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29th Mechanisms and Robotics Conference

2005;():3-13. doi:10.1115/DETC2005-84073.

This paper presents three planar mechanisms capable of performing the functions of a bearing and a spring: the compliant rolling-contact element (CORE), the CORE bearing, and the elliptical CORE bearing. The designs use compliant rolling-contact joints to achieve low friction rotation and to bear high in-plane lateral loads. A model for predicting the behavior of the designs is presented, and manufacturing considerations are discussed for the macro, meso, and micro scales. A case study is presented, and the designs are shown to be capable of meeting the demanding design constraints of the study.

Commentary by Dr. Valentin Fuster
2005;():15-24. doi:10.1115/DETC2005-84371.

In this paper, a new topology that is a symmetric five bar profile for displacement amplification is proposed, and a compliant mechanical amplifier (CMA) based on the new topology is designed to amplify the stroke of a piezoelectric actuator. The new CMA can convert the motion generated by a PZT actuator with a large amplification ratio (24.4) in a very compact size, and it has a high natural frequency (573 Hz) and no lateral displacement. First, three existing topologies of CMA are analyzed and evaluated, which results in the new topology of CMA. After that, the new CMA is designed with different flexure hinges. The finite element analysis for the CMA shows that the double-beam symmetric five bar structure using the corner-filleted hinges can provide the best performance in terms of the displacement amplification and natural frequencies. The designed CMA is clearly better than the CMA based on the topology of a double symmetric four bar profile. Finally, the design is fine-tuned by examining critical parameters for the proposed CMA in light of a large displacement amplification ratio.

Topics: Design
Commentary by Dr. Valentin Fuster
2005;():25-34. doi:10.1115/DETC2005-84492.

A Robotic ‘Jack Spring’™ is a new type of mechanical actuator, which is based upon the concept of structure control. A Jack Spring™ mechanism is used to create an adjustable Robotic Tendon, which is a spring based linear actuator in which the properties of a spring are crucial to its successful use in gait assistance. Like its human analog, the adjustable Robotic Tendon uses its inherent elastic nature to reduce both peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250W to just 81 W. In addition, ideal energy requirements are reduced from nearly 36 Joules to just 25 Joules per step. Using this approach, an initial prototype is expected to provide 100% of the power and energy neccessary for ankle gait in a compact 0.84kg package. This weight is 8 times less than that predicted for an equivalent direct drive approach.

Commentary by Dr. Valentin Fuster
2005;():35-41. doi:10.1115/DETC2005-84605.

A wide curve is a curve with width or cross-section. This paper presents a geometric optimization method of compliant mechanisms based on the free form wide curve theory. With the proposed method, geometric optimization can be performed to further improve the performance of a compliant mechanism after its topology is selected. Every connection in the topology is represented as a parametric wide curve in which variable shape and size are fully described and conveniently controlled by the limited number of parameters. The geometric optimization is formulated on the control parameters of the wide curves corresponding to all connections in the topology. Problem-dependent objectives are optimized and practical constraints are imposed during the optimization process. The optimization problem is solved by the constrained nonlinear programming algorithm in Matlab Optimization Toolbox. An example is presented to verify the effectiveness of the proposed optimization procedure.

Commentary by Dr. Valentin Fuster
2005;():43-50. doi:10.1115/DETC2005-84608.

In graph theory, spanning trees connect all the vertices together using minimum number of edges. A topological optimization method of compliant mechanisms is presented based on spanning tree theory. A valid topology is regarded as a network connecting input, output, support and intermediate nodes, which contains at least one spanning tree among the introduced nodes. Invalid disconnected topologies can be weeded out if no spanning tree is included. No further deformation analysis and performance evaluation is needed for invalid disconnected topologies. Problem-dependent objectives are optimized for topological optimization of compliant mechanisms. Constraints about maximum input displacement and input force, maximum stress and overlapping connections are directly imposed during the optimization process. The discrete optimization problem is solved by genetic algorithm with penalty function handling constraints. An example is presented to verify the effectiveness of the proposed optimization procedure.

Commentary by Dr. Valentin Fuster
2005;():51-60. doi:10.1115/DETC2005-84748.

We present a level set based method for optimal design of compliant mechanisms. The focus of the investigation is on how to preserve the structural connectivity in the optimization process of the level set method. By introducing an extra constraint using the connected components labeling technique, the structural connectivity of the design is well maintained during the topology optimization process.

Commentary by Dr. Valentin Fuster
2005;():61-69. doi:10.1115/DETC2005-85085.

This paper presents a synthesis procedure for a compliant four-bar linkage with three specified equilibrium configurations. The finite position synthesis equations are combined with equilibrium constraints at the flexure pivots to form design equations. These equations are simplified by modeling the joint angle variables in the equilibrium equations using sine and cosine functions. Solutions to these design equations were computed using a polynomial homotopy solver. In order to provide a design specification, we first compute the six equilibrium configurations of a known compliant four-bar mechanism. We use these results as design requirements to synthesize a compliant four-bar. The solver obtained eight real solutions which we refined using a Newton-Raphson technique. A numerical example is provided to verify the design methodology.

Commentary by Dr. Valentin Fuster
2005;():71-78. doi:10.1115/DETC2005-85241.

This paper presents control system formulations of a planar parallel 3-RRR parallel compliant micromanipulator. The design methodology is illustrated with one of such designs constructed at Beijing University of Aeronautics and Astronautics, China. Compliant joints and motion-amplifying mechanism allow rapid and accurate response as well as larger workspace. The three PZT actuators attached on the linkages produce the bending moments. The sensor is a CCD camera feeding back the tool point position. The plant is the equations of motion which can be formulated using the Lagrangian method and dynamics software. The system dynamic model was developed with ADAMS which can export the nonlinear and linearized control plant to Matlab Simulink. Overall dynamic behavior of the manipulator will be illustrated through simulations with Matlab Simulink Toolbox. After comparison of two different control plans, the controller obtained from LQR method was chosen to achieve the control objectives. Closed-loop performance in response to a step reference was plotted. Bode plots of the sensitivity and complementary sensitivity showed their relation to the step response. Gain and phase margins was computed.

Commentary by Dr. Valentin Fuster
2005;():79-87. doi:10.1115/DETC2005-85379.

This paper will propose the use of control maps along with discretized elements or meshes in the design parameter set for optimizing compliant mechanisms. The use of control maps will be demonstrated to encode the motion of groups of nodes or control points defining the mesh with simple mapping rules. The technique will serve as an alternative to increased mesh size or node wandering techniques that have been proposed to increase the number of alternative design shapes that may be considered. As an alternative approach, the proposed control map parameterization has the significant benefit that it minimizes the number of design parameters necessary (parameters increase linearly with the mesh size) in describing a given design making it computationally efficient. A limited number of tiles can produce a map that has a significant effect on the final shape. If the tiles are chosen appropriately, the problems such as material overlap and non-convex mesh elements are avoided automatically. This paper will describe the implementation of these control maps and provide several examples showing their implementation in the compliant mechanism topology synthesis process.

Commentary by Dr. Valentin Fuster
2005;():89-99. doi:10.1115/DETC2005-85413.

This paper presents parallel kinematic XY mechanism designs that are based on a systematic constraint pattern. The constraint pattern, realized by means of double parallelogram flexure modules, is such that it allows large ranges of motion without over-constraining the mechanism or generating significant error motions. Nonlinear force-displacement characteristics of the double parallelogram flexure are used in analytically predicting the performance measures of the proposed XY mechanisms. Comparisons between closed-form linear and nonlinear analyses are presented to highlight the inadequacy of the former. Fundamental design tradeoffs in flexure mechanism performance are discussed qualitatively and quantitatively. It is shown that geometric symmetry in the constraint arrangement relaxes some of the design tradeoffs, resulting in improved performance. The nonlinear analytical predictions are validated by means of Finite Element Analysis and experimental measurements.

Commentary by Dr. Valentin Fuster
2005;():101-110. doi:10.1115/DETC2005-85440.

The simple beam acts as a constraint element when used in flexure mechanisms. Non-linearities arising from the force equilibrium conditions in a beam significantly affect its properties as a constraint element. Consequently, beam-based flexure mechanisms typically suffer from performance tradeoffs in terms of motion range, accuracy and stiffness. This paper presents simple yet accurate approximations that capture this non-linearity and allow for the closed-form analysis of flexure mechanisms of moderate complexity. These general analytical tools enable a designer to parametrically predict key performance parameters of a conceived mechanism such as mobility, over-constraint, stiffness variation, and error motions, without resorting to tedious numerical or computational methods. To illustrate their effectiveness, these approximations are used in deriving the closed-form force-displacement characteristics of several important beam-based flexure modules, and the results are validated using Finite Element Analysis. Variations in the beam shape and flexure module geometry are also considered analytically.

Commentary by Dr. Valentin Fuster
2005;():111-119. doi:10.1115/DETC2005-85448.

Lightly damped poles and zeros in the response of flexure-based servomechanisms often limit their dynamic performance. In this paper, we measure the frequency response of a single-and a double-parallelogram flexure stage coupled to low-density, low-wave-speed foams in various configurations, and find that addition of the foam yields relatively high damping of in-plane, out-of-plane, and higher-order resonances. At frequencies high enough for waves to propagate into the foam, strong interactions between the foam and flexure structure occur, giving rise to a great deal of damping. This is a promising method for improvement of the dynamic performance of positioning and constraint systems that employ flexures.

Commentary by Dr. Valentin Fuster
2005;():121-126. doi:10.1115/DETC2005-85576.

In this paper, a new all-polymer actuation approach for binary mechatronic systems is demonstrated. The technology consists of using Dielectric Elastomer actuators in a binary fashion by coupling them with a properly designed compliant structure. Here, a bistable actuator based around the “flip-flop” concept is implemented in which two antagonistic actuators switch a compliant truss between two stable positions. This prototype shows promising performance with output forces ranging from 1 to 3.5 N and displacements of 30% of the actuator dimension.

Topics: Elastomers , Actuators
Commentary by Dr. Valentin Fuster
2005;():127-131. doi:10.1115/DETC2005-84204.

Hybrid actuator is a new type of planar parallel robot, and requires precise control of the position of the mechanism. In order to achieve the desired accuracies, nonlinear factors as friction must be accurately compensated in the real-time servo control algorithm. According to the characteristics of the hybrid actuator, a hybrid intelligent control algorithm based on PID control and cerebellar model articulation control (CMAC) techniques was presented and used to perform control of hybrid actuator for the first time. Simulation results show that this method can improve the control effect remarkably compared with the traditional control strategy.

Commentary by Dr. Valentin Fuster
2005;():133-140. doi:10.1115/DETC2005-84207.

Hybrid mechanism is a kind of controllable mechanism. It may be composed of one or multiple coupled kinematic loops forming a mechanism network, and is highly nonlinear devices. The bond graph approach provides a compact and versatile representation for kinematics and dynamics of hybrid mechanism, and is more suitable for automatic derivation and computation on a computer. Here, an analysis procedure that can be used to produce the dynamics equations of hybrid mechanism is presented. According to bond graph model, dynamics equations can be derived. The unified formula of dynamics equations derived here is a regularized one. The driving powers of hybrid mechanism can be obtained in terms of physical parameters of mechanism and kinematic states, and no need to analyze acceleration of mechanism. Finally, a numerical example is presented illustrating its validity. The results show that efficiency and reliability of dynamics analysis for hybrid mechanism are enhanced obviously.

Commentary by Dr. Valentin Fuster
2005;():141-150. doi:10.1115/DETC2005-84562.

A systematic methodology combining optimization, three dimensional analytical rigid body dynamics and a novel method, namely, Pseudo-Interference Stiffness Estimation method (PISE) [1]- [2], is proposed to dramatically reduce gear design time and improve the spur gear system dynamic performance. The main aim of this methodology is to search for the pro les of tooth crowning and shaving that eventually lead to the optimum dynamic tooth load in the gear mesh. An example of the detailed design study is numerically investigated. The results show that the dynamic tooth load can be reduced to up to 50 percent of its original value. However, this reduction is only valid at the operating ranges of the design load and design speed. It is also found that the effect of pro le modi cation on the dynamic response of the gear system was mostly observed to be a reduction in the peak dynamic tooth load at the resonance speed. Later, the investigation of gear tooth durability was conducted to validate an improvement of gear life. The rating factors given in AGMA publication, Hertzian contact stress, bending fatigue stress, ash temperature and PV index are employed in gear durability determination. The results show that, with the reduction of 50 percent in dynamic tooth load, the reductions in PV index, bending fatigue, Hertzian contact stress, and ash temperature can be achieved up to 64, 58, 28 and 39 percent, respectively.

Commentary by Dr. Valentin Fuster
2005;():151-158. doi:10.1115/DETC2005-84704.

Magnetic fluids are added to a torque motor of hydraulic servo-valve, to improve the performance of the torque motor and the servo-valve. The construction and principle of the torque motor are introduced. Using finite element analysis method, the magnetic field distribution of the torque motor is analyzed. The static and dynamic performance of the torque motor with or without magnetic fluids is studied and compared. The simulation results are shown.

Commentary by Dr. Valentin Fuster
2005;():159-166. doi:10.1115/DETC2005-84706.

Smart (active) material based actuators, hereinafter called micro-actuators, have been shown to be well suited for the elimination of high harmonics in joint and/or end-effector motions of the robot manipulators and reduce actuator dynamic response requirements. Low harmonic joint and end-effector motions as well as low actuator dynamic response requirements are essential for a robot manipulator to be capable of operating at high speeds with greater precision and with less vibration and control problems. Micro-actuators may be positioned at the end-effector to obtain a micro and macro robot manipulation. Alternatively, micro-actuators may be integrated into the links to vary a link parameter such as the link length. In this paper, the kinematics and dynamics consequences of each alternative are studies for manipulators with serial and closed-loop chains. It is shown that for the robot manipulator constructed with closed-loop chains, the high harmonic components of all joint motions can be eliminated only when micro-actuators are integrated into the structure of the closed-loop chain links. The latter configuration is also shown to have dynamics advantage over micro and macro configuration. thereby reducing the potential vibration and control problems at higher operating speeds. The conclusions also apply to closed-loop chains of parallel and cooperating robot manipulators.

Commentary by Dr. Valentin Fuster
2005;():167-173. doi:10.1115/DETC2005-84848.

This paper introduces a methodology for the integration of mechanical and control system design of planar biped robots. The control approach is a procedure for the systematic design, analysis, and performance enhancement of controllers that induce provably stable dynamic walking in planar bipeds. Iterative application of this procedure with variations in the mechanical parameters of the biped model enables a designer to drive design changes based upon analytical metrics of stability and efficiency. The outcomes are a dynamically-informed mechanical design and controllers that maximally exploit the unforced dynamics of that design. This methodology has been applied to the design and construction of the prototype biped BIRT (BIped Robot with Three legs). BIRT is a planar biped whose two outside legs are slaved by means of control to act together. The paper provides a detailed description of BIRT’s mechanical system.

Topics: Robots , Design
Commentary by Dr. Valentin Fuster
2005;():175-181. doi:10.1115/DETC2005-85252.

Inverse dynamic analysis of a three degree of freedom parallel mechanism driven by three electrical motors is carried out to study the effect of motion speed on the system dynamics and control input requirements. Availability of inverse dynamics models offer many advantages, but controllers based on real-time inverse dynamic simulations are not practical for many applications due to computational limitations. An off-line linearisation of system and error dynamics based on the inverse dynamic analysis is developed. It is shown that accurate linear models can be obtained even at high motion speeds eliminating the need to use computationally intensive inverse dynamics models. A point-to-point motion path for the mechanism platform is formulated by using a third order exponential function. It is shown that the linearised model parameters vary significantly at high motion speeds, hence it is necessary to use adaptive controllers for high performance.

Commentary by Dr. Valentin Fuster
2005;():183-194. doi:10.1115/DETC2005-84002.

This paper shows that there is a correlation between basic concepts underlying the kinematics of mechanisms and the statics of trusses. The implication of this correlation, referred to here as duality, is that the science of kinematics can be utilized in a systematic manner to yield insight into the statics of mechanical systems. The paper begins by proving the existence of a unique line (referred to as the equimomental line) where the moments, at each point on this line, caused by two arbitrary co-planar forces are equal. The dual concept in kinematics is the instantaneous center of zero velocity and two theorems are presented based on the duality between equimomental lines and instantaneous centers. The first theorem states that the three equimomental lines defined by three co-planar forces must intersect at a unique point. The second theorem states that the equimomental line for two co-planar forces acting in a trusss with two degrees of indeterminacy must pass through a unique point. The paper presents several practical examples to demonstrate how the duality between kinematics and statics provides a better understanding of planar linkages and trusses. The new concepts are used to identify the singular configurations of linkages and the configurations of determinate trusses where they are not rigid. Finally, the paper takes advantage of some important relationships between linkages and trusses to provide a general perspective of the duality between the kinematics of mechanisms and the statics of trusses.

Topics: Kinematics , Statics
Commentary by Dr. Valentin Fuster
2005;():195-200. doi:10.1115/DETC2005-84258.

In this paper, the kinematic synthesis of a chopstick-type gripping mechanism containing rolling pairs is studied. The design equations of the mechanism used as a rigid-body, guidance are established. The number of free choices in design variables in the kinematic synthesis is also discussed. The optimization-based numerical technique is applied to solve the design equations. The synthesized solutions are illustrated to discuss the kinematic states of the mechanism. It is also shown that the optimization-based method is effective in finding the admissible synthesis solution of the mechanism.

Topics: Motion , Mechanisms
Commentary by Dr. Valentin Fuster
2005;():201-210. doi:10.1115/DETC2005-84282.

In this paper, based on perimeter topological graphs of kinematic chains, many novel topological concepts including the synthetic degree-sequence, the characteristic adjacency matrix and the characteristic representation code of kinematic chain are proposed. Both the characteristic adjacency matrix and the characteristic representation code are unique for any kinematic chain and easy to be set up. Therefore a quite effective isomorphism identification method is presented depending on the characteristic adjacency matrix. It high effectiveness is proved by many examples. With object-oriented programming language, a program which can sketch topological graphs of kinematic chains has been developed based on the characteristic representation code. Finally, an application software system establishing the atlas database of topological graphs is introduced. And some functions about the atlas database are also presented in this paper.

Topics: Chain
Commentary by Dr. Valentin Fuster
2005;():211-218. doi:10.1115/DETC2005-84301.

A method for the synthesis of four-bar mechanisms to generate closed paths through shape optimization is herein introduced. The objective function is not based on Fourier descriptors, rather on the cyclic angular deviation (CAD) vector associated with a set of desired points on the curve. A simple method is introduced to account for the starting point shift between the desired CAD and the generated one. Following shape optimization, a simple mathematical approach is devised to properly scale, rotate, and translate the mechanism to the desired configuration. A case study is presented to demonstrate the effectiveness and robustness of the proposed method.

Commentary by Dr. Valentin Fuster
2005;():219-226. doi:10.1115/DETC2005-84339.

The aim of this article is to provide a simple method to solve the mixed exact-approximate dimensional synthesis problem of planar mechanism. The method results in a mechanism that can traverse a closed path with the choice of any number of exact points while the rest are approximate points. The algorithm is based on optimum synthesis rather than on precision position methods. Ant-gradient search is applied on an objective function based on log10 of the error between the desired positions and those generated by the optimum solution. The log10 function discriminates on the side of generating miniscule errors (on the order of 10−14 ) at the exact points while allowing for higher errors at the approximate positions. The algorithm is tested by way of five examples. One of these examples was used to test exact/approximate synthesis method based on precision point synthesis approach.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2005;():227-236. doi:10.1115/DETC2005-84441.

This paper deals with the design of double-wishbone and multilink independent suspension systems. To achieve this objective, the proposed method uses a dimensional synthesis technique based on local optimization. An objective function is defined using exact-gradient determination to search for the optimal solution. The multibody system is described by a set of constraint equations which are used to perform the necessary differentiation. Due to the kinematic characteristics of suspension systems, the technique developed here provides a valuable tool for obtaining the optimal solution fulfilling typical requirements imposed in this kind of problems. In this way, double-wishbone and multilink mechanisms are synthesized solving path generation and rigid-body guidance problems at the same time. Finally, two examples are shown to illustrate the application of the method to this kind of systems.

Commentary by Dr. Valentin Fuster
2005;():237-246. doi:10.1115/DETC2005-84595.

A wearable robot is a controlled and actuated device that is in direct contact with its user. As such, the implied requirements of this device are that it must be portable, lightweight and most importantly safe. To achieve these goals an actuator with a good ‘power to weight’ ratio, good mechanical efficiency, good ‘strength to weight’ ratio and that is safe is desired. The design of the standard lead screw does not normally perform well in any of these categories. The typical lead screw has low pitch angles and large radii, thereby yielding low mechanical efficiencies and high weight. However, using the design procedure outlined in this text both efficiency and weight are improved, thus yielding a lead screw system with performances that rival human muscle. The result of an example problem reveals a feasible lead screw design that has a ‘power to weight’ ratio of 277W/kg, approaching that of the DC motor driving it, at 312W/kg, as well as a mechanical efficiency of 0.74, and a maximum ‘strength to weight’ ratio of 11.3kN/kg(1154kgf/kg).

Commentary by Dr. Valentin Fuster
2005;():247-254. doi:10.1115/DETC2005-84609.

The kinematic chain isomorphism problem is one of the most challenging problems facing mechanism researchers. Methods using the spectral properties, characteristic polynomial and eigenvectors, of the graph related matrices were developed in literature for isomorphism detection. Detection of isomorphism using only the spectral properties corresponds to a polynomial time isomorphism detection algorithm. However, most of the methods used are either computationally inefficient or unreliable (i.e., failing to identify non-isomorphic chains). This work establishes the reliability of using the characteristic polynomial of the Laplace matrix for isomorphism detection of a kinematic chain. The Laplace matrix of a graph is used extensively in the field of algebraic graph theory for characterizing a graph using its spectral properties. The reliability in isomorphism detection of the characteristic polynomial of the Laplace matrix was comparable with that of the adjacency matrix. However, using the characteristic polynomials of both the matrices is superior to using either method alone. In search for a single matrix whose characteristic polynomial unfailingly detects isomorphism, novel matrices called the extended adjacency matrices are developed. The reliability of the characteristic polynomials of these matrices is established. One of the proposed extended adjacency matrices is shown to be the best graph matrix for isomorphism detection using the characteristic polynomial approach.

Topics: Chain , Polynomials
Commentary by Dr. Valentin Fuster
2005;():255-263. doi:10.1115/DETC2005-84626.

Mobility analysis is one of the fundamental problems of structural studies of kinematic chains. Degeneracy testing, an important step in structural synthesis, can be considered as a part of the mobility analysis due to the similarity of the two problems. One common error in the algorithms for these two problems is the assumption that the graph of a planar kinematic chain is a planar graph. This work shows that almost all the mobility analysis algorithms, except that of Lee and Yoon, have this error. This work also critically reviews the two most efficient algorithms on degeneracy testing, those by Hwang and Hwang, and Lee and Yoon. It is shown that due to the errors in the Hwang and Hwang’s algorithm, it failed to identify some of the degenerate chains. Furthermore, the accuracy of the Lee and Yoon’s algorithms for mobility analysis and degeneracy testing is proved by providing the mathematical justification of the individual steps of the algorithms.

Topics: Algorithms , Chain , Testing
Commentary by Dr. Valentin Fuster
2005;():265-273. doi:10.1115/DETC2005-84649.

The computation of the equilibrium configurations of tensegrity mechanisms is often a very tedious task even for relatively simple architectures. However, it has been observed that the complexity of this problem is significantly reduced when gravitational loads are compensated with the use of static balancing techniques. In this work, the general static balancing conditions are adapted for the case of tensegrity mechanisms. Afterwards, the modified conditions are applied to two new spatial three-degree-of-freedom tensegrity mechanisms.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2005;():275-283. doi:10.1115/DETC2005-84658.

This paper presents a new method, termed as patterned bootstrap (PB), which is suitable for precision position synthesis of planar linkages. The method solves a determined system of equations using a new bootstrapping strategy. In principle, a randomly generated starting point is advanced to a final solution through solving a number of intermediate systems. The structure and the associated parameters of each intermediate system is defined as a pattern. In practice, a PB procedure generally consists of two levels: an upper level which controls the transition of patterns, and a lower level which solves intermediate systems using globally convergent root-finding algorithms. Besides introducing the new method, tunnelling functions have been added to several systems of polynomials derived by formal researchers in order to exclude degenerated solutions. Our numerical experiments demonstrate that many precision position synthesis problems can be solved efficiently without resorting to time-consuming polynomial homotopy continuation methods or interval methods. Finding over 95 percentages of the complete solutions of the 11 precision position function generation problem of a Stephenson-III linkage has been achieved for the first time.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2005;():285-290. doi:10.1115/DETC2005-84713.

It is known that the punch motion has a significant effect on sheet metal stamping operations. For example, for deep drawing operations long dwelling is desirable. For blanking operations, on the other hand, the two-step motion can reduce the noise [1]. However, the controlled punch motion cannot be realized using conventional mechanical presses, which has the advantage of being energy efficient, fast and easier to make / maintain. Servo mechanical presses solved some of the problems, but are not energy efficient (because they cannot use flywheels as the conventional mechanical presses). Following our previous research [2–4], this paper presents a new type of controllable mechanical press. It is a 2-DOF planar mechanism driven by a large constant speed motor (which takes 75% of the load) and a small servomotor (which takes 25% of the load). Though, unlike the first design, the new design uses the servomotor to drive a ball screw instead of a crank, which makes building the press simpler and controlling the press easier. The paper describes various issues in designing and controlling the press including (a) Kinematics and inverse kinematics; (b) Static force distribution analysis and parameter design; and (c) Punch motion programming and control. A 250 KN prototype has been built and the experimental testing results confirm that the press is working properly. Comparing to the existing technology, the new press is controllable and energy efficient. It is expected that it will have a significant value to the metal forming industry.

Commentary by Dr. Valentin Fuster
2005;():291-295. doi:10.1115/DETC2005-84750.

When it comes to the researches of valve-less pumps with nozzle/diffuser elements of different cone angles, they were usually achieved by manufacturing plural pumps, and the number of the pumps is determined by the accuracy of experiments required. However, the traditional way in which finite pumps of different cone angles were used to simulate the changeable cone angle and it would probably conceal some properties of the nozzle/diffuser elements. Meanwhile, many parameters of the nozzle/diffuser elements other than cone angle can not be kept in consistency. In the research, a new kind of 2-Dimensional nozzle/diffuser elements whose cone angles are changeable is created, and the cone angle of the new nozzle/diffuser elements can be adjusted through adjusting the position of the changeable flow passage. Furthermore, when liquid flow through nozzle/diffuser element, the nozzle/diffuser elements could make consecutive loss coefficient, which makes the changes of flux and flow direction. And the kind of pump with the new structure was developed in the research; the effectiveness and usefulness are also demonstrated and proved in the experiments.

Topics: Diffusers , Nozzles , Pumps , Valves
Commentary by Dr. Valentin Fuster
2005;():297-305. doi:10.1115/DETC2005-84762.

Dimension synthesis for higher-order kinematic parameters is a method to realize higher motion accuracy and to control the motion characteristics of planar linkage mechanisms. In this paper, taking a two-output impulse generator as an example, the construction of dimension synthesis equations for higher-order kinematic parameters and their solutions were carried out in four steps. In addition, to realize the self-adjustability of planar linkage mechanisms, a novel non-overconstraint basic bar group method was established to eliminate the overconstraint present in the mechanisms, which forms obstacles to planar motions. A prototype of a two-output impulse generator was produced based on the synthesis and self-adjustability design. Experimental results showed that fluctuation range of the output velocity of the two-output impulse generator was reduced by 10.3 % in comparison with a conventional impulse generator and a more steady motion was achieved, indicating the reliable motion accuracy and self-adjustability.

Commentary by Dr. Valentin Fuster
2005;():307-314. doi:10.1115/DETC2005-84871.

The Burmester problem aims at finding the geometric parameters of a planar four-bar linkage for a prescribed set of finitely separated poses. The synthesis related to the Burmester problem deals with both revolute-revolute (RR) and prismatic-revolute (PR) dyads. A PR dyad is a special case of RR dyad, i.e., a dyad with one end-point at infinity. The special nature of PR dyads warrants a special treatment, outside of the general methods of four-bar linkage synthesis, which target mainly RR dyads. In this paper, we study the synthesis of planar four-bar linkages addressing the problem of the determination of PR dyads. The conditions for the presence of PR dyads with the prescribed poses are derived. A synthesis method is developed by resorting to the parallelism condition of the displacement vectors of the circle points of PR dyads. We show that the “circle” point of a PR dyad can be determined as one common intersection of three or four circles, depending on whether four or, correspondingly, five poses are prescribed.

Commentary by Dr. Valentin Fuster
2005;():315-324. doi:10.1115/DETC2005-84903.

This paper presents a robustness study of 3R manipulators and aims at answering the following question: are generic manipulators more robust than non-generic manipulators? We exploit several properties specific to 3R manipulators such as singularities, cuspidality, homotopy classes, and path feasibility, in order to find some correlations between genericity and robustness concepts. For instance, we show that generic manipulators, close to non-generic ones in the space of geometric parameters, are not robust with respect to their homotopy class and to the feasibility of paths. Moreover, we notice that the dexterity and the accuracy of 3R manipulator do not depend on genericity.

Commentary by Dr. Valentin Fuster
2005;():325-342. doi:10.1115/DETC2005-84937.

This contribution presents a mobility criterion applicable to parallel platforms based on an analysis of the Jacobian matrices associated with the platform legs. It is important to note that this criterion is based on an analysis of the subalgebras of the Lie algebra, se(3), also known as screw algebra, of the Euclidean group, SE(3). The mathematical foundations of the method have been already presented in [1]. In this contribution it is shown that, employing a basic knowledge of linear algebra, it is possible to compute the correct mobility of a wider class of parallel manipulators, including the mobility of kinematically deficient parallel platforms and platforms with inactive pairs. Moreover, the criterion computes the passive degrees of freedom in parallel platforms. Finally, it should be emphasized that, unlike other attempts to develop a mobility criterion, the criterion developed in this contribution does not require any consideration of reciprocal screws.

Commentary by Dr. Valentin Fuster
2005;():343-350. doi:10.1115/DETC2005-84978.

A methodology is presented, based on combinatorial theory, for the enumeration of non-isomorphic mechanisms precisely from kinematic chains. According to the defined permutation groups, an algorithm for generating all non-isomorphic identified mechanisms by assigning various types of links and joints to kinematic chains is proposed. Based on the concepts of Polya’s theory and generating function, mathematical expressions are derived for counting the number of the identified mechanisms subject to the design constraints of adjacent/incident relationship between links and joints. Examples are provided to illustrate the proposed approach.

Topics: Chain , Design , Mechanisms
Commentary by Dr. Valentin Fuster
2005;():351-357. doi:10.1115/DETC2005-85120.

An attempt has been made to evolve an approach for the synthesis of contact breaker mechanisms used in electrical switchgear. These mechanisms belong to a class of devices in which the input and output links (and other links of interest) occupy only two positions of primary interest and hence the devices could be looked upon as binary mechanical systems. In this paper we demonstrate that application of binary logic greatly simplifies the type synthesis of such binary mechanical systems.

Commentary by Dr. Valentin Fuster
2005;():359-366. doi:10.1115/DETC2005-85150.

We present an investigation of a novel variable valve-lift mechanism known as the Variable Rocker-Arm mechanism (VR-Arm, for short). This mechanism has simple construction, low friction due to rolling contact, and provides continuously variable lift. Dynamic analysis of the mechanism using ADAMS shows that frictional losses at the intake camshaft are of the order of 1 Newton-meter for a four-cylinder engine.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2005;():367-373. doi:10.1115/DETC2005-85169.

The paper discusses the stiffness of flexure hinge made by rubber material. A revolute compliant joint made by rubber is proposed which offer improvements over existing flexures made by metal in the qualities of large range of motion, long lift, and reduced weight. Based on the theory of nonlinear deformation and the characters of strain-energy functions of Mooney-Rivlin model, the stiffness of rubber flexure hinge is obtained by piece-wise linearization of the stress-strain curve. Some geometric parameters such as t/R ratios affecting the stiffness of rubber hinge are calculated. Thereby, the problem of the relationship between moment and large angle deformation is resolved. The result from the FEA performed on the various flexures to find the angle displacement shows ideal consistency. Finally, the application of rubber flexure hinge using in the compliant thorax of micro air vehicle with flapping wings is given.

Commentary by Dr. Valentin Fuster
2005;():375-382. doi:10.1115/DETC2005-85247.

The focus of this paper is on the synthesis of path generation mechanisms based on shape optimization. The principle component analysis (PCA) technique used in image processing is employed to represent the desired coupler curve of the mechanism and simulated annealing is used as the optimization tool. PCA representation is invariant under rotation, translation, scaling, and starting point. Once a shape-optimized mechanism is found, it is translated, rotated, and scaled to its final form. An illustrative example is introduced to demonstrate the proposed method.

Commentary by Dr. Valentin Fuster
2005;():383-392. doi:10.1115/DETC2005-85288.

In this paper, we investigate the effect of using springs and wing motions to minimize the power required by a mechanical bird to fly. Inertia forces as well as aerodynamic forces on the wing are included. The design takes into account different flight speeds in the range from 0 to 20 m/s. Two ways in which springs can be attached, are considered. The frequency of wing beat is kept fixed and both flapping and feathering are assumed to be simple harmonic. Constraints are imposed on the maximum power expended by the two actuators of a wing. The results show that introduction of springs increases the power required at lower speeds, marginally reducing the power at higher speeds. In the manner in which they are used here, springs do not appear to be useful to reduce power. However, the optimal solutions obtained without springs indicate that it is possible to develop pigeon like mechanical birds which can hover and fly steadily up to 20 m/s.

Topics: Motion , Springs , Wings , Flight
Commentary by Dr. Valentin Fuster
2005;():393-403. doi:10.1115/DETC2005-85315.

This work is a specific application of a particular one degree of freedom six-link geared planar mechanism. A procedure to synthesize non-circular gear pitch profiles to generate any prescribed function of position and orientation in a determined range is presented. The geometry of the mechanism, i.e. the link lengths of the six-bar mechanisms, is assumed known. The input parameters are the prescribed path, the orientation angle at each position along the path, and the interval along which the motion is required. A generic function y = f(x) = ax2 + bx + c, in a particular interval of x, was used to define the desired path. The desired orientation of the coupler link was specified as being tangent to the path at each point. An analysis was performed and complete non-circular profiles were successfully synthesized. Numerical examples are presented.

Topics: Motion , Mechanisms
Commentary by Dr. Valentin Fuster
2005;():405-414. doi:10.1115/DETC2005-85478.

This paper presents grasping mechanism configurations that are self-centering with balanced reaction forces, and develops the design principles, models, and analysis methods of achieving these characteristics in compliant mechanisms. The configurations emulate the self-centering and balanced actuation force characteristics exhibited by hydraulic disc-brake systems. Purely mechanical grasping systems, in which both the mechanism and the object being grasped are rigidly attached to ground, require 2 degrees of freedom in the grasping mechanism. It is shown that compliant configurations can exhibit the balanced-force behavior as well as rigid-link mechanisms.

Topics: Force , Grasping , Mechanisms
Commentary by Dr. Valentin Fuster
2005;():415-423. doi:10.1115/DETC2005-85510.

The objective of this study is to develop an analytical method for the optimization of the design of the coring bits of vibratory drills with cutting teeth that percussively penetrate into brittle material. This optimization is intended to improve the drill rate of the Ultrasonic Driller and Corer (USDC) that was developed by scientists from JPL and engineers from Cybersonics, Inc. The USDC was developed for possible in-situ sample and other extraterrestrial applications in future NASA missions. A theoretical investigation was undertaken to study the rock-bit penetration characteristics and derive the analytical formulation of the specific energy for a coring bit with wedge-shape cutting teeth, based on two analytical models from rock fracture mechanics. It was found that there exists an optimal spacing/depth ratio for the cutting teeth, and the optimal number of cutting teeth on the bottom annulus of the coring bit can be designed to achieve a minimum total coring bit specific energy. Experimental tests were performed to corroborate the analytical results. It was shown that the laboratory drilling tests follow the trend predicted by the theoretical analysis. The methodology developed here can be used for the optimization of any coring/drill bit with a wedge-shape cutting teeth array in percussive/vibratory drills into brittle material.

Topics: Drilling , Design , Cutting
Commentary by Dr. Valentin Fuster
2005;():425-432. doi:10.1115/DETC2005-85516.

In this paper, we consider the complete synthesis of planar 2R chains, in which the five design parameters of the chain are determined using kinematic specifications on the movement of the floating link. We use three positions and two velocities to define algebraic design equations which are solved to obtain multiple solutions. Our primary concern is how to ensure that a 4R chain constructed from two of these solutions moves smoothly through the given task. This is achieved by mapping the design data to an image space of planar displacements and comparing it to the curve traced by the movement of the coupler of the resulting design. Examples show that a designer can work in this image space to adjust the task specification to obtain an effective linkage design.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2005;():433-440. doi:10.1115/DETC2005-84577.

In this paper, a new robotized needle insertion device is proposed for computer-assisted percutaneous therapy. The insertion device is integrated in a robotic system dedicated to gesture guidance in a Computed Tomography (CT) scan. The presented design fulfills the stringent requirements of such a medical application: compatibility with a CT-scan and haptic control by the practitioner are ensured as well as safety and sterilization. The novel design of the insertion device is first presented, outlining its main properties, before introducing preliminary experimental results.

Topics: needles
Commentary by Dr. Valentin Fuster
2005;():441-447. doi:10.1115/DETC2005-84759.

A new method for optimizing the dimensions of a nonlinear static balance mechanism has been created. A rigid link slider-crank mechanism with a nonlinear spring is designed to balance a compliant mechanism. This is accomplished by determining the potential energy of the compliant mechanism using finite element analysis and then optimizing the dimensions of the static balance mechanism to balance the potential energy stored in the compliant forceps. The optimization is performed using a sequential quadratic programming algorithm in Matlab’s optimization toolbox. It is seen that using higher order nonlinear springs results in a system that is better statically balanced. The mechanism that is statically balanced is a compliant forceps that has previously been designed for use in ophthalmic surgery. The compliant forceps stores energy when it creates motion, which then creates neutral positions of the mechanism with minimum potential energy. This situation is often unwanted in surgical situations. This paper uses the compliant forceps as an example of how to optimize the dimensions of a nonlinear static balance mechanism.

Commentary by Dr. Valentin Fuster
2005;():449-457. doi:10.1115/DETC2005-84939.

The identification of an equivalent mechanism which may reproduce at best the relative passive motion of the main anatomical structures of a human articulation is a target of great importance in the study of diarthrodial joints. Passive motion, that is the motion of the joint under virtually unloaded condition, is of basic importance for understanding the role of elements like bones, ligaments, etc. The identification is based on measurements performed during in vitro experiments. Passive motion of a number of human diarthrodial joints may be reproduced by equivalent mechanisms. However, the most critical points when devising the equivalent mechanism are represented by the changes of the subject articulation geometry due to age, sex, body constitution, etc. Thus, the equivalent mechanism sensitivity to the variations of the geometric parameters needs a careful investigation. The passive motion of many diarthrodial joints can be modeled by an equivalent mechanism with one degree of freedom (dof). This paper shows how the sensitivity of a one-dof equivalent mechanism with a finite number of geometric parameters can be studied in a systematic way. A sensitivity index together with some coefficients, called influence coefficients, are proposed which enable measuring the sensitivity of a mechanism, thus allowing the comparison of different equivalent mechanisms from the sensitivity viewpoint. Finally, a case study shows the application of the proposed methodology.

Commentary by Dr. Valentin Fuster
2005;():459-465. doi:10.1115/DETC2005-85071.

In this paper, we discuss the design and control strategies for an active gait rehabilitation device for the lower extrmity. This device uses gravity balancing to reduce the net torque required by the actuators during motion. Two controllers are proposed in this paper. The first uses a robust controller and the second uses a torque assisting control law. Simulations of these controllers are presented in this paper. Experiments are currently being conducted with this orthosis on healthy and stroke subjects.

Topics: Orthotics
Commentary by Dr. Valentin Fuster
2005;():467-473. doi:10.1115/DETC2005-85083.

Currently available prosthetic devices for trans-tibial (below the knee) amputees allow a great deal of mobility, but they do not allow amputees to walk with a normal gait. Most designs utilize passive elements to approximate the complex nonlinear response of the foot and ankle. This paper outlines early work in the design of a hybrid passive/active prosthesis that uses the inherent nonlinearity of a four bar mechanism and the power of numerical optimization to more closely duplicate the function of the human foot/ankle complex during walking.

Commentary by Dr. Valentin Fuster
2005;():475-480. doi:10.1115/DETC2005-85357.

The small size of microfabricated structures are opening new avenues in the field of biomedical engineering where structures are being developed to process [1] and analyze [2,3] nanolitre quantities of biological fluids, and cellular tissues. This paper outlines the design and manufacture principals of a passive micro-mechatronic device for the filtration and sorting of spermatogenic cells. This device is to be applied in a urological clinical environment where it can be used to semi-automate the spermatozoa selection process from non-obstructive azoospermic testis biopsies. Detailed and discussed herein are the advantages and drawbacks of Micro-Electro-Mechanical Systems (MEMS) as applied to clinical biomedical situations, and requirements for the design methodology and process of a microfluidic system based on MEMS technology with a view to manufacture by Deep Reactive Ion Etching process. The modelling of the micro device using computational fluid dynamic simulation methods is also covered in this paper.

Topics: Fluids , Design , Modeling , Filters
Commentary by Dr. Valentin Fuster
2005;():481-489. doi:10.1115/DETC2005-85387.

This paper describes a teleoperated needle guidance and insertion tool to assist doctors in performing minimally invasive percutaneous biopsies remotely under computed tomography [CT] guidance. Robopsy is a user-friendly robotic device that grips, positions and inserts a biopsy needle while the patient is imaged to provide the radiologist with simultaneous needle position feedback. Patient care is improved through more precise targeting and shortened procedure times. Robopsy is made primarily of simple, lightweight, snap-together, disposable plastic parts and modular motors; contrasting devices are heavy, complex and expensive. It is designed to be taped onto a patient so as to passively compensate for respiratory chest motion and, additionally, it incorporates a novel feature, which compensates for passive needle oscillation. The design process is outlined and the first prototype presented. Initial results from testing on a cardiac phantom indicate that artifacts from the device in the CT images are negligible and that the device can successfully orientate and insert a needle remotely.

Topics: needles
Commentary by Dr. Valentin Fuster
2005;():491-500. doi:10.1115/DETC2005-85442.

People with (neuro-)muscular diseases have problems lifting their arms against gravity because of degeneration of their muscles. Many of them are in need of a device that supports the weight of their arms, so as to regain some independence. Existing solutions do not meet all of the requirements. This paper presents the design of a new type of spring-compensation mechanism which is adjustable to varying load. The most important part of this design is a wrapping cam with variable transmission to compensate for errors, which rolls on a support plane to minimize friction.

Topics: Design , Mechanisms
Commentary by Dr. Valentin Fuster
2005;():501-510. doi:10.1115/DETC2005-85517.

In this paper we present several new advancements in the area of smart rehabilitation devices that have been developed by the Northeastern University Robotics and Mechatronics Laboratory. They are all compact, wearable and portable devices and boast re-programmable, real time computer controlled functions as the central theme behind their operation. The sensory information and computer control of the three described devices make for highly efficient and versatile systems that represent a whole new breed in wearable rehabilitation devices. Their applications range from active-assistive rehabilitation to resistance exercise and even have applications in gait training. The three devices described are: a transportable continuous passive motion elbow device, a wearable electro-rheological fluid based knee resistance device, and a wearable electrical stimulation and biofeedback knee device.

Commentary by Dr. Valentin Fuster
2005;():511-517. doi:10.1115/DETC2005-84217.

Micro mirrors have emerged as key components for optical microelectromechanical system (MEMS) applications. Electrostatic vertical comb drives are attractive because they can be fabricated underneath the mirror, allowing for arrays with a high fill factor. Also, vertical comb drives are more easily controlled than parallel plate actuators, making them the better choice for analog scanning devices. The device presented in this paper is a one-degree of freedom vertical comb drive fabricated using Sandia National Laboratories SUMMiT™ five-level surface micromachining process. The electrostatic performance of the device is investigated using finite element analysis to determine the capacitance for a unit cell of the comb drive as the position of the device is varied. This information is then used to design a progressive linkage that will seek to alleviate or eliminate the effects of instability. The goal of this research is to develop an electrostatic model for the behavior of the vertical comb drive mirror and then use this to design a progressive-linkage that can delay or eliminate the pull-in instability.

Commentary by Dr. Valentin Fuster
2005;():519-528. doi:10.1115/DETC2005-84352.

Dihedral angles as generalized coordinates define the geometric conformation of a peptide chain. Given the exact coordinates of the atoms, it is possible to rigorously calculate the dihedral angles. We will refer to this calculation process as the residue level inverse kinematics of peptide chains. However uncertainties and experimental observation inaccuracies in the atoms’ coordinates handicap this otherwise simple and straightforward process. In this paper, we present three new efficient methodologies to find all the dihedral angles of a peptide chain for a given conformation. Comparison of these results with the dihedral angle values reported in the PDB (Protein Data Bank) indicates significant improvements. While these improvements benefit most modeling methods in protein analysis, it is in particular, very significant in homology modeling where the dihedral angles are the structural variables. The first method presented here fits a best plane through five atoms of each peptide unit. The angle between the successive planes is defined as the dihedral angle. The second method is based on the Zero-Position analysis method. Successive links in this method rotate by the dihedral angles so as to minimize the structural error between respective atoms in the model conformation with given atoms’ coordinates. Dihedral angle final values correspond to the minimum structural error configuration. In this method, singular value decomposition (SVD) technique is used to best fit the atoms in the two conformations. The third method is a variant of the second method. In this instead of rotating all the links successively only three links are matched each time to extract the dihedral angle of the middle link. By doing so, the error accumulation on the successive links is reduced. This paper focuses on the Euclidean norm as the measure of merit (structural error) to compare different methods with the Protein Data Bank (PDB). This Euclidean norm is further, minimized by optimizing the geometrical features of the peptide plane.

Topics: Kinematics , Chain
Commentary by Dr. Valentin Fuster
2005;():529-535. doi:10.1115/DETC2005-84672.

Microelectromechanical systems (MEMS) are usually fabricated using planar processing methods which complicates the design of devices capable of complex motions. For applications that need a micro mechanism that rotates out of the plane of fabrication with an in-plane rotational input, or that rotates spatially about a point, spherical kinematics may represent an appropriate solution. This paper describes the design of spherical mechanisms for MEMS including the design of joints and links, and what may be the first demonstration of two spherical micro mechanism building blocks: the spherical four-bar micromechanism and the spherical slider-crank micromechanism. Two other micromechanisms are demonstrated to illustrate how the building block devices may be used to create more complex devices.

Commentary by Dr. Valentin Fuster
2005;():537-546. doi:10.1115/DETC2005-84697.

A set of mechanisms called Double Tensural Bistable Mechanisms (DTBM) is presented. DTBMs are fully compliant linear bistable mechanisms that have two bending segments that undergo tension loading. Five configurations of the DTBM are designed, fabricated using surface micromachining, and tested. Measured force and displacement are compared with finite element analysis (FEA) predictions. For two DTBM configurations, a novel post-switch, large-displacement, low-k linear spring behavior is predicted by the FEA models and verified through experimental testing. On-chip actuation of two devices is achieved using thermomechanical in-plane microactuators (TIMs). The DTBM mechanism set explores a relatively new design space for fully compliant micromechanisms, and mechanisms from this class have promise in such applications as shutter positioning, microvalves, electrical relays, inertial sensors and g/time switches.

Topics: Springs , Mechanisms
Commentary by Dr. Valentin Fuster
2005;():547-554. doi:10.1115/DETC2005-85380.

Stability of a dual-axis vibratory MEMS gyroscope that is subject to periodic fluctuations in input angular rates is investigated. For the purpose of acquiring stability conditions, when the angular rate input is subject to small intensity periodic fluctuations, dynamic behavior of periodically perturbed linear gyroscopic systems is studied in detail. An asymptotic approach based on the method of averaging has been employed for this purpose, and closed-form conditions for the onset of instability due to parametric resonances have been obtained for this type of vibrating gyroscope. Furthermore, for characterizing the effect due to change in angular rate input, an in-depth natural frequency analysis has been performed. Stability predictions have been illustrated via plots in the excitation amplitude-frequency space. Based on these results, the dangerous critical frequencies can be avoided in the design to achieve a high performance.

Commentary by Dr. Valentin Fuster
2005;():555-563. doi:10.1115/DETC2005-84174.

One of the biggest challenges in the manufacturing of high temperature fuel cells is the creation of the Membrane Exchange Assembly (MEA). This is the heart of the fuel cell, where the 4–5 components must be assembled with very high tolerances to perform successfully. One of the key components, the membrane, is similar to plastic food wrap. Handling plastic wrap alone in a wrinkle free mode, with precision cut edges is difficult enough. But it also must be saturated in acid, creating a very slippery product. And the membrane will grow or shrink in a matter of 5 minutes when exposed to moisture in the air. So this material handling effort is orders of magnitude more difficult than the established methods for “simple” items like paper. This paper will document the research conducted into the robotic material handling of the fuel cell membranes. It requires a mix of traditional robotic techniques, some techniques from the fabric handling arena, and some new approaches. The issues from lifting a wet film from a PET backer sheet consistently and the sensing requirements for accurate placement have made this a challenging effort.

Commentary by Dr. Valentin Fuster
2005;():565-572. doi:10.1115/DETC2005-84191.

The Biped Robots have specific dynamical constraints and stability problems, which reduce significantly their motion range. In these conditions, path planning and tracking becomes very important. The joint profiles have been determined based on constraint equations cast in terms of step length and high, step period, maximum step height etc. In this paper Fuzzy Neural Network Controller for Path-Planning and Tracking on incline terrain (up stairs) of a planar five-link Biped Robot is presented. The locomotion control structure is based on integration of kinematics and dynamics model of Biped Robot. The proposed Control Scheme and Fuzzy Neural Algorithm could be useful for building an autonomous non-destructive testing system based on Biped Robot. Structure of Fuzzy Neural Network Controller is optimized using Genetic Algorithm. The effectiveness of the method is demonstrated by simulation example using Matlab software.

Commentary by Dr. Valentin Fuster
2005;():573-581. doi:10.1115/DETC2005-84227.

This paper presents the research and design of a novel parallel architecture of pre-stressed six-component force/torque sensor based on the Stewart platform. The mathematical model of the structure was build by using the screw theory. The influence of joint frictional moment on the performances of the sensor is analyzed by using the concept of kinematic influence coefficient. In this paper, we define the indices of force/torque isotropy and generalized amplifying index to evaluate the performances of the sensor and discuss the optimal design of the sensor dimensions considering these indices. The prototype sensor was designed and manufactured. The theoretical and experimental study of the static calibration of the prototype is carried out, and the problem of the hyperstatic is solved perfectly. The results from the static calibration experimentation validate the correctness of the theoretical analysis.

Topics: Force , Torque , Sensors , Design
Commentary by Dr. Valentin Fuster
2005;():583-587. doi:10.1115/DETC2005-84251.

The actuating input selection is an important basic problem for the parallel mechanism. Based on the screw theory, the constraint screw can be got after locking a kinematic pair in any limb, which can be taken as actuating wrench acted on the moving platform of the parallel mechanism. The constraint screw matrix is composed of the structure constraint screws and the constraint screws of the actuating pairs. The reasonableness of input selection can be judged by the rank of the constraint matrix. The performance of the combinations of actuating inputs is evaluated by the condition numbers of the force constraint matrix and the torque constraint matrix respectively. The theory presented is validated by the simulation and the maching test.

Commentary by Dr. Valentin Fuster
2005;():589-598. doi:10.1115/DETC2005-84324.

This paper introduces a new concept for robotic search and rescue systems. This system uses a rapidly deployable cable robot to augment existing search and rescue mobile robots. This system can greatly increase the range of mobile robots as well as provide overhead views of the disaster site, allowing rescue workers to reach survivors as quickly as possible while minimizing the danger posed to rescue workers. In addition to the system concept, this paper presents a novel kinematic structure for the cable robot, allowing simple translation-only motion (with moment-resisting capability) and easy forward and inverse kinematics for a 3-DOF spatial manipulator. Also, a deployment sequence is described, a rapid calibration algorithm is presented and the workspace of the manipulator is investigated.

Topics: Robots , Cables
Commentary by Dr. Valentin Fuster
2005;():599-608. doi:10.1115/DETC2005-84333.

In this paper, a new adaptive switching control approach, called adaptive evolutionary switching PD control (AES-PD), is proposed for iterative operations of robot manipulators. The proposed AES-PD control method is a combination of the feedback of PD control with gain switching and feedforward using the input torque profile obtained from the previous iteration. The asymptotic convergence of the AES-PD control method is theoretically proved using Lyapunov’s method. The philosophy of the switching control strategy is interpreted in the context of the iteration domain to increase the speed of the convergence for trajectory tracking of robot manipulators. The AES-PD control has a simple control structure that makes it easily implemented. The validity of the proposed control scheme is demonstrated for the trajectory tracking of robot manipulators through simulation studies. Simulation results show that the AES-PD control can improve the tracking performance with an increase of the iteration number. The EAS-PD control method has the adaptive and learning ability; therefore, it should be very attractive to applications of industrial robot control.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2005;():609-614. doi:10.1115/DETC2005-84596.

One of the major limitations of mobile robots for unstructured environments is their lack of general mobility. Wheeled, treaded, and legged robots each have their advantages and disadvantages, but they all lack the flexibility to be able to cope with a wide range of terrain. The actuated spoke wheel concept is presented in this paper as an alternative locomotive method that allows multiple modes of motion, which give it the ability to stride quickly using one contact point per wheel, walk with static stability with two contact points per wheel, or assume a stable stance using three contact points per wheel. This paper presents the preliminary kinematic analyses of the actuated spoke wheel with no-slip constraints at the ground contacts for a robot using a two actuated spoke wheel configuration. Straight-line motion and considerations for turning are discussed for the one- and two-point contact schemes followed by recommendations for future study.

Topics: Wheels
Commentary by Dr. Valentin Fuster
2005;():615-621. doi:10.1115/DETC2005-84868.

This paper presents a model-based sliding mode control law for a planar three-degree-of-freedom robot arm actuated by two rotary Shape Memory Alloy (SMA) actuators and a servomotor. The SMA actuators use a combination of SMA wires and pulleys to produce rotational motion. A model of the robot is developed which combines robot equations of motion with the SMA wire heat convection, constitutive law, and phase transformation equations. Two second-order sliding surfaces are defined leading to derivation of asymptotically stable control laws within the actuation region of the SMA wires. Outside the actuation region, constant inputs are used based on the one-way nature of the SMA actuators. The control law is shown to be effective in several simulations for both set point and trajectory tracking of the robot.

Commentary by Dr. Valentin Fuster
2005;():623-632. doi:10.1115/DETC2005-84992.

From the viewpoint of kinematics, a three-dof H-type pure translational parallel manipulator is presented for the development of automatic assembly devices and a regional structure of a six-dof hybrid parallel platform. First, we describe the structural properties of manipulator and analyze its kinematic mobility. A pure translational motion is verified to exist through the well-known D-H symbolic notations and the coordinate transformation technique. What follows are the forward and inverse kinematic analysis and their analytical closed-form solutions by the matrix algebra approach. For further confirmation of the derived equations, some numerical examples are also given. Moreover, with the help of the analytical displacement kinematics, we identify the volume of workspace. At last, taking account of the overall Jacobian matrix provides the condition number and the identification of singularity of configuration is explored based on the direct and inverse kinematics Jacobian matrix.

Commentary by Dr. Valentin Fuster
2005;():633-639. doi:10.1115/DETC2005-84993.

In this paper we propose a new path planning method for robot manipulators in cluttered environments, based on lazy grid sampling. Grid cells are built while searching for the path to the goal configuration. The proposed planner acts in two modes. A depth mode, while the robot is far from obstacles, makes it evolve toward its goal. While a width search mode becomes active when the robot gets close to an obstacle. This method provides the shortest path to go around the obstacle. It also reduces the gap between pre-computed grid methods and lazy grid methods. No heuristic function is needed to guide the search process. An example dealing with a robot in a cluttered environment is presented to show the efficiency of the method.

Commentary by Dr. Valentin Fuster
2005;():641-649. doi:10.1115/DETC2005-85069.

The importance of energy efficiency of a robotic manipulator is clearly evident when the manipulator has to use on-board power. With miniature machines, this issue is even more important since the size and the weight guides the performance of the design. In this paper, a design methodology is proposed which may allow a robot to follow desired trajectories approximately without actuator inputs. Actuator inputs can be used to further modify the trajectories. The design philosophy has the following key elements: (i) the inertia matrix of the device is suitably altered using mass distribution, (ii) compliant elements are introduced to take away the gravity terms, and (iii) additional springs are used to create certain periodic gait motion. If the generated motion is the desired motion, then no external inputs are needed. Otherwise, actuators can be added to get the desired motion. The energy efficiency with this design philosophy is compared using an example of a two degree-of-freedom leg executing a swing motion.

Commentary by Dr. Valentin Fuster
2005;():651-660. doi:10.1115/DETC2005-85131.

This paper presents a study of the dynamics and control of a helicopter carrying a payload through a cable-suspended robot. The helicopter can perform gross motion, while the cable suspended robot underneath the helicopter can modulate a platform in position and orientation. Due to the under-actuated nature of the helicopter, the operation of this dual system consisting of the helicopter and the cable robot is challenging. We propose here a two time scale control method, which makes it possible to control the helicopter and the cable robot independently. In addition, this method provides an effective estimation on the bound of the motion of the helicopter. Therefore, even in the case where the helicopter motion is unknown, the cable robot can be stabilized by implementing a robust controller. Simulation results of the dual system show that the proposed control approach is effective for such a helicopter-robot system.

Commentary by Dr. Valentin Fuster
2005;():661-666. doi:10.1115/DETC2005-85200.

Presented in this paper is a 2-dof robomech that carries two end effectors to perform two functions simultaneously. The robomech has a 7R architecture consisting of two triad wings connected to form two cells. The over-constrained kinematic chain cannot traverse continuous trajectories but may be synthesized to move the end effectors through a set of desired locations. The article presents the architecture of the proposed robomech, establishes its kinematic relations and constraints, and provides dimensional synthesis scheme based on genetic algorithm and gradient search methods. Two case studies are included to demonstrate the applicability of the proposed robomech.

Commentary by Dr. Valentin Fuster
2005;():667-675. doi:10.1115/DETC2005-85217.

In our previous work, we have treated the collision-free path-planning problem for a nonholonomic mobile robot in a cluttered environment. The method we have used is based on a representation of the obstacles in the robot’s velocity space, called Feasible Velocities Polygon (FVP). Every obstacle in the robot’s influence zone is represented by a linear constraint over the robot’s velocities such that it could not be collision between the robot and the obstacle. These constraints define a convex subset in the velocity space, the FVP. Every velocity vector of the FVP ensures a safe motion for the given obstacle configuration. The path-planning problem is solved by an optimization approach between the FVP and a reference velocity to reach the goal. In this paper, we have extended our work to an articulated mobile robot. This robot is composed of a differential mobile robot as tractor and a trailer, linked by off-center joints. We have modified the reference velocity in order to consider the constraints imposed by the trailer over the robot’s velocities. The control law is a nonlinear control law, which is asymptotically stable to the goal. We use the virtual robot concept, to solve the stability problem when the robot and its trailer move backwards. An articulated mobile robot is a strongly constrained system. Even in a free environment, under some circumstances, the robot may get blocked by its trailer in its progression towards the goal. To solve these situations, we have developed a heuristic algorithm. This algorithm is based in human experience: when a blocking situation is detected, a forward-backward maneuver is made, in order to increase the distance between the tows until a maximal value. After this maneuver, the robot takes the path to the original goal. Some numerical results show that our method leads the robot and the trailer to the final position in a stable way.

Commentary by Dr. Valentin Fuster
2005;():677-682. doi:10.1115/DETC2005-85419.

In this paper, we present a novel locomotion mechanism for mobile robots inspired by the motility mechanisms of single celled organisms that use cytoplasmic streaming to generate pseudopods for locomotion. The Whole Skin Locomotion, as we call it, works by way of an elongated toroid which turns itself inside out in a single continuous motion, effectively generating the overall motion of the cytoplasmic streaming ectoplasmic tube in amoebae. With an elastic membrane or a mesh of links acting as its outer skin, the robot can easily squeeze between obstacles or under a collapsed ceiling and move forward using all of its contact surfaces for traction, or even squeeze itself through holes with diameters smaller than its nominal width by actively changing its cross section diameter making this the ideal locomotion method for search and rescue robots that need to traverse over or under rubble, or for applications where a robot needs to move in and maneuver itself into tight spaces such as for robotic endoscopes. This paper summarizes the many existing theories of amoeboid motility mechanisms, and examines how these can be applied on a macro scale as a novel mobile robot locomotion concept. Four locomotion mechanism models are presented with preliminary experiments and their results, demonstrating the feasibility of the whole skin locomotion strategy.

Topics: Skin , Mechanisms
Commentary by Dr. Valentin Fuster
2005;():683-689. doi:10.1115/DETC2005-84031.

The sudden change of joint velocity in fault tolerant operation of two coordinating manipulators for joint-locking failures is studied. First, the difference between the joint velocity of original manipulator and that of reduced manipulator is defined as the sudden change in joint velocity. Then, a corresponding fault tolerant planning algorithm based on this criterion is proposed. At last, a simulation example of fault tolerant operations is implemented with two planar 3R manipulators. Simulation results show that this algorithm can effectively avoid the sudden change of joint velocity occurring in fault tolerant operation of two coordinating manipulators, strengthen their motion stability and so improve their kinematical and dynamic properties in fault tolerant operations.

Commentary by Dr. Valentin Fuster
2005;():691-697. doi:10.1115/DETC2005-84098.

The instantaneous kinematics of a special 3-UPU parallel platform manipulator is discussed in this paper. First, the instantaneous motions of the 3-UPU manipulator in four position and a special manipulator are studied by reciprocal screw theory. Then, the principal screws in one of four position are obtained. It is shown that the moving platform has five DOF (degrees of freedom) in the initial position or after a translation along the Z-axis; in the generic position, the mechanism only has three DOF, moreover the three DOF characteristics are difference in different position. The instantaneous kinematic characteristics of alike 3-UPU mechanisms are very different in different position and special structure. The results presented in this paper are important to the use of alike 3-UPU parallel manipulator and contribute to the mechanism theory.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2005;():699-704. doi:10.1115/DETC2005-84099.

In order to enrich deficient-DOF parallel mechanism models, a novel model of a 3-DOF platform manipulator is presented and establish its inverse kinematics equation. Here, studies instantaneous motions of 3-RRRRR parallel manipulator at initial configuration and general configuration. Find: it has three degrees of freedom at initial configuration and after translated along the X, Y, Z axis. Secondly, the relation is given between every active input (θ1 ) and moving platform position by using D-H means, the solution is developed for inverse kinematics, numerical example for the position kinematic is presented, the figure of workspace along the Z-axis is drawn finally. The mechanism can be applied to jiggle mechanism.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2005;():705-710. doi:10.1115/DETC2005-84112.

The determination of the 6-dimensional singular configurations (SC) space of 3/6-SPS Stewart parallel manipulator is a very important and quite complicated problem. For a long time, its developments, however, have been very limited, especially the general-linear complex-SC (GSC). Currently, the Jacobian matrix and the Grassmann line geometry have been used to solve the SC space of the Stewart parallel robot. However, these two approaches are not straightforward. In this paper, a novel computer aided geometric approach is proposed for solving the 6-dimensional SC space of the 3/6-SPS Stewart parallel manipulator. First, a simulation mechanism of the 3/6-SPS parallel manipulator is created. Second, its equivalent SC simulation mechanism is created. Third, from the equivalent SC simulation mechanism, some analytical geometry formulas for solving 6-dimension SC space are derived. Finally, some SC space characteristics are analyzed, and some important developments are achieved.

Commentary by Dr. Valentin Fuster
2005;():711-715. doi:10.1115/DETC2005-84160.

The dynamics and motion control of flexible robot manipulators is an advanced topic in the study of robotics. The precise tracking of the end-effector trajectory of flexible robots can be improved by the self-motion of redundant manipulators. The flexible manipulator with single-degree of kinematic redundancy has been considered only at present. This study addresses on the dynamics and motion control of flexible robots with multi-degree of kinematic redundancy. Compared with the robot with one-degree of redundancy, the optimal motion programming of a flexible robot manipulator with two-degree of redundancy has been obtained successfully based on pseudo-inverse solution. The numerical results of planar three-link and four-link flexible manipulators show the advantage of multi-degree of redundancy in improving the kinematic and dynamic performances of flexible robot manipulators.

Commentary by Dr. Valentin Fuster
2005;():717-726. doi:10.1115/DETC2005-84180.

An analytical method is presented to obtain all surfaces enveloping the workspace of a general n degree-of-freedom mechanism with non-unilateral constraints. The method is applicable to kinematic chains that can be modeled using the Denavit-Hartenberg representation method for serial manipulators. The method introduced in this paper is based upon analytical criteria for determining singular behavior of the mechanism. A perturbation approach is implemented to determine the interior and exterior of the workspace. The complete mathematical formulation is presented and illustrated using 3 and 4 DOF spatial manipulators. The paper present a rigorous analysis of the sub-Jacobians to determine a classification of singularities: Type I sets are position Jacobian singularities; Type II sets are instantaneous singularities that are due to a generalized joint that is reaching its apex; Type III sets are domain boundary singularities, which are associated with the initial and final values of the time interval; Type IV sets are coupled singularities, which are associated with a relative singular Jacobian, where the null space is reduced in one submatrix due to either of two occurrences: a Type II or Type III singularities. The paper presents a general formulation for determining the workspace.

Commentary by Dr. Valentin Fuster
2005;():727-733. doi:10.1115/DETC2005-84199.

The purpose of this paper is to use the Taguchi method on the tolerance design of a four-bar function generator in order to obtain the structural error that is insensitive to variations in manufacturing tolerance and joint clearance. The contribution of each control factor to the variations was also examined to further determine if the tolerance of the factor should be tightened to improve the precision of the mechanism. From the study of the four-bar function generator, it was revealed that the control factor B had the most significant effect on the variation of the structural errors. These were closely followed by factors E, C and D. On the whole, experimental errors contributed only 2.69% to the structural errors, much smaller than the contribution by individual factors, indicating that the design of the experiments was appropriate and the results were highly reliable. By tightening the tolerance, it is apparent that the mean of structural errors is reduced by 0.227 and the change in variance is 69.81% of the initial value, i.e. a reduction of 30.19%.

Commentary by Dr. Valentin Fuster
2005;():735-747. doi:10.1115/DETC2005-84223.

Motion planning in cluttered environments is a weakness of current robotic technology. While research addressing this issue has been conducted, few efforts have attempted to use minimum distance rates of change in motion planning. Geometric influence coefficients provide extraordinary insight into the interactions between a robot and its environment. They isolate the geometry of distance functions from system inputs and make the higher-order properties of minimum distance magnitudes directly available. Knowledge of the higher order properties of minimum distance magnitudes can be used to predict the future obstacle avoidance, path planning, and/or target acquisition state of a manipulator system and aid in making intelligent motion planning decisions. Here, first and second order geometric influence coefficients for minimum distance magnitudes are rigorously developed for several simple modeling primitives. A general method for similar derivations using new primitives and an evaluation of finite difference approximations versus analytical second order coefficient calculations are presented. Two application examples demonstrate the utility of minimum distance magnitude influence coefficients in motion planning.

Commentary by Dr. Valentin Fuster
2005;():749-756. doi:10.1115/DETC2005-84291.

This paper proposes a generalized transmission index for spatial mechanisms, based on the transmission index introduced by Sutherland and Roth. This index is more general and welldefined in all the cases; it matches the virtual coefficient between the transmission wrench screw and the output twist screw exactly. A method is developed to compute the transmission wrench screw in spatial single-loop linkages. We illustrate the application of this index in a RSCR linkage.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2005;():757-764. doi:10.1115/DETC2005-84313.

The paper presents singularity-free fully-isotropic T1R2-type parallel manipulators (PMs) with three degrees of freedom. The mobile platform has one independent translation (T1) and two rotations (R2). A method is proposed for structural synthesis of fully-isotropic T1R2-type PMs based on the theory of linear transformations. A one-to-one correspondence exists between the actuated joint velocity space and the external velocity space of the moving platform. The Jacobian matrix mapping the two vector spaces of fully-isotropic T1R2-type PMs presented in this paper is the 3x3 identity matrix throughout the entire workspace. The condition number and the determinant of the Jacobian matrix being equal to one, the manipulator performs very well with regard to force and motion transmission capabilities. As far as we are aware, this paper presents for the first time in the literature solutions of singularity-free T1R2-type PMs with decoupled an uncoupled motions, along with the fully-isotropic solutions.

Commentary by Dr. Valentin Fuster
2005;():765-774. doi:10.1115/DETC2005-84326.

This paper investigates the problem of defining a consistent kinetostatic performance index for symmetric planar 3-DOF parallel manipulators. The condition number of the Jacobian matrix is known to be an interesting index. But since the Jacobian matrix is dimensionally inhomogeneous, a normalizing length must be used. This paper proposes two distinct kinetostatic indices. The first one is defined as the reciprocal of the condition number of the Jacobian matrix normalized with a convenient characteristic length. The second index is defined by a geometric interpretation of the “distance” to singularity. The two indices are compared and applied to the kinematic inversion in the presence of redundancy.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2005;():775-784. doi:10.1115/DETC2005-84349.

This paper presents a new manipulation theory for controlling compliant motions of a robotic manipulator. In previous closed loop control methods, both direct kinematics and inverse kinematics of a manipulator must be resolved to convert feedback force and position data from Cartesian space to joint space. However, in many cases, the solution of direct kinematics in a parallel manipulator or the solution of inverse kinematics in a serial manipulator is not easily available. In this study, the force and position data are packed into one set of “motion feedback,” by replacing the force errors with virtual motion quantities, or one set of “force feedback,” by replacing motion errors with virtual force quantities. The joint torques are adjusted based on this combined feed back package. Since only Jacobian of direct kinematics or Jacobian of inverse kinematics is used in the control scheme, the computational complexity is reduced significantly. The applications of this theory are demonstrated in simulation experiments with both serial and parallel manipulators.

Commentary by Dr. Valentin Fuster
2005;():785-792. doi:10.1115/DETC2005-84551.

In this article kinematic analysis of a 3 Leg-Spherically Actuated (3SA) parallel manipulator will be addressed. Since each leg has a spherical actuator (three inputs for each leg) and manipulator has three legs; totally, there are nine inputs. Due to the fact that the manipulator has six degree of freedom, only six independent inputs are needed. Thus actuation could be done in different ways. If the triangles representing base and platform are equilateral, there are twenty different ways of actuation that should be studied during forward kinematic analysis. Rather than adopting the standard Denavit-Hartenberg approach, a simple method for forward kinematic analysis for all these different ways of twenty ways has been introduced. Considering all these ways, it will be shown that at least two and at most six nonlinear algebraic equations should be solved during forward kinematic analysis, while choosing the standard approach twelve nonlinear equations should be solved for each way of actuation. A unique inverse kinematic method has been presented. The singularly analysis for all these different ways of actuation has also been studied. For two out of the twenty different ways, closed form solutions for the singularity analysis have been obtained, for other ways; conditions which result in singularity configuration has been presented and simulation justified the proposed criteria.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2005;():793-801. doi:10.1115/DETC2005-84612.

The problem of self-reconfiguration planning for chain-type unit-modular robots is a complex one, with many issues yet to be successfully addressed. This paper describes an approach to several sub-problems associated with self-reconfiguration, namely kinematic modeling and analysis, including kinematic constraint satisfaction, and load analysis and redistribution. These issues are addressed in a unified framework whose primary objective is minimization of the time and mechanical energy expended during reconfiguration. Computer simulation efforts are described and results presented.

Commentary by Dr. Valentin Fuster
2005;():803-809. doi:10.1115/DETC2005-84679.

In this paper we present an analytical approach for the static and dynamic analysis of the PAMINSA, a new 4 degrees of freedom parallel manipulator that has been designed at the I.N.S.A. in Rennes. On the base of the developed static model, the input torques due to the static loads are reduced by means of the optimum redistribution of the moving link masses. The analytical dynamic modeling of the PAMINSA by means of Lagrange equations is achieved. A numerical example and a comparison between the suggested analytical model and an ADAMS software simulation are presented.

Commentary by Dr. Valentin Fuster
2005;():811-825. doi:10.1115/DETC2005-84699.

This paper presents a novel methodology for detecting collisions of cylindrically shaped rigid bodies moving in three dimensions. This algorithm uses line geometry and dual number algebra to exploit the geometry of right circular cylindrical objects to facilitate the detection of collisions. First, the rigid bodies are modelled with infinite length cylinders and a necessary condition for collision is evaluated. If the necessary condition is not satisfied then the two bodies are not capable of collision. If the necessary condition is satisfied then a collision between the bodies may occur and we proceed to the next stage of the algorithm. In the second stage the bodies are modelled with finite length cylinders and a definitive necessary and sufficient collision detection algorithm is employed. The result is a straight-forward and efficient means of detecting collisions of cylindrically shaped bodies moving in three dimensions. This methodology has applications in spatial mechanism design, robot motion planning, workspace analysis of parallel kinematic machines such as Stewart-Gough platforms, nuclear physics, medical research, computer graphics and well drilling. A case study examining a spatial 4C robotic mechanism for self collisions is included.

Commentary by Dr. Valentin Fuster
2005;():827-840. doi:10.1115/DETC2005-84712.

The kinematics of rigid body mechanisms is considered from a differential-geometric perspective. Geometric properties of a mechanism are intrinsically determined by the topology of its configuration space — the solution set of closure functions. The mechanism kinematics is usually characterized by the tangent space and tangent cone to the configuration space, i.e. by locally considering its topology. There are, however, mechanisms for which this is not sufficient. Generally, beside the topology, a complete picture of the kinematics needs both, the configuration space and the ideal generated by the closure functions. Tangent spaces/cones are differential-geometric objects associated to a variety. Two additional objects are introduced in this paper: the kinematic tangent space and the kinematic tangent cone. Three locally equivalent models for the mechanism kinematics are introduced. Due to their different mathematical nature the different models admit to apply specific mathematical tools. The analysis of model I is based on Lie group and screw algebraic methods, while model II and III are analyzed using methods from algebraic geometry. A computationally efficient algorithm for the construction of the kinematic tangent cone is presented. Its application is shown for several examples. A novel mechanism is presented of which the differential and local degree of freedom are different in regular points, so-called ‘paradox-in-the-small’.

Commentary by Dr. Valentin Fuster
2005;():841-846. doi:10.1115/DETC2005-84865.

Analysis and evaluation of singularities play an important role in several aspects of mechanisms and robotics including design, trajectory planning, and control. In this paper, taking the Watt linkage as an example, the bifurcation characteristics of a six-bar linkage have been investigated. It has been found that the bifurcation characteristics of the mechanism belong to the turning point bifurcation and sometimes a kind of dual turning point bifurcation will take place, and selecting different driving link and Ground, the bifurcation characteristics will not be changed but it only has effects on the number of singularities.

Topics: Linkages , Bifurcation
Commentary by Dr. Valentin Fuster
2005;():847-853. doi:10.1115/DETC2005-84919.

Underactuated robots have fewer control inputs than the degrees of freedom of the system. Dynamic model of an underactuated robot considering link flexibility is firstly proposed based on finite element method. Several dynamic coupling indices for underactuated flexible manipulators are analyzed and discussed including acceleration coupling between active and passive joints, dynamic coupling between passive joints and drive torques, and the coupling effect of elastic deformations and joints. The simulation results illustrate that these coupling effects are very important in structure design, configuration design, actuator placement and the control to underactuated robots system, and show that the elastic deformations of links have influence on dynamic coupling indices.

Commentary by Dr. Valentin Fuster
2005;():855-861. doi:10.1115/DETC2005-84987.

This paper presents a recursive approach for solving kinematic and dynamic problem in snake-like robots using Kane’s equations. An n-link model with n-nonholonomic constraints is used as the snake robot model in our analysis. The proposed algorithm which is used to derive kinematic and dynamic equations recursively enhances the computational efficiency of our analysis. Using this method we can determine the number of additions and multiplications as a function of n. The proposed method is compared with the Lagrange and Newton-Euler’s method in three different aspects: Number of operations, CPU time and error in the computational procedures.

Topics: Robots , Equations
Commentary by Dr. Valentin Fuster
2005;():863-870. doi:10.1115/DETC2005-85008.

In this paper we present a novel planar structure of a snake-like robot. This structure enables passive locomotion in snake-like robots through an auxiliary link in joint and a torsional spring. Dynamic equations are derived, using Gibbs-Appell method. Kinematic model of the robot include numerous non-holonomic constraints, which can be omitted at the beginning by choosing proper coordinates to describe the model in Gibbs-Appell framework. In such a case, dynamic equations will be significantly simplified, resulting in significant reduction of simulation time. Simulation results show that, by proper selecting initial conditions, joint angles operate in a limit cycle and robot can locomote steadily on a passive trajectory. It can be seen that the passive trajectory is approximately a Serpenoid curve.

Commentary by Dr. Valentin Fuster
2005;():871-879. doi:10.1115/DETC2005-85237.

This paper presents modeling and simulation of a flapping wing micro air vehicle. The overall geometry of this vehicle is based on hummingbirds and large insects. The purpose of this study is to understand the mechanics of flight and to achieve a preliminary design based on simulation results. A quasi-unsteady aerodynamic model is used based on in-house experimental investigation of flapping wing aerodynamics. The simulation results reveal important information regarding the behaviour of the system, that could be used in future designs.

Commentary by Dr. Valentin Fuster
2005;():881-890. doi:10.1115/DETC2005-85242.

A method is proposed for the identification of the inertial parameters of a free-flying robot directly in orbit, using accelerometers. This can serve to improve the path planning and tracking capabilities of the robot, as well as its efficiency in energy consumption. The method is applied to the identification of the base body and of the load on the end-effector, giving emphasis to the experimental design. The problem of the identification of the full system is also addressed in its theoretical aspects. The experience from the Getex Dynamic Motion experiments performed on the ETS-VII satellite have allowed to determine a most suitable model for the identification.

Commentary by Dr. Valentin Fuster
2005;():891-901. doi:10.1115/DETC2005-85269.

Vehicle localization and environment mapping are the most essential parts of the robot navigation in unknown environments. Since the problem of localization in indoor environments is directly related to the problem of online map generation, in this paper a new and efficient algorithm for simultaneous localization and map generation is proposed and novel results for real environments are achieved. This new algorithm interprets and validates the raw sonar measurements in first step, and applies them to the environment map in the next step. There are various adjustable parameters which make the algorithm flexible for different sonar types. This algorithm is efficient and is robust to sonar failure; if sonar does not work properly data can be discarded. These abilities make the algorithm efficient for sonar navigation in flat environments even by poor sonar and odometers perception data. This algorithm has the ability of matching with various types of sonar and even to be used with laser scanner data, whenever each laser scanner data is treated as multiple sonar detections with narrow beam detection patterns.

Commentary by Dr. Valentin Fuster
2005;():903-909. doi:10.1115/DETC2005-85304.

In this paper a new approach to dynamics optimization of rough terrain rovers is introduced. Since rover wheels traction has a significant role in rover mobility, optimization is based on the minimization of traction at rover wheel-ground interfaces. The method of optimization chosen is Genetic Algorithm (GA) which is a directed random search technique along with the usual optimization based on directional derivatives. GA is a suitable and efficient method of optimization for nonlinear problems. The procedure is applied on a specific rough terrain rover called CEDRA-I Shrimp Rover. Dynamical equations are obtained using Kane’s method. Finally, the results are verified by modeling of the rover in ADAMS® software package.

Commentary by Dr. Valentin Fuster
2005;():911-920. doi:10.1115/DETC2005-85337.

This paper presents a systematic approach for the mobility analysis of parallel mechanisms. The method is based on screw theory and the concept of equivalent serial chain. An equivalent serial kinematic chain of a k-legged PKC (parallel kinematic chain) is defined as a serial kinematic chain which has the same twist system and the wrench system as the k-legged PKC. Using the proposed approach, the mobility analysis of a PKC is performed in two steps. The first step is the instantaneous mobility analysis, and the second step is the full-cycle mobility inspection. The first step is dealt with based on screw theory. The second step is performed with the aid of the concept of equivalent serial chain and the types of multi-DOF overconstrained single-loop kinematic chains. The proposed approach is illustrated with several examples.

Commentary by Dr. Valentin Fuster
2005;():921-926. doi:10.1115/DETC2005-85460.

The Denavit-Hartenberg conventions model chains of bodies connected by joints. Originally they were applied to single-loop chains but are now almost universally applied to open-loop serial chains such as robotic manipulators. Unfortunately there are several popular variations of the notation: the original, the distal variant, and the proximal variant. These three cases are compared for their application to serial robots. The proximal variate is advanced as the most notationally transparent for the mechanical analysis of serial manipulators.

Commentary by Dr. Valentin Fuster
2005;():927-938. doi:10.1115/DETC2005-85565.

An effective teaching strategy that integrates computer aided design and programming into a course on mechanism analysis and design is presented. Mechanism analysis is enhanced when coupled with basic programming that allows students to find solutions to more complex systems than would otherwise be possible. Web-based distance learning is part of the class and students also learn how to create these kinds of materials themselves. Students can better understand the course material through an integrated computing environment. By solving mechanism design problems in C/C++, the programming skills gained in the course are widely applicable in other areas of engineering. Ch, a C/C++ interpreter, is used to incorporate programming and mechanism design because of its high-level numerical and graphical plotting capabilities, scripting capability, and a mechanism toolkit with easy and quick animation. A student project is given as an example to show how computers are integrated for effective learning. This teaching strategy has been actively used at UC Davis for several years in an undergraduate course in computer-aided mechanism design.

Commentary by Dr. Valentin Fuster
2005;():939-947. doi:10.1115/DETC2005-84059.

Closed-form direct and inverse kinematics of a new three degree-of-freedom (DOF) parallel manipulator with inextensible limbs and base-mounted actuators are presented. The manipulator has higher resolution and precision than the existing three DOF mechanisms with extensible limbs. Since all of the manipulator actuators are base-mounted; higher payload capacity, smaller actuator sizes, and lower power dissipation can be obtained. The manipulator is suitable for alignment applications where only tip, tilt, and piston motions are significant. The direct kinematics of the manipulator is reduced to solving an eighth-degree polynomial in the square of tangent of half-angle between one of the limbs and the base plane. Hence, there are at most sixteen assembly configurations for the manipulator. In addition, it is shown that the sixteen solutions are eight pairs of reflected configurations with respect to the base plane. Numerical examples for the direct and inverse kinematics of the manipulator are also presented.

Commentary by Dr. Valentin Fuster
2005;():949-955. doi:10.1115/DETC2005-84081.

In the family of lower-mobility (degrees of freedom Nf <6) parallel mechanisms, there is a class of mechanisms whose degrees of freedom equal the number of single-degree-of-freedom pairs in each limb. This paper proposes a novel forward/reverse kinematic analyses method for this class of mechanisms, which can build Nf ×Nf square Jacobian matrix and Nf ×Nf ×Nf cubic Hessian matrix. Thus both forward/reverse velocity and acceleration analyses for this class of mechanisms are derivable. In this method, the formulas for different parallel mechanisms have unified forms and consequently the method is convenient for programming. The more complicated the mechanism is (for instance, the mechanism has more kinematic pairs), the more effective the method is. In the rear part of the paper, a 5-DOF mechanism 3-RCRR is analyzed as an example.

Commentary by Dr. Valentin Fuster
2005;():957-962. doi:10.1115/DETC2005-84117.

An analytic approach and a simulation mechanism for solving position and the workspace of a 3-SPR parallel manipulator are proposed. First, a simulation mechanism of the 3-SPR parallel manipulator and a simulation mechanism of the 3-RPS parallel manipulator are created by using the computer aided geometry constraints and dimension-driving techniques. Second, some analytic formulas are derived for inverse and forward solving position and orientation of the 3-SPR parallel manipulator. Third, some available solutions from multi-solutions during deriving analytic formula are determined, and analytic inverse and forward solutions are verified by using simulation mechanisms. Finally, the workspace of the 3-SPR parallel manipulator is created and three key parameters for determining work space of two kinds of parallel manipulators are solved. Calculation results prove that the position working space of the 3-SPR parallel manipulator is much larger than that of the 3-RPS parallel manipulator, and the orientation workspace of the 3-SPR parallel manipulator is less than that of 3-RPS parallel manipulator.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2005;():963-971. doi:10.1115/DETC2005-84283.

Based on the array representation of loop in topological graph of kinematic chains, this paper proposes two basic loop operations. Their existent conditions and properties of the two operations are also researched. In further loop analysis we discuss the important concepts including the independent loop, canonical degree-sequence and perimeter topological graph. Two Theorems deal with the relationship of loops. Based on above basic theory some important applications are given, such as the isomorphism identification based on the loop set concept, the detection of the rigid sub-chains in a kinematic chain and the type analysis of freedom of kinematic chains.

Topics: Chain
Commentary by Dr. Valentin Fuster
2005;():973-982. doi:10.1115/DETC2005-84353.

Robot Capability Analysis (RCA) is a process in which force/motion capabilities of a manipulator are evaluated. It is very useful in both the design and operational phases of robotics. Traditionally, ellipsoids and polytopes are used to both graphically and numerically represent these capabilities. Ellipsoids are computationally efficient but tend to underestimate while polytopes are accurate but computationally intensive. This article proposes a new approach to RCA called the Vector Expansion (VE) method. The VE method offers accurate estimates of robot capabilities in real time and therefore is very suitable in applications like task-based decision making or online path planning. In addition, this method can provide information about the joint that is limiting a robot capability at a given time, thus giving an insight as to how to improve the performance of the robot. This method is then used to estimate capabilities of 4-DOF planar robots and the results discussed and compared with the conventional ellipsoid method. The proposed method is also successfully applied to the 7-DOF Mitsubishi PA10-7C robot.

Topics: Robots
Commentary by Dr. Valentin Fuster
2005;():983-991. doi:10.1115/DETC2005-84442.

The paper describes a systematic approach to define geometrical and dimensional overconstraint conditions for single-loop kinematic chains of both “banal” and “exceptional” types. The approach is an application of the theory of displacement groups. It presents several interesting features: it can be easily integrated with mobility analysis; it makes use of geometric data local to links and does not require a preliminary mechanism assembly nor a given initial congruent position; it is systematic and can be suitably implemented in a computer code; it suggests where geometrical and dimensional tolerances have to be located; it can be embedded in other group-based approaches, like kinematic synthesis or dynamic analysis. After a brief summary of the properties of displacement groups and their operations, the paper shows how they can be used to formulate systematically the overconstraint conditions in kinematic chains. A computer implementation of the approach is also outlined, and several examples with different complexities are given.

Topics: Chain , Displacement
Commentary by Dr. Valentin Fuster
2005;():993-999. doi:10.1115/DETC2005-84462.

This paper presents the kinematic analyses of a 5-DOF 3-RCRR parallel mechanism. The end-effector of this mechanism can rotate round rotation center and one reference point on it can translate in a plane parallels to the base platform. Since the traditional Kutzbach-Grübler formula is not valid for this mechanism, the modified Kutzbach-Grübler formula and screw theory are used in the mobility analysis. The Duffy’s spherical analytic theory is used in forward/reverse position analyses. In forward/reverse velocity/acceleration analyses, virtual mechanism principle is used to build a virtual parallel mechanism (3-Pv RCRR), which is equivalent to the initial mechanism (3-RCRR) on kinematics if all rates of virtual pairs (Pv ) are set to be zero. At the end, some kinematics curves are presented with a numerical example.

Commentary by Dr. Valentin Fuster
2005;():1001-1007. doi:10.1115/DETC2005-84513.

This paper proposes a new approach for tool tip error estimation for reconfigurable machine tools by linearly adding the module errors represented by a screw in global coordinate. The presented method is ideal for modular structured reconfigurable machine tools since the errors are represented in modules’ coordinate system in coordinate independent screw representation method. The contribution of each error sources is then estimated by linear combination (AKA parallel combination) after the error screws are transformed into the global coordinate system of the machine tools. The presented method is verified through the comparison with the serial matrix multiplication method proposed by Moon et al. [3] Simulations for the above mentioned methods are run and total tool tip errors are compared to study the feasibility of parallel method. The study shows the errors are smaller for parallel combination and both methods have similar trends over the work volume.

Commentary by Dr. Valentin Fuster
2005;():1009-1015. doi:10.1115/DETC2005-84556.

In this paper, the orientation-singularity and orientation capability analyses of the Stewart-Gough manipulator are presented. Based on a particular kind of orientation representation of the manipulator, a polynomial expression of degree thirteen is derived, which represents the orientation-singularity locus of the manipulator at a given position, and examples are given to illustrate the result. The description of the orientation capability of the manipulator and the orientation capability index are discussed. In addition, effects of the geometry parameters of the moving platform, including the central angle, the ratio of the moving platform to the base one and the position of the moving platform on the orientation capability of the manipulator are also presented in this paper.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2005;():1017-1023. doi:10.1115/DETC2005-84637.

A point-line is the combination of a directed line and an endpoint on the line. A pair of point-line positions corresponds to a point-line displacement, which is known to be associated with a set of rigid body displacements whose screw axes are distributed on a cylindroid. Different associated rigid body displacements generally correspond to different distances under Riemannian metrics on the manifold of SE(3). A unique measure of distance between a pair of point-line positions is desirable in engineering applications. In this paper, the distance between two point-line positions is investigated based on the left-invariant Riemannian metrics on the manifold of SE(3). The displacements are elaborated from the perspective of the soma space. The set of rigid body displacements associated to the point-line displacement is mapped to a one-dimensional great circle on the unit sphere in the space of four dual dimensions, on which the point with the minimum distance to the identity is indicated. It is shown that the minimum distance is achieved when an associated rigid body displacement has no rotational component about the point-line axis. The minimum distance, which has the inherited property of independence of inertial reference frames, is referred to as the point-line distance. A numerical example shows the application of point-line distance to a point-line path generation problem in mechanism synthesis.

Commentary by Dr. Valentin Fuster
2005;():1025-1030. doi:10.1115/DETC2005-84698.

An open research question is how to define a useful metric on SE(n) with respect to (1) the choice of coordinate frames and (2) the units used to measure linear and angular distances. We present two techniques for approximating elements of the special Euclidean group SE(n) with elements of the special orthogonal group SO(n+1). These techniques are based on the singular value and polar decompositions (denoted as SVD and PD respectively) of the homogeneous transform representation of the elements of SE(n). The projection of the elements of SE(n) onto SO(n+1) yields hyperdimensional rotations that approximate the rigid-body displacements (hence the term projection metric. A bi-invariant metric on SO(n+1) may then be used to measure the distance between any two spatial displacements. The results are PD and SVD based projection metrics on SE(n). These metrics have applications in motion synthesis, robot calibration. motion interpolation, and hybrid robot control.

Commentary by Dr. Valentin Fuster
2005;():1031-1038. doi:10.1115/DETC2005-84745.

In this paper a new and very efficient algorithm to compute the inverse kinematics of a general 6R serial kinematic chain is presented. The main idea is to make use of classical multidimensional geometry to structure the problem and to use the geometric information before starting the elimination process. For the geometric preprocessing we use the Study model of Euclidean displacements, sometimes called kinematic image, which identifies a displacement with a point on a six dimensional quadric S6 2 in seven dimensional projective space P7 . The 6R chain is broken up in the middle to form two open 3R chains. The kinematic image of a 3R chain turns out to be a Segre-manifold consisting of a one parameter set of 3-spaces. The intersection of two Segre-manifolds and S6 2 yields 16 points which are the kinematic images representing the 16 solutions of the inverse kinematics. Algebraically this procedure means that we have to solve a system of seven linear equations and one resultant to arrive at the univariate 16 degree polynomial. From this step in the algorithm we get two out of the six joint angles and the remaining 4 angles are obtained straight forward by solving the inverse kinematics of two 2R chains.

Commentary by Dr. Valentin Fuster
2005;():1039-1045. doi:10.1115/DETC2005-84788.

A new polynomial solution to the synthesis of the body guided by plane-sphere contacts through six assigned poses will be presented. The proposed procedure starts from a system of seven quadratic compatibility equations in seven unknowns and computes a 10th -degree eliminant without passing through a fictitious polynomial equation with degree greater than ten. In particular, the proposed solution procedure requires the computation of the determinant of a 30×30 matrix that has 20 columns with constant entries and the remaining 10 columns with entries that are linear in one out of the seven unknowns. The entries of this matrix are obtained by simply permuting the coefficients appearing in the compatibility equations. Moreover, it will be shown that, due to the special structure of this matrix, the solution procedure can be reduced further so that it involves only the computation of the determinant of a 10×10 matrix. Finally, the proposed procedure is applied to a real case.

Topics: Chain , Polynomials
Commentary by Dr. Valentin Fuster
2005;():1047-1055. doi:10.1115/DETC2005-84910.

Single loop N-bar linkages that contain one prismatic joint are common in engineering. This paper presents a systematical study on the mobility of this type of mechanism. It is found that this type of mechanisms can be divided into three categories: Class I, Class II and Class III. For each category, the slide reachable range is cut into different regions: Grashofian region, non-Grashofian region and change-point region. At each region, the rotation range of the revolute joint or rotatability of the linkage is able to determine based on Ting’s criteria. The characteristics charts are given to describe the rotatability condition. For active prismatic joint, the input revolute joint(s) is/are dependent in non-Grashofian region but independent in other regions. For passive prismatic joint, the revolvability of input revolute joints is dependent on the offset distance of the prismatic joint. Two special cases are illustrated with four and five bars. Examples are given to demonstrate the presented method able to cover all the cases of N-bar linkages with one or a set of adjoined prismatic joints and N-bar open-loop robotic mechanisms.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2005;():1057-1073. doi:10.1115/DETC2005-84936.

It is well known that the Kutzbach-Grübler criterion fails in computing the mobility of exceptional and paradoxical linkages, these two classes of linkages are sometimes referred to as overconstrained. Recently, the authors [1] developed a new mobility criterion that correctly computes the mobility of trivial and exceptional linkages. In the form presented in [1; 2] the mobility criterion can not compute the mobility of paradoxical linkages. This paper presents an extension of the mobility criterion developed by the authors that allows the computation of the degrees-of-freedom of large classes of paradoxical linkages, the conditions for taking advantage of this extension are revealed. Moreover, a hypothesis for applying this extension to classical paradoxical linkages such as the Bennett and Goldberg linkages is presented. Several examples are used to illustrate the method.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2005;():1075-1081. doi:10.1115/DETC2005-85037.

This paper presents a new method to determine if two task positions used to design a four-bar linkage lie on separate circuits of a coupler curve, known as a “branch defect.” The approach uses the image space of a kinematic mapping to provide a geometric environment for both the synthesis and analysis of four-bar linkages. In contrast to current methods of solution rectification, this approach guides the modification of the specified task positions, which means it can be used for the complete five position synthesis problem.

Commentary by Dr. Valentin Fuster
2005;():1083-1089. doi:10.1115/DETC2005-85240.

Recently, it has been discovered that RF waveguides can be used as onboard wireless sensors for the direct measurements of angular positions of a moving object and that a combination of RF waveguides may be used to measure full spatial angular orientation of the object. This paper deals with the computational issues that arise in resolving the spatial orientation from the measurement data of a set of RF waveguide sensors. The paper presents an algorithm that combines a heuristic search method with the least-squares approach for computing the full orientation of an object. The goal is to develop a general and efficient method for computing spatial orientation from the sensor data of a class of angular position sensors that have smooth sensor profiles.

Topics: Sensors , Computation
Commentary by Dr. Valentin Fuster
2005;():1091-1099. doi:10.1115/DETC2005-85272.

One significant and common trait of a conjugate pair is the occurrence of geometric singularities in the contacting surfaces, which typically prevents the correct meshing of the two contacting parts. These singularities, which have been naturally linked to the concept of “undercutting” in a conjugate pair, are notoriously difficult to determine both formally and computationally. On the other hand, it is surprising that, although the concept of undercutting has been known for a long time, it has not yet been formally defined or studied except for some very specific applications. Consequently, general purpose algorithms for undercutting detection and quantification remain elusive. We argue that detecting points around a singularity appears to be significantly easier than detecting the singularity itself. Thus, we propose that undercutting be unambiguously defined in terms of points in the neighborhood of geometric singularities, which may lead to general computational algorithms to detect and quantify undercutting in a conjugate pair.

Topics: Algorithms
Commentary by Dr. Valentin Fuster

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