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34th Annual Mechanisms and Robotics Conference

2010;():3-9. doi:10.1115/DETC2010-28022.

A lightweight adjustable exoskeleton is designed to exercise human legs of varying size and weights. The exoskeleton is actuated by three DC motors at the hip, knee, and ankle. An experimental setup with motor controllers, power supplies, a controlled board, and a computer is developed for closed loop control. A sliding mode control law is designed and implemented to exercise an articulated mannequin leg. It is shown that the exoskeleton is able to adapt to external forces making it suitable to aid in the human leg rehabilitation process.

Commentary by Dr. Valentin Fuster
2010;():11-17. doi:10.1115/DETC2010-28367.

In the design of robotic manipulators for minimally invasive surgery (MIS), the spherical mechanism is a very important kinematic entity, since it can be used to mimic the constraint that the incision point provides to the surgical tool. In previous research by the authors, a bevel-gear-based spherical manipulator was designed whose actuators could be located on a fixed base link. In this paper, concepts of mechanism equivalency are applied to improving the manipulator design. The guidelines arrived at in this work can inform design of future spherical manipulators, especially those created with surgical tool manipulation in mind.

Commentary by Dr. Valentin Fuster
2010;():19-28. doi:10.1115/DETC2010-28371.

The use of robotics to enhance visualization and tissue manipulation capabilities is contributing to the advancement of minimally invasive surgery (MIS). For the development of surgical robot manipulators, the use of advanced dynamic control is an important aspect at the design stage to determine the driving forces and/or torques which must be exerted by the actuators in order to produce a desirable trajectory of the end effector. Therefore, this study focuses on the generation of inverse dynamic models for a spherical bevel-geared mechanism called CoBRASurge (Co mpact B evel-geared R obot for A dvanced Surge ry), which is used as a surgical tool manipulator. For given typical trajectories of end effectors in clinical experiments, the motion of each element in the mechanism can be derived using the inverse kinematic equations. The driving torques exerted by actuators can be determined according to the presented inverse dynamic formulations. The simulation results of CoBRASurge reveal the nature of the driving torques in spherical bevel-geared mechanisms. Such models can be used for the design of advanced dynamic control systems, including gravity compensation and haptic interfaces for enhanced surgical functionality. In addition, sensitivity analysis of mass contribution has been performed to evaluate the effect of individual elements on the peak driving torques, which provides a solid guideline for the design of the next-generation CoBRASurge prototype. The present dynamic modeling methodology also presents a general dynamic analysis approach for other spherical articulated linkage mechanisms.

Commentary by Dr. Valentin Fuster
2010;():29-36. doi:10.1115/DETC2010-28418.

This paper presents the design of a robotic hand for prosthetic applications. The main characteristic of this robotic hand is its biologically-inspired parallel actuation system, which is based on the behavior/strength space of the Flexor Digitorum Profundus (FDP) and the Flexor Digitorum Superficialis (FDS) muscles. The design separates the strength space of the FDS and FDP muscles into a lighter strength region where finer manipulation and general approach tasks are executed, and a higher strength region where the more robust grasps are achieved. Two parallel actuator types and kinematic structures are designed to complement the requirements of both strength space regions. This unique structure is intended to be driven by electromyographical (EMG) signals captured at the surface of the skin. The direct relation between signal and actuation system lends itself well to interpreting the EMG signals from the FDP and FDS muscles into effective task execution, with the goal of helping the user to achieve a good approximation of the full capabilities associated with the human hand, without compromising strength, dexterity, appearance, or weight; which are common issues associated with prosthetic hands.

Commentary by Dr. Valentin Fuster
2010;():37-46. doi:10.1115/DETC2010-28476.

This paper presents modeling of a novel compliant spinal implant designed to reduce back pain and restore function to degenerate spinal disc tissues as well as provide a mechanical environment conducive to healing of the tissues. Modeling was done through the use of the pseudo-rigid-body model. The pseudo-rigid-body model is a 3 DOF mechanism for flexion-extension (forward-backward bending) and a 5 DOF mechanism for lateral bending (side-to-side). These models were analyzed using the principle of virtual work to obtain the force-deflection response of the device. The model showed good correlation to finite element analysis and experimental results. The implant may be particularly useful in the early phases of implant design and when designing for particular biological parameters.

Commentary by Dr. Valentin Fuster
2010;():47-55. doi:10.1115/DETC2010-28500.

A great number of kinematic, kinetostatic and dynamic models of human diarthrodial joints, such as the hip, the knee and the ankle, have been presented in the literature. On the contrary, comprehensive models of the lower limb are lacking and often oversimplify its anatomical structures by considering only 2D motion. This paper will focus on the 3D kinematic model of the articulation that involves four bones: the tibia, fibula, talus and calcaneus. In particular, a new spatial equivalent mechanism with one degree of freedom is proposed for the passive motion simulation of this anatomical complex. The geometry of the mechanism is based on the main anatomical structures of the complex, namely the talus, the tibia and the fibula bones at their interface, on the main ligaments of the ankle joint, and on the interosseus membrane of the leg. An iterative refinement process is presented, that provides the optimal geometry of the mechanism which allows the best fitting of simulation versus measurement data. Simulation results show the efficiency of the proposed mechanism that is believed to play an important role for future developments of models of the whole human lower limb.

Topics: Motion
Commentary by Dr. Valentin Fuster
2010;():57-67. doi:10.1115/DETC2010-28513.

Physical and aerodynamic characteristics of the bird in flight may offer benefits over typical propeller or rotor driven miniature air vehicle (MAV) locomotion designs in certain types of scenarios. A number of research groups and companies have developed flapping wing vehicles that attempt to harness these benefits. The purpose of this paper is to report different types of flapping wing designs and compare their salient characteristics. For each category, advantages and disadvantages will be discussed. The discussion presented will be limited to miniature-sized flapping wing air vehicles, defined as 10–100 grams total weight. The discussion will be focused primarily on ornithopters which have performed at least one successful test flight. Additionally, this paper is intended to provide a representation of the field of current technology, rather than providing a comprehensive listing of all possible designs. This paper will familiarize a newcomer to the field with existing designs and their distinguishing features. By studying existing designs, future designers will be able to adopt features from other successful designs. This paper also summarizes the design challenges associated with the further advancement of the field and deploying flapping wing vehicles in practice.

Commentary by Dr. Valentin Fuster
2010;():69-80. doi:10.1115/DETC2010-28519.

Successful realization of a flapping wing micro air vehicle (MAV) requires development of a light weight drive mechanism converting the rotary motion of the motor into flapping motion of the wings. Low weight of the drive mechanism is required to maximize the payload and battery capacity. In order to make flapping wing MAVs attractive in search, rescue, and recovery missions, they should be disposable from the cost point of view. Injection molded compliant drive mechanisms are an attractive design option to satisfy the weight, efficiency and cost requirements. In the past, we have successfully used multi-piece molding to create mechanisms utilizing distributed compliance for smaller MAVs. However, as the size of the MAV increases, mechanisms with distributed compliance exhibit excessive deformation. Therefore localizing rather than distributing the compliance in the mechanism becomes a more attractive option. Local compliance can be realized through multimaterial designs. A multi-material injection molded mechanism additionally offers reduction in the number of parts. This paper describes an approach for determining the drive mechanism shape and size that meets both the functional design and multi-material molding requirements. The design generated by the approach described in this paper was utilized to realize a flapping wing MAV with significant enhancements in the payload capabilities.

Commentary by Dr. Valentin Fuster
2010;():81-90. doi:10.1115/DETC2010-28631.

Over-automated equipments and modern city life style lead to the diminishing opportunities for muscle using; however, the comfortable life is not always good for human health, and appropriate muscle training can not only enhance muscular strength and endurance but improve the health and fitness. Different kinds of ideas have been proposed for muscle training by exercise machines, which control direction of resistance for safety sake but isolate specific muscle groups to be trained. Compared with machines, free-weight exercise is a whole-body training in which human limbs can be moved on different planes to train more muscle groups. In this study, an upper limb exoskeleton design is proposed for free-weight exercise to strengthen the principal muscles of upper limb and shoulder. The upper limb exoskeleton is constituted of 3-DOF shoulder joint and 1-DOF elbow joint. The joint torques of shoulder and elbow joint of the exoskeleton match the objective joint torques from a model of free-weight exercise. The principal muscles of human arm and shoulder are training by dumbbell lateral raise, dumbbell frontal raise, dumbbell curl motion, and overhead triceps extension motion. With the arrangement of small-inertia springs, the exoskeleton is capable of preventing the muscle from injuries caused by the huge inertia change. The evaluation of the model was conducted by using isokinetic dynamometer to measure shoulder abduction-adduction, shoulder flexion-extension, and elbow flexion-extension for the male and female adults, and the results matched with the data obtained from the derived model.

Topics: Wounds
Commentary by Dr. Valentin Fuster
2010;():91-99. doi:10.1115/DETC2010-28681.

Recently, there has been a growing body of research that supports the effectiveness of using non-pharmacological cognitive and social training interventions to reduce the decline of or improve brain functioning in individuals suffering from cognitive impairments. However, implementing and sustaining such interventions on a long-term basis is difficult as they require considerable resources and people, and can be very time-consuming for healthcare staff. The objectives of our research are to validate the effectiveness of these training interventions and make them more accessible to healthcare professionals through the aid of robotic assistants. Our work focuses on designing a human-like socially assistive robot, Brian 2.0, with abilities to recognize and identify human affective intent to determine its own appropriate emotion-based behavior while engaging in natural and believable social interactions with people. In this paper, we present the design of a novel human-robot interaction (HRI) control architecture for Brian 2.0 that allows the robot to provide social and cognitive stimulation in person-centered cognitive interventions. Namely, the novel control architecture is designed to allow a robot to act as a social motivator by encouraging, congratulating and assisting a person during the course of a cognitively stimulating activity. Preliminary experiments validate the robot’s ability to provide assistive interactions during a HRI-based person-directed activity.

Topics: Robots , Design
Commentary by Dr. Valentin Fuster
2010;():101-106. doi:10.1115/DETC2010-28687.

The paper presents an ongoing project aiming to build a robot, composed of Assur tensegrity structures, that mimics the caterpillar locomotion. Caterpillars are soft bodied animals capable of making complex movements with an astonishing fault-tolerance. In this model, a caterpillar segment is represented as a 2D tensegrity triad, consists of two cables and a linear actuator which are connected between two bars. The unique engineering properties of Assur tensegrity structures which were mathematically proved only this year, together with the suggested control algorithm share several analogies with the biological caterpillar. It provides each triad with an adjustable structural softness. Therefore, the proposed robot has a fault-tolerance and can adjust itself to the terrain roughness. This algorithm also reduces the control demands of the non-linear model of the triad by enabling simple motion control for the linear actuator and one of the cables, while the other cable is force controlled.

Commentary by Dr. Valentin Fuster
2010;():107-114. doi:10.1115/DETC2010-28688.

The multi-fingered metamorphic hand discussed in this paper is a robotic hand that allows complex and accurate kinematic and dynamic movement of all its elements. The novelty lies in the metamorphic palm that increases dexterity of the hand to grasp complex shapes. Although the hand is actuated through a wired control real-time system, a need for a better, modular and user friendly control interface is required, especially when all hand elements are expected to move simultaneously and grasp various objects. This paper introduces a control interface based on wireless Bluetooth remote connection. Whereby, wireless control is implemented by means of a game controller known as the “Wii-remote”, and a supplement of that controller known as the “Nunchuck”, with emphasis on controlling the novel metamorphic palm by mimicking the movement of the human hand whilst holding the Wii-remote controller. The paper will also highlight distinctive features of the controller along with suggested developments and sensor feedback improvements.

Commentary by Dr. Valentin Fuster
2010;():115-123. doi:10.1115/DETC2010-28710.

This paper presents the kinematic design of a thumb metacarpal for a cable-driven anthropomorphic robotic hand. The general problem of finding the position and orientation of an axis around which a given vector is rotated from a position to another is first assessed. A particular case of this problem follows, in which the final direction of the vector has to be in opposition to the initial one, as for the adduction-opposition movement of the thumb. The configuration of the transmission system for the flexor tendon of the thumb is then established. This allows the calculation of the position and orientation of the deflecting pulley in the metacarpal, followed by the evaluation of the trajectory of the pulley system. Finally, a prototype of the thumb metacarpal is presented.

Topics: Design , End effectors
Commentary by Dr. Valentin Fuster
2010;():125-134. doi:10.1115/DETC2010-28759.

The primary objective of this project is to design, fabricate, and test a small, integrated camera system for aiding in the visualization and surgical repair of ventricular septal defects (VSDs), or holes in the heart wall, in pediatric patients. Currently, a less invasive device to view VSDs from the left ventricle of the heart does not exist. This left perspective is ideal for obtaining an unobstructed view of the VSD. The proposed VSD camera device would also provide a platform for passing a suture through the hole in the septal wall, with future work implementing additional tools capable of more advanced tasks. This camera device will help solve some of the major issues currently associated with both cardiac imaging and surgical intervention of VSDs by providing a minimally invasive camera platform for viewing VSDs from the left ventricle. This paper examines the design development and preliminary evaluation of a proof of concept device. Included are preliminary results of image quality comparisons and design details of a pediatric-specific VSD camera device.

Commentary by Dr. Valentin Fuster
2010;():135-144. doi:10.1115/DETC2010-28769.

Despite revolutionary advances in many fields of medicine, there are no active mobile in vivo devices commercially available, or in use, today. Several research groups are actively looking at a number of mobility methods in a number of lumens, but little commercial work has been done. While robotic surgery is available today thanks to robots such as the da Vinci surgical system, these methods are very expensive, require heavy external equipment, and are still constrained by entry incisions. An alternative approach may be to place the robot completely inside the patient. Such devices may enable non-invasive imaging and diagnostics. These devices may be significantly less expensive than current minimally invasive methods, without extensive support equipment, which may allow them to be also used routinely in the ER/trauma sites and remote locations. This paper explores using mobile capsule crawlers inside the body. Preliminary designs are discussed, and current research efforts into providing contact locomotion using micro-tread tracks are explored including initial drawbar force generation experimental results.

Topics: Force , Robots , Robotics , Surgery , Imaging
Commentary by Dr. Valentin Fuster
2010;():145-154. doi:10.1115/DETC2010-28843.

The heart motion is the main hindrance to the development of recent less invasive surgical techniques in the cardiac field. The problem can be partially solved by maintaining the intervention area with stabilizers but the remaining displacements are still important. We propose a device able to exert a torque on the stabilizer in order to compensate for heart action in real time. The system is based on gyroscopic actuation associated with acceleration sensing which allows to free from grounding constraints. In this paper we present first the system architecture and its mechanical model. We describe afterward the prototype design and the experimental setup. Then we detail the control strategy which includes a Kalman filter dedicated to the observation of both the state and the disturbance signals. Several control laws are compared based on disturbance compensation and static feedforward, taking into account gyroscopic actuation specificities. Finally these controls are tested in simulation on a more detailed model.

Topics: Design
Commentary by Dr. Valentin Fuster
2010;():155-164. doi:10.1115/DETC2010-28933.

Considering the many advantages of underactuation in anthropomorphic hands, such as lightness, ease of control and compactness, it is of interest to develop mechanisms that aim at achieving underactuation between the fingers. This paper presents several tendon-driven underactuated mechanisms that can drive four outputs from one input. These mechanisms could typically be used to drive four fingers of an underactuated hand from a single input. Among these mechanisms, some are built by combining one-input/two-output differential mechanisms, while others are fully integrated systems of pulleys. For each mechanism, a static analysis is presented. Then, a discussion based on the static analysis and experimentation on models highlights their strengths and weaknesses. Finally a new anthropomorphic hand used as an experimental platform to test these mechanisms is introduced.

Commentary by Dr. Valentin Fuster
2010;():165-174. doi:10.1115/DETC2010-28965.

In order to overcome the limits due to the fact that homogeneous layers of soft material placed over robotic limbs behave differently with respect to biological models, this paper suggests the adoption of soft covers (pads) with differentiated structure. In particular, it is proposed to divide the allowable pad thickness into two layers: a continuous external layer (skin) and a discontinuous internal layer, so that the overall stiffness can be adjusted by properly shaping the discontinuous layer. The methodology adopted for designing the internal layer is composed of two steps. Firstly, the cover surface is conceptually split into finite elementary triangular sub-regions. Secondly, the internal layer of each triangular element is designed in order to replicate the shape of the non-linear compression law which is typical of endoskeletal structures covered by pulpy tissues. A series of symmetrically-disposed inclined micro-beams is used for the purpose. Once the compression law of each triangular element is known, the overall pad compliance can be modulated by correctly choosing the number and size of the elements composing the pad. Equipment and results of a combined experimental and numerical analysis (FEM) are presented. The results confirm that the proposed concept can be an effective solution when designing soft covers whose behavior need to match the compliance of the biological counterpart. As an example, artificial pads which mimic the human finger behavior are presented.

Topics: Design , Robotics
Commentary by Dr. Valentin Fuster
2010;():175-184. doi:10.1115/DETC2010-29004.

With the goal of improving the performance of underactuated robotic hands in grasping, we investigate the influence of the underlying coupling mechanism on the robustness of underactuated hands to external disturbance. This paper identifies unique behaviors in the hand’s response as a function of the coupling mechanism and the actuation mode the hand is operated in. Specifically, we show that in conditions when the actuator position is fixed, hands with single-acting mechanisms exhibit a bimodal behavior in contrast to hands with double-acting mechanisms that exhibit a unimodal behavior. We then present an analysis of how these behaviors influence grasping capability of the hand and then discuss implications for underactuated hand design and operation.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2010;():185-191. doi:10.1115/DETC2010-29060.

The Atlantic razor clam (Ensis directus) reduces burrowing drag by using motions of its shell to fluidize a thin layer of substrate around its body. We have developed RoboClam, a robot that digs using the same mechanisms as Ensis, to explore how localized fluidization burrowing can be extended to engineering applications. In this work we present burrowing performance results of RoboClam in two distinctly different substrates: ideally granular 1mm soda lime glass beads and cohesive ocean mudflat soil. Using a genetic algorithm to optimize RoboClam’s kinematics, the machine was able to burrow in both substrates with a power law relationship between digging energy and depth of n = 1.17. Pushing through static soil has a theoretical energy-depth power law of n = 2, which means that Ensis-inspired burrowing motions can provide exponentially higher energy efficiency. We propose a theoretical constitutive model that describes how a fluidized region should form around a contracting body in virtually any type of saturated soil. The model predicts fluidization to be a relatively local effect, extending only two to three characteristic lengths away from the body, depending on friction angle and coefficient of lateral earth pressure, two commonly measured soil parameters.

Commentary by Dr. Valentin Fuster
2010;():193-202. doi:10.1115/DETC2010-28036.

This work addresses the problem for determining the position and orientation of an object with regular polygon suspended from n cables with the same length when the n robots form a regular polygon on the horizontal plane. First, an analytic algorithm based on resultant elimination is presented to determine all possible equilibrium configurations of the planar 4-bar linkage. As the nonlinear system can be reduced to a polynomial equation in one unknown with a degree 8, this algorithm is more efficient than numerical search algorithms. Then, considering that the motion of the 3D cable system in its vertical planes of symmetry can be regarded as the motion of an equivalent planar 4-bar linkage, the proposed algorithm is used to solve the direct kinematic problem of objects suspended from multiple cables. Then, case studies with three to six cables are conducted for demonstration. Finally, experiments are conducted for validation.

Topics: Kinematics , Cables
Commentary by Dr. Valentin Fuster
2010;():203-212. doi:10.1115/DETC2010-28135.

The wrench-closure workspace of parallel cable-driven mechanisms is the set of poses for which any wrench can be produced at the end-effector by a set of a non-negative cable tensions. It is already known that the boundary of the constant-orientation wrench-closure workspace of a planar parallel cable-driven mechanism is composed of segments of conic sections. However, the relationship between the geometry of the mechanism and the types of these conic sections is unknown. This paper proposes a graphical method for determining the types of these conic sections. It is also shown that the proposed method can be applied to find the constant-orientation singularities of a 3-RPR planar parallel robot, since these contours correspond to the boundary segment of the analogous three-cable driven planar parallel mechanism.

Topics: Cables , Mechanisms
Commentary by Dr. Valentin Fuster
2010;():213-222. doi:10.1115/DETC2010-28228.

In this article, the effect of uncertainties in wire connections on the workspace generation of wire-actuated parallel manipulators is investigated. The geometric representations of uncertainties in the attachments points of wires to the base and to the mobile platform are developed. Two methods for workspace generation with uncertainty are presented. The first method is based on the calculation of positive wire tensions derived from the static force/moment balance. The second method is based on the direction of the wire forces applied to the mobile platform, and does not take into account the wire tensions. The proposed methods are applied for the workspace generation of two planar wire-actuated parallel manipulators.

Topics: Wire , Manipulators
Commentary by Dr. Valentin Fuster
2010;():223-232. doi:10.1115/DETC2010-28257.

Tensegrity mechanisms are interesting candidates for high-acceleration robotic applications since their use of cables allows for a reduction in the weight and inertia of their mobile parts. In this work, a planar two-degree-of-freedom translational tensegrity mechanism that could be used for pick and place applications is introduced. The mechanism uses a strategic actuation scheme to generate the translational motion as well as to ensure that the cables remain taut at all times. Analytical solutions to the direct and inverse kinematic problems are developed and the mechanism’s workspace boundaries are computed in both the actuator and Cartesian spaces. The influence of the mechanism’s geometry on the size and shape of the Cartesian workspace are then studied. Based on workspace size only, it is found that the optimal mechanism geometry corresponds to a relatively large ratio between the length of the struts and the width of the base and end-effector.

Commentary by Dr. Valentin Fuster
2010;():233-241. doi:10.1115/DETC2010-28292.

In this paper, we advance a methodology for obtaining the statics solution of lumped mass cable system. The method presented here is general enough for most cable configurations (slack or taut), and works well for a broad range of cable elasticity. The forces considered acting on the cable are due to elasticity, weight, buoyancy and aero/hydrodynamics. A shooting method is used to generate the statics solution for the lumped mass model and thus find the equilibrium position of all the cable nodes. This approach converges onto a solution more efficiently compared to other conventional approaches. In particular, for the two-dimensional problem, the solution is obtained from a set of two equations, regardless of how fine the cable discretization is.

Topics: Cables
Commentary by Dr. Valentin Fuster
2010;():243-252. doi:10.1115/DETC2010-28366.

In the work presented, the optimal trajectory planning in wire-actuated parallel manipulators in the presence of an obstacle is investigated. The kinematics and dynamics of a wire-actuated parallel manipulator considering the elasticity and damping effects of wires are described. The redundancy resolution of planar wire-actuated parallel manipulators is investigated at the torque level in order to perform desirable tasks to minimize the effect of impact, while maintaining positive tension in each wire. A local optimization routine is used in the simulation to minimize the tension in the wires while modifying the trajectory of the mobile platform and maintaining positive wire tensions. During collision, the tension in the wires is optimized to reduce the effect of impact, and after collision, the trajectory is modified and the wire tensions are minimized in order to avoid collision for the remainder of the trajectory. The effectiveness of the presented approach is studied through a simulation of an example planar wire-actuated manipulator.

Commentary by Dr. Valentin Fuster
2010;():253-260. doi:10.1115/DETC2010-28374.

In the work presented, the complete form of stiffness of planar wire-actuated parallel manipulators is formulated. The differential form of the static force and moment equations is used to formulate the symmetric stiffness matrix of the manipulator. Stiffness maps over the workspace of manipulators about and along different directions are developed and the effect of wire failure on the stiffness maps is investigated. Some strategies for retrieving the lost stiffness after the wire failure are discussed. The effects of the presented strategies on stiffness maps over the workspace of example planar wire-actuated manipulators are presented.

Commentary by Dr. Valentin Fuster
2010;():261-270. doi:10.1115/DETC2010-28405.

In most studies on parallel cable-driven robots, cables are supposed to be massless and inextensible. However, in the case of large dimension robots, cable mass and elasticity cannot be neglected anymore. Based on a well-known cable static model which takes these characteristics into account, the formulation of the inverse kinematics of n cable/n-DOF cable-driven robots is presented. The consequences of this modeling on the usual static workspace definition is then discussed. Notably, as the tension in a cable is not constant, the maximal tension along the cable has to be found. An example of a planar 3 cable/3-DOF robot is used to highlight that, in some particular poses, the mobile platform can be in static equilibrium while some cables are hanging below the platform. Finally, new limiting factors for the definition of the static workspace are introduced and applied to the same planar robot example which shows the significance of taking into account cable mass and elasticity.

Topics: Dimensions , Robots , Cables
Commentary by Dr. Valentin Fuster
2010;():271-280. doi:10.1115/DETC2010-28424.

A novel architecture of planar spring-loaded cable-loop-driven parallel mechanism is introduced in this paper. By attaching springs to the cable loops, two degrees of freedom can be controlled using only two actuators. In this mechanism, spools are eliminated. Therefore, it is expected that the accuracy of this mechanism is improved compared with conventional cable-driven mechanisms making use of spools. The mechanism can be actuated using either linear sliders or rotary actuators driving the motion of a cable or belt. This paper presents the inverse kinematics and the static equilibrium equations for the new architecture. It is verified that the cables and the springs can be kept in tension within the workspace. Results of numerical simulations are also given.

Commentary by Dr. Valentin Fuster
2010;():281-290. doi:10.1115/DETC2010-28718.

SCARA-type manipulators are widely used in industry. SCARA motions can be produced by serial SCARA arms or by Cartesian rail-mounted mechanisms, such as in overhead cranes. This paper focusses on the latter mechanisms which are referred to here as Cartesian SCARA-type manipulators. When such mechanisms are actuated, the motors are generally moving, which increases the inertia of the system. In this paper, several closed-loop cable/belt routings are proposed in order to allow the actuation of Cartesian SCARA-type manipulators from four actuators fixed to the ground. Then, the kinematic analysis of these routings is performed, which reveals that decoupled actuation is possible and leads to great advantages regarding the power needed. Finally, preferred routings are selected and an example of application is given.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2010;():291-299. doi:10.1115/DETC2010-28733.

This paper presents an analysis of a planar tensegrity-based mechanism. In this study, a moving body is joined to ground by four compliant leg connectors. Each leg connector is comprised of a spring in series with an adjustable length piston. Two problems are solved in this paper. In the first, the values of the four spring constants and free lengths are given and the lengths of the four pistons are determined such that: (1) the top body is positioned and oriented at a desired pose; (2) the top body is at equilibrium while a specified external wrench is applied; and (3) the total potential energy stored in the four springs equals some desired value. In the second problem, the values for the four spring free lengths are given and the values for the four spring constants and the lengths of the four pistons are determined such that conditions (1) and (2) from above are met and also the instantaneous stiffness matrix of the top body equals a specified set of matrix values. The paper formulates the solutions of these two problems. Numerical examples are presented.

Commentary by Dr. Valentin Fuster
2010;():301-307. doi:10.1115/DETC2010-28798.

A novel design of a semi-active variable stiffness element is proposed, with possible applications in vibration isolation. Semi-active vibration isolators usually use variable dampers. However, it is known from the fundamental vibration theory that a variable spring can be far more effective in shifting the frequencies of the system and providing isolation. Geometry change is a common technique for building variable springs, but has disadvantages due to the complexity of the required mechanism, and slow response due to the inertia of moving parts. In the variable spring introduced here (VS), the stiffness is changed by force control in the links which corresponds to infinitesimal movements of the links, and does not need a change of geometry to provide a change of stiffness. This facilitates a fast response. The proposed VS is a simple prestressed cable mechanism with an infinitesimal mechanism. Theoretically the level of the prestress in the cables can be used to control the stiffness from zero to a maximum value that is only limited by the strength of the links. In this work, the statics, kinematics and stability of the VS are studied, the stiffness is formulated, and possible configurations of the VS are found.

Commentary by Dr. Valentin Fuster
2010;():309-318. doi:10.1115/DETC2010-28863.

This paper presents the kinematic and pseudostatic analyses of a fully cable-actuated robotic lumbar spine (RLS) which can mimic in vivo human lumbar spine movements to provide better hands-on training for medical students. The design incorporates five active lumbar vertebrae between the first lumbar vertebra and the sacrum, with dimensions of an average adult human spine. Medical schools can benefit from a tool, system, or method that will help instructors train students and assess their tactile proficiency throughout their education. The robotic lumbar spine has the potential to satisfy these needs in palpatory diagnosis. Medical students will be given the opportunity to examine their own patient that can be programmed with many dysfunctions related to the lumbar spine before they start their professional lives as doctors. The robotic lumbar spine can be used to teach and test medical students in their capacity to be able to recognize normal and abnormal movement patterns of the human lumbar spine under flexion-extension and lateral bending. This project focus is on palpation, but the spine robot could also benefit surgery training/planning and other related biomedical applications.

Commentary by Dr. Valentin Fuster
2010;():319-327. doi:10.1115/DETC2010-29153.

High-performance robust controller design for nonlinear uncertain dynamical systems such as cable-driven parallel robot manipulators is a challenging work. In this paper, a new and systematic approach to combine sliding mode control, adaptive control design techniques and PID control for tracking control of cable-driven parallel robot manipulators, in the presence of model uncertainties is presented. In the proposed method, structured (parametric) and unstructured (un-modeled) uncertainties are lumped into one term and one uncertain parameter (term) is considered corresponding to each degrees of freedom of robot manipulator. Therefore, the problem of computation burden and large number of parameters, which are not addressed in the literature, is solved to a large extent. The global uniform ultimate boundedness stability is obtained in the presence of fast time-varying uncertainties. The simulation and experimental results revealed that the proposed method is robust against uncertainties and its simplicity makes the approach attractive for industrial applications.

Commentary by Dr. Valentin Fuster
2010;():329-340. doi:10.1115/DETC2010-28046.

A new distributed-compliance module, which can be used as a building block, is proposed at first. A novel 3-DOF compliant parallel mechanism (CPM) and its improved configuration for large range of translation are then proposed using the new building blocks. The analytical models of the spatial modules and 3-DOF translational CPMs are then presented and analyzed. The proposed improved 3-DOF translational CPM has the following merits: (1) It is approximately decoupled and has a workspace of 0.1Lmm×0.1Lmm×0.1Lmm (L: the beam length in the module) with constrained parasitic error, maximal actuation isolation and minimal lost motion. (2) Its configuration is simple and compact, and it is actuated by three linear actuators directly. (3) The normalization strategy not only simplifies the representation and derivation of the equations, but also makes the compliance matrix reflect the displacement associated with each degree of freedom in a straightforward manner. The proposed analytical model for the improved 3-DOF CPM has been verified using FEA.

Commentary by Dr. Valentin Fuster
2010;():341-353. doi:10.1115/DETC2010-28071.

Static balance can be applied to improve energy efficiency of mechanisms. In the field of static balancing, a lack of knowledge and design methods exists that are capable of dealing with torsional stiffness. This paper presents a design approach for statically balanced mechanisms, with the focus on mechanisms with torsional stiffness. The approach is graphical of nature and it is based on the requirement of constant potential energy. The first achievements of the presented approach are presented as five conceptual designs of four different types of mechanisms. One of them is developed further into a prototype, which has been tested. The prototype has a correlation coefficient of 0.96 and a normalized mean squared error of 0.12 with respect to the mechanical model of the conceptual design.

Topics: Torsion , Stiffness
Commentary by Dr. Valentin Fuster
2010;():355-363. doi:10.1115/DETC2010-28127.

Many existing problems in conventional prosthetic fingers are related to the use of rigid links and kinematic joints and to the lack of adaptability of the finger. In this paper these problems are addressed by proposing a new design of a fully compliant underactuated prosthetic finger. First a general topology was defined. Subsequently a Pseudo Rigid Body method was used for a type synthesis and rough dimensional analysis in order to determine the conceptual design. In order to evaluate the grasping behavior of the conceptual design, four mock-ups were created. Detailed dimensional design was performed by a semi-automatic numerical analysis using a finite element method. A prototype based on this final design was manufactured and experimentally evaluated. It was found that the combination of underactuation and compliance is promising for the design of simple adaptive prosthetic fingers. As a result of the design process and the use of a predefined structure a fully compliant under-actuated finger with a monolithic structure and largely distributed compliance was obtained. The design shows potential of being applied in the field of prosthetics as well as robotic graspers.

Topics: Design
Commentary by Dr. Valentin Fuster
2010;():365-374. doi:10.1115/DETC2010-28150.

Hybrid discretization model for topology optimization of compliant mechanisms is introduced in this paper. The design domain is discretized into quadrilateral design cells. Each design cell is further subdivided into triangular analysis cells. This hybrid discretization model allows any two contiguous design cells to be connected by four triangular analysis cells no matter they are in the horizontal, vertical or diagonal direction. Topological anomalies such as checkerboard patterns, diagonal element chains and de facto hinges are completely eliminated. In the proposed topology optimization method, design variables are all binary and every analysis cell is either solid or void to prevent grey cell problem that is usually caused by intermediate material states. Von Mises stress constraint is directly imposed on each analysis cell to make the synthesized compliant mechanism safe. Genetic algorithm is used to search the optimum and avoid the need to choose the initial guess solution and conduct sensitivity analysis. The obtained topology solutions require no postprocessing or interpretation, and have no point flexure, unsmooth boundary and zigzag member. The introduced hybrid discretization model and the proposed topology optimization procedure are illustrated by two classical synthesis examples in compliant mechanisms.

Commentary by Dr. Valentin Fuster
2010;():375-386. doi:10.1115/DETC2010-28184.

In the past, we have introduced the Beam Constraint Model (BCM), which captures pertinent non-linearities to predict the constraint characteristics of a generalized beam flexure in terms of its stiffness and error motions. In this paper, a non-linear strain energy formulation for the beam flexure, consistent with the transverse-direction load-displacement and axial-direction geometric constraint relations in the BCM, is presented. An explicit strain energy expression, in terms of beam end-displacements, that accommodates generalized loading conditions, boundary conditions, initial curvature, and beam shape is derived. Using the Principle of Virtual Work, this strain energy expression for a generalized beam is employed in determining the load-displacement relations, and therefore constraint characteristics, for flexure mechanisms comprising multiple beams. The benefit of this approach is evident in its mathematical efficiency and succinctness, which is to be expected with the use of energy methods. All analytical results are validated to a high degree of accuracy via non-linear Finite Element Analysis. Furthermore, the proposed energy formulation leads to new insights into the nature of the BCM.

Commentary by Dr. Valentin Fuster
2010;():387-399. doi:10.1115/DETC2010-28185.

Achieving large motion range (> 1 mm) along with nanometric motion quality (< 10 nm), simultaneously, has been a key challenge in nanopositioning systems. Practical limitations associated with the individual physical components (flexure bearing, actuators, and sensors) and their integration, particularly in the case of multi-axis systems, have restricted the range of current nanopositioning systems to about 100 μm. This paper presents a novel physical system layout, with a parallel-kinematic XY flexure mechanism at its heart, that provides a high degree of decoupling between the two motion axes by avoiding geometric over-constraints, provides actuator isolation that allows the use of large-stroke single-axis actuators, and enables a complementary end-point sensing scheme that employs commonly available sensors. These attributes help achieve an unprecedented 10 mm × 10 mm motion range in the proposed nanopositioning system. Having overcome the physical system design challenges, a dynamic model of proposed nanopositioning system is created and verified via system identification methods. In particular, dynamic non-linearities associated with the large displacements of the flexure mechanism and resulting controls challenges are identified. The physical system is fabricated, assembled, and tested to validate its simultaneous large range and nanometric motion capabilities. Preliminary closed-loop test results, which highlight the potential of this new design configuration, are presented.

Topics: Design
Commentary by Dr. Valentin Fuster
2010;():401-408. doi:10.1115/DETC2010-28186.

In this paper, a spatial hybrid motion system is developed that integrates two types of motions through one compliant mechanism: a macro motion driven by a DC servomotor and a micro motion driven by a PZT actuator. A unique feature of the developed hybrid motion system is the elimination of interaction between the macro motion and micro motion. Three issues are addressed in this study: (1) the design principle and implementation of the hybrid motion system; (2) the kinematic analysis and dynamic analysis; and (3) the optimization design of the hybrid motion system. For the micro motion, the five-bar topology of a mechanical amplifier is used to increase amplifying ratio and improve dynamic performance of the system. Finite element analysis results verify the design principle of the parallel architecture for the hybrid motion system.

Topics: Motion , Design , Optimization
Commentary by Dr. Valentin Fuster
2010;():409-418. doi:10.1115/DETC2010-28235.

Polymer-based binary robots and mechatronics devices can lead to simple, robust, and cost effective solutions for Magnetic Resonnace Image-guided (MRI) medical procedures. A binary manipulator using 12 elastically averaged air muscles has been proposed for MRI-guided biopsies and brachytherapies procedures used for prostate cancer diagnostic and treatment. In this design, radially-distributed air muscles position a needle guide relatively to the MRI table. The system constitutes an active compliant mechanism where the compliance relieves the over-constraint imposed by the redundant parallel architecture. This paper presents experimental results for repeatability, accuracy, and stiffness of a fully functional manipulator prototype. Results show an experimental repeatability of 0.1 mm for point-to-point manipulation on a workspace diameter of 80 mm. Manipulator average accuracy is 4.7 mm when based on the nominal (uncalibrated) model and improves to 2.1 mm when using a calibrated model. The estimated stiffness at the end-effector is ∼0.95 N/mm and is sufficient to withstand the needle insertion forces without major deflection. Needle trajectories during state change appear to be primarily driven by the system’s elastic energy gradient. The study shows the manipulator prototype to meet its design criteria and to have the potential of becoming an effective and low-cost manipulator for MRI-guided prostate cancer treatment.

Commentary by Dr. Valentin Fuster
2010;():419-426. doi:10.1115/DETC2010-28329.

This paper presents a new method for the realization of a planar compliant behavior with an elastic mechanism. The mechanisms considered are parallel mechanisms with symmetric geometry. We show that any planar stiffness matrix can be realized using a parallel mechanism with four line springs connected symmetrically. Among the four springs, two are identical parallel springs equidistant from the stiffness center, and the other two identical springs intersect at the stiffness center. A synthesis procedure is presented.

Commentary by Dr. Valentin Fuster
2010;():427-435. doi:10.1115/DETC2010-28351.

The objective of this paper is to design a generic zero stiffness compliant joint. This compliant joint could be used as a generic construction element in a compliant mechanism. To avoid the spring-back behavior of conventional compliant joints, the principle of static balancing is applied, implying that for each position of the joint the total potential energy should be constant. To this end, a conventional balanced mechanism, consisting of two pivoted bodies which are balanced with two zero-free-length springs, is taken as an initial concept. The joint is replaced by a compliant cross-axis flexural pivot and each spring is replaced by a pair of compliant leaf springs. For both parts an analytic model was implemented and a configuration with the lowest energy fluctuation was found through optimization. A FEA model was used to verify the analytic model of the optimized design. A prototype was manufactured and tested. Both the FEA model and the experiment confirm the reduction of the needed moment to rotate the compliant joint. The experiment shows the balanced compliant joint is not completely balanced but the moment required to rotate the joint is reduced by 70%. Thus, a statically balanced compliant generic joint element was designed which bears great promise in designing statically balanced compliant mechanisms and making this accessible to any designer.

Topics: Design , Stiffness
Commentary by Dr. Valentin Fuster
2010;():437-446. doi:10.1115/DETC2010-28388.

A compliant multistable mechanism is capable of steadily staying at multiple distinct positions without power input. Many applications including switches, valves, relays, positioners, and reconfigurable robots may benefit from multistability. In this paper, two new approaches for synthesizing compliant multistable mechanisms are proposed, which enable designers to achieve multistability through the use of a single bistable mechanism. The synthesis approaches are described and illustrated by several design examples. Compound use of both approaches is also discussed. The design potential of the synthesis approaches is demonstrated by the successful operation of several instantiations of designs that exhibit three, four, five, and nine stable equilibrium positions, respectively. The synthesis approaches enable us to design a compliant mechanism with a desired number of stable positions.

Commentary by Dr. Valentin Fuster
2010;():447-454. doi:10.1115/DETC2010-28406.

Compliant mechanisms play an important role in micro mechanical structures for MEMS applications. However, the positive stiffness of these mechanisms remains a significant drawback. This stiffness can be compensated by including a static balancing mechanism (SBM), resulting in a statically balanced compliant micro mechanism (SB-CMM). This paper presents concepts and simulation results of such mechanisms, which could be applied to MEMS (SB-MEMS). Two categories of SB-CMMs are presented for different situations: the balancing force and travel path are either (1) perpendicular to each other, or (2) parallel to each other. The presented concepts provide compliant mechanisms with a finite zero stiffness range at the start or at a further predefined position of the overall mechanism travel range, respectively. The simulation results confirm the validity and performance of the presented concepts, which have been optimized for further evaluation. Incorporation of these concepts can ultimately result in a reliable, smaller, and energy efficient microsystem, having a larger useful travel range.

Commentary by Dr. Valentin Fuster
2010;():455-464. doi:10.1115/DETC2010-28447.

This paper presents a novel straight-line self-guiding statically-balanced mechanism which reflects on the advantages of lumped compliant mechanisms. The forthcoming structural design is conceived with an energy approach for static balancing of mechanisms. In this paper the application and effectiveness of the energy approach as a synthesis tool is validated. Moreover the paper demonstrates the translation from pseudo-rigid body model to lumped compliance in statically-balanced mechanisms. A physical prototype and a finite-element model served to evaluate the conceptual design. Manufacturing techniques are suggested for rapid, light-weight and cost-efficient prototyping. The presented self-guiding mechanism is statically-balanced along its straight-line range of motion while showing stable behavior in other directions.

Commentary by Dr. Valentin Fuster
2010;():465-473. doi:10.1115/DETC2010-28469.

Compliant mechanisms achieve their mobility through the deformation of their members, this means that part of the energy transmitted from the input to the output of the mechanisms will be stored in the mechanisms as strain energy. This energy storage in some cases is not a desired characteristic and a way to solve this problem is by static balancing the behavior of the mechanisms. Here five criteria are presented that can be used in the static balancing of compliant mechanisms. The criteria are combined in a systematic way with design methods for compliant mechanisms as an exercise to find feasible combinations for the development of design methods for statically balanced compliant mechanisms. The feasibility of the combination between criteria and design methods for compliant mechanisms is demonstrated by using rigid body mechanisms with torsion springs, roughly emulating their compliant counterpart.

Commentary by Dr. Valentin Fuster
2010;():475-489. doi:10.1115/DETC2010-28473.

The knowledge related to the synthesis and analysis of compliant mechanisms continues to grow and mature. Building on this growth, a classification scheme has been established to categorize compliant elements and mechanisms in a manner that engineers can incorporate compliance into their designs. This paper demonstrates a design approach engineers can use to convert an existing rigid-body mechanism into a compliant mechanism by using an established classification scheme. This approach proposes two possible techniques that use rigid-body replacement synthesis in conjunction with a compliant mechanism classification scheme. One technique replaces rigid-body elements with a respective compliant element. The other technique replaces a complex rigid-body mechanism by decomposing the mechanism into simpler functions and then replacing a respective rigid-body mechanism with a compliant mechanism that has a similar functionality.

Commentary by Dr. Valentin Fuster
2010;():491-502. doi:10.1115/DETC2010-28474.

An under-actuated or underconstrained compliant mechanism may have a determined equilibrium position because its energy storage elements cause a position of local minimum potential energy. The minimization of potential energy (MinPE) method is a numerical approach to finding the equilibrium position of compliant mechanisms with more degrees of freedom (DOF) than inputs. Given the pseudo-rigid-body model of a compliant mechanism, the MinPE method finds the equilibrium position by solving a constrained optimization problem: minimize the potential energy stored in the mechanism, subject to the mechanism’s vector loop equation(s) being equal to zero. The MinPE method agrees with the method of virtual work for position and force determination for under-actuated 1-DOF and 2-DOF pseudo-rigid-body models. Experimental force-deflection data is presented for a fully compliant constant-force mechanism. Because the mechanism’s behavior is not adequately modeled using a 1-DOF pseudo-rigid-body model, a 13-DOF pseudo-rigid-body model is developed and solved using the MinPE method. The MinPE solution is shown to agree well with non-linear finite element analysis and experimental force-displacement data.

Commentary by Dr. Valentin Fuster
2010;():503-512. doi:10.1115/DETC2010-28517.

In this paper, we study the synthesis of wire flexures to achieve orthogonal motion by using a recently developed screw theory based approach. For a given desired mobility pattern, our goal is to find a system of wire flexures that are simply connected in parallel between the functional stage and the ground. It has been shown that a wire flexure is essentially a pure force or a line screw. An n dof motion space (allowable motion) is realizable if its reciprocal constraint space can be spanned by 6 – n line screws or forces. We first enumerate all possible one to five degree of motion spaces that are formed by motions along the coordinate axes attached on the functional stage. For each of these 34 motion spaces, we apply the screw theory approach to find its reciprocal force space as well as its rank. We conclude that 18 of them are realizable, 4 are realizable only when their pitches have opposite signs and 12 are not realizable. For each of these 34 cases, we provide an example showing the maximum number of independent wire flexures.

Topics: Motion , Wire
Commentary by Dr. Valentin Fuster
2010;():513-521. doi:10.1115/DETC2010-28531.

The maturation of lamina emergent mechanism (LEM) technology allows for incorporation into new products. LEMs are defined by three basic, functional characteristics: they (1) are compliant; (2) are fabricated from planar materials; and (3) emerge from a flat initial state. The associated advantages, design challenges, and design tools of each of these characteristics are described. A discussion of opportunities for LEMs that are enabled by the advantages of the functional characteristics is also included. Technology push product development processes were employed in a LEM workshop where seventeen industry professionals helped identify over 200 potential applications for the technology. The most promising ideas are described for disposable LEMs, novel arrays of LEMs, scaled LEMs, LEMs with surprising motion, shock absorbing LEMs, and deployable LEMs.

Commentary by Dr. Valentin Fuster
2010;():523-531. doi:10.1115/DETC2010-28546.

This paper presents a direct displacement synthesis method for the design of shape morphing skin structures using compliant mechanisms. The objective of this method is to design a skin structure that will deform to a desired final shape when acted on by a specific load. The method utilizes a ground structure geometry which can facilitate variable bending stiffness along the length of the skin using compliant spring members. Synthesis procedures involve the use of direct displacement to determine how the bending stiffness of the skin must vary to produce the desired shape change. The direct displacement synthesis method differs from other compliant mechanism synthesis methods found in literature, such as pseudo-rigid-body and continuum structure optimization, in the approach taken to solve for the unknown variables in the system. By using direct displacement to determine how the structure must respond to a specific load to achieve the desired shape change, the unknown variables within the system can be extracted directly without the use of optimization techniques.

Commentary by Dr. Valentin Fuster
2010;():533-541. doi:10.1115/DETC2010-28672.

Motivated by the authors’ previous study on flexible honeycomb design with negative Poisson’s ratio (NPR) often called ‘auxetic’ [1], more geometric options of hexagonal honeycomb meso-structures are explored with various ratios of the vertical cell length, h to the inclined length, l. While designing an effective shear modulus, e.g., G12 * of 10MPa, of hexagonal honeycombs, we are searching honeycomb geometries. Using an aluminum alloy (7075-T6) as the constituent material, the in-plane linear elastic honeycomb model is employed to get effective shear moduli, effective shear yield strengths and effective shear yield strains of hexagonal honeycombs. The numerical parametric study based on the linear cellular theory is combined with honeycomb design to get the optimal cell geometry associated with a manufacturing limitation. The re-entrant geometry makes 7075-T6 NPR honeycombs flexible, resulting in an effective shear yield strength, (τpl *)12 of 1.7MPa and an effective shear yield strain, (γpl *)12 of 0.17 when they are designed to have a G12 * of 10MPa.

Commentary by Dr. Valentin Fuster
2010;():543-552. doi:10.1115/DETC2010-28783.

The systematic methodologies involved in type synthesis of flexure systems are no doubt helpful to generate one and more high-performance precision machine designs at the stage of conceptual design with a rapid and effective way. This paper provides a systematic formulation of the type synthesis of parallel, serial, and hybrid flexure systems via a mapping from a geometric concept to physical entity. The whole type synthesis principle is built upon screw system theory and the geometric Freedom and Constraint Topology (FACT) approach, also combining with other concepts and methods including equivalent compliance mapping, building block etc, which enables the type synthesis of flexure systems deterministic, simple and practical. After that, Type synthesis procedure for various flexure systems are elaborated with examples. As a result, as many specified-DOF (Degree of Freedom) flexure systems as possible can be found and therefore pave the way for obtaining an optimal configuration.

Commentary by Dr. Valentin Fuster
2010;():553-561. doi:10.1115/DETC2010-28794.

In recent years, the increasing of application requirements call for development of a variety of high-performance (e.g. large-displacement, high-precision) flexible joints. In this paper we demonstrate how to use the proposed methodology for the type synthesis of flexure systems given in the companion paper to synthesize concepts for complex flexible joints. According to the joint characteristics other than other flexure systems, a basic design philosophy and a general type synthesis process for flexible joints are presented firstly. The numerations and type synthesis for four commonly used flexible joint types, i.e. flexible revolute joints (FRJs), flexible translational joints (FTJs), flexible universal joints (FUJs), and flexible spherical joints (FSJs) are investigated in detail. As a result, not only a variety of known flexible joints are systematically surveyed and classified, but also are some new flexible joints developed. The output of this process is the derivation of a multiple of flexible joint concepts that would then be modeled and optimized by existing modeling and analysis methods.

Commentary by Dr. Valentin Fuster
2010;():563-575. doi:10.1115/DETC2010-28810.

Visualizing load flow aids in conceptual design synthesis of machine components. In this paper, we present a mathematical framework to visualize load flow in compliant mechanisms and structures. This framework uses the concept of transferred forces to quantify load flow from input to the output of a compliant mechanism. The key contribution of this paper is the identification a fundamental building block known as the Load-Transmitter Constraint (LTC) set, which enables load flow in a particular direction. The transferred force in each LTC set is shown to be independent of successive LTC sets that are attached to it. This enables a continuous visualization of load flow from the input to the output. Furthermore, we mathematically relate the load flow with the deformation behavior of the mechanism. We can thus explain the deformation behavior of a number of compliant mechanisms from literature by identifying its LTC sets to visualize load flow. This method can also be used to visualize load flow in optimal stiff structure topologies. The insight obtained from this visualization tool facilitates a systematic building block based design methodology for compliant mechanisms and structural topologies.

Commentary by Dr. Valentin Fuster
2010;():577-587. doi:10.1115/DETC2010-28819.

Designers have always conceptualized of load flow as a part of their initial design process for mechanisms and structures. However, the lack of mathematical representation of load flow makes it inappropriate to be included in systematic design processes. Load Transmitter Constraint (LTC) sets provide a mathematical framework for visualizing load paths in compliant mechanisms. In this paper we propose a systematic design methodology for compliant mechanisms by systematic combination of LTC sets. This enables the designer to conceptualize load flow and choose relevant LTC sets to enforce it. Apart from being intuitive this process gives an understanding of the importance of each member in the mechanism. Furthermore this theory enables accurate and deterministic design for given motion specification without the aid of extensive computation. In this paper we propose guidelines for the design of mechanisms with a single load flow path and multi load flow path, particularly relevant in shape morphing applications.

Commentary by Dr. Valentin Fuster
2010;():589-596. doi:10.1115/DETC2010-28834.

The design and analysis of a mechanism with variable stiffness is examined. The mechanism, which is a simple arrangement of two springs, a lever arm and a pivot bar, has an effective stiffness that is a rational function of the horizontal position d of the pivot. The external pure force acting on the system is constrained to always remain vertical. The effective stiffness is varied by changing d while keeping the point of application of the external load constant. The expression for the effective stiffness is derived. A reverse analysis is also carried out on the mechanism. Special design cases are considered. The dynamic equation of the system is derived and used to deduce the natural frequency of the mechanism from which some insights were gained on the dynamic behavior of the mechanism.

Commentary by Dr. Valentin Fuster
2010;():597-605. doi:10.1115/DETC2010-28943.

This paper presents a stability model for predicting the snap-in behavior of electrostatic comb-drive actuators, while taking into account the bearing direction stiffness and error motion of the associated flexure suspension. Error motions typically arise from the flexure suspension kinematics or manufacturing variations. The presented model allows for a more accurate determination of the comb-drive actuator’s motion range, limited by snap-in instability, as well as robustness against this instability over the motion range. Ultimately, this model is used as an effective design tool to help evaluate several existing and new flexure suspension geometries for range and robustness.

Topics: Stability , Actuators , Design
Commentary by Dr. Valentin Fuster
2010;():607-618. doi:10.1115/DETC2010-28953.

The constraint-based design of flexure mechanisms requires a qualitative and quantitative understanding of the constraint characteristics of flexure elements that serve as constraints. This paper presents the constraint characterization of a slender, uniform and symmetric cross-section, spatial beam, which is one of the most basic flexure elements used in three-dimensional flexure mechanisms. The constraint characteristics of interest, namely stiffness and error motions, are determined from the non-linear load-displacement relations of the beam. Appropriate simplifying assumptions are made in deriving these relations so that relevant non-linear effects (load-stiffening, kinematic, and elastokinematic) are captured in a compact, closed-form, and parametric manner. The resulting spatial beam constraint model is shown to be accurate, using non-linear finite element analysis, within a load and displacement range of practical interest. The utility of this model lies in the physical and analytical insight that it offers into the constraint behavior of a spatial beam flexure, its use in 3D flexure mechanism geometries, and fundamental performance tradeoffs in flexure mechanism design.

Commentary by Dr. Valentin Fuster
2010;():619-628. doi:10.1115/DETC2010-28963.

In recent years, the increasing of application requirements call for development of a variety of flexure mechanisms with high precision or large motion and both. Therefore, in Part III of this series of papers we demonstrate how to use the methodology addressed in Part I to synthesize concepts for two kinds of flexure mechanisms, i.e. kinematics-type flexure mechanisms (KFMs) and constraint-type flexure mechanisms (CFMs) with the specified-DOF (Degree of Freedom) characteristics. Although most of them utilize parallel configurations and flexure elements, there is a clear difference in the behavior of flexures between KFMs and CFMs, The resultant type synthesis approaches fall into two distinct categories i.e. freedom-based and constraint-based one, both of which have presented in Part I. In order to derive useful flexure mechanism concepts available for different applications, a general design philosophy and rules are summarized firstly. As the main content of this part, the classifications, numerations, and synthesis for KFMs and CFMs are made in a systematic way. As a result, a majority of new precision flexure mechanisms are developed. In addition, qualitative comparisons are provided to demonstrate the performance and application differences between kinematic-type and constraint-type flexure mechanisms with the same DOF.

Commentary by Dr. Valentin Fuster
2010;():629-635. doi:10.1115/DETC2010-29002.

Robot manipulators having elastic links or flexure joints have a number of advantages, especially in simplifying the control of contact with other objects. However, current simplified parametric models of flexure motion do not accurately predict the behavior of these mechanisms under large deflections. This paper presents a “smooth curvature model” of flexure behavior that describes the curvature of a highly flexible member such as a flexure joint using a basis of three orthogonal polynomials. Using this model, we show that it is possible to predict the planar stiffness these mechanisms, even in cases where the deformation of the hinge is too large for the linear Euler-Bernoulli beam bending model. Using both finite element methods and the much less computationally expensive proposed model, numerical results will demonstrate that it is possible to accurately predict the in-plane compliance of a highly flexible mechanism in the presence of an external load. The results of this work are significant because they demonstrate that the behavior of flexure-based robotic mechanisms can be modeled quickly and with few parameters, enabling their use in closed-loop control for situations where collision safety is a concern, and rigorous model-based path planning for obstacle avoidance, among other applications.

Commentary by Dr. Valentin Fuster
2010;():637-644. doi:10.1115/DETC2010-29017.

This manuscript outlines a novel approach to the design of compliant shape-morphing structures using constraint-based design method. Development of robust methods for designing shape-morphing structures is the focus of multiple current research projects, since the ability to modify geometric shapes of the individual system components, such as aircraft wings and antenna reflectors, provides the means to affect the performance of the corresponding mechanical systems. Of particular interest is the utilization of compliant mechanisms to achieve the desired adaptive shape change characteristics. Compliant mechanisms, as opposed to the traditional rigid link mechanisms, achieve motion guidance via the compliance and deformation of the mechanism’s members. The goal is to design a single-piece flexible structure capable of morphing a given curve or profile into a target curve or profile while utilizing the minimum number of actuators. The two primary methods prevalent in the design community at this time are the pseudo-rigid body method (PRBM) and the topological synthesis. Unfortunately these methods either tend to suffer from a poor ability to generate potential solutions (being more suitable for the analysis of existing structures) or are susceptible to overly-complex solutions. By utilizing the constraint-based design method (CBDM) we aim to address those shortcomings. The concept of CBDM has generally been confined to the Precision Engineering community and is based on the fundamental premise that all motions of a rigid body are determined by the position and orientation of the constraints (constraint topology) which are placed upon the body. Any mechanism motion path may then be defined by the proper combination of constraints. In order to apply the CBDM concepts to the design and analysis of shape-morphing compliant structures we propose a tiered design method that relies on kinematics, finite element analysis, and optimization. By discretizing the flexible element that comprises the active shape surface at multiple points in both the initial and the target configurations and treating the resulting individual elements as rigid bodies that undergo a planar or general spatial displacement we are able to apply the traditional kinematics theory to rapidly generate sets of potential solutions. The final design is then established via an FEA-augmented optimization sequence. Coupled with a virtual reality interface and a force-feedback device this approach provides the ability to quickly specify and evaluate multiple design problems in order to arrive at the desired solution.

Commentary by Dr. Valentin Fuster
2010;():645-654. doi:10.1115/DETC2010-29076.

This paper explored the deflection and buckling of fixed-guided beams. It uses an analytical model for predicting the reaction forces, moments, and buckling modes of a fixed-guided beam undergoing large deflections. One of the strengths of the model is its ability to accurately predict buckling behavior and the buckled beam shape. The model for the bending behavior of the beam is found using elliptic integrals. A model for the axial deflection of the buckling beam is also developed based on the equations for stress and strain and the buckling profile of the beam calculated with the elliptic integral solution. These two models are combined to predict the performance of a beam undergoing large deflections including higher order buckling modes. The force vs. displacement predictions of the model are compared to the experimental force vs. deflection data of a bistable mechanism and a thermomechanical in-plane microactuator (TIM). The combined models show good agreement with the force vs. deflection data for each device. The paper’s main contributions include the addition of the axial buckling model to existing beam bending models, the exploration of the deflection domain of a fixed-guided beam, and the demonstration that nonlinear finite element models may incorrectly predict a beam’s buckling mode unless unrealistic constraints are placed on the beam.

Topics: Buckling , Deflection
Commentary by Dr. Valentin Fuster
2010;():655-664. doi:10.1115/DETC2010-29079.

Each manned space exploration mission requires a significant amount of microgravity or reduced-gravity (physical) simulation before the mission to train astronauts and verify some mission requirements. An appealing new simulation technique for such an application must be effective, safe, and inexpensive. This paper presents a novel design concept of a reduced-gravity simulator for simulating human walking in a controllable reduced-gravity condition. Designed based on the spring-based passive gravity-balancing technology, the 3D passive reduced-gravity simulator has sufficient mobility to allow the attached human to walk while feeling less gravity effects. The system is completely passive and thus, it is intrinsically stable, safe and cost effective. A concept study of the new mechanism using multibody dynamics simulations including a full-scale human dynamics model has demonstrated the effectiveness of the device for offloading any desired amount of gravity force. A scaled-down nonhuman experimental test using a walking robot and a passive jump device is currently underway.

Commentary by Dr. Valentin Fuster
2010;():665-674. doi:10.1115/DETC2010-29109.

Previous versions of the Material Mask Overlay Strategy (MMOS) for topology synthesis have primarily employed circular masks to simulate voids within the design region. MMOS operates on the photolithographic principle by appropriately positioning and sizing a group of negative masks to create voids within the design region and thus iteratively improve the material layout to meet the desired objective. The fundamental notion has been that a group of circular masks can represent a local void of any shape. Thus, circular masks, as opposed to those modeled using simple, non-intersecting, closed curves of generic shapes, have been employed. This paper investigates whether employing masks of more general shapes (e.g., any two-dimensional polygon) offers significant enhancements in efficiently attaining the appropriate topological features in a continuum. Here, performance of two other mask shapes, namely, elliptical and rectangular are compared with that of the circular masks. For fair comparison, two mean compliance minimization examples under resource constraints are solved as each design space is known to contain a unique minimum.

Commentary by Dr. Valentin Fuster
2010;():675-684. doi:10.1115/DETC2010-29113.

A stochastic topology design approach is presented that yields binary, well connected continua. Inspired by the well known photolithographic technique used in the fabrication of micro-components, a number of negative-masks are appropriately laid over the design region to simulate voids. A unique feature is the effective use of the masks. In addition to their position and sizes, the number of circular masks is adaptively determined in each step of the optimization process. Thus, not only the void shapes but also their number is varied. The proposed method is significantly efficient compared to the previous implementations [21] and [23] and requires much less computational effort to yield good solutions. The honeycomb parameterization employed eliminates all subregion connectivity anomalies by ensuring edge connectivity throughout. Boundary smoothening is performed as a preprocessing step to moderate the notches, and to obtain an honest evaluation of a candidate design. Thus, both material and contour boundary interpretation steps are no longer required when post-processing the synthesized solutions. Various features of the method are demonstrated through the synthesis examples of small deformation compliant mechanisms.

Commentary by Dr. Valentin Fuster
2010;():685-694. doi:10.1115/DETC2010-29137.

Linkages are broadly classified as rigid-body, partially and fully compliant, capable of accomplishing a specified kine(tostatic)matic task. Path generating partially compliant linkages can generate prescribed non-smooth paths with high fidelity. Kempe’s linkages too can trace the non-smooth paths. But their complexity makes partially compliant linkages superior in terms of compactness and connectivity. A unified procedure to synthesize a solution set of all path generating linkage kinds is implemented in [1]. While there can be many solutions that can satisfy a given kinematic objective, choosing one may not be straightforward. This work proposes a set of criteria to choose the best linkage design. The proposed criteria are categorized as General and Specific. General criteria are applied to evaluate the solutions for any application whereas Specific criteria pertain to the application at hand. As an example, the solutions are generated for the displacement delimited gripper using the unified procedure. The solutions are then evaluated by the user with respect to these criteria. The solution appraisal is performed using a variant of the Pugh’s decision matrix and thereafter, the best solution is identified.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2010;():695-703. doi:10.1115/DETC2010-29172.

A contact-aided compliant mechanism (CCM) is a single piece flexible continuum that uses the contact interactions between different portions in addition to the elastic deformation. Our work deals with the design of contact aided compliant mechanisms with initially curved frame elements to trace more complex and non smooth paths. We can achieve these kinematic tasks by using partially compliant mechanisms as well. But the presence of hinges is a disadvantage in terms of increased friction, backlash, need for lubrication, noise and vibrations. In this paper, we propose an automated procedure to obtain the optimum design of large deformation CCMs. Through commercial software, we simulate the formation of pseudo hinges at contact sites that get formed dynamically as the mechanism deforms. By appropriately positioning these pseudo hinges, i.e., by designing a suitable CCM, the aim, in general, is to achieve a variety of function, path and motion generation characteristics via single piece continua.

Commentary by Dr. Valentin Fuster
2010;():705-713. doi:10.1115/DETC2010-29190.

This paper discusses the application of Castigliano’s Theorem to a half circular beam intended for use as a shaped, tunable, passively compliant robot leg. We present closed-form equations characterizing the deflection behavior of the beam (whose compliance properties vary along the leg) under appropriate loads. We compare the accuracy of this analytical representation to that of a Pseudo Rigid Body (PRB) approximation in predicting the data obtained by measuring the deflection of a physical half-circular beam under the application of known static loads. We briefly discuss the further application of the new model for solving the dynamic equations of a hexapod robot with a C-shaped leg.

Commentary by Dr. Valentin Fuster
2010;():715-722. doi:10.1115/DETC2010-29230.

This paper introduces a parametric beam model for describing the kinematics and elastic properties of ortho-planar compliant beams subject to specific buckling loads. This model uses an approach similar to the Pseudo-Rigid-Body Model but differs that in a key parameter, the characteristic radius factor, is not a constant, but a rational function of the moment. The rational function coefficients are determined by least squares, along with the statistical significance of the coefficients. Results are calculated for straight beams for two cases: a vertical displacement and a horizontal displacement.

Commentary by Dr. Valentin Fuster
2010;():723-732. doi:10.1115/DETC2010-28020.

This paper presents an approach for velocity and acceleration analyses of lower mobility parallel manipulators. Based on the definition of the acceleration motor, the forward/inverse velocity and acceleration equations are formulated with the goal to integrate the relevant analyses under a unified framework based on the generalized Jacobian. A new Hessian matrix of serial kinematic chains (or limb) is developed in an explicit and compact form using Lie bracket. This idea is then extended to cover parallel manipulators by considering the loop closure constraints. A 3-P RS parallel manipulator with coupled translational and rotational moving capabilities is taken as example to illustrate the generality and effectiveness of this approach.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2010;():733-741. doi:10.1115/DETC2010-28072.

In this paper we present a novel methodology for orientation order analysis of spherical RR dyads. The methodology is a spherical generalization of the recent works of Myszka, Murray, and Schmiedeler for assessing position order of planar RR dyads. The objective of the methodology is to determine if a prescribed fixed axis location for a spherical RR dyad will result in the dyad guiding a moving rigid-body through a set of finitely separated spherical orientations in the desired order (e.g. 1, 2, 3, 4, etc.). First, the prior works on the order analysis of planar RR dyads via the propeller method are briefly reviewed. Next, the planar propeller methodology of Myszka, Murray, and Schmiedeler is extended to yield a spherical hoop methodology. The result is a useful tool to determine if a given spherical RR dyad will guide a moving body through a set of prescribed orientations in the desired order. Finally, we demonstrate the utility of the hoop method for order analysis of spherical RR dyads in three case studies.

Commentary by Dr. Valentin Fuster
2010;():743-752. doi:10.1115/DETC2010-28082.

This paper deals with the formulation of an algebraic algorithm for the kinematic analysis of slider-crank/rocker mechanisms, which is based on the use of geometric loci, as the fixed and moving centrodes, the cubic of stationary curvature and the inflection circle. In particular, both centrodes are formulated in implicit and explicit algebraic forms by using the complex algebra. Moreover, the algebraic curves representing the moving centrodes are also recognized and proven to be Jeřábek’s curves for the first time. Then, the cubic of stationary curvature along with the inflection circle are expressed in algebraic form by using the geometric invariants. Finally, the proposed algorithm has been implemented in a Matlab code and interesting numerical and graphical results are shown along with some particular cases in which the geometric loci degenerate in lines and circles.

Commentary by Dr. Valentin Fuster
2010;():753-762. doi:10.1115/DETC2010-28107.

In this paper, a new methodology for the optimal design of the secondary geometric parameters (shape of links, size of the platform, etc.) of parallel kinematic machine tools is proposed. This approach aims at minimizing the total mass of the robot under position accuracy constraints. This methodology is applied to two translational parallel robots with three degrees-of-freedom (DOF): the Y-STAR and the UraneSX. The proposed approach is able to speed up the design process and to help the designer to find more quickly a set of design parameters.

Commentary by Dr. Valentin Fuster
2010;():763-769. doi:10.1115/DETC2010-28108.

This paper introduces mechanism state matrices as a novel way to represent the topological characteristics of planar reconfigurable mechanisms. As part of this new concept, these matrices will be used as an analysis tool to automatically determine the degrees of freedom (DOF) of planar mechanisms that only contain one DOF joints. The DOF at each state can be combined with a mechanism state matrix to form an augmented mechanism state matrix. A series of examples will be used to illustrate the proposed concept.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2010;():771-781. doi:10.1115/DETC2010-28188.

The identification of motion characteristics and assembly circuits is fundamental in creating a workable mechanism. A circuit defect prevents a mechanism from moving between desired positions. This paper extends the established methods for analyzing multi-degree-of-freedom platforms to gain insight on single-actuated linkages. Specifically, from a plot of the singularity locus projected onto the input joint space, the number of singularities, number of geometric inversions and circuit regimes are revealed. The input/output motion of the linkage can be inferred from the locus. The methodology to produce the singularity locus is general and does not rely on geometric insights of a particular mechanism. By using the locus, desired operational features can be readily identified, such as a fully rotatable crank. Unique motion characteristics, such as a greater than 360° non-rotatable crank, can be also be detected. Further, it is observed that transition linkages serve as bounds between the regions of circuit change.

Topics: Linkages , Circuits
Commentary by Dr. Valentin Fuster
2010;():783-790. doi:10.1115/DETC2010-28189.

The problem of spherical four-bar linkage synthesis is revisited in this paper. The work is aimed at developing a robust synthesis method by taking into account both the formulation and the solution method. In addition, the synthesis of linkages with spherical prismatic joints is considered by treating them as a special case of the linkages under study. A two-step synthesis method is developed, which sequentially deals with equation-solving by a semigraphical approach and branching-detection. Examples are included to demonstrate the proposed method.

Commentary by Dr. Valentin Fuster
2010;():791-800. doi:10.1115/DETC2010-28263.

In this paper, a new 4UP S+PU redundantly actuated parallel manipulator is proposed. This mechanism possesses three degrees of freedom (DOF), one translation and two rotations. Different from general parallel manipulators, a passive leg is connected to both centers of the base and the moving platform to constrain the unwanted motion. The mobility study and inverse kinematic analysis are conducted. The reachable workspace is generated with boundary-searching based discretization method. The local and global performance indices including stiffness and dexterity and their atlas are investigated in details. Comprehensive simulation of kinematics, dynamics and proportional-integral-derivative (PID) position control are implemented based on Adams to evaluate and testify the high operational capacity and well motion characteristics.

Commentary by Dr. Valentin Fuster
2010;():801-810. doi:10.1115/DETC2010-28287.

A motion task can be given in various ways. It may be defined parametrically or discretely in terms of an ordered sequence of displacements or in geometric means. This paper studies a new type of motion analysis problem in planar kinematics that seeks to acquire geometric constraints associated with a planar motion task which is given either parametrically or discretely. The resulting geometric constraints can be used directly for type as well as dimensional synthesis of a physical device such as mechanical linkage that generates the constrained motion task. Methods for kinematic acquisition of geometric constraints bridge the gap between type and dimensional synthesis and provide the foundation for task centered mechanism design.

Topics: Design , Mechanisms
Commentary by Dr. Valentin Fuster
2010;():811-817. doi:10.1115/DETC2010-28308.

The kinematic synthesis of planar motion generators in the presence of an incomplete set of finitely separated poses is the subject of this paper. Given that the planar rigid-body guidance problem in the realm of four-bar linkage synthesis can be solved exactly for up to five prescribed poses of the coupler link, any number of poses smaller than five is considered incomplete in this paper. The poses completing the set are determined so as to produce a robust linkage against variations in the unspecified poses. To this end, a theoretical framework for model-based robust design is invoked and a general methodology for robust kinematic synthesis is laid down. Robustness is needed in this context to overcome the presence of uncertainty due to the selection of the unprescribed poses, which many a time are left up to the mechanism designer’s judgment. To validate the concepts and illustrate the application of the methodology proposed here, an example is included.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2010;():819-827. doi:10.1115/DETC2010-28368.

A new kinematic design methodology is presented for optimization of spherical serial mechanisms. This method integrates multiple criteria (workspace, manipulability, and size) linearly in one objective function. All these criteria are optimized simultaneously to lead to a more realistic solution. By changing the priorities of each criterion, different sets of desirable kinematic performance can be expressed. The global manipulability and the uniformity of manipulability over the workspace are combined in a single index to improve the synthesis results. The optimization result for a spherical bevel-geared mechanism using a genetic algorithm demonstrated that the proposed method effectively improves the quality of the optimum solution and provides insight into the workings of the mechanism. In addition, this flexible and adaptable methodology may also be extended for use in general optimization for linkage synthesis.

Commentary by Dr. Valentin Fuster
2010;():829-838. doi:10.1115/DETC2010-28383.

We perform the dimensional synthesis of a parallel manipulator to be used as a force-feedback device in a virtual reality application for surgeon training in prostate brachytherapy. For such brachytherapy operations, the characteristics of the required workspace point towards the architecture of the linear DELTA robot to be used as the force-feedback device to the surgeon. In this paper, we address the dimensional synthesis of the linear DELTA robot for the prescribed workspace. To this end, we propose the minimum relative kinematic sensitivity as an objective function, a kinematic performance index that is different from most of the commonly used metrics, i.e., manipulability and dexterity. The minimum relative kinematic sensitivity represents the ratio of the minimum to the maximum effect of a unity-bounded set of actuator displacements on the moving-platform pose. These extremum sensitivities are computed independently over the prescribed workspace. Thence, the dimensional synthesis problem consists in finding the robot dimensions that maximize the minimum relative kinematic sensitivity, so it is guaranteed within a narrow interval over the prescribed workspace. This optimization problem is nonconvex, which poses a challenge from the computational point of view. However, because of symmetry in the mechanism and other simplifications, the number of optimization variables is reduced to four. This allows a reasonably fine discretization of the search domain, giving the designers confidence that the ensuing local optimum is close to the global optimum.

Commentary by Dr. Valentin Fuster
2010;():839-850. doi:10.1115/DETC2010-28540.

We present an automated method for type and dimensional synthesis of planar linkage mechanisms. In the kinematic problem, a graph representation called initial graph is given to the parts to move. The type synthesis stage consists of an exhaustive subgraph search of the initial graph inside the graphs taken from a previously enumerated atlas of mechanisms. Each alternative resulting from the type synthesis is dimensioned using the Precision Position Method and Genetic Algorithms: the closed-chain topology is decomposed into single-open chains of two and three links programmed as dyad and triad modules; these modules are executed to compute all the significant dimensions of the linkage. Using this type and dimensional synthesis method, a fast generation and evaluation of many mechanisms can be done in few minutes using a desktop personal computer. The enumeration of mechanisms for a path following task, including eight-bar solutions, illustrates the whole design process.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2010;():851-860. doi:10.1115/DETC2010-28627.

Atlases of admissible graphs of geared kinematic chains (GKCs) had been enumerated through the studies of topological synthesis for decades. However, these enumerated GKCs are mostly synthesized according to the prescribed numbers of DOFs and links. Investigation on the topological and kinematic relations among GKCs of various DOFs and links is few. Motivated by the fact that the topological structure and the number of DOFs of a GKC can be changed by engaging clutches or brakes to connect two or more coaxial links, this work is aimed to reveal how non-fractionated GKCs of higher-DOF are related to those of lower-DOF. The process of connecting coaxial links, leading to the degeneration of DOFs of a GKC is defined as the mobility degeneration of a GKC. It is shown that the mobility degeneration of GKCs depends both on the locations of coaxial links as well as on the configuration of the fractionated kinematic units (KUs) within the GKC. In this paper, characteristics and rules to obtain changed GKCs based on mobility degeneration is developed and degenerated isomorphism of GKCs is discussed. Kinematic families of GKCs with up to three-DOF and eight-link are classified. It is shown that GKCs of different DOFs can be associated to form several kinematic families, indicating that these GKCs of various DOFs are not as independent as previously considered.

Topics: Chain
Commentary by Dr. Valentin Fuster
2010;():861-870. doi:10.1115/DETC2010-28650.

This paper deals with the comparison of planar parallel manipulator architectures based on a multi-objective design optimization approach. The manipulator architectures are compared with regard to their mass in motion and their regular workspace size, i.e., the objective functions. The optimization problem is subject to constraints on the manipulator dexterity and stiffness. For a given external wrench, the displacements of the moving platform have to be smaller than given values throughout the obtained maximum regular dexterous workspace. The contributions of the paper are highlighted with the study of 3-P RR, 3-RP R and 3-R RR planar parallel manipulator architectures, which are compared by means of their Pareto frontiers obtained with a genetic algorithm.

Commentary by Dr. Valentin Fuster
2010;():871-875. doi:10.1115/DETC2010-28829.

The Cartesian workspace of an n-DOF parallel robot (n < 6) is generally divided by singularity hyper-surfaces of dimension n−1. A common approach to reducing the dimension of the singularity manifold is to use actuation redundancy. However, in all previously reported works, adding one redundant actuator reduces the dimension of the singularity manifold by only one. This paper is the first to demonstrate that a properly designed actuation redundancy can be much more effective than this. Specifically, a 3-R PR design is presented in which the mobile platform and the base are equilateral triangles and show that adding a single R PR leg connecting the centers of these two triangles completely eliminates the singularities of the robot, which are otherwise a surface in the Cartesian space.

Commentary by Dr. Valentin Fuster
2010;():877-887. doi:10.1115/DETC2010-28865.

Based on the newly invented reconfigurable Hooke joint which changes the joint property, this paper investigates synthesis of limbs using the new joint based on constraint analysis. The procedure of the limb synthesis is put forward to fully use the property of the new joint for generating the reconfigurable limbs. Further, the paper presents a way of synthesising the parallel mechanism with metamorphic characteristics by starting from the aim at mobility-change. This is then integrated into the forward-based limb synthesis. A general procedure is proposed and applied to construct two classes of metamorphic parallel mechanisms. Their topological configuration change is investigated by examining the constraint change stemming from the phase alteration of the reconfigurable Hooke joint.

Commentary by Dr. Valentin Fuster
2010;():889-897. doi:10.1115/DETC2010-28874.

In this paper, we present an interactive, visual design approach for the dimensional synthesis of spherical 6R closed chains for a given rational motion using constraint manifold modification. This work is an extension of our previous work on the dimensional synthesis of planar 6R closed chains using the aforementioned approach. The theoretical underpinning of this work is based on representation of spherical displacements by quaternions and the kinematic mapping approach. In this way, motion of the coupler of a spherical 6R chain motion maps to a rational curve and the kinematic constraints of a spherical 6R closed chain map to hyper-dimensional algebraic surfaces in the image space of spherical displacements. Thus, the problem of determining dimensional parameters of the chain is reduced to finding the surface parameters that satisfy the geometry of the curve. This, in turn, resolves into satisfying the kinematic constraints of the chain. We provide designers an interactive, user friendly graphical tool that allows them to visually contain the image curve by simple geometric manipulation of the size, orientation, and the location of the constraint surfaces. This simple and straightforward design process lends designers an understanding of the mechanism design methodology.

Topics: Motion , Chain , Manifolds
Commentary by Dr. Valentin Fuster
2010;():899-906. doi:10.1115/DETC2010-28896.

This paper presents a method of selecting joints relative to a fixed and moving (coupler) frame that can be used to actuate a single degree of freedom planar mechanism using a revolute-prismatic-revolute (RPR) chain or a spherical mechanism via a spherical-prismatic-spherical (SPS) chain. Given a single degree of freedom mechanism, a moving reference frame attached to any link has a motion that can be described with a single parameter. A point relative to this moving frame is sought such that it either continually increases or decreases in distance from a point in the fixed frame over the entire motion. The mechanism can then be moved by placing an actuated prismatic joint between the two points. Moreover, the singularities relative to the joints in the original mechanism are not a concern and the dimensional synthesis can focus on creating the set of circuit-defect free solutions. From this analysis, a unique fixed point is determined relative to two positions and their velocities with the following characteristic. All points in the moving reference frame that are moving away from it in the first position are approaching it in the second position, and vice versa.

Commentary by Dr. Valentin Fuster
2010;():907-915. doi:10.1115/DETC2010-28947.

An intuitive approach for the structural synthesis of serial robotic manipulator subject to specific motion constraints is presented in this paper. According to the required f-DOF αRβT motion of the end-effector, for f = 2, 3, [[ellipsis]] or 6 and α, β = 0, 1, 2 or 3, all feasible serial-type robot structures can be systematically generated via the proposed method. The approach begins at the enumeration of joint connectivity, proceeds with the assignment of joint types, and continues by the consideration of motion constraints for the robot. A couple of examples, including the synthesis of the 3-, 4- and 5-DOF serial manipulators, are furnished for illustration. It shows that this method is especially exploitable when the end-effector is required to be immovable in certain orientations or directions with respect to either local coordinate system or global coordinate system. The result is particularly beneficial for practical industrial applications.

Topics: Motion , Manipulators
Commentary by Dr. Valentin Fuster
2010;():917-922. doi:10.1115/DETC2010-28962.

Five-bar planar parallel robots for pick and place operations are always designed so that their singularity loci are significantly reduced. In these robots, the length of the proximal links is different from the length of the distal links. As a consequence, the workspace of the robot is significantly limited, since there are holes in it. In contrast, we propose a design in which all four links have equal lengths. Since such a design leads to more parallel singularities, a strategy for avoiding them by switching working modes is proposed. As a result, the usable workspace of the robot is significantly increased. The idea has been implemented on an industrial-grade prototype and the latter is described in detail.

Topics: Robots
Commentary by Dr. Valentin Fuster
2010;():923-932. doi:10.1115/DETC2010-29028.

In an earlier work, we have presented an efficient method for synthesizing crank-rocker mechanisms that are capable of generating perceptually simple and smooth low-harmonic closed curves. In this paper, we seek to extend this approach to the synthesis of four-bar linkages for the generation of open curves. Instead of using Fourier transform that requires a function to be defined over the entire period, we combine finite Fourier series in a curve-fitting scheme for the approximation of periodic as well as non-periodic paths. This yields a general method for four-bar path generation that is applicable to both closed and open paths.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2010;():933-942. doi:10.1115/DETC2010-29151.

Slider-crank mechanisms used in open/close motion from toggle positions can be driven at the crank by many devices. Usually, the slider motion is defined first to synthesize crank motion. When slider motion has acceleration continuity only, crank acceleration is discontinuous causing shock loading at high speeds. To avoid such behavior, motion constraints must be assigned up to ping continuity at the limiting positions. This paper presents kinematic motion equations of slider-crank mechanisms with input from both the slider and crank. Toggle and limiting positions having required transmission angles at varied link ratios are determined. Motion functions that yield continuous crank acceleration are demonstrated.

Topics: Motion , Mechanisms
Commentary by Dr. Valentin Fuster
2010;():943-952. doi:10.1115/DETC2010-29199.

This paper presents an approach to the configuration synthesis of metamorphic mechanisms with consideration of both link and joint changes. The technique, referred to here as computational geometry, uses a constraint graph to represent topological structure of metamorphic mechanisms instead of traditional graph representation that can not distinguish link types and multi-joints. Based on the constraint graph, a characteristic incidence matrix is proposed with the characteristic relationships between links and joints. Then, a synthetic method based on characteristic incidence matrix is put forward in this paper using operations among matrixes with different orders by binary computing. Through an example of a four-bar mechanism synthesizing into five-bar mechanisms with the proposed configuration synthetic method, it is confirmed that the approach is correct and effective for the configuration synthesis of all metamorphic mechanisms with single or multiple joints.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2010;():953-959. doi:10.1115/DETC2010-29227.

In the last few decades, researchers have proposed a few different methods to synthesize parallel mechanisms. In this paper, we propose both the natural law for kinematic mobility and the generalized function sets (GF set for short) which are used for the type synthesis of parallel mechanisms, particularly for those having two rotations. The natural law for kinematic mobility lays the foundation for the algorithms of the intersection of GF sets. Moreover, the GF sets are used for describing the performance criteria of the end-effectors of robotic manipulators in a clear and systematic way, including the mechanisms having two rotations. Finally, several novel parallel mechanisms having two rotations have been illustrated to show the effectiveness of the proposed methodology.

Commentary by Dr. Valentin Fuster
2010;():961-968. doi:10.1115/DETC2010-28372.

This paper presents an online robot simulation tool built using X3D, extensible 3D graphics that can be used as either an educational or design tool. A literature review of some current web-based learning tools is outlined in the context of mechanisms and robotics. Also, different web technologies that were tested in the process of building the simulation tool are discussed, along with a technical review of current desktop sharing software available online. Lastly, an example of a virtual robot is presented with the technical design information explained in detail. Enhanced by a robust user interface, the simulation environment is intuitive for users with limited mechanical design background. A powerful “back-end” computational engine is envisioned to allow for various interactive features in simulations to be accomplished.

Commentary by Dr. Valentin Fuster
2010;():969-977. doi:10.1115/DETC2010-28501.

This paper discusses challenge based instruction (CBI) and associated materials developed for courses in Dynamics, Mechanisms, and Biomechanics. This effort is related to a College Cost Reduction and Access Act (CCRAA) grant from the Department of Education, and focuses primarily on the development of adaptive expertise. In science, technology, engineering, and math (STEM) fields the conventional approach is to teach for efficiency first and innovation only in the latter years of their curriculum. This focus on efficiency first can actually stifle attempts at innovation in later courses. One response to this issue is to change the way we teach. CBI, a form of inquiry based learning, can be simply thought of as teaching backwards. In this approach, a challenge is presented first, and the supporting theory (required to solve the challenge) second. Our implementation of CBI is built around the How People Learn (HPL) framework for effective learning environments and is realized and anchored by the STAR Legacy Cycle, as developed and fostered by the VaNTH (Vanderbilt-Northwestern-Texas-Harvard/MIT) NSF ERC for Bioengineering Educational Technologies. This cycle provides students the opportunity to immediately engage in creative activity in the “generate ideas” phase where they are asked what they think is important to know and do in solving the challenge. They are then led through a natural process of inquiry culminating in their “going public” with a solution to the challenge. Ideally, this approach develops both efficiency and innovation in parallel and results a student who is an “adaptive expert”. That is, one who can adapt their knowledge to new and novel situations outside of the context in which the knowledge was obtained.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2010;():979-986. doi:10.1115/DETC2010-28537.

This paper details some innovations developed at Ohio University for augmenting the teaching and learning of mechanism kinematics and dynamics, robot kinematics, dynamics, and control, and the musculoskeletal biomechanics of human motion. Common to all three courses are NotesBooks, significant MATLAB use in class, homework, and projects, term projects simulated from real-world applications, and Internet resources developed and hosted by the author at Ohio University.

Commentary by Dr. Valentin Fuster
2010;():987-994. doi:10.1115/DETC2010-28930.

This paper presents some experiences on the teaching of kinematics and robotics in Mexican universities. A short sociological background information together with generalities about the curricula of mechanical and mechatronics engineers is shown. After that, the contents of two courses Mechanisms and Robotics are presented in detail. Finally, three unrelated examples of learning aids design and the introduction of more advanced mathematical tools to the study of kinematics of machinery and robotics are discussed. Nevertheless, the examples show the effort to overcome some of the deficiencies of our incoming engineering students.

Commentary by Dr. Valentin Fuster
2010;():995-1002. doi:10.1115/DETC2010-28994.

In recent years there has been a significant increase in the variety and complexity of Articulated-Multi-Body-Systems (AMBS) used in various applications. There is also increased interest in the model-based design-refinement and controller-development, which is critically dependent upon availability of underlying plant-models. Kinematic and dynamic plant-models for AMBSs can be formulated by systematic application of physics postulates. This process, in its various variants, forms the basis of various mechanisms/robotics courses. However, the type and complexity of the example systems is often limited by the tractability of first generating and subsequently analyzing complex equations-of-motion. Nevertheless, using simpler examples alone may sometimes fail to capture important physical phenomena (e.g. gyroscopic, coriolis). Hence, we examine the use of some contemporary symbolic- and numeric-computation tools to assist with the automated symbolic equation generation and subsequent analysis. We examine a host of examples beginning with simple pendulum, double pendulum; building up to intermediate examples like the four-bar mechanism and finally examine the implementation of 3-P RR and 3-R RR planar parallel platform mechanisms. The principal underlying philosophy of our effort is to establish linkage between traditional modeling approaches and use of these contemporary tools. We also try to make a case for use of automatic symbolic computation and manipulation as a means for enhancing understanding of both basic and advanced AMBS concepts. Lastly, we document our efforts towards creation of self-paced tutorials and case-studies that serve to showcase the benefits.

Commentary by Dr. Valentin Fuster
2010;():1003-1009. doi:10.1115/DETC2010-29019.

The Early Intervention and Mechanical Engineering (EIME) project provides real-world engineering design experience to undergraduate engineering students while significantly enhancing the services provided to children with special needs in the region surrounding Tennessee Technological University (Upper Cumberland region). These enhanced services are provided through a mutually beneficial collaboration between early intervention and engineering at Tennessee Tech. Engineering students engage in this project as part of a Design of Machinery Course. Student teams are matched with children with needs for novel applications of adaptive and assistive technology to facilitate transitioning of children from early intervention to preschool programs and inclusive environments. The projects are selected to emphasize motion control tasks. Examples include improved mobility, exercise, adaptations for feeding and everyday functioning, and interactive play. The project serves the engineering program by providing real-world design experiences as well as resources to develop and test projects. This paper will describe how the project is integrated into the design of machinery curriculum and present several examples of typical projects. Assessment of student outcomes relative to design and learning experience will be discussed. The paper will conclude with lessons learned and recommendations for future implementation of this project.

Commentary by Dr. Valentin Fuster
2010;():1011-1018. doi:10.1115/DETC2010-29136.

This paper presents the details of a compact embedded-computing module designed to meet a variety of pedagogical objectives within mechatronics, controls, and robotics. Built around an ATmega32U4 microcontroller, the 1.8 × 4.0 centimeter module has flash memory for program and data storage, 25 general-purpose input/output lines, four timer/counters, 12 channels of 10-bit analog-to-digital conversion, and support for a variety of serial communications protocols, including USB. The unit adapts easily to a solderless breadboard for quick prototyping, and requires only an external 5-volt power source for operation. Furthermore, it can be programmed directly over a USB connection to a computer, thereby eliminating the need for a separate programming device. As a member of the AVR family of microcontrollers, the development tools for the processor are freely available for Windows, Mac, and Linux. When assembled in sufficient quantity, the part cost for each module is approaching $ 10US, making it a low-cost solution for a variety of tasks. To enable students and professors to explore both the module and the host of application principles, we have chosen to post the design files and documentation on a publicly-accessible wiki, leaving room for collaborative improvements and the sharing of technology with other educational institutions.

Commentary by Dr. Valentin Fuster
2010;():1019-1028. doi:10.1115/DETC2010-29154.

We have developed an intensive, three-week summer robotics program for high school students. The program requires special teaching methods since it is offered to rising 10th through 12th grade students with diverse backgrounds, and a low student/teacher ratio to ensure all students grasp the material. We use a project-based learning approach, assigning the students a series of specially tailored labs and projects designed to engage and challenge while preparing them for the main element of the program, the design of a semi-autonomous robotic vehicle whose mission emulates that of NASA’s Martian rovers. The project culminates with testing of their vehicles on an obstacle course. A series of targeted design reviews are held as the project unfolds to keep all designs on schedule. We leverage the spirit of competition to heighten the enthusiasm of the students and sustain their interest through the long-hours required to design and build a successful robot. The students get hands-on experience with mechanism design, electronics, computer-aided-design and manufacturing, and microprocessor programming, and are engaged in discussions on applications of robotics in both academia and industry to provide a “grounding” of the material.

Commentary by Dr. Valentin Fuster
2010;():1029-1036. doi:10.1115/DETC2010-29211.

This paper describes the pre-training approach using research projects to get the in-coming mechanical engineering undergraduate student jump started for their four years of college career. We used a robotics research project to go through the full engineering design lifecycle, including (a) brain-storming, (b) feasibility studies, (c) building simple models for evaluation, and (d) engineering/construction. With the help of the mentors, the approach has effectively involved the students to identify potential problems and solve them effectively during the execution of the projects. The resulting constructed robotic delivery truck is a mathematically interesting problem that will be solved as a research problem.

Commentary by Dr. Valentin Fuster
2010;():1037-1047. doi:10.1115/DETC2010-28141.

A novel XY compliant parallel manipulator (CPM) and a spatial double three-beam module both with distributed compliance are first proposed for large range of translation. Then, an improved XY CPM is proposed by combining the above XY CPM and a spatial double three-beam module in parallel. The normalized analytical models are further presented for the novel XY CPM, double three-beam module and improved XY CPM. It is shown that the improved XY CPM has the following merits: (1) large range of motion, constrained parasitic error motion, output-decoupling, maximal actuation isolation and minimal lost motion; and (2) large out-of-plane stiffness and no friction with base. The improved XY CPM may also be used as a building block to construct new spatial CPMs.

Commentary by Dr. Valentin Fuster
2010;():1049-1058. doi:10.1115/DETC2010-28153.

Mobile robotics has seen a wide variety of mechanisms and strategies for motion in diverse terrain. Some robots employ rolling, some use legs for walking, some can hop, and some are capable of multiple of these modes. In this paper, we present the latest Robotic All-Terrain Surveyor (RATS) prototype as a unique design that can emulate a variety of locomotion modes by virtue of its geometric design and type of actuation. The novel robot has a spherical body the size of a soccer ball with 12 legs symmetrically distributed around its surface. Each leg is a single-DOF pneumatic linear actuator, oriented normal to the spherical body. Thorough investigation of this prototype’s mobility and actuation behavior has demonstrated the feasibility of tipping, hopping, and prolonged rolling locomotion by altering the actuation patterns of its legs. Here we summarize the experimental results of this characterization and present an understanding of the system’s performance limitations in an effort to draw insight for controlling its movements. We also discuss the effectiveness of RATS mobility strategies for varied terrains in light of initial testing on flat surfaces.

Topics: Robots
Commentary by Dr. Valentin Fuster
2010;():1059-1067. doi:10.1115/DETC2010-28422.

It is difficult to manufacture parallel manipulators(PMs) with multiple revolute joint axes intersecting at one point. These types include the 3-DOF spherical parallel manipulators (SPMs), the 4-DOF 3R1T and 2R2T PMs, the 5-DOF 3R2T PMs. This problem makes it hard to achieve the expected mobility of these PMs. In this paper, a 3-RPS cubic PM is studied which has three rotational freedoms and no intersecting axes. The orientation workspace of this PM is analyzed. Some discussions about the differences between the traditional SPMs and this PM are proposed. The results show that the 3-RPS cubic PM can achieve three rotational motions and has no intersecting axes.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2010;():1069-1078. doi:10.1115/DETC2010-28425.

The development of safe and dependable robots for physical human-robot interaction is actually changing the way robot are designed introducing several new technological issues. Outstanding examples are the adoption of soft covers and compliant transmissions or the definition of motion control laws that allow a compliant behavior in reaction to possible collisions, while preserving accuracy and performance during the motion in the free space. In this scenario, a growing interest is devoted to the study of variable stiffness joints. With the aim of improving the compactness and the flexibility of existing mechanical solutions, a variable stiffness joint based on the use of compliant flexures is investigated. The proposed concept allows the implementation of a desired stiffness profile and range along with the selection of the maximum joint deflection. In particular, this paper reports a systematic procedure for the synthesis of a fully-compliant mechanism used as a non-linear transmission, together with a preliminary design of the overall joint.

Topics: Design , Modeling , Stiffness
Commentary by Dr. Valentin Fuster
2010;():1079-1088. doi:10.1115/DETC2010-28426.

The four-degree-of-freedom (4-DoF) Schoenflies-motion (briefly termed X-motion) manipulator with the fast pick-and-place operation is essential for industrial assembly and packaging. For the development of this kind of industrial manipulator, we provide architectures and inverse kinematics of four X-motion isoconstrained parallel mechanisms with two limbs, Cu u Uw Hw -//-Cv v Uw Hw , Cu Ru u Uhw -//-Cv Rv v Uhw , Cu Ru PHw -//-Cv Rv PHw and Cu Pu Uhw -//-Cv Pv Uhw (R, P, H and C denote revolute, prismatic, screw and cylindrical pairs respectively; U indicates a universal joint). These novel manipulators are excerpted from numerous general architectural types of isoconstrained parallel generators of X-motion. In this work, their architectures and mobility are first elucidated in detail. With the help of the well-known D-H symbolic notations, their three translational and one rotational motion are comprehensively verified through the four-by-four coordinate transformation matrix approach. Inverse kinematic solutions of joint displacements of each manipulator are further established by using the matrix algebra method for the reference of potential applications.

Commentary by Dr. Valentin Fuster
2010;():1089-1099. doi:10.1115/DETC2010-28502.

The 3-UPU three degrees of freedom fully parallel manipulator, where U and P are for universal and prismatic pair respectively, is a very well known manipulator that can provide the platform with three degrees of freedom of pure translation, pure rotation or mixed translation and rotation according to the relative directions of the revolute axes. Many studies have been reported in the literature on singularities, workspace and joint clearance influence on the platform accuracy of this manipulator. However, much work has still to be done to reveal all the features this topology can offer to the designer. This paper collects the previous most relevant work done on the 3-UPU parallel manipulator and shows the main results in a coherent general frame. The paper proposes new architectures of the 3-UPU manipulator which offer interesting features to the designer. Finally, based on a number of indexes, a procedure is proposed that allows the designer to select the best architecture of the 3-UPU manipulator for a given task.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2010;():1101-1111. doi:10.1115/DETC2010-28551.

We investigate various algorithms for analyzing the characteristics of the internal motion of proteins based on the analogies between their kinematic structures and robotic mechanisms. First, we introduce an artificial simple protein model, planar main chain (PMC), composed of a planar serial link mechanism to investigate the algorithms. Then, we develop algorithms for analyzing the conformational fluctuations by applying the manipulability analysis of robot manipulators and control strategies for redundant manipulators. Next, we develop algorithms for analyzing the conformational deformation caused by the external forces and to evaluate the compliances of the specified parts of proteins. Finally, we show that the proposed algorithms developed by using PMC models are applicable for the three dimensional main chain structures of real proteins, and may be used to analyze their characteristics of the internal motion. We also reveal some preliminary simulation results of the analysis of a real protein.

Commentary by Dr. Valentin Fuster
2010;():1113-1122. doi:10.1115/DETC2010-28673.

A new kinematic pair called an algebraic screw pair, or A-pair, is introduced that utilizes the self-motions inherent to a specific configuration of Griffis-Duffy platform. Using the A-pair as a joint in a hybrid parallel-serial kinematic chain results in a sinusoidal coupling of rotation and translation between adjacent links. This motion affects both the direct and inverse kinematics of such chains. Presented in this paper are the direct kinematics of chains using A-pairs and an algorithm for the inverse kinematics of a 4A-pair chain.

Topics: Kinematics , Linkages
Commentary by Dr. Valentin Fuster
2010;():1123-1130. doi:10.1115/DETC2010-28676.

This paper presents an innovative 5 DOF robot that generates 3T1R motion (3 translations + 1 rotation) plus a linear grasping motion. To generate this type of grasping motion, a robot needs two end-effectors. Grasping motions are usually generated by adding a grasping device at the top of an already existing robot or by coordinating two distinct robots. We propose in this paper a new robot architecture which includes the grasping degree of freedom as a part of the mechanism itself. The two end-effectors of the mechanism are mounted on an articulated platform and can move together in a 3T1R motion and their distance to each other can be controlled to generate the grasping capability. The 5 actuators are located on the base and are connected with five identical legs to the two end-effectors using only mechanical links, forming a fully parallel robot with 5 DOF. The architecture of the robot will be presented in detail. Then, we will describe the kinematics needed for the control of the robot. Finally, geometric optimization results will be presented and discussed.

Topics: Motion , Robots , Grasping
Commentary by Dr. Valentin Fuster
2010;():1131-1140. doi:10.1115/DETC2010-28715.

This paper describes a new parallel kinematics mechanism for Schönflies motion: the Lambda-Quadriglide. The structure of Lambda-Quadriglide provides four degrees of freedom (DOF) with three translations and one rotation around a horizontal axis. Four linear actuators with the same direction are used, which allows the workspace to be particularly long in this direction. The special feature of this mechanism is the lambda-configuration, based on two kinematic chains acting directly on the traveling plate, and two other kinematic chains acting on the first ones. This configuration allows a large rotational angular range for the mobile platform. The design concept of Lambda-Quadriglide is introduced and kinematics models are derived. Optimization of the mechanism parameters and the workspace of the optimized mechanism are also presented. This architecture allows a physical implementation with no collision problems between the arms. Finally, the Lambda-Quadriglide prototype is presented, together with experimentation results.

Commentary by Dr. Valentin Fuster
2010;():1141-1147. doi:10.1115/DETC2010-28716.

Considerable potentials with regard to mobility in unstructured environment offer actively articulated mobile robots equipped with powered wheels or tracks. These potentials are obvious when dealing with a system’s trafficability and terrainability. However, maneuverability and steerability of articulated mobile robots are challenging. This is due to the fact that these robots represent a form of truck-trailer systems leading to interactions and influences between the individual vehicles resulting in significant problems like e.g. off-tracking with regard to a given path. Further on, when dealing with a mobile robot’s maneuverability there are only few scientific contributions covering articulated vehicles with actively powered trailers using tracks as propulsive elements. The described systems differ significantly with regard to their configuration with respect to the multi-redundant mobile robot in this work. To investigate the maneuverability of articulated tracked mobile robots a demonstrator has been developed. It is built up out of three identical modules which are connected with each other in a rowby means of a rotational and a translational degree-of-freedom. Each module has two tracks which can be powered independently. Overall, the system has got ten degrees-of-freedom whereas six of them are active and four passive. The developed demonstrator has been used for investigations dealing with maneuverability and steerability as well as modularization of the system’s control architecture. The paper summarizes the development of the mobile robot, its feedback control strategy as well as the tests carried out. The achieved results show a satisfying performance with regard to the implemented control strategy and the system’s maneuverability.

Topics: Mobile robots
Commentary by Dr. Valentin Fuster
2010;():1149-1156. doi:10.1115/DETC2010-28729.

Effective continuously variable transmission (CVT) designs have been sought after for many years as their integration into many different mechanical systems can give many advantages over a discrete transmission system. Currently, CVTs are becoming popular for applications from automotive power transmission to wind power generation. Most CVT technologies, however, are friction- or hydraulic-based designs limited by both performance and system characteristics. This paper will evaluate a new, patented form of purely mechanical, intrinsically automatic CVT which is not based on belts, pulleys, gears or hydraulics. This new transmission is based on a deformable four-bar design incorporating a one-way clutch for positive displacement of the output. As torque demand on the system output is varied, the output’s displacement varies inversely to maintain a constant peak torque on the input shaft. The end result of this behavior is a possible instantaneous variation of speed ratio over an extreme range with a lightweight, simple mechanical design. This paper provides an analysis of the mechanism and its performance, as well as simulation results incorporating real-world measurement of system output into several different mechanical applications: a human-powered vehicle, an automobile and a centrifugal pump.

Commentary by Dr. Valentin Fuster
2010;():1157-1165. doi:10.1115/DETC2010-28811.

This paper presents preliminary results on the dynamic modelling of a cubic flying robot referred to as the Tryphon. Several Tryphons and other similar cubic flying robots have been built in the course of this project. They are used for artistic performances in museums, art galleries or theatres. Although the Tryphons are functional, they are difficult to control because of limited knowledge of their behaviour. Hence, the development of a dynamic model has the potential to significantly improve the control performances. Based on models found in the literature, the aerostatics, aerodynamics, gravity, buoyancy and inertial effects of the Tryphon are combined into a dynamic model in this paper. The parameters of the proposed model are adjusted based on experimental data obtained with the Tryphons. It is shown that a proper selection and optimization of the parameters can accurately predict the dynamics of the robot. Further extensions of the model are discussed and potential applications are proposed.

Commentary by Dr. Valentin Fuster
2010;():1167-1176. doi:10.1115/DETC2010-28838.

This paper presents a toolchain for the design and simulation of reconfigurable robots that can be built from a single rigid sheet of smart material with embedded actuators and sensors along regular crease patterns. We call such sheets Foldable Programmable Matter (FPM ). The toolchain we have created comprises an editor for drafting or modifying FPM , including locations and angles for folds. Algorithms for generating a class of folding structures are available for use. Also included is a dynamic simulation of the fold process, which provides collision detection and visualization. Thus our Foldable Programmable Matter Editor allows us to synthesize and design FPMs and simulate them in a virtual environment before committing to manufacture. The toolchain also incorporates a method of strength analysis, which is used to determine the suitability of a folded shape for specific loadings. Examples are shown for each subsection, including a beam example spanning the toolchain.

Topics: Matter , Simulation , Design
Commentary by Dr. Valentin Fuster
2010;():1177-1186. doi:10.1115/DETC2010-28875.

Precision mirrors are required for effective solar energy collectors. Manufacturing such mirrors and making them robust to disturbances such as thermal gradients is expensive. In this paper, the use of parallel binary actuation to control the shape of mirrors for solar concentrators is explored. The approach embeds binary actuators in a compliant mirror substructure. Actuators are deployed in a specified pattern to correct the mirror shape. The analysis for binary-actuated compliant mirror structures is presented. Analytical models are developed for one-dimensional and two-dimensional compliant structures with embedded binary actuators. These analytical models are validated using finite element analysis and experimental studies. The models and experiments demonstrate the capabilities of binary actuated mirrors. System workspace is explored, the principle of superposition required for their control is demonstrated, as is the mirror ability to correct its figure.

Commentary by Dr. Valentin Fuster
2010;():1187-1194. doi:10.1115/DETC2010-28878.

Skid steer tracked-based robots are popular due to their mechanical simplicity, zero-turning radius and greater traction. This architecture also has several advantages when employed by mobile platforms designed to climb and navigate ferrous surfaces, such as increased magnet density and low profile (center of gravity). However, creating a kinematic model for localization and motion control of this architecture is complicated due to the fact that tracks necessarily slip and do not roll. Such a model could be based on a heuristic representation, an experimentally-based characterization or a probabilistic form. This paper will extend an experimentally-based kinematic equivalence model to a climbing, track-based robot platform. The model will be adapted to account for the unique mobility characteristics associated with climbing. The accuracy of the model will be evaluated in several representative tasks. Application of this model to a climbing mobile robotic welding system (MRWS) is presented.

Topics: Robotic welding
Commentary by Dr. Valentin Fuster
2010;():1195-1204. doi:10.1115/DETC2010-28902.

The subject of this paper is the synthesis of the pitch surfaces of non-circular skew gears, intended to generate any motion program with a periodically varying transmission ratio. This is done by extending an existing algorithm, which was formulated through the application of dual algebra and the Principle of Transference. In particular, the variable transmission ratio of N-lobed elliptical and logarithmical cylindrical gears is expressed and analyzed along with their main characteristics to test the proposed algorithm, which is implemented in Matlab. The code generates the pitch surfaces of N-lobed elliptical and logarithmical skew gears, along with those of indexing skew gears. Finally, significant numerical and graphical results are shown to analyze the geometrical characteristics of the gear engagement. Not unexpectedly, cylindrical and bevel non-circular gears become particular cases thereof.

Topics: Gears
Commentary by Dr. Valentin Fuster
2010;():1205-1212. doi:10.1115/DETC2010-29053.

Whole Skin Locomotion (WSL) is an amoeba inspired locomotion mechanism for mobile robots in which an elongated torus turns itself inside out in a single continuous motion. Since the entire surface is used as a traction surface, WSL has the potential to traverse highly unstructured terrain, and when filled with fluid with an elastic membrane skin, it has the potential to squeeze through holes smaller than its nominal diameter. Previous work has investigated the mechanics of a concentric solid tube (CST) model in which motion is generated by expanding and contracting actuator rings pushing and pulling the membrane around a solid inner tube. In this paper, we present the mechanics of a fluid filled toroid (FFT) model which replaces the solid inner tube with incompressible fluid. Locomotion using contracting ring actuation is described for the FFT model and compared to the CST model. A novel actuation scheme which exploits the chemo-mechanics of soft polymeric elastic skin is also introduced to elicit useful locomotive behavior. Chemically induced swelling in polymeric skin is demonstrated to be a viable propulsion mechanism for a toroidal membrane under pressure. Finally, preliminary analysis is presented for finding forces required for a WSL robot to squeeze through a hole of a given depth and diameter to investigate the feasibility of using contracting ring actuation and chemically induced swelling for hole traversal.

Topics: Fluids , Robots , Propulsion
Commentary by Dr. Valentin Fuster
2010;():1213-1215. doi:10.1115/DETC2010-28465.

This is a review of two patents relating to electrical power generation on-board gun-fired munitions. The devices harvest mechanical energy from the motion of the projectile (e.g. the axial firing acceleration), and then convert the energy from mechanical to electrical using novel mechanisms and materials such as piezoelectric elements. The devices are particularly important for several reasons. Firstly, the devices are inherently safe because the root source of the electrical energy is the motion of the projectile; therefore no electrical energy can be produced until after the projectile is fired. Second, the devices have a much longer shelf-life than competing electrical power sources such as batteries. Finally, the devices are simple, rugged, and reliable making them ideal for the harsh environment on-board gun-fired projectiles. In addition to presenting the general approach, the logical framework of the patented embodiments is presented, especially with respect to the types of motion used for harvesting and the challenges presented by the varied magnitudes of those motions in different weapon platforms.

Commentary by Dr. Valentin Fuster
2010;():1217-1218. doi:10.1115/DETC2010-28468.

This is a review of a series of three patents issued for inertia igniters: devices which are generally used on-board gun-fired munitions to provide pyrotechnic initiation of a thermal battery. The igniters use the overwhelming firing acceleration to drive various mechanism components which provide event-sensing and a time time-delay in addition to the mechanical striking which ignites the pyrotechnic element of the igniter. The embodiments in the three patents progresses from a novel approach to achieve greater axial compactness while maintaining equivalent performance to a benchmark design, to a two-stage design which expands the range of performance of the event-sensing and time-delay characteristics of the devices, and finally to several novel approaches for producing arbitrarily long delays and the sensing of large impulses in highly compact multi-stage inertia-driven devices. The expansion of the range of operation of such devices is particularly important because prior to these innovative approaches, long delays or the practical measurement of large impulses required electronic methods and an additional tier of electrical power in addition to the thermal battery which is to be initiated.

Commentary by Dr. Valentin Fuster
2010;():1219-1220. doi:10.1115/DETC2010-28827.

The state of the art in shock resistant accelerometer and gyro design is to use smaller proof mass, thereby reducing the related forces that are generated as a result of high acceleration levels. Physical stops are also provided to limit the maximum proof mass displacement/rotation. The introduction of MEMS technology has made it possible to significantly reduce the proof mass. However, all existing accelerometer/gyro designs for high shock resistance suffer from low sensitivity at the very low acceleration levels required for guidance and control purposes, and from long settling time. The basic method of design and the concepts described in this patent provide the means to alleviate these shortcomings. The novelty in these designs is in the provision of the means to lock the proof mass in its “null” position during the high accelerations, such as during shock (impact) loading, and release it afterwards. The locking mechanism may be passive or active. As a result, the settling time of the proof mass is minimized and the precision with which the sensor can make its measurements is significantly increased.

Topics: Sensors
Commentary by Dr. Valentin Fuster
2010;():1221-1229. doi:10.1115/DETC2010-28908.

Surgery, especially intra-abdominal surgery, has taken large steps away from the conventional method of open incisions during the last two decades. Intra-abdominal surgery is now successfully performed through minimally invasive approaches. This paradigm overcomes problems encountered in the conventional method, which include substantial blood loss and long recovery periods for patients. However, a newer approach to surgery involves inserting tools through natural orifices of the patient rather than creating skin incisions. Natural orifice surgery is performed through body orifices like the esophagus or anus. This approach has substantially reduced certain disadvantages of both the conventional and minimally invasive surgeries. Natural orifice surgery has been extensively researched of late, and many institutions and companies have filed patents regarding this approach. Due to the constraints on motion and manipulation, coupled with the continued need for precise control of tool position and forces, mechanical design is an important aspect of these new technologies.

Topics: Surgery , Mechanisms
Commentary by Dr. Valentin Fuster
2010;():1231-1240. doi:10.1115/DETC2010-28061.

Path tracking can be accomplished by separating the control of the desired trajectory geometry and the control of the path variable. Existing methods accomplish tracking of up to third-order geometric properties of planar paths and up to second-order properties of spatial paths using non-redundant manipulators, but only in special cases. This paper presents a novel methodology that enables the geometric tracking of a desired planar or spatial path to any order with any non-redundant regional manipulator. The governing first-order coordination equation for a spatial path-tracking problem is developed, the repeated differentiation of which generates the coordination equation of the desired order. In contrast to previous work, the equations are developed in a fixed global frame rather than a configuration-dependent canonical frame, providing a significant practical advantage. The equations are shown to be linear, and therefore, computationally efficient. As an example, the results are applied to a spatial 3-revolute mechanism that tracks a spatial path. Spatial, rigid-body guidance is achieved by applying the technique to three points on the end-effector of a six degree-of-freedom robot. A spatial 6-revolute robot is used as an illustration.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2010;():1241-1247. doi:10.1115/DETC2010-28126.

A quadratic parallel manipulator refers to a parallel manipulator with a quadratic characteristic polynomial. This paper revisits the forward displacement analysis (FDA) of a linearly actuated quadratic spherical parallel manipulator. An alternative formulation of the kinematic equations of the quadratic spherical parallel manipulator is proposed. The singularity analysis of the quadratic spherical parallel manipulator is then dealt with. A new type of singularity of parallel manipulators — leg actuation singularity — is identified. If a leg is in a leg actuation singular configuration, the actuated joints in this leg cannot be actuated even if the actuated joints in other legs are released. A formula is revealed that produces a unique current solution to the FDA for a given set of inputs. The input space is also revealed for the quadratic spherical parallel manipulator in order to guarantee that the robot works in the same assembly mode. This work may facilitate the control of the quadratic spherical parallel manipulator.

Commentary by Dr. Valentin Fuster
2010;():1249-1258. doi:10.1115/DETC2010-28149.

This paper proposes a design for a machine tool based on a parallel kinematic manipulator with three degrees of freedom, including rotations about x and y axis and translation along z axe. Based on the investigated displacement and inverse kinematics, the system stiffness of the parallel manipulator is conducted. Then in order to observe the highest system stiffness single and multi objective optimizations are performed in terms of rotation angles about x and y axis and translation displacement along z axe. Finally, a case study of tool path planning is presented to demonstrate the application of stiffness mapping.

Topics: Machinery , Motion , Stiffness
Commentary by Dr. Valentin Fuster