frequently occur between sub-components. Numerical models are able to adequately capture the salient features of these events; however, with high fidelity finite element models, an unreasonably large number of elements are needed to accurately model just the elastic regime when arbitrary contact is considered. In order to solve real engineering problems with elastic-plastic impacts in complex or built up systems, an analytical expression is needed to make solutions practical. To this end, a series of experiments are designed to test a new elastic plastic model for impact dynamics. A hard metal ball is attached as the end of a pendulum, and is struck against a relatively compliant metal puck. Digital image analysis is used to measure the displacement and velocity of the metal ball across the impact events. Frictional losses in the system are minimized, and the coefficient of restitution is calculated as a function of velocity. These measurements are used to validate an elastic-plastic impact model, which is further compared to and other models from the literature. Good agreement is found between the new analytical model and the experiments.

Commentary by Dr. Valentin Fuster
2011;():745-749. doi:10.1115/IMECE2011-62505.

This paper presents a unique approach for integrating a finite element analysis (FEA) model using a dynamic explicit of Abaqus with a nonlinear process of the mold’s open/close phase in an injection molding machine. This opening/closing phase is considered to have one of the highest impacts on reducing an overall cycle duration since it has no impact on the final part quality. Reducing the overall cycle duration has a big positive impact on productivity and enhancing efficiency of the manufacturing processes of injection molding systems. Therefore, one of the objectives of the injection molding manufacturers is increasing efficiency by reducing the time duration of this phase to a possible minimum. In this work, a 3-dimensional (3D) solid model of the mold, toggle mechanism, and hydraulic cylinder were developed and then superimposed with Abaqus software to animate the motion of the movable part of the mold. The position of the movable part of the mold is traced and used as a controlled variable while the inputted force and initial velocity were considered as the manipulated variables. The innovation of this strategy is that the controller structure uses the nonlinear model to update the process variables at every sampling instant while the closed-loop control is executed. This allows the determination of the plant’s variables resulting in a new set of the controller parameters with every sampling instant.

Commentary by Dr. Valentin Fuster
2011;():751-759. doi:10.1115/IMECE2011-62706.

Bistable compliant flexures serve as mechanical memory and threshold devices for switches and sensors. One class of bistable compliant flexures is the annular, spherical shell, termed a bistable snap disc. These structures offer flexibility for mechanical memory and threshold devices because large changes in buckling loads can be achieved without significantly modifying the geometry. The sensitivity of these bistable snap discs to imperfections, however, prevents them from withstanding pre-buckling loads predicted by idealized models. A method to incorporate geometric imperfections into an existing finite element mesh of the idealized geometry using a set of orthonormal polynomials, specifically the annular Zernike polynomials, is proposed in this paper. A sensitivity analysis of five terms from the Zernike polynomial expansion is performed with a geometrically nonlinear finite element model to identify their effect on buckling, snap-through, and quasi-static stability. The effects of the perturbations are established by identifying key points on a force-deflection curve and potential energy curve. Results show that the geometric perturbations may account for the discrepancy in buckling between the idealized model and experiments. Error between the experiments and the model with geometric perturbations persist because the actual imperfections of the discs used in the experiments have not yet been characterized, and the finite element model does not account for non-homogeneous material properties and residual stresses.

Commentary by Dr. Valentin Fuster
2011;():761-765. doi:10.1115/IMECE2011-62856.

In this paper, nonlinear oscillation of a pendulum wrapping and unwrapping around two cylindrical bases is studied and an analytical solution is obtained using multiple scales method. Equations of motion are derived based on energy conservation technique. Applying perturbation method on the equations, nonlinear natural frequency of the system is calculated along with its time response. Analytical results are compared with numerical findings and good agreement is found. Effect of nonlinearity due to large amplitude and radius of cylinders on the system frequency is evaluated. Results indicate that as the radius of cylinder is increased, nonlinear frequency is enhanced. Initial amplitude plays a dual role on the frequency. As initial amplitude increases up to a certain point, frequency increases and decreases after wards.

Commentary by Dr. Valentin Fuster
2011;():767-773. doi:10.1115/IMECE2011-63554.

This paper describes a comparison study of power consumption of power minimizing controllers for active magnetic bearing (AMB) system. AMB system usually used bias currents in order to linearize force-current nonlinear relation. Using linearization with bias currents, AMB system achieves better dynamic performance and system linearity while bias currents always have to be consumed. The ohmic loss caused by them is one of the major energy losses of magnetic bearing systems. There are several researches to reduce constant power consumption by bias current. However, they all claim to reduce the power consumption of AMBs compared to the conventional PD-type controller, no study has been to compare these techniques. In this paper, we studied and implement previous researches with identical system frame for reasonable comparison. For comparison study, we derived simulation models using identical frame work and also built 2 degree-of-freedom (DOF) test bed.

Commentary by Dr. Valentin Fuster
2011;():775-781. doi:10.1115/IMECE2011-63829.

Cavity-vehicle interactions play a significant role in the dynamics of supercavitating underwater vehicles. To date, in the vast majority of planing force models for supercavitating vehicle dynamics, a steady planing assumption is utilized, wherein the vehicle-cavity interaction is only dependent on the vehicle’s position relative to the cavity. In this work, a framework to properly account for the vehicle radial motions into and out of the fluid is presented. This effectively introduces damping or velocity related dependence into the planing force formulation. The planing force is applied to cavity sections that are described by a previous (or delayed) position and orientation of the cavitator. The physical basis for the advection delay and the expressions used to determine the vehicle immersion and immersion rate are presented. Analysis and simulations for the time-delayed, non-steady planing system are carried out, and the delay effect in this system is shown to be stabilizing for certain values of the cavitation number that is contrary to previous results that have assumed steady planing force models.

Commentary by Dr. Valentin Fuster
2011;():783-792. doi:10.1115/IMECE2011-64349.

Geometrically nonlinear forced vibrations of shells based on the domains with cut-outs are investigated. Classical nonlinear shallow-shell theories retaining in-plane inertia is used to calculate the strain energy; the shear deformation is neglected. A mesh-free technique based on classic approximate functions and the R-function theory is used to build the discrete model of the nonlinear vibrations. This allowed for constructing the sequences of admissible functions that satisfy given boundary conditions in domains with complex geometries. Shell displacements are expanded by using Chebyshev orthogonal polynomials. A two-step approach is implemented to solve the problem: first a linear analysis is conducted to identify natural frequencies and corresponding natural modes to be used in the second step as a basis for nonlinear displacements. The system of ordinary differential equations is obtained by using Lagrange approach on both steps. The convergence of the solution is studied by using different multimodal expansions. The pseudo-arclength continuation method and bifurcation analysis are used to study the nonlinear equations of motion. Numerical responses are obtained in the spectral neighbourhood of the lowest natural frequency. When possible, obtained results are compared to those available in the literature.

Topics: Vibration , Shells
Commentary by Dr. Valentin Fuster
2011;():793-804. doi:10.1115/IMECE2011-64639.

Gearboxes have been prone to early failure rather than any mechanical part of modern wind turbines, much earlier than their predicted design life. Some studies indicated that gearboxes of wind turbines fail during the first 3 to 5 years of operation of the system as opposed to the total design life of the wind turbine, which usually is 20 years. Consequently, such failures cause the highest down time and extremely expensive replacement activities. Gearboxes are subjected to torsional, bending and axial wind loads which are yet not fully defined. The uncertainty in loading conditions and system design parameters has brought about the importance of considering probabilistic design and modeling approach than the traditional deterministic approach. Accordingly, the motivation of this study is to improve the reliability of gearboxes for wind turbine applications. A probabilistic multibody dynamic modeling of the gearbox, that fully integrates uncertainties in wind loading and design parameters, is sought. This paper presents previous studies and finally proposes the above mentioned approach as a potential way of improving, in general, the reliability of wind energy and, in particular, the gearboxes in wind turbines.

Commentary by Dr. Valentin Fuster
2011;():805-811. doi:10.1115/IMECE2011-64792.

Time delay is a long standing impediment of bilateral control and can destabilize the system evidently. We have already proposed a model-based approach for bilateral control of master-slave robot using time-domain passivity control. This method consists of a virtual slave environment model on the master side and the slave feedback force is modified. However, the chattering phenomena of force can be observed when the model based approach is activated or inactivated. In this paper, the viscosity of the master manipulator is modified according to the output of passivity observer rather than slave feedback force. The energy of the system is discussed using the proposed method and experiments about hard and soft environment contact have been carried out for verification of the proposed approach.

Topics: Force , Robots
Commentary by Dr. Valentin Fuster
2011;():813-820. doi:10.1115/IMECE2011-64818.

This paper presents an introduction to Evolving Systems, which are autonomously controlled subsystems which self-assemble into a new Evolved System with a higher purpose. Evolving Systems of aerospace structures often require additional control when assembling to maintain stability during the entire evolution process. This is the concept of Adaptive Key Component Control which operates through one specific component to maintain stability during the evolution. In addition this control must overcome persistent disturbances that occur while the evolution is in progress. We present theoretical results for the successful operation of Adaptive Key Component control in the presence of such disturbances and an illustrative example.

Commentary by Dr. Valentin Fuster
2011;():821-830. doi:10.1115/IMECE2011-64823.

Forcespinning™ is a novel method that makes used of centrifugal forces to produce nanofibers rapidly and at high yields. To improve and enhance this new nanofiber production method a model of the system is begun. The process is started by deriving the governing equations of the forcespinning™ sytem and the constraints associated it. A simple 2D model is then obtained using the derived governing equations for the inviscid case to determine the trends of fiber diameter and trajectories. Then, focus is given to the time-dependency of these equations, and the effects of parametric excitation of the system on fiber formation are analyzed. The equations are solved using a combination of the method of multiple scales and the finite difference method with slender-jet theory assumptions.

Commentary by Dr. Valentin Fuster
2011;():831-839. doi:10.1115/IMECE2011-65356.

Analytical and numerical methods are applied in order to study the response behavior of the constrained motion of a cantilevered beam for off-resonance excitation. Studies are conducted by using a multi-mode representation of the beam in order to accurately depict the influence of the bifurcation on the spatial response behavior. When modeling this system, the periodic collisions of the cantilevered beam with the compliant material result in a discontinuous force being applied to the free end of the beam. The constraining material is modeled by using the Kelvin-Voigt model. Due to the coupling of the damping and stiffness properties of the modal responses when in contact with the constraining material, a simplified single-mode approximation is used. A shooting method is used with the analytical solution of the simplified model in order to study the qualitative behavior of the system. Preliminary results using the analytical solution agree with the numerical results. The results of the shooting method reveal multiple stable solutions and suggest the presence of additional unstable periodic solutions.

Commentary by Dr. Valentin Fuster
2011;():841-848. doi:10.1115/IMECE2011-65404.

We investigate the nonlinear oscillations in a free surface of a fluid in a cylinder tank excited by non-ideal power source, an electric motor with limited power supply. We study the possibility of parametric resonance in this system, showing that the excitation mechanism can generate chaotic response. Additionally, the dynamics of parametrically excited surface waves in the tank can reveal new characteristics of the system. The fluid-dynamic system is modeled in such way as to obtain a nonlinear differential equation system. Numerical experiments are carried out to find the regions of chaotic solutions. Simulation results are presented as phase-portrait diagrams characterizing the resonant vibrations of free fluid surface and the existence of several types of regular and chaotic attractors. We also describe the energy transfer in the interaction process between the hydrodynamic system and the electric motor.

Commentary by Dr. Valentin Fuster
2011;():849-855. doi:10.1115/IMECE2011-65429.

Active vibration control of structures under earthquake excitation has attracted considerable attention in the recent years. In this study, attention was given to optimal preview control methodology for protection of building with and without base isolation systems against earthquakes. A three-story building model was used and several earthquake records including El Centro, Mexico City and Tabas earthquake records were used as excitation. Acceleration and displacement responses of the structure with active preview control were evaluated and the results are compared with those for the unprotected buildings. It was shown that using properly designed active preview control systems can effectively reduce the acceleration transmitted to structures during a major earthquake. The study was repeated for a base isolated structure. It was shown that that the using the information obtain from the preview sensors in the active control strategy would improve the system performance significantly. The influence of the preview time on the system performance was also studied. It was found that the range of preview time needed for improved performance is quite small but depends on the frequency contend of the earthquake excitation.

Commentary by Dr. Valentin Fuster
2011;():857-862. doi:10.1115/IMECE2011-65462.

This paper deals with the nonlinear response of an electrostatically actuated cantilever beam system composed of two micro beam resonators near natural frequency. The mathematical model of the system is obtained using Lagrange equations. The equations of motion are nondimensionalized and then the method of multiple scales is used to find steady state solutions. Both AC and DC actuation voltages of the first beam are considered, while the influence on the system of DC on the second beam is explored. Graphical representations of the influence of the detuning parameters are provided for a typical micro beam system structure.

Commentary by Dr. Valentin Fuster
2011;():863-870. doi:10.1115/IMECE2011-65716.

This paper deals with the dynamic analysis of a delaminated composite beam under the action of moving oscillatory mass. The beam is analyzed as four interconnected sub-beams using the delamination limits as their boundaries. The constrained model is used to model the delamination region. The continuity and equilibrium conditions are satisfied between the adjoining beams. The beam response variation due to the delamination with respect to the intact beam has been investigated. Furthermore, the possible separation of the moving oscillator from the beam during the course of the motion is investigated by monitoring the contact force between the oscillator and the beam. The effect of the parameters such as the oscillator axial velocity and the size, depth and spanwise location of the delamination on the dynamic response of the beam and on the oscillator separation from the delaminated beam has been studied. It is shown that the delamination has significant influence on the dynamic response of the beam and on the oscillator separation from the beam.

Commentary by Dr. Valentin Fuster
2011;():871-877. doi:10.1115/IMECE2011-65867.

Current field unbalance estimation methods regards “flexible rotors with lumped mass” as the main research object, and most of them need a stop running to take trial weights. Due to its test speed closing to the critical speed, the process of balance is really complicated and dangerous. This paper concerns rotors which unbalance state shows a continuous spatial distribution. Firstly, a dynamic finite element (FE) model of the rotor system is built, the inherent relations and differences between the dynamics transfer matrix and influence coefficient (IC) matrix are analyzed, and then, an extended dynamics matrix with arbitrary dimension is obtained based on the principle of IC balancing method. Secondly, the continuous distribution mass eccentricity curve is represented as mass eccentricity point on each FE model node, and the unbalance forces imposing on each FE model node are identified by the extended dynamics matrix. Finally, the theoretic analysis and experiment is presented to verify this method, and the result shows that unbalance forces on all FE model nodes can be identified accurately with less measuring points, and higher order modal components of the distributed unbalance are balanced effectively.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2011;():879-886. doi:10.1115/IMECE2011-65868.

This paper presents the implementation of a three degree-of-freedom magnetic levitation system. First the dynamic model of the magnetic levitation is developed. Then based on the nonlinear model, a robust nonlinear double-loop control algorithm is applied to stabilize the system. The double-loop control architecture consists of two components: 1) terminal sliding mode control (TSMC) is employed in the outer loop to stabilize the rigid dynamic model while maintains robustness.2) Auto disturbance rejection control (ADRC) is applied in the inner loop as a current loop controller to track current command. Finally, experimental results are presented to illustrate the performance of the system dynamic response and current response in each coil. The experiment results show that the terminal sliding mode algorithm combined with auto disturbance rejection control algorithm is effective in the nonlinear MIMO magnetic levitation system.

Commentary by Dr. Valentin Fuster
2011;():887-895. doi:10.1115/IMECE2011-62887.

We applied a novel sensing and data processing technique to analyze the water-interaction dynamics of a thin-walled aluminum beam filled with micro-structured material. The spatial impulse response is sensed at three spatial points in the form of ensembles of collocated acceleration signals. Processed by the powerful POD Transforms, the modal-like decomposition of collocated acceleration signals provides interesting insight on the nature of impulse-induced vibrations of this complex structure-water system. When not interacting with water, the point impulse excited structure vibrates in a dominant POD mode with energy-transfer wave form characteristics. When interacting with water, the point impulse excited structure vibrates in two POD modes. One POD mode is vibration while the other one is rigid-flexible body motion. The POD modes capture characteristics of interactions between flexible body (vibration-wave) and rigid body motions. This modal identification technique is potentially useful for reduced model identification and parameter estimation of hard to model complex structural-fluid interacting systems encountered in aerospace and ocean environments.

Commentary by Dr. Valentin Fuster
2011;():897-906. doi:10.1115/IMECE2011-63435.

The necessity of providing reduced models of dynamical systems is growing continuously. Model-based control and model-based design are exemplary fields of applications. In this contribution, the reduction of a controlled drivetrain of a rolling mill using the method of Proper Orthogonal Decomposition is investigated, where the specific choice of the control law leads to equations of motion with time-periodic coefficients. Depending on amplitudes and frequency parameters of the time-periodic coefficients, artificial damping is introduced, referred to as parametric control. The maximum damping effect depends on these parameters in a nonlinear manner, as it is shown by means of a stability-parameter from Floquet theory. The reduced model set-up approximates the stability-parameter of the full model in an appropriate way within a wide range of the parameters. A measure based on the linear time-invariant system is developed that gives insight into the effect of the simulated timeseries on the properties of the reduced model.

Commentary by Dr. Valentin Fuster
2011;():907-915. doi:10.1115/IMECE2011-63797.

A cycle-mean-value, quasi-steady, thermodynamic model of slow-speed, two-stroke marine Diesel engines, used for performance prediction and engine-propeller/turbocharger matching, is converted into a power-plant analytic model. The dynamic part of the cycle-mean model consists of the two first-order differential equations for the cycle-mean crankshaft and turbocharger shaft rotational accelerations. This form implies a state-space formulation of the power-plant modeling approach. However, engine, turbine and compressor torques have to be calculated through the solution of the algebraic part of the model, which consists of a nonlinear, perplexed algebraic system of equations not analytically solvable. This inhibits the formulation of the power-plant state-space description. By approximating the torque maps, generated by the thermodynamic model, with neural nets, explicit functional relationships are obtained. Identification of the power-plant operating regimes through linearization and decomposition is performed. In effect, a supervisory power-plant controller structure, applicable to real-time control and diagnostics, is proposed, incorporating the nonlinear state-space description of the plant.

Commentary by Dr. Valentin Fuster
2011;():917-925. doi:10.1115/IMECE2011-64638.

The present work concerns the study of the experimental Proper Orthogonal Decomposition (POD) modes of three simultaneously acquired ensembles of collocated impulse-induced acceleration signals in a complex multi-beam aluminum structure. The impact-induced locally transverse acceleration of a three-beam structure is measured simultaneously at three fixed points with state-of-the-art piezoelectric sensors. Each ensemble of collocated databases is processed by the POD Transform to find out that it is underlined by strong coherence in space and time manifested by a small number of POD modes. It is found that the unit space modulations of the first-the dominant-POD modes of the three databases of experimental acceleration signals form an orthonormal set. The same is true for their companion unit time modulations. This original result leads to the identification of three normal modes of vibration for the complex beam structure.

Topics: Aluminum , Signals
Commentary by Dr. Valentin Fuster
2011;():927-934. doi:10.1115/IMECE2011-62277.

A new method for identifying multiple damages in a structure using embedded sensitivity functions and optimization algorithms is presented in this work. Optimization techniques are used to minimize the difference between the measured frequency response functions from a damaged structure and the predicted FRFs from the baseline structure. The predicted FRF functions are calculated directly from the undamaged system response data using the embedded sensitivity functions and their Taylor series expansions. The optimal damage parameters are identified in engineering units as changes in stiffness, damping, or mass through the optimization process for minimizing the difference between those two FRFs. The method is applied to a two degree of freedom analytical model to determine the accuracy of the diagnostic results. Finite element analyses are then conducted on a three-story structure with damages in the form of stiffness and mass perturbations to demonstrate the applicability of this method to more complicated structural systems. It is shown that the suggested technique can detect and quantify multiple damages in a structure with high numerical accuracy in the level of the estimated damages.

Commentary by Dr. Valentin Fuster
2011;():935-941. doi:10.1115/IMECE2011-63159.

In this paper, a four-rigid-body element model is presented for description of flexible components of a horizontal axis wind turbine (HAWT). The element consists of four rigid bodies arranged in a chain structure fashion. The bodies of each element are linked by two universal joints at two ends, and one cylindrical joint at the middle. Thus each element has six degrees of freedom. They are four degrees of freedom for bending, one degree of freedom for torsion, and one degree of freedom for axial stretching. For each degree of freedom, a spring is used to describe the stiffness of the component. Stiffness of each spring is obtained by using potential energy equivalence between a Timoshenko beam and these springs. With these considerations, flexible components of a HAWT such as blades and tower may then be represented by connecting several such elements together. Based on four-rigid-body element model, the tower and blades of a HAWT are constructed. Their equations of motion are then derived via Kane’s dynamical method. Commercial computational multibody dynamic analysis software Autolev has been used for motion simulation of tower and blades under given initial conditions. Simulation results associated with the tower indicate that four-rigid-body element model is suitable for analysis of dynamic loads, modal, and vibration of wind turbines with respect to fixed and moving references at high computational efficiency and low simulation costs. The approach is also a good candidate for simulating dynamical behaviors of wind turbines and preventing their fatigue failures in time domain.

Commentary by Dr. Valentin Fuster
2011;():943-952. doi:10.1115/IMECE2011-63452.

In a wind-turbine gearbox, planet bearings exhibit a high failure rate and are considered as one of the most critical components. Development of efficient vibration based fault detection methods for these bearings requires a thorough understanding of their vibration signature. Much work has been done to study the vibration properties of healthy planetary gear sets and to identify fault frequencies in fixed-axis bearings. However, vibration characteristics of planetary gear sets containing localized planet bearing defects (spalls or pits) have not been studied so far. In this paper, we propose a novel analytical model of a planetary gear set with ring gear flexibility and localized bearing defects as two key features. The model is used to simulate the vibration response of a planetary system in the presence of a defective planet bearing with faults on inner or outer raceway. The characteristic fault signature of a planetary bearing defect is determined and sources of modulation sidebands are identified. The findings from this work will be useful to improve existing sensor placement strategies and to develop more sophisticated fault detection algorithms.

Commentary by Dr. Valentin Fuster
2011;():953-961. doi:10.1115/IMECE2011-63509.

A common treatment in manufacturing web-like thin materials like paper is to manipulate it between two cylinders under rolling contact. A roll press is sensitive to vibration, which is unwanted, because it marks the web by periodical stripes. The excitations can be external ones, which are transmitted by the web in terms of periodic thickness or stiffness distributions, or internal ones, which are related to the shape or elasticity distributions of the roll and cover layer. When such excitation mechanisms are working and the rolls are interacting over the contact zone, the role of the roll cover becomes very important. Because the cover material is visco-elastic, the delayed recovery response of the polymer during each roll revolution starts to initialize self-excited vibrations. This contact vibration is known as barring. A piezoelectric actuator is an excellent device for vibration control applications because of its large force generation, very short response time and easy controllability. Control of piezoelectric actuator is straightforward by direct compensation of input voltage, which in turn can be generated from vibration data measured from the system. This presentation gives an overview how to approach the vibration control problem of complex roll press systems. A vibration damping system based on piezoelectric actuators with a feedback control loop and with a passive electric circuit is introduced to eliminate/reduce resonance oscillations.

Commentary by Dr. Valentin Fuster
2011;():963-973. doi:10.1115/IMECE2011-63903.

The role of the “geometric stiffening” nonlinearities played in the stability analysis of a rotating beam is investigated. It is a well established fact that nonlinear theory must be employed to capture geometric stiffening effect, which has been extensively investigated. In this work, two models are built for a rotating blade with periodically perturbed rotation rate, one is the “effective load” linear model and the other is “geometric stiffening” nonlinear model. Both of these two models are discretisized via Galerkin’s method and a set of parametric excited gyroscopic equations are obtained. The dynamic stability of these two models are studied and compared by the generalized harmonic balance method.

Commentary by Dr. Valentin Fuster
2011;():975-984. doi:10.1115/IMECE2011-63965.

Modal vibration parameters such as frequency, damping ratio and mode shape have long been considered useful for identifying damage in structures. In this paper a generalized approach is presented that allows for damage to be localized and quantified using regression and response surface modeling of modal frequency. Regression models or response surface models are developed to characterize how modal frequencies of structures are affected by variations in parameters such as defect depth, width and location. Design of experiments (DOE) techniques are used in conjunction with experimental modal frequency measurements to solve for defect parameters of test specimens in the field for condition monitoring. Determining defect parameters can be done by inverting and explicitly solving regression model equations, employing software-driven numeric optimization or through a graphical approach that overlays contour lines of multiple response surface models. Either of these methods can be automated. This approach is explored and validated with finite element and theoretical beam models along with a series of physical experiments on cantilevered aluminum rods. The method performs well for detecting simple and distinct defects. Implementation complexity increases when detecting multiple or more variable, less-easily quantifiable defects. In its general form, the method shows promise for damage detection when a specific type of consistent defect is known to occur or for applications such as quality control on production lines and monitoring of deposit buildup in pipes.

Commentary by Dr. Valentin Fuster
2011;():985-990. doi:10.1115/IMECE2011-64689.

This study investigates the motion of micro parts on several vibratory plates with saw-tooth surface profile driven by a piezoelectric actuator. The surfaces are made of carbide, brass, and zirconia with the same profiles as a saw-tooth. The velocity and position of micro-parts are time-dependently measured by the particle tracking velocimetry (PTV) method where the Canny edge detection technique is used. In the present experiment, 2012-type micro-parts whose dimensions are 2.0 × 1.2 × 0.6 mm3 in length, width, and depth, respectively, are employed. The mass of each micro-part is 7.5 mg. Using a high-speed camera, the tracked longitudinal displacement resolution is found to be about 0.01 mm, which is small in comparison with the length of each micro-part. The obtained results show that unidirectional motion can be attained by the present feeder system. For the same oscillating frequencies and amplitudes applied to the sawtooth surfaces, the motion behavior of micro-parts varies for different experiments and surfaces. This implies that the motion of micro-parts is affected by uncertain causes. However, the probability distribution of the micro-parts’ velocity can be approached by a Gaussian distribution.

Commentary by Dr. Valentin Fuster
2011;():991-1001. doi:10.1115/IMECE2011-64778.

Structural health monitoring (SHM) is the process of implementing a damage identification strategy which can be utilized in several applications including aerospace, civil and mechanical engineering infrastructure. Damage is defined as changes to the material and/or geometric properties of these systems. These changes adversely affect the current or future performance of the system. In order to identify damage in a suitable and meaningful manner, the damaged state is compared with other usually undamaged states. This study focuses on a structural health monitoring (SHM) system based on detecting shifts in natural frequencies of the structure. This structural health monitoring system incorporates a low power wireless transmitter that sends a warning signal when damage is detected in a structure. The damage detection technique is implemented on composite structures which are widely used in many applications including aeronautical and aerospace. An automated damage detection system capable of providing information of damage locations based on the finite element analysis and able to compare damage events to other historical data is also proposed in this paper and initially implemented using a microcontroller chip. Moreover, a control methodology using piezoelectric fiber composites, such as active fiber composites (AFCs) and microfiber composites (MFCs), is included as part of the system for vibration suppression purposes. The advantages of using piezoelectric fiber composite actuators are their high performance, flexibility, and durability when compared with the traditional piezoceramic (PZT) actuators. The proposed system may be implemented in many structural components such as aircraft frames and bridges. This SHM technology may help replace the current time-based maintenance scheme with a condition-based one. The condition-based maintenance scheme relies on the ability to monitor the condition of the system and supply information of damage detection to allow a corrective action to be taken.

Commentary by Dr. Valentin Fuster
2011;():1003-1011. doi:10.1115/IMECE2011-65117.

Vibration-based techniques are increasingly being recognized as effective non-destructive structural damage identification tools. One promising technique relies on combining a finite element model (FEM) of the structure under investigation with a set of experimental frequency response functions (FRFs) to construct a so-called Damage Location Vector (DLV). This paper aims to assess damage detection using DLVs both theoretically and experimentally. To this end, the method is first studied theoretically on a thin plate using simulated damage. The method is then tested experimentally on a free-free plate provided with several damage cases using impact hammer testing. The main contribution of the present work lies in attempting to improve the DLV techniques through the use of the experimental FRF data of the intact structure in addition to the theoretical FRF from a finite element. The results obtained indicate that the improved algorithm can be used to successfully detect structural damage.

Commentary by Dr. Valentin Fuster
2011;():1013-1026. doi:10.1115/IMECE2011-65691.

Based on a recent asymptotic analysis of a nonlinear model of elevator traveling and compensation cables, a computationally efficient, linear model is developed for calculating the natural frequencies, mode shapes, and dynamic responses of stationary elevator traveling and compensation cables. The linear cable model consists of two vertical cable segments connected by a half circular loop at the bottom. The two vertical cable segments are modeled as a string with a variable tension due to the weight of the cable. The horizontal displacements of the cable segments consist of boundary induced displacements and internal displacements, where the boundary induced displacements are interpolated from the displacements of the two ends of the cable segments, and the internal displacements satisfy the corresponding homogeneous boundary conditions of the cable segments. The horizontal displacement of the lower loop is interpolated from those of the two lower ends of the two cable segments, and the bending stiffness of the lower loop is represented by a spring with a constant stiffness, which can be calculated from the nonlinear model. Given a car position, the natural frequencies and mode shapes of an elevator traveling or compensation cable are calculated using the linear model and compared with those from the nonlinear model. The calculated natural frequencies are also compared with those from a full-scale experiment. In addition, the dynamic responses of a cable under a boundary excitation are calculated and compared with those from the nonlinear model. There is a good agreement between the predictions from the linear and nonlinear models and between the measured natural frequencies from a full-scale experiment and the corresponding calculated ones.

Topics: Cables , Elevators
Commentary by Dr. Valentin Fuster

Mechatronics and Intelligent Machines

2011;():1027-1033. doi:10.1115/IMECE2011-62783.

An electromagnetic micro-actuator operating on the principle of voice-coil actuators is presented. Using finite element analysis of several conceptual designs of actuators [1–3], it was established that the voice-coil type device (where the coil is the moving part) has most beneficial characteristics for the envisioned application. These include sufficient force over a relatively large distance, allowing tactile stimulation of surfaces with irregular shape, fast response, and small footprint that matches the density of the tactile sensory neurons in the finger. Finite element analysis based on ANSYS was used to determine the dimensions of the components of the actuator. In comparison to earlier designs [3–5], this novel device has smaller sizes (2.28 mm in diameter and 7 mm in length), which makes it suitable for use in an array to be worn on the fingertip. Based on the static measurements of a test prototype, it is estimated, that the micro-actuator can produce at least 26 mN of repulsive force on the fingertip over a stroke of 2100 μm with a peak force of 34 mN. The driving circuit operates with 13.5V and generates a vibration frequency of up to 265 Hz without significant change of the force-displacement characteristics. In the higher frequency range (above 100 Hz) the actuator provides at least 15 mN of force over a stroke of 2300 μm, and a peak force of 21mN. The perceivability of the device on human fingertip approves the expectations drawn from the fact that all of the above parameters meet the required values of the thresholds of the human perception known from [4] and [5]. Due to its increased stroke, the voice-coil micro-actuator proved to be very suitable for the envisioned application allowing contact with the curved surface of the fingertip.

Topics: Microactuators
Commentary by Dr. Valentin Fuster
2011;():1035-1039. doi:10.1115/IMECE2011-64070.

Magnetically levitated robots can move without lubrication, they generally have advantages to the use in the various special environments such as in a dust-free room, in a vacuum, in a flammable atmosphere, and in vivo. Meanwhile, they have a disadvantage of small working volume corresponding to the allowable air gap between the levitated object and the electromagnets. In some cases, to construct a combination of a magnetically levitated robot and an industrial robot which has a comparatively large working volume seems an effective way to expand the whole working volume. On that premise, we are developing an experimental system and simulator for collaborative work between a magnetically levitated robot and an industrial robot. This paper presents the system concept and the configuration of the simulator which is corresponding to the actual elements: magnetically levitated robot, industrial robot and manipulation device.

Topics: Motion , Robots
Commentary by Dr. Valentin Fuster
2011;():1041-1050. doi:10.1115/IMECE2011-64074.

Many diseases and conditions can cause reduced motor function in joints throughout the body. This paper identifies such health issues that affect the function of the wrist and hand in particular. After identifying these conditions, a concept three degree of freedom (two DOFs of the wrist plus cylindrical grip) robotic exoskeleton design is presented that is intended to augment a patient’s remaining function and strength while remaining portable and lightweight. With this in mind, the device is intended to allow a patient to use and operate it independently, without the presence of a therapist. The mechanical design of the exoskeleton is described in depth, along with details of potential actuation methods. The main idea for control of the device is to detect small torque values as a patient attempts a movement and in turn predict what the intended outcome would be if the patient were at full strength. After processing this information the robot would assist the patient in facilitating the anticipated movement. This is in contrast to alternate control methods, which rely primarily on electromyography (EMG) to detect signals to muscles that control certain movements. Electromyography can be unreliable because many of the conditions that cause debilitated function also cause an interruption or break in these signals.

Topics: Robotics
Commentary by Dr. Valentin Fuster
2011;():1051-1055. doi:10.1115/IMECE2011-64160.

Magnetic actuation has opened a new horizon in biological/biomedical applications. A novel magnetic actuation platform has been developed at Maglev Microrobotics Laboratory, University of Waterloo. In the previous work, laser sensors were used for positioning the levitated microrobot. This technique can be used only in transparent environment. In this paper, for applications in an enclosed environment, which may not be transparent, a novel position estimation method was proposed. The proposed method uses hall sensors, mounted on the disk pole-piece. The hall sensors’ optimal installation position has been investigated, and a function which relates hall sensors’ output and the position of robot was derived. Based on this function, position control of horizontal axis using hall sensors in place of laser sensor can be achieved. Usability of two dimensional controls in horizontal axis without laser sensors will be experimentally validated as future work of this research.

Commentary by Dr. Valentin Fuster
2011;():1057-1058. doi:10.1115/IMECE2011-65039.

Current techniques focus on generating ZnO nanowires with uniform density and length on a substrate. However, ZnO nanowires with gradients of density and length over a single substrate could make the corresponding devices have varied properties. Here, we have explored the possibility of fabricating nanowires with gradients in density and length using the vapor-solid method via tilting of the substrate using a mixture of ZnO and graphite powder. This setup creates a non-uniform boundary layer (δ) over the substrate which varies the concentration of reactants reaching the surface leading to the asymmetric growth of the nanowires. A 2-D model was developed in Fluent in order to determine the distribution of velocities around the substrate and calculate δ, with the following substrate tilt angles: 0°, 30°, 45°, 60° and 80°. From the simulation results, the variation of δ was maximum for the 80° tilted substrate. Hence, this angle of tilt was chosen for our experiment. The nanowires were sampled for their densities, lengths and diameters at four locations (L1–L4), spaced 5 mm apart. As an application, we have demonstrated the formation of a surface with continuously varying hydrophobicity. The water contact angles measured were as follows: L1: 105°; L2: 116.5°; L3: 129.5°; and L4: 171.0°. A water droplet (volume: 4 μL) was able to move a distance of 10 mm in 0.8 s, with a substrate tilt of ∼1°.

Commentary by Dr. Valentin Fuster
2011;():1059-1060. doi:10.1115/IMECE2011-65041.

Current microsystems primarily have a planar form. On the other hand, substrate sidewalls of these microsystems have not been well used in constructing devices. When patterns are generated on those sidewalls, they could be potentially used as electronic components of 3-D circuits or vertical interconnects. Existing photo-lithographic approaches are not capable of patterning the sidewalls of structures. Therefore, in this work, we have developed a novel method to generate line and dot patterns on the sidewalls of microchannels using strain-recovery property of polystyrene (PS), which is a thermal shape-memory polymer. The fabrication procedure consists of three basic steps. Firstly, microchannels were generated on a PS film using oxygen reactive ion etch. Secondly, 50 nm-thick Ag lines (100-, 150-μm-wide) and dots (50 × 50 μm2 ) were sputtered on the etched PS film with the aid of another SU-8 stencil. Thirdly and finally, the PS film was heated to 160 °C for 30 min. This caused the decrease in width and increase in depth of the channels induced by the strain recovery of the PS. The sidewall inclination of the microchannels increased greatly after heating causing the Ag lines and dots to transfer to the channel sidewalls. These experimental results demonstrate the possibility of fabricating Ag lines and dots on the sidewalls of an array of microchannels using the developed approach.

Commentary by Dr. Valentin Fuster
2011;():1061-1064. doi:10.1115/IMECE2011-65147.

In this work, we explored the possibility to reduce the friction drag and increase buoyant force of a SU-8 microboat by incorporation of micropillars. We considered mechanism, design, and fabrication, followed by experimental tests. Through two sets of tests, we demonstrated that the incorporation of the micropillars reduced the friction drag and increase buoyant force as expected.

Commentary by Dr. Valentin Fuster
2011;():1065-1066. doi:10.1115/IMECE2011-65155.

As a liquid droplet is placed on a rough surface, the wetting may be either in Wenzel state [1] or in Cassie-Baxter state [2]. In the Wenzel state, the droplet completely penetrates between microstructures (e.g., lines and pillars), while in the Cassie-Baxter state air is trapped between these microstructures and the droplet stays on top of the microstructures and trapped air. The Cassie-Baxter state may be transited to the Wenzel State when Laplace pressure reaches a certain value [3]. To date, three pressure criteria have been reported in the literature to predict when the transition may occur from the Cassie-Baxter state to the Wenzel State. The first criterion is [4]

Pl−Pg>−4γlg cos θe2b(1+b2a),    (1)
where Pl is the pressure in liquid, Pg is the pressure in gas, (Pl Pg ) is so-called Laplace pressure, γlg is surface tension between liquid and gas, θe is the equilibrium contact angle on the flat surface and b is the space between two adjacent pillars. The second criterion has the form
Pl−Pg>−4γlg cos θe2b.    (2)
The third criterion is given by [5]
Pl−Pg>−4γlg cos θe2b.    (3)
Although these pressure criteria have similar forms, there still exist differences in their denominators. It is not clear which criterion gives the best prediction of the transition during the evaporation of a water droplet. Therefore, in this work, we examined these three criteria based on the experimental data obtained through in-situ observation of the transition of a droplet.

Topics: Evaporation
Commentary by Dr. Valentin Fuster
2011;():1067-1070. doi:10.1115/IMECE2011-62396.

A combined elastica and magnetic modeling is presented in this paper with focus given to understanding effect of flexible printed circuit cable and voice coil motor’s dynamic effect on tape head actuator’s lateral motion in advanced, high capacity tape drives. The flexible printed circuit cable which connects the actuator to printed circuit board is first examined through establishment of analytical model to predict its profile with considerations of boundary conditions and mechanical design parameters. Secondly, equivalent stiffness produced by the flexible printed circuit cable when the linear tape head actuator is positioned along its lateral positions is examined. Finally, effect of tape head actuator’s voice coil motor is studied and modeled as a magnetic suspension, contributing to stability and controllability of the actuator lateral motion dynamics. Validated by calibrated laboratory experiments, the work presented in this paper can add to the literature regarding dynamics and control of LTM in modern LTO drives.

Commentary by Dr. Valentin Fuster
2011;():1071-1075. doi:10.1115/IMECE2011-62408.

The polygonal airflow patterns between disks in hard disk drives (HDDs) were investigated by using fluid simulations and pressure measurements. These patterns were found from the radial velocity distributions of airflows on the mid-plane between disks. Several peaks of pressure increases caused by rotating polygonal-airflow patterns with several modes were measured with a pressure sensor placed on the tip of the carriage arm and spoiler. Several modes of polygonal patterns were observed at the outer diameter (OD) and the middle diameter (MD) arm positions, but not at the inner diameter (ID) arm position. These peaks on the arm were weakened by the spoiler.

Commentary by Dr. Valentin Fuster
2011;():1077-1084. doi:10.1115/IMECE2011-63533.

Flow inside a hard-disk drive (HDD) is investigated using a simplified 3.5″ HDD model with shroud opening and read-and-write arm (RWA). The model is designed to serve as a benchmark of HDD flow study both in experiments and in numerical simulations. The complex flow behavior in the narrow disk-to-disk space is focused with the RWA inserted into the space. The velocity statistics are acquired at totally 8 different locations using a velocity profile sensor with a spatial slot resolution of 30 μm along the axial direction. The measurement was carried out at the disk Reynolds number Red = 2.4×105 which corresponds to the rotation speed of 7700 rpm at a real 3.5″ HDD for desktop computers. The resulting mean velocities and Reynolds stress components are influenced by the shroud opening and especially by the RWA, compared to an axisymmetric model without an RWA. The highly sheared flow between the RWA and adjacent upper/lower disk was successfully captured in the experiment.

Commentary by Dr. Valentin Fuster
2011;():1085-1094. doi:10.1115/IMECE2011-63954.

Precise and accurate manufacturing became an obligation in aerospace industry in last decades. Uniformity of turbine blades, nozzle geometries, gaps, diameter changes and misalignment issues in turbine assemblies have to be inspected carefully in terms of quality and exactitude. Like broadly used aluminum and titanium based materials, ceramics and special coated composites are also used in aerospace applications. A wide selection of measurement methods used is based on intensity sensing and range imaging. With the recent development in advanced laser techniques, new methods that involve non contact measurement methodologies are being investigated by many industries. In addition to their accuracy and precision, speed of measurement and compactness of such systems are also of high significance. In this paper, a hybrid approach consisting of laser based triangulation, photogrammetry and edge detection techniques has been investigated to measure inner surfaces of parts that have limited access, especially where human presence is impossible. The system is capable of detecting and measuring misalignments, gaps, inclinations as well as surface variations such as cracks and dents. The system employs the accuracy and speed of measurement of triangulation systems and combines these with the mobility and cost effectiveness of photogrammetry and edge detection techniques. In addition to gap and alignment offset inspections, the methodology and the instrument enables angle measurements, detailed surface texture examinations and other inspections needed to be done inside assemblies with narrow openings, with its compact body. Additionally, a comprehensive experimental study has been conducted to show that two different edge detection methods, namely, the “Simple Edge Tool” and “Straight Edge (Rake) Tool” can be used with great accuracy and precision for such measurement purposes. With this system, any surface, whether they have a reflectance or not, can be scrutinized.

Topics: Lasers
Commentary by Dr. Valentin Fuster
2011;():1095-1098. doi:10.1115/IMECE2011-64328.

A non-contact angular measurement system for Pitch Static Attitude (PSA) and Roll Static Attitude (RSA) of hard disk drive sliders is designed and built. Real-time sampling at over 15 KHz is achieved with accuracy of +/−0.05 degrees over a range of approximately 2–3 degrees. Measuring the PSA and RSA is critical for hard drive manufacturers to control and improve the quality and reliability of hard drives. Although the hard drive industry is able to measure the PSA and RSA at the subassembly level at this time, there is no system available that is able to measure PSA/RSA at the final assembly level. This project has successfully demonstrated a methodology that the PSA/RSA can be reliably measured in-situ using a laser and position sensitive detector (PSD) technology. A prototype of the measurement system has been built. This device will allow a continuous measurement between the parked position on the ramp and the loading position just off of the disk surface. This measured data can be used to verify manufacturing processes and reliability data.

Commentary by Dr. Valentin Fuster
2011;():1099-1103. doi:10.1115/IMECE2011-64416.

Optical imaging system always appears an asymmetric displacement under finite element analysis (FEA) for the asymmetry of the loads and the optomechanical structure, although the system is designed by an axisymmetric way. The asymmetric displacement can generate a misalignment, between “the (0,0) field” of the aberration analysis and “the central field” through the optical axis, and decline the accuracy of objective function of an optimization design. An algorithm is presented to separate the rigid-body linear displacement, which has no influence on the imaging quality, from the FEA data. Actually the linear displacement of system is a special region around the (0,0) field on the image surface rather than a displacement such as any single optical element. In the algorithm, the region with the same value of optical modulation transfer function (MTF) calculated by the optical ray tracing tools is defined as a domain D(x,y), where the (x,y) is a set or subset of (x0 ,y0 ) and MTF(x0 ,y0 ) is equal to MTF(0,0). The nodal displacements can add or subtract a certain value while the modified central point on or in the region in an optimal design of optical system under any static, dynamic and vibratory loads. And an example is demonstrated that the nodal displacement processed by the algorithm is more suitable to optimize the imaging system suffered from the static and vibration conditions than the original FEA data.

Commentary by Dr. Valentin Fuster
2011;():1105-1111. doi:10.1115/IMECE2011-62168.

In this paper, a mathematical model has been developed and later combined with dynamic performance test methodology to investigate and understand the dynamic characteristics of different types of rotary Electronic Fuel Control (EFC) valves. The model takes into account the dynamics of the electrical and mechanical portions of the EFC valves. A recursive least squares (RLS) type system identification methodology has been utilized to determine the transfer functions of the different types of EFC valves that were investigated. Methods have been used both in frequency domain as well as time domain. Based on the characteristic patterns exhibited by the EFC valves, a fuzzy logic based pattern classification method was utilized to identify faulty EFC valves from good ones. The developed methodology was shown to provide robust diagnostics for a wide range of EFC valves.

Topics: Fuels , Valves , Failure
Commentary by Dr. Valentin Fuster
2011;():1113-1122. doi:10.1115/IMECE2011-62391.

In-process electronic high speed weighing systems play an important role in the highly automated, continuously evolving industrial world of today. They are an essential component in sorting, grading and quality control within a diverse range of industries, including; robotics, automotive and food. Load cells are considered to be the definitive force sensor for industrial weighing systems. Load cell output is in the form of an oscillatory response in which the measurand contributes to the response parameters. Current methods require the oscillatory response to settle in order to achieve an accurate measurement. This is time consuming and speed limiting. The focus of this paper is to find alternative weighing analysis methods for a system which utilises two load cells, placed either side of a carrier travelling on a chain conveyor, running at speeds of 10 items a second. It is necessary to determine the value of the measurand in the fastest time possible to speed up the process and increase throughput. This has been approached by mathematically modelling the system to allow accurate prediction of the weights passing the load cells before the settling time of the oscillatory response. Simple models of harmonic motion have been considered for the motion of a load cell. An experimental system was built and weighing data collected for different speeds and loads. Power spectra of the weighing data was analysed to determine dominant frequencies and estimate system parameters. This paper describes the work done to date on load cell modelling and improving an in-process electronic weighing system by successfully predicting the weight during the transient period of the oscillatory response. The assumptions and results of both simulations and experimental data are presented.

Commentary by Dr. Valentin Fuster
2011;():1123-1133. doi:10.1115/IMECE2011-62450.

Effective path planning techniques for mobile robots have potential uses and ramifications in a wide range of fields. As a result, the study of these techniques is highly diverse, and historically rich. In this vein we present a path planning methodology for a particular type of robot — one which flies above a terrain but must periodically land at waypoints. The approach demonstrated here is notable for drawing its inspiration and working basis from several different engineering fields. NURBs-based metamodels, a concept developed in the field of engineering design, are used to represent terrain to be navigated. Goal programming, largely used in operations research, is used to determine optimal landing waypoints. Graph theory concepts (derived from the field of computer science) are used to generate robot paths, and more broadly as data structures for information management. We demonstrate the new method on a variety of terrain maps, and present our conclusions on the effectiveness of the algorithm. We close with remarks regarding potential future developments and improvements that may be made to increase the utility of this approach.

Commentary by Dr. Valentin Fuster
2011;():1135-1138. doi:10.1115/IMECE2011-62465.

In this paper, development of a prototypical microcontroller controlled ultrasonic actuator system incorporating a plate-like piezoelectric actuator is discussed to provide an alternative means in actively guiding the tape laterally. Structural vibration modes are first experimentally examined through standard modal analyses. Method of modal superposition is used in programming the micro-controller so as to provide excitations to the PZT actuator resulted in traveling waves in the plate-like structure. Promising results are demonstrated in the proposed system that have rich implications in providing active guiding mechanism to minimize and even actively control the tape’s lateral motion.

Topics: Motion
Commentary by Dr. Valentin Fuster
2011;():1139-1151. doi:10.1115/IMECE2011-62494.

Control of redundant robotic manipulators has proven to be troublesome in the past. Redundant manipulators exhibit more degrees of freedom than there are constraints on their pose. As a result the robot’s kinematics are non-deterministic, and an infinite number of robot poses satisfy any given set of constraints. Thus there are an infinite number of paths that a robot may take whilst following a trajectory planned in Cartesian space (as opposed to joint space). We present a trajectory following method for a redundant welding robot with nine degrees of freedom (DOF). A powerful modeling tool widely used in operations research, AMPL, is leveraged to this end. The paths developed for the 9-DOF robot are optimized for minimum energy consumption by the robot motors. We also demonstrate a simulated robot work cell which is used to visualize and demonstrate the paths produced in this manner. Common robotic welding tasks are used to demonstrate the effectiveness of these optimization and visualization tools. We conclude with a discussion of the computational efficiency and limitations of this new method, and highlight several paths forward for this line of research.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2011;():1153-1158. doi:10.1115/IMECE2011-62500.

Wearable assistive devices’ (WADs) development is impeded by traditional actuators’ and control paradigms’ lack of compliance and adaptability; as such, the central nervous system’s (CNS) actuation and control principles have been investigated in order to overcome these limitations in a novel way. A bio-mimetic model of a limb joint, which is antagonistically actuated by two Hill-type muscles, is presented. Limb joint stability and transient response, as functions of co-activation, have been investigated. Three simulations have been carried out: equal (Af(f,f)), unequal (Af(3,f)), and differential (Af(3,Ramp(g))) co-activation. For normalized stimulus frequency range: 1 ≤ f ≤ 3, equal and unequal co-activation leads to increased limb joint damping and reduced transient oscillation. For the equally/unequally co-activated case, the linearized model’s dominant complex-conjugate poles become increasingly negative and tend towards the real axis, which indicate that increased co-activation leads to increased joint stability. With respect to differential co-activation, increasing the limb joint’s antagonistic muscle’s normalized stimulus frequency’s (f) rate of change (g) leads to increased angular velocity (ω); however, at a cost of increased overshoot. Differential activation of the antagonistic muscle results in positive angular rotation (Θ).

Commentary by Dr. Valentin Fuster
2011;():1159-1163. doi:10.1115/IMECE2011-62650.

Piezoelectric actuators for dynamic applications must be pre-stressed to avoid tensile stress and to improve their reliability. The actuating behavior of piezoelectric actuators depends strongly on the load characteristics: If the load increases with extension of the piezoelectric ceramic, e.g. when using a classical spring, the actuator cannot reach its nominal displacement; when the load remains constant, e.g. when acting against a mass load, full nominal displacement can be obtained at a maximum operating voltage. A general objective for the design of pre-stressing elements is to realize a small stiffness and sufficient load capacity. For standard materials this requires a good compromise in dimensioning. The nonlinear, hysteretic stress-strain diagram of superelastic shape memory alloys (SMA) is characterized by two stress plateaus during loading and unloading. In this strain range of up to 8%, the stress is nearly constant. Uniaxial tensile loaded spring bars made of superelastic SMA exhibit a theoretical stiffness of 0 N/m in the superelastic range of deformation. Therefore, the constant stress plateaus can provide both, low stiffness and sufficient load capacity. The concept of pre-stressing piezoelectric actuators with superelastic SMA will be analytically designed. In particular, the stress-strain behavior of NiTi-based superelastic SMA will be investigated by measuring major and minor hysteretic loops.

Commentary by Dr. Valentin Fuster
2011;():1165-1172. doi:10.1115/IMECE2011-62674.

The family of Epi.q mobile robots is based on a three-wheeled locomotion unit which is capable of switching between wheeled locomotion and legged locomotion depending on the dynamic conditions, without control intervention. This feature allows to conjugate the benefits of both the locomotion modes: high speed and energetic efficiency on even terrains with the wheeled locomotion, and mobility performance on uneven terrains and in presence of obstacles with the legged locomotion. Two prototypes of the Epi.q family have been already realized and tested, with positive results; a further evolution with four actuated locomotion units (instead of two active and two idle units) is currently under construction. The present paper outlines the evolution of the family of Epi.q mobile robots and proposes several possible architectural evolutions exploiting a modular approach; this approach could be used also to simplify the design phase, obtaining different mobile robots from a limited set of base modules.

Topics: Mobile robots
Commentary by Dr. Valentin Fuster
2011;():1173-1177. doi:10.1115/IMECE2011-63057.

In order to solve energy supply problems in ubiquitous information systems, a new driving technique for the gyroscopic power generator has been developed. The generator was made to work as a motor, Which was started automatically by providing an initial velocity. The ability to generate 0.7 W of power from vibration, the frequency of which is as low as 1 Hz, as well as the ability to charge 5-cells of NiMH batteries were demonstrated.

Topics: Generators
Commentary by Dr. Valentin Fuster
2011;():1179-1180. doi:10.1115/IMECE2011-63149.

For higher positioning accuracy of the low-power-consumption tracking terminal specific to the physical distribution management, a positioning technique using the Personal Handy-phone System (PHS) was developed.

Topics: Networks , Logistics
Commentary by Dr. Valentin Fuster
2011;():1181-1185. doi:10.1115/IMECE2011-63212.

Radio-frequency identification (RFID) and mechatronic technology has been applied to a laundry sorting system which can potentially be used by rest homes in the future to reduce the labour intensity of care givers, to increase the efficiency of laundry sorting, and to reduce the chance of garments being lost. A laboratory laundry identifying and sorting conveyor belt has been built. Several different types of RFID labels/tags have been considered and tested. A type of small RFID laundry tag, suitable for the laundry sorting conditions of a rest home, has been selected. The laundry tags have undergone endurance testing under actual washing and drying conditions with typical commercial laundry chemical products used in rest homes. There was a major challenge using commercial RFID tags in the proposed intelligent laundry sorting system due limitations in their antenna and signal receiving systems. A strategy to coordinate the orientations of the tags, range of the antenna, and the amplification of signal receiving units has been investigated. Several antenna designs to improve the identification rate have been tested and analysed for the selected small laundry tags, since the tag-receiver system has to work beyond the recommended range. A programme for signal detection and processing has been produced. The programme has taken into consideration the speed of the conveyor belt, antenna receiving range and the time required to process signals. It works with satisfactory precision at a satisfactory speed. A sorting strategy for implementation after laundry garment identification has been investigated. This strategy considers aspects of simplicity, multifunction and compactness of mechanical structure. A virtual sorting system has been produced to test the principles of the sorting strategy and the antenna design. The results of these tests will help us to move to the next stage, the design of a prototype laundry sorting system.

Commentary by Dr. Valentin Fuster
2011;():1187-1190. doi:10.1115/IMECE2011-63420.

The paper presents the numerical design and performance of a triple-axis thermal accelerometer. In a typical thermal accelerometer, a heater is suspended at the center and sensing elements are located around the heater on the opening side of a cavity. Consequently, the sensitivity of the vertical axis measurement is very low in comparison with the horizontal axes measurements and the cross-sensitivity between these measurements is very high. In our new design, the heater is formed a wide ring and the sensing elements are located both inside and outside of the heater ring with a small elevation from the heater plane. The obtained results show that the sensitivity of the vertical axis measurement attains to the order of the horizontal axes measurements. The cross-sensitivities among three axes are less than 4%. For instance, at the supplied power of 15mW to the heating resistor, the sensitivity of the accelerometer is 0.12°C/g in the vertical axis and 0.25°C/g in the horizontal axes.

Topics: Accelerometers
Commentary by Dr. Valentin Fuster
2011;():1191-1192. doi:10.1115/IMECE2011-63428.

The gyroscopic power generator produces a high-speed rotation of magnets from low-frequency vibrations and supplies electric power to information and communication devices that use human vibrations in daily life. In this paper, in order to increase the stability and the output power of the generator, a simple equation that indicates the steady state approximate solution of the phase difference is derived. From the derived solution, a control method for the steady state is verified by the simulations. In order to maintain the stability and high power generation for variable input vibrations, the impedance control method using the phase difference is developed and verified experimentally.

Commentary by Dr. Valentin Fuster