ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V06AT00A001. doi:10.1115/DETC2013-NS6A.

This online compilation of papers from the ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2013) 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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

37th Mechanisms and Robotics Conference: Biologically Inspired and Health Motivated Mechanisms and Robotics

2013;():V06AT07A001. doi:10.1115/DETC2013-12088.

A handheld, portable cranial drilling tool for safely creating holes in the skull without damaging brain tissue is presented. Such a device is essential for neurosurgeons and mid-level practitioners treating patients with traumatic brain injury. A typical procedure creates a small hole for inserting sensors to monitor intra-cranial pressure measurements and/or removing excess fluid. Drilling holes in emergency settings with existing tools is difficult and dangerous due to the risk of a drill bit unintentionally plunging into brain tissue. Cranial perforators, which counter-bore holes and automatically stop upon skull penetration, do exist but are limited to large diameter hole size and an operating room environment. The tool presented here is compatible with a large range of bit diameters and provides safe, reliable access. This is accomplished through a dynamic bi-stable linkage that supports drilling when force is applied against the skull but retracts upon penetration when the reaction force is diminished. Retraction is achieved when centrifugal forces from rotating masses overpower the axial forces, thus changing the state of the bi-stable mechanism. Initial testing on ex-vivo animal structures has demonstrated that the device can withdraw the drill bit in sufficient time to eliminate the risk of soft tissue damage. Ease of use and portability of the device will enable its use in unregulated environments such as hospital emergency rooms and emergency disaster relief areas.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A002. doi:10.1115/DETC2013-12167.

We have developed a compliant robotic tendon mechanism for a robotic ankle. In this paper, we analyze the differences between a stiff and compliant robotic tendon versus a stiff and compliant slider crank mechanism. The compliant, slider-crank mechanism reduces peak forces and speed required by an actuator at the ankle.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A003. doi:10.1115/DETC2013-12272.

This research explored the development of a new haptic device for wrist rehabilitation therapy. Specifically, the therapy requires providing resistive forces against the adduction/abduction, flexion/extension of the wrist and pronation/supination of the forearm. The new haptic device employs a spherical magnetorheological brake (MR-brake). This brake was developed by our research group for a previous study and is the only one of its kind. It resembles a typical ball-joint with 3 degrees of freedom (DOF). It can apply high levels of variable resistive force in a very compact single actuator. The new device was coupled to the spherical MR-brake via linkages so that the virtual center of rotation was placed at the center of the patient’s wrist. Compared to similar devices that use motors, conventional rotary MR-brakes or hybrid MR-motor actuators, our device has the advantage of using just a single compact actuator to control all 3 DOF. The interface is inherently safe in such a rehabilitation application as the MR-brakes are passive devices. Details of the design, the MR-brake and a series of experiments to characterize the device are presented. The experimental results indicate minimal backlash in the linkages and the device can provide easily controllable resistive forces in its range of motion. Such a haptic interface is promising since it can enable a computer-controlled and -monitored rehabilitation therapy with a virtual training environment.

Topics: Haptics , Brakes
Commentary by Dr. Valentin Fuster
2013;():V06AT07A004. doi:10.1115/DETC2013-12374.

Navigation aids rely mostly on (audio)visual cues when it comes to communication with the user. An alternative and more intuitive communication modality may be provided by means of haptic guidance generated by a portable mechatronic device. Especially visually impaired and blind people may benefit from a device that generates the illusion of an external force; it may possibly eliminate the need for a guide dog. This paper investigates constant-velocity crank-driven mechanisms which are able to generate such a force illusion by means of a reciprocating mass. The focus of this paper is on the generation of the illusion itself rather than manipulating the direction of this force. The force illusion is a result of successive positive and negative reaction forces with unequal amplitude, generated by a reciprocating mass. The acceleration ratio of the mass is selected as the main evaluation criterion for comparing different types of candidate mechanisms. Because the input is a simple motor rotating at a constant velocity, the synthesis of the mechanism is key to generating proper acceleration profiles. A brute-force approach is used for the synthesis procedure, i.e., characteristic distances and link lengths are varied with steps of 1mm for each of the candidate mechanisms, thereby generating very large numbers of variants. Kinematic performance reveal typical acceleration ratios in the range of 1 to 19; where a ratio of one does not result in a force illusion while a ratio of 19 might be demanding on the physical design. An objective evaluation leads to selecting the Square Recti-Linear mechanism as the overall most promising candidate mechanism. A prototype of this mechanism is then presented to demonstrate the working principle. The shape of the prototype’s force profile over time is measured experimentally and is shown to be very similar to the profile obtained by simulation. The reciprocating mass accounts for almost one fifth of the total mass of the prototype, resulting in a strong force illusion in comparison with gravitational forces.

Topics: Design , Navigation
Commentary by Dr. Valentin Fuster
2013;():V06AT07A005. doi:10.1115/DETC2013-12527.

There is an analogy between the kinematic structures of proteins and robotic mechanisms. On the basis of this analogy, we have so far developed some methods for predicting the internal motions of proteins from their three-dimensional structural data in protein data bank (PDB). However, these methods are basically applicable to a single protein molecule. In this study, we extended these methods to apply them to systems that consist of multiple molecules including proteins (protein systems), and developed a computational framework for predicting the motions of the molecules. The model used in this method is a type of elastic network model. In particular, proteins are modeled as a robot manipulator constrained by the springs (the dihedral angles on the main chains correspond to the joint angles). The interactions between molecules are also modeled as springs. The basic concept for predicting the motions is based on the analysis of structural compliance. By applying statically balanced forces to the model in various directions, we extracted those motions with larger structural compliance. To reduce the computational time, we formulated the method with the prospect of efficient computation including parallel computation. In addition, we developed a preparatory computer program implementing the proposed algorithms, and analyzed some protein systems. The results showed that the proposed computational framework can efficiently analyze large protein systems.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A006. doi:10.1115/DETC2013-12671.

Protein structure prediction remains one of the significant challenges in computational biology. We have previously shown that our kinetostatic compliance method can overcome some of the key difficulties faced by other de novo structural prediction methods, such as the very small time steps required by the molecular dynamics approaches, or the very large number of samples required by the sampling based techniques. In this paper we extend the previous free energy formulation by adding the solvent effects, which contribute predominantly to the folding phenomena. We show that the addition of the solvation effects, which complement the existing Coulombic and van der Waals interactions, lead to a physically effective energy function. Furthermore, we achieve significant computational speed-up by employing efficient algorithms and data structures that effectively reduce the time complexity from O(n2) to O(n), n being the number of atoms. Our simulations are consistent with the general behavior observed in protein folding, and show that the hydrophobic atoms tend to pack inside the core of the molecule in an aqueous solvent, while a vacuum environment produces no such effect.

Topics: Simulation , Proteins
Commentary by Dr. Valentin Fuster
2013;():V06AT07A007. doi:10.1115/DETC2013-12798.

The Atlantic razor clam (Ensis directus) burrows into underwater soil by using motions of its shell to locally fluidize the surrounding substrate. The energy associated with movement through fluidized soil — characterized by a depth-independent density and viscosity — scales linearly with depth. In contrast, moving through static soil requires energy that scales with depth squared. For E. directus, this translates to a 10X reduction in the energy required to reach observed burrow depths. For engineers, localized fluidization offers a mechanically simple and purely kinematic method to dramatically reduce burrowing energy. This concept is demonstrated with RoboClam, an E. directus-inspired robot. Using a genetic algorithm to generate digging kinematics, RoboClam has achieved localized fluidization and burrowing performance comparable to that of the animal, with a linear energy-depth relationship. In this paper, we present the critical timescales and associated kinematics necessary for achieving localized fluidization, which are calculated from soil parameters and validated via RoboClam and E. directus testing.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A008. doi:10.1115/DETC2013-12918.

Unlike open surgery, minimally invasive surgery (MIS) involves small incisions through which instruments are passed to perform surgery. This technique is preferred since it reduces postoperative pain and recovery time. Laparoendoscopic single-site (LESS) surgery is the next step in MIS; a single incision is created instead of multiple access points for allowing the instruments to enter the peritoneal cavity. However, such minimally invasive techniques force the surgeon to perform more complex movements, hence the interest to use robotic systems. Design of robots for LESS is challenging to avoid collisions, reduce weight, and improve compactness while respecting the technical requirements (minimum forces, velocities). In this paper, we present the dimensional synthesis of a two-arm robot used for LESS. Each arm has a 2R-R-R architecture with link lengths optimized to respect the workspace constraints and maximize compactness while improving the performance in terms of forces and velocities (kinetostatic properties).

Commentary by Dr. Valentin Fuster
2013;():V06AT07A009. doi:10.1115/DETC2013-13004.

In this paper, we present the design, fabrication and characterization of fully soft pneumatic artificial muscles (PAMs) with low threshold pressures that are intended for direct cardiac compression (DCC). McKibben type PAMs typically have a threshold pressure of at least 100 kPa and require rigid end fittings which may damage soft tissue and cause local stress concentrations, and thus failure points in the actuator. The actuator design we present is a variant on the McKibben PAM with the following key differences: the nylon mesh is embedded in the elastomeric tube, and closure of the end of the tube is achieved without rigid ends. The actuators were tested to investigate the effects of mesh geometry and elastomer material on force output, contraction, and rise time. Lower initial mean braid angles and softer elastomer materials provided the best force, contraction, and rise times; Up to 50 N of force, 24% contraction, and response times of 0.05 s were achieved at 100 kPa. The actuators exhibited low threshold pressures (<5 kPa) and high rupture pressures (138 kPa – 720 kPa) which suggest safe operation for the DCC application. These results demonstrate that the actuators can achieve forces, displacements, and rise times suitable to assist with cardiac function.

Topics: Compression , Muscle
Commentary by Dr. Valentin Fuster
2013;():V06AT07A010. doi:10.1115/DETC2013-13028.

This paper explores the benefits of vacuum assistance to 18 gauge needle biopsy. Current biopsy methods are inefficient or have a high rate of failure, causing the need for further painful insertions. A novel needle insertion device was developed to create the vacuum in the needle. Using multiple pneumatic cylinders, a vacuum is created inside the end-cut needle by retracting the trocar while inserting the needle. Calculations were done to determine the force caused by the vacuum. Experiments inserting the needle into porcine kidney have shown that the vacuum assistance increases cutting efficiency.

Topics: Vacuum , needles
Commentary by Dr. Valentin Fuster
2013;():V06AT07A011. doi:10.1115/DETC2013-13086.

The small scale of microsurgery poses significant challenges for developing robust and dexterous tools to grip, cut, and join sub-millimeter structures such as vessels and nerves. The main limitation is that traditional manufacturing techniques are not optimized to create smart, articulating structures in the 0.1–10 mm scale. Pop-up book MEMS is a new fabrication technology that promises to overcome this challenge and enable the monolithic fabrication of complex, articulated structures with an extensive catalog of materials, embedded electrical components, and automated assembly with feature sizes down to 20 microns. In this paper, we demonstrate a proof-of-concept microsurgical gripper and evaluate its performance at the component and device level to characterize its strength and robustness. 1-DOF Flexible hinge joints that constrain motion and allow for out-of-plane actuation were found to resist torsional loads of 22.8±2.15 N·mm per mm of hinge width. Adhesive lap joints that join individual layers in the laminate structure demonstrated a shear strength of 26.8±0.53 N/mm2. The laminate structures were also shown to resist peel loads of 0.72±0.10 N/mm2. Various flexible hinge and adhesive lap components were then designed into an 11-layered structure which ‘pops up’ to realize an articulating microsurgical gripper that includes a cable-driven mechanism for gripping actuation and a flexural return spring to passively open the gripper. The gripper prototype, with final weight of 200 mg, overall footprint of 18 mm by 7.5 mm, and features as small as 200 microns, is able to deftly manipulate objects 100 times is own weight at the required scale, thus demonstrating its potential for use in microsurgery.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A012. doi:10.1115/DETC2013-13132.

Cryoablation is a percutaneous procedure for treating solid tumors using needle-like instruments. This paper presents an interventional guidance device for faster and more accurate alignment and insertion of multiple probes during cryoablation performed in closed bore magnetic resonance (MR) imaging systems. The device is compact and is intended to be mounted onto a Siemens 110 mm MR loop coil. A cable-driven two-degrees-of-freedom spherical mechanism mimics the wrist motion as it orients the intervention probes about a remote center of motion located 15 mm above the skin. A carriage interfaces with the probes via a thumbscrew-fastened latch to passively release the probes from their tracks, enabling them to be inserted sequentially and freeing them to move with respiration. Small actuator modules containing piezoelectric encoder-based motors are designed to be snap-fit into the device for ease of replacement and sterilization. The robot MRI compatibility was validated with standard cryoablation imaging sequences in 3T MR environment, yielding a maximum of 4% signal to noise ratio during actuator motion. Bench-level device characterization demonstrated a maximum error of 0.78° in the carriage movement. Needle-tip placement experiments for multiple targets in gelatin were performed using our image-guided navigation software, measuring an average targeting error of 2.0 mm.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A013. doi:10.1115/DETC2013-13161.

Colorectal surgery is an area of active research within general surgery. However, over 80% of these procedures currently require an open surgery based on the size and location of the tumor. The current state-of-the-art surgical instruments are unintuitive, restricted by the incision site, and often require timely repositioning tasks during complex surgical procedures. A multi-quadrant miniature in vivo surgical robot has been developed to mitigate these limitations as well as the invasiveness of colorectal procedures. By reducing invasiveness, the patient benefits from improved cosmetics, decreased postoperative pain, faster recovery time, and reduced financial burden. A paradigm shift in invasiveness is often inversely proportional to surgeon benefits. Yet, through the use of a robotic device, the surgeon benefits from improved ergonomics, intuitive control, and fewer required repositioning tasks. This paper presents a two armed robotic device that can be controlled from a remote surgical interface. Each arm has six internally actuated degrees of freedom, decoupling the system from the incision site. Each arm is also equipped with a specialized interchangeable end effector. For the surgical procedure, visual feedback is provided through the use of a standard laparoscope with incorporated light source. The robotic device is introduced into the abdominal cavity through a hand-assisted laparoscopic surgery (HALS) port that is placed within the navel. The device is then grossly positioned to the site of interest within the abdominal cavity through the use of a protruding rod that is rigidly attached to each arm. The surgeon can then begin to manipulate tissue through the use of the surgical interface that is remotely located within the operating room. This interface is comprised of a monitor to provide visual feedback, foot pedals to control the operational state of the device, and two haptic devices to control the end point location of each arm and state of the end effectors.

Topics: Robots , Surgery
Commentary by Dr. Valentin Fuster
2013;():V06AT07A014. doi:10.1115/DETC2013-13289.

Micro Unmanned Aerial Vehicles (MAVs) have been used in a wide range of applications [1, 2, 3]. However, there are few papers addressing high-speed grasping and transportation of pay-loads using MAVs. Drawing inspiration from aerial hunting by birds of prey, we design and equip a quadrotor MAV with an actuated appendage enabling grasping and object retrieval at high speeds. We develop a nonlinear dynamic model of the system, demonstrate that the system is differentially flat, plan dynamic trajectories using the flatness property, and present experimental results with pick-up velocities at 2 m/s (6 body lengths / second) and 3 m/s (9 body lengths / second). Finally, the experimental results are compared with observations derived from video footage of a bald eagle swooping down and snatching a fish out of water.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A015. doi:10.1115/DETC2013-13294.

In recent years, snake-inspired locomotion has garnered increasing interest in the bio-inspired robotics community. This positive trend is largely due to the unique and highly effective gaits utilized by snakes to traverse various terrains and obstacles. These gaits make use of a snake’s hyper-redundant body structure to adapt to the terrain and maneuver through tight spaces. Snake-inspired robots utilizing rectilinear motion, one of the primary gaits observed in natural snakes, have demonstrated favorable results on various terrains. However, previous variations of the rectilinear gait were inefficient in cyclic displacement. These gaits generated vertical waves traveling along the length of the robot. Generating these waves required significant joint energy for relatively small horizontal displacements. This paper presents analytical and experimental results for a rectilinear gait, which demonstrates significant linear displacement for relatively low joint effort. The low effort gait functions by propagating a wave through the length of the robot via expansions and contractions of the body segments, propelling the robot platform forward. The low effort rectilinear gait is demonstrated on a robot platform that incorporates high speed linear motion and variable traction through friction. We also report the results of a case study showcasing the practical benefits of the low effort gait.

Topics: Robots
Commentary by Dr. Valentin Fuster
2013;():V06AT07A016. doi:10.1115/DETC2013-13349.

In recent years, there has been a steep rise in the quality of prostheses for patients with upper limb amputations. One common control method, using electromyographic (EMG) signals generated by muscle contractions, has allowed for an increase in the degrees of freedom (DOFs) of hand designs and a larger number of available grip patterns with little added complexity for the wearer. However, it provides little sensory feedback and requires non-natural control which must be learned by the user. Another recent improvement in prosthetic hand design instead employs electroneurographic (ENG) signals, requiring an interface directly with the peripheral nervous system (PNS) or the central nervous system (CNS) to control a prosthetic hand. While ENG methods are more invasive than using surface EMG for control, an interface with the PNS has the potential to provide more natural control and creates an avenue for both efferent and afferent sensory feedback. Despite the recent progress in design and control strategies, however, prosthetic hands are still far more limited than the actual human hand. This review outlines the recent progress in the development of EMG and ENG controlled prosthetic hands, discussing advancements in the areas of sensory feedback and control. The potential benefits and limitations of both control strategies, in terms of signal classification, invasiveness, and sensory feedback, are examined. A brief overview of interfaces with the CNS is provided, and potential future developments for these control methods are discussed.

Topics: Prostheses
Commentary by Dr. Valentin Fuster

37th Mechanisms and Robotics Conference: Compliant Mechanisms and Micro/Nano Mechanisms (A. Midha Symposium)

2013;():V06AT07A017. doi:10.1115/DETC2013-12124.

The relatively new technology of additive manufacturing (also known as “3-D printing” or “rapid prototyping”) presents some intriguing possibilities for the design of compliant mechanisms. This paper introduces a new category of compliant mechanisms — Fully Compliant Layered Mechanisms (FCLMs) — that rely on additive manufacturing to produce mechanisms with complex geometry. An FCLM is a fully compliant mechanism whose geometry requires two or more links to cross over one another to achieve a desired motion. The need to have crossing links requires the mechanism to have multiple layers. Such a mechanism is fairly easy to produce using additive manufacturing systems, but the more brittle materials associated with additive manufacturing also impose some limitations on the design of FCLMs. This paper presents an overview of some of these limitations along with approaches that are being developed to solve the challenges of using additive manufacturing in the production of compliant linkages. The focus is on lumped compliant mechanisms with key challenges that include: the selection of a proper joint type; the layering of the compliant mechanism; and the stability of the mechanism. Beam type joints such as a spiral joint are found to be suitable for use with additive manufacturing. These joints have some lateral instability which can be reduced by proper layering and structural reinforcements in the mechanism. These joints also pose the potential for increased parasitic motion, which can be minimized by joint design approaches. Preliminary ideas are presented for the solution of these problems along with some needs for future development.

Topics: Manufacturing , Design
Commentary by Dr. Valentin Fuster
2013;():V06AT07A018. doi:10.1115/DETC2013-12178.

How do we assess the capability of a compliant mechanism of given topology and shape? The kinetoelastostatic maps proposed in this paper help answer this question. These maps are drawn in 2D using two non-dimensional quantities, one capturing the nonlinear static response and the other the geometry, material, and applied forces. Geometrically nonlinear finite element analysis is used to create the maps for compliant mechanisms consisting of slender beams. In addition to the topology and shape, the overall proportions and the proportions of the cross-sections of the beam segments are kept fixed for a map. The finite region of the map is parameterized using a non-dimensional quantity defined as the slenderness ratio. The shape and size of the map and the parameterized curves inside it indicate the complete kinetoelastostatic capability of the corresponding compliant mechanism of given topology, shape, and fixed proportions.

Static responses considered in this paper include input/output displacement, geometric amplification, mechanical advantage, maximum stress, etc. The maps can be used to compare mechanisms, to choose a suitable mechanism for an application, or re-design as may be needed. The usefulness of the non-dimensional maps is presented with multiple applications of different variety. Non-dimensional portrayal of snap-through mechanisms is one such example. The effect of the shape of the cross-section of the beam segments and the role of different segments in the mechanism as well as extension to 3D compliant mechanisms, the cases of multiple inputs and outputs, and moment loads are also explained. The effects of disproportionate changes on the maps are also analyzed.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A019. doi:10.1115/DETC2013-12179.

In this paper, we integrate two or more compliant mechanisms to get enhanced functionality for manipulating and mechanically characterizing the grasped objects of varied size (cm to sub-mm), stiffness (1e5 to 10 N/m), and materials (cement to biological cells). The concepts of spring-lever (SL) model, stiffness maps, and non-dimensional kinetoelastostatic maps are used to design composite and multi-scale compliant mechanisms. Composite compliant mechanisms comprise two or more different mechanisms within a single elastic continuum while multi-scale ones possess the additional feature of substantial difference in the sizes of the mechanisms that are combined into one. We present three applications: (i) a composite compliant device to measure the failure load of the cement samples; (ii) a composite multi-scale compliant gripper to measure the bulk stiffness of zebrafish embryos; and (iii) a compliant gripper combined with a negative-stiffness element to reduce the overall stiffness. The prototypes of all three devices are made and tested. The cement sample needed a breaking force of 22.5 N; the zebrafish embryo is found to have bulk stiffness of about 10 N/m; and the stiffness of a compliant gripper was reduced by 99.8 % to 0.2 N/m.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A020. doi:10.1115/DETC2013-12206.

This paper presents a large-range decoupled XY compliant parallel manipulator (CPM) with good dynamics (no under-constrained/non-controllable mass). The present XY CPM is composed of novel parallelogram flexure modules (NPFMs) that are parallel four-bar mechanisms as prismatic (P) joints with four identical monolithic cross-spring flexural pivots, flexure revolute (R) joints. The parasitic translation of the NPFM is compensated via the rotational centre shift of the flexure R joint thereof based on the prior art. The optimization function and optimised geometrical parameters are investigated for the NPFM at first to achieve the largest translation. The design of a large-range XY CPM is then implemented according to the fully symmetrical 4-PP parallel kinematic mechanism (PKM) and through using the optimised NPFMs. Finally, the simplified analytical stiffness modelling and finite element analysis (FEA) are undertaken for the static and/or dynamic characteristics analysis of the 4-PP XY CPM. It is shown from FEA in the example case that the present 4-PP XY CPM has good performance characteristics such as large-range motion space (10 mm × 10 mm with the total dimension of 465 mm× 465 mm), no non-controllable mass, monolithic configuration, maximal kinematostatic decoupling (cross-axis coupling effect less than 1.2%), maximal actuator isolation (input coupling effect less than 0.13%) and well-constrained parasitic rotation (less than 0.4 urad). In addition, the stiffness-enhanced NPFM using over-constraint is proposed to produce a first/second modal frequency of about 100 Hz for the resulting XY CPM.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A021. doi:10.1115/DETC2013-12213.

In the field of soft robotics, granular jamming is a newly adopted variable stiffness mechanism involving the use of vacuum pressure to control soft, particulate matter to become a unified, solid-like structure. However, granular jamming is conventionally controlled with air, which reduces the mobility of the robot. This is because the compressibility of air requires large vacuum pumps or chambers. Instead, we propose the use of an incompressible fluid, such as water, to control the stiffness of the mechanism. This paper presents comparative studies that shows that a hydraulic granular jammed joint using deaired water can both achieve the same stiffness level with just one twentieth of the volume extraction and maintain the same hysteresis level of an air-based system.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A022. doi:10.1115/DETC2013-12273.

Topology uncertainty leads to different topology solutions and makes topology optimization ambiguous. Point connection and grey cell might cause topology uncertainty. They are both eradicated when hybrid discretization model is used for discrete topology optimization. A common topology uncertainty in the current discrete topology optimization stems from mesh dependence. The topology solution of an optimized compliant mechanism might be uncertain when its design domain is discretized differently. To eliminate topology uncertainty from mesh dependence, the genus based topology optimization strategy is introduced in this paper. The topology of a compliant mechanism is defined by its genus which is the number of holes in the compliant mechanism. With this strategy, the genus of an optimized compliant mechanism is actively controlled during its topology optimization process. There is no topology uncertainty when this strategy is incorporated into discrete topology optimization. The introduced topology optimization strategy is demonstrated by examples with different degrees of genus.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A023. doi:10.1115/DETC2013-12338.

A novel contact aided compliant mechanism called a bend-and-sweep compliant mechanism is presented. This mechanism has tailorable nonlinear stiffness properties in two orthogonal directions. The fundamental element of this compliant mechanism is the Angled Compliant Joint (ACJ), and the geometric parameters determine the stiffness. This paper presents the design and optimization of such a compliant mechanism.

A multi-objective optimization problem was formulated for design optimization of the bend-and-sweep compliant mechanism. The objectives of the optimization problem were to maximize the bending and sweep displacements while minimizing the von Mises stress and mass of each mechanism. This optimization problem was solved using NSGA-II (a genetic algorithm). The results of this optimization for a single ACJ during upstroke and downstroke are presented. Results of two different loading conditions used during optimization of a single ACJ for upstroke are presented. Finally, optimization results comparing the performance of compliant mechanisms with one and two ACJs are also presented. It can be inferred from these results that the number of ACJs and the design of each ACJ determines the stiffness of the bend-and-sweep compliant mechanism. These mechanisms can be used in various applications.

Ornithopters or flapping wing unmanned aerial vehicles have unique potential to revolutionize both civil and military applications. The overall goal of this research is to improve the performance of such ornithopters by passively morphing their wings. Passive wing morphing of ornithopters can be achieved by inserting contact-aided compliant mechanisms in the leading edge wing spar. Previously the authors have shown that bending of ornithopter wings can be achieved by integrating a one degree of freedom contact aided compliant mechanism called a compliant spine. The spine was inserted into the leading edge spar and successful flight testing has shown that passive wing bending in ornithopters is feasible and results in significant improvements in lift and thrust. In order to achieve a bio-inspired wing gait called continuous vortex gait, the wings of the ornithopter need to bend, sweep, and twist simultaneously. This can be achieved by using the bend-and-sweep compliant presented in this paper.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A024. doi:10.1115/DETC2013-12385.

Inspiration for the creation of mechanical devices often comes from observing the natural structures and movements of living organisms. Understanding the wide use of modularity and compliance in nature may lead to the design of high-performance flexure systems or compliant devices. One of the most important nature-inspired paradigms for constructing flexure systems is based on the effective use of symmetry. With a rigid mathematical foundation called screw theory and Lie group. The research of this paper mainly focuses on: (i) Mathematical explanation or treatment of symmetry design wildly used in flexure systems, concerning with a series of topics such as the relationship between degree of freedom (DOF), constraint, overconstraint, decouple motion and symmetrical geometry, and How to guarantee the mobility unchanged when using symmetry design? (ii) A compliance-based analytical verification for demonstrating that the symmetry design can effectively improve accuracy and dynamic performances. (iii) The feasibility of improving accuracy performance by connecting symmetry design with the principle of elastic averaging. The whole content is organized around a case study, i.e. symmetrical design of 1-DOF translational flexure mechanisms. The results are intent to provide a rigid theoretical foundation and significant instruction for the symmetry design philosophy in flexure systems using kinematic principles.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A025. doi:10.1115/DETC2013-12443.

The objective of this paper is to introduce and demonstrate a new method for the topology optimization of compliant mechanisms. The proposed method relies on exploiting the topological derivative, and it exhibits numerous desirable properties including: (1) the mechanisms are hinge-free, (2) mechanisms with different geometric and mechanical advantages can be generated by varying a single control parameter, (3) a target volume fraction need not specified; instead numerous designs, of decreasing volume fractions, are generated in a single optimization run, and (4) the underlying finite element stiffness matrices are well-conditioned, permitting the use of high-performance iterative solvers. The proposed method and implementation are illustrated through numerical experiments in 2D and 3D.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A026. doi:10.1115/DETC2013-12473.

In this paper we introduce the principles necessary to analyze and design serial flexure elements, which may be used to synthesize advanced compliant mechanisms (CMs). The most commonly used flexure elements (e.g., wire, blade, or living hinge flexures) are often parallel and thus impose constraining forces directly through all parts of their geometry to the rigid bodies that they join within the CM. Serial flexure elements, on the other hand, constrain rigid bodies with a larger variety of forces and moments and thus enable CMs to achieve (i) more degrees of freedom (DOFs), (ii) larger dynamic and elastomechanic versatility, and (iii) greater ranges of motion than parallel elements. In this paper, we extend the principles of the Freedom and Constraint Topologies (FACT) synthesis approach such that it enables the synthesis of CMs that are not only constrained by parallel flexure elements, but also by serial elements. FACT utilizes geometric shapes to intuitively guide designers in visualizing compliant element geometries that achieve any desired set of DOFs. In this way, designers can rapidly generate a host of new serial flexure elements for various CM applications. Such elements are provided here as case studies.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A027. doi:10.1115/DETC2013-12496.

Coupling of tangential and centripetal acceleration components occurs in the estimation of rigid-body pose and twist with current accelerometer strapdowns. To address this shortcoming and its pernicious effects, a novel design of biaxial accelerometer strapdown is proposed. By virtue of its inherent isotropy, point tangential acceleration is decoupled from its centripetal counterpart, thereby realizing a straightforward and accurate acceleration estimation. The algorithm associated with the strapdown is validated by means of a numerical example, which shows the precision of the strapdown in estimating rigid-body pose and twist.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A028. doi:10.1115/DETC2013-12576.

This paper uses rigid-body mechanism topologies to synthesize distributed compliant mechanisms that approximate a shape change defined by a set of morphing curves in different positions. A single-actuator compliant mechanism is synthesized from a single degree-of-freedom rigid-body mechanism’s base topology in one of two ways. In one case, the base topology is directly evaluated through dimensional synthesis to determine the compliant mechanism’s optimal dimensions. In the second, the base topology establishes an initial element network for an optimization routine that determines topologies and dimensions simultaneously, and an improved design domain parameterization scheme ensures that only topologies with well-connected structures are evaluated. A multi-objective genetic algorithm is employed to search the design space, and the deformation is evaluated using geometrically nonlinear finite element analysis. The procedure’s utility is demonstrated with two practical examples — one approximating open-curve profiles of an adaptive antenna and the other closed-curve profiles of a morphing wing.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A029. doi:10.1115/DETC2013-12582.

We present an extensible-link kinematic model for characterizing the motion trajectory of an arbitrary planar compliant mechanism. This is accomplished by creating an analogous kinematic model consisting of links that change length over the course of actuation to represent elastic deformation of the compliant mechanism. Within the model, the motion trajectory is represented as an analytical function. By Taylor series expansion, the trajectory is expressed in a parametric formulation composed of load-independent and load-dependent terms. Here, the load-independent terms are entirely defined by the shape of the undeformed compliant mechanism topology, and all load-geometry interdependencies are captured by the load-dependent terms. This formulation adds insight to the process for designing compliant mechanisms for high accuracy motion applications because: (1) inspection of the load-independent terms enables determination of specific topology modifications for improving the accuracy of the motion trajectory; and (2) the load-dependent terms reveal the polynomial orders of principally uncorrectable error components of the motion trajectory. The error components in the trajectory simply represent the deviation of the actual motion trajectory provided by the compliant mechanism compared to the ideally desired one. We develop the generalized model framework, and then demonstrate its utility by designing a compliant micro-gripper with straight-line parallel jaw motion. We use the model to analytically determine all topology modifications for optimizing the jaw trajectory, and to predict the polynomial order of the uncorrectable trajectory components. The jaw trajectory is then optimized by iterative finite elements (FE) simulation until the polynomial order of the uncorrectable trajectory component becomes apparent.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A030. doi:10.1115/DETC2013-12623.

Compliant mechanisms have many advantages over rigid-link mechanisms. However, one of the challenges of compliant mechanisms is the trade-off between a large range of motion and a high out-of-plane stiffness. Furthermore, the out-of-plane stiffness is shown to vary over the range of motion. Especially for large-displacement compliant mechanisms this can be by a significant amount. In this paper the use of curved beam elements in a compliant mechanism is shown to have impact on this trade-off. The influence of curved beam elements on the out-of-plane stiffness over the entire range of motion is presented for simple structures such as a single beam element and double beam elements, as well as a compliant finger. With the use of a genetic algorithm optimization, the difference in performance of a design with only straight beam elements versus one with curved beam elements is highlighted and the effect on the out-of-plane stiffness profile is presented. The optimization with curved beam elements results in solutions with a performance in terms of objective function values that cannot be found by the optimization with only straight beam elements. It is shown that for simple structures the use of curved beam elements has a large influence on the shape of the out-of-plane stiffness profile along the range of motion, while for the compliant finger the influence is mainly in the variables of the out-of-plane stiffness profile.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A031. doi:10.1115/DETC2013-12657.

Soft robots allow for complex continuum motions and shapes that conform to their environment. Using a fiber-reinforced elastomeric enclosure (FREE) driven by fluid provides a high power density, soft continuum actuator. While the force generation for a small subset of this structure known as McKibben actuators has been studied extensively, the force and moments generated by a wider set of fiber reinforcements have not been previously investigated. Using virtual work and kinematics derived from fiber inextensibility and fluid incompressibility, the force and moments for the entire design space of FREEs has been determined analytically. Graphical representations have been created, providing easy tools for synthesis and analysis of force and moments in all possible FREEs. The hydraulic displacement amplification, or volumetric transduction, of output motion to fluid displacement has also been determined using kinematics; this transduction gives an indication of stiffness of the structure. Graphical representations have also been created, providing a designer with an intuitive understanding of the behavior all FREE topologies.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A032. doi:10.1115/DETC2013-12718.

In this paper, we apply screw theory to the type synthesis of compliant parallel mechanisms (PMs). Compliant PMs are formed by a moving stage supported by three or more limbs each of which is a serial chain of flexure joints and rigid bodies. They achieve movement through the deformation of flexure joints and have been widely used in precision machinery. As an important task in the conceptual design stage, the goal of type synthesis is to determine the chain of each limb as well as their relationship when they are assembled in parallel for a prescribed motion pattern. Our approach starts with a category of commonly used flexure primitives and flexure elements whose freedom and constraint spaces are characterized by twists and wrenches in screw theory. Following the well-studied synthesis procedure for rigid body PMs, we propose a synthesis procedure for compliant PMs via screw theory. This procedure consists of four basic steps: decomposition of the screw system of the constraint space, type synthesis of limbs, assembling limbs and design of flexure joints. As an example, we demonstrate the procedure for synthesizing compliant PMs for three degree-of-freedom (DOF) translational motions. Tables of limbs, types and geometric conditions for the assemblies of these limbs are presented. The paper provides a catalogue of compliant PM designs with three translational motions. At last, we provide a case study of applying finite element simulation to validate one of the synthesized designs.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A033. doi:10.1115/DETC2013-12727.

Lightweight mechanical energy-storage devices or springs with nonlinear strain-energy absorption rate are important building blocks for passive/quasi-passive rehabilitation robotics. They provide support and controllable energy storage/release into the system thereby making daily activities such as walking/running metabolically efficient for the disabled. These devices have stringent footprint constraints and must withstand 10 million cycles of loading for successful implementation on an orthotic device. Currently, there are no off-the-shelf springs or a systematic synthesis methodology that can meet these requirements in a deterministic fashion. In this paper, we demonstrate how existing body of knowledge in compliant mechanisms can be systematically leveraged to design spring geometries with distributed compliance that meet fatigue criteria and weight requirements. Towards this, we implement a strength-based approach to determine feasible initial solutions that upon optimization yield geometries with maximally distributed stresses. Such a framework is general and can be adapted for designing any compliant mechanism.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A034. doi:10.1115/DETC2013-12956.

The elastic deflection of a comb drive tooth in an electrostatic field is considered. The tooth can be symmetrically located between two rigid teeth of the matching comb, in which case the problem reduces to a pure bifurcation problem for which the critical voltage can be determined. Alternatively, due to an approximate straight-line mechanism, the tooth can have a uniform initial lateral displacement and a smooth curve of equilibria is found which has a limit point, after which pull-in occurs.

An assumed deflection shape and a series expansion of the electrostatic capacity yield the deflection curves for the case with a uniform initial lateral displacement. This shows that pull-in occurs at a voltage that is reduced by a factor that is about proportional to the two-third power of the relative lateral initial displacement.

The theoretical results have been experimentally tested. The results show a qualitative agreement, but the experimental deflections are larger and the pull-in voltages are lower. These differences can be explained from neglected fringe fields and deviations from the nominal shape.

Topics: Deflection
Commentary by Dr. Valentin Fuster
2013;():V06AT07A035. doi:10.1115/DETC2013-13142.

This paper describes a fully compliant statically balanced mechanism that can undergo greater than 100° of motion. Because compliant mechanisms achieve their motion from the deflection of their constituent members, there is some strain energy associated with actuated positions. By introducing an appropriate preload, strain energy can be held constant. This can reduce or nearly eliminate the input force required from the actuating device. This paper describes the statically balanced concept and demonstrates its optimization, testing, and implementation for a haptic pantograph mechanism. The statically balanced properties of the constituent mechanisms result in an assembly with two balanced degrees of freedom.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A036. doi:10.1115/DETC2013-13537.

This paper extends a previously developed Pseudo Rigid Body (PRB) analytical model for miniature elastomeric joints by introducing correction factors for joints with geometry not previously considered. Inclusion of these correction factors has resulted in an increase in the accuracy of the model from 20% to within 3% in bending and from 25% to within 7% in tension, when compared to equivalent Finite Element Analysis (FEA) models. Additionally, using the PRB model, a robotic leg with four elastomeric joints has been modeled, resulting in a maximum error of 12% when compared to an equivalent FEA model. Finally, the PRB model was used to optimize the robotic leg for minimum motor torque required to drive a hexapedal robot with six identical legs.

Commentary by Dr. Valentin Fuster

37th Mechanisms and Robotics Conference: Mechanism Analysis and Synthesis

2013;():V06AT07A037. doi:10.1115/DETC2013-12021.

A novel dimensional synthesis technique for solving the mixed exact and approximate motion synthesis problem for planar RR kinematic chains is presented. The methodology uses an analytic representation of the planar RR dyads rigid body constraint equation in combination with an algebraic geometry formulation of the exact synthesis for three prescribed locations to yield designs that exactly reach the prescribed pick & place locations while approximating an arbitrary number of guiding locations. The result is a dimensional synthesis technique for mixed exact and approximate motion generation for planar RR dyads. A solution dyad may be directly implemented as a 2R open chain or two solution dyads may be combined to form a planar 4R closed chain; also known as a planar four-bar mechanism. The synthesis algorithm utilizes only algebraic geometry and does not require the use of a numerical optimization algorithm or a metric on planar displacements. Two implementations of the synthesis algorithm are presented; computational and graphical construction. Moreover, the kinematic inversion of the algorithm is also included. An example that demonstrates the synthesis technique is included.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A038. doi:10.1115/DETC2013-12036.

A graphical four bar linkage synthesis method for planar rigid body guidance is presented. This method, capable of synthesis for up to five specified coupler positions, uses the poles and rotation angles, which are constraints, to define guiding links. Faster and simpler than traditional graphical synthesis methods, this method, allows the designer to see and consider most or all the possible solutions within a few seconds before making any free choices. All of the guiding links satisfying five specified coupler positions can be obtained graphically within 30 minutes without plotting any Burmester curves and without any mechanism design software. For four positions, both the circle and center point curves are simultaneously traced by corresponding circle-center point pairs using three poles having a common subscript and the corresponding rotation angles without any additional construction. This method eliminates the iterative construction required in previous methods which were based on free choices rather than constraints. The tedious plotting of Burmester curves graphically using pole quadrilaterals is also eliminated. The simplicity of the method makes four and five position synthesis practical to do graphically.

A corresponding analytical solution is presented which provides a simpler formulation than the previous solution method. This new method requires two fewer equations and provides a new way to plot Burmester curves analytically.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A039. doi:10.1115/DETC2013-12060.

Instantaneous kinematics of complex multi-loop mechanisms is modeled by linear and homogeneous mappings whose coefficient matrices have also important static meanings. As a consequence, the analysis of these models is a mandatory step, during design, that can be implemented by using the superposition principle. Here, spherical mechanisms are considered. Their general instantaneous-kinematics model is written by exploiting the properties of the instantaneous pole axes and the superposition principle. Then, this general model is analyzed to deduce an exhaustive analytic and geometric technique for identifying all the singular configurations of these mechanisms.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A040. doi:10.1115/DETC2013-12081.

In the design of spatial linkages, the finite-position kinematics is fully specified by the position of the joints in space. However, most of the tasks have additional requirements regarding motion smoothness, obstacle avoidance, force transmission or physical dimensions. Many of these additional performance requirements are independent of the finite-position kinematic task and can be solved using link optimization for an already defined set of joints.

In this paper we develop a methodology to optimize spatial mechanisms after a first kinematic synthesis stage, by considering the links as anchored to sliding points of a given set of joint axes, which have to meet constraints including link dimension, restricted region of operation and force transmission. The optimization is performed using a hybrid algorithm, including a genetic algorithm (GA) and a gradient-based minimization solver.

The methodology has been applied to a spatial CRR-RRR, one-degree-of-freedom closed linkage. The additional requirements in this example are used to control the position and size of the mechanism, and for reducing friction loads at the joints.

The combination of the kinematic synthesis together with the link optimization developed in this paper allows interactive monitoring and control of the objectives and constraints, to yield practical solutions for realistic spatial mechanism design problems.

Topics: Optimization
Commentary by Dr. Valentin Fuster
2013;():V06AT07A041. doi:10.1115/DETC2013-12282.

In this paper, a kind of 6-degree of freedom parallel earthquake simulator is proposed, which has 28 -input, two types of the branches and the redundant and fault-tolerant actuators. Based on the theory of the parallel mechanism, the mechanism of the 6-degree of freedom parallel earthquake simulator with 28 -input and the redundant and fault-tolerant actuators is constructed. The kinematic model of the earthquake simulator is established by D-H method. The kinematic simulation and the dynamic simulation of the earthquake simulator are carried out with ADAMS software. Finally, FEM model of the earthquake simulator is given and the modal analysis of the earthquake simulator is made with ANSYS software.

Topics: Earthquakes
Commentary by Dr. Valentin Fuster
2013;():V06AT07A042. doi:10.1115/DETC2013-12305.

Two-degree-of-freedom (2-DOF) rotational parallel manipulators (RPMs) have been widely used in pointing devices and robot wrists. This paper focuses on a class of 2-DOF RPMs achieving an equal-diameter spherical pure rolling motion (ESPRM) around the base. At first, a theoretical model of spherical pure rolling motion is analyzed and the characteristic of the associated constraint space is derived. Taking the Omni-Wrist III as a typical 2-DOF RPMs with an equal-diameter spherical pure rolling motion, mappings between the geometry and the motion are established and eight useful constraint conditions are derived which will be instructive for the type synthesis. Then, with focus on symmetrical structures, nine classes of 2-DOF RPMs with equal-diameter spherical pure rolling motion are synthesized based on the graphic method. Most of these RPMs have already been used in practice. Unlike the conventional type synthesis of lower-mobility parallel manipulators in literatures, some geometrical parameters of links, in addition to the distributions of joints and limbs, are taken into consideration in the type synthesis in this paper. This proposed research may help produce novel architectures.

Topics: Manipulators
Commentary by Dr. Valentin Fuster
2013;():V06AT07A043. doi:10.1115/DETC2013-12327.

Hydraulic rescue spreaders are used by emergency response personnel to extricate occupants from a vehicle crash. A lighter and more portable rescue spreader is required for better usability and to enable utilization in a variety of scenarios. To meet this requirement, topological synthesis, dimensional synthesis, and an optimization were used to develop a solution linkage. The topological synthesis technique demonstrates that ten links are the minimum possible number that achieves the desired motion without depending primarily on rotation of the spreader jaws. A novel integrated kinematic-structural dimensional synthesis technique is presented and used in a grid-search optimizing the linkage dimensions to minimize linkage mass. The resulting ten-bar linkage meets or exceeds the kinematic performance parameters while simultaneously achieving a near-optimum predicted mass.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A044. doi:10.1115/DETC2013-12379.

Safety is the most important issue that should be considered when designing collaborative robots that are intended to physically interact with humans. This paper investigates the force capabilities of two-degree-of-freedom planar parallel mechanisms that are equipped with torque limiters (safety clutches). Joint torque limiting devices are used in these mechanisms in order to limit the forces that the robot can apply to its environment. Such devices aim at ensuring the safety of the human beings interacting with the robot. However, because the torque-limiting devices are mounted at the joints of the robot, the end-effector force capabilities induced by these devices are dependent on the pose (Jacobian matrix) of the robot. Therefore, the characteristics of the torque limiting devices must be determined at the design stage in order to ensure safety and maximize effectiveness in all possible poses of the robot. Two types of planar two-degree-of-freedom parallel mechanisms are considered in this paper. Their architecture is first described. Then, the force capabilities are studied based on the Jacobian matrices. The maximum force that can be applied at the end-effector for given torque limits (safety index) is determined together with the maximum isotropic force (effectiveness) that can be produced. The ratio between these two forces, referred to as the force efficiency, can be considered as a performance index. Finally, some numerical results are proposed which can provide insight into the design of cooperation robots based on parallel architectures.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A045. doi:10.1115/DETC2013-12462.

This paper introduces a metamorphic parallel mechanism which has three topologies with pure translational, pure rotational and 3T1R degrees of freedom. Mobility change stemming from the reconfigurability of a reconfigurable Hooke (rT) joint is illustrated by change of the limb twist screw systems and the platform constraint screw system. Then the paper focuses on the pure rotational topology of the mechanism of which the rotational center can be altered along the central line perpendicular to the base plane by altering the radial rotational axes in the limbs. Singularity analysis is conducted based on the dependency of constraint forces and actuation forces in a screw based Jacobian matrix. Following these, rotation workspace variation is demonstrated in a 2D projection format using the Tilt-and-Torsion Euler angles based on the actuation limits and joint rotation ranges.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A046. doi:10.1115/DETC2013-12510.

Identifying all the functional topological structures embedded in a variable topology mechanism (VTM) is a leading step when analyzing the topological characteristics of the mechanism. Such an identification task is equivalent to the structure decomposition of the VTM. In this paper, we introduce a systematic approach, which is both algebraically and computationally manipulate-able, for the structure decomposition of VTMs. Based on a given source mechanism of a VTM, all its embedded functional topological structures can be identified through an algebraic computation via this method. For illustrating the presented approach, the decomposition of an automatic steel clamping and sawing mechanism is demonstrated.

Topics: Topology
Commentary by Dr. Valentin Fuster
2013;():V06AT07A047. doi:10.1115/DETC2013-12575.

A kinematically redundant parallel manipulator (PM) is a PM whose degrees-of-freedom (DOF) are greater than the DOF of the moving platform. It has been revealed in the literature that a kinematically redundant PM has fewer Type II kinematic singular configurations (also called forward kinematic singular configurations, static singular configurations or parallel singular configurations) and/or constraint singular configurations than its non-redundant counterparts. However, kinematically redundant PMs have not been fully explored, and the type synthesis of kinematically redundant PMs is one of the open issues. This paper deals with the type synthesis of kinematically redundant 3T1R PMs (also called SCARA PMs or Schoenflies motion generators), in which the moving platform has four DOF with respect to the base. At first, the virtual-chain approach to the type synthesis of kinematically redundant parallel mechanisms is recalled. Using this approach, kinematically redundant 3T1R PMs are constructed using several compositional units with very few mathematical derivations. The type synthesis of 5-DOF 3T1R PMs composed of only revolute joints is then dealt with systematically. This work provides a solid foundation for further research on kinematically redundant 3T1R PMs.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A048. doi:10.1115/DETC2013-12586.

Development of a new parallel manipulator can be very time consuming due to the traditional method of producing kinematic, dynamic and static calculation models and then evaluating them to determine aspects of the manipulator’s performance indices such as the mechanism’s workspace and singularity analysis. By extending the virtual chain approach to the type synthesis of parallel manipulators, this paper proposes a virtual-chain approach to the workspace analysis of parallel manipulators. This method is illustrated by producing and evaluating the workspace of several parallel robots including the well known DELTA robot by utilising the three-dimensional CAD software SolidWorks to produce a virtual prototype of a manipulator with an embedded virtual chain. The virtual chain represents the motion pattern of a manipulator’s end-effector and is very useful in the production of a graphical representation of the workspace of the manipulator. Using this approach, the link interferences and transmission indices can be easily taken into consideration in determining the workspace of a parallel manipulator.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A049. doi:10.1115/DETC2013-12716.

Knee bracing has been used to realize a variety of functional outcomes in both sport and rehabilitation application. Much of the literature focuses on the effect of knee misalignment, force reduction and superiority of custom braces over commercial over-the-counter braces. Efforts on developing exoskeletons to serve as knee augmentation systems emphasize actuation of joints, which then adds to bulkiness of ensuing designs.

In lieu of this, we would like to employ a semi-active augmentation approach (by addition of springs and dampers). Such an approach serves to redirect power (motions and forces) to achieve the desired functional outcomes from the knee braces. However, the suitable selection of geometric dimensions of the brace and spring parameters to achieve desired motion- and force-profiles at the knee remains a challenge. We therefore introduce a two-stage kinetostatic design process to help customize the brace to match a desired kinematic/static performance.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A050. doi:10.1115/DETC2013-12763.

This paper presents a synthesis methodology for a Stephenson II six-bar function generator that provides eight accuracy points, that is it ensures the input and output angles of the linkage match at eight pairs of specified values. A complex number formulation of the two loop equations of the linkage and a normalization condition are used to form the synthesis equations, resulting in 22 equations in 22 unknowns. These equations are solved using the numerical homotopy continuation solver, Bertini. The approach is illustrated with an example.

Topics: Generators
Commentary by Dr. Valentin Fuster
2013;():V06AT07A051. doi:10.1115/DETC2013-12799.

This paper details the dimensional synthesis for the rigid body guidance of planar eight-bar linkages that could be driven by a prismatic joint at its base. We show how two RR cranks can be added to a planar parallel robot formed by a PRR and 3R serial chain to guide its end-effector through a set of five task poses. This procedure is useful for designers who require the choice of ground pivot locations. The results are eight different types of one-degree of freedom planar eight-bar linkages. We demonstrate the design process with the design of a multifunctional wheelchair that could transform its structure between a self-propelled wheelchair and a walking guide.

Topics: Robots , Linkages
Commentary by Dr. Valentin Fuster
2013;():V06AT07A052. doi:10.1115/DETC2013-12838.

The general motion of a spatial mechanism is a screw motion about an instantaneous screw axis (ISA). The locus of a series of ISAs will form a ruled surface, which can be called as an axode. For a spatial mechanism with only one degree of freedom (DOF), the ISAs or the axodes of the moving platform are unique. However, the axodes of the parallel mechanisms (PMs) with multi DOF are related to the specific motion which has various possibilities. In this paper, the ISAs of the multi DOF PMs are studied using the jacobian matrix which is changing with the configurations of the moving platform. The axodes of the multi DOF PMs with different inputs or outputs are obtained using this method. Based on the analyzed results, it is very clear that the general motions of the PMs are screw motions or rotations about a series of ISAs. In the end, the parasitic motion of the PMs is studied. For a PM, the parasitic motion will exist if the rotational freedoms are not rotations about a fixed point or axis.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A053. doi:10.1115/DETC2013-12915.

It is very important to synthesize as many feasible kinematic structures of mechanisms as possible in the conceptual design of mechanisms. Besides simple joint mechanisms, multiple joint mechanisms are also widely used in various mechanical systems. This paper proposes an automatic method for the synthesis of planar multiple joint kinematic chains which are seldom addressed in literature. The bicolor topological graph and the bicolor contracted graph are adopted to represent the topological structures of multiple joint kinematic chains. The characteristic number string of bicolor topological graphs is proposed and used to detect efficiently isomorphism in the synthesis progress. A systematic method for the synthesis of kinematic chains with one multiple joint is proposed, and the whole families of multiple joint kinematic chains with up to 16 links and all possible degrees of freedom are obtained for the first time.

Topics: Kinematics , Chain
Commentary by Dr. Valentin Fuster
2013;():V06AT07A054. doi:10.1115/DETC2013-12969.

This paper develops techniques that address the design of planar four-bar linkages for tasks common to pick-and-place devices, used in assembly and manufacturing operations. Pick-and-place tasks often require the exact position and orientation of an object (motion generation) at the end points of the task. Within the range of movement, the motion restrictions are less rigorous with only the position of the object (path-point generation) being specified to avoid obstacles. Established synthesis theory has been developed for either motion generation or path-point generation tasks. This paper presents four-bar linkage synthesis methods for tasks that include a combination of motion and path requirements. This synthesis challenge is addressed via two approaches: Geometric Constraint Programming (GCP) and numerical solutions to synthesis equations. Using GCP, a step-by-step methodology has been established to find solutions to these synthesis challenges. Using numerical methods, techniques are presented to formulate kinematic chain constraint equations and solve for appropriate link lengths and pivot locations. Examples of various combinations of motion and path-point generation are presented.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2013;():V06AT07A055. doi:10.1115/DETC2013-12977.

This paper studies the problem of planar four-bar motion approximation from the viewpoint of extraction of geometric constraints from a given set of planar displacements. Using the Image Space of planar displacements, we obtain a class of quadrics, called Generalized- or G-manifolds, with eight linear and homogeneous coefficients as a unified representation for constraint manifolds of all four types of planar dyads, RR, PR, and PR, and PP. Given a set of image points that represent planar displacements, the problem of synthesizing a planar four-bar linkage is reduced to finding a pencil of G-manifolds that best fit the image points in the least squares sense. This least squares problem is solved using Singular Value Decomposition. The linear coefficients associated with the smallest singular values are used to define a pencil of quadrics. Additional constraints on the linear coefficients are then imposed to obtain a planar four-bar linkage that best guides the coupler through the given displacements. The result is an efficient and linear algorithm that naturally extracts the geometric constraints of a motion and leads directly to the type and dimensions of a mechanism for motion generation.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A056. doi:10.1115/DETC2013-13037.

This paper deals with the design optimization of the IRSBot-2 based on an optimized test trajectory for fast pick and place operations. The IRSBot-2 is a two degree-of-freedom translational parallel manipulator dedicated to fast and accurate pick-and-place operations.

First, an optimization problem is formulated to determine the optimal test trajectory. This problem aims at finding the path defined with s-curves and the time trajectory that minimize the cycle time while the maximum acceleration of the moving platform remains lower than 20 G and the time trajectory functions are C2 continuous.

Then, two design optimization problems are formulated to find the optimal design parameters of the IRSBot-2 based on the previous optimal test trajectory. These two problems are formulated so that they can be solved in cascade. The first problem aims to define the design parameters that affect the geometric and kinematic performances of the manipulator. The second problem is about the determination of the remaining parameters by considering elastostatic and dynamic performances.

Finally, the optimal design parameters are given and will be used for the realization of an industrial prototype of the IRSBot-2.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A057. doi:10.1115/DETC2013-13051.

In this paper we present an algorithm applicable to the Watt I and Stephenson I six-bar linkage designs which determines if a candidate linkage moves smoothly through a desired range of input angles. Intended for use with a synthesis routine our algorithm uses the Jacobian of the linkage to determine if a linkage moves smoothly by identifying the continuous existence of a desired branch of a single circuit for all input angles within a bounded range. With the constraint that the input angle must be contained within the four-bar loop, the determinant of the Jacobian is factored into components that represent the individual linkage loops. The algorithm starts with a linkage of a known configuration which reaches one of the desired task positions to establish the set of signs for these determinants and this set is tracked for consistency throughout the bounded range of input angles. Linkages with defects that exist in a narrow range of input angles are addressed by numerically identifying the input angles which correspond to the minimal value of the Jacobian determinants. We verify that at these input angles the linkage remains on the same branch of the same circuit. A Watt I and Stephenson I six-bar linkage that passes this test will move smoothly through the desired range of input angles. Examples using Mathematica demonstrate the application of the algorithm on both the Watt I and Stephenson I linkage types.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A058. doi:10.1115/DETC2013-13084.

The subject of this paper is about the conceptual design of parallel Schoenflies motion generators based on the wrench graph.

By using screw theory and Grassmann geometry, some conditions on both the constraint and the actuation wrench systems are generated for the assembly of limbs of parallel Schoenflies motion generators, i.e., 3T1R parallel manipulators. Those conditions are somehow related to the kinematic singularities of the manipulators. Indeed, the parallel manipulator should not be in a constraint singularity in the starting configuration for a valid architecture, otherwise it cannot perform the required motion pattern. After satisfying the latter condition, the parallel manipulator should not be in an actuation singularity in a general configuration, otherwise the obtained parallel manipulator is permanently singular.

Based on the assembly conditions, six types of wrench graphs are identified and correspond to six typical classes of 3T1R parallel manipulators. The geometric properties of these six classes are highlighted. A simplified expression of the superbracket decomposition is obtained for each class, which allows the determination and the comparison of the singularities of 3T1R parallel manipulators at their conceptual design stage. The methodology also provides new architectures of parallel Schoenflies motion generators based on the classification of wrench graphs and on their singularity conditions.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A059. doi:10.1115/DETC2013-13109.

The application of manipulators is becoming more and more popular in object handling especially when it is desired to have access to remote areas in destructive or hazardous taskspaces. For this purpose, a hand-like mechanism must be designed to be used as an end-effector, which can grasp objects. In this paper a cable driven grasping mechanism has been presented. In the proposed mechanism each finger consists of three phalanxes which are actuated by a single motor. Locking and unlocking constraints are used in the mechanism in order to generate an anthropomorphic motion, in which, the order of reaching phalanxes to the object is sequential. In this way, each phalanx starts moving toward the object when the previous phalanx had already made its contact. The gripping motion of the mechanism has been classified into five steps according to each phalanx’s status as being locked or unlocked. For each step, dynamics equations are derived involving kinematic parameters of the mechanism as well as the tension in the cables. Finally a numerical example is provided to obtain tensions in the gripper cables.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A060. doi:10.1115/DETC2013-13120.

This paper introduces planar, higher variable joints as essential components of reconfigurable mechanisms that change topology due to a joint geometry change. Higher variable joints are higher pair equivalent lower pairs that are geometrically different. It will be shown that 2nd order effects, or surface curvature, of higher variable joints is critical to achieve a particular joint motion. A practical application of higher variable joints will also be presented.

Topics: Geometry , Topology
Commentary by Dr. Valentin Fuster
2013;():V06AT07A061. doi:10.1115/DETC2013-13168.

This paper deals with the problem of integrated joint-type and dimensional synthesis of planar four-bar and six-bar linkages with revolute (R) and prismatic (P) joints for guiding through five specified task positions of the end-effector. In a recent work, we developed a simple algorithm for analyzing a set of given task positions to determine all feasible planar dyads with revolute and/or prismatic joints that can be used to guide through the given positions. The current paper extends this algorithm to the integrated joint-type and dimensional synthesis of Watt I and II and Stephenson I, II, and III six-bar linkages with a combination of R and P joints. In the process, we developed a new classification for planar six-bar linkages according to whether the end-effector can be constrained by two dyads (Type I), one dyad (Type II), or no dyad (Type III). We demonstrate this task driven synthesis approach with three examples including a novel six-bar linkage for lifting an individual with age disability from seating position to standing position.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2013;():V06AT07A062. doi:10.1115/DETC2013-13179.

This paper studies the problem of spherical 4R motion approximation from the viewpoint of extraction of circular geometric constraints from a given set of spherical displacements. This paper extends our planar 4R linkage synthesis work to the spherical case. By utilizing kinematic mapping and quaternions, we map spherical displacements into points and the workspace constraints of the coupler into intersection of algebraic quadrics (called constraint manifold), respectively, in the image space of displacements. The problem of synthesizing a spherical 4R linkage is reduced to finding a pencil of quadrics that best fit the given image points in the least squares sense. Additional constraints on the pencil identify the quadrics that represent a spherical circular constraint. The geometric parameters of the quadrics encode information about the linkage parameters which are readily computed to obtain a spherical 4R linkage that best navigates through the given displacements. The result is an efficient and largely linear method for spherical four-bar motion generation problem.

Topics: Linkages , Fittings
Commentary by Dr. Valentin Fuster
2013;():V06AT07A063. doi:10.1115/DETC2013-13244.

This paper provides examples of a method used to analyze the motion characteristics of single-degree-of-freedom, closed-loop linkages under study a designated input angle and one or two design parameters. The method involves the construction of a singularity trace, which is a plot that reveals changes in the number of geometric inversions, singularities, and changes in the number of branches as a design parameter is varied. This paper applies the method to Watt II, Stephenson III and double butterfly linkages. For the latter two linkages, instances where the input angle is able to rotate more than one revolution between singularities have been identified. This characteristic demonstrates a net-zero, singularity free, activation sequence that places the mechanism into a different geometric inversion. Additional observations from the examples are given. Instances are shown where the singularity trace for the Watt II linkage includes multiple coincident projections of the singularity curve. Cases are shown where subtle changes to two design parameters of a Stephenson III linkage drastically alters the motion. Additionally, isolated critical points are found to exist for the double butterfly, where the linkage becomes a structure and looses the freedom to move.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2013;():V06AT07A064. doi:10.1115/DETC2013-13454.

This paper presents a software system for the kinematic synthesis of useful spherical Watt I six-bar linkages that can guide a body through five task positions. The design procedure begins with the specification of a spherical 3R open chain that reaches five specified task positions. The six-bar linkage is designed by constraining the 3R spherical chain to the topology of a Watt I spherical six-bar linkage. The CAD software SolidWorks is used to specify the 3R chain and the five spherical task positions. We describe the SolidWorks Add-In MechGen that reads the SolidWorks data and generates candidate linkages. Included in the task specification are tolerance zones that allow random adjustments to the task positions to search for defect-free linkages. An example is provided that demonstrates the five position synthesis of a useful spherical Watt I six-bar linkage.

Commentary by Dr. Valentin Fuster

37th Mechanisms and Robotics Conference: Mobile Robots and Cable-Driven Systems

2013;():V06AT07A065. doi:10.1115/DETC2013-12108.

Time-optimal trajectory planning (TOTP) is a well-studied problem in robotics and manufacturing, which involves the minimization of the time required for the operation point of a mechanism to follow a path, subject to a set of constraints. A TOTP technique, designed for fully-specified paths that include abrupt changes in direction, was previously introduced by the first author of this paper: an incremental approach called minimum-time trajectory shaping (MTTS) was used. In the current paper, MTTS is adapted for use with cable-driven parallel robots, which exhibit the additional constraint that all cable tensions remain positive along a path to be followed. For many applications, cable tensions along a path are verified after trajectory generation, rather than imposed during trajectory generation. For the technique proposed in this paper, the minimum-tension constraint is imposed directly and is fully integrated with MTTS, during trajectory generation, thus maintaining a time-optimal solution. This approach is relevant for cable-driven mechanism applications that involve high accelerations, particularly in the vertical direction.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A066. doi:10.1115/DETC2013-12140.

Researchers have evaluated the stiffness matrix for different robots and structures, including the Stewart platform style tensile truss. However, none of the configurations analyzed to date involve “dual-reeving,” a common industrial rigging technique whereby cables are spatial loops, vs. open-loop elements, such as those represented by simple line segments. The 4-node/4-loop kinematic configuration analyzed contains 4 symmetric nodes and loops and provides competition for a comparable-sized Stewart platform from the perspective of directional stiffness. Additionally, like the Stewart platform, only a modest amount of off-diagonal compliance matrix elements are present, which from a practical and intuitive point of view, can be advantageous. The methodology used and illustrated in detail is easily generalized to adapt to more involved configurations. Numerical results are obtained for a specific example and compared with those from a Stewart platform. Lastly, some experimental results compare favorably with those derived analytically and evaluated numerically.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A067. doi:10.1115/DETC2013-12142.

This paper proposes an SSM (Sensor Steering Mechanism) for a lateral guided vehicle with an articulated body. Authors demonstrated a simple lateral guiding method SSM for front wheel steer type, the reverse phase four-wheel steer type and rear wheel steer type vehicles. SSM presents a stable lateral guiding performance for automated vehicle that following a straight and curved path created by a guideway. This paper proposes a simplified SSM to remove the following servo system for a rotating camera. The simplified SSM is applied to 1/25 scale articulated dump truck that was developed and discussed in the previous paper. The stability of the simplified SSM is discussed. Experimental and simulation results show stable movement and performance of the proposed method.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2013;():V06AT07A068. doi:10.1115/DETC2013-12158.

The United States Army began developing Unmanned Ground Vehicles (UGV) in the early 1900’s. Concurrently, researchers developed and enhanced passenger and commercial ground vehicles. Although significant progress has been made for improving vehicle mobility for all ground vehicles throughout the past century, mobility has lacked a concise mutually agreed definition and analytical standardized criteria. The implementations of improved technologies, such as vehicle traction control, stability control, and torque vectoring systems require researchers to take a step back and reevaluate mobility criteria. UGVs require additional enhancement to include on-line mobility estimation since the vehicle cannot predict nor anticipate terrain conditions on their own prior to the vehicle traversing those conditions.

This paper analyzes methodologies researchers have employed for defining and improving vehicle mobility of wheeled vehicles. The analysis is done from a view point of concurrent mobility methodologies’ enhancement and applicability to wheeled UGVs.

This analysis is then used to develop off-line and on-line analytical criterion for mobility estimation, and to derive a strategy which can be applied to wheeled vehicles, both manned and unmanned. The on-line mobility estimation enables the UGV to make control changes as the events occur rather than after the event, causing the vehicle to then optimize its reaction to regain control.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2013;():V06AT07A069. doi:10.1115/DETC2013-12261.

The choice of cable placement and routing for a cable-driven serial manipulator has profound effects on the operational workspace of the mechanism. Poor choices in cable attachment can hamper or preclude the ability of the mechanism to perform a desired task, while a clever configuration might allow for an expanded workspace and kinematic redundancies, providing additional capability and flexibility.

This paper outlines a methodology to identify and analyze optimal cable configurations for a serial manipulator which maximize operational workspace subject to mechanism design and configuration constraints. This process is first described in general terms for a generic 2-link robot and then applied to an illustrative example of a cable-driven robot leg. The methodology is used to determine the placement and routing of the cables to achieve the desired range of motion, as well as highlight the critical parameters within the cable configuration and identify possible areas of improvement in the overall robot design.

Topics: Cables , Design , Manipulators
Commentary by Dr. Valentin Fuster
2013;():V06AT07A070. doi:10.1115/DETC2013-12401.

The Articulated Wheeled Vehicle (AWV) paradigm examines a class of wheeled vehicles where the chassis is connected via articulated chains to a set of ground-contact wheels. Actively- or passively-controlled articulations can help alter wheel placement with respect to chassis during locomotion, endowing the vehicle with significant reconfigurability and redundancy. The ensuing ‘leg-wheeled’ systems exploit these capabilities to realize significant advantages (improved stability, obstacle surmounting capability, enhanced robustness) over both traditional wheeled- and/or legged-systems in a range of uneven-terrain locomotion applications. In our previous work, we exploited the reconfiguration capabilities of a planar AWR to achieve internal shape regulation, secondary to a trajectory-following task. In this work, we extend these capabilities to the full 3D case — in order to utilize the full potential of kinematic- and actuation-redundancy to enhance rough-terrain locomotion.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A071. doi:10.1115/DETC2013-12646.

Cable-driven parallel robots have several outstanding characteristics that make them unique in many robotic applications. Since cables can only pull, one of the most important issues associated with these robots is obtaining their workspace. In this paper a spatial translational cable-driven robot with active/passive cables is considered and its workspace is investigated from several points of views. First the moment resisting capability of the robot is discussed and the effects of some robot’s parameters on the workspace are studied. Then, both force-feasibility and moment-resisting capability of the robot are considered to find the region where the end-effector may exert the required force-set and resist an external moment simultaneously. Furthermore, the wrench-feasibility of the redundant cable-driven robot is studied and finally a method of obtaining non-fluctuating positive tensions in all cables is proposed by using a particle swarm optimization approach.

Topics: Robots , Cables
Commentary by Dr. Valentin Fuster
2013;():V06AT07A072. doi:10.1115/DETC2013-13091.

In our previous paper [1], we examined enhancing manipulation capabilities of cable robots by addition of base mobility to the spooling-winches. Base mobility facilitated the regulation of the tension-direction (via active repositioning of the mobile bases) and allowed for better conditioning of the wrench feasible workspace. In this paper, we explore design-modifications on the attachment to the common payload (merging multiple cables, attachment via pulleys) as alternate means to improve quality of the wrench-feasible workspace. Specifically we systematically examine the role played by attachment-modality and location, focusing on the benefits/drawbacks of the ensuing natural mechanical averaging behavior. Further, by using the notion of virtual cable subsystems, we illustrate the subsumption of this case into our previous mobile-cable-robot analysis framework. We seek improvement of the overall tension distribution by utilizing configuration space redundancy to shape the tension null-space. This is implemented computationally within the framework of a Tension Factor optimization problem over the workspace and explored via both simulation and experiments.

Topics: Robots , Cables , Design
Commentary by Dr. Valentin Fuster
2013;():V06AT07A073. doi:10.1115/DETC2013-13277.

In this paper, we present the transmission mechanism design for a fully actuated Invertible Flying Quadrotor (IFQ) micro aerial vehicle (MAV). At the heart of the mechanism is a gearbox which couples and counter rotates two pairs of shafts that have the quadrotor propellers mounted at their ends. This mechanism will allow for the IFQ to follow aggressive maneuvers, hover at an arbitrary attitude, and have sustained inverted flight capabilities. The paper presents the mechanical design challenges and solutions in designing such a transmission mechanism with minimal weight along with low cost and easy manufacturing. The dynamic model for the IFQ MAV is presented along with an optimal open loop trajectory control scheme and related simulations. An approach for a full closed loop control scheme is also discussed. A prototype of the mechanism has been manufactured and functionally tested. The entire transmission mechanism was able to be prototyped with a weight of only approximately 100 grams.

Topics: Design
Commentary by Dr. Valentin Fuster
2013;():V06AT07A074. doi:10.1115/DETC2013-13371.

Accurately aiming and firing a pistol requires a steady hand. While many devices can steady a shooter’s arm or hand by restricting movement or degrees-of-freedom, few devices actively reduce involuntary tremors while allowing larger voluntary aiming movements. This paper details the design and fabrication of an arm exoskeleton that can actively damp arm tremors while allowing voluntary aiming movements. The device allows five degrees-of-freedom and is very lightweight due to its cable-driven architecture and use of carbon fiber composite materials. Tremorous movement is filtered out from voluntary motion, and an adaptive algorithm provides a tremor-cancelling signal to the cable control motors.

Topics: Manufacturing , Design
Commentary by Dr. Valentin Fuster
2013;():V06AT07A075. doi:10.1115/DETC2013-13377.

Since anticipating or recovering infeasibility in optimal motion planning is not always possible, infeasibilities occur frequently and are not completely avoidable. We introduce an enhanced sequential quadratic programming (SQP) based framework of controlled infeasibility for physically valid solutions, based on our previous study. A priority weight function is incorporated into an SQP algorithm combined with constraints and objective function normalization to ensure strict satisfaction of high-priority constraints. These are embedded in the SQP algorithm through its merit function and composite cost function, in which general nonlinear functions can be incorporated in a unified approach. Several simple mobile manipulator examples demonstrate the advantages of the proposed method.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A076. doi:10.1115/DETC2013-13523.

A new method for real-time navigation of mobile robots in complex and mostly unstructured environment is presented. This novel human-inspired method (HIM) uses distance-based sensory data from a laser range finder for real-time navigation of a wheeled mobile robot in unknown and cluttered settings. The approach requires no prior knowledge from the environment and is easy to be implemented for real-time navigation of mobile robots. HIM endows the robot a human-like ability for reasoning about the situations to reach a predefined goal point while avoiding static and moving or unforeseen obstacles; this makes the proposed strategy efficient and effective. Results indicate that HIM is capable of creating smooth (no oscillations) paths for safely navigating the mobile robot, and coping with fluctuating and imprecise sensory data from uncertain environment. HIM specifies the best path ahead, according to the situation of encountered obstacles, preventing the robot to get trapped in deadlock and impassable conditions. This deadlock detection and avoidance is a significant ability of HIM. Also, this algorithm is designed to analyze the environment for detecting both negative and positive obstacles in off-road terrain. The simulation and experimental results of HIM is compared with a fuzzy logic based (FLB) approach.

Commentary by Dr. Valentin Fuster
2013;():V06AT07A077. doi:10.1115/DETC2013-13548.

This paper proposes a method to estimate and compensate for the changes of cable tension in the control of cable driven mechanisms. Cable tension may depend on various factors, including mechanism design, fabrication and operation. In many systems it is also an adjustable parameter that affects the performance of the control system. An implementation of the unscented Kalman filter is used for the simultaneous estimation of the states and parameters of a cable driven mechanism. Changes in cable tension are captured in the estimated parameters which, along with system states, are used by a model predictive controller to generate appropriate control actions. The method is described and its effectiveness is shown for a single degree of freedom cable driven robot. In addition, the correlation between the cable tension and the estimated robot parameters provides a way of estimating the tension. It is shown that cable tension can be inferred from one of the estimated robot parameters, namely cable stiffness.

Topics: Cables , Tension
Commentary by Dr. Valentin Fuster
2013;():V06AT07A078. doi:10.1115/DETC2013-13672.

Developments in mobile robotic systems are leading to new methods and techniques for manufacturing processes in fields that traditionally have not seen much automation. Some of these tasks require process validation prior to use in the manufacturing process. One such example process is welding. However, there is a lack of industry standards for mechanized or robotic welding that can impede the introduction of mobile robotic welding systems in the market place. There is also a lack of generalized fitness measures that gauge the suitability of mobile robot topologies or dimensional designs to a set of tasks and can be used in the design or verification process. This paper will propose such a metric and demonstrate its use in evaluating mobile robot designs for welding tasks. The approach will be based on the representation of a general task as a pair of n-dimensional subsets in the Euclidean n-space. Similarly, the robot capabilities are represented as n-dimensional subsets (manipulability and torque ellipse) in the Euclidean n-space. The motivation is to enable a direct geometric comparison of the capabilities of the robot to the requirements of the task yielding a quantitative measure of fitness. This method is suggested to be well suited to tasks comprised of a relatively short sequence of well-defined motions, called gaits, which are performed repeatedly or in a periodic manner. Some examples are welding, swimming, painting or inspection. The paper will demonstrate the use of this metric in the evaluation and design of mobile robots for welding tasks with a desired set of weld pattern motions. Three mobile welding platforms having different topological kinematic arrangements will be evaluated based on this design verification metric. This metric will further be shown to supplement the weld qualification process through verification of the motion control portions of the weld process based on a specific robot design. The method will contribute to the design and development of mobile robotic welding systems to become viable and accepted manufacturing processes.

Commentary by Dr. Valentin Fuster

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