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ASME Conference Presenter Attendance Policy and Archival Proceedings

2012;():i. doi:10.1115/DETC2012-NS4.
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This online compilation of papers from the ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2012) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

36th Mechanisms and Robotics Conference: Biologically Inspired and Health Motivated Mechanisms and Robotics

2012;():3-12. doi:10.1115/DETC2012-70108.

This paper introduces a new snake robot with binary actuators and mainly focuses on the simulations of various snake gaits. Three categories of fitting algorithms are proposed. They are 1) Fitting Algorithm of One Module; 2) Position-Fitting Algorithm of Multiple Modules; 3) Configuration-Fitting Algorithm of Multiple Modules. All the fitting algorithms and their fitting results are elaborated in simulations of lateral undulation, one of the most widely used snake gaits. As the best fitting algorithm for lateral undulation, Configuration-Fitting Algorithm of Four Modules is also applied to a snake robot of different dimensions to demonstrate that it is a universal gait fitting algorithm for all kinds of snake robots with binary actuators.

Commentary by Dr. Valentin Fuster
2012;():13-17. doi:10.1115/DETC2012-70244.

A high versatility, low degrees-of-freedom (DOF) gripper was designed based on avian morphology. Grasping mechanisms for robotic manipulators are often developed for application-specific tasks, such as manipulating a single part or performing a repetitive action. In contrast, more dexterous grippers are complex, multiple-DOF mechanisms. A simple, minimal-DOF, versatile gripper has been developed based on the morphology of the Psittacus Erithacu (African Grey Parrot) beak shape. This species is highly intelligent and uses its beak for digging, gripping, climbing, and foraging. Giving a robot a similar capability would allow the platform to pick up targets such as single, small seeds, liquids, large irregular rocks and soft Robocup style balls. By using the beak as a model for a grasping mechanism the design maintains its versatility without the need for a complex system and allows a large range of targets to be gripped. This gripper is intended for use in the new open-source humanoid robot DARwIn-OP.

Topics: Design , Robotics , Grippers
Commentary by Dr. Valentin Fuster
2012;():19-26. doi:10.1115/DETC2012-70293.

This paper presents the dynamics and nonlinear control of the Robotic Lumbar Spine (RLS). The RLS is a 15 degree-of-freedom, fully cable-actuated robotic lumbar spine which can mimic in vivo human lumbar spine movements to provide better hands-on training for medical students. The current design includes five active lumbar vertebrae and the sacrum, with dimensions of an average adult human spine. It is actuated by 20 cables connected to electric motors. Every vertebra is connected to the neighboring vertebrae by spherical joints. 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. Additionally, a new approach to solve for positive and nonzero cable tensions that are also continuous in time is introduced.

Commentary by Dr. Valentin Fuster
2012;():27-34. doi:10.1115/DETC2012-70409.

Current passive prosthetic ankles are lighter, simpler, and less expensive than powered prosthetic ankles. These current passive designs, however, do not provide adequate torque at the instant when it is needed to propel the body forward. This paper presents a novel 2 degree of freedom (DOF) passive compliant prosthetic ankle that uses a network of conventional springs. One DOF allows the lower leg component to compress when the weight of the amputee is applied during walking. The second DOF allows rotation about the prosthetic ankle joint. The force generated along the leg during walking is converted into ankle torque used to propel the body forward during push-off. An optimization routine is used to select the stiffness values and connection locations of the springs used in the compliant mechanism. The optimization yields a design that generates a torque-deflection profile that is very similar to that of a natural ankle. The mechanism demonstrates apparent active behavior (negative spring constant) at the ankle during push-off without using active components.

Commentary by Dr. Valentin Fuster
2012;():35-42. doi:10.1115/DETC2012-70439.

Although many different kinematic structures have been employed in the design of elliptical machines for exercise and fitness, these devices in general do not produce pedal paths that promote lower extremity kinematics similar to overground gait. This is unfortunate given the growing interest in using these devices as a gait rehabilitation tool. In this paper, we present a novel design strategy for elliptical machines intended to create a movement profile that more closely simulates the lower extremity kinematics of gait. This involves replacement of the typical crank link with a modified Cardan gear system. Simulations of typical rear-drive (crank-rocker) and front-drive (crank-slider) elliptical designs validate the improvement in lower limb hip and knee kinematics using this approach, suggesting that assistive elliptical rehabilitation systems can be more optimally designed to promote normal lower extremity gait kinematics compared to currently available devices.

Topics: Biomechanics , Gears
Commentary by Dr. Valentin Fuster
2012;():43-48. doi:10.1115/DETC2012-70454.

The transition from open surgery to Laparoendoscopic Single-Site (LESS) surgery to minimize cost and recovery time and improve cosmetic scarring has introduced complexities such as reduced dexterity, restricted workspace, and unintuitive controls. Surgical robotic systems can come into play to address these complexities. The most recent miniature in vivo robots have demonstrated the capability of performing LESS surgery. Since size has been a key driving force for designing these motor-driven robotic platforms, delivering adequate force and torque to perform the surgical tasks has been a primary challenge for improving these robots.

This paper presents a robotic platform actuated primarily by pneumatics, offering the following advantages over motor-driven systems: higher joint torque and tool actuation force, faster actuation, better biocompatibility, better overall robustness, and lower cost. Initially one representative robot joint has been fabricated, to demonstrate the proof of concept and investigate the feasibility of angular position control of the pneumatic joint by deploying a minimal number of electronic components and two low-cost solenoid valves in place of costly fast solenoid valves or expensive servo valves.

The robot design, pneumatic system, implementation of PID and PWM controls, and experimental results are presented.

Topics: Robots , Surgery
Commentary by Dr. Valentin Fuster
2012;():49-54. doi:10.1115/DETC2012-70579.

This paper presents the Jacobian analysis of a parallel manipulator that has a fully decoupled 4-DOF remote center-of-motion for application in minimally invasive surgery. Owing to the special structure of the manipulator, the Jacobian matrix of the manipulator is expressed as a combination of three special Jacobian matrices, namely the Jacobian of motion space, Jacobian of constraints, and Jacobian of actuations. Based on these Jacobian matrices, the singular configurations of the manipulator are then identified. It shows that the configuration singularity only exists at the central point and the boundary of the reachable workspace of the manipulator.

Topics: Surgery , Manipulators
Commentary by Dr. Valentin Fuster
2012;():55-64. doi:10.1115/DETC2012-70591.

An analogous relationship exists between the kinematic structures of proteins and robotic mechanisms. Hence, using this analogy, we attempt to understand the internal motions of proteins from the perspective of robot kinematics. In this study, we propose a method called group forced response (GFR) method for predicting the internal motion of proteins on the basis of their three-dimensional structural data (PDB data). In this method, we apply forces in static equilibrium to groups of atoms (e.g., secondary structures, domains, and subunits) and not to specific atoms. Furthermore, we predict the internal motion of proteins by analyzing the relative motion caused among groups by the applied forces. First, we show a method for approximately modeling protein structures as a robotic mechanism and the basic kinematic equations of the model. Next, the GFR method is formulated (e.g., Jacobian matrix for group motions, magnitude of forces applied to groups, and decomposition of motions into modes according to structural compliances). Finally, we present example applications of the proposed method in real protein structures. Despite the approximations in the model, low computational cost, and use of simple calculation parameters, the results almost agree with measured internal motions.

Commentary by Dr. Valentin Fuster
2012;():65-73. doi:10.1115/DETC2012-70634.

This paper presents the development of NGDs (needle grasping devices) capable of handling elongated objects such as surgical needles. After describing the main demands of medical needle-based procedures, a requirement list for a typical NGD is presented. Some solution principles for a grasping device are generated, combined and then classified to obtain a set of principle variant solutions. The design study of some of these variant solutions is then developed and a discussion on two device candidates constructed using either interconnected rigid bodies or compliant parts will be presented. The mechanical behavior of the compliant mechanism acting on a needle barrel is simulated with a FEM analysis including the model of non-linearities induced by large deformations and the contact between the needle and the grasping device. Functional prototypes of both NGDs have been constructed and a first experimental assessment of their service capability is finally exposed.

Commentary by Dr. Valentin Fuster
2012;():75-83. doi:10.1115/DETC2012-70638.

A dynamically dexterous legged robot has the distinct property that the legs are continuously interacting with the environment. During walking and running, this interaction generates acoustic signals that carry considerable information about the surface being traversed, state of the robot legs and joint motors as well as the stability of the locomotion. Extracting a particular piece of information from this convolved acoustic signal however is an interesting and challenging area of research which we believe may have fundamental benefits for legged robotics research. For example, the identification of the surface that the robot travels on gives us the ability to dynamically adapt gait parameters hence improve dynamic stability. In the present paper, we investigate this particular sub-problem of surface identification using naturally occurring acoustic signals and present our results. We show that a spectral energy based feature set augmented by time derivatives and an average zero crossing rate carries enough information to accurately classify a number of commonly occurring indoor and outdoor surfaces using a popular higher dimensional vector quantizer classifier. Our experiments also suggest that VQ surface models may be velocity dependent. These initial results with a carefully collected but relatively limited dataset indicate a promising direction for our future research on improving outdoor mobility for dynamic legged robots.

Commentary by Dr. Valentin Fuster
2012;():85-94. doi:10.1115/DETC2012-70705.

This paper presents several innovative features that aim at improving the mechanical design of underactuated anthropomorphic grippers. Based on prototypes previously developed, the characteristics of a tendon-driven underactuated finger and a reconfigurable thumb are first presented. Their geometry, coverings and attachment principles are detailed. Then, a novel approach to mechanically couple the thumb with the four fingers is presented. Using a lever, this approach provides the ability to mechanically prescribe a desired distribution of the forces/velocities during the actuation. A static model is developed to visualize the possibilities offered by this principle. Also, a compact mechanism that allows underactuation between the four fingers is described. This mechanism significantly improves the synchronization of the outputs. Additionally, a mechanical selector is introduced that makes the gripper mechanically programmable by allowing to selectively block one or many outputs. The use of this mechanical selector, combined with the reconfigurable thumb and the underactuation between the fingers, allows a gripper to produce several grasping modes without the need of additional actuation. Finally, a prototype including all these features is briefly described.

Commentary by Dr. Valentin Fuster
2012;():95-104. doi:10.1115/DETC2012-70711.

A new class of actuated Spring-Loaded Inverted Pendulum (SLIP) models with hip actuation and leg damping has been developed, and is found to be more stable than the canonical version. However, it is not known how the addition of hip torque and leg damping change locomotion stability. In this paper, we study the effects of leg damping and hip torque on locomotion stability of actuated-SLIP models. All other modeling assumptions of SLIP are conserved. And hip torque is turned off during the flight phase. We show that for a given set of nondimensional SLIP parameters the hip torque and leg damping required for a periodic solution are not independent. Further, we show that adding hip torque and damping changes the dynamics of actuated-SLIP solutions in a non-intuitive way. When a very small amount of torque and damping are added the affect is initially to destabilize SLIP solutions. As torque and damping are added further, it eventually improves the stability properties of solutions.

Topics: Torque , Stability , Damping
Commentary by Dr. Valentin Fuster
2012;():105-115. doi:10.1115/DETC2012-70953.

The purpose of this paper is to categorize the current state of technology in flapping wing mechanisms of micro air vehicles (MAVs). One of the major components of MAVs is the flapping mechanism, which actuates wings to generate sufficient lift and propulsion force. The goal of the flapping wing mechanism design is to develop a highly efficient and highly robust mechanism, which converts the input motion, either rotational or translational, to a beating motion at a frequency ranging from several to hundreds of Hz. The current practice of designing flapping mechanisms follows an ad-hoc approach with multiple design, build, and test cycles. This design process is very inefficient, costly, time-consuming, and not applicable to mass production of MAVs. This work will be an important step towards a systematic approach for the design of flapping mechanisms for MAVs. In this paper, we will study 15 flapping mechanisms used in recent MAV projects worldwide. We classify these mechanisms based on workspace, compliant or rigid body, type synthesis, mobility, and actuator type. This survey of mechanism classification will serve as a resource for the continued design and development of smaller and more efficient MAVs.

Topics: Vehicles , Wings
Commentary by Dr. Valentin Fuster
2012;():117-124. doi:10.1115/DETC2012-71016.

Most existing lower limb orthosis use actuators and active controller to guide the motion of human lower limbs. Actuators with relatively large power are usually required to compensate the gravity effect of the human lower limbs, even for a normal walking. Hence, design of an orthosis for the weight balance of human lower limbs is desired. For the motion compatibility, the human hip joint is treated as a planar pair and the knee joint as a revolute pair. As a consequence, while the lower limb is in motion, the exact positions of the mass centers of the human lower limbs cannot be obtained. Hence, in this work, topological synthesis of the orthosis mechanisms, which can trace the mass centers of the human thigh and shank, respectively, is implemented. The weight balance of the human lower limbs is achieved by fitting a minimum number of zero-free-length springs. Based on the anthropometric parameters, dimensions of the lower limb orthosis is determined and the proposed design is justified by the simulation executed by the software of ProEngineer. Finally, a first generation prototype is built.

Commentary by Dr. Valentin Fuster
2012;():125-132. doi:10.1115/DETC2012-71083.

In the past few years, the authors have proposed several prototypes of a Cable-driven upper ARm EXoskeleton (CAREX) for arm rehabilitation. The key advantages of CAREX over conventional exoskeletons are: (i) It is nearly an order of magnitude lighter. (ii) It does not have conventional links and joints, hence does not require joint axes alignment and segment lengths adjustment. (iii) It does not limit the natural degrees-of-freedom of the upper limb. (iv) The structure of the exoskeleton is novel as the cables are routed from the proximal to the distal segments of the arm. Preliminary experimental results with CAREX on a robotic arm and on healthy subjects have demonstrated the effectiveness of the exoskeleton within “assist-as-needed” training paradigm. In this paper, we propose a novel approach to estimate the glenohumeral joint rotation center (GH-c) using measurements of shoulder joint angles and cable lengths. This helps in locating the glenohumeral joint rotation center appropriately within the kinematic model. As a result, more accurate kinematic model can be used to improve the training of human users. An estimation algorithm is presented to compute the GH-c in real-time. The algorithm was implemented on the latest prototype of CAREX which controls four degrees-of-freedom of the shoulder and elbow. Preliminary experiments were performed on two healthy subjects under two different scenarios: (i) GH-c was assumed to be a fixed point and (ii) GH-c was estimated using the proposed algorithm. Experimental results are presented to compare the two scenarios.

Topics: Rotation , Cables
Commentary by Dr. Valentin Fuster
2012;():133-141. doi:10.1115/DETC2012-71106.

Over the last fifty years there has been a steady advance in prosthetic foot technologies. These advances have primarily focused on more accurately mimicking the biologic foot for amputees. One field of research currently being explored is active/powered prosthetic feet in which the movement of the foot is actively controlled through the use of electric motors. Some of these feet also seek to reproduce the ankle torques seen in the biologic foot. This paper proposes a novel method for more accurately reproducing these ankle torques through the use of piezoelectrics in conjunction with the electric motors. FEA software is used to simulate the modification of ankle torques through the use of piezoelectric bending actuators in a general case. A number of different configurations for the piezoelectric strips are examined to test the versatility of the piezoelectrics in this application. The general trends of the ankle torque vs gait cycle found in the literature have been reproduced in the simulations.

Commentary by Dr. Valentin Fuster
2012;():143-149. doi:10.1115/DETC2012-71149.

In this paper, a novel simple robotic system is developed for surgical training in minimally invasive surgery (MIS). The robot automatically measures motion data of instruments in real time using internal encoders, without additional sensing mechanisms. Kinematics equations are integrated in the control software to map motor motion to the instrument tip motion. These recorded motion data then can be analyzed in the computer system for objective evaluation using well established criteria. A neural network algorithm is employed in real time as the observer of weight and inertia effects which are compensated through motor control. Experiment results show that this compact robot provides good stability and smooth motion while guiding instruments using surgeon input. The tracking resolution is sufficient for objective evaluation purposes. The robot combines the realistic feel of MIS instruments with the capability of the computer to tabulate objective measures of performance and skill. Its flexibility as a training instrument can be of great benefit in both providing surgeons with much-needed practice and assessing the outcomes of that practice.

Topics: Robots , Surgery
Commentary by Dr. Valentin Fuster
2012;():151-160. doi:10.1115/DETC2012-71256.

Snake-inspired locomotion is much more maneuverable compared to conventional locomotion concepts and it enables a robot to navigate through rough terrain. A rectilinear gait is quite flexible and has the following benefits: functionality on a wide variety of terrains, enables a highly stable robot platform, and provides pure undulatory motion without passive wheels. These benefits make rectilinear gaits especially suitable for search and rescue applications. However, previous robot designs utilizing rectilinear gaits were slow in speed. This paper introduces a new class of rectilinear gaits to be utilized by a snake-inspired robot design which is capable of pure linear motion and variable traction. The general model for the gait class is based on serial robot dynamics using the Lagrangian formulation. The gait class includes four unique gaits: a forward and a turning gait, which both emphasize speed for the robot; and a forward and turning gait which emphasize traction. Also, we perform an analysis of the variable traction concept.

Commentary by Dr. Valentin Fuster

36th Mechanisms and Robotics Conference: Compliant Mechanisms and Micro/Nano Mechanisms (A. Midha Symposium)

2012;():161-167. doi:10.1115/DETC2012-70045.

To meet the need of advanced compliant parallel grippers (CPGs), this paper deals with the conceptual design and modelling of a novel self-adaptive CPG for high-precision manipulation. A self-adaptive CPG is proposed by using a cymbal-type amplifier and two parallelogram modules at first. The self-adaptive grasping function ensures the mobility of one jaw if another jaw is constrained. Then the displacement amplification ratio and the force-displacement equations of the self-adaptive CPG are derived and compared with the FEA results. Finally, the variations, especially the case with a bistable mechanism as the jaw, are discussed. The self-adaptive grasping function of the proposed CPG is unique compared with the existing CPGs driven by only one linear actuator. Other good performance characteristics of the proposed self-adaptive CPG include: large-stroke, no stress-concentration, minimized parasitic rotation of the jaw, actuator isolation, and a simple and compact configuration.

Commentary by Dr. Valentin Fuster
2012;():169-179. doi:10.1115/DETC2012-70238.

Although there are many examples of multistable compliant mechanisms in the literature, most of them are of planar configurations. Considering that a multistable mechanism providing spatial motion could be useful in numerous applications, this paper explores the multistable behavior of the overconstrained spatial Sarrus mechanisms with compliant joints (CSMs). The kinetostatics of CSMs have been formulated based on the pseudo-rigid-body method. The kinetostatic results show that a CSM is capable of exhibiting bistability, tristability, and quadristability. Possible applications of multistable CSMs include deployable structures, static balancing of human/robot bodies and weight compensators.

Commentary by Dr. Valentin Fuster
2012;():181-190. doi:10.1115/DETC2012-70239.

The elliptic integral solution is often considered as the most accurate method for analyzing large deflections of cantilever beams in compliant mechanisms. In this paper, by explicitly including the number of inflection points (m) and the sign of the end-moment load (SM) in the derivation, a comprehensive solution based on the elliptic integrals is proposed for solving the large deflection problems. The comprehensive solution is capable of solving large deflections of cantilever beams subject to any kind of load cases and of any kind of deflected modes. A few deflected configurations of complex modes solved by the comprehensive solution are presented and discussed. The use of the comprehensive solution in analyzing compliant mechanisms is also demonstrated by a few case studies.

Commentary by Dr. Valentin Fuster
2012;():191-198. doi:10.1115/DETC2012-70321.

This paper describes a fully compliant constant-force micro-mechanism that enables dual-stage motion for nanoinjection. Nanoinjection is a recently developed process for delivering DNA into mouse zygotes via electrostatic accumulation and release of the DNA onto a microelectromechanical system (MEMS) lance.

The fully compliant constant-force nanoinjector is a concatenation of two separate mechanisms: a six-bar mechanism with compliant lamina-emergent torsional (LET) joints to raise the lance, and a pair of constant-force crank-sliders with LET joints positioned on either side of the six-bar mechanism to drive the lance forward.

The fully compliant nanoinjector exhibits self-reconfiguring metamorphic motion to first raise the lance to the midline of the zygote and then translate the lance forward with a controlled motion. This dual-stage motion is necessary for the lance to pierce the zygote without causing damage to the cell membrane.

The device achieves two sequential displacement behaviors in a compliant mechanism fabricated from a single, continuous piece of material.

Commentary by Dr. Valentin Fuster
2012;():199-210. doi:10.1115/DETC2012-70359.

This paper presents a procedure using Pseudo-Rigid-Body Models (PRBMs) to synthesize partially compliant mechanisms capable of approximating a shape change defined by a set of morphing curves in different positions. To generate a single-piece compliant mechanism, flexural pivots and flexible beams are both utilized in the mechanism. New topologies defined by compliant mechanism matrices are enumerated by modifying the components that make up a single degree-of-freedom (DOF) rigid-body mechanism. Because of the introduction of the PRBM for flexural pivots and the simplified PRBM for flexible beams, torsional springs are attached at the characteristic pivots of the 1-DOF rigid-body mechanism in order to generate a corresponding pseudo-rigid-body mechanism. A multi-objective genetic algorithm is employed to find a group of viable compliant mechanisms in the form of candidate pseudo-rigid-body mechanisms that tradeoff minimizing shape matching error with minimizing actuator energy. Since the simplified beam model is not accurate, an optimization loop is established to find the position and shape of the flexible beam using a finite link beam model. The optimal flexible beams together with the pseudo-rigid-body mechanism define the solution mechanism. The procedure is demonstrated with an example in which a partially compliant mechanism approximating two closed-curve profiles is synthesized.

Commentary by Dr. Valentin Fuster
2012;():211-219. doi:10.1115/DETC2012-70367.

Monolithic Flexure-based Compliant Mechanisms (MFCM) can functionally act as nonlinear springs by providing a desired load-displacement profile at one point on their structure. Once the MFCM topology is chosen, these particular springs can be conveniently synthesized by resorting to the well-known Pseudo-Rigid-Body approximation, whose accuracy strongly depends on the modeling precision of the flexures’ principal compliance. For various types of flexures, closed-form solutions have been proposed which express the compliance factors as functions of the flexure dimensions. Nonetheless, the reliability of these analytical relations is limited to slender, beam-like, hinges undergoing small deflections. In order to overcome such limitations, this paper provides empirical equations, derived from finite element analysis, that can be used for the optimal design of circular, elliptical, and corner-filleted flexural hinges with general aspect ratios on the basis of both principal compliance and maximum bearable stress. As a case study, a nonlinear spring conceived as a four-bar linkage MFCM is synthesized and simulated by means of finite element analysis. Numerical results confirm that the aforementioned empirical equations outperform their analytical counterparts when modeling thick cross-section hinges undergoing large deflections.

Commentary by Dr. Valentin Fuster
2012;():221-228. doi:10.1115/DETC2012-70377.

Flexure based stages are particularly important for vacuum applications because they combine low hysteresis, no wear and no contamination with a high supporting stiffness. However, flexure hinges inherently lose stiffness in supporting directions when deflected. Therefore the workspace to footprint ratio is limited. In this article we present the design and modeling of a two degrees of freedom cross flexure based stage that combines a large workspace to footprint ratio with high vibration mode frequencies. Because the mechanism is an assembly of optimized components, the stage is designed according to the exact constraint principle to avoid build-up of internal stresses due to misalignment. FEM results have been validated by measurements on an experimental test setup. The test setup has a workspace-area to footprint ratio of 1/32. The lowest measured natural frequency with locked actuators over a 60 × 60mm workspace was 80Hz.

Commentary by Dr. Valentin Fuster
2012;():229-238. doi:10.1115/DETC2012-70383.

This paper presents a design method dedicated to compliant mechanisms, with emphasis on the use of ant colony optimization to determine the optimal geometry of a mechanism. Ant colony optimization is of particular interest because it does not need any fine tuning of its internal parameters. This robustness and the efficiency of the design method are assessed in the context of the design of a surgical tool. The method is then used to propose a new architecture for an active cardiac stabilizer with integrated actuation, contrary to existing architectures.

Commentary by Dr. Valentin Fuster
2012;():239-247. doi:10.1115/DETC2012-70412.

In the discrete topology optimization, material state is either solid or void and there is no topology uncertainty problem caused by intermediate material state. The outer corner cutting and inner corner filling strategy is introduced in this paper for the discrete topology optimization of compliant mechanisms. The design domain is discretized into quadrilateral design cells and every quadrilateral design cell is further subdivided into triangular analysis cells. All outer and inner corners are eliminated with the corner handling strategy. To make the designed compliant mechanisms safe, the local stress constraint is directly imposed on each triangular analysis cell. To circumvent the geometrical bias against the vertical design cells, the binary bit-array genetic algorithm is used to search for the optimal topology. Two topology optimization examples of compliant mechanisms are solved based on the proposed corner handling strategy and subdivision approach.

Commentary by Dr. Valentin Fuster
2012;():249-258. doi:10.1115/DETC2012-70479.

The aim of this paper is to demonstrate how the principles of the Freedom, Actuation, and Constraint Topologies (FACT) synthesis approach may be applied to the design of compliant microstructural architectures that possess extreme or unusual thermal expansion properties (e.g., zero or large negative thermal expansion coefficients). FACT provides designers with a comprehensive library of geometric shapes, which may be used to visualize the regions wherein various microstructural elements can be placed for achieving desired bulk material properties. In this way, designers can rapidly consider and compare every microstructural concept that best satisfies the design requirements before selecting the final design. A screw-theory-based analytical tool is also provided in this paper to help designers calculate and optimize the thermal properties of microstructural concepts, which are generated using FACT. As a case study, this tool is used to calculate the negative thermal expansion coefficient of a microstructural architecture synthesized using FACT.

Commentary by Dr. Valentin Fuster
2012;():259-265. doi:10.1115/DETC2012-70592.

Annulus-shaped flexural pivots (ASFP), composed of three or more identical leaves that are symmetrically arrayed in an annulus, can be used widely in compliant mechanisms for their excellent performances. This paper proposes the accurate load-rotation models of ASFP with three straight leaves, which include the load cases of bending moment combined with horizontal force and vertical force. Firstly, the load-rotation models of ASFP are derived based on the Beam Constraint Model (BCM). Then, the rotational stiffness and buckling characteristics are analyzed based on the derived models. Finally, the accuracy of the models is validated by the finite element analysis (FEA). The relative error of the load-rotation models is within 7% for various load cases even if the rotational angle reaches 0.07 (4°). The results show that the models are accurate enough to be used for initial parametric designing of ASFP.

Topics: Modeling , Annulus
Commentary by Dr. Valentin Fuster
2012;():267-275. doi:10.1115/DETC2012-70670.

We propose a novel, high degree of freedom variable stiffness joint for use in a miniature snake-like robot for minimally invasive surgeries via granular jamming. By pulling granule filled membrane-columns under vacuum, the columns and joint stiffen as the granular matter begin to jam. In our experiments, we achieved a four-fold increase in stiffness, and the stiffness can be achieved while the columns are straight or bent. Current flexible manipulators in industrial and medical robotics have followed two dominating methods of actuation and stiffness control. The first method is the continuum manipulator, which utilizes tendons or rods to bend the manipulator in a continuous fashion. The second method is classified as the highly articulated robot, where the manipulator is comprised of multiple segments linked by motor-driven universal joints. Like the latter, our manipulator is highly articulated, however stiffness of each joint can be independently controlled by the granular jamming principle. This paper studies the effect of grain type and vacuum pressure for stiffness tuning. We found that granules with a matte surface were able to achieve higher stiffnesses, with a cube shape exhibiting the highest stiffness, but at the cost of high levels of hysteresis.

Topics: Stiffness
Commentary by Dr. Valentin Fuster
2012;():277-283. doi:10.1115/DETC2012-70689.

This paper presents a concept for producing a Statically Balanced Shape-Shifting Surface (SB-SSS). In this context, an SB-SSS is a surface that can require near-zero magnitude force changes to accomplish a change in shape while retaining effectiveness as a physical barrier. This paper focuses on how to statically balance a specifically-designed compliant mechanism and how to incorporate this mechanism into a polygonal cell. The mechanism consists of a compliant Peaucellier-Lipkin linkage layered with a pre-stressed link as the balancer. Prior art is presented that can show how a polygonal cell can be incorporated into a surface via a tiling array. Specifically shaped overlapping thin plates are used to retain the physical barrier requirement. The demonstration of a virtually zero-force Shape-Shifting Surface (SSS) suggests that SSS’s can be designed with a wide range of force-displacement properties, i.e. ranging from that of a square of the parent material to the zero-force mechanism presented here. Applications for an SB-SSS may be macro-scale or micro-scale and may include sensors, biomedical applications, defense applications, and variable stiffness materials.

Topics: Shapes
Commentary by Dr. Valentin Fuster
2012;():285-292. doi:10.1115/DETC2012-70772.

This paper presents two compliant micro-manipulators with different structures. One uses 3-PRR mechanism while the other one adopts 3-RPR mechanism. Both of the two micro-manipulators have two translational degrees of freedom (DOF) and one rotational DOF. But the properties, such as workspace, of the two micro-manipulators are not the same. In this paper, the workspaces are studied and compared. First, the structural differences are presented. Then, the stiffness derivations of the two micro-manipulators are given and the workspaces are calculated considering the properties of piezoelectric (PZT) actuators. Finally the finite element analysis and prototype experiments are performed to validate the obtained results.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2012;():293-301. doi:10.1115/DETC2012-71018.

This paper presents an approach of utilizing parasitic motion compensation for designing high-precision flexure mechanism. This approach is expected to improve the accuracy of flexure mechanism without changing its degree of freedom (DOF) characteristic. Different from the method which mainly concentrates on how to compensate the parasitic translation error of a parallelogram-type flexure mechanism existing in most of the literatures, the proposed approach can compensate the parasitic motion produced by rotation in company with translation. Besides, the parasitic motion of a flexure mechanism is formulated and evaluated by utilizing its compliance. To specify it, the compliance of a general flexure mechanism is calculated firstly. Then the parasitic motions introduced by both rotation and translation are analyzed by utilizing the resultant compliance. Subsequently, a compliance-based compensation approach is addressed as the most important part of this paper. The design principles and procedure are further proposed in detail to help with improving the accuracy of the flexure mechanism. Finally, a case study of a 2R1T flexure mechanism is provided to illustrate this approach, and FEA simulation is implemented to demonstrate its validity. The result shows that it is a robust design method for the design of high-precision flexure mechanism.

Commentary by Dr. Valentin Fuster
2012;():303-310. doi:10.1115/DETC2012-71092.

Accurate analysis models are critical for effectively utilizing elastomeric joints in miniature compliant mechanisms. This paper presents work toward the characterization and modeling of miniature elastomeric hinges. The modeling portion is achieved using finite element analysis (FEA). Also presented is a 2-dimensional pseudo rigid body (PRB) analytical model for these hinges. Characterization was carried out in the form of several experimental bending tests and tension tests on representative hinges in 5 different configurations. The results of these experiments were then compared to the same tests modeled using FEA. We have represented the experimental results using FEA to within 12% error. This allows the use of FEA to model more complicated mechanisms’ behavior with some assurance of accuracy. Based on these tests and FEA models, a simplified 2-dimensional PRB analytical model was developed, consisting of a torsional spring, a linear spring, and another torsional spring in series. These analytical models enable us explore large design spaces efficiently. The accuracy of this model for geometries without corner effects has been verified to within 3% error when compared to FEA models in bending, and 17% in tension.

Commentary by Dr. Valentin Fuster
2012;():311-320. doi:10.1115/DETC2012-71115.

This paper presents the optimization of hexagonal honeycomb structures with internal contact mechanisms for energy absorption applications. While extensive work has been reported in the literature on traditional honeycombs of varying geometries under dynamic and static loading, contact-aided compliant cellular mechanisms under quasi-static crushing or impact have not been previously considered. This paper addresses this void through the optimization of a hexagonal honeycomb unit cell containing a contact mechanism. An optimization problem is formulated that maximizes the strain energy per area of a contact-aided compliant cellular mechanism. Two- and three-variable optimization problems are considered, using variables that define the cell geometry and the initial contact gap. It is found that with the addition of a contact mechanism, more strain energy can be absorbed when compared to the same cell without a contact mechanism.

Commentary by Dr. Valentin Fuster
2012;():321-330. doi:10.1115/DETC2012-71159.

This paper presents designs for Multistable Shape-Shifting Surfaces (MSSS) by introducing bistability into the Shape-Shifting Surface (SSS). SSSs are defined as surfaces that retain their effectiveness as a physical barrier while undergoing changes in shape. The addition of bistability to the SSS gives the surface multiple distinct positions in which it remains when shifted to, i.e. by designing bistability into a single SSS link, the SSS unit cell can change into multiple shapes, and stabilize within the resulting shape, while maintaining integrity against various forms of external assaults normal to its surface. Planar stable configurations of the unit cell include, expanded, compressed, sheared, half-compressed, and partially-compressed, resulting in the planar shapes of a large square, small square, rhombus, rectangle, and trapezoid respectively. Tiling methods were introduced which gave the ability to produce out-of-plane assemblies using planar MSSS unit cells. Applications for MSSSs include size-changing vehicle beds, expandable laptop screens, deformable walls, and volume-changing rigid-storage containers. Analysis of the MSSS was done using Pseudo-rigid-Body Models (PRBMs) and Finite Element Analysis (FEA) which ensured bistable characteristics before prototypes were fabricated.

Topics: Shapes
Commentary by Dr. Valentin Fuster
2012;():331-340. doi:10.1115/DETC2012-71247.

In a Solar Power Tower (SPT) system, the ideal shape of a heliostat concentrator is a section of paraboloid which is a function of the location in the array and the incidence sun angle. This shape is difficult to achieve and limits the system efficiency. A shape-optimized compliant (SOC) design of parabolic heliostats is presented here to solve this problem. An approximation of the ideal shape is suggested to use an optimized stationary paraboloid shape which only varies with heliostat location in the array. A compliant structure design is proposed that to use a simple flat mirror with a two-dimensional tailored stiffness profile to form the required parabolic surface using adjustment mechanisms at each corner. This design is validated by numerical simulations including FEA tools, ray tracing, and classical nonlinear optimization. The annual performance shows that the SOC heliostat will substantially improve the efficiency and benefit the SPT system.

Commentary by Dr. Valentin Fuster
2012;():341-349. doi:10.1115/DETC2012-71250.

This paper studies the workspace of a flexure-based, hexa-pod nanopositioner previously built by the National Institute of Standards and Technology (NIST) which can produce high-resolution motions in six degree of freedom by actuating linear actuators on planar tri-stage. Because there is a lack of work in workspace of such kind of compliant mechanisms, the controller is typically limited to a very small range of motion in order to avoid material failure. In this work, we seek to derive a kinematic model for predicting the workspace of such kind of flexure based platforms by assuming that their workspace is mainly constrained by the deformation of flexure joints. We first study the maximum deformation including bending and torsion angles of each flexure joint. We then derive the inverse kinematics and calculation of bending and torsion angles of this compliant platform. To obtain the workspace of the mechanism, we developed a computational algorithm that varies the displacement of the top platform to extreme positions till the deformation of any flexure exceeding a maximum value. To demonstrate this approach, we provided example studies including constant orientation workspace and constant position workspace. We compare results with a finite element model of the entire platform. The error is 4.74% for original analytical model and 8.26% for simplified analytical model. This model is beneficial in guiding design engineers in maximizing workspace of flexure based parallel compliant mechanisms. To the end-users of the positioner, it gives them a guidance on how to efficiently exploit the workspace of the nanopositioner.

Commentary by Dr. Valentin Fuster
2012;():351-361. doi:10.1115/DETC2012-71400.

This paper provides an efficient method of analysis for a fixed-guided compliant beam with an inflection point, subjected to beam end load or displacement boundary conditions, or a combination thereof. To enable this, such a beam is modeled as a pair of well-established pseudo-rigid-body models (PRBMs) for fixed-free compliant beam segments. The analysis procedure relies on the properties of inflection in developing the necessary set of static equilibrium equations for solution. The paper further discusses the multiplicity of possible solutions, including displacement configurations, for any two specified beam end boundary conditions, depending on the locations of the effecting force and/or displacement boundary conditions. A unique solution may exist when a third beam end boundary condition is specified; however, this selection is not unconditional. A deflection domain concept is proposed to assist with the selection of the third boundary condition in a more realistic manner.

Commentary by Dr. Valentin Fuster
2012;():363-371. doi:10.1115/DETC2012-71498.

The objective of this work is to create an analytical framework to study the non-linear dynamics of beam flexures with a tip mass undergoing large deflections. Hamilton’s principal is utilized to derive the equations governing the non-linear vibrations of the cantilever beam and the associated boundary conditions. Then, using a single mode approximation, these non-linear partial differential equations are reduced to two coupled non-linear ordinary differential equations. These equations are solved analytically using combination of the method of multiple time scales and homotopy perturbation analysis. Closed-form, parametric analytical expressions are presented for the time domain response of the beam around and far from its internal resonance state. These analytical results are compared with numerical ones to validate the accuracy of the proposed closed-form model. We expect that the qualitative and quantitative knowledge resulting from this effort will ultimately allow the analysis, optimization, and synthesis of flexure mechanisms for improved dynamic performance.

Commentary by Dr. Valentin Fuster
2012;():373-377. doi:10.1115/DETC2012-71509.

Static balancing is an important contribution to compliant mechanisms enabling low operating force, thus allowing high mechanical efficiency. Preloading is generally needed in statically balanced compliant mechanisms, which at smaller scales presents a significant challenge. Physical handling of zero-force structures without causing damage also becomes difficult. This paper presents a solution to both of these issues. A novel compliant connection mechanism based on bistable beams was used to precisely preload the system in the direction of motion without backlash. Once this bistable mechanism is engaged by loading beyond its threshold, the system is in operating condition, i.e. the ON position. When the connection mechanism is disengaged (OFF position), it is much stiffer than it is in the statically balanced state and therefore more robust for handling purposes. As a demonstrator, we present the first statically balanced gripper with a fully compliant ON/OFF-connection mechanism allowing pre-loading collinear with the direction of motion. The combination of a pre-loaded bistable mechanism (i.e. negative stiffness) and a voluntary closing gripper (i.e. positive stiffness) is used for static balancing (i.e. zero stiffness and zero actuation force). The results show that the actuation force is reduced by at least 91% when the preload is engaged. The proposed ON/OFF connection shows a promising method for pre-loading compliant mechanisms or related devices.

Commentary by Dr. Valentin Fuster
2012;():379-392. doi:10.1115/DETC2012-71514.

Many applications require a compliant mechanism to transmit rotation from one direct to another direct with constant velocity. This paper presents a literature survey towards the design of compliant constant velocity universal joints. The traditional constant velocity universal joints available from the literature were studied, classified and their mechanical efficiencies were compared. Also the graph representation of them was studied. In the same manner, literature review for different kind of compliant joints suitable for the Rigid-Body-Replacement of constant velocity universal joints was also performed. For the first time a comparison with analytical data of compliant joints was performed. All of compliant universal joints are non-constant velocity and designed based on rigid Hooke’s universal joint. Also we show there are no equivalent compliant joints for some rigid-body joints such as cylindrical joint, planar joint, spherical fork joint and spherical parallelogram quadrilateral joint. However, we may achieve them by combining numbers of available compliant joints. The universal joints found are non-compliant non-constant velocity universal joint, non-compliant constant velocity universal joint or compliant non-constant velocity universal joint. A compliant constant velocity universal joint has a great horizon for developments, for instance in medical or rehabilitation devices.

Commentary by Dr. Valentin Fuster
2012;():393-402. doi:10.1115/DETC2012-71515.

In this paper, we present the different steps towards the development of miniature compliant bending joint and gripper with high mechanical performances. These low encumbrance structures (5 mm cross-section) should deliver, with few actuation force, a large output displacement (90° bending, and 60° jaws opening respectively) under large output loads.

Firstly, we describe the theoretical studies that have been investigated in order to optimally dimension these structures. For the bending joint, the design has been inspired from the literature and optimized. For the gripper, a non-intuitive design has been generated using a multi-objective optimal synthesis method. Finally, these compliant structures have been prototyped, and characterized.

As an applicative example, they have been integrated into the end-effector of a surgical instrument. Despite the limited output load performances obtained (12.5 mN.m output torque with a 2.1 N actuation force, and 0.2 N gripping force respectively), these new building blocks demonstrate the ability of millimeter-size robotic devices further miniaturization.

Commentary by Dr. Valentin Fuster
2012;():403-410. doi:10.1115/DETC2012-71536.

Turbo-machinery sealing is a challenging problem due to the varying clearances caused by thermal transients, vibrations or bearing lift–off. Conventional labyrinth seals have to be assembled with large clearances to avoid rubbing during rotor transients and this results in large leakage and lower efficiency. In our previous work, we have proposed a Progressive Clearance Labyrinth Seal which is mounted on flexures and employs progressively tighter teeth from the upstream to the downstream direction. The clearance progression gives rise to a feedback phenomenon whereby a small tip-clearance is maintained between the seal and the rotor. The flexures play a very important role in the design of this seal. They are required to have low radial stiffness relative to the fluidic feedback stiffness, so that the seal can move freely in response to the self-correcting forces. The axial stiffness has to be high to limit the displacement in that direction. Most importantly, the flexures need to provide extremely high twist stiffness, since a small twist can cause large changes in the clearance progression necessary for the self–correcting behavior. In this paper, we propose a novel zero–twist flexure architecture which preserves radial compliance and twist stiffness. We first create a simple analytical model to illustrate the design concept. An experimental setup is built and the design is validated on representative flexure geometry.

Commentary by Dr. Valentin Fuster

36th Mechanisms and Robotics Conference: Mechanism Analysis and Synthesis

2012;():411-418. doi:10.1115/DETC2012-70034.

In this paper, the complete shaking force and moment balancing conditions for a special class of planar 5R linkages, the contra 5R linkage, is considered. Contra 5R linkages are planar 5R linkages in which the two input links are mechanically coupled and rotate at the same speed in opposite directions. A method to derive necessary and sufficient conditions on the design parameters to achieve moment balancing without introducing additional components is presented. Using this method, a complete classification of all shaking force and moment balanced contra 5R linkages is given.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2012;():419-426. doi:10.1115/DETC2012-70162.

This paper deals with the three-position motion generation problem with two specific grounded link lengths. There are two infinities of solutions for selecting the two links on the derived contours of the link lengths. These points on the contours are circle points or center points. After one half of the basic four bar had been selected on the contour, two infinities of solutions remained. These solutions can be mapped in a plane to determine where the particular types of mechanisms occur. Furthermore after one half of the basic four bar had been selected on the contour, one infinity of solutions still remained on the other contour. This indicates two infinities of solutions are still remained for the two given link lengths. These contours can be displayed in the solution space in which the motion generation is defined. With these significant useful information the better mechanism can be obtained, which satisfies more design conditions. Expressions of the contours are derived. Two numerical examples are used for illustration, but the results can be applied to any three-position motion generation problem.

Commentary by Dr. Valentin Fuster
2012;():427-434. doi:10.1115/DETC2012-70191.

A novel type of parallel wrist (PW) is proposed which, differently from previously presented PWs, features a single-loop architecture and only one nonholonomic constraint. Due to the presence of a nonholonomic constraint, the proposed PW type is under-actuated, that is, it is able to control the platform orientation in a three-dimensional workspace by employing only two actuated pairs, one prismatic (P) and the other revolute (R); and it cannot perform tracking tasks. Position analysis and path planning of this novel PW are studied. In particular, all the relevant position analysis problems are solved in closed form, and, based on these closed-form solutions, a path-planning algorithm is built.

Commentary by Dr. Valentin Fuster
2012;():435-440. doi:10.1115/DETC2012-70193.

In both planar and spatial parallel mechanisms, selection of the structural parameters for a desired workspace generally employs the use of numerical methods. However, using the closed-form solution, if it exists, facilitates workspace-based design and optimization of the mechanism, and may significantly reduce the required time and calculation for finding the workspace of the mechanism. This paper presents a general and comprehensive closed-form solution for the reachable workspace of a 2-RPR planar parallel mechanism. The workspace of the mechanism is analyzed step-by-step in detail and its boundary is derived analytically. Since the solution is closed-form, it has high accuracy and reliability. Furthermore, the provided solution can be employed to solve the workspace of similar mechanisms in a closed-form manner including other n-RPR planar parallel mechanisms.

Commentary by Dr. Valentin Fuster
2012;():441-449. doi:10.1115/DETC2012-70211.

This paper addresses the synthesis problem of Watt-I and Stephenson-IIIa six-bar linkages motion generation for four specified task positions. Both of them have one thing in common — theirs floating links which used as end-effectors are connected to a coupler plane of a four-bar linkage. Once the task positions of end-effector are given, we can calculate the corresponding positions of the coupler plane. Then our focus is on the synthesis of a four bar-linkage and the way that a RR chain can be attached to constrain the links of this four-bar linkage. This synthesis problem of four-bar linkage motion generation can be settled by a solution region method. And then we can present an equation of pivot curve that each point on this curve can generate a satisfactory RR chain. A new local solution region that is more practicable is presented by the last numerical example.

Commentary by Dr. Valentin Fuster
2012;():451-459. doi:10.1115/DETC2012-70254.

This paper investigates the nature of the contact between the load transferring surfaces in the roller screw mechanism, i.e., between the screw and roller threads and between the nut and roller threads. The analysis is applied to both planetary roller screws and recirculating roller screws. Prior work has neglected to take a fundamental approach toward understanding the mechanics of the contact between these components, and as a consequence, detailed analysis of aspects such as contact mechanics, friction, lubrication, and wear are not carried out correctly. Accordingly, in this paper, the principle of conjugate surfaces is used to establish contact at the screw-roller and nut-roller interfaces. The in-plane angles to the contact points are derived and it is shown that for the screw-roller interface, the contact point cannot lie on the bodies’ line of centers as has been the assumption in previous papers. Then, based on the curved profile of the roller thread, the radii of contact on the roller, screw, and nut bodies are also derived. Knowledge of the contact point locations is necessary to understand the interaction forces between the key components of the roller screw mechanism. In addition, accurate estimates of the radii of contact are necessary for minimizing the phenomenon of roller migration, a condition that can cause binding between components and eventually lead to the destruction of the mechanism. Last, the principal radii of curvature at the contact points and the angle between the principal axes are derived. These are essential for further development of the contact mechanics, such as the surface stresses, deformations, and consideration of wear.

Topics: Kinematics , Screws , Rollers
Commentary by Dr. Valentin Fuster
2012;():461-467. doi:10.1115/DETC2012-70441.

The Peaucellier linkage is one of only a handful of known, single-degree-of-freedom mechanisms that trace an exact straight line. Although the traced output is straight, the relation between input rotation angle and output position along the traced line is nonlinear. The purpose of this study is to investigate the composite motion of stacked Peaucellier straight-line mechanisms. After stacking, the original straight-line output transforms into a complex curve whose shape is dependent on the motion of all of the component mechanisms, their geometric parameters, and how the component Peaucellier cells are interconnected. MATLAB software was used to generate output curves considering different stacking configurations and mechanism sizes. MATLAB was also used to analyze the final data and identify correlations between the mechanism link sizes, stacking configurations, and relative output curves. Based on a polynomial fitting technique, resultant output of the stacked mechanisms was generally found to be of 6th order except when purposefully constrained. This is a first attempt to characterize kinematic trace curves for this type of stacked straight-line linkage system.

Commentary by Dr. Valentin Fuster
2012;():469-476. doi:10.1115/DETC2012-70457.

The paper focuses on the extension of the virtual-joint-based stiffness modeling technique for the case of different types of loadings applied both to the robot end-effector and to manipulator intermediate points (auxiliary loading). It is assumed that the manipulator can be presented as a set of compliant links separated by passive or active joints. It proposes a computationally efficient procedure that is able to obtain a non-linear force-deflection relation taking into account the internal and external loadings. It also produces the Cartesian stiffness matrix. This allows to extend the classical stiffness mapping equation for the case of manipulators with auxiliary loading. The results are illustrated by numerical examples.

Commentary by Dr. Valentin Fuster
2012;():477-483. doi:10.1115/DETC2012-70458.

While there have been ample amount of publication on traditional four-bar transmission characteristics, little is found in the field relating to the transmission of a singular type of four-bar, namely, the force-input, coupler-driven variety. In contrast to the conventional torque-input, crank-driven four-bars, the use of this new category of linkage is only gradually surfacing. In this paper, a novel performance indicator called the Collinearity Circle is proposed, which is used to monitor the effectiveness of the transmission in a force-input, coupler-driven four-bar. The salient feature of this Collinearity Circle lies not only in its convenient shape, but also in its simple derivation, which can be shown to be merely geometry-dependent. Like the well known instant center, which is also only geometry-dependent, the proposed Collinearity Circle will be proved to be a handy addition to the kinematics toolbox for its power to enable speedy construction and ballpark estimations on the transmission properties of force-input, coupler-driven mechanisms.

Commentary by Dr. Valentin Fuster
2012;():485-495. doi:10.1115/DETC2012-70490.

This paper presents optimizations of a parallel kinematic manipulator used for a machine tool in terms of its workspace and stiffness. The system stiffness and workspace of the parallel manipulator are conducted in the paper. In order to locate the maximum system stiffness and workspace, single and multi objective optimizations are performed in terms of rotation angles in x and y axes and translation displacement in z axis with Genetic Algorithms. By optimizing the design variables including geometric dimensions of the manipulator, the system stiffness and workspace of the proposed parallel kinematic manipulator has been greatly improved.

Commentary by Dr. Valentin Fuster
2012;():497-504. doi:10.1115/DETC2012-70621.

Parallel manipulators (PMs) with multiple operation modes are novel reconfigurable PMs which use less number of actuators and can be reconfigured without disassembly. Although several classes of PMs with multiple operation modes that have the same DOF (degrees-of-freedom) in all the operation modes have been proposed, only one class of variable-DOF PMs with multiple operation modes — PMs with multiple operation modes that do not have the same DOF in all the operation modes — have been proposed so far. This paper deals with the type synthesis of variable-DOF PMs with both planar and 3T1R (or Schönflies motion which has three translational DOF and 1 rotational DOF) operation modes. The axes of rotation of the moving platform in the planar operation mode are not parallel to the axes of rotation of the moving platform in the 3T1R operation mode. At first, an approach to the type synthesis of PMs with multiple operation modes is recalled. Based on the results on the type synthesis of planar PMs and 3T1R PMs, the types of variable-DOF PMs with both planar and 3T1R operation modes are then obtained. This work can be extended to the type synthesis of other classes of PMs with multiple operation modes.

Commentary by Dr. Valentin Fuster
2012;():505-511. doi:10.1115/DETC2012-70626.

This paper presents a simple and systematic method for type synthesis of four-degree-of-freedom uncoupled parallel manipulators with two-translational and two-rotational (2T2R) motion components. Based on the concept of hybrid manipulator, one uncoupled 2T2R hybrid manipulator, which is composed of one full-isotropic planar 2T1R parallel manipulator and one revolute joint in serial assembly, is designed first. Then the structure synthesis of the fourth leg of 2T2R parallel manipulator is performed in terms of the reciprocal screw theory. Finally, the type synthesis of uncoupled 2T2R parallel manipulators is realized by combining the uncoupled 2T2R hybrid manipulator and one of the synthesized fourth legs. The Jacobian of the uncoupled 2T2R parallel manipulator is a 4×4 diagonal matrix. Therefore, there exists a one-to-one correspondence between the input velocity space of the actuated joints and the output velocity space of the moving platform. Moreover, both the control design and the path planning of these proposed manipulators are very simple.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2012;():513-523. doi:10.1115/DETC2012-70665.

The graph layout problem arises frequently in the conceptual stage of mechanism design, specially in the enumeration process where a large number of topological solutions must be analyzed. Two main objectives of graph layout are the avoidance or minimization of edge crossings and the aesthetics. Edge crossings cannot be always avoided by force-directed algorithms since they reach a minimum of the energy in dependence with the initial position of the vertices, often randomly generated. Combinatorial algorithms based on the properties of the graph representation of the kinematic chain can be used to find an adequate initial position of the vertices with minimal edge crossings. To select an initial layout, the minimal independent loops of the graph can be drawn as circles followed by arcs, in all forms. The computational cost of this algorithm grows as factorial with the number of independent loops. This paper presents a combination of two algorithms: a combinatorial algorithm followed by a force-directed algorithm based on spring repulsion and electrical attraction, including a new concept of vertex-to-edge repulsion to improve aesthetics and minimize crossings. Atlases of graphs of complex kinematic chains are used to validate the results. The layouts obtained have good quality in terms of minimization of edge crossings and maximization of aesthetic characteristics.

Commentary by Dr. Valentin Fuster
2012;():525-534. doi:10.1115/DETC2012-70680.

This paper presents an evolutionarily design change for the Delta parallel robot. The proposed design change increases the useful workspace of the robot and aids in permanently avoiding singularities on the workspace. This is accomplished by means of a new intermediate parallel link.

This also simultaneously increases the total workspace volume and the stiffness at the outer limits of the workspace.

The design is analyzed and the inverse kinematics, stiffness and dexterity relations are formulated. Subsequently, an optimization problem is formulated that aims at taking advantage of the new attributes and illustrate its benefits to the robotic design. The results are clearly illustrated by comparing the robot with the new link to an equivalent robot without it.

Lastly, the developed design is 3D modeled to test and verify functionality.

Commentary by Dr. Valentin Fuster
2012;():535-540. doi:10.1115/DETC2012-70693.

In this paper, a new type of the positioner is proposed, which has with dual-drive and dual-screw. Comparing with the positioner of the traditional gear transmission system, the positioner with the new mechanism has less power and less work space. Based on the designing requirements, we optimized the dimensions of the mechanism of the positioner, and carried out the kinematic and dynamic analysis of the positioner. The strength and the rigidity of the positioner are analyzed by the use of FEM. Finally, according to fuzzy mathematical theory, the reliability of the mechanism motion of the positioner is studied.

Commentary by Dr. Valentin Fuster
2012;():541-550. doi:10.1115/DETC2012-70720.

Slat/flap driven mechanisms are essential transmission components of high lift systems and may contain combinations of linkages, ball screws, cam tracks and gears. This paper is, therefore, devoted to the structural synthesis of the aircraft slats/flaps driven mechanisms with six links. Based on the concept of generalization and specialization of mechanisms, all feasible new design alternatives are systematically derived and summarized as a complete atlas listed in Appendix. The provided atlas is useful for designers when considering alternative topological structures of the slats/flaps driven mechanisms in the future.

Topics: Aircraft
Commentary by Dr. Valentin Fuster
2012;():551-557. doi:10.1115/DETC2012-70721.

In this paper, we consider the problem of designing planar six-bar linkages which can be driven by prismatic joints at its base. We explore various ways on how two RR chains can be used to constraint a PRR planar serial chain such that the system yields one-degree of freedom yet passes through a set of five specified task positions. We formulate and solve the design equations as well as analyze the resulting planar six-bar linkage. We demonstrate the synthesis process with the design of the seat of a wheelchair such that it is able to transform itself to be used as a rehabilitation guide during rehabilitation.

Topics: Linkages , Chain
Commentary by Dr. Valentin Fuster
2012;():559-564. doi:10.1115/DETC2012-70795.

The fundamental work of type synthesis of robot mechanisms is to research and develop the performance criterion for evaluating the characteristics of robot end-effectors and consequently come up with the classification of mechanisms. The motion characteristics of end-effectors contain translation and rotation. Traditionally, mechanisms are classified only according to the existence and quantity of these two kinds of motion characteristics without considering the succession of motion, which has remarkable influence on the topological performance property of end-effectors. In this paper, we propose the conception of rotational completeness, which describes the rotational ability of end-effectors, based on the axis movement theorem. The GF Sets are classified into three categories according to the rotational completeness of end-effectors. We enumerated all three classes of GF sets and illustrated the effectiveness of GF sets in evaluating the characteristics of robot end-effectors.

Commentary by Dr. Valentin Fuster
2012;():565-572. doi:10.1115/DETC2012-70846.

Parallel mechanisms which can realize three rotational motions are very important in the parallel mechanism family. Not the same with the traditional spherical parallel mechanism, a new kind of 3-DOF (degree of freedom) rotational parallel mechanism with no intersecting axes (RPMNIA) are proposed in this paper. This kind of rotational parallel mechanisms have the advantages of easy manufacturing. A new approach using the screw theory and the subchain theory is proposed to design the branches with only one constraint force and some new one-force-branches are found. Using these new branches, a group of 3-DOF rotational parallel mechanisms without intersecting axes are synthesized.

Commentary by Dr. Valentin Fuster
2012;():573-578. doi:10.1115/DETC2012-70849.

In this paper a new rotational parallel mechanism which has three rotational freedoms is studied. This mechanism consists of only revolute joints. In this mechanism, no joints intersect with each other. The constraint and motion properties are analyzed. The inverse kinematics is solved and the orientation workspace is studied. In the end, the relationship between the orientation workspace and the link lengths is shown.

Commentary by Dr. Valentin Fuster
2012;():579-588. doi:10.1115/DETC2012-70878.

Proposed in this paper is a methodology to synthesize a RCCC four-bar linkage intended for pick-and-place operations. The synthesis problem is set in the context of rigid-body guidance, which can be solved exactly for up to four prescribed poses of the coupler link. As a consequence, for a pick-and-place operation, the selection of the unspecified two intermediate poses is thus left up to the mechanism designer’s judgment. In this paper, we propose a method to determine the two intermediate poses resorting to the concept of robustness. In fact, robustness is needed in this context to overcome the presence of uncertainty due to the selection of the two 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. A numerical example is included to validate the concepts and illustrate the application of the methodology proposed here.

Topics: Kinematics
Commentary by Dr. Valentin Fuster
2012;():589-604. doi:10.1115/DETC2012-70880.

Structure equations of mechanisms are well-known to give rise to algebraic constraint manifolds that describe the space of poses available to a certain link (usually, end-effector or coupler) of open chains or mechanisms. In this paper, by using planar quaternion representation for planar displacements, we obtain constraint manifold of such manipulators and show that the task of dimensional synthesis of a planar parallel manipulator (PPM) is reduced to simple geometric manipulation of the manifold in the Image Space. Earlier, this approach has been shown to work for planar 6R closed chain mechanisms as well as for RRR- and RPR-type leg topologies of a PPM. Here, we complete the extension to other five leg topologies and provide a developer version software tool for dimensional synthesis of a PPM.

Topics: Design , Manipulators
Commentary by Dr. Valentin Fuster
2012;():605-614. doi:10.1115/DETC2012-70904.

This paper introduces a novel way to augment the knowledge and methods of rigidity theory to the topological decomposition and synthesis of gear train systems. A graph of gear trains, widely reported in the literature of machine theory, is treated as a graph representation from rigidity theory—the Body-Bar graph. Once we have this Body-Bar graph, methods and theorems from rigidity theory can be employed for analysis and synthesis. In this paper we employ the pebble-game algorithm, a computational method which allows determination of the topological mobility of mechanisms and the decomposition of gear trains into basic building blocks—Body-Bar Assur Graphs. Once we gain the ability to decompose any gear train into standalone components (Body-Bar Assur Graphs), this paper suggests inverting the process and applying the same method for synthesis. Relying on rigidity theory operations (Body-Bar extension, in this case), it is possible to construct all of the Body-Bar Assur Graphs, meaning the building blocks of gear trains. Once we have these building blocks at hand, it is possible to recombine them in various ways, providing us with a topological synthesis method for constructing gear trains. This paper also introduces a transformation between the Body-Bar graph and other graph representations used in mechanisms, thus leaving room for the application of the proposed synthesis and decomposition method directly to known graph representations already used in machine theory.

Commentary by Dr. Valentin Fuster
2012;():615-626. doi:10.1115/DETC2012-70918.

This paper presents a family of one-DOF highly overconstrained regular and semi-regular deployable polyhedral mechanisms (DPMs) that perform radially reciprocating motion. Based on two fundamental kinematic chains with radially reciprocating motion, i.e. the PRRP chain and a novel plane/semi-plane-symmetric spatial eight-bar linkage, two methods, i.e. the virtual-axis-based (VAB) method and the virtual-centre-based (VCB) method are proposed for the synthesis of the family of regular and semi-regular DPMs. Procedure and principle for synthesizing the mechanisms are presented and selected DPMs are constructed based on the five regular Platonic polyhedrons and the semi-regular Archimedean polyhedrons, Prism polyhedrons and Johnson polyhedrons. Mobility of the mechanisms is then analysed and verified using screw-loop equation method and degree of overconstraint of the mechanisms are investigated by combing the Euler’s formula for polyhedrons and the Grübler-Kutzbach formula for mobility analysis of linkages.

Commentary by Dr. Valentin Fuster
2012;():627-636. doi:10.1115/DETC2012-70965.

One of the most important considerations in the design of robots is mobility. How does the system traverse the terrain and environment where it is expected to operate? In past efforts, engineers and scientists have received inspiration from man-in-the-loop vehicles and modes of mobility used by animals. While amazing advancements have been achieved, this top-down approach tends to focus on one specific solution to a problem which may cause other solutions to be overlooked. This paper approaches the mobility problem from a different point of view. Starting with the most basic three dimensional shape, a regular tetrahedron, we explore seven different modes of mobility arising from simple modifications of the initial shape. These resultant modes are then resolved into corresponding, existing mechanisms that are already widely applied. By using this bottom-up approach, we are able to explore available mobility modes in a much more comprehensive manner. Instead of starting with a complex system in mind, engineers will be able to use simple building blocks to enable different desired mobility behaviors.

Commentary by Dr. Valentin Fuster
2012;():637-645. doi:10.1115/DETC2012-70993.

The Exechon X150, a new smaller member of a successful series of parallel kinematic machines, has been recently developed as a component of a mobile self-reconfigurable fixture system within an inter-European project. This paper is the first to address the stiffness analysis of the parallel mechanism on which the design is based. The stiffness modeling method uses reciprocal screw theory as well as the virtual work principle, resulting in a simpler formulation and more convenient than ones obtained with traditional stiffness-modeling methods. Based on this model, the stiffness map within the workspace is obtained. The stiffness of the mechanism at a typical configuration is carried out. The complete finite element analysis and simulation used to verify the effectiveness of the stiffness model. Using geometric spatial decomposition, numerical examples of the mechanism at three typical configurations are presented.

Topics: Stiffness
Commentary by Dr. Valentin Fuster
2012;():647-658. doi:10.1115/DETC2012-71028.

Mechanisms usually have to be particularly designed to meet the high-performance requirements in terms of different applications. For instance, Two degrees of freedom (DOF) rotational parallel mechanisms (RPMs) with a fixed center-of-rotation can eliminate parasitic motion and could provide the rotary stage with excellent dynamic stability, good controllability and easy operation. Therefore, this paper mainly aims at synthesizing 2-DOF RPMs with fixed center-of-rotation, a class of special RPMs with potential excellent performances. A graphic approach based on freedom and constraint spaces is introduced firstly. The constraint spaces of a class of the existing 2-DOF RPMs are illustrated, and the corresponding type synthesis patterns are summarized by comparing the geometric properties of those spaces with the mechanism characteristic. After fully decomposing the four-dimensional constraint space into sub-constraint spaces, a general type synthesis procedure is proposed based on the freedom and constraint topology. Two novel 2-DOF RPMs with fixed center-of-rotation are constructed based on the proposed method and procedure. The proposed graphic approach proves to be effective and simple to synthesizing those parallel mechanisms with some special performance.

Commentary by Dr. Valentin Fuster
2012;():659-667. doi:10.1115/DETC2012-71052.

Due to advantages of large-span, compact storage and high portability, foldable mechanisms have a promising prospect in aeronautics and astronautics applications. Two configurations of 3US parallel mechanisms with full foldability are constructed and their mobility and motion characteristics are further analyzed. This paper starts from geometrical arrangements of Hooke joints. Aimed at achieving full foldability, Hooke joints axes are placed along opportune directions, and lead to two configurations of 3US parallel mechanisms with anticlockwise folding and clockwise deploying motions. The analytic expression of the deployable ratio is presented and a numerical example is evaluated. This paper then applies constraint analysis in two configurations. In particular, constraint-screw systems of three limbs and those of platforms are investigated, followed by twist systems of platforms being derived as reciprocals of their wrench systems. The similarity and difference of motions allowed by two configurations are further addressed by comparison of their platform twist systems.

Commentary by Dr. Valentin Fuster
2012;():669-677. doi:10.1115/DETC2012-71146.

This paper presents a new approach to the analysis and synthesis of planar variable kinematic joints using a configuration space approach. The advantage of this approach is that the configuration space representation contains both the joint topology and the configuration variables. Based on the same configuration space, different combinations of higher pair equivalent revolute and prismatic joints can be used to analyze and synthesize planar variable kinematic joints. Two practical examples will be presented to illustrate the proposed method.

Topics: Kinematics
Commentary by Dr. Valentin Fuster
2012;():679-688. doi:10.1115/DETC2012-71184.

The paper discusses mobility and singularities of the Exechon three-degree-of-freedom (dof) parallel mechanism (PM) on which a family of parallel kinematic machines is based. Exechon designs are used by a number of machine-tool makers. A new version of the manipulator has been developed as a component of a mobile self-reconfigurable fixture system within an inter-European project. The PM has two UPR (4-dof) legs, constrained to move in a common rotating plane, and an SPR (5-dof) leg. The paper focuses on the constraint and singularity analysis of the mechanism. The screw systems of end-effector freedoms and constraints are identified. The singular configurations are classified in detail and their geometric interpretation is discussed. The velocity kinematics and the Jacobian operator are formulated via a screw-system approach. A fully parameterized package of Maple tools has been developed and used to visualize singularities and their consequences.

Commentary by Dr. Valentin Fuster
2012;():689-697. doi:10.1115/DETC2012-71192.

This paper deals with the kinematic synthesis of volumetric rotary machines, which are generated by the planetary motion of regular curve-polygons.

In particular, the synthesis of both outer and inner conjugate profiles has been formulated as envelope of the polycentric profiles of a generating regular curve-polygon with any number of lobes, different radii of the circumcircle and rounded corners.

A regular curve-polygon with cusp corners can be obtained as a particular case, like the Reuleaux triangle.

Finally, the proposed formulation has been implemented in a Matlab code and several examples are reported.

Topics: Kinematics , Machinery
Commentary by Dr. Valentin Fuster
2012;():699-708. doi:10.1115/DETC2012-71264.

This paper deals with the classical problem of dimensional synthesis of planar four-bar linkages for motion generation. Using Fourier Descriptors, a given motion is represented by two finite harmonic series, one for translational component of the motion and the other for rotational component. It is shown that there is a simple linear relationship between harmonic content of the rotational motion and that of the translational motion for a planar four-bar linkage. Furthermore, it is shown that the rotational component can be used to identify the initial angle and the link ratios of a four-bar linkage. The rest of the design parameters of a four-bar linkage such as location of the fixed and moving pivots can be obtained from the translational component of the given motion. This leads naturally to a decomposed design space for four-bar motion synthesis for approximate motion generation.

Topics: Design , Approximation
Commentary by Dr. Valentin Fuster
2012;():709-714. doi:10.1115/DETC2012-71361.

This paper improves augmented mechanism state matrices by replacing joint code with screw system notation. The proposed substitution allows for a more specific description of the joints in the mechanism and the capability to describe both spatial and planar mechanisms. Examples are provided which elucidate the proposed approach.

Topics: Screws
Commentary by Dr. Valentin Fuster
2012;():715-724. doi:10.1115/DETC2012-71379.

In four-bar mechanism synthesis, solutions to both the three-position and four-position synthesis problems are well-known. However, certain practical synthesis problems also require consideration of the instantaneous center of velocity for one of the precision positions. Examples are the double-wishbone front suspension of an automobile (camber in jounce and rebound, along with roll center), and four-bar prosthetic knee (standing stability, flexion length, and sitting cosmetic advantage).

Because specifying the location of the instant center constrains the solution by one free choice per dyad, it reduces the number of free choices available in a three-position problem from two to one. Thus, center point and circle point solutions to the three-position, instant center specified synthesis (TPICS) problem are located along point-pair solution curves similar to the Burmester curves in four-position synthesis.

The purpose of this paper is to present a direct, graphical method for finding pivot locations in three-position, instant-center synthesis of four-bar mechanisms. The method uses pole triangle theory to determine pivot locations along center point and circle point curves. A summary of a previously-presented computational method is included.

As an example, both the graphical and the computational method are used to generate TPICS center-point curves for an automotive front suspension.

Commentary by Dr. Valentin Fuster
2012;():725-735. doi:10.1115/DETC2012-71405.

This paper presents the kinematic synthesis of a steering linkage that changes track, wheelbase, camber, and wheel height in a turn, while maintaining Ackermann geometry. Each wheel is controlled by a 5-SS platform linkage, which consists of a moving platform connected by five SS chains to the vehicle chassis. Ackermann steering geometry ensures all four wheels will travel on circular arcs that share the same center point. S denotes a spherical or ball-in-socket joint.

The kinematic synthesis problem is formulated using seven spatial task positions. The procedure computes the SS chains that guide the platform through the seven task positions, and examines all combinations of five that form a single degree-of-freedom linkage. A kinematic analysis identifies the performance of each design candidate, and eliminates functional defects.

In the design process, the task positions are modified randomly within constraints in order to find a useful mechanism design. Mechanisms are deemed useful if they travel smoothly through all seven task positions. Upon analyzing 1000 sets of task positions, only 10 useful mechanisms were found. A second iteration produced 22 useful mechanisms from 1000 task sets. An example of the design of a steering linkage is presented. A video of this linkage can be seen at http://www.youtube.com/watch?v=hEvbDiyQMiw.

Topics: Linkages , Design
Commentary by Dr. Valentin Fuster

36th Mechanisms and Robotics Conference: Mobile Robots and Cable-Driven Systems

2012;():737-743. doi:10.1115/DETC2012-70078.

The travel time models of automated storage and retrieval systems (AS/RS’s) have been widely used in distribution and production environments. This paper extends previous work presented on impact design aspects of automated storage/retrieval systems by determining the expected cycle travel time for single command. Our new study improves the throughput performance rate of new AS/RS’s design on cycle travel time that will be specified by estimating travel time for dual command to serve as storage and retrieval (S/R) machine using a parallel wire-based Stewart-Gough platform (parallel wire robot). This improved efficiency in new design is called Stewart-Gough Platform based Automated Storage and Retrieval Systems (SGP-AS/RS’s). A numerical case study has been presented to clarify the travel time analysis based on mini unit-load storage and retrieval system. The improved throughput has been demonstrated by making a comparison between the conventional AS/RS results and the (SGP-AS/RS’s) results in the numerical case study. The effectiveness and ability of (SGP-AS/RS’s) has been proofed by determining the expected travel time for single command and dual command for random and classed-based analysis of storage assignment.

Topics: Cycles , Storage
Commentary by Dr. Valentin Fuster
2012;():745-751. doi:10.1115/DETC2012-70161.

In this work a novel command strategy is presented for tele-operating a mobile-manipulator system. To test its effectiveness, the command strategy was implemented on the mobile-manipulator system “Omnibot MMS”. The Omnibot MMS is teleoperated using a three degree-of-freedom haptic joystick and is controlled by driving either the base or the manipulator using an intuitive automatic mode switching command strategy. Virtual fixtures are used to provide additional information to the operator about the configuration of the Omnibot MMS, as well as increase accuracy and decrease errors. Through testing it was shown that new operators increased performance faster using the novel command strategy, and both accuracy and efficiency were improved, when compared to the traditional method of control using two joysticks.

Commentary by Dr. Valentin Fuster
2012;():753-761. doi:10.1115/DETC2012-70195.

This paper presents simulation and optimization of a 3-D three cable driven manipulator. For some specific paths in the workspace volume, motions of the robot before optimization are simulated and tension in the cables and stiffness of the cable robot for various points on the paths are determined. By selecting a function which is related to the stiffness matrix of the robot and considering it as the objective function of genetic algorithm, vertical positions of the connection points on the base platform as the optimization variables for each point on the paths can be determined in a way that the related function of the robot is optimized and a tension reduction in all the cables can be observed for most of the paths. Finally, the results of using different kinds of objective functions derived from the stiffness matrix are presented for three different criteria: workspace volume, kinematic performance indices and actuating energy of the robot. The results indicate which function has the largest workspace volume with tension reduction property in all the three cables, which has the highest values for the kinematic performance indices and which has the lowest actuating energy.

Commentary by Dr. Valentin Fuster
2012;():763-769. doi:10.1115/DETC2012-70310.

By using the variational principle to set up the mathematical model of the reflector for the FAST, we can get the node location of the cable-net and tension of the main cable by solving highly nonlinear equations of the mathematical model. A new layer-by-layer substitution approach has been proposed for solving the highly nonlinear equations, through the calculation and simulation it verifies the correctness of this method.

Topics: Cables
Commentary by Dr. Valentin Fuster
2012;():771-780. doi:10.1115/DETC2012-70389.

Intralogistics systems are a rapidly growing market. Today, high racks and automated storage retrieval machines are widely used to store and handle industrial goods. Conventional storage retrieval machines show a major drawback: While the containers or goods to be moved are often very lightweight, the storage retrieval machine itself may weight up to two tons which limits the energy efficiency and the motion capabilities. This limitation is a problem since the reduction of cycle times is crucial in logistics applications. Therefore, faster motions are desired. At the same time, a main focus in intralogistics development is on energy-saving solutions as part of the ongoing climate change debate. Together with the rising energy costs, this paves the way for radical new concepts which go beyond the lightweight construction of conventional storage retrieval machines. Recently, a huge research project started to realize an alternative approach for a storage retrieval machine system. This approach uses a parallel wire robot system to move the goods to be stored to the desired position. The system is extremely lightweight and therefore, fast motions are possible while the required energy is comparably low. Therefore, cycle times for the transport of the goods can be drastically reduced which is crucial in this application. The paper presented here describes both design concepts which were already presented, as well as optimized geometries which are superior in terms of workspace coverage and stiffness. First simulation results are shown and discussed with a focus on the potential of the system for precise loading and unloading of containers. Besides that, the overall mechatronic system design is introduced.

Topics: Machinery , Robots , Wire , Storage
Commentary by Dr. Valentin Fuster
2012;():781-790. doi:10.1115/DETC2012-70442.

A novel two-degree-of-freedom cable-loop slider-driven parallel mechanism is introduced in this paper. The two degrees of freedom of the mechanism are decoupled and only two actuators are needed to control the motion. There are two cable loops for each direction of motion: one acts as the actuating loop while the other is the constraint loop. Due to the simple geometric design, the kinematic and static equations of the mechanism are very compact. The stiffness of the mechanism is also analyzed in the paper. It can be observed that the mechanism’s stiffness is much higher than the stiffness of the cables. Finally, the dynamic equations of the mechanism, including the compliance and the damping of the cables are obtained. The proposed mechanism’s workspace is essentially equal to its footprint and there are no singularities. The mechanism does not require the use of a rigid-link passive bridge and trolley (only cables are connected to the end-effector). Sliders located on the edges of the workspace are used and actuation redundancy is eliminated while providing force closure everywhere in the workspace.

Commentary by Dr. Valentin Fuster
2012;():791-798. doi:10.1115/DETC2012-70443.

This paper presents a method to compare area coverage paths in the context of energy efficiency. We examine cover-age paths created from the Boustrophedon Decomposition and Spanning Tree methods in an optimal control setting. Our cost function weights the force inputs to drive the robot and the currently uncovered region. We derive an optimal traversal of the path in a point-to-point manner. In particular, we introduce a meas function that represents the percentage of the area that is still to be visited. The effect of meas on the optimal traversal is derived. Trade-offs between area covered versus the time and energy required are presented. A simple trajectory modification allows the vehicle to continue moving through a turn to reduce energy consumption.

Commentary by Dr. Valentin Fuster
2012;():799-806. doi:10.1115/DETC2012-70486.

In this paper, linear control techniques are applied to a novel Omnicopter MAV design. This design is unique in its ability to withstand external disturbance and translate horizontally with more stable attitude. A dynamic model of the Omnicopter MAV has been developed using the Newton-Euler formalism. Based on a linearized version of the model with a fixed vertical ducted fan angle configuration, three different control schemes, namely PD control, Lyapunov-based control and optimal LQ control have been designed and proposed. Comparisons and relations between the three control schemes are discussed and simulations are presented. Finally, details on the Omnicopter prototype and initial test flights are presented. Controlled flights with vertical take-offs and landings have been achieved utilizing the PD control scheme.

Commentary by Dr. Valentin Fuster
2012;():807-813. doi:10.1115/DETC2012-70503.

In small mobile robot research, autonomous platforms are severely constrained in navigation environments by the limitations of accurate sensory data to preform critical path planning, obstacle avoidance and self-localization tasks. The motivation for this work is to enable small autonomous mobile robots with a local stereo vision system that will provide an accurate reconstruction of a navigation environment for critical navigation tasks. This paper presents the KCLBOT, which was developed in King’s College London’s Centre for Robotic Research and is a small autonomous mobile robot with a stereo vision system.

Topics: Mobile robots
Commentary by Dr. Valentin Fuster
2012;():815-824. doi:10.1115/DETC2012-70557.

Although the nature of their gaits is similar, planar bipeds with curved feet have been shown experimentally to be more energetically efficient than those with point feet. Further, both healthy human feet and prosthetic feet can be modeled as a circular arc with the center of curvature in front of the shank. Thus, understanding the effects of a curved foot’s properties on the energetic cost of gait and on gait kinematics has the potential to improve both bipedal robots and prosthesis design. To date, there has not been a systematic study of the effects of changing the foot radius and center of curvature location on symmetric bipeds. This paper explores the effects of changing the curved foot’s geometric properties for both two- and five-link planar, underactuated bipeds with instantaneous transfer of support at impact. It is found that the foot radius has a substantial effect on the energetic efficiency of a gait regardless of the morphology of the biped. The effect of foot center of curvature location on energy efficiency is dependent on the morphology of the biped and is much less significant than the effect of foot radius. Both the foot radius and center of curvature location affect the knee kinematics of the five-link biped. The foot radius affects the hip kinematics of the two-link biped.

Topics: Design
Commentary by Dr. Valentin Fuster
2012;():825-831. doi:10.1115/DETC2012-70920.

Battery-powered wheelchairs require accurate and reliable range prediction to offer the maximum visibility of the current battery state to users, and to help them schedule future trip plans as well as fulfill the maximum battery economy potential. It is also one of the most critical parameters of wheelchairs to ensure the safety of users. However, range prediction is a very complicated issue by the fact that batteries are subject to current profiles, external influences, history of battery use, and aging. The prediction is even more challenging with unknown future driving conditions. The aim of this paper is to use a preview of a 3-D map, geographic information systems, and global positioning systems to develop an accurate range estimation system for battery-powered wheelchairs. This allows range prediction based on previewed driving road conditions. The nonlinearity of Li-ion batteries is also taken into consideration by using a circuit based battery model. Altogether, this methodology offers robustness and accuracy under varying operating conditions. Simulation results are presented to validate the proposed estimation method.

Topics: Wheelchairs
Commentary by Dr. Valentin Fuster
2012;():833-841. doi:10.1115/DETC2012-70949.

The design of cable-driven robots is complicated by the fact that cables can only apply force in one direction using tension, requiring a minimum of n+1 cables to fully constrain an n-DOF mechanism. Underconstrained systems with fewer than n+1 cables are not able to resist an arbitrary force, but may still be operational within a subset of their reachable workspace depending on the design of the mechanism. This paper focuses on an underconstrained two-link planar manipulator controlled using two cables. The equations of motion are presented and the system is numerically analyzed to determine the joint-angles and end-effector positions which can be achieved under quasi-static equilibrium with positive cable tensions. The positive tension workspace of the mechanism is shown to be governed by a collection of discrete constraint curves, which are presented and analyzed. The effects of changing cable configuration on the positive tension workspace are explored, and the cable configurations which result in the largest manipulator reachable workspace and dexterity are identified.

Topics: Cables , Manipulators
Commentary by Dr. Valentin Fuster
2012;():843-849. doi:10.1115/DETC2012-71070.

This paper addresses design of a motion controller for a teen sized biped robot, Archie. The main goal is to develop a motion controller for a cost oriented robot to assist human in daily life. The proposed real-time controller enables each joint individually to receive reference speed and position to provide a smooth motion. In this scheme, action commands are transmitted via Control Area Network (CAN) bus from a PC to robot. Aim of using such a communicator is to provide error process mechanism with a message priority concept. The main advantage of this method is to synchronize the motion of all joints necessary for biped walking motion. Finally test and implementation results are presented to demonstrate the good performance.

Commentary by Dr. Valentin Fuster
2012;():851-858. doi:10.1115/DETC2012-71076.

This paper deals with the design of singularity-free cable-driven parallel mechanism. Due to the negative effect on the performance, singularities should be avoided in the design. The singular configurations of mechanisms can be numerically determined by calculating the rank of its Jacobian matrix. However, this method is inefficient and non-intuitive. In this paper, we investigate the singularities of planar and spatial cable-driven parallel mechanisms using Grassmann line geometry. Considering cables as line vectors in projective space, the singularity conditions are identified with clear geometric meaning which results in useful method for singularity analysis of the cable-driven parallel mechanisms. The method is applied to 3-DOF planar and 6-DOF spatial cable-driven mechanisms to determine their singular configurations. The results show that the singularities of both mechanisms can be eliminated by changing the dimensions of the mechanisms or adding extra cables.

Commentary by Dr. Valentin Fuster
2012;():859-866. doi:10.1115/DETC2012-71154.

The SLIP model has shown a way to easily represent the center of mass dynamics of human walking and running. For 2D motions in the sagittal plane, the model shows self-stabilizing effects that can be very useful when designing a humanoid robot. However, this self-stability could not be found in three-dimensional running, but simple control strategies achieved stabilization of running in three dimensions. Yet, 3D walking with SLIP has not been analyzed to the same extent. In this paper we show that three-dimensional humanoid SLIP walking is also unstable, but can be stabilized using the same strategy that has been successful for running. It is shown that this approach leads to the desired periodic solutions. Furthermore, the influence of different parameters on stability and robustness is examined. Using a performance test to simulate the transition from an upright position to periodic walking we show that the stability is robust. With a comparison of common models for humanoid walking and running it is shown that the simple control mechanism is able to achieve stable solutions for all models, providing a very general approach to this problem. The derived results point out preferable parameters to increase robustness promising the possibility of successfully realizing a humanoid walking robot based on 3D SLIP.

Topics: Stability , Robustness
Commentary by Dr. Valentin Fuster
2012;():867-875. doi:10.1115/DETC2012-71205.

In this paper, the dynamic point-to-point trajectory planning of cable-suspended robots is investigated. A simple planar two-degree-of-freedom (2-dof) robot is used to demonstrate the technique. In order to maintain the cables’ positive tension, a set of algebraic inequalities is derived from the dynamic model of the 2-dof robot. The trajectories are defined using parametric polynomials with the coefficients determined by the prescribed initial and final states, and the variable time duration. With the polynomials substituted into the inequality constraints, the planning problem is then converted into an algebraic investigation on how the coefficients of the polynomials will affect the number of real roots over a given interval. An analytical approach based on a polynomial’s Discrimination Matrix and Discriminant Sequence is proposed to solve the problem. It is shown that, by adjusting the time duration within appropriate ranges, it is possible to find positive-definite polynomials such that the polynomial-based trajectories always satisfy the inequality constraints of the dynamic system. Feasible dynamic trajectories that are able to travel both beyond and within the static workspace will exploit more potential of the cable-suspended robotic platform.

Commentary by Dr. Valentin Fuster
2012;():877-883. doi:10.1115/DETC2012-71240.

Recent locomotion models have demonstrated the benefits of hip torques on legged locomotion stability. Here, a simple constant radial forcing function along the leg of the Spring-Loaded Inverted Pendulum (SLIP) model is added. This model is analyzed in order to determine what effect such a radial force might have on the stability of locomotion versus the more commonly used hip-torque forcing. The model is found to be unstable for the vast majority of the parameter space studied, for any amount of added forcing and damping constants. This suggests that simple constant forcing along the leg does not produce stable locomotion, unlike the case where forcing happens via hip torque.

Topics: Pendulums , Springs
Commentary by Dr. Valentin Fuster
2012;():885-889. doi:10.1115/DETC2012-71295.

This paper presents the design and experimental characterization of a continuously variable linear force amplifier based on the theory of capstans. In contrast to traditional capstan amplifiers, the design presented here uses an elastic cable, enabling a control actuator to not only continuously clutch output to a rotating drum but also passively declutch by releasing tension. Our experimental results demonstrate successful declutching at all force amplification ratios up to the limit of our experimental apparatus, 21 — significantly higher than previously published values. A system of distributed capstan amplifiers driven by a central torque source with cable engagement switched by lightweight, low torque actuators has potential to reduce the mass of distal actuators and enable more dynamic performance in robotic applications.

Topics: Cables
Commentary by Dr. Valentin Fuster
2012;():891-899. doi:10.1115/DETC2012-71334.

Object transportation is an especially suitable task for cooperative mobile robots where the carrying capacity of an individual robot is naturally limited. In this work, a unique wheeled robot is presented that, when used in homogeneous teams, is able to lift and carry objects which may be significantly larger than the robot itself. A key feature of the presented robot is that it is devoid of articulated manipulation mechanisms, but instead relies on its drive wheels for object interaction. After a brief introduction to the mechanics of this mobile robot, a behavior-based lifting and carrying strategy is developed that allows the robot to cooperatively raise an object from the ground, transition into a carrying role, and then transport the object across cluttered, unstructured terrain. The strategy is inherently decentralized, allowing an arbitrary number of robots to participate in the transportation task. Dynamic simulation results are then presented, showing the effectiveness of the strategy.

Commentary by Dr. Valentin Fuster
2012;():901-908. doi:10.1115/DETC2012-71348.

Investigation on development of autonomous mobile robots for agricultural use in a complex and mostly unstructured environment is studied. An approach that uses fuzzy-logic control and distance-based sensory data for real-time navigation of a mobile robot in an unknown farm setting is proposed. This approach requires no prior knowledge of the environment and adjusts a safety margin to cope with dynamic and unforeseen conditions. The simulation and experimental results indicate that the proposed strategy navigates robot in different conditions safely and efficiently. Comparing our results with vector field histogram and preference-based fuzzy approaches revealed that the approach suggested here produces shorter and smoother paths toward goal in almost all of the test cases examined.

Commentary by Dr. Valentin Fuster
2012;():909-917. doi:10.1115/DETC2012-71351.

This paper presents a new and practical method for mapping and annotating indoor environments for mobile robot use. The method makes use of 2D occupancy grid maps for metric representation, and topology maps to indicate the connectivity of the ‘places-of-interests’ in the environment. Novel use of 2D visual tags allows encoding information physically at places-of-interest. Moreover, using physical characteristics of the visual tags (i.e. paper size) is exploited to recover relative poses of the tags in the environment using a simple camera. This method extends tag encoding to simultaneous localization and mapping in topology space, and fuses camera and robot pose estimations to build an automatically annotated global topo-metric map. It is developed as a framework for a hospital service robot and tested in a real hospital. Experiments show that the method is capable of producing globally consistent, automatically annotated hybrid metric-topological maps that is needed by mobile service robots.

Topics: Mobile robots
Commentary by Dr. Valentin Fuster
2012;():919-926. doi:10.1115/DETC2012-71360.

This paper investigates the effect of upper body on balancing by comparing balanced state domain in the phase space. Biped mechanism is simplified to multi-segment model which consists of one stance foot, leg, and upper body in sagittal plane. System parameters such as link mass and link length are chosen appropriately based on human anthropometry data. In addition to the system parameters, the necessary and sufficient conditions for balancing are implemented as constraints. Proposed algorithm iteratively solves nonlinear constrained optimization problem to find velocity extrema for a given set of joint variables and a maximum actuation torque. The balanced state domain of an actively controlled swinging arm demonstrates larger domain compared to the domain without swinging arm. While similar results are shown by other various approaches, the proposed algorithm demonstrates identification of the balanced state domain in a deterministic scheme using numerical optimization.

Commentary by Dr. Valentin Fuster
2012;():927-934. doi:10.1115/DETC2012-71365.

Understanding electrical energy consumption in a robotic system leads to the ability to minimize energy consumption for a given task. This is particularly important for mobile robots and redundant manipulators where extended operating times and non-optimized movement patterns lead to increased operating costs. However, current research shows conflicting formulas for predicting energy consumption in robotic joints driven by DC motors, specifically when negative work is involved. A breakdown of energy consumption for DC motors is introduced with respect to different operating states and phases of positive and negative work. Additionally, the energy consumption of a two degree of freedom manipulator is simulated and verified experimentally. The same task — lowering the manipulator from point a to b in a vertical line — is completed in both elbow up and elbow down configurations to illustrate the difference in energy consumption during a task that consists of mostly negative work. Finally, this energy expenditure equation is extended to a multi degree of freedom simulated humanoid robot to demonstrate validity and generality.

Commentary by Dr. Valentin Fuster
2012;():935-940. doi:10.1115/DETC2012-71372.

The Spring Loaded Inverted Pendulum (SLIP) model was developed to describe center of mass movement patterns observed in animals, using only a springy leg and a point mass. However, SLIP is energy conserving and does not accurately represent any biological or robotic system. Still, this model is often used as a foundation for the investigation of improved legged locomotion models. One such model called Torque Damped SLIP (TD-SLIP) utilizes two additional parameters, a time dependent torque and dampening to drastically increase the stability. Forced Damped SLIP (FD-SLIP), a predecessor of TD-SLIP, has shown that this model can be further simplified by using a constant torque, instead of a time varying torque, while still maintaining stability.

Using FD-SLIP as a base, this paper explores a leg placement strategy using a simple PI controller. The controller takes advantage of the fact that the energy state of FD-SLIP is symmetric entering and leaving the stance phase during steady state conditions. During the flight phase, the touch down leg angle is adjusted so that the energy dissipation due to dampening, during the stance phase, compensates for any imbalance of energy. This controller approximately doubles the region of stability when subjected to velocity perturbations at touchdown, enables the model to operate at considerably lower torque values, and drastically reduces the time required to recover from a perturbation, while using less energy. Finally, the leg placement strategy used effectively imitates the natural human response to velocity perturbations while running.

Commentary by Dr. Valentin Fuster
2012;():941-950. doi:10.1115/DETC2012-71382.

Advances in mobile robotics make these systems viable alternatives for developing new methods and techniques for manufacturing processes such as welding. When considering welding as a manufacturing process, the ability of the equipment to conduct the weld process must be verified. This step is called weld process validation and is generally conducted when a new machine or technique is introduced to the weld process. Traditionally, the weld validation process has focused on the electro-thermal aspects of the weld process, while the (human) welder qualification provides a certification step to ensure that an operator can perform the motion-control aspects of the weld operation while welding. The lack of industry standards for mechanized welding makes it difficult to introduce mobile robotic welding systems with validated performance in the market place. This paper will propose one approach to consider the motion control portion of the weld process validation for welding systems based on mobile robotic platforms. In particular, this paper will consider a skid-steer type mobile robot that is able to weld in flat, horizontal and vertical orientations. The paper will consider the motion-control portion of the weld validation process and will suggest a method that compares a mobile-robot-based welding process to a baseline (fixed-base track system) welding process through spanning manipulability ellipses. This approach allows general topologies of a mobile robotic welding system to be considered in a general way as a step to making mobile robotic welding a viable welding process.

Topics: Robotic welding
Commentary by Dr. Valentin Fuster
2012;():951-956. doi:10.1115/DETC2012-71394.

In planetary exploration and other similar robotic applications, it is possible to encounter obstacles on multiple scales, making it difficult to design wheeled locomotion that works well for all terrain types. Legged locomotion tends to be less efficient and slower, but allows better obstacle clearance. This paper describes a novel method of achieving robotic locomotion over uneven terrain using a passive underactuation technique. Using planetary gear trains with one input degree of freedom and two output degrees of freedom, the natural obstacle-based locking of select outputs can cause the transition of power through the alternate outputs. By designing the primary outputs as wheels and the secondary outputs as legs with more ground clearance, a naturally adaptive hybrid gait incorporating both rolling and walking can be generated without the need for sophisticated sensing and control. Derivation and simulation validation are presented.

Commentary by Dr. Valentin Fuster
2012;():957-965. doi:10.1115/DETC2012-71411.

The clock-torqued spring-loaded inverted pendulum (CT-SLIP) model describes the robust dynamic stability properties observed in most animals and some legged robots. However, the model’s behavior is sensitive to changes in liftoff conditions such as those experienced on realistic terrain. Here the incorporation of friction at the foot-ground interface is explored on the CT-SLIP model with specific interest in improving the transient center-of-mass dynamics. Multiple friction models are presented and tuned to reflect a periodic center-of-mass gait. The transient dynamics with friction are analyzed in comparison to the CT-SLIP model and improvements to the settling time and disturbance rejection were found. This addition of foot-ground contact friction may allow for better understanding of center-of-mass system dynamics on realistic terrain.

Topics: Clocks , Pendulums , Springs
Commentary by Dr. Valentin Fuster
2012;():967-976. doi:10.1115/DETC2012-71452.

Although legged locomotion is better at tackling complicated terrains compared with wheeled locomotion, legged robots are rare, in part, because of the lack of simple design tools. The dynamics governing legged locomotion are generally nonlinear and hybrid (piecewise-continuous) and so require numerical simulation for analysis and are not easily applied to robot designs. During the past decade, a few approximated analytical solutions of Spring-Loaded Inverted Pendulum (SLIP), a canonical model in legged locomotion, have been developed. However, SLIP is energy conserving and cannot predict the dynamical stability of real-world legged locomotion. To develop new analytical tools for legged robot designs, we first analytically solved SLIP in a new way. Then based on SLIP solution, we developed an analytical solution of a hip-actuated Spring-Loaded Inverted Pendulum (hip-actuated-SLIP) model, which is more biologically relevant and stable than the canonical energy conserving SLIP model. The analytical approximations offered here for SLIP and the hip actuated-SLIP solutions compare well with the numerical simulations of each. The analytical solutions presented here are simpler in form than those resulting from existing analytical approximations. The analytical solutions of SLIP and the hip actuated-SLIP can be used as tools for robot design or for generating biological hypotheses.

Topics: Robots , Design
Commentary by Dr. Valentin Fuster

36th Mechanisms and Robotics Conference: Novel Mechanisms, Robots and Applications

2012;():977-985. doi:10.1115/DETC2012-70064.

This paper introduced a new metamorphic parallel mechanism consisting of four reconfigurable rTPS limbs. Based on the reconfigurability of the reconfigurable Hooke (rT) joint, the rTPS limb has two phases while in one phase the limb has no constraint to the platform, in the other it constrains the spherical joint center to lie on a plane. This results in the mechanism to have ability of reconfiguration between different topologies with variable mobility. Geometric constraint equations of the platform rotation matrix and translation vector are set up based on the point-plane constraint, which reveals the bifurcated motion property in the topology with mobility 2 and the geometric condition with mobility change in altering to other mechanism topologies. Following this, a unified kinematics limb modeling is proposed considering the difference between the two phases of the reconfigurable rTPS limb. This is further applied for the mechanism modeling and both the inverse and forward kinematics is analytically solved by combining phases of the four limbs covering all the mechanism topologies.

Commentary by Dr. Valentin Fuster
2012;():987-996. doi:10.1115/DETC2012-70147.

The Single-Track Three Legged Mobile Robot achieves the form and function of a motorcycle but with the added benefit of legs and partial or fully automatic stability of balance. The robot comprises a body and three articulated legs arranged one behind the other in a narrow profile to walk and maneuver along narrow trails and paths, by placing successive footfalls in a generally single-track or in-line fashion. It achieves stability of balance without motion by positioning the three legs in a tripod stance. It maintains (or regains) stability of balance during locomotion through controlled foot placement and repeating intervals of a bipedal or tripod stance. It executes a single-track turn by leaning the body into the turn, using gravitational forces to counteract the outward centripetal force. The proposed gait strategy keeps two legs on the ground at all times, simplifying balance control to the roll direction. The control system comprises feedback sensors, digital computer, and software for foot position planning. This paper presents the robot design, various three-legged gaits, control method and architecture, experimental results from a digital simulation, and a proof-of-concept prototype.

Topics: Mobile robots
Commentary by Dr. Valentin Fuster
2012;():997-1006. doi:10.1115/DETC2012-70177.

Shape–controlled adaptable building structures have a potential of superior performance and flexibility compared to traditional fixed–shape ones. A building concept is proposed consisting of a number of interconnected planar n–bar linkages performing coordinated motions thus resembling a system of cooperating closed–loop robotic manipulators. For shape control an “effective 4–bar” linkage concept is proposed. That is, each individual n–bar mechanism is equipped with one motion actuator, and at any time of motion its degrees–of–freedom are reduced to one through the selective locking of (n – 4) joints using brakes. Shape adjustments of the overall structure can be carried out through appropriate control sequences where in each step exactly four joints of each linkage are unlocked giving rise to an effective 4–bar system. Motion planning is considered together with the relevant limitations arising from singular configurations that need to be taken into account. The concept is demonstrated through simulation examples.

Commentary by Dr. Valentin Fuster
2012;():1007-1014. doi:10.1115/DETC2012-70250.

This paper presents the development efforts for a set of software activities and tutorials to augment teaching and learning in standard required undergraduate engineering mechanics courses. Using these software activities, students can change parameters, predict answers, compare outcomes, interact with animations, and feel the results. The overall system aims to increase teaching and learning effectiveness by rendering the concepts compelling, fun, and engaging. The problem with current examples and homework problems is that they are flat, static, boring, and non-engaging, which may lead to student attrition and a less than full grasp of fundamental principles. We implement integration of haptics technology with educational products to enable improvement in undergraduate engineering mechanics education. The current system is composed of a computer (laptop or desktop), a haptic device and a set of haptic modules. Currently, two modules, Interactive Free-Body Diagram (Box Motion) and Rigid Body Dynamics (Box Motion), were developed and several others are under development.

Commentary by Dr. Valentin Fuster
2012;():1015-1024. doi:10.1115/DETC2012-70320.

Tensegrity systems have been used in several disciplines such as architecture, biology, aerospace, mechanics and robotics during the last fifty years. However, just a few references in literature have stated the possibility of using tensegrity systems in ocean or energy-related applications. This work addresses the kinematic and dynamic analyses of a planar tensegrity mechanism for ocean wave energy harvesting. A planar tensegrity mechanism is proposed based on a planar morphology known as “X-frame” that was developed by Kenneth Snelson in 1960s. A geometric approach is used to solve the forward and reverse displacement problems. The theory of screws is used to perform the forward and reverse velocity analyses of the device. The Lagrangian approach is used to deduce the equations of motion considering the interaction between the mechanism and a linear model of ocean waves. The result shows that tensegrity systems could play an important role in the expansion of clean energy technologies that help the world’s sustainable development.

Commentary by Dr. Valentin Fuster
2012;():1025-1031. doi:10.1115/DETC2012-70449.

The dangerous nature and history of railroad grade crossings (especially unprotected crossings in remote areas lacking costly electrical infrastructure) motivates engineering efforts to reduce the number of fatalities and injuries. Several approaches and devices have been investigated and developed to harvest energy, mostly from vertical deflection of railroad track to power automated warning systems and track health monitoring sensors. While most of this previous work relied on harvesting energy from the vertical deflection of the railroad track, this paper proposes a mechanism for generating electricity from the passage of each train wheel. A cam-follower mechanism was designed initially to meet the requirements of low noise, shock and wear, and was subsequently used and improved to design a system capable of generating electricity efficiently from the motion of trains traveling in either direction. The development of the device as well as analysis of its predicted power production capability is presented in this paper.

Topics: Safety , Railroads , Trains , Wheels
Commentary by Dr. Valentin Fuster
2012;():1033-1039. doi:10.1115/DETC2012-70515.

For traditional 2-DoF excavating mechanism of electric mining shovel, the log spiral trajectory is regarded as the optimal digging trajectory with less energy consumption. The design of new 3-DoF excavating mechanism is aimed for a mechanism more dexterous than the traditional 2-DoF one, thus reduces the digging energy consumption. The optimal trajectory of the new mechanism should be different from the traditional one. This paper considers different possibilities of excavating manners and different kind of digging trajectories. With the method of polynomial fitting, the approximately optimal trajectory is obtained. With the numerical simulation, it shows that the new 3-DOF excavating mechanism is energy-efficient compared with the traditional excavating mechanism.

Commentary by Dr. Valentin Fuster
2012;():1041-1049. doi:10.1115/DETC2012-70570.

This paper describes the application of classical design methodology toward the design of a robotic gripper. This gripper is designed to meet or exceed the mechanical properties of the BarrettHand for a lower cost. The design process followed a classical design process as previously introduced by Streusand and Turner with some modifications due working as an individual rather than as a design team member. This process proved effective in the design of the gripper, though there are some recommendations for improving the method and some improvements need to be made to the current gripper design before it is ready for use.

Commentary by Dr. Valentin Fuster
2012;():1051-1058. doi:10.1115/DETC2012-70741.

This paper investigates how the passive adaptability of an underactuated robot leg to uneven terrain is affected by variations in design parameters. In particular, the ratio between the joint torques, the ratio between the link lengths, and the initial joint rest angles are varied to determine configurations that allow for maximum terrain roughness adaptability while minimizing the transmission of disturbance forces to the body. The results show that a proximal/distal joint torque coupling ratio of 1.58, proximal/distal leg length ratio of 0.5, and an initial proximal joint angle of −49 degrees maximize the terrain variability over which the robot can remain stable by exerting a near-constant vertical reaction force while minimizing lateral force and moment disturbances. In addition, the spring stiffness ratio allows for a tradeoff to be made between the different performance metrics.

Commentary by Dr. Valentin Fuster
2012;():1059-1066. doi:10.1115/DETC2012-70917.

One of the most challenging and risky operations for spacecraft is to perform proximity Rendezvous and Docking (R&D) autonomously in space. To ensure a safe and reliable operation, such a mission must be carefully designed and thoroughly verified before a real space mission can be launched. This paper describes the control strategy for achieving high fidelity contact dynamics simulation of a new, robotics-based, hardware-in-the-loop (HIL) R&D simulation facility which uses two industrial robots to simulate the 6-DOF dynamic maneuvering of the two docking satellites. The facility is capable of physically simulating the final approaching within a 25-meter range and the entire docking or capturing process in a satellite on-orbit servicing mission. The paper discusses the difficulties of using industrial robots for HIL contact dynamics simulation and the proposed robot control strategy for dealing with these difficulties.

Commentary by Dr. Valentin Fuster
2012;():1067-1072. doi:10.1115/DETC2012-71062.

The design and experimental prototype of a hybrid robot capable of both aerial and terrestrial locomotion is presented in this paper. A unique compliant mechanism design makes it possible to use a single actuator set for both walking and flying. This is advantageous because it reduces both the total weight of the system and the control system complexity. The basic structure is similar to a quadrotor aerial vehicle, i.e. four brushless DC motors provide the required thrust for flying. The desired leg motion is derived from two separate linear movements. Horizontal motion of the legs is achieved by driving the main actuators in reverse. A second linear actuation unit, which is set into motion by shape memory alloy (SMA) wires, enables vertical movement of the leg during terrestrial locomotion.

Topics: Design
Commentary by Dr. Valentin Fuster
2012;():1073-1078. doi:10.1115/DETC2012-71200.

In mechanism theory and design, no work has been reported on the kinematic synthesis and dynamic analysis of the dual-rod slider rocker mechanism. By definition, this system is equivalent to two traditional slider-rocker mechanisms that share a common rocker, where the two sliders translate along two opposite directions of motion. Unlike a single slider-rocker mechanism, the dual-rod-based mechanism exhibits unique kinematic characteristics in which the two sliders do not travel the same distance for the same rocker rotation. This paper presents an optimal analysis that outlines the early investigations on the kinematic design and dynamic analysis of the dual-rod slider rocker mechanism. Because of the translation difference that exists between the two sliders, an expression for the relative position error is derived. This error is integrated as a cost function in an optimization problem which calculates the optimal rod length that allows the two sliders to meet terminal boundary conditions. These kinematics are validated experimentally through a case-study application in modular robotic docking.

Commentary by Dr. Valentin Fuster
2012;():1079-1087. doi:10.1115/DETC2012-71261.

Complex controlled motions, flexible surfaces, and minimal moving mass all drive the need for soft robots using fiber reinforced elastomer enclosures (FREEs) in a parallel configuration. This paper addresses the challenge of synthesizing a design with desired kinematics, as only small portions of the entire design space have been previously investigated. A systematic characterization of the kinematic freedom, constraint, and actuation directions of all circumferentially and longitudinally repeating fiber topologies is determined. The parallel kinematics is mapped for the combinations of actuators by determining the sets of mobilities necessary in the constituent members for all possible output motions. The kinematics of all possible parallel combinations for pairs and triangular triplets of FREEs are mapped. A graphical user interface (GUI) is presented, which allows a user to input a kinematic specification and generate all feasible FREE sets and their respective kinematics. With the entire design space mapped and easily accessible, a range of possible applications across a span of kinematic requirements becomes readily attainable. A case study is performed to verify the ability of the GUI to determine feasible FREE sets for a pick-and-place manipulator task.

Commentary by Dr. Valentin Fuster
2012;():1089-1099. doi:10.1115/DETC2012-71278.

Fluid filled Fiber Reinforced Elastomeric Enclosures (FREE) have been popular choices for actuators in prosthetics and soft robots owing to their large power density and cost effective manufacturing. While a narrow class of FREEs known as McKibben’s actuators have been extensively studied, there is a wide unexplored class that could be potentially used as actuators and load bearing members. This paper analyzes the mobility of a large class of FREEs based on simple geometric relationships that originate due to the inextensibility of fibers and incompressibility of fluids. The analysis conducted on various families of fibers reveal certain configurations that are locked under fluidic actuation. Furthermore the analysis reveals unrestricted motion in certain directions (freedom) and restrictions in certain other directions (constraint). Such an analysis is deemed to be useful as a preliminary design tool to pick the appropriate geometry for use in design of soft robots and actuators.

Commentary by Dr. Valentin Fuster
2012;():1101-1108. doi:10.1115/DETC2012-71283.

Manual Sorting of silverware pieces after being washed by a high-volume commercial dishwasher is a costly and time consuming process which can be improved by automation. This paper describes the design, construction, and testing of an automated silverware sorting process. The process employs machine vision with simple, but effective, high-volume mechanisms to detect the type and orientation of different types of silverware pieces and place them into different bins. The project was conducted in two major phases:

1) Design and Construction of the Mechanism: a simple and effective mechanism was designed to sort the pieces into separate bins off of a conveyor belt. Pneumatic actuators provided the key mechanical sorting.

2) Design of the Control System: a computer program was developed that detects the entrance of a piece into the machine and recognizes the type and orientation of each silverware piece using computer vision techniques. The software then commands the proper mechanical component at the proper time to actuate, so that each piece ends up in the designated bin.

The machine was tested with different silverware input sequences The accuracy of the software in identifying the type and direction of the pieces, the accuracy of the mechanical system in sorting the pieces, and the accuracy of the overall system were found to be 100%, 90.63% and 88.75% respectively.

Commentary by Dr. Valentin Fuster
2012;():1109-1114. doi:10.1115/DETC2012-71284.

This paper presents a bidirectional teleoperation admittance haptic glove (RML glove) which can be used to control mobile robots. The glove receives information from the environment and the internal status of the mobile robot, and generates a force feedback to the operator through the wireless module which in return communicates command signals to the robot. This haptic device is a lightweight and portable actuator system that fits on bare hands, and adds a haptic sense of force feedback to all fingers without constraining their natural movement. An embedded lead screw mechanism provides force feedback that ranges from zero up to 35 N for each finger. Based on this force feedback, the operator can feel what the robot feels (e.g., link torque amount and distance to an obstacle) which enables a smoother and safer human-control of the robot. To evaluate the performance of the haptic glove, a master-slave control experiment based on force feedback between the glove and the mobile robot is conducted. The results demonstrate that the proposed admittance glove can augment tele-presence.

Commentary by Dr. Valentin Fuster
2012;():1115-1124. doi:10.1115/DETC2012-71302.

Discrete joint manipulators are a potential alternative to common continuous joint robots used in industry today. Applications of a discrete joint manipulator include proximity positioning tasks, space exploration, camera placement, and automation systems. Discrete robots are potentially useful for small scale robots because it is difficult to implement sensors and motors at small scales. This work discusses the results obtained with an experimental 7 link robot designed for an 8 × 12 inch grid.

Results show that a discrete robot can successfully be used for proximity positioning tasks. The performance depends on the location of discrete points relative to the desired points and also on the repeatability of the experimental manipulator. Results obtained via a vision system demonstrate the potential capabilities of the planar discrete manipulator. Results include subsets of end-effector positions in the gridspace and training results.

Topics: Robots , Optimization
Commentary by Dr. Valentin Fuster
2012;():1125-1131. doi:10.1115/DETC2012-71335.

Bridge scour is an important concern for standing structures with piles footed underwater. The scour process that leads to the weakening of bridge foundations can result in (unexpected) loss of service, and can create unsafe conditions for the vehicles and persons using the bridge, particularly during flood conditions. Currently, stationary devices or divers are deployed to detect this condition; however these devices are expensive and diving in such conditions is inherently dangerous. Therefore, a need exists for an inexpensive and portable system that is able to determine and estimate the amount of scour around a pile. One approach is to use a sonar based scanning system, to construct a 3D image for interpretations and evaluations analysis. This paper details prototype development, image processing procedure, and initial experimental results of such a device.

Commentary by Dr. Valentin Fuster
2012;():1133-1142. doi:10.1115/DETC2012-71380.

Magnetic Resonance Imaging (MRI) compatible robots can assist physicians in precisely inserting biopsy needles or therapeutic instruments directly into millimeter-size tumors using MR imaging feedback. MRI systems although present a challenging environment, including high magnetic fields and limited space, making the development of MRI-compatible robots complex. This paper presents an MRI-compatible pneumatic actuation technology consisting of molded polymer structures with embedded air-muscle, operated in a binary fashion. While having good positioning accuracy, the technology presents advantages of compactness, perfect MRI-compatibility, simplicity, and low cost. Here we specifically report the design and validation of a transperineal prostate cancer manipulator prototype having 20 embedded air-muscles distributed in four star-like polymer structures. Structures are made of silicone elastomer, using lost-core injection molding. The molded compliant joints of the muscles eliminate sliding surfaces, for low motion hysteresis and good repeatability. A simple and effective two-level design method for polymer air-muscles is proposed, using a manipulator model and three muscle models: geometrical, finite elements and uniaxial analytic. Binary control of each air-muscle assures stability and accuracy with minimized costs and complexity. The manipulator is tested MRI-compatible with no effects on the signal-to-noise ratio and, with appropriate image feedback, reaches targets with repeatability and accuracy under 0.5 mm. The embedded approach reveals to be a key feature since it reduces hysteresis errors by a factor of 6.6 compared to a previous non-embedded version of the manipulator. The successful validation of this binary manipulator opens the door to a new design paradigm for low cost and highly capable pneumatic robots, specifically for the intra-MRI manipulation.

Commentary by Dr. Valentin Fuster
2012;():1143-1152. doi:10.1115/DETC2012-71384.

This paper investigates the optimization of electrode geometry in electrostatic adhesives to enhance adhesion forces for use in robotic climbing and gripping applications. Electrostatic adhesion provides an attachment mechanism that is both controllable and effective over a wide range of surfaces including conductive, semi-conductive, and insulating materials. The adhesives function by utilizing a set of high voltage electrodes that generate an electric field. This electric field polarizes the substrate material, thus generating an adhesion force. Optimizing the geometry of these conductive electrodes provides enhanced adhesion forces that increase attachment robustness. To accomplish this, FEA software was used to evaluate the generated electric field for a given electrode configuration. A range of electrode widths and gap sizes were evaluated to find the optimal configuration. These findings were compared with experimental results for different pad geometries over a range of surface types. Experimental results indicate that on smooth surfaces the simulation results are representative of the actual recorded adhesion forces. Rough surfaces provide similar trends but with varying optimal configurations, likely due to the level of electric field dispersion.

Commentary by Dr. Valentin Fuster
2012;():1153-1159. doi:10.1115/DETC2012-71401.

Elastically suspending a load from humans and animals can increase the energy efficiency of legged locomotion and load carrying. Similarly, elastically-suspended loads have the potential to increase the energy efficiency of legged robot locomotion. External loads and the inherent mass of a legged robot, such as batteries, electronics, and fuel, can be elastically-suspended from the robot chassis with a passive compliant suspension system, reducing the energetic cost of locomotion. In prior work, we developed a simple model to examine the effect of elastically-suspended loads on the energy cost of locomotion from first principles. In this paper, we present experimental results showing the energy cost of locomotion for a simple hexapod robot over a range of suspension stiffness values. Elastically-suspended loads were shown to reduce the energy cost of locomotion by up to 20% versus a rigidly-attached load. We compare the experimental results to the theoretical results predicted by the simple model.

Commentary by Dr. Valentin Fuster
2012;():1161-1168. doi:10.1115/DETC2012-71403.

In recent times, Origami has received an increasing research interest because of its capability to produce foldable tessellations and structures. This paper describes a new modular tetrahedral representation called “Kinetogami”. We embed the cuts and joining patterns into the crease pattern and create folded hinges across basic structural units (BSU), typically not done in Origami. We demonstrate sets of explicit 2D fabrication lay-outs and construction rules in order to fold reconfigurable structures and mechanisms in 3D by using a single flat paper sheet. The structural and combinatorial characteristics of Kinetogamic derivatives are further explored in a hierarchical manner. Inspired by Kinetogami, we design a family of multi-limbed tetrahedral robotic form that reconfigures and adapts. The kinematic properties of individual limbs are investigated and multiple gaits involving flipping, squatting/rising, squirming and slithering are synthesized for a representative hexapod robot. Our newly developed folding design paradigm provides affordances for a novel generation of robotic motion actuation and transformable reconfiguration.

Topics: Robotics
Commentary by Dr. Valentin Fuster
2012;():1169-1176. doi:10.1115/DETC2012-71488.

This paper proposes a reconfiguration mechanism modelling for puzzles with its interlocking geometric constraints analysis. Wooden puzzles consisting of interlocking assemebly of notched sticks are often referred to as bar-puzzles, sometime known as the Chinese Puzzles or Chinese Cross. The puzzle with multiple reconfigurable pieces as kinematic links leads to topology arrangements. Although its partition or assembly process can be operated as mechanism motions, there does not appear to be any evidence that the idea of its mechanism property and any configuration analysis originated. To this purpose, this paper set up a static and discrete reconfiguration theory of geometric puzzles for modeling the topology changement as Put Together, Take Apart, Sequential Movement and various others. The partition and assembly process analysis aims to extract the kinematic chains as links and joints. The puzzle unlocking leads to configuration constraints rearrangement problems which accompanying pieces of bars self-grouped as defined reconfiguration links and joints. The mathematical recreation of the mechanism structure stems from its interlocking geometric constraints property. This paper reveals its interlocking property as configuration constraints including many passive constraints and further discloses the mechanism constraints modeling in two different partition methods. The puzzle solutions are first described as reconfigurable topology mechanism and the constrained mobility is analyzed based on an ingenious and distinctive reconfiguration property.

Commentary by Dr. Valentin Fuster

36th Mechanisms and Robotics Conference: Robot Kinematics and Motion Planning

2012;():1177-1186. doi:10.1115/DETC2012-70105.

Proteins are biological macromolecules that play essential roles in living organisms. Furthermore, the study of proteins and their function is of interest in other fields in addition to biology, such as pharmacology and biotechnology. Understanding the relationship between protein structure, dynamics and function is indispensable for advances in all these areas. This requires a combination of experimental and computational methods, whose development is the object of very active interdisciplinary research. In such a context, this paper presents a technique to enhance conformational sampling of proteins carried out with computational methods such as molecular dynamics simulations or Monte Carlo methods. Our approach is based on a mechanistic representation of proteins that enables the application of efficient methods originating from robotics. The paper explains the generalities of the approach, and gives details on its application to devise Monte Carlo move classes. Results show the good performance of the method for sampling the conformational space of different types of proteins.

Topics: Robotics , Proteins
Commentary by Dr. Valentin Fuster
2012;():1187-1196. doi:10.1115/DETC2012-70265.

This paper presents kinematics analysis for the DARwIn-OP (Dynamic Anthropomorphic Robot with Intelligence – Open-Platform) robot. This is a 20-dof humanoid walking robot developed by Virginia Tech, Purdue, and the University of Pennsylvania and marketed by Robotis Inc. The robot version analyzed in this paper is 455 mm tall and has a mass of 2.8 kg. Ohio University has two of these units for robot applications research and teaching.

Presented are a description of DARwIn-OP, the Denavit-Hartenberg Parameters for each serial chain (2-dof head pan/tilt, 3-dof arms, and 6-dof legs), specific length parameters, joint angle limits, plus forward pose kinematics equations and partial inverse pose kinematics solutions, with examples.

Commentary by Dr. Valentin Fuster
2012;():1197-1205. doi:10.1115/DETC2012-70371.

In this paper, a new kind of 6-legged robot is presented. It was designed for drilling holes on the aircraft surface. Each leg of the robot is a 3-DOF parallel mechanism and the actuation can be controlled both by position and for