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32nd Annual Mechanisms and Robotics Conference (MR)

2008;():3-12. doi:10.1115/DETC2008-49280.

This paper addresses the issues of control and workspace determination of planar active tensegrity or tensegrity-like structures. The motion of such structures is generally produced by actuated cables, which cannot tolerate compressive forces. Hence, a controller which not only satisfies the system dynamic equations, but also maintains positive tension in cables is necessary. A null-space controller based on feedback linearization theory is developed for this purpose. This controller utilizes redundant active cables to overactuate the system. The concept of a ‘dynamic workspace’ for these structures is then introduced. This workspace consists of all configurations that are achievable from a given initial configuration while maintaining positive tensions throughout the entire system motion and is a powerful tool in analyzing the performance of a variety of tensegrity structures. This idea extends the concept of the static workspace, which consists of statically maintainable configurations, by incorporating system motion and dynamics to guarantee positive tensions during transition between the states. A critical benefit of this procedure is that it may be used to find the dynamic workspace of a system regardless of whether actuator redundancy is utilized, and thus can be used to objectively illustrate the degree to which overactuation improves mobility of a tensegrity structure. The effectiveness of the developed concepts is demonstrated through computer simulation and actual physical experimentation.

Commentary by Dr. Valentin Fuster
2008;():13-19. doi:10.1115/DETC2008-49414.

Variable stiffness elements (VSE) or variable springs have wide applications in vibration control systems and robotics. In this work, the concept of a new VSE is introduced and the criteria for the design are explained. The new VSE is based on a special case of cable-driven mechanisms at a singular configuration and is called antagonistic variable stiffness element (AVSE). Singularity of the mechanism provides interesting characteristics for the AVSE such as zero elastic (passive) stiffness and fully controllable stiffness along the infinitesimal flex. Based on the given criteria, the possible configurations of the AVSE are found.

Topics: Stiffness
Commentary by Dr. Valentin Fuster
2008;():21-30. doi:10.1115/DETC2008-49467.

The pose of the mobile platform of a parallel cable-driven robot is said to be fully constrained if any wrench can be created at the platform by pulling on it with the cables. A fully constrained pose is also known as a force-closure pose. In this paper, a review of three useful characterizations of a force-closure pose is proposed. These characterizations are stated in the form of theorems for which proofs are presented. Tools from linear algebra allow to derive some of these proofs while the others are more difficult and can hardly be obtained in this manner. Therefore, polyhedral cones, which are special cases of convex cones, are introduced along with some of their well-known fundamental properties. Then, it is shown how the aforementioned difficult proofs can be obtained as direct consequences of these properties.

Topics: Robots , Cables
Commentary by Dr. Valentin Fuster
2008;():31-38. doi:10.1115/DETC2008-49478.

Contour crafting (CC) is a new technology that is proposed for construction. Formerly we presented a cable-suspended robot to implement CC technology with Cartesian motion. The current paper proposes an improved Contour-Crafting-Cartesian-Cable (C4 ) robot. Although the new concept is preferable in structural design, here we compare the original and improved C4 robot concepts with regard to kinematics, workspace, and stiffness.

Topics: Robots , Cables , Stiffness
Commentary by Dr. Valentin Fuster
2008;():39-45. doi:10.1115/DETC2008-49480.

This paper presents dynamics equations and controller simulation for the Contour-Crafting-Cartesian-Cable (C4 ) Robot. The C4 robot was previously introduced for large-scale contour crafting construction. The pseudostatic and dynamics equations are presented, including how to maintain positive cable tensions. A controller design is also proposed for the C4 robot, based on the computed-torque method. MATLAB simulation is presented for controller simulation with different trajectories and controller gains.

Commentary by Dr. Valentin Fuster
2008;():47-58. doi:10.1115/DETC2008-49518.

This paper presents a new geometry-based method to determine if a cable-driven robot operating in a d-degree-of-freedom workspace (2 ≤ d ≤ 6) with nd cables can generate a given set of wrenches in a given pose, considering acceptable minimum and maximum tensions in the cables. To this end, the fundamental nature of the Available Wrench Set is studied. The latter concept, defined here, is closely related to similar sets introduced in [23, 4]. It is shown that the Available Wrench Set can be represented mathematically by a zonotope, a special class of convex polytopes. Using the properties of zonotopes, two methods to construct the Available Wrench Set are discussed. From the representation of the Available Wrench Set, computationally-efficient and non-iterative tests are presented to verify if this set includes the Task Wrench Set, the set of wrenches needed for a given task.

Topics: Robots , Cables
Commentary by Dr. Valentin Fuster
2008;():59-66. doi:10.1115/DETC2008-49532.

Wire robots (also called Tendon-based parallel manipulators) use a movable end-effector which is connected to a machine frame by motor driven tendons. Since tendons can transmit only pulling forces, at least m = n + 1 cables are needed to tense a system having n degrees-of-freedom. The resulting redundancy gives m − n degrees-of-freedom in the wire force distribution, making workspace analysis a complex and computationally expensive task. Discrete methods are widely used to solve this problem, but their drawback is that intermediate points on the discrete calculation grid are neglected which may lead to false results. This paper provides detailed algorithms for continuous workspace analysis for wire robots which avoid the discretization and have additional advantages. Especially, it is easy to extend the analysis methods to methods usable for the workspace synthesis.

Topics: Robots , Wire , Optimization
Commentary by Dr. Valentin Fuster
2008;():67-72. doi:10.1115/DETC2008-49658.

A new hybrid cable-driven manipulator is introduced. The manipulator is composed of a Cartesian mechanism to provide three translational degrees of freedom and a cable system to drive the mechanism. The end-effector is driven by three rotational motors through the cables. The cable drive system in this mechanism is self-stressed meaning that the pre-tension of the cables which keep them taut is provided internally. In other words, no redundant actuator or external force is required to maintain the tensile force in the cables. This simplifies the operation of the mechanism by reducing the number of actuators and also avoids their continuous static loading. It also eliminates the redundant work of the actuators which is usually present in cable-driven mechanisms. Forward and inverse kinematics problems are solved and shown to have explicit solutions. Static and stiffness analysis are also performed. The effects of the cable’s compliance on the stiffness of the mechanism is modeled and presented by a characteristic cable length. The characteristic cable length is calculated and analyzed in representative locations of the workspace.

Topics: Cables , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():73-83. doi:10.1115/DETC2008-49771.

This paper presents a general method to perform the stiffness analysis of tensegrity mechanisms. The method is based on an existing stiffness matrix model. Several stiffness indices having physical meaning are introduced. As an example, the method is applied to a planar 2-DoF tensegrity mechanism. Stiffness mappings based on the stiffness indices are generated for the mechanism’s workspace. It is shown for the example mechanism that the effect of the prestress on the stiffness is not significant when linear stiffness models of the components are assumed.

Topics: Stiffness , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():85-92. doi:10.1115/DETC2008-49867.

Cable-driven mechanisms can be used as fast pickup-and-place manipulators due to the low inertia of the cables. Maintaining cable tension can be achieved by cylinders applying forces on the mobile platform to generate tensile forces in the cables to prevent cable slack during the operation. This paper presents an optimization approach to determine the optimum layout of the cylinders in the manipulator, i.e., the optimum positions of the cylinders connection points on the mobile platform and the base. The goal of this optimization is to achieve the desired distribution of the generated tension across the cables. An example 6-degree-of-freedom spatial manipulator is presented where this approach is applied to optimize the layout of one, two and three cylinders.

Commentary by Dr. Valentin Fuster
2008;():93-99. doi:10.1115/DETC2008-49927.

In this work, an impedance control method is developed and applied to two cable-driven mechanisms. The first one is a classical problem of driving a rigid body in 3-D space by seven cables. Our approach is based on the impedance control of rigid link manipulators which is then extended to include the specific considerations of the cable-driven mechanisms such as maintaining the tensile force in the cables. The method is then extended to the serial multibody cable-driven mechanisms. The motivation for this problem is the possible application of cable-driven systems in the rehabilitative exercises such as physical and/or occupational therapies. In this case, the human body acts as a multibody system which is driven by cables attached. The impedance control in such application facilitates the comfort of the patient by providing the necessary compliance while moving the body parts. The formulation of the problem is developed using Lagrange’s equation and the control input (which is the cable forces) is calculated based on the position and/or force feedback from the multibody. Simulation results demonstrate the effectiveness of the presented method.

Commentary by Dr. Valentin Fuster
2008;():101-108. doi:10.1115/DETC2008-49969.

This paper introduces a lower mobility parallel kinematic crane able to generate Scara motions (three translations and one rotation about a vertical axis). A crane is an underconstrained cable robot: it requires gravity acting on the traveling plate in order to tense the cables. The proposed crane can resist, to a certain extent, against outside forces and torques in all directions of the 6-dimensional task space. This feature results from the use of pairs of cables linking the actuators and the traveling plate. The proposed crane is derived from the I4 parallel robot. Thus, its traveling plate is articulated which provides a wide range of orientation. It is hyperstatic in the sense that one of the eight cables can be removed while keeping the same kinematic relationships. However, for symmetry reasons all the eight cables are kept (this feature is interesting in case of a cable breakdown). The input/output geometrical and kinematic models required for control are derived. Then, the cables tensions are obtained enabling the determination of the static workspace defined as the domain of reachable space where the cables remain taut under the action of gravity.

Topics: Motion , Cranes , Cables
Commentary by Dr. Valentin Fuster
2008;():109-121. doi:10.1115/DETC2008-49041.

Modeling flexible beams that undergo large deflection is one of the key steps in analyzing and synthesizing compliant mechanisms. Geometric nonlinearities introduced by large deflections often complicate the analysis of mechanism systems comprising such members. Several pseudo-rigid-body (PRB) or multi segment models in the literature have been proposed to approximate the tip deflection and slope. However these models are either dependent on external loads or too complicated to analyze. They are neither appropriate for analyzing mechanisms in which loads change significantly as they move, nor for synthesizing mechanisms where a parametric model is preferred. In this paper, a load independent PRB 3R model which comprises of four rigid links joined by three revolute joints and three torsion springs is proposed. The traditional PRB 1R models are first studied for both small deflection beams and large deflection beams. These studies provide fundamental insights to the geometric nonlinearity of large deflection beams. Numerical integration is applied to compute tip deflections for various loads. A three-dimensional search routine has been developed to find the optimal set of characteristic radius factors for the proposed PRB 3R model. Detailed error analysis and comparison against the result by the numerical integration and the PRB 1R model are accomplished for different load modes. The benefits of the PRB 3R model include (a) high accuracy for large deflection beams, (b) load independence which is critical for applications where loads vary significantly and (c) explicit kinematic and static constraint equations derived from the model. To demonstrate the use of the PRB 3R model, a compliant 4-bar linkage is studied and verified by a numerical example. The result shows a maximum tip deflection error of 1.2% compared with the FEA model.

Commentary by Dr. Valentin Fuster
2008;():123-132. doi:10.1115/DETC2008-49045.

This paper presents an analytical method to design a mechanical finger for robotic manipulations. As traditional mechanical fingers require bulky electro-magnetic motors and numerous relative-moving parts to achieve dexterous motion, we propose a class of fingers the manipulation of which relies on finger deflections. These compliant fingers are actuated by shape memory alloy (SMA) wires that exhibit high work-density, frictionless, and quite operations. The combination of compliant members with embedded SMA wires makes the finger more compact and lightweight. Various SMA wire layouts are investigated to improve their response time while maintaining sufficient output force. The mathematical models of finger deflection caused by SMA contraction are then derived along with experimental validations. As finger shapes are essential to the range of deflected motion and output force, we find its optimal initial shapes through the use of a shape parameterization technique. We further illustrate our method by designing a humanoid finger that is capable of three-dimensional manipulation. As compliant fingers can be fabricated monolithically, we expect the proposed method to be utilized for applications of various scales.

Commentary by Dr. Valentin Fuster
2008;():133-142. doi:10.1115/DETC2008-49047.

A three-dimensional wide curve is a spatial curve with variable cross sections. This paper introduces a geometric synthesis method for spatial compliant mechanisms by using three-dimensional wide curves. In this paper, every connection in a spatial compliant mechanism is represented by a three-dimensional wide curve and the whole spatial compliant mechanism is modeled as a set of connected three-dimensional wide curves. The geometric synthesis of a spatial compliant mechanism is considered as the generation and optimal selection of control parameters of the corresponding three-dimensional parametric wide curves. The deformation and performance of spatial compliant mechanisms are evaluated by the isoparametric degenerate-continuum nonlinear finite element procedure. The problem-dependent objectives are optimized and the practical constraints are imposed during the optimization process. The optimization problem is solved by the MATLAB constrained nonlinear programming algorithm. The effectiveness of the proposed geometric procedures is verified by the demonstrated examples.

Commentary by Dr. Valentin Fuster
2008;():143-149. doi:10.1115/DETC2008-49234.

Dynamic effects are very important to improving the design of compliant mechanisms. An investigation on the dynamic characteristics of planar compliant parallel-guiding mechanism is presented. Based on the pseudo-rigid-body model, the dynamic model of planar compliant parallel-guiding mechanisms is developed using the numerical methods at first. The natural frequency is then calculated, and frequency characteristics of this mechanism are studied. The numerical results show the accuracy of the proposed method for dynamic modeling of compliant mechanisms, and the relationships between the natural frequency and design parameters are analyzed clearly.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2008;():151-161. doi:10.1115/DETC2008-49253.

Starting from the definition of a stiffness matrix, the authors present the Cartesian stiffness matrix of parallel compliant mechanisms. The proposed formulation is more general than any other stiffness matrix found in the literature since it can take into account the stiffness of the passive joints and remains valid for large displacements. Then, the validity, the conservative property, the positive definiteness and the relation with other stiffness matrices of this matrix are discussed theoretically. Finally, a numerical example is given in order to illustrate the correctness of this matrix.

Topics: Stiffness
Commentary by Dr. Valentin Fuster
2008;():163-173. doi:10.1115/DETC2008-49265.

In this paper, the number of degrees of freedom, the kinematic constraints, the pose of the end-effector and the static constraints that lead to the Kinemato-Static Model of a Compliant Mechanism are introduced. A formulation is then provided for the Instantaneous Kinemato-Static Model. This new model enables to calculate the variation of the pose as a linear function of the motion of the actuators and the variation of the external loads through two new matrices: the compliant Jacobian matrix and the matrix of compliance that give a simple and meaningful formulation of the model of the mechanism.r Finally, a simple application to a 4-bar mechanism is presented to illustrate the use of this model and the new possibilities that it opens, notably the study of the kinematics for any range of applied load.

Commentary by Dr. Valentin Fuster
2008;():175-182. doi:10.1115/DETC2008-49267.

Compliant mechanisms are devices which utilize the flexibility of their constituent members to transmit motion and forces. Unlike their rigid body counterparts, compliant mechanisms typically contain no traditional joints. The focus of this research is the development of a building block approach for the synthesis of compliant mechanisms. Building block methods better facilitate the augmentation of designer intuition while offering a systematic approach to open-ended problems. In this paper, we investigate the use of the eigentwists and eigenwrenches of a deformable body to characterize basic kinematic function. The eigentwists and eigenwrenches are shown to demonstrate parametric behavior when applied to the compliant dyad building block, and in special cases may be compared to compliance ellipsoids. The paper concludes by articulating future research in a building block approach to compliant mechanism synthesis.

Commentary by Dr. Valentin Fuster
2008;():183-195. doi:10.1115/DETC2008-49426.

This paper presents a new approach to designing continuum compliant mechanisms—the kinetoelastic approach. We present a new formulation of the design problem, incorporating not only the kinematic function requirements of the mechanism but, more importantly, the compliance characteristics of the mechanism’s structure. In our kinetoelastic model, the kinematics of the compliant mechanism is defined on rigid-bodies of input/output ports and is related to a set of kinetoelastic factors of mechanism’s structure in a state equation of the mechanism defined by the elasticity theory. Central to defining the compliance characteristics of the mechanism is the mechanism eigensystem with principal eigen-stiffness or eigen-compliance. In this new perspective, we further apply the kinetoelastic model to the problem of designing compliant translational joints with a structure topology optimization technique. This application demonstrates the capability of the kinetoelastic approach in producing compliant designs with desirable compliance properties, such as in the leaf-spring type sliding joint as opposed to the notch-type joint. The paper represents an initial development towards a complete methodology for continuum compliant mechanism design.

Commentary by Dr. Valentin Fuster
2008;():197-203. doi:10.1115/DETC2008-49451.

This paper outlines the research, design and testing of a compliant staple gun style mechanism for use in a desktop model stapler. A survey of existing staple gun style desktop staplers is used to create target specifications to design the new compliant stapler. The initial proof of concept satisfies the primary function and user specifications. Future iterations of the mechanism will be tested and designed to be capable of performing the repeated iteration of long term stapler use.

Commentary by Dr. Valentin Fuster
2008;():205-216. doi:10.1115/DETC2008-49612.

The topology optimization problem for the synthesis of compliant mechanisms has been formulated in many different ways in the last 15 years, but there is not yet a definitive formulation that is universally accepted. Furthermore, there are two unresolved issues in this problem. In this paper, we present a comparative study of five distinctly different formulations that are reported in the literature. Three benchmark examples are solved with these formulations using the same input and output specifications and the same numerical optimization algorithm. A total of 35 different synthesis examples are implemented. The examples are limited to desired instantaneous output direction for prescribed input force direction. Hence, this study is limited to linear elastic modeling with small deformations. Two design parameterizations, namely, the frame element based ground structure and the density approach using continuum elements, are used. The obtained designs are evaluated with all other objective functions and are compared with each other. The checkerboard patterns, point flexures, the ability to converge from an unbiased uniform initial guess, and the computation time are analyzed. Some observations are noted based on the extensive implementation done in this study. Complete details of the benchmark problems and the results are included. The computer codes related to this study are made available on the internet for ready access.

Commentary by Dr. Valentin Fuster
2008;():217-225. doi:10.1115/DETC2008-49614.

Novel designs for two-axis, high-resolution, monolithic inertial sensors are presented in this paper. Monolithic, i.e., joint-less single-piece compliant designs are already common in micromachined inertial sensors such as accelerometers and gyroscopes. Here, compliant mechanisms are used not only to achieve de-coupling between motions along two orthogonal axes but also to amplify the displacements of the proof-mass. Sensitivity and resolution capabilities are enhanced because the amplified motion is used for sensing the measurand. A particular symmetric arrangement of displacement-amplifying compliant mechanisms (DaCMs) leads to de-coupled and amplified motion. An existing DaCM and a new topology-optimized DaCM are presented as a building block in the new arrangement. A spring-mass-lever model is presented as a lumped abstraction of the new arrangement. This model is useful for arriving at the optimal parameters of the DaCM and for performing system-level simulation. The new designs improved the performance by a factor of two or more.

Commentary by Dr. Valentin Fuster
2008;():227-235. doi:10.1115/DETC2008-49623.

Some of the well known formulations for topology optimization of compliant mechanisms could lead to lumped compliant mechanisms. In lumped compliance, most of the elastic deformation in a mechanism occurs at few points, while rest of the mechanism remains more or less rigid. Such points are referred to as point-flexures. It has been noted in literature that high relative rotation is associated with point-flexures. In literature we also find a formulation of local constraint on relative rotations to avoid lumped compliance. However, it is well known that a global constraint is easier to handle than a local constraint, by a numerical optimization algorithm. The current work presents a way of putting global constraint on relative rotations. This constraint is also simpler to implement since it uses linearized rotation at the center of finite-elements, to compute relative rotations. I show the results obtained by using this constraint on the following benchmark problems — displacement inverter and gripper.

Commentary by Dr. Valentin Fuster
2008;():237-248. doi:10.1115/DETC2008-49688.

The basic premise of a compliant system is the integration of motion/force transmission via elastic deformation with embedded actuation and sensing. Current electromechanical systems are generally fashioned in the rigid-and-discrete paradigm where one first designs a rigid structure with mechanical joints and then adds actuators and sensors, with the design of controls only following as an afterthought. The objective of this research is a systems approach to synthesis of mechanism, structure, actuation, and sensing, thereby advancing from traditional mechanical design to automated compliant system design. In previous studies of compliant mechanisms and their synthesis, single-actuator mechanisms have primarily been considered, with the determination of the actuator’s type, orientation, size, and location occurring outside of the automated design synthesis, at the designer’s option. A new algorithmic framework is presented, in which structural topology and actuator/sensor placement are simultaneously synthesized for adaptive performance. Significantly, this is not a traditional ad hoc method; sensor and actuator placement affect structural topology and vice versa. This is a continuation of our previously reported actuation-placement work [1–2], updated here to include the sensor placement co-synthesis and new tasks in addition to shape change. The methods used include genetic algorithms, graph searches for connectivity, and multiple load cases implemented with linear finite element analysis. Fundamental metrics for the inclusion of embedded components in a multifunctional compliant system are developed and investigated. The essential framework for the integration of controls with compliant mechanisms is established. Specifically, the concepts of controllability and observability, as redefined for compliant systems, are proven as a successful starting point for the design of multifunctional, adaptive systems. These concepts refer to the unique system response for each component (actuator or sensor) it contains. Results are presented for several problems, focusing on the application of shape-morphing aircraft structures. Through examples and design studies, the metrics and the methodology demonstrate that multiple, optimally-placed components indeed offer performance benefits for mechanical systems, in terms of multifunctional execution. Finally, the extension of controllability to address the problem of single-point multidegree-of-freedom manipulation is performed to show the generalized use of the new methodology in benefitting the design of compliant systems.

Topics: Sensors , Actuators , Topology
Commentary by Dr. Valentin Fuster
2008;():249-255. doi:10.1115/DETC2008-49693.

A curved flexure element such as an initially-curved beam can deflect largely and facilely. Using curved flexure elements in compliant mechanisms allows the mechanism to move a longer distance or undergo a larger rotation angle stroke than using conventional notch flexures. This paper presents a novel large-deflection annulus-shaped flexure hinge covering multiple curved-beam flexure elements. It has been shown that geometric symmetry in the constraint arrangement relaxes some of the design tradeoffs, resulting in some improved performances of the flexure hinge. Additional fixed RCM characteristic of isosceles-trapezoidal flexure modules existed in this compliant joint further improve its accuracy. A master-motion pseudo-rigid-body model provides a simple and accurate method to analyze the force-deflection behavior of this new rotary flexure hinge. The accuracy of the model is verified by comparing outcomes to non-linear finite element analysis. The result shows the proposed rotary flexure hinge has a large stroke angle, a low axial and radial stiffness.

Commentary by Dr. Valentin Fuster
2008;():257-263. doi:10.1115/DETC2008-49694.

The load-displacement behavior of a cross-spring pivot as a kind of rotational element or module in compliant mechanisms is a subject of keen interest for many researchers. The model allowing not only quick design but also characteristics capture is pursued. This paper addresses some accurate closed-form results via approximations. These expressions are simple for a designer to understand the parameters without resorting to a tedious iterative procedure. The rotational displacement and center shift of the pivot are analyzed both qualitatively and quantitatively, with a general-purposed load applied including bending moment, horizontal and vertical forces. Meanwhile, a concise expression for center shift without approximations is proposed. The validity of the model is verified by finite element analysis (FEA). The relative error of the rotational displacement is less than 1.8% even if the rotational angle reaches ±20° the relative errors for the two components of center shift are less than 6% and 4% respectively, in the case of typical but general configurations and loads.

Commentary by Dr. Valentin Fuster
2008;():265-272. doi:10.1115/DETC2008-49717.

This paper proposes a multi-stage design method for a design of practical compliant mechanisms. The proposed method consists of topology and shape optimizations and a shape conversion method that incorporates two optimizations. In the 1st stage, an initial and conceptual compliant mechanism is created by topology optimization. In the 2nd stage, an initial model of shape optimization is created from the result of topology optimization by the shape conversion method based on the level set method. In the 3rd stage, the shape optimization yields a detailed shape of the compliant mechanism by considering non-linear deformation and stress concentration. Execution of the shape optimization after the topology optimization enables evaluation of stress concentration and large deformation effect that are normally difficult for the traditional topology optimization. On the other side, the precise conversion from the model by topology optimization to the one for the shape optimization becomes possible by the shape conversion method that is utilizing the level set method. Using the proposed multi-stage method, a practical compliant mechanism can be designed with the designer’s minimum efforts that are indications of design conditions of the topology and shape optimizations and several parameters and threshold values of the shape conversion method.

Commentary by Dr. Valentin Fuster
2008;():273-282. doi:10.1115/DETC2008-49755.

Our research investigates a new approach to design of bistable compliant mechanisms using the bistability of a clamped-free beam. Bistability plays an important role for a variety of applications since energy is applied only to move the mechanism from one stable position to another and no energy needs to be expended once a stable position is reached. Behavior of a bistable compliant mechanism, in general, is highly non-linear and relies on the buckling phenomenon. Normally, buckling is very sensitive to imperfections in manufacturing processes, operating conditions and boundary conditions. We present a method for designing bistable mechanisms that are robust against such imperfections by utilizing the behavior of a simple clamped-free beam. A solution for large deformation of a simple clamped-free beam is first obtained to study its bistable behavior under various loading conditions. If the load is greater than the critical buckling load, the beam can be deflected not only in the normal direction but also in a ‘reverse-lateral’ (RL) direction. First, an initially straight beam must be bent to a certain curvature under the action of the applied force. In the second loading condition, the partially bent beam is further loaded so that it buckles in the RL direction into a stable position. The magnitude and direction of the forces in both loading conditions that are conducive to bistability are thus determined. A compliant mechanism is then designed such that its output generates desired forces on the beam to deform it in the RL direction. We demonstrate that the RL deformation is less sensitive to the imperfections and ensures bistable behavior. Using clamped-pinned beams, two design examples (symmetric and asymmetric cases) of bistable compliant mechanisms are presented. Results show very good correlation between the finite element analysis and experimental tests on prototypes.

Commentary by Dr. Valentin Fuster
2008;():283-292. doi:10.1115/DETC2008-49769.

A pseudo-rigid-body model (PRBM) which describes a class of curved compliant beams in terms of spherical mechanism kinematics was developed. The topology of the spherical compliant segment and its rigid-body equivalent were chosen to be analogous to planar models. The nomenclature for the spherical PRBM was also chosen to facilitate comparison with planar models. The motion of the compliant segment was calculated Finite Element Analysis and the PRBM parameters were determined. The characteristic radius and parametric angle coefficient were found to decrease as the angle subtended by the beam increases. The kinematic and elastic parameterization limits of the model increase with increasing beam angle. The stiffness of the beam is described by two separate spring elements, which describe the appropriate combination of moment and force which produces spherical motion. A previous planar PRBM is shown to be the small angle limit of the new spherical PRBM.

Commentary by Dr. Valentin Fuster
2008;():293-305. doi:10.1115/DETC2008-49794.

This paper presents the design of a grasping instrument for minimally invasive surgery. Due to its small dimensions a compliant mechanism seems promising. To obtain force feedback, the positive stiffness of the compliant grasper must be statically balanced by a negative-stiffness compensation mechanism. For the design of compliant mechanisms, topology optimization can be used. The goal of this paper is to investigate the applicability of topology optimization to the design of a compliant laparoscopic grasper and particularly a compliant negative-stiffness compensation mechanism. In this study, the problem is subdivided in the grasper part and the compensation part. In the grasper part the deflection at the tip of the grasper is optimized. This results in a design that has a virtually linear force-displacement characteristic that forms the input for the compensation part. In the compensation part the difference between the force-displacement characteristic of the grasper part and the characteristic of the compensation part is minimized. An optimization problem is formulated enabling a pre-stress to be incorporated, which is required to obtain the negative stiffness in the compensation part. We can conclude that topology optimization is a promising approach in the field of statically balanced compliant mechanism design, even though there is great scope improvement of the method.

Commentary by Dr. Valentin Fuster
2008;():307-312. doi:10.1115/DETC2008-49797.

The knee joint is a very complex joint stabilized by two opposing sets of ligaments. A mathematical model of the knee with an appropriate level of complexity and accuracy is needed for valid and useful static or dynamic analysis. Existing work has focused on the knee as either a one degree of freedom pin joint (simple) or based on a more complex sliding motion of two surfaces (complex). In this work, MATLAB and Working Model© were used to design three intermediate level models describing the motion of the knee assuming only movement in the sagittal plane by changing the shape of the tibial plateau (flat, concave, or convex). From these, it was determined that the simple flat model, while not perfect, most appropriately modeled the knee joint.

Topics: Springs , Knee , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():313-321. doi:10.1115/DETC2008-49836.

The interest in actuators based on dielectric elastomer films as a promising technology in robotic and mechatronic applications is increasing. The overall actuator performances are influenced by the design of both the active film and the film supporting frame. This paper presents a single-acting actuator which is capable of supplying a constant force over a given range of motion. The actuator is obtained by coupling a rectangular film of silicone dielectric elastomer with a monolithic frame designed to suitably modify the force generated by the dielectric elastomer film. The frame is a fully compliant mechanism whose main structural parameters are calculated using a pseudo-rigid-body model and then verified by finite element analysis. Simulations show promising performance of the proposed actuator.

Commentary by Dr. Valentin Fuster
2008;():323-330. doi:10.1115/DETC2008-49862.

This paper presents the design of a damped ortho-planar spring that uses viscoelastic constrained-layer damping to reduce the free response oscillations of the spring and suppress modal resonances in that response. Background, theory, and applications surrounding fully-compliant ortho-planar springs and viscoelastic damping treatments are first discussed. Next, the effect of various constrained layer thickness on the spring constant, damping ratio, equivalent viscous damping ratio, modal frequencies, and modal damping ratios are compared, and trends discussed. The results show that the equivalent viscous damping co-efficient of the viscoelastically-damped spring can be increased to nearly 2.5 times that of the reference configuration without significantly changing the size of the constraining layer or the spring constant of the ortho-planar spring. Viscoelastically-damped ortho-planar springs are also shown to successfully remove mechanical noise from a contact resistance test stand.

Topics: Damping , Springs
Commentary by Dr. Valentin Fuster
2008;():331-338. doi:10.1115/DETC2008-49902.

Mechanisms formed by rigid elements are not suitable for applications at the microlevel due to manufacturing limitations. For the same reason, devices for microelectromechanical systems (MEMS) are basically planar mechanisms. This paper addresses a microplatform able to move in the three dimensional space. It is formed by bimorph actuators connected to the central platform by compliant elements. The forward and reverse analyses for the microplatform are presented.

Commentary by Dr. Valentin Fuster
2008;():339-349. doi:10.1115/DETC2008-49914.

One way to save space and reduce cost in a competitive environment is to use ortho-planar compliant mechanisms which can be made from sheets of material, or lamina emergent mechanisms (LEMs). One major challenge associated with LEM design, however, is creating joints with the desired motion characteristics, especially where complex spatial mechanism topologies are required. This paper presents some important considerations for designing joints for LEMs. A technique commonly used in robotics, using serial chains of revolute and prismatic joints to approximate the motion of complex joints, is presented for use in lamina emergent mechanisms. Important considerations such as linkage configuration and simple prototyping are also discussed.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2008;():351-360. doi:10.1115/DETC2008-49915.

This work focuses on the multi-objective optimization of a compliant-mechanism accelerometer. The method is used to optimally design an accelerometer with the architecture of a novel version of the Sarrus mechanism. The purpose is to maximize the sensitivity of the accelerometer in its sensing direction, while minimizing its sensitivity in all other directions. The paper starts with a brief description of the dynamics model of the compliant mechanism, followed by the formulation of the a posteriori multi-objective optimization. By using the normalized constrained method, an evenly distribution of the Pareto frontier is found. The paper also provides several optimum solutions on a Pareto plot, as well as the CAD model of the selected solution.

Commentary by Dr. Valentin Fuster
2008;():361-370. doi:10.1115/DETC2008-49917.

A novel fabrication process and design optimization method for a micro forceps is presented. This work is part of a larger research effort to design and fabricate nanoparticulate enabled surgical instruments. The micro forceps is a monolithic compliant mechanism that due to its two-dimensional design can be manufactured using the new fabrication process. The process begins with fabrication of an array of molds on refractory substrates using a modified UV lithography technique. In parallel, engineered ceramic nanocolloidal slurries are prepared for gel-casting into the molds. Mold infiltration takes place via a squeegee technique adapted from screen printing with excess slurry removed using an ethanol wipe. Finally, the photoresist molds are removed with a reactive ion etch (RIE) step, and ceramic parts sintered to full density. Employing this manufacturing technique for the compliant micro forceps design is advantageous because a large number of parts can be produced with a large aspect ratio (≥40:1), sharp edges (∼ 1 μm), and a resolution of 2 μm. Two optimization problems are formulated to determine the effect of dimensional parameters and material strength on the performance of the compliant micro forceps. First, performance is sensitive to small changes in the geometry, indicating that dimensions and shrinkage rates must be carefully controlled during processing. Second, performance can also be improved by using very large aspect ratios and/or improvements in material strength. A sample part manufactured using the new process is presented.

Topics: Manufacturing , Design
Commentary by Dr. Valentin Fuster
2008;():371-377. doi:10.1115/DETC2008-49939.

Researchers in the field of optimal synthesis of compliant mechanisms have been working to develop design tools that yield distributed compliant devices from a continuum design domain. However, it has been demonstrated in the literature that much of this work has resulted in mechanisms that localize compliance rather than distribute it as desired. Inaccurate representation of the stiffness or strain energy due to the existence of point flexures in the mechanism was identified as the cause of this behavior by early researchers. To eliminate this cause, several approaches have been tried to improve the design of distributed mechanisms, for example additional constraints on the optimization process, alternate parameterization techniques that avoid point flexures and additional objective functions evaluated as Pareto sets. In this paper, the authors further investigate the fundamental reasons for the prevalence of lumped designs. Representative simple compliant mechanisms are investigated analytically and numerically and the influence of various additional objectives on the final design is evaluated. To extrapolate these results to more complex mechanisms, examples are constructed that show evidence that a preference remains for lumped compliance, despite the countermeasures that have been applied. Pareto compatibility analysis developed by the authors is used to analyze the influence of various objectives on the distributive nature of the final design. These conditions that influence the distribution of compliance fall into two basic categories: those specific to the numerical methods applied and those of purely mechanical (i.e. fundamental) nature. This work will examine conditions of the latter type and will demonstrate that such a preference for lumped compliance exists. This preference is shown to be contained in the classic objectives; flexibility and stiffness. Based on these results, greater insight into the optimization process is gained and applied to improve the search for distributed compliant mechanisms.

Commentary by Dr. Valentin Fuster
2008;():379-392. doi:10.1115/DETC2008-49982.

Present building-block synthesis techniques for compliant mechanisms [4–7] account for the kinematic behavior of the mechanism alone, leaving the stiffness, manufacturability and mechanical efficiency to be determined by the shape-size optimization process. In this effort, we aim to generate practical and feasible conceptual designs by designing for kinematics and stiffness simultaneously. To enable this, we use a lumped spring-lever model, which intuitively characterizes the stiffness and the kinematics of a deformable-complaint building block with distinct input and output points. This model aids in the understanding of how the stiffness and the kinematics of building blocks combine when concatenated to form a mechanism. We use this understanding to synthesize compliant mechanisms by combining building blocks of known motion characteristics. A simple compliant-dyad building block is characterized for its lumped values of stiffness and kinematics. The concatenation of these dyad-building blocks is solved in detail, and guidelines for conceptual synthesis are proposed. Two practical examples are solved; a motion amplifier for a piezo-stack and a compliant energy storage mechanism for a staple-gun. The conceptual designs obtained from this approach are very close to the kinematic and the stiffness requirements of the application, thus minimizing the role of shape and size optimization to achieve the problem specification. The model, when extended to higher dimensions may be used to solve for precision positioning and other applications.

Commentary by Dr. Valentin Fuster
2008;():393-404. doi:10.1115/DETC2008-50111.

Flexure-based selectively compliant mechanisms with less than six degrees of freedom are capable of meeting the demanding requirements of ultra precision positioning and scanning systems. However, machining imperfections induce undesirable motion and limit the mechanisms precision capability. A spatial kinematics based kinetostatic model is presented here that not only enables determination of inherently spatial parasitic motion due to machining imperfections, but also offers critical geometric insight into the motion characteristics of flexure mechanisms. The analytical development reveals that the geometric errors induced by machining imperfections perturb the special screw systems of motion of ideal flexure mechanisms to their corresponding general screw systems. This insight leads to clearly defined metrics that can capture the non-ideal behavior using screw system theory and is applicable to all selectively compliant mechanisms. This result is illustrated using one and two DOF mechanisms as examples. In the case of rotational DOF flexure mechanisms, the pitch of twist of motion captures the difference between the special and general screw systems and represents the intrinsic parasitic motion. The machining imperfections are regarded as Gaussian random variables with known variance, and the model is used to determine the variance of the pitch of twist via Monte Carlo simulation, leading to determination of the precision capability of the flexure mechanisms. The modeling and analysis is illustrated using one and two DOF rotation flexure mechanisms. Finally, the details of a test setup built to determine the parasitic motion of the one DOF rotational mechanism are presented. Experimental results indicate that the one DOF flexure mechanism is indeed executing screw motion rather than pure rotation.

Commentary by Dr. Valentin Fuster
2008;():405-416. doi:10.1115/DETC2008-50121.

A healthy spinal disc is capable of 3 degrees of rotation and has a force-deflection response that helps to stabilize the spine. Age or trauma can cause the stability of the spine to decrease. Spinal fusion, the current surgical treatment of choice, stabilizes the spine by rigid fixation, reducing spinal mobility at the cost of increased stress at adjacent levels. This paper introduces a compliant mechanism that has the potential to closely mimic the physiological motion profile of the natural spinal disc. Compliant mechanisms have properties that make them well suited for spinal implants that restores the range of motion and the forcedeflection response of the spine. This paper presents an introduction to the biomechanics of the spinal disc, reviews the state of the art in spinal care, and proposes the use of the Flexure-based Bi-Axial Contact-aided (Flex-BAC) compliant mechanism as a spinal arthroplasty device (artificial disc). The Flex-BAC compliant mechanism offers the potential to restore both the kinematics and kinetics of a damaged spinal disc. The disc provides the ability to eliminate wear through rolling. An overview of the device and a preliminary kinematic and kinetic analysis are given.

Commentary by Dr. Valentin Fuster
2008;():417-425. doi:10.1115/DETC2008-49020.

This paper introduces an approach to kinematic and dynamic mechanisms analysis where one or more joints are modeled using joint component relative displacements that approximate real joint behavior. This approach allows for the simultaneous nonrecursive solution for both mechanism kinematic parameters and selected dynamic joint reaction forces. Also, for closed loop mechanisms, the approach eliminates the need for forming explicit loop closure constraint equations, so that the dynamic equations of motion, derived using either the Newtonian or Lagrangian method, have a simplified unconstrained form. The key element underlying the approach is the formation of axioms for the standard mechanism joint types that describe the form of the joint reaction force and/or moment in terms of a virtual (or real) displacement between the joint components.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2008;():427-434. doi:10.1115/DETC2008-49096.

This paper is focusing on the control strategy design of a long-range single-axis positioning system [1], which has a travel range of 100 mm. The positioning system was constructed by a linear guide, a feeding mechanism and three stacked piezoelectric actuators. The stacked piezoelectric actuators were used to drive the feeding mechanism with a circular movement, which will feed the linear guide by friction force. Through continuous feeding, an unlimited travel range positioning system can be achieved. Two-stage control strategy was introduced for the positioning control, i.e. coarse motion control and fine motion control. At coarse motion stage, impact-drive motion combined with fuzzy control was used to accelerate the linear guide to approach the target position. At fine motion stage, stick-drive motion combined with classical feedback–feedforward control can provide a nanometer positioning accuracy. The control algorithm was implemented on TMS320F240 DSP-based control board, and the experimental results show that the proposed feeding mechanism system with two-stage control strategy can achieve a travel range more than 90 mm with maximum velocity of 5.8 mm/s, average velocity 1 mm/s, steady state error is less than 20 nm, positioning bias is less than 0.5 nm and standard deviation is less than 7 nm.

Commentary by Dr. Valentin Fuster
2008;():435-442. doi:10.1115/DETC2008-49158.

Analysis of the kinematics and dynamics of a helicopter main rotor is presented in the paper. A rigid rotor type is assumed, where feathering angle of the blade is controlled by a swashplate mechanism. Kinematic constrains and links equilibrium are studied in order to determine the mechanism movement and the forces on the servoactuators which drive the swashplate position and orientation. The modeling presented is intended to be part of a simulation platform to evaluate fly-by-wire actuation systems performances applied to helicopter main rotors control.

Commentary by Dr. Valentin Fuster
2008;():443-452. doi:10.1115/DETC2008-49244.

A study of how joint wear affects the kinematics of a simple slider-crank mechanism and in turn how change in kinematics of the mechanism affects the joint wear is presented. The coupling between joint wear and system kinematics is modeled by integrating a wear prediction process, built upon a widely used finite-element-based iterative scheme, with the dynamic model that has an imperfect joint whose kinematics changes progressively according to joint wear. Three different modeling techniques are presented based on different assumptions, and their performances are compared in terms of joint forces and wear depths. It turns out that the joint wear increases the joint force and accelerates the wear progress. The accuracy of integrated dynamic model is validated by measuring joint force and wear depth of the slider-crank mechanism. Details of instrumentation are also presented.

Commentary by Dr. Valentin Fuster
2008;():453-463. doi:10.1115/DETC2008-49402.

Complete dynamic balancing principles still cannot avoid a substantial increase of mass and inertia. In addition, the conditions for dynamic balance and the inertia equations can be complicated to derive. This article shows how a double pendulum can be fully dynamically balanced by using counter-rotary counter-masses (CRCMs) for reduced additional mass and inertia. New CRCM-configurations were derived that have a low inertia, a single CRCM or have all CRCMs near the base. This article also shows how a CRCM-balanced double pendulum can be used as building element in the synthesis of balanced mechanisms for which the balancing conditions and inertia equations can be written down quickly. For constrained mechanisms the procedure is to first write down the known balancing conditions and inertia equations for the balanced double pendula and subsequently substitute the kinematic relations.

Topics: Pendulums , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():465-470. doi:10.1115/DETC2008-49408.

Recent results in condition monitoring of machine elements by acoustic emission analysis are presented. A special method based on the evaluation of structure-borne noise emissions in the ultrasonic range is described. The ultrasound-signals caused by friction processes are captured by a broadband piezoelectric sensor and analyzed subsequently. The method has proven to be suitable for detecting the occurrence of friction between solid objects in a very reliable way. This leads to a variety of possible applications wherever occurrence of solid body friction has to be considered as an indication of failure or wear. In addition to tribometer tests, experiments with sliding bearings and slide ring seals are presented exemplarily. In both cases promising results were achieved. The significant difference of the presented method compared to other sound-based methods is in the nature of the analyzed signals: Harmonic waves of audible sounds or percussion-type stimulations are not evaluated but the portion of friction sounds emerging in the ultra-sonic range beyond audible frequencies. These friction sounds are widely unaffected by ambient noise and other sources of interference.

Commentary by Dr. Valentin Fuster
2008;():471-479. doi:10.1115/DETC2008-49440.

In recent years, engine researchers have been trying to replace traditional cam shafts with systems that provide valve timing independent of crank motion. Such systems must be fast, quiet and energy efficient. One solution is a spring driven cam that performs a rocking motion between two stable endpoints rather than a continuous rotation. Since the cam motion is not at constant speed, traditional methods for synthesizing the cam profile cannot be applied directly. This paper illustrates a methodology for synthesizing a time optimal cam profile for a spring driven cam that is bound by simultaneous constraints of contact force, contact stress, radius of curvature, jerk, and pressure angle.

Topics: Cams , Springs
Commentary by Dr. Valentin Fuster
2008;():481-492. doi:10.1115/DETC2008-49442.

In a gas turbine engine, the forced vibration of a turbine blade under resonant conditions is undesirable and may lead to premature high cycle fatigue failure. From the aspect of structural integrity, this demonstrates that it is extremely important to tune the excited vibration mode out of the operating speed range. This leads to the question: Is it possible to perform structural perturbations, namely to the mass and stiffness, in such a way that only the eigenvalue of choice significantly changes — while causing little or no change in the other natural frequencies? This is focus of the present paper. Due to the complexity of the blade structure, it is difficult to obtain an analytical solution from the eigenvalue perturbation theory. Nevertheless, the derived analytical expressions provide guidance from which the finite element method may successfully be applied as an alternative approach. This tuning approach is validated experimentally.

Commentary by Dr. Valentin Fuster
2008;():493-500. doi:10.1115/DETC2008-49459.

The experimental knowledge about medium lubricated journal bearings (e.g. diesel-oil lubricated sliding bearings in fuel-injection systems) is far too small in order to confirm the different hypotheses of the actual simulation models. The study of such components implicates very restrictive requirements on security against explosion, exact measurement of the friction torque and so on. A new test bench design to meet these requirements is presented, allowing a system-conform study of the components. For a high resolution of the temperature repartition in the smearing gap, thin film sensors, which have allowed the verifications experiments in the field of the Elastohydrodynamic-lubrication (EHL) are being enhanced. Beside a higher wear resistance, a reduction of the sensor size is an important requirement for the new sensor generation, allowing the resolution of local phenomena in the mixed lubrication. For the electrical isolation and wear protection of the new sensors developed at the Institute of Product Development of the University of Karlsruhe (TH) (IPEK), diamond like carbon (DLC) coatings are used. For the fulfillment of the requirements on the size of the sensors, a new concept of micro thermocouples is presented.

Commentary by Dr. Valentin Fuster
2008;():501-510. doi:10.1115/DETC2008-49537.

It is well known that due to the nonlinearity of the kinematics of linkage mechanisms, their output motion contains harmonics of the input motion. In most mechanisms, the generated high harmonic components in the output motion are the main source of vibration excitation that the mechanism imparts on the overall system, including its own structure. For simple linkage mechanisms such as slider-cranks and four-bar linkage mechanisms, the amplitudes of the harmonics of the output motion for constant input rotation have been derived. In the present study, it is shown that certain relationships exist between the amplitudes of the harmonic of the output motions. In particular, odd and even harmonic amplitudes are shown to be related through an inequality relationship. These relationships are due to the basic characteristics of the linkage mechanisms motions, which are significantly simplified for certain linkage geometries. The relationships between the amplitudes of the output velocity harmonics are derived for slider-crank and four-bar linkage mechanisms.

Topics: Motion , Linkages , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():511-519. doi:10.1115/DETC2008-49579.

Global simulation of mechanisms with time-varying topology is a tough task because the kinematic and kinetic equations of the whole system should be reformulated at each different topological stage, which increases the difficulty and decreases the efficiency. This paper proposes a new dynamics simulation approach of topology-varying mechanisms by replacing local modeling units. The interchangeability of unit models makes it possible to switch among different topologies automatically without rebuilding the system model. The topology-varying part of the system can be modeled as changeable modeling units, which leaves the other part as a settled one. Local replacement of changeable units will realize the reconfiguration of system model from one topological stage to another. This method has been used to analysis two typical kinds of mechanisms with time-varying topology: mechanism with “lock-unlock” process and with “opening-closing” loop. The simulation of the buffering motion in a forging manipulator is presented here as a case study, which proves the feasibility and efficiency of this new approach.

Commentary by Dr. Valentin Fuster
2008;():521-531. doi:10.1115/DETC2008-49585.

Fully flexible engine valve actuation systems are enablers for improvements in engine fuel consumption and power delivery, as well as the implementation of advanced combustion strategies like homogeneous charge compression ignition (HCCI). Hydraulically actuated valve actuation systems provide the greatest operating flexibility but have generally required precision flow control (i.e., servovalves) for viable operation while consuming more power than conventional cam-driven valvetrains. This paper describes an electrohydraulic fully flexible engine valve actuator with a mechanical feedback linkage between the engine valve and the spool in the hydraulic flow control valve. This feedback linkage is intended to simplify the control of the engine valve motion and eliminate the need for servovalve-class performance in the hydraulic control valve. The feedback mechanism reduces the control effort needed to operate the flow control valve since the spool position is not solely a function of the control input. With the assistance of mechanical feedback, the flow through the control valve is throttled in proportion to the engine valve motion. Thus, while throttling losses are not eliminated, there is no excessive flow throttling. This will have a beneficial impact on the energy consumption of the actuator. For preliminary study and validation of the concept, a model of the actuator was developed using ADAMS mechanical system simulation software and AMESim hydraulic simulation software. Results for the combined mechano-hydraulic model are presented to illustrate potential performance benefits and pitfalls of the concept, including effects of dimensional tolerances in the flow control valve. The simulation data was also used to size an electromechanical actuator that would be used to the flow control valve in conjunction with the feedback mechanism.

Commentary by Dr. Valentin Fuster
2008;():533-540. doi:10.1115/DETC2008-49646.

A novel class of two-stage, vibration-based electrical energy generators is presented for linear or rotary input motions in applications which the input speed is relatively low and varies significantly over time such as wind mills, turbo-machinery used to harvest tidal flows, devices for harnessing coastal wave energy, and the like. Current technologies use magnet-and-coil based electrical generators in such machinery. However, to make the generation cycle efficient, gearing or other similar mechanisms must be used to increase the input speed. Variable speed-control mechanisms are also usually needed to achieve high energy conversion efficiency. Additionally, in many applications, such as those where energy is to be harvested from very low frequency oscillations of a platform such as a buoy or a ship, the use of speed increasing mechanisms such as gearing or the like is impractical. In this paper, a novel class of two-stage electrical energy generators that could operate with very low speed and highly variable input rotations and/or oscillations is described. The first stage consists of simple linkage mechanisms, which are used to excite vibratory elements. These two-stage generators are designed to convert low-speed and highly variable input rotations and oscillations to relatively high and constant frequency vibratory motions, which are then used to generate electrical energy using mechanical to electrical energy conversion devices such as piezoelectric elements. The design of a number of such two-stage generators together with a discussion of their potential applications is presented.

Commentary by Dr. Valentin Fuster
2008;():541-548. doi:10.1115/DETC2008-49715.

A smart material made by piezoelectric ceramics to have the function of both the sensor and actuator is developed for vibration suppression. Unlike the passive method that implements suitable components to modify the structural effect of equivalent mass, damping, or stiffness etc. under a known and defined condition, this smart material is designed with the capability of self-detecting and self-actuating so that it can actively damp variant changing vibrations. Interdigital electrode method is used to make the smart material in order to enhance the sensitivity and the piezoelectric strain effect for the sensor and actuator. Polarized electric field of the interdigital electrode influential to the performance is investigated in particular. Various smart materials and thickness affecting polarized electric field of the interdigital electrode is studied and evaluated by ANSYS analysis. Dynamic modeling by using finite element method and Hamilton theory is derived for both the sensor and actuator. Internal model control structure is used for vibration control design. Predictive control method based on finite-element dynamic modeling is developed. Moving optimization method is also used to deal with the uncertainties of the environment so that the robustness of the device is improved. Practical experiment is carried out for performance evaluation.

Commentary by Dr. Valentin Fuster
2008;():549-559. doi:10.1115/DETC2008-50070.

One means of designing reduced vibration mechanisms is to ensure that the mechanism’s natural frequency be sufficiently greater than the driving frequencies of the actuators. In this paper we consider the problem of determining a mechanism’s mass, inertial, and joint stiffness parameters so as to maximize the lowest natural frequency of the mechanism. We show that this leads to a convex programming problem, which is characterized by global optima that can be found with efficient interior point algorithms. Several case studies involving closed chain mechanisms and hydraulically actuated excavators demonstrate the viability of the design methodology.

Commentary by Dr. Valentin Fuster
2008;():561-566. doi:10.1115/DETC2008-49040.

An analytical solution to moving pivot specification of motion generating dyads at three precision positions is derived using the complex number formulation. This solution enables replicating the functionality of a well-known graphical construction for three position synthesis. It complements an existing complex number based solution for ground pivot specification. The solution is demonstrated by a practical example of designing a vehicle suspension linkage. The example also demonstrates how moving pivot specification can be applied to synthesize multiloop linkages.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2008;():567-574. doi:10.1115/DETC2008-49046.

Regular nonadjustable four-bar linkages can only generate the desired continuous paths approximately. The whole desired continuous path can be generated precisely by an adjustable four-bar linkage with the one-degree-of-freedom adjustment of the pivot location of the driven side link. In this paper, an adjustment R joint is used to adjust the pivot location of the driven side link in the four-bar linkage. A closed-loop 5R linkage is formed by the adjustable four-bar linkage. The linkage feasibility conditions and path generation flexibilities of the adjustable four-bar linkages are analyzed. The synthesis model of the adjustable four-bar linkages is set up based on the required optimal adjustment of the pivot location when the desired continuous path is precisely generated. The global optimal solution is searched by a genetic algorithm in which the involved constraints are handled using the function penalty method. The effectiveness of the synthesis approach proposed in the paper is verified by two demonstrated examples.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2008;():575-579. doi:10.1115/DETC2008-49059.

A new method is proposed, which is the core of parametric simulation based on complicated mechanism design. Furthermore, the connotation of parametric simulation is affirmed and the flow of parametric simulation based on complicated mechanism design is put forward. At last, taking a parallel mechanism as example, the technology of parametric simulation proposed is applied to the simulation study used ADAMS, which consist of analyzing mechanism, parametric modeling, creating GUI, creating menu and parametric simulation. The practice indicates that the method is effectual.

Commentary by Dr. Valentin Fuster
2008;():581-590. doi:10.1115/DETC2008-49180.

Full rotatability identification is a problem frequently encountered in linkage analysis and synthesis. The full rotatability of a linkage is referred to a linkage in which the input may complete a full revolution without the possibility of encountering a dead center position. In a complex linkage, the input rotatability of each branch may be different. This paper presented a unified and comprehensive treatment for the full rotatability identification of six-bar and geared five-bar linkages disregard the choice of input and output joints or fixed link. A simple way to identify all dead center positions and the associated branches is discussed. Special attention and detail discussion is given to the more difficult condition with the input given through a link or joint not in the four-bar loop or on a gear-link. A branch without a dead center position has full rotatability. Using the concept of joint rotation space, the branch of each dead center position, and hence the branch without a dead center position can be identified easily. The proposed method is simple and conceptually straightforward and the process can be automated easily. It can be extended to any other single-degree-of-freedom complex linkages.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2008;():591-595. doi:10.1115/DETC2008-49285.

For a Stephenson II Six-Bar mechanism, because the rotatability of its input link is different corresponding to its different circuit and the input link even oscillate with respect to the frame through an angle more than 360°, the problem of whether a crank exist in this type of mechanisms is still pending. Based on the model established for circuit analysis of Stephenson six-bar chains, this paper presents a method of detecting the existence of a crank in this type of mechanisms. The result has significant value for linkages synthesis.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2008;():597-602. doi:10.1115/DETC2008-49294.

The conceptual and closed-form dimensional synthesis of a high-accuracy four-position tilt mechanism is discussed in detail. The mechanism, which consists of a customized five-bar linkage, is capable of accurately rotating an optical bench, which supports an object such as a space instrument, or another type of similar platform to four required and discrete angular postures. The mechanism is driven by two stepper motors. Due to the special characteristics of the five-bar linkage, even relatively large stepper motor errors produce very minor errors in the four desired angular postures of the optical bench. The dimensional synthesis of the mechanism involves solving a system of four non-linear equations in four unknowns. A methodology is introduced for reducing this system of non-linear equations to a closed-form quadratic equation in one unknown. A numerical example of the closed-form dimensional synthesis methodology is also presented.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2008;():603-609. doi:10.1115/DETC2008-49301.

This work presents a systematic procedure for completely generating the number of non-isomorphic specialized mechanisms from kinematic chains subject to design constraints for planar mechanisms. By assigning the specific types of members and joints in the available atlas of candidate kinematic chains, the atlas of specialized mechanisms are obtained. Furthermore, based on the combinatorial mathematics, the number of specialized mechanisms are counted and verified from the mathematical expressions. A motorcross suspension mechanism and the interior mechanism of Zhang Heng’s seismoscope are used as examples to illustrate this procedure.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2008;():611-616. doi:10.1115/DETC2008-49466.

The simulation of the operating conditions of transmission gear is strongly influenced by the inevitable presence of various types of errors and/or tolerances, manufacturing processes and assembly, in the kinematic simulation. As a result, the path of contact moves from the theoretical position and appear transmission errors, increasing overload dynamics and the level of noise and vibration. The presence of errors produced that the position angle of the gear with respect to pinion differs from the theoretical transmission ratio, in general there is a delay in the gear, which generates: 1) loss of the conjugate action and transmission error, which causes jumps in the angular velocity, which indicates the presence of shocks, with a high level of noise and vibration, and 2) loss of contact linear transforms into contact point. The shift in the trajectory of the contact can lead to the contact edge, which increases substantially, the levels of tension reducing load capacity, [1]. The method of analysis of tooth contact (TCA) is included in the kinematic simulation, and allows investigating the displacement of the contact and the slope of the function of transmission errors, considering the gears as rigid bodies or under light loads. To solve the above problems, Krenzer and Litvin have proposed programs TCA in what pre-design a parabolic function square transmission errors to get continuity in the transmission. This paper presents the model and analysis of a pre-designed polynomial function of transmission errors (parabolic function of order n) with the aim of ensuring that the function of movement meets the basic law of the design of gears, for transmissions with high speeds of operation, which should be designed with the following restrictions: the transmission must be continued through the first and second derivative of displacement, and the function of the derivative of acceleration (jerk) must be finite, throughout the interval.

Topics: Gears , Polynomials
Commentary by Dr. Valentin Fuster
2008;():617-625. doi:10.1115/DETC2008-49509.

A systematic methodology for the design of a statically balanced, single degree-of-freedom planar linkage is presented. This design methodology is based on the concept of conservation of potential energy, formulated by the use of complex number notations as link vectors of the linkage. By incorporating the loop closure equations, the gravitational potential energy of the system can be simplified as the function of the vectors of all ground-adjacent links. The balance of the gravitational potential energy of the system is then accomplished by the elastic potential energy of a zero free-length spring on each ground-adjacent link of the linkage. As a result, spring constants and installation configurations of the ground-attached springs are obtained. Since the variation of the gravitational potential energy of the linkage at all configurations can be fully compensated by that of the elastic potential energy of springs, this methodology provides an exact solution for the design of a general spring balancing mechanism without auxiliary parallel links. Illustrations of the methodology are successfully demonstrated by the spring balancing designs of a general Stephenson-III type six-bar linkage and a Watt-I type six-bar linkage with parallel motion.

Topics: Linkages , Design
Commentary by Dr. Valentin Fuster
2008;():627-635. doi:10.1115/DETC2008-49510.

Although the atlas of the geared kinematic chains (GKCs) had been enumerated decades ago, few studies had focused on how these synthesized GKCs can be applied according to the kinematic requirements of geared mechanisms in practice. In this paper, the kinematic behaviors of one-DOF, single-output geared mechanisms of up to six links are analyzed based on the concept of kinematic fractionation and the formulas of global gains are established. Classification of the geared mechanisms is obtained according to the gain types, ordinary, subtractive, fractional and composite. A set of rules for the assignment of ground, input and output links of single-KU and multiple-KU geared mechanisms without redundant links are proposed according to gain types. As a result, the kinematic synthesis of the one-DOF, single-output geared mechanisms of up to six links according to their associated gain types can be easily accomplished. An exemplary design of a geared mechanism with subtractive gain type is provided for the illustration of the proposed methodology.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2008;():637-645. doi:10.1115/DETC2008-49534.

This paper deals with the sensitivity analysis of planar parallel manipulators. A methodology is introduced to derive the sensitivity coefficients by means of the study of 3-RP R manipulators. As a matter of fact, the sensitivity coefficients of the pose of its moving platform to variations in the geometric parameters are expressed algebraically, the variations being defined both in Polar and Cartesian coordinates. The dexterity of the manipulator is also studied by means of the conditioning number of its normalized kinematic Jacobian matrix. As an illustrative example, the sensitivity of a symmetrical planar parallel manipulator is analyzed in detail. Finally, the accuracy of the manipulator is compared with its dexterity.

Commentary by Dr. Valentin Fuster
2008;():647-655. doi:10.1115/DETC2008-49549.

We review variable valve actuation (VVA) concepts and also present the results of our work in the creative synthesis of these devices. We begin with a comprehensive survey of existing VVA devices. We then describe our work on four VVA concepts which we have explored in considerable detail. These include hydraulic lost-motion variable-lift systems, in both the direct acting and the roller-finger-follower configurations, several valve deactivation mechanisms with unique features, a variable valve-lift mechanism, and a variable-lift and duration concept. These devices differ in their complexity and versatility but offer a spectrum of design solutions applicable to a range of products. The strengths and weaknesses of these different approaches are discussed and analyzed, and some test results are presented.

Topics: Valves
Commentary by Dr. Valentin Fuster
2008;():657-664. doi:10.1115/DETC2008-49627.

To extract the features from a coupler curve is one of key issues in the synthesis of path generating mechanism. Fourier transformation is widely used at present. A new method of feature extraction, named mathematical morphology based method, emerges in resent years. Based on the essential operations of mathematical morphology, the shape spectrum (SS) of the coupler curve is computed. SS is rotation-scale-translation invariant. Therefore, as a means of describing coupler curve, it has possesses advantage over that based on Fourier transformation. In this paper, what kind information involved in SS of a curve is revealed. It is shown that the largest radius of internally tangent circle and the area inside of the curve can be inferred from its SS. This paper also shows that SS is without the information of the structure feature which is necessary to describe a nonsimple closed coupler curve. Eight-figure-shaped coupler curve is the simplest nonsimple closed curve. To describe such curve, three structure parameters of the curve should be involved besides that provided by SS of curve. A method using five numbers to describe and differentiate an eight-figure-shaped coupler curve is proposed in this paper. The five numbers can be obtained from its SS and the structure of the curve. A new formula to compute the similarity between two eight-figure-shaped couplers using the five numbers is presented.

Commentary by Dr. Valentin Fuster
2008;():665-670. doi:10.1115/DETC2008-49644.

This paper presents an analysis to create a general singularity condition for a mechanism that contains a deformable closed contour. This kinematic architecture is widely used in rigid-body shape changing mechanisms. The general singularity equation is reduced to a condensed form, which allows geometric relationships to be readily detected. A method for formulating the singularity condition for a mechanism with N links in the closed contour, knowing the condition for the N − 1 mechanism, is also given.

Topics: Shapes , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():671-678. doi:10.1115/DETC2008-49711.

The gear noise has been reduced by reducing the meshing transmission error to improve the gear noise up to now. However, it seems that there is no research that considers even human aural characteristic yet in this field. Therefore, we propose a new design method of the low noise gear, which according to human aural characteristic. The proposed technique is a gear design to control the frequency of the gear noise by changing number of tooth. First of all, human aural characteristic was researched in a special acoustic environment in the vehicle. Secondly, the characteristic of vehicle interior sound was investigated. Thirdly, the relationship between the number of teeth and the sound level of the gear noise was investigated. Finally, it was demonstrated that a proposed method was effective to design an advantageous number of gear teeth according to human aural characteristic. It was found that the proposed method of varying the number of teeth was effective for designing gears with optimal human aural characteristics.

Commentary by Dr. Valentin Fuster
2008;():679-688. doi:10.1115/DETC2008-49863.

This paper deals with the analysis and synthesis of slider-crank mechanisms, which are aimed to give suitable coupler curves for automatic machinery, as path generators. A practical method for the dimensional synthesis of slider-crank mechanisms is proposed by referring to a classical approach, which is based on the use of the centrodes, inflection circle, cubic of stationary curvature, cubic curve of centers and Ball’s point. Usually, in the industrial practice, the generation of a specific continuous path is not required because, very often, only the shape and the overall size of a coupler curve is sufficient to satisfy the design specifications. Thus, this paper gives a contribution to the dimensional synthesis of slider-crank mechanisms by formulating a practical and intuitive procedure, in order to obtain two different shapes of path, a symmetric egg shape path with a straight segment part and/or stationary curvature and a raindrop shape path, which both respect the required overall sizes.

Topics: Machinery , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():689-696. doi:10.1115/DETC2008-49889.

This paper presents a geometric synthesis procedure for spherical (6, 7) linkages, often known as spherical six-bar linkages, based on adding two spherical RR constraints to a spherical 3R serial chain. The design can use the spherical 3R chain to shape the movement of the linkage and identify a set of task positions that shape the trajectory of the end-effector. We use five task positions to completely specify the two RR chains that constrain the system to one degree-of-freedom. This procedure yields spherical versions of the various topologies for the planar Watt and Stephenson six-bar linkages. We find that for any design problem we obtain at a minimum of two design candidates for the Watt-type linkage, and as many as 185 different design for all of the topologies obtained by constraining the spherical 3R chain. Wampler’s method for the analysis of spherical loops is used to analyze these linkages. An example design is presented in detail.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2008;():697-706. doi:10.1115/DETC2008-49910.

A new methodology for automated conceptual design of hybrid combined mechanical system based on the characteristic state space approach is developed. The goal is to conceive the appropriate hybrid system given only the kinematic function posed in the problem specifications. The key enabler of the conceptual synthesis is the method of capturing kinematic behavior and transforming the continuous and non-linear motion into the discrete states and linear relation characteristic stack representation. A new characteristic state analyzing method for multi-dof primary mechanism blocks is proposed. Then the characteristic state equations are established by motion relationship between the multiple inputs and the outputs, which including characteristic transformation matrices and the characteristic state vectors established through the method of linearization for kinematic equations according to the specific input and output motion transformation. Thus the multi-dof primary mechanism blocks are identified, classified and represented qualitatively from characteristic perspectives. And then, generalized characteristic state modeling method is used to describe the behavior of the multi-loop combined mechanism. The generalized characteristic state model sets are established according to the classified primary combination patterns. The mathematical model of the hybrid combination system facilitates the characterization of the primary mechanism blocks and primary combination patterns, transformation of problem specifications, decomposition into sub-problems, and the ability to search for alternate solutions. The characteristic state space graph theory and the space vector routing model between the random input-output dual vectors in state space are established. Furthermore, with the manipulation of the dual vectors, the mathematic synthesis model is presented leading to the characteristic equation operation and the groundwork is laid for the conceptual design. To fine present the automated decomposition and the synthesis algorithm, the suggested design examples are compact and compatible with the general design principles.

Commentary by Dr. Valentin Fuster
2008;():707-715. doi:10.1115/DETC2008-49947.

In the recent past, we have studied the problem of synthesizing rational interpolating motions under the kinematic constraints of any given planar and spherical 6R closed chain. This work presents some preliminary results on our initial attempt to solve the inverse problem, that is to determine the link lengths of planar and spherical 6R closed chains that follow a given smooth piecewise rational motion under the kinematic constraints. The kinematic constraints under consideration are workspace related constraints that limit the position of the links of planar and spherical closed chains in the Cartesian space. By using kinematic mapping and a quaternions based approach to represent displacements of the coupler of the closed chains, the given smooth piecewise rational motion is mapped to a smooth piecewise rational curve in the space of quaternions. In this space, the aforementioned workspace constraints on the coupler of the closed chains define a constraint manifold representing all the positions available to the coupler. Thus the problem of dimensional synthesis may be solved by modifying the size, shape and location of the constraint manifolds such that the mapped rational curve is contained entirely inside the constraint manifolds. In this paper, two simple examples with preselected moving pivots on the coupler as well as fixed pivots are presented to illustrate the feasibility of this approach.

Topics: Motion , Chain , Interpolation
Commentary by Dr. Valentin Fuster
2008;():717-725. doi:10.1115/DETC2008-50046.

The paper presents the first elastic meshing law and spatial elastic conjugation tooth profile for harmonic gear drives. The kinematics and geometry of harmonic drives that have a cup-type flexible spline with an oval wave generator is investigated. The deformation function of the neutral layer of a flexspline is investigated and calculation example is taken by non-linear finite element software. The mathematic model of kinematics of harmonic drive is set up, in which the spatial deformation of a flexspline is separated into a set of deformed curves on the cross sections vertical to the axis. Thus, the spatial engagement in harmonic drive can be visualized as a set of planar engagement. The properties of the instant center and the centrodes of the flexspline tooth relative to the circular spline are studied. The phenomenon of twice engagement at one tooth point of circular spline is found for the first time. The planar gearing engagement and the instant center equation are analyzed and a vigorous spatial elastic conjugation theory is provided for harmonic gear drive.

Commentary by Dr. Valentin Fuster
2008;():727-736. doi:10.1115/DETC2008-49157.

Minimally invasive abdominal surgery (laparoscopy) results in superior patient outcomes as measured by less painful recovery and an earlier return to functional health compared to conventional open surgery. However, the difficulty of manipulating traditional laparoscopic tools from outside the patient’s body generally limits these benefits to patients undergoing procedures with relatively low complexity. The use of miniature in vivo robots that fit entirely inside the peritoneal cavity represents a novel approach to laparoscopic surgery. Our previous work has demonstrated that mobile and fixedbased in vivo robots can successfully operate within the abdominal cavity and provide surgical vision and task assistance. All of these robots used tethers for power and data transmission. This paper describes recent work focused on developing a modular wireless mobile platform that can be used for in vivo sensing and manipulation applications. The robot base can accommodate a variety of payloads. Details of the designs and results of ex vivo and in vivo tests of robots with biopsy grasper and physiological sensor payloads are presented. These types of self-contained surgical devices are much more transportable and much lower in cost than current robotic surgical assistants. These attributes could ultimately allow such devices to be carried and deployed by non-medical personnel at the site of an injury. A remotely located surgeon could then use these robots to provide critical first response medical intervention irrespective of the location of the patient.

Topics: Robots , Surgery
Commentary by Dr. Valentin Fuster
2008;():737-745. doi:10.1115/DETC2008-49163.

The size and limited dexterity of current surgical robotic systems are factors which limit their usefulness. To improve the level of assimilation of surgical robots in minimally invasive surgery (MIS), a compact, lightweight surgical robotic positioning mechanism with four degrees of freedom (DOF) (three rotational DOF and one translation DOF) is proposed in this paper. This spatial mechanism based on a bevel-gear wrist is remotely driven with three rotation axes intersecting at a remote rotation center (the MIS entry port). Forward and inverse kinematics are derived, and these are used for optimizing the mechanism structure given workspace requirements. By evaluating different spherical geared configurations with various link angles and pitch angles, an optimal design is achieved which performs surgical tool positioning throughout the desired kinematic workspace while occupying a small space bounded by a hemisphere of radius 13.7 cm. This optimized workspace conservatively accounts for collision avoidance between patient and robot or internally between the robot links. This resultant mechanism is highly compact and yet has the dexterity to cover the extended workspace typically required in telesurgery. It can also be used for tool tracking and skills assessment. Due to the linear nature of the gearing relationships, it may also be well suited for implementing force feedback for telesurgery.

Commentary by Dr. Valentin Fuster
2008;():747-754. doi:10.1115/DETC2008-49587.

Brain tumors are among the most feared complications of cancer and they occur in 20–40% of adult cancer patients. Despite numerous advances in treatment, the prognosis for these patients is poor, with a median survival of 4–8 months. The primary reasons for poor survival rate are the lack of good continuous imaging modality for intraoperative intracranial procedures and the inability to remove the complete tumor tissue due to its placement in the brain and the corresponding space constraints to reach it. Intraoperative magnetic resonance imaging (MRI) supplements the surgeon’s visual and tactile senses in a way that no other imaging device can achieve resulting in less trauma to surrounding healthy brain tissue during surgery. To minimize the trauma to surrounding healthy brain tissue, it would be beneficial to operate through a narrow surgical corridor dissected by the neurosurgeon. Facilitating tumor removal by accessing regions outside the direct “line-of-sight” of the neurosurgical corridor will require a highly dexterous, small cross section, and MRI-compatible robot. Developing such a robot is extremely challenging task. In this paper we report a preliminary design of 6-DOF robot for possible application in neurosurgery. The robot actuators and body parts are constructed from MRI compatible materials. The current prototype is 0.36” in diameter and weighs only 0.0289 N (2.95 grams). The device was actuated using Flexinol® which is a shape memory alloy manufactured by Dynalloy, Inc. The end-effector forces ranged from 12 mN to 50 mN depending on the robot configuration. The end-effector force to robot weight ratio varied from 0.41 to 1.73. During trials the robot motion was repeatable and the range of motion of the robot was about 90 degrees for the end-effector when one side shape memory alloy (SMA) channel was actuated. The actuation time from the start to finish was about 2.5 s.

Commentary by Dr. Valentin Fuster
2008;():755-761. doi:10.1115/DETC2008-50082.

It is anticipated that the use of assistive robots will be one of the most important service applications of robotic systems of the future. In this paper, a unique non-contact socially assistive robot consisting of a human-like demeanor is presented for utilization in hospital wards and veteran homes to study its role and impact on the well-being of patients, addressing patient’s needs and its overall effect on the quality of patient care. The robot will be an embodied entity that will participate in hands-off non-contact social interaction with a patient during the convalescence, rehabilitation or end-of-life care stage. The robot has been designed as a platform to incorporate the three design parameters of embodiment, emotion and non-verbal communication to encourage natural interactions between a person and itself. In this paper, we present the mechanical design of the robot. The robot is able to communicate via: (i) a unique human-like face with artificial skin that utilizes the modeling of muscles of a human face to express facial expressions, (ii) a 3 degrees-of-freedom (DOF) neck capable of expressing head gestures, and (iii) an upper torso consisting of a 2 DOF waist and two 4 DOF arms designed to mimic human-like body language.

Topics: Robots , Health care
Commentary by Dr. Valentin Fuster
2008;():763-770. doi:10.1115/DETC2008-49007.

A micro-array based automated hybridization platform, ITRI HybOne, with the throughput rate of 12-sets per lot has been proposed and developed for whole human genome expression profiling test. A special handling module has been designed for capturing of Whole Human Genome Micro-array which is a glass slide 75mm in length and 25mm in width and 1mm in thickness. According to the user-defined protocol, an operator can set the heating temperature, washing temperature, heating hours and washing hours before starting the profiling test. Operator inputs target samples and micro-arrays to ITRI HybOne, pushes the Cycle-Start button to start. With the help of the handling module and other automatic devices, after hours of automatic process, the micro-arrays are ready for profile scanning. All the handling modules used in the platform are recycled for next profiling test.

Topics: Glass
Commentary by Dr. Valentin Fuster
2008;():771-780. doi:10.1115/DETC2008-49118.

Various patents relating fixed center steering wheels are studied. The corresponding topological characteristics, design specifications, and design requirements and constraints of mechanisms are concluded. A methodology for the creative design of mechanisms is applied to generate all possible design concepts of mechanisms subjected to the concluded design requirements and constraints. In conclusion, 29 new design concepts of fixed center steering wheels are synthesized.

Commentary by Dr. Valentin Fuster
2008;():781-787. doi:10.1115/DETC2008-49151.

It frequently comes to building collapses all over the world. Often people are buried alive. They must be rescued and saved by rescue teams. It depends on the time that passes during a rescue whether a person can still be rescued alive. Especially the information which is available about the exact position of a person buried alive is decisive for a fast accomplishment of rescue actions. Accordingly the exact localization of victims buried alive is of primary importance. It is the only way, a fast rescue and salvation can be started. However, biological and technical locating equipment available today shows numerous weak points. This refers particularly to the precision of position determination of the victims. But the essential disadvantage of the utilizable technologies is that a collapsed building cannot be entered actively. There is no equipment available that enables a deep penetration into ruins for inspection and exploration tasks, without the necessity of using heavy machines. In a research project currently funded in Germany these difficulties shall be encountered by a part autonomous, energy self-sufficient and remotely controlled reconnaissance robot. It will become a motion system, which orientates its design and behavior at the biological archetype snake. The paper at hand introduces the state-of-the-art of technology and research in the fields of locating, reconnaissance robots as well as snake robots. Originating from a multifunctional locomotion system that has been already implemented successfully, elements for a robot system to be newly developed are introduced and discussed.

Topics: Robots
Commentary by Dr. Valentin Fuster
2008;():789-796. doi:10.1115/DETC2008-49167.

A novel piano action mechanism is presented, which is based on a multi-lobed lifting cam. The cam replaces several bodies in the standard action mechanism and allows the upright piano to achieve fast repetition of a single note, which is a quality more commonly attributed to grand piano actions. The use of simulation software to aid in tuning of the design is described, and the final simulation results are presented. These results indicate the ability of the new mechanism to achieve good performance over a range of playing intensities and to play repeated notes in rapid succession.

Commentary by Dr. Valentin Fuster
2008;():797-804. doi:10.1115/DETC2008-49263.

Robots based on parallel kinematics feature low moved masses, allowing for better dynamic performance compared to serial mechanisms. Otherwise, the known drawbacks, like occurrence of singularities or bad radio of work space to installation area, hinder their fully industrial establishment. In order to overcome some of these drawbacks, development of specific and optimized robot components, like rods or joints, becomes necessary. Development of joints for parallel robots is determined by numerous contradictory requirements which cause different goal conflicts. In this work, possibilities for dissolving of such goal conflicts by means of adaptronic joints (joints with integrated piezo-actuators) are discussed. To deal with these complex issues this paper focuses on three major areas: firstly, conventional joint concepts, including their main flaws; secondly, new, adaptronic joint concepts based on quasi-statical clearance adjustment with two laboratory prototypes and their improvements over the old solutions; thirdly and finally, some of possible consequences of the new joint concepts for the overall performance of parallel robots. By drawing on experimental results derived from laboratory tests, it is possible to show how implementation of the developed joint prototypes could influence friction characteristic of the whole robot system.

Commentary by Dr. Valentin Fuster
2008;():805-810. doi:10.1115/DETC2008-49337.

Locks are important safety devices in our daily lives. The purpose of this study is to design new mechanisms of multipoint mortise locks based on a systematic approach. Firstly, the classification and advantages of mechanical locks are introduced, and the definitions and the development of mortise locks are described. Then, the multipoint mortise locks are decomposed into four sub-parts by the different functions, including the latch bolt lock, the dead bolt lock, the dead-latch bolt lock, and the connecting mechanism. The four sub-parts are further analyzed to conclude their structural characteristics as well as design requirements and constraints. Based on Yan’s creative mechanism design methodology, the concepts and the atlas of designs are synthesized systematically. One feasible mechanism is further chosen for detail design. Finally, a computer program for simulation is developed and prototypes are built for verifying the design results. The results of this study provide a valuable reference for designing multipoint mortise locks and for the analysis of mechanism characteristics of mortise locks.

Topics: Design
Commentary by Dr. Valentin Fuster
2008;():811-818. doi:10.1115/DETC2008-49448.

This paper has presented two constructive solutions of rational using of frontal rigid gear couplings with spherical gear in circle arc type Gleason, knowing as curved frontal gear coupling, on small dimensions, ones for simple direct dividing and second for simple differential dividing, and geometrical development possibility of new family of frontal coupling and small size. The frontal gear coupling type Gleason are formed from two rings, one with concave gear and other with convex gear, being characterized by great twist moments of capacity transmission, realizing a precision angular position, fast central connection and assuring of optimal conditions for manufacturing of mass production and low cost. One new application of small frontal gear couplings was external diameter of O̸100mm and O̸120mm, assured a higher accuracy of angular location of ±2″ and a great carrying capacity for couplings by using of compound rest of lathe with ultra precision location. A second application has presented a new landing of simple direct and differential dividing using one or more pair of Gleason’s gear coupling due to construction of new indexing tables with ultra precision in metal cutting.

Topics: Gears , Couplings
Commentary by Dr. Valentin Fuster
2008;():819-826. doi:10.1115/DETC2008-49453.

This paper focuses on the experiments conducted using a telerobot for the augmentation of wheelchair users. After providing the motivation and the background material, a strawman task is formulated. A robot is then conceived to meet the assigned task (i.e. user, environment and payload definitions). The proposed robot meets both cost and control simplification requirements necessary to the success of a robotic assistive device. A minimalistic design allows to achieve the requirements on cost and control complexity. An architecture based on a minimum number of driving units and sensors is devised. Experiments on the interactive control of the robot are performed. We demonstrate that the robot is capable to navigate through a cluttered environment while being teleoperated. Experiments also show that the system remains in its footpring when a rotation in place is assigned by the user; this is an important feature that prevents the system from colliding with any object nearby. Finally, always via experiments, we show that the system is capable to bring a tray of drinks, food and reading material while being teleoperated.

Topics: Wheelchairs
Commentary by Dr. Valentin Fuster
2008;():827-832. doi:10.1115/DETC2008-49485.

To fulfill a low cost required solution for automation in replacing human labor efforts in a candy factory, this paper focuses on the design and building of a low cost machine. Simplicity was the key requirement of the design. Tray motion is analyzed and different design concepts are brainstormed and evaluated. The final machine prototype was built and tested for its functionality.

Commentary by Dr. Valentin Fuster
2008;():833-839. doi:10.1115/DETC2008-49527.

Project critical mission requirements often drive design decisions and processes. This was the case for National Aeronautics and Space Administration (NASA) funded DEep Phreatic THermal eXplorer (DepthX), an underwater robot designed to autonomously map, navigate, and acquire biological samples. Mission requirements led the authors to develop a novel core sampling mechanism for variable density materials. Preliminary testing was conducted on variable density materials simulating real world specimens to identify the series of motions to acquire an acceptable core and optimize the geometry of the coring tube. A geometric modeling approach with configuration functions was employed to design the overall mechanism and establish the cam profile. The design was tested and evaluated during multiple field expeditions to cenotes (sinkholes) in Mexico. The culmination of the preliminary testing and the selected design methodology resulted in a core sampling mechanism that is compact, has minimal operational torque requirements, and utilizes a single motor to complete a series of complex functions. Future applications are envisioned for space expeditions, underwater exploration, and medical sampling.

Commentary by Dr. Valentin Fuster
2008;():841-849. doi:10.1115/DETC2008-49557.

This paper presents the design and implementation of systems for autonomous tracking, payload pickup, and deployment of a 1/10th scale RC vehicle via a UAV helicopter. The tracking system uses a visual servoing algorithm and is tested using open loop velocity control of a three degree of freedom gantry system with a camera mounted via a pan-tilt unit on the end effecter. The pickup system uses vision to control the camera pan tilt unit as well as a second pan tilt unit with a hook mounted on the end of the arm. The ability of the pickup system to hook a target is tested by mounting it on the gantry while recorded helicopter velocities are played back by the gantry. A preliminary semi-autonomous deployment system is field tested, where a manually controlled RC car is transported by a UAV helicopter under computer control that is manually directed to GPS waypoints using a ground station.

Commentary by Dr. Valentin Fuster
2008;():851-858. doi:10.1115/DETC2008-49559.

The Whole Skin Locomotion (WSL) robotic platform is a novel biologically inspired robot that uses a fundamentally different locomotion strategy than other robots. Its motion is similar to the cytoplasmic streaming action seen in single celled organisms such as the amoeba. The robot is composed of a closed volume, fluid filled skin which generally takes the shape of an elongated torus. When in motion the outer skin is used as the traction surface. It is actuated by embedded smart material rings which undergo cyclical contractions and relaxations, generating an everting motion in the torroidially shaped skin. To better understand, design, and optimize this mechanism, it is necessary to have a model of the skin, fluid, and actuators and their interactions with the environment. This paper details the first steps in the development of a non-linear finite element (FE) model which will allow us to study these interactions and predict the shape and motion of the robot under various actuation strategies. A simple membrane element model is introduced from literature and is modified such that an incremental loading strategy can be employed. Finally, an underlying physical mechanism is introduced which could possibly describe the relationship between the shape of and pressure within the membrane skin and motion of the whole skin locomotion robot.

Commentary by Dr. Valentin Fuster
2008;():859-866. doi:10.1115/DETC2008-49562.

HyDRAS (Hyper-redundant Discrete Robotic Articulated Serpentine) is a novel serpentine robot comprising a serial chain of actuated universal joints for climbing structures such as poles or scaffoldings. To do so, it wraps its body around the structure in a helical shape, and rotates its body along its own central body axis to roll up the structure. This paper presents a method and considerations for selecting the optimal design parameters for the development of HyDRAS. The geometry equations derived in this paper will allow for a parametric approach that will aid in the selection of the appropriate design parameters such as module length, module diameter, helical pitch, and allowable range of motion for the given task of climbing pole like structures. Several examples are used to illustrate the method. The results obtained will be used in the analysis of the mechanical advantage of the mechanism and future research on the motion planning of HyDRAS.

Commentary by Dr. Valentin Fuster
2008;():867-875. doi:10.1115/DETC2008-49602.

As the number of UAVs increase, the risk of accidental crashes also grows. A critical examination of these accidents reveals that human error is a major cause. This suggests a need to improve the remote piloting of UAVs. This paper explores the use of motion platforms to augment pilot performance. This approach follows studies on human factors performance and cognitive loading. The resulting design serves as a test bed to study UAV pilot performance, create training programs, and ultimately a platform to avoid UAV accidents.

Commentary by Dr. Valentin Fuster
2008;():877-884. doi:10.1115/DETC2008-49630.

A design for autonomous control of a novel omni-directional platform is presented. This platform is to be used in conjunction with a robotic arm to further research of mobile-manipulator systems. This design differs from other omni-directional platforms that use omniwheels in that its drive axes do not intersect its geometric centre. The platform can be controlled autonomously through multiple sub-systems that have been designed including a closed-loop velocity controller, a localization system, an obstacle avoidance and collision detection system, a vision system, and a data routing system. These sub-systems communicate with a remote computer which plots the path and sends data to guide the platform. The closed-loop velocity controller provides feedback which can be used to analyze and correct the path of travel.

Topics: Design , Vehicles
Commentary by Dr. Valentin Fuster
2008;():885-893. doi:10.1115/DETC2008-49632.

This paper describes the mechanical design and analysis of a mobile-manipulator system comprised of a robot manipulator and a mobile base. The combination of the two is known as a mobile manipulator and combines the maneuverability of the mobile base with the accuracy of the robot manipulator. The mechanical design of a new mobile-manipulator system with the robot manipulator mounted on the front is discussed. The device features an innovative 2-DOF (degree-of-freedom) parallelogram coupling device that allows the base of the robot manipulator to translate vertically and roll longitudinally relative to the mobile base. The coupling device has dampers to reduce the vibrations caused by the motion of the mobile base on the robot manipulator and vice versa. The design features the use of omni-wheels that eliminate the problems inherent with traditional caster wheels.

Commentary by Dr. Valentin Fuster
2008;():895-902. doi:10.1115/DETC2008-49847.

Sea waves are one of the most interesting and well distributed renewable energy sources in the world. At the current state of the art, all the existing sea wave energy conversion systems are designed to operate offshore, mainly in the oceans where the waves’ height is definitely high. In the Mediterranean Sea, waves are generally low, except under particular meteorological conditions. Thus, it is necessary to develop devices that can exploit other properties of the waves instead of their height, like wave slopes. In this work a solution for this application is analysed, based on a conversion device characterised by floating positioning (without fixed link or basement at depth level), vertical axis geometry (to exploit any kind of wave, regardless of their direction, without the need for orientation systems), working principle based on an inertial system obtained by a rotor thanks to gyroscopic effect (that can be tuned to maximise the efficiency of the transformation process), and ability to work even with low amplitude waves (up to 0.5 m) typical of the Mediterranean Sea. The work follows three steps: first of all, the mechanical system is described with an analytical approach, secondly the mathematical model is implemented, and, finally, it’s tested in simulated sea environments. A system analytical model will be shown and some numerical results will be remarked.

Commentary by Dr. Valentin Fuster
2008;():903-911. doi:10.1115/DETC2008-49879.

Discretely actuated or digital robotic manipulators have become popular because they are highly repeatable, need no feedback control, and are relatively less expensive and lightweight compared to continuously actuated manipulators. This research investigates trajectory planning for discretely actuated manipulators within a static environment without obstacles and with known initial and final positions. In particular, the focus will be on minimizing oscillations of a path trajectory and minimizing the deviation from the ideal path, as well as minimizing the torque required to actuate each joint. Motion strategies are developed and their effect studied.

Commentary by Dr. Valentin Fuster
2008;():913-924. doi:10.1115/DETC2008-49972.

Physical parameters of modules and gait parameters affect the overall snake-inspired robot performance. Hence the system-level optimization model has to concurrently optimize the module parameters and the gait. The equations of motion associated with the rectilinear gait are quite complex due to the changing topology of the rectilinear gait. Embedding these equations in the system-level optimization model leads to a computationally challenging formulation. This paper presents a system-level optimization model that utilizes a hierarchical optimization approach and meta-models of the pre-computed optimal gaits to reduce the complexity of the optimization model. This approach enabled us to use an experimentally validated physics-based model of the rectilinear gait and yet at the same time enabled us to create a system-level optimization model with a manageable complexity. A detailed case study is presented to show the importance of concurrently optimizing the module parameters and the gait using our model to obtain the optimal performance for a given mission.

Topics: Robots , Optimization
Commentary by Dr. Valentin Fuster
2008;():925-931. doi:10.1115/DETC2008-49999.

This paper presents design for a finger mechanism that has evolved from the stringent requirement of ruggedness and reliability in an industrial application. The paper initially describes the need for a special purpose end effector to operate in a constrained environment and then takes through the various stages of design modifications that were required to ensure safety and reliability. This resulted into a rigid link finger design, which is adaptive to different shapes and operated by a single actuator providing up to 3 degrees of freedom to the finger. A number of such finger mechanisms can be assembled together in different configurations to design special purpose end effectors. This paper covers two such designs and briefly discusses the grasping and control issues associated with the limited number of actuators built into the end effector, and evaluates their suitability in industrial environments. The design overcomes limitations of majority of existing tendon based end effectors requiring a large number of actuators to be controlled thus meeting the space and safety requirements for constrained industrial applications.

Commentary by Dr. Valentin Fuster
2008;():933-943. doi:10.1115/DETC2008-50000.

Gravity compensation of spatial parallel manipulators is a relatively recent topic of investigation. Perfect balancing, by either counterweights or elastic elements, has been accomplished, so far, only for parallel mechanisms in which the weight of the moving platform is sustained by legs comprising purely rotational joints. Indeed, balancing of parallel mechanisms with translational actuators, which are among the most common and used ones, has been traditionally thought possible only by resorting to additional legs containing no prismatic joints between the base and the end-effector. This paper presents the conceptual and mechanical design of a balanced Gough/Stewart-type manipulator, in which the weight of the platform is entirely sustained by the legs comprising the extensible jacks. By the integrated action of both elastic elements and counterweights, each leg is statically balanced and it generates, at its tip, a constant force balancing the weight of the end-effector in any admissible configuration. If no elastic elements are used, the resulting manipulator is balanced with respect to the shaking force too. Two Appendices are also provided, presenting formal and novel derivations of the necessary and sufficient conditions allowing i) a body arbitrarily rotating in space to rest in a state of neutral equilibrium under the action of general constant-force generators, ii) a body pivoting about a universal joint and acted upon by a number of zero-free-length springs to exhibit constant potential energy regardless of its configuration.

Commentary by Dr. Valentin Fuster
2008;():945-953. doi:10.1115/DETC2008-50066.

Design of flapping-wing micro air-vehicles presents many engineering challenges. As observed by biologists, insects and birds exhibit complex three-dimensional wing motions. It is believed that these unique patterns of wing motion create favorable aerodynamic forces that enable these species to fly forward, hover, and execute complex motions. From the perspective of micro air-vehicle applications, extremely lightweight designs that accomplish these motions of the wing, using just a single, or a few actuators, are preferable. This paper presents a method to design a spherical four-bar flapping mechanism that approximates a given spatial flapping motion of a wing, considered to have favorable aerodynamics. A spherical flapping mechanism was then constructed and its aerodynamic performance was compared to the original spatially moving wing using an instrumented robotic flapper with force sensors.

Commentary by Dr. Valentin Fuster
2008;():955-963. doi:10.1115/DETC2008-50108.

Previous research and publications at Brigham Young University have established the new positive engagement continuously variable transmission (PECVT) family of continuously variable transmissions (CVTs). Various embodiments of PECVTs have been identified and surveyed; resulting in the identification of the behavior termed the non-integer tooth problem. Additional research has been conducted to further explore the non-integer tooth problem and identify a feasible solution to the problem through the use of a product development method. This publication will address the conceptual design phase of the product development process for a PECVT. This will include: the identification of the operating conditions of a PECVT, i.e. further detail of the non-integer tooth problem, identification of required characteristics for a solution, design specifications, concept generation, concept evaluation, and concept selection. The conceptual design phase will result in a conceptual solution which will satisfy the identified characteristic requirement and designs specifications.

Commentary by Dr. Valentin Fuster
2008;():965-972. doi:10.1115/DETC2008-49105.

A serial robotic manipulator arm is a complex electro-mechanical system whose performance is highly characterized by its actuators. The actuator itself is a complex nonlinear system whose performance can be represented by the speed and torque capabilities of its motor and its accuracy depends on the resolution of the encoder as well as its ability to resist deformations under load. The mechanical gain associated with the transmission is critical to the overall performance of the actuator since it amplifies the motor torque thus improving the force capability of the manipulator housing it, reduces the motor speed to a suitable output speed operating range, enables an improvement in responsiveness (acceleration) and amplifies the stiffness improving the precision under load of the overall system. In this work, a basic analytic process that can be used to manage the actuator gain parameters to obtain an improved arm design based on a set of desired/required performance specifications will be laid out. Key to this analytic process is the mapping of the actuator parameters (speed, torque, stiffness and encoder resolution) to their effective values at the system output via the mechanical gains of the actuators as well as the effective mechanical gains of the manipulator. This forward mapping of the actuator parameters allows the designer to determine how each of the parameters influences the functional capacity of the serial manipulator arm. The actuator gains are then distributed along the effective length of the manipulator to determine the distribution effects on the performance capabilities of the system. The analytic formulation is used to address the issue of configuration management of serial robotic manipulators where the goal is to assemble a system from a finite set of components that meets some required performance specifications. To this end, two examples demonstrating a solution of the configuration management problem are presented. In the first, a manipulator is configured that is intended for light-duty applications while in the second, several manipulators intended for medium and heavy-duty applications are configured. The analytic process developed in this work can reduce the effort in the initial phases of the design process and the total number of design iterations can be reduced.

Commentary by Dr. Valentin Fuster
2008;():973-981. doi:10.1115/DETC2008-49113.

The inverse dynamics and control of redundantly actuated PKM in the presence of uncertainties is the focus of this paper. Actuation redundancy allows for a purposeful distribution of control forces, taking into account secondary tasks, such optimal force distribution, active stiffness, and backlash avoiding control. A closed form solution of the inverse dynamics problem for simply redundantly actuated PKM is given. The applicability of the augmented PD and computed torque control schemes is analyzed. It is shown that, in the presence of model uncertainties, adopting the standard control schemes leads to parasitic perturbation forces that can not be compensated by the controls. An amended version of these control scheme is proposed that does not suffer from such effects.

Commentary by Dr. Valentin Fuster
2008;():983-992. doi:10.1115/DETC2008-49164.

We introduce a dual input Parallel Force/Velocity Actuation (PFVA) concept in this paper to enable variable response manipulation. The objective of this paper is to develop an analytical model for power flow in PFVA systems. We studied the functional dependence of external and internal power flow phenomena on two dimensionless parameters we define in this paper, namely Relative Scale Factor (ρ) and Velocity Mixing Ratio (λ). We observed that overall mechanical efficiency of the PFVA decreases approximately 16% from the basic efficiency when the RSF was increased 5x and the VMR was increased 10x. For a specified load torque of −100 Nm at the output of a positive-ratio PFVA and a fixed VA angular velocity of 150 RPM, the Futile Power Ratio (FPR) was observed to increase by approximately 40% when the RSF was increased by 5x and the FA velocity was increased from 0–80 RPM. Based on our analytical development we suggest some design and operational guidelines for PFVA based systems.

Commentary by Dr. Valentin Fuster
2008;():993-998. doi:10.1115/DETC2008-49400.

This paper demonstrates that the predicted grasp stability is highly sensitive to only small changes in the character of the contact forces. The contribution of the geometry and stiffness at the contact points to the grasp stability is investigated by a planar grasp with three contact points. Limit cases of zero and infinite contact curvatures, and finite to infinite contact stiffnesses are considered. The stability is predicted based on the approach of Howard and Kumar [1], and verified with multibody dynamic simulations. For rigid objects and fingers with only normal contact stiffness, the grasp stability is dominated by the contact geometry, whereas the local contact stiffness and preload have a minor effect. Furthermore, grasps with pointed finger tips are more likely to be stable than grasps with flat finger tips.

Topics: Stability , Geometry
Commentary by Dr. Valentin Fuster
2008;():999-1008. doi:10.1115/DETC2008-49454.

This is the study of the motion, vibration and contact force control of a flexible master-slave system (FMSS). In this study, the master arm is a one-link arm that consists of a rigid body and the slave arm is a one-link arm that consists of a flexible link. Bilateral control based on passivity and a type-1 optimal servo system based on a linear quadratic regulator (LQR) are applied to the system. Fuzzy control is employed to reinforce the advantages of these control methods. A state observer is employed to construct these controllers, however, the accuracy of state estimation deteriorates while the slave-arm is in contact with objects. Therefore improvements in the accuracy of the state estimation are attempted by applying the disturbance-state observer. The performance of the present method is evaluated by experimental results.

Topics: Force , Motion , Fuzzy control
Commentary by Dr. Valentin Fuster
2008;():1009-1015. doi:10.1115/DETC2008-49538.

Whenever bipedal robots need to make turns, the ability to walk stably and precisely along a circular curve of an arbitrary radius will be quite beneficial. This motivates us to derive new Zero Moment Point (ZMP) constraint equations with respect to a rotating coordinate frame, seek appropriate dynamic gaits based on them, and address the forward and inverse kinematics. After the relevant body and feet trajectories are fully prescribed, joint motions are determined using the inverse kinematics. A set of dynamic walking patterns including the transient are herein proposed and applied to an exemplificative case of turning locomotion. Conclusively, dynamic simulations prove the patterns to be successful even in the presence of distributed-mass and ground contact effects.

Topics: Robots
Commentary by Dr. Valentin Fuster
2008;():1017-1025. doi:10.1115/DETC2008-49719.

In this paper a new strategy for dynamic modeling and parameter identification of complex parallel robots including parallel crank mechanisms is presented. Based on a model reduction strategy motivated by the structure of the parallel robot SpiderMill, kinematics and dynamics are derived in a compact form by applying the modified Denavit-Hartenberg method and the Newton-Euler approach. The obtained parameter-linear dynamical description is reduced to a parameter-minimal form using analytical and numerical reduction methods. Rigid body parameters of the model are identified using optimized trajectories and linear estimators. Through the whole modeling and verification process MSC.ADAMS and Solid Edge models of the demonstrator SpiderMill are used.

Topics: Robots , Modeling
Commentary by Dr. Valentin Fuster
2008;():1027-1036. doi:10.1115/DETC2008-49753.

Fast human walking includes a phase where the stance heel rises from the ground and the stance foot rotates about the stance toe. This phase where the biped becomes under-actuated is not present during the walk of humanoid robots. The objective of this study is to determine if the introduction of this phase for a biped robot is useful to reduce the energy consumed in the walking. For simplicity only a planar biped is considered. In order to study the efficiency of this phase, four cyclic gaits are presented. For these gaits optimal motions with respect to the torque cost are defined for given performances of actuators. It is shown that for fast motions a foot rotation sub-phase is useful to reduce the criteria cost. In the optimization process, under-actuated phase (foot rotation phase), fully-actuated phase (flat foot phase) and over-actuated phase (double support phase) are considered.

Topics: Rotation , Motion
Commentary by Dr. Valentin Fuster
2008;():1037-1046. doi:10.1115/DETC2008-49756.

In this paper a novel concept for active vibration control of storage and retrieval machines is presented. The storage and retrieval machine is modeled based on the Bernoulli-Euler beam theory, yielding an infinite-dimensional model, and the assumed modes method in order to obtain a finite-dimensional model. The resulting model is of low order, a fourth-order model regarding the first and the second eigenfrequency describes the dynamics sufficiently. The model is verified on an experimental storage and retrieval machine. Several active vibration control strategies are studied, including trajectory planning approaches like higher-order trajectory planning, feedforward control approaches like trajectory filtering and input shaping, and feedback control approaches like state-feedback control. The strategies are evaluated by simulation and compared via performance measures.

Commentary by Dr. Valentin Fuster
2008;():1047-1055. doi:10.1115/DETC2008-49789.

Considering slippage between finger tips and an object, adaptive control synthesis of grasping and manipulating an object by a multi-fingered system is addressed in this paper. Slippage can occur due to many reasons such as disturbances, uncertainties in parameters and dynamics. In this paper, using a novel representation of friction and slippage dynamics, a new approach is introduced to analyze the system dynamics. Then an adaptive controller with a simple update rule is proposed to ensure the bounded trajectory tracking and slippage control, and at the same time to compensate for parameter uncertainties including coefficients of friction. The performance of the proposed adaptive controller is shown analytically and studied numerically.

Commentary by Dr. Valentin Fuster
2008;():1057-1063. doi:10.1115/DETC2008-49793.

In this paper, we introduce a novel concept for parametric studies in multibody dynamics. This is based on a technique that makes it possible to perform a natural normalization of the dynamics in terms of inertial parameters. This normalization technique rises out from the underlying physical structure of the system, which is mathematically expressed in the form of eigenvalue problems. It leads to the introduction of the concept of dimensionless inertial parameters. This, in turn, makes the decomposition of the array of parameters possible for studying design and control problems where parameter estimation and sensitivity is of importance.

Commentary by Dr. Valentin Fuster
2008;():1065-1072. doi:10.1115/DETC2008-49820.

Today’s UAVs are being tasked to fly missions in increasingly difficult environments. Buildings, trees and thin wires form challenging terrain for the UAV to negotiate. The current paradigm of UAV research typically moves from computer simulation and individual subsystem testing to full integration in the field. The reactions of control algorithms to realistic sensor data are difficult to capture in simulation and can result in costly crashes. This paper introduces a methodic approach to developing UAV missions. A scaled down urban environment provides a facility to perform testing and evaluation (T&E) on control algorithms before flight. A UAV platform and test site allow the tuned control algorithms to be verified and validated (V&V) in real world flights. The resulting design methodology reduces risk in the development of UAV missions.

Commentary by Dr. Valentin Fuster
2008;():1073-1084. doi:10.1115/DETC2008-49925.

An approach of generating dynamic biped motions of a human-like mechanism is proposed. An alternative and efficient formulation of the Zero-Moment Point for dynamic balance and the approximated ground reaction forces/moments are derived from the resultant reaction loads, which includes the gravity, the externally applied loads, and the inertia. The optimization problem is formulated to address the redundancy of the human task, where the general biped and task-specific constraints are imposed depending on the task requirements. The proposed method is fully predictive and generates physically feasible human-like motions from scratch; it does not require any input reference from motion capture or animation. The resulting generated motions demonstrate how a human-like mechanism reacts effectively to different external load conditions in performing a given task by showing realistic features of cause and effect. In addition, the energy-optimality of the upright standing posture is numerically verified among infinite feasible static biped postures without self contact. The proposed formulation is beneficial to motion planning, control, and physics-based simulation of humanoids and human models.

Topics: Motion , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():1085-1094. doi:10.1115/DETC2008-49944.

A new controller for the end-effector trajectory tracking (EETT) of a class of flexible link manipulators which composed of a chain of rigid links with an end-link flexible (CREF) is introduced. The dynamic model of the CREF is expressed into the standard singularly perturbed form; that is, the dynamic model is decomposed into slow and fast subsystems. The states of the slow subsystem are the joints’ rotations and their time derivatives, while the states of the fast subsystem are flexible variables, which model the lateral deflection of the end-link, and their time derivatives. For the slow subsystem, corrective torque is added to the computed torque control commands of the rigid link counterpart of the CREF to reduce the EETT error. This corrective torque is derived based on the concept of the integral manifold of the singularly perturbed differential equations. It was shown that this corrective term is of order ε2 where ε = 1/(2πf) and f is the smallest non-zero natural frequency of the CREF. To stabilize the fast subsystem, an observer-based controller is designed by the gain-scheduling technique. Due to the application of the observer-based controller there is no need for the measurement of the time derivative of the flexible variables, which their measurements are hardly practical. To facilitate the derivation and implementation of introduced controller here, several properties of the mass matrix of the CREF are introduced and used. The effectiveness and feasibility of the new controller are shown through the simulation and experimental studies.

Commentary by Dr. Valentin Fuster
2008;():1095-1100. doi:10.1115/DETC2008-50009.

This paper presents an experimental study on active vibration control of a moving 3-PRR parallel manipulator with three flexible intermediate links, with bonded lead zirconate titanate (PZT) actuators and sensors. Experimental modal tests are conducted to identify structural vibration mode shapes and natural frequencies used. These modal tests provide guidance to design the filter and determine the location of PZT transducers. A PZT actuator controller is developed based on strain rate feedback (SRF) control. A state-space model is formulated with the control input voltage applied to PZT actuators, and output generated from PZT sensors. Then, the design of an optimal active vibration controller is presented based on SRF for the parallel manipulator with flexible links with multiple bonded PZT transducers. Active vibration control experiments are conducted to demonstrate that the proposed active vibration control strategy is effective. Power spectral density (PSD) plots of vibrations illustrate that the structural vibration of flexible links is reduced effectively when the proposed vibration control strategy is employed.

Commentary by Dr. Valentin Fuster
2008;():1101-1110. doi:10.1115/DETC2008-50072.

Quadruped walking robots need to handle high obstacles like steps that are often not kinematically reachable. We present a dynamic leap that allows a quadruped robot to put its front legs up onto a high rock or ledge, a motion we have found is critical to being able to locomote over rough terrain. The leaping motion was optimized using a simulated planar quadruped model. We present experimental results for the implementation of this optimized motion on a real quadruped robot.

Commentary by Dr. Valentin Fuster
2008;():1111-1119. doi:10.1115/DETC2008-49089.

The evaluation and representation of the orientation workspace of robotic manipulators is a challenging task. This work focuses on the determination of the orientation workspace of the Gough-Stewart platform with given leg length ranges [ρi min , ρi max ]. By use of the Roll–Pitch–Yaw angles (φ, θ, ψ), the orientation workspace at a prescribed position can be defined by 12 workspace surfaces. The obtained orientation workspace is a region in the 3D Cartesian orientation space O φ θ ψ. As all rotations R (x, φ), R (y, θ) and R (z, ψ) take place with respect to the fixed frame, any point of the orientation workspace provides a clear measure for the platform to respectively rotate in order around the (x, y, z) axes of the fixed frame. Also, as the shape of the 3D orientation workspace is very complex, a numerical algorithm is presented to compute its volume.

Commentary by Dr. Valentin Fuster
2008;():1121-1130. doi:10.1115/DETC2008-49112.

Different types of redundancy in parallel kinematics machines (PKM) can be used to improve their kinematic and dynamic properties. The meaning of redundancy of PKM is often differently understood in the literature. In this paper a terminology for redundant PKM is proposed. The basis for this classification is a general mathematical model. With the help of this model PKM are regarded as non-linear control systems. The different types of redundancy are clearly distinguished, and their potential applications are discussed. Redundancy is considered from a geometric point of view. Redundancy is a means to deal with singularities of PKM. The different types of singular configurations are considered in the paper, and the potential of redundancy to cope with such situations is discussed. Again singularities are considered from a geometric point of view.

Commentary by Dr. Valentin Fuster
2008;():1131-1139. doi:10.1115/DETC2008-49117.

This paper presents a procedure to obtain a singularity-free task workspace with a new method to deal with singularities. In order to get an enlarged singularity-free task workspace, we first optimize the volume of the workspace, then we identify singularities in the optimal workspace, and finally we refine the singularity-free task workspace from the optimal workspace. The effects of four physical constraints on the workspace are analyzed, subject to which the optimization is realized. The traditional approach of singularity analysis is based on the Jacobian Matrix which is direct but has limitations, especially when the analytical form of the Jacobian is difficult to obtain. To solve this problem, we define a pseudo-singular space which encloses all singularity loci. By searching the pseudo-singular space numerically, we are able to obtain a singularity-free task workspace. We illustrate this method in the designing process of a 6-RSS parallel mechanism as a haptic device which has been integrated in a simulated dentist training system.

Topics: Design , Haptics
Commentary by Dr. Valentin Fuster
2008;():1141-1150. doi:10.1115/DETC2008-49268.

This paper presents an optimization-based method to solve the smooth trajectory planning problem where the user knows only the start and end points of the end-effector or the via point plus the start and end target points. For the start and end target points, we use an optimization approach to determine the manipulator configurations. Having obtained the desired minimum jerk path in the Cartesian space using the minimum jerk theory and having represented each joint motion by the third-degree B-spline curve with unknown parameters (i.e., control points), an optimization approach, rather than the pseudoinverse technique for inverse kinematics, is used to calculate the control points of each joint spline curve. The objective function includes several parts: (a) dynamic effort; (b) the inconsistency function, which is the joint rate change (first derivative) and predicted overall trend from the initial point to the end point; and (c) the nonsmoothness function of the trajectory, which is the second derivative of the joint trajectory. This method can be used for robotic manipulators with any number of degrees of freedom. Minimum jerk trajectories are desirable for their similarity to human joint movements, for their amenability to limit robot vibrations, and for their control (i.e., enhancement of control performance). Illustrative examples are presented to demonstrate the method.

Commentary by Dr. Valentin Fuster
2008;():1151-1158. doi:10.1115/DETC2008-49436.

A quadratic parallel manipulator refers to a parallel manipulator with a quadratic characteristic polynomial. This paper revisits the forward displacement analysis (FDA) of a quadratic parallel manipulator: 3-RP R planar parallel manipulator with similar triangular platforms. Although it has been revealed numerically elsewhere that for this parallel manipulator, the four solutions to the FDA fall, respectively, into its four singularity-free regions (in its workspace), it is unclear if there exists a one-to-one correspondence between the four formulas, each producing one solution to the FDA, and the four singularity-free regions. This paper will prove that such a one-to-one correspondence exists. Therefore, a unique solution to the FDA can be obtained in a straightforward way for such a parallel manipulator if the singularity-free region in which it works is specified.

Commentary by Dr. Valentin Fuster
2008;():1159-1168. doi:10.1115/DETC2008-49519.

The kinematic analysis of a spherical wrist with parallel architecture is the object of this article. This study is part of a larger French project, which aims to design and to build an eel like robot to imitate the eel swimming. To implement direct and inverse kinematics on the control law of the prototype, we need to evaluate the workspace without any collisions between the different bodies. The tilt and torsion parameters are used to represent the workspace.

Topics: Robots
Commentary by Dr. Valentin Fuster
2008;():1169-1176. doi:10.1115/DETC2008-49535.

We propose a stochastic, decentralized algorithm for the self-assembly of a group of modular robots into a geometric shape. The method is inspired by chemical kinetics simulations, particularly, the Gillespie algorithm [1, 2] that is widely used in biochemistry, and is specifically designed for modules with dynamic constraints, such as the XBot [3]. The most important feature of our algorithm is that all modules are identical and all decision making is local. Individual modules decide how to move based only on information available to them and their neighbors and the geometric, kinematic and dynamic constraints. Each module knows the details of the goal configuration, keeps track of its own location, and communicates position information locally with adjacent modules only when modules in their vicinity have reconfigured. We show that this stochastic method leads to trajectories with convergence comparable to those obtained from a brute-force exploration of the state space. However, the computational power (speed and memory) requirements are independent of the number of modules, while the brute-force approach scales quadratically with the number of modules. We present the schematic of the modules, preliminary experimental results to illustrate the basic moves, and simulation results to demonstrate the efficacy of the algorithm.

Topics: Self-assembly
Commentary by Dr. Valentin Fuster
2008;():1177-1186. doi:10.1115/DETC2008-49550.

In this paper, the mobility and geometrical analysis of a novel mobile robot that utilizes two actuated spoke wheels is presented. Intelligent Mobility Platform with Active Spoke System (IMPASS) is a wheel-leg hybrid robot that can walk in unstructured environments by stretching in or out three independently actuated spokes of each wheel. First, the unique locomotion scheme of IMPASS is introduced and the definitions of the coordinate systems are developed to describe the kinematic configurations. Since this robot is capable of utilizing its metamorphic configurations to implement different types of motion, its topology structures are classified into different groups based on the cases of ground contact points. For each contact point case, the mobility analysis is performed using the conventional Grübler and Kutzbach criterion. However, as for the cases in which the structure is overconstrained, the Modified Grübler and Kutzbach criterion based on reciprocal screws are implemented to obtain the correct number of degrees of freedom. Line geometry is adopted to assist in the process. Additionally, the geometrical constraint equations of the robot are derived. The results in this work lay the foundation of the future research on inverse and forward kinematics, instantaneous kinematics, dynamics analysis and motion planning of this unique locomotion robot.

Commentary by Dr. Valentin Fuster
2008;():1187-1194. doi:10.1115/DETC2008-49551.

In this paper, the inverse and forward kinematics of a novel mobile robot that utilizes two actuated spoke wheels is presented. Intelligent Mobility Platform with Active Spoke System (IMPASS) is a wheel-leg hybrid robot that can walk in unstructured environments by stretching in or out three independently actuated spokes of each wheel. First, the unique locomotion scheme of IMPASS is introduced. Then the configuration of the robot when each of its two spoke wheels has one spoke in contact with the ground is modeled as a two-branch parallel mechanism with spherical and prismatic joints. An equivalent serial manipulator of the 2-SP mechanism with the same degrees of freedom is proposed to solve for the inverse and forward kinematic problems. The relationship between the physical limits of the stroke of the spokes (effective spoke length) and the limits of its equivalent degree of freedom is established. This approach can also be expanded to deal with the forward and inverse kinematics of other configurations which has more than two ground contact points. Several examples are used to illustrate the method. The results obtained will be used in the future research on the motion planning of IMPASS walking in unstructured environment.

Topics: Robots , Manipulators , Wheels
Commentary by Dr. Valentin Fuster
2008;():1195-1206. doi:10.1115/DETC2008-49552.

STriDER (Self-excited Tripedal Dynamic Experimental Robot) is a unique three-legged walking robot that utilizes its innovative tripedal gait to walk. Previous work on the kinematic analysis of STriDER mainly focused on solving the forward and inverse displacement problems. As a continuation, this paper addresses the instantaneous kinematics and singularity analysis. The kinematic configuration of STriDER is modeled as a three-legged in-parallel manipulator when all three feet of the robot are in contact with the ground without slipping. The results obtained from this study can be implemented to the velocity control and the resistance of disturbance forces, thus improving the motion accuracy and stability of the robot. By using screw theory, the screw-based Jacobian matrices of the manipulator can be derived since the forward displacement problems have already been solved. Based on these Jacobian matrices, the transformation equations from the active joint rates to the velocities of the body and vice versa are derived. Then, a complete investigation on the identification and elimination of singularities is presented. Unlike serial manipulators, in-parallel manipulators have two types of singularities, i.e., forward and inverse singularities. The inverse singularities are identified by checking the singular configurations of individual legs and the determinant of the inverse Jacobian matrix. By using Grassmann line geometry, the analytical conditions under which the forward singularities occur are obtained. A study on each case of these singular configurations shows that the redundant-actuation scheme of the active joints can effectively eliminate forward singularities.

Commentary by Dr. Valentin Fuster
2008;():1207-1214. doi:10.1115/DETC2008-49615.

The Multi-Appendage Robotic System (MARS) is a hexapedal robotic platform capable of walking and of performing manipulation tasks. Each of the six limbs of MARS incorporates a three-degree of freedom (DOF), kinematically spherical proximal joint, similar to a shoulder or hip joint, and a 1-DOF distal joint, similar to an elbow or knee joint. The generation of walking gaits for such robots with multiple limbs requires a thorough understanding of the kinematics of the limbs, including their workspace. Since the entire limb workspace cannot be used in a statically stable alternating tripedal gait for such a robot, a subset of the general limb workspace is defined to be used for walking gait generation algorithms. The specific abilities of a walking algorithm dictate the usable workspace for the limbs. Generally speaking, the more general the walking algorithm is, the less constricted the workspace becomes. In this paper we develop the workspaces for the limb of MARS in the knee up configuration, which range from simple 2D geometry to complex 3D volume, and analyze its limitations for use in walking on flat level surfaces. Next we discuss the case when the robot body is not parallel to the ground. The results from this paper can be applied to the development of walking gait generation algorithms.

Topics: Robots , Algorithms
Commentary by Dr. Valentin Fuster
2008;():1215-1220. doi:10.1115/DETC2008-49616.

This paper explores the interdependance of walking algorithm and limb workspace for the Multi-Appendage Robotic System (MARS). While MARS is a hexapedal robot, the tasks of defining the workspace and walking agorthm for all six limbs can be abstracted to a single limb using the constraint of a tripedal statically stable gait. Thus, by understanding the behavior of an individual limb, two walking algorithms have been developed which allow MARS to walk on level terain. Both algorithms are adaptive in that they continously update based on control inputs. The differences between the two algorithms is that they were developed for different limb workspaces. The simpler algorithm developed for a 2D workspace was implemented, resulting in smooth gait generation with near instantaneous response to control input. This accomplishment demonstrates the feasibility of implementing a more sophisticated algorithem which allows for inputs of: x and y velocity, walking height, yaw, pitch and roll. This algorithm uses a 3D workspace developed to afford near maximum step length.

Commentary by Dr. Valentin Fuster
2008;():1221-1230. doi:10.1115/DETC2008-49621.

We propose a six-degrees-of-freedom manipulator with an unconventional topological structure. Because of the complex kinematic structure, it might seem that we cannot actually build such a manipulator. However, we show that we can construct a working model and control its hand configuration. First, we discuss the mobility of the proposed manipulator, and present the conditions imposed on the kinematic structure and the active joint selection. Then, we derive a numerical solution of the inverse kinematics problem by making the best use of the mechanical features, and present the simulation results of trajectory tracking of the hand configuration obtained using the solution. Next, under static equilibrium, we derive the conditions for the singular configurations, where the hand cannot support specific force moments. Finally, we construct an equivalent spherical joint that has a large movable range, and we present a working skeletal model of the proposed manipulator using the joints.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2008;():1231-1239. doi:10.1115/DETC2008-49635.

The study presents a detailed discussion on the classification and solution space atlases for planar serial manipulators. Similar to closed-loop planar linkage with one prismatic joint, a planar manipulator is categorized into three classes with further several subclasses based on link lengths in terms of orientation capability. Furthermore, by introducing the non-dimensional length, an improved physical model of the solution space is proposed to display global performances of the manipulators which facilitates the design of the manipulator with global optimization. Examples are given to illustrate the method.

Topics: Design , Manipulators
Commentary by Dr. Valentin Fuster
2008;():1241-1248. doi:10.1115/DETC2008-49764.

In this paper, a simple and efficient formulation is presented to optimize the kinematic error mapping from the Cartesian space of the end-effector position and orientation to the inputs space. The results are optimized allocation of the joints’ errors for the accepted end-effector positioning errors. The linearized relation (Jacobian) between the end-effector position and the joints’ errors is used. Upper bounds of the error are developed so that the error function is defined in the form of posinomials of joint errors. An optimization problem is set up to find the optimum error allocation at each joint. The problem is then formulated as a zero degree-of-difficulty geometric programming. It is shown that the weight of each term in the total cost function is constant and independent of manipulator’s design. As a result, the solution to the error optimization is readily available. Explicit solutions to these weight factors are presented.

Commentary by Dr. Valentin Fuster
2008;():1249-1258. doi:10.1115/DETC2008-49768.

This paper discusses improvements in gripping efficiency of a simple gripping mechanism. The simple gripping mechanism has flexible fingers, and the multi-fingered gripper holds the gripped object by elastically deforming the fingers. The two-fingered gripper is formed by bending a narrow strip of thin elastic plate into an appropriate shape. It is simple in structure and is able to be easily miniaturized. The deformations of the gripper and gripped object are analyzed to ascertain its gripping efficiency. The two-fingered gripper is considered as a rigid frame whose both ends are fixed, and its deformation is analyzed. Since this structure is statically indeterminate, the virtual work method is used to analyze it. The gripped object is considered as two cantilever beams arranged parallel to each other, and its deformation is analyzed. Effectiveness of this analysis is verified in comparison between calculated results and experimental results. Moreover, by comparing gripping efficiency of the conventional structure of the simple gripping mechanism and the other three different structures with hinges, the effects of these differences between the node conditions on gripping efficiency are clarified.

Topics: Hinges , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():1259-1267. doi:10.1115/DETC2008-49890.

This paper presents a new class of parallel mechanism which is constructed with a 5-limb R SP architecture. To provide insight into the geometry and the position analysis of this mechanism, the paper presents closed-form solutions to the inverse and forward kinematic problems. Then the Kutzbach mobility criterion is used to show that the platform of the 5-R SP mechanism has a single degree of freedom. A mobility analysis based on the reciprocal constraint and motion sets of screws shows that the platform exhibits a screw motion, that is, a translation along and a rotation about the screw axis. The ratio of the translation to the rotation (referred to as the instantaneous pitch of the screw) is shown to be a function of the platform position. The screw axis is perpendicular to the base of the mechanism for all positions of the platform and passes through the centroids of the base and the platform. The attractive features of centralization are the simple design, and the wide range of possibilities for the pitch of the screw motion of the platform. Finally, the paper presents geometrical conditions that result in the pure translation of the platform; i.e., the rotational degree-of-freedom is eliminated.

Commentary by Dr. Valentin Fuster
2008;():1269-1276. doi:10.1115/DETC2008-49916.

In this paper, we address the cooperative towing of payloads by multiple mobile robots in the plane. Robots are attached via cables to a planar object or a pallet carrying a payload. Coordinated motion by the robots allow the payload to be manipulated through a planar, warehouse-like environment. We formulate a quasi-static model for manipulation and derive equations of motion that yield the motion of the payload for a prescribed motion of the robots in the presence of dry friction and tension constraints. We present experimental and simulation results that demonstrate the basic concepts.

Topics: Robots
Commentary by Dr. Valentin Fuster
2008;():1277-1284. doi:10.1115/DETC2008-49918.

Model based geometric calibration is well known to be an efficient way to enhance absolute accuracy of robotic systems. Generally its application requires redundant measurements, which are achieved by external metrology equipment in most traditional calibration techniques. However, these methods are usually time-consuming, expensive and inconvenient. Thus, so-called self-calibration methods have achieved attention from researchers, which either use internal sensors or rely on mechanical constraints instead. In this paper a new self-calibration technique is presented for parallel robots which is motivated by the idea of constrained calibration. The new approach utilizes a special machine component called the adaptronic swivel joint in order to achieve the required redundant information. Compared to similar approaches it offers several advantages. The new calibration scheme is described and verified in simulation studies using a R RRRR -structure as an example.

Topics: Robots , Calibration
Commentary by Dr. Valentin Fuster
2008;():1285-1293. doi:10.1115/DETC2008-49954.

In this paper, we study the problem of rational motion interpolation under kinematic constraints of spatial SS open chains. The objective is to synthesize a smooth rational motion that interpolates a given set of end effector positions and satisfies the kinematic constraints imposed by spatial SS open chains. The kinematic constraints under consideration define a constraint manifold representing all the positions available to the end effector. By choosing dual quaternion representation for the displacement of the end effector, the problem is reduced to designing a smooth curve in the space of dual quaternions that is constrained to lie inside the constraint manifold of the spatial SS open chain. An iterative numerical algorithm is presented that solves this problem effectively. The results presented in this paper are extension of our previous work on the synthesis of piecewise rational planar and spherical motions for open and closed chains under kinematic constraints.

Commentary by Dr. Valentin Fuster
2008;():1295-1303. doi:10.1115/DETC2008-50012.

In this paper a unique landmark identification method is proposed for identifying large distinguishable landmarks for 3D Visual Simultaneous Localization and Mapping (SLAM) in unknown cluttered urban search and rescue (USAR) environments. The novelty of the method is the utilization of both 3D (i.e., depth images) and 2D images. By utilizing a Scale Invariant Feature Transform (SIFT) -based approach and incorporating 3D depth imagery, we can achieve more reliable and robust recognition and matching of landmarks from multiple images for 3D mapping of the environment. Preliminary experiments utilizing the proposed methodology verify: (i) its ability to identify clusters of SIFT keypoints in both 3D and 2D images for representation of potential landmarks in the scene, and (ii) the use of the identified landmarks in constructing a 3D map of unknown cluttered USAR environments.

Topics: Robots , Cities
Commentary by Dr. Valentin Fuster
2008;():1305-1312. doi:10.1115/DETC2008-50056.

This paper introduces a novel distributed algorithm for deploying multi-robot systems, consisting of mobile robots with onboard sensing and wireless communication of limited ranges, to approach the desired sensory coverage while maintaining communication connection over targeted 2D environments. A virtual potential energy is defined for each mobile robot according to the difference between the actual and desired configurations in the neighborhood of the robot, which generates the actuating force to move the robot towards the desired local coverage. The Rayleigh’s dissipation function is adopted to provide the necessary damping mechanism which maintains the stability of the deployment motion for each robot. The equation of deployment motion for each mobile robot is then derived from the Hamilton’s principle using the method of the variational calculus, which defines the movement of the robot to approach the desired local configuration. The formulation of the variational calculus also provides a convenience way to incorporate the nonholonomic constraint arising in wheeled robots. Since the equation of deployment motion for each robot depends on only the robot’s own kinematic state and its detectable positional relationship with nearby objects, the proposed algorithm decentralizes the multi-robot deployment problem into the motion control of individual robots. Simulation results show the feasibility of the proposed approach in guiding the deployment of multi-robot systems.

Commentary by Dr. Valentin Fuster
2008;():1313-1324. doi:10.1115/DETC2008-50059.

In recent years there has been several contributions that approach the velocity and acceleration analyses of the so-called “lower mobility platforms” by employing kinematic influence co-efficients. The present contribution shows that, employing simple modifications, a method presented eight years ago for the velocity and acceleration analyses of Gough-Stewart platforms can be applied also to lower mobility platforms. Since the method is based on screw theory, it is simpler than that based on kinematic influence coefficients and it does not require the use of cumbersome three-dimensional arrays of real numbers.

Topics: Screws
Commentary by Dr. Valentin Fuster
2008;():1325-1336. doi:10.1115/DETC2008-50109.

This paper introduces a reconfigurable closed-loop spatial mechanism that can be applied to repetitive motion tasks. The concept is to incorporate five pairs of non-circular gears into a six degree-of–freedom closed-loop spatial chain. The gear pairs are designed based on given mechanism parameters and a user defined motion specification of a coupler link of the mechanism. It is shown in the paper that planar gear pairs can be used if the spatial closed-loop chain is comprised of six pairs of parallel joint axes, i.e. the first joint axis is parallel to the second, the third is parallel to the fourth, ..., and the eleventh is parallel to the twelfth. This paper presents the synthesis of the gear pairs that satisfy a specified three-dimensional position and orientation need. Numerical approximations were used in the synthesis the non-circular gear pairs by introducing an auxiliary monotonic parameter associated to each end-effector position to parameterize the motion needs. The findings are supported by a computer animation. No previous known literature incorporates planar non-circular gears to fulfill spatial motion generation needs.

Topics: Gears , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():1337-1345. doi:10.1115/DETC2008-49043.

An algorithm of generalized kinematic chains and its computer program are developed in this paper. By this program, users can give the number of links and joints and then the link assortments and contracted link assortments can be calculated. The synthesis of multiple link adjacency matrix (MLAM) and the cut-link diagnosis are proposed to produce effectively the generalized kinematic chains. The algorithm can automatically determine the feature of a chain, which is connected, closed, non-isomorphism, without any cut-link (or cut-joint), and with simple joint only. Then, it can be called a generalized kinematic chain. Finally, various given number of links and joints, the nice looking atlas of generalized kinematic chains can also be generated. The developed computer program could help designers to be able to study and compare different devices in a very basic way.

Topics: Chain
Commentary by Dr. Valentin Fuster
2008;():1347-1356. doi:10.1115/DETC2008-49074.

This paper presents the explicit mapping relations between topological structure of mechanism and position and orientation characteristic (abbreviated as POC hereafter) of its motion output link. It deals with: (1) The symbolic representation and the invariant of topological structure of mechanism; (2) The matrix representation of POC of mechanism motion output; (3) The POC equation of serial mechanism and its symbolic operation rules. The symbolic operation involves simple mathematic tools and fewer operation rules, and has clear geometrical meaning. So it is easy to use. The POC equation can be used for structural analysis and synthesis of serial and parallel mechanisms. The method proposed in this paper is totally different from the methods based on screw theory and based on displacement subgroup/sub-manifold.

Commentary by Dr. Valentin Fuster