ASME Conference Presenter Attendance Policy and Archival Proceedings

2014;():V05AT00A001. doi:10.1115/DETC2014-NS5A.

This online compilation of papers from the ASME 2014 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2014) 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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

38th Mechanisms and Robotics Conference: Biologically Inspired and Health Motivated Mechanisms and Robotics

2014;():V05AT08A001. doi:10.1115/DETC2014-34057.

This paper addresses the dimensional synthesis of an adaptive mechanism of contact points ie a leg mechanism of a piping inspection robot operating in an irradiated area as a nuclear power plant. This studied mechanism is the leading part of the robot sub-system responsible of the locomotion. Firstly, three architectures are chosen from the literature and their properties are described. Then, a method using a multi-objective optimization is proposed to determine the best architecture and the optimal geometric parameters of a leg taking into account environmental and design constraints. In this context, the objective functions are the minimization of the mechanism size and the maximization of the transmission force factor. Representations of the Pareto front versus the objective functions and the design parameters are given. Finally, the CAD model of several solutions located on the Pareto front are presented and discussed.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A002. doi:10.1115/DETC2014-34299.

Traditionally, the design of exoskeletons (from choice of configuration to selection of parameters) as well as the process of fitting this exoskeleton (to the individual user/patient) has largely depended on intuition and/or practical experience of a designer/physiotherapist. However, improper exoskeleton design and/or incorrect fitting can cause buildup of significant residual forces/torques (both at joint and fixation site). Performance can be further compromised by the innate complexity of human motions and need to accommodate the immense individual variability (in terms of patient–geometries, motion–envelopes and musculoskeletal–strength). In this paper, we propose a systematic and quantitative methodology to evaluate various alternate exoskeleton designs using twist- and wrench-based modeling and analysis. This process is applied in the context of a case-study for developing optimal configuration and fixation of a knee brace/exoskeleton. An optimized knee brace is then prototyped using 3D printing and instrumented with 6–DOF force-torque transducer. Knee brace is then physically tested together with a saw-bones knee model in a scaled knee bracing test. Preliminary results of the physical testing of the knee brace show promise and are discussed.

Topics: Design , Knee
Commentary by Dr. Valentin Fuster
2014;():V05AT08A003. doi:10.1115/DETC2014-34369.

This paper presents a novel articulated drive mechanism (ADM) for a multifunctional natural orifice transluminal endoscopic surgery (NOTES) robotic manipulator. It consists mainly of three major components including an articulated snake-like linkage, motor housing and an arm connector. The ADM contains two independent curvature sections which can articulate into complex S shapes for improved access to surgical targets. A connector between the bimanual arms and the ADM provides an efficient and convenient way to assemble and disassemble the system as necessary for insertion and removal of the robot. Four DC motors guide four pairs of cables with linear actuation to steer the robot. The workspace, cable displacement and force transmission relationships are derived. Experimental results give preliminary validation of the feasibility and capability of the ADM system.

Topics: Robots , Design
Commentary by Dr. Valentin Fuster
2014;():V05AT08A004. doi:10.1115/DETC2014-34405.

We are developing methods to add a bounded amount of energy to assist body motion. Energy is added based on the phase angle of the limb to create a “phase oscillator.” The energy is added assisting motion creating an oscillatory behavior. An anti-phase angle can be used to subtract energy from body motion as well. Using a “phase oscillator” controller, a powered hip exoskeleton assisted a runner and demonstrated a reduction in metabolic cost.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A005. doi:10.1115/DETC2014-34406.

The human body is a mass spring system that oscillates up and down while running. We add energy to the running gait by oscillating a secondary mass in phase with the motion. A phase oscillator adds a bounded amount of energy to the limit cycle to make it easier to run. In an anti-phase oscillator, energy in the gait cycle is reduced and it is harder to run.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A006. doi:10.1115/DETC2014-34426.

A Jet Pack was designed to augment the physical ability of a person running. The Jet Pack is a light weight back pack style device that produces a forward and upward thrust propelling the user forward. The external force is produced by two variable speed, electric ducted fans, which unlike other running assistive devices, allows for completely unrestricted movement as the device does not connect to the user’s joints or leg segments. The Jet Pack has shown successful running augmentation by significantly increasing a runner’s overall speed while decreasing their heart rate in 200 meter time trials as well as 1 mile time trials when comparing running with the device versus running with no device.

Topics: Weight (Mass) , Thrust , Fans
Commentary by Dr. Valentin Fuster
2014;():V05AT08A007. doi:10.1115/DETC2014-34576.

On the basis of an analogy between the kinematic structures of proteins and robotic mechanisms, we have so far developed methods for predicting the internal motion of proteins from three-dimensional structural data in the protein data bank (PDB). With these methods, we model proteins as serial manipulators constrained by springs, and calculate the structural compliance of the protein model. In this study, toward more practical purposes, we reformulate and extend the existing methods by broadening the definition of structural compliance and reducing the number of variables for expressing the conformation of the model. The broadening is performed by separating the parts whose deformations are evaluated from those where forces are applied. This separation allows the calculation of the effective forces causing deformation in other specified parts. We also reduce the number of conformation variables from the consideration based on the algebraic structure of the basic equations. The size of the matrix whose inverse must be calculated is thus minimized, and the computational cost is reduced. We verify the effectiveness of these extensions by analyzing the PDB data of some proteins.

Topics: Kinematics , Proteins
Commentary by Dr. Valentin Fuster
2014;():V05AT08A008. doi:10.1115/DETC2014-34675.

This paper presents the design and application of a newly developed five-fingered haptic glove mechanism. This haptic device is a lightweight and portable actuator system that fits on a hand. The new five-fingered glove is adaptable to a wide variety of finger sizes, without constraining the range of motion which makes it possible to accurately and comfortably track the complex motion of the finger joints and add a sense of touch to each finger of the user. Based on this glove, a novel method was developed to build an accurate human hand model which includes finger length and joints location. The parameters of the hand are determined by a circle fitting procedure from a collection of points. The method of least squares fitting of circles is used to analyze the kinematic model. The center and the radius of the fitting circle are the joint location and the finger length respectively. The experimental results demonstrate that the newly developed five-fingered glove is capable of reliably modeling hand kinematics and measuring fingers’ motion. These capabilities are often needed for monitoring and assisting rehabilitation activities of the hand as well as applications involving virtual reality and teleoperation.

Topics: Haptics , Modeling
Commentary by Dr. Valentin Fuster
2014;():V05AT08A009. doi:10.1115/DETC2014-34678.

This paper presents the analysis of a continuum robot for use as a robotic tail. The tail is envisioned for use on-board a mobile robot to provide a means separate from the locomotion mechanism (e.g., legs or wheels) to generate external forces and moments to stabilize and/or maneuver the robot. A Cosserat rod model is used to simulate the mechanics of the tail. In these analyses, a prescribed tail configuration (for static analysis) or trajectory (for dynamic analysis) is applied, and the governing equations are used to calculate the loading at the base of the tail, which will be transmitted to the mobile robot. This analysis studies the impact of both trajectory and design factors on the resulting loading profiles. Trajectory factors considered include the mode shape, speed, bending magnitude and bending plane angle. Design factors considered for a fixed mass tail include segment length(s) and mass distribution. This research will ultimately assist future continuum robotic tail designs.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A010. doi:10.1115/DETC2014-34679.

In this paper, we present the design of RoboCrab, an amphibious robot capable of traversing moderate surf zone environments. By taking inspiration from the morphology, locomotion, and righting behaviors of a horseshoe crab, the robot is designed for traversal and righting on granular terrain, open water, and turbulent surf zones. We present the details of the crab’s morphology that informed the design of our robot. Next, we present the mechanical design, material selection, and manufacturing of the various parts of the robot. We report the results from the computational fluid dynamics simulations used to characterize the robot shell performance. Finally, we present demonstrations of the physical robot walking and righting in a granular environment.

Topics: Robots
Commentary by Dr. Valentin Fuster
2014;():V05AT08A011. doi:10.1115/DETC2014-34719.

Flapping wing unmanned air vehicles (UAVs) are small light weight vehicles that typically have short flight times due to the small size of the batteries that are used to power them. During longer missions, the batteries must be recharged. The lack of nearby electrical outlets severely limits the locations and types of missions that these UAVs can be flown in. To improve flight time and eliminate the need for electrical outlets, solar cells can be used to harvest energy and charge/power the UAV. Robo Raven III, a flapping wing UAV, was developed at the University of Maryland and consists of wings with integrated solar cells. This paper aims to investigate how the addition of solar cells affects the UAV. The changes in performance are quantified and compared using a load cell test as well as Digital Image Correlation (DIC). The UAV platform reported in this paper was the first flapping wing robotic bird that flew using energy harvested from on-board solar cells. Experimentally, the power from the solar cells was used to augment battery power and increase operational time.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A012. doi:10.1115/DETC2014-34720.

Sleeve muscle is a new class of pneumatic muscle actuator that provides significant performance improvement and new design characteristics in comparison with the traditional pneumatic muscle. Inspired by the force-generating mechanism of traditional pneumatic muscle, the sleeve muscle incorporates a unique insert structure to eliminate the loss of extension force capacity due to the air pressure applied to the moving end connector. Two types of sleeve muscle are presented in this paper, including a single-acting type that enables the integration of the actuator with the load bearing structure, and a double-acting type that provides a unique capability of bi-directional actuation. The designs of these sleeve muscle actuators are discussed, along with their potential applications in bio-robotic systems.

Topics: Actuators , Design , Muscle
Commentary by Dr. Valentin Fuster
2014;():V05AT08A013. doi:10.1115/DETC2014-34752.

Flapping wing miniature aerial vehicles (FWMAVs) offer advantages over traditional fixed wing or quadrotor MAV platforms because they are more maneuverable than fixed wing aircraft and are more energy efficient than quadrotors, while being quieter than both. Currently, autonomy in FWMAVs has only been implemented in flapping vehicles without independent wing control, limiting their level of control. We have developed Robo Raven IV, a FWMAV platform with independently controllable wings and an actuated tail controlled by an onboard autopilot system. In this paper, we present the details of Robo Raven IV platform along with a control algorithm that uses a GPS, gyroscope, compass, and custom PID controller to autonomously loiter about a predefined point. We show through simulation that this system has the ability to loiter in a 50 meter radius around a predefined location through the manipulation of the wings and tail. A simulation of the algorithm using characterized GPS and tail response error via a PID controller is also developed. Flight testing of Robo Raven IV demonstrated the success of this platform, even in winds of up to 10 mph.

Topics: Aircraft , Wings
Commentary by Dr. Valentin Fuster
2014;():V05AT08A014. doi:10.1115/DETC2014-34783.

Understanding the 3D structure and consequently the motion of protein molecules contributes to simulate their function. Modeling protein molecules as kinematic chains has been used to predict protein molecules flexible and rigid regions as well as their degrees of freedom to predict their mobility. However, high computational cost for relatively large molecules is one of the major challenges in this field.

In this paper we have combined our previously developed rigidity analysis (ProtoFold) with pebble game thus improving computational cost of our simulation. Here, we have determined the required time for all steps of ProtoFold and subsequently the most time consuming step. Results have shown that finding rigid loops inside the protein structure using graph theory and Grübler-Kutzbach criterion is the slowest part of the procedure, taking an average of 75% of the time required for the rigidity analysis. Therefore we have replaced this step with pebble game. The modified method has been applied to a random group of protein molecules and its efficiency in significantly improving the simulation speed has been verified.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A015. doi:10.1115/DETC2014-34914.

We developed an assistance apparatus for upper limbs for patients who can control their finger but they cannot lift up their arms themselves, for example myopathy and hemiplegic patients. The mechanism of assistance is utilized the differential gears to lose the weight and volume of the mechanical arm. That enabled us to configure three motors to drive two DOFs (Degrees of freedom) for the shoulder and one DOF for the elbow around the root of the mechanical arm. This arm has two support trays, for wrist and upper arm. Furthermore, to realize other ADL (activities of daily living) motions (for instance, eating, writing, putting on makeup, wiping his/her face, and so on) them selves, we proposed to control the device using the targeted posture map for the mechanical arm. To be able to choose the appropriate input for each patient, various input interfaces, for example, joy-stick, push buttons, sensor glove using bending sensors, and so on, are equipped.

In general, even though a human behaves an atonic motion, the maximum voluntary contraction (%MVC) outputs at least from 5 to 10%. The usage of this apparatus is to move the user’s upper limbs with dependence completely, and the purpose of this apparatus is to decrease the value of %MVC up to approximately 10%. Therefore, in this paper, the muscles of the user were evaluated with the ratio of %MVC. To confirm the effectiveness of assistance ability, we measured muscle activity while using the device, and compared the %MVC data between using the device or not. As a result, the activity decreased up to 80%, and the effectiveness of this device could be confirmed.

Finally, to expand the usage of this apparatus to encompass Neuro-Rehabilitation as well, we measured cerebral activity while using the device for rehabilitation with a near-infrared spectroscopy (NIRS). Then we compared the data from using the device or not, and input motion from a third person. By using this device, the cerebral activity decreased especially when the target motion was complex. However, when the subject input the motion themselves, the cerebral activity increased more than when the data is input by a third person, especially, when the target motion was complex. Therefore, for use in Neuro-Rehabilitation, we found it is important the subject input the target motion him/herself.

Topics: Muscle
Commentary by Dr. Valentin Fuster
2014;():V05AT08A016. doi:10.1115/DETC2014-34953.

The Atlantic razor clam (Ensis directus) burrows by contracting its valves, fluidizing the surrounding soil and reducing burrowing drag. Moving through a fluidized, rather than static, soil requires energy that scales linearly with depth, rather than depth squared. In addition to providing an advantage for the animal, localized fluidization may provide significant value to engineering applications such as vehicle anchoring and underwater pipe installation. This paper presents the design of a self-actuated, radially expanding burrowing mechanism that utilizes E. directus’ burrowing methods. The device is sized to be a platform for an anchoring system for autonomous underwater vehicles. Scaling relationships presented allow for design of burrowing systems of different sizes for a variety of applications. The minimum contraction time for a given device size governs how quickly the device must move. Contraction displacement necessary to achieve fluidization is presented. The maximum force for a given size mechanism is also calculated, and allows for sizing actuators for different systems. This paper presents the design of a system that will allow testing of these parameters in a laboratory setting. These relationships provide the optimal sizing and power needs for various size subsea borrowing systems.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A017. doi:10.1115/DETC2014-35065.

We quantify how the hip energetics and knee torque required for an above-knee prosthesis user to walk with the kinematics of able-bodied humans vary with the inertial properties of the prosthesis. We also select and optimize passive mechanical components for a prosthetic knee to accurately reproduce the required knee torque.

Previous theoretical studies have typically investigated the effects of prosthesis inertial properties on energetic parameters by modifying both mass and mass distribution of the prosthesis and computing kinetic and energetic parameters only during swing. Using inverse dynamics, we determined the effects of independently modifying mass and mass distribution of the prosthesis, and we computed parameters during both stance and swing. Results showed that reducing prosthesis mass significantly affected hip energetics, whereas reducing mass distribution did not. Reducing prosthesis mass to 25% of the mass of a physiological leg decreased peak stance hip power by 26%, average swing hip power by 74%, and absolute hip work over the gait cycle by 22%.

Previous studies have also typically optimized prosthetic knee components to reproduce the knee torque generated by able-bodied humans walking with normative kinematics. However, because the prosthetic leg of an above-knee prosthesis user weighs significantly less than a physiological leg, the knee torque required for above-knee prosthesis users to walk with these kinematics may be significantly different. Again using inverse dynamics, it was found that changes in prosthesis mass and mass distribution significantly affected this required torque. Reducing the mass of the prosthesis to 25% of the mass of the physiological leg increased peak stance torque by 43% and decreased peak swing torque by 76%.

The knee power required for an above-knee prosthesis user to walk with the kinematics of able-bodied humans was analyzed to select passive mechanical components for the prosthetic knee. The coefficients of the components were then optimized to replicate the torque required to walk with the kinematics of able-bodied humans. A prosthetic knee containing a single linear spring and two constant-force dampers was found to accurately replicate the targeted torque (R2=0.90 for a typical prosthesis). Optimal spring coefficients were found to be relatively insensitive to mass alterations of the prosthetic leg, but optimal damping coefficients were sensitive. In particular, as the masses of the segments of the prosthetic leg were altered between 25% and 100% of able-bodied values, the optimal damping coefficient of the second damper varied by 330%, with foot mass alterations having the greatest effect on its value.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A018. doi:10.1115/DETC2014-35174.

This paper presents an analysis of the rollover shape and energy storage and return in a prosthetic foot made from a compliant cantilevered beam. The rollover shape of a prosthetic foot is defined as the path of the center of pressure along the bottom of the foot during stance phase of gait, from heel strike to toe off. This path is rotated into the reference frame of the ankle-knee segment of the leg, which is held fixed. In order to achieve correct limb loading and gait kinematics, it is important that a prosthetic foot both mimic the physiological rollover shape and maximize energy storage and return.

The majority of prosthetic feet available on the market are cantilever beam-type feet that emulate ankle dorsiflexion through beam bending. In this study, we show analytically that a prosthetic foot consisting of a beam with constant or monotonically decreasing cross-section cannot replicate physiological rollover shape; the foot is either too stiff when the ground reaction force (GRF) acts near the ankle, or too compliant when the GRF acts near the toe. A rigid constraint is required to prevent the foot from over-deflecting.

Using finite element analysis (FEA), we investigated how closely a cantilever beam with constrained maximum deflection could mimic physiological rollover shape and energy storage/return during stance phase. A constrained beam with constant cross-section is able to replicate physiological rollover shape with R2 = 0.86. The ratio of the strain energy stored and returned by the beam compared to the ideal energy storage and return is 0.504. This paper determines that there is a trade off between rollover shape and energy storage and return in cantilever beam-type prosthetic feet. The method and results presented in this paper demonstrate a useful tool in early stage prosthetic foot design that can be used to predict the rollover shape and energy storage of any type of prosthetic foot.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A019. doi:10.1115/DETC2014-35238.

Knee pain, muscle weakness, and their associated medical conditions cause a significant loss of mobility for a large and growing number of people. Accordingly, the need for effective, simple, and noninvasive methods for controlling these problems is becoming more apparent. To that end, we have designed a quasi-passive knee-orthosis that employs a “hybrid joint mechanism” as a central component. This joint combines a four-bar linkage with a compliant mechanism to follow natural knee motion. A poorly fitted knee orthosis can detrimentally affect its effectiveness due to the large variability in the patient-specific knee motion. Our design can be optimized to fit a given user, based on both motion capture data and their particular condition, which leads to several potential advantages over standardized hinges. In this paper, we will explore the design and individualization process of the joint mechanism as well as the background covering various design decisions.

Topics: Orthotics , Knee
Commentary by Dr. Valentin Fuster
2014;():V05AT08A020. doi:10.1115/DETC2014-35398.

In this paper, a lower limb orthosis is proposed to form the human gait neuromuscular patterns in patients with myelomeningocele. The orthosis has two lower limbs of 2–DOF each which reduces the motion of the hip and knee to the sagittal plane. The orthosis are assembled in a back support which also supports the patients weight. The control system for the orthosis allows to reproduce in a repetitive, controlled and autonomous way the human gait cycle at different velocities according to the patient requirements; so that, the neuromuscular patterning can be supervised by a therapist. The development of these orthosis seeks to improve the quality of life of those infants with myelomenigocele and to introduce a lower cost Mexican technology with Mexican anthropometric dimensions.

Topics: Orthotics
Commentary by Dr. Valentin Fuster
2014;():V05AT08A021. doi:10.1115/DETC2014-35406.

Robotic neurorehabilitation is a rapidly growing field in both research and industry. Robotics offer the ability to create less labor-intensive rehabilitation for therapists, while providing an interactive experience for patients. Furthermore, the ability to implement assistive robotic therapy in the home setting has the potential to increase the frequency of patient rehabilitation sessions while decreasing the overall cost of therapy. Therefore, the design, control, and initial testing of an actuated 2 degree of freedom hand rehabilitation device is presented.

A 2 degree of freedom hand rehabilitation device, named the Navigator, is mechanically capable of assistive or resistive mode exercise for flexion and extension of the fingers, as well as pronation and supination of the wrist. A series elastic actuator incorporating a rack and pinion provides actuation to flexion and extension of the fingers. A belt drive is used to provide actuation to pronation and supination of the wrist. Position and load sensors are integrated into both actuators to provide feedback for the control system.

The implementation of an impedance control system utilizing position, force, and torque feedback is also presented. Automated control results as well as preliminary pilot data of resistive mode exercises are presented. The impedance controller interacts with a virtual environment. Preliminary results of the controller confirm the efficacy of the device’s mechanical design.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A022. doi:10.1115/DETC2014-35472.

This paper explores the design of a robotic device for gait rehabilitation and assessment, as well as a method to estimate a patient’s orientation within the rehabilitation device. Current rehabilitation methods require the patient to propel the assistive device or offer limited walking distance. Additionally, current devices do not measure the patient’s reliance on the assistive device, possibly prolonging the rehabilitation period or even preventing satisfactory function to be regained. A novel robotic parallel bar platform was designed to address the shortfalls of current assistive devices. A complementary filter was developed to estimate the patient’s orientation within the device using a magnetometer and gyroscope. Experiments of the complementary filter on a test platform show that the filter provides estimates within five degrees of the true value over a range of angular velocities.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A023. doi:10.1115/DETC2014-35539.

Our research examines the feasibility of usign a wearable scissored-pair control moment gyroscope (CMG) for human balance assist. The CMG is a momentum exchange device consisting of a fast spinning flywheel mounted on a gimbal. The gimbal motion changes the direction of the flywheel rotation axis, which generates a reactionless torque. A scissored-pair CMG has the additional advantage of isolating the output torque to a single axis, where off-axis torques are canceled out. A properly designed CMG device worn as a backpack can apply a torque in the sagittal plane of the human trunk. This can help in restoring postural balance and in fall mitigation.

This paper describes the complete design process of a scissored-pair CMG device with constraints on size, mass and dynamic properties for human wearability. A prototype of this device is built, utilizing a novel dual-flywheel design; it weighs about 8kg and is able to generate over 20Nm of torque. A custom hardware is built specifically for verifying the torque output of the device. To our knowledge this is the only device that generates the range of reactionless torque given its weight and size.

Topics: Design
Commentary by Dr. Valentin Fuster
2014;():V05AT08A024. doi:10.1115/DETC2014-35653.

A Joint Torque Augmentation Robot (JTAR) was developed to aid walking in an unconstrained outdoor environment. JTAR is a unidirectional, compliant actuator based wearable robot that is designed to power an ankle joint. Since the robot is used to navigate uneven terrain, nearly full ankle range of motion is required to accomplish this goal. The device powers the forward locomotion while permitting out of plane kinematic motion to occur. Metabolic savings of 9% to 20% have been observed while using the JTAR device, when compared to an unpowered/uncoupled state.

Topics: Torque , Robots
Commentary by Dr. Valentin Fuster

38th Mechanisms and Robotics Conference: Compliant Mechanisms and Micro/Nano Mechanisms (A. Midha Symposium)

2014;():V05AT08A025. doi:10.1115/DETC2014-34006.

Cross-Spring Flexural Pivot (CSFP) has some advantages compared with rigid bearing. However, this kind of flexural pivot is limited in the field of precision positioning due to its small motion stroke, large axis drift, and sensitivity to temperature, etc. In this paper, topology structures of the CSFP were analyzed through defining different geometric parameters λ, spring crossing angle α, and spring number N. Characteristics of stiffness, axis drift, maximum stress, and temperature drift were compared and summarized by the Finite Element Analysis (FEA). Ultimately, a class of flexural pivots, called Inner and Outer Ring Flexural Pivots (IORFP), were selected for their excellent comprehensive performances. This type of flexural pivots has some significant advantages, such as large stroke, approximate zero axis drift and no temperature drift. Finally, the stiffness characteristic of IORFP with different geometrical parameters λ was compared by FEA, and law of stiffness variation was obtained. When λ is 0.1273, the IORFP has linear stiffness characteristics.

Topics: Springs , Topology
Commentary by Dr. Valentin Fuster
2014;():V05AT08A026. doi:10.1115/DETC2014-34075.

This paper examines the use of a trispiral hinge in compliant mechanisms generated by low cost, ABS-based, rapid prototyping machines. Hinges are examined to establish relationships between hinge geometry parameters (core radius, spiral angle, spiral pitch, and spiral thickness) and hinge performance (in-plane rotation, off-axis stability). A number of joint parameter combinations are found that provide good joint rotation characteristics with minimal off-axis instability. These joints allow for joint rotations up to ±90 degrees from a neutral position with little parasitic motion during the rotation. The implementation of these joints is further examined through the building and testing of fully compliant mechanisms based on the Roberts and Hoeken approximate straight-line mechanism geometries. The fully compliant mechanisms are shown to have the ability to closely recreate the approximate straight-line motion of the equivalent 4-bar chains. As such, the trispiral joint provides promise as a joint type that can be used effectively in conjunction with fused deposition modeling (FDM) machines that use ABS as the build material.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A027. doi:10.1115/DETC2014-34140.

Modeling large deflections has been one of the most fundamental problems in the research community of compliant mechanisms. Although many methods are available, there still exists a need for a method that is simple, accurate, and can be applied to a vast variety of large deflection problems. Based on the beam constraint model (BCM), we propose a new method for modeling large deflections called chained BCM (CBCM), which divides a flexible beam into a few elements and models each element by BCM. It is demonstrated that CBCM is capable of modeling various large and complicated deflections of flexible beams in compliant mechanisms. In general, CBCM obtains accurate results with no more than 6 BCM elements, thus is more efficient than most of the other discretization-based methods.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A028. doi:10.1115/DETC2014-34285.

This paper presents a new model for a linear bistable compliant mechanism and design guidelines for its use. The mechanism is based on the crank-slider mechanism. This model takes into account the first mode of buckling and post-buckling behavior of a compliant segment to describe the mechanism’s bistable behavior. The kinetic and kinematic equations, derived from the Pseudo-Rigid-Body Model, were solved numerically and are represented in plots. This representation allows the generation of step-by-step design guidelines. The design parameters consist of maximum desired deflection, material selection, safety-factor, compliant segments’ widths, maximum force required for actuator selection and maximum footprint (i.e. the maximum rectangular area that the mechanism can fit inside of and move freely without interfering with other components). Because different applications may have different input requirements, this paper describes two different design approaches with different parameters subsets as inputs.

Topics: Design
Commentary by Dr. Valentin Fuster
2014;():V05AT08A029. doi:10.1115/DETC2014-34292.

This paper presents the first three-dimensional pseudo-rigid body model (3-D PRBM) for straight cantilever beams with rectangular cross sections and spatial motion. Numerical integration of a system of differential equations yields approximate displacement and orientation of the beam’s neutral axis at the free-end, and curvatures of the neutral axis at the fixed-end. This data was used to develop the 3-D PRBM which consists of two torsional springs connecting two rigid links for a total of 2 degrees of freedom (DOF). The 3-D PRBM parameters that are comparable with existing 2-D model parameters are characteristic radius factor (means: γ = 0.8322), bending stiffness coefficient (means: KΘ = 2.5167) and parametric angle coefficient (means: cΘ = 1.2501). New parameters are introduced in the model in order to capture the spatial behavior of the deflected beam including two parametric angle coefficients (means: cΨ = 1.0714; cΦ = 1.0087).

Commentary by Dr. Valentin Fuster
2014;():V05AT08A030. doi:10.1115/DETC2014-34325.

This paper presents a novel method for the topological synthesis of flexure-based compliant mechanisms. Such kind of mechanisms are usually obtained by replacing the kinematic pairs of existing rigid-body mechanisms with flexure hinges, which is often regarded as the rigid-body replacement approach. This approach uses the topologies from rigid-body mechanism and pays little attention to the selection of the optimal topology among them. The proposed method tries to find out the optimal topology directly from design problem, without referencing to the existing rigid-body mechanisms. The topology of the flexure-based compliant mechanisms is represented by the pseudo-rigid-body model (PRBM). The PRBM is expressed in a ground structure using an adjacency matrix. An analysis method based on the principle of minimum potential energy is introduced to evaluate the static performance of the PRBM candidates quantitatively. Using genetic algorithm (GA), the optimal PRBM can be found out according to the objective function that is based on the analysis results. The validity of the proposed method is tested on a single-input-output compliant mechanism design problem.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A031. doi:10.1115/DETC2014-34514.

Compliant mechanisms (CMs) utilize elastic deformations for mechanism functions. Their merits primarily come from jointless structures. The structure of a fully CM is a piece of elastic material and is defined by its topology, shape and size. Topology is the overarching material layout of a CM while shape and size are on its structural details, but topology is entangled with shape and size in the synthesis process of a CM because its elastic deformation is from the joint effect of topology, shape and size. Degree of freedom (DOF) and number of links used in rigid mechanism synthesis are not effective to guide the synthesis of CMs since any point of a fully CM can deform and its whole structure forms a single piece. Without effective synthesis guidance, the structural complexity of a synthesized CM can be undesirably high. In this paper, degree of genus (DOG) is introduced for topology guidance of CM synthesis. DOG of a CM is the number of holes and is actively controlled during its synthesis process. With DOG guidance, a synthesized CM will not have overcomplicated topology. Variable width curves (VWCs) are introduced in this paper for shape and size description. Any connection in a CM is defined as a VWC and the entire CM is modeled as a network of VWCs. With VWC description, a synthesized CM will not have unsmooth connection. Under DOG and VWC strategies, CM synthesis is systematized as optimizing control parameters of networks of VWCs. The proposed CM synthesis using DOG and VWC strategies is demonstrated by synthesizing shape morphing compliant mechanisms.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A032. doi:10.1115/DETC2014-34520.

Compliant mechanisms achieve motion utilizing deformation of elastic members. However, analysis of compliant mechanisms for large deflections remains a significant challenge. In this paper, we will develop a 3-spring pseudo-rigid-body model for 2D beams that are often used in compliant joints in robots. First, we utilize the Timoshenko beam theory to calculate the tip deflection for a large range of loading conditions. An optimization process is then carried out to calculate the values of the parameters of the PRB model. The errors in the model will be analyzed and compared to the beam model. An example based on a robotic grasper finger is provided to demonstrate how the model can be used in analysis of such a system. This model will provide a much simpler approach for the analysis of compliant robotic mechanisms.

Topics: Robotics , Springs
Commentary by Dr. Valentin Fuster
2014;():V05AT08A033. doi:10.1115/DETC2014-34532.

Compliant joints are widely used in mechanisms when accurate movements are required. With no assembly requested, they are also a great tool for mesoscale robotics, a field in which compactness and large joint amplitudes are necessary features. In this paper, an original multi-material compliant revolute joint is presented. Taking advantage of multi-material 3D printing, it exhibits a novel design with the integration of an hyper-elastic material. Thanks to a helical shape design, a large range of motion is obtained, and the incompressibility of the hyper-elastic material is used to improve the stiffness properties of the joint while keeping it compact. The spring effect of compliant joints makes mechanism actuation more difficult. The proposed joint is therefore designed with an integrated static balancing system in order to minimize actuation torques. The balancing system is composed of a bistable mechanism, which geometry optimization is presented. Experimental assessment demonstrate that the joint possesses a range of motion of 120°, and the balancing system reduces actuation moments by almost 60%.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A034. doi:10.1115/DETC2014-34551.

In this paper, we introduce a new type of spatial parallel robot that is comprised of soft inflatable constraints called Tri-Chamber Actuators (TCAs). We extend the principles of the Freedom and Constraint Topologies (FACT) synthesis approach to enable the synthesis and analysis of this new type of soft robot. The concepts of passive and active freedom spaces are introduced and applied to the design of general parallel systems that consist of active constraints (i.e., constraint that can be actuated to impart various loads onto the system’s stage) that both drive desired motions and guide the system’s desired degrees of freedom (DOFs). We provide the fabrication details of the TCA constraints introduced in this paper and experimentally validate their FACT-predicted kinematics. Examples are provided as case studies.

Topics: Robots
Commentary by Dr. Valentin Fuster
2014;():V05AT08A035. doi:10.1115/DETC2014-34605.

This paper presents a novel compliant parallel mechanism that utilizes shape-memory-alloy (SMA) spring based actuators. By employing SMA coil springs, the traditional line constraint that resists translation along its axis but no other forms of motions is transformed into a linear actuator that can generate deflection along its axis, which leads to the design of SMA-spring linear actuators. In accordance with this SMA actuator, an constraint-based approach in the framework of screw theory is utilized to synthesize the constraint and actuation space of parallel mechanisms, and a novel 4 DOF parallel platform is developed based on this analytical approach. A physical prototype is manufactured by employing the SMA-spring actuators, and its mobility and workspace are verified with both finite element simulation and experiment observations. The results illustrate this parallel mechanism has a large workspace in all desired mobility configurations. The presented work on the parallel platform demonstrates the efficiency of the constraint-based approach in determining the layout of actuation systems, also the developed SMA actuators pave a new way for applying the SMA technique in the future development of compliant parallel mechanisms and robotics.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A036. doi:10.1115/DETC2014-34607.

Ortho-planar spring is a compact spring that generates the motion based on the deformation of flexure elements, and it has wide applications in the compliant robotic designs. Previous studies only investigate the out-of-plane compliance of ortho-planar spring and fewer work pays attention to its angular compliance. To address this issue, this paper provides an analytical method to study both the linear and angular compliance characteristics of ortho-planar spring for the first time. In the frame work of screw theory, the symbolic formula of platform’s compliance matrix was obtained based on the hybrid integration of beam elements. Subsequently non-dimensional geometric parameters were introduced to compare the compliance characteristics of planar spring, which revealed the ortho-planar spring also demonstrates large bending compliance. Numerical studies of angular compliance of planar spring were provided, and they showed good agreements with the finite element simulations in a large working range. Based on the numerical study, a physical prototype of one continuum structure assembled with planar springs was provided and it demonstrated a large flexibility compared to other previous designs, which suggests the ortho-planar spring has potential value in developing continuum manipulators in related medical surgery and biorobotic research fields.

Topics: Manipulators , Springs
Commentary by Dr. Valentin Fuster
2014;():V05AT08A037. doi:10.1115/DETC2014-34915.

Automotive wings are considered to be aerodynamic devices which have a significant effect on the driving, braking and cornering performances by influencing the flow of fluids around the vehicle without changing the weight of the vehicle. The wings have developed from having a fixed shape to multi-sectional wings in order to amplify the advantages of their aerodynamic effect in specific situations such as cornering and braking. However, the multi-sectional wings based on flaps, ailerons, and slats have to modify their surface or camber using hinged parts. These discrete sections create aerodynamic losses during shape changes. In this paper, a morphing car-spoiler based on a reinforced elastomer capable of continuous self-actuation throughout its surface was applied to a small-scale vehicle without slotted parts or mechanical elements. The designed morphing car-spoiler consists of a woven type Smart Soft Composite (SSC) which was made by weaving Shape Memory Alloy (SMA) wires and glass fibers embedded in a polydimethylsiloxane (PDMS) polymeric soft matrix. The phase transformation from martensite to austenite of the SMA wires creates an axial load in the longitudinal direction resulting in symmetric bending of the spoiler. Using an open-blowing type wind tunnel, tests were conducted on the stand-alone spoiler to verify its aerodynamic effects. Furthermore, to evaluate its performance in practice, the morphing car-spoiler was mounted on a small-scale vehicle and tested in a closed-type wind tunnel. Results show that the morphing car-spoiler generates a downforce which increases the normal tire adhesion and that it is possible to adapt its shape for various situations such as cornering and braking.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A038. doi:10.1115/DETC2014-34982.

The need for a compliant parallel micromanipulator (CPM) providing large motion range and high precision is increasing. Existing CPMs vary in constraint configurations and therefore it is necessary to verify/compare their characteristics. This paper compares three kinds of typical over-constrained CPMs, and derives their theoretical compliance matrix models pointing out constraint characteristics of the three kinematic configurations. Then the three CPMs are analyzed with FEA (finite element analysis), and results illustrate that the theoretical compliance matrix models are close to their FEA models. Moreover, cross-axis coupling along two motion axes (X&Y), parasitic motion and compliance fluctuation of motion stages are described in details. Through analyzing the FEA results, we present an improved CPM with a mirror-symmetry structure and redundant-constraint characteristic which can effectively constrain in-plane yaw and cross-axis coupling. It is shown that the improved CPM presented in this paper has a series of merits: large motion range up to 10mm×10mm in the dimension of 311mm×311mm×24mm, small compliance fluctuation (only 37.32% of that of the initial model), a smaller cross-axis coupling (only 24.39% of that of the initial model generated by a single-axis 5mm driving), a smaller in-plane parasitic yaw (only 53.57% of that of the initial model generated by double-axis 5mm driving).

Commentary by Dr. Valentin Fuster
2014;():V05AT08A039. doi:10.1115/DETC2014-34996.

This paper presents an approach based on parameterized compliance for type synthesis of flexure mechanisms with serial, parallel, or hybrid topologies. The parameterized compliance matrixes have been derived for commonly used flexure elements which are significantly influenced by flexure parameters including material and geometric properties. Different parameters of flexure elements generate different degree of freedom (DOF) characteristic of types. Enlightened by the compliance analysis of flexure elements, a parameterization approach with detailed processes and steps is introduced in this paper to help analyze and synthesize flexure mechanisms in the case study as serial chains, parallel chains, and combination hybrid chains. For a hybrid flexure, finite element modeling simulations results are compared to analytical compliance elements characters. Within linear deformations, the maximum compliance errors of analytical models are less than 6% compared with FE models. The final goal of this work is to provide a parameterized approach for type synthesis of flexure mechanisms that can be used to configure and change the parameters of flexure mechanisms to achieve desired DOF requirements of types initially.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A040. doi:10.1115/DETC2014-35054.

Instigated by the need to statically balance compliant mechanisms, this paper presents a compliant internally static balanced monolithic four-bar linkage which can be used as generic building block in any compliant mechanism. The pivots of the four-bar are made compliant by the use of initially curved leaf springs. The balancing energy is provided by two pre-loaded opposing cantilever leaf springs that follow a circular path imposed by the input link in a range of forty degrees. The monolithic four-bar and its balancing mechanism are dimensioned by means of an analytical model (decoupled segments), optimized with a FE-analysis (coupled), and validated with a prototype and accompanying experiment. FEA shows a peak moment reduction of 95% (elastic material, working range: 40°), and the experiment of a lasercut 10 mm thick PMMA (visco-elastic material) prototype shows a peak moment reduction of 63% (working range: 36°) up to 88% (working range: 20°).

Commentary by Dr. Valentin Fuster
2014;():V05AT08A041. doi:10.1115/DETC2014-35114.

This paper presents a new synthesis approach for expandable polyhedral linkages, which are synthesized by inserting appropriate link groups into the faces of polyhedron and interconnecting them by a special composite hinges (called gusset by K. Wohlhart). The overconstrained expandable polyhedral linkages are movable with one degree of freedom (DOF).The link groups are single DOF scaling planar linkages. The gussets are multiple rotary joints whose axes converge at the corresponding vertices of the polyhedron and the number of the rotary joints equals the one of the faces which meet at the vertices. This new approach is suitable for any polyhedron whatever is regular or irregular polyhedron. To verify this new approach, the expandable regular hexahedral linkage is modeled in the SolidWorks and its mobility are studied based on screw theory and topology graph.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2014;():V05AT08A042. doi:10.1115/DETC2014-35131.

This paper presents a novel pressure-compensating flow restrictor for low-cost/low-pressure drip irrigation systems. There are nearly one billion subsistence farmers in the developing world who lack the resources and opportunities to rise out of poverty. Irrigation is an effective development strategy for this population, enabling farmers to increase crop yields and grow more lucrative plant varieties. Unfortunately, as a large fraction of subsistence farmers live off the electrical grid, the capital cost of solar or diesel powered irrigation systems makes them unobtainable. This cost could be drastically reduced by altering drip irrigation systems to operate at a decreased pressure such that lower pumping power is required. The work presented here aims to accomplish this by designing a drip emitter that operates at 0.1 bar, 1/10 the pressure of current products, while also providing pressure-compensation to uniformly distribute flow over a field.

Our proposed pressure compensating solution is inspired by the resonating nozzle of a deflating balloon. First, a reduced order model is developed to understand the physical principles which drive the cyclic collapse of the balloon nozzle. We then apply this understanding to propose a pressure compensating emitter consisting of compliant tube in series with a rigid diffuser. A scaling analysis is performed to determine the ideal geometry of the system and the reduced order model is applied to demonstrate that the proposed design is capable of pressure compensation in the required operation range. Preliminary experiments demonstrating the collapse effect are presented, along with initial work to translate the concept to a robust physical device.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A043. doi:10.1115/DETC2014-35181.

In this paper, we introduce the principles necessary to guide designers in determining the optimal number and placement of actuators for driving the stage of a general serial or hybrid flexure system at any desired speed. Although the degrees of freedom (DOFs) of a flexure system are largely determined by the location and orientation of its flexure elements, the system’s stage will tend to displace in unwanted directions (i.e., parasitic errors) while attempting to traverse its intended DOFs if it is not actuated correctly. The problem of correctly placing actuators is difficult because the optimal location changes depending on the speed with which the stage is driven. Moreover the issue of correctly actuating the stage of a serial or hybrid flexure system is substantially more complicated than actuating the stage of a parallel system because serial and hybrid systems possess multiple rigid bodies, which greatly enhance the system’s dynamic complexity, and provide a host of alternative options for actuating the system with its intended DOFs. In this paper we review the principles of static and dynamic actuation space and provide the mathematics necessary to apply these spaces to serial and hybrid systems such that designers can rapidly visualize all the ways actuators can be placed to correctly drive any combination of the system’s rigid body constituents such that the system’s stage achieves the desired DOFs with minimal parasitic error at any speed.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A044. doi:10.1115/DETC2014-35268.

Compliant mechanisms gain some or all of their mobility from the deflection of their flexible members. The pseudo-rigid-body model (PRBM) concept allows compliant mechanisms to be modeled using existing knowledge of rigid-body mechanisms, thereby, simplifying the design process. A pseudo-rigid-body model represents a compliant segment with two or more rigid-body segments, connected by pin joints or characteristic pivots. A compliant segment that is small in length, compared to the relatively rigid segments between which it is affixed, is termed a small-length flexural pivot (SLFP). This paper presents closed-form deflection solutions using the elliptic integral method for initially-straight and initially-curved SLFPs. The assumptions made in modeling the small-length flexural pivots in a PRBM are validated by means of the elliptic integral solutions.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A045. doi:10.1115/DETC2014-35366.

The pseudo-rigid-body model (PRBM) concept allows compliant mechanisms to be modeled using existing knowledge of rigid-body mechanisms, thereby considerably simplifying their analysis and design. The PRBMs represent the compliant segments with two or more rigid-body segments, connected using pin joints (characteristic pivots). The beam compliance is modeled using a torsional spring placed at the characteristic pivot, whose spring constant K is evaluated using a pseudo-rigid-body parameter termed as the beam stiffness coefficient. This paper presents a method to more accurately calculate the beam stiffness coefficient for a fixed-free compliant beam subjected to a combination of horizontal and vertical forces. The improved stiffness coefficient (KΘ) expressions are derived as a function of the pseudo-rigid-body angle, Θ and the load factor, n. To exemplify the application of the improved results, the expressions derived are successfully implemented in modeling a fixed-guided beam with an inflection point, allowing it to be modeled as two fixed-free beams pinned at the inflection point.

Topics: Stiffness
Commentary by Dr. Valentin Fuster
2014;():V05AT08A046. doi:10.1115/DETC2014-35373.

This paper presents a method for the design of compliant mechanisms with large deflections and prescribed load paths. While the approach is general, this paper treats the shape optimization for two dimensional beams. Due to the geometric non-linearity of the problem the non-linear analysis is nested into the optimization procedure. This requires accurate and efficient analysis of the structural problem. The analysis of the beam is based on the Isogeometric Analysis formulation, an alternative for conventional FEA especially appreciated for its shape-accuracy and efficiency. The method is applied to the synthesis of a balancer for a pendulum, which involves a two step load case: first a prestressing phase and subsequently a motion phase under the influence of gravity. To this end, a prestressed compliant beam was optimized with respect to its initial shape and the preload conditions. The rotationless character of the degrees of freedom of the Isogeometric beam requested the formulation of specific boundary conditions in order to apply rotations on the beam. The results of the shape optimization have been validated with a prototype out of carbon fiber composite material, which has been successfully tested. The experimental results are in agreement with the simulation results, with an error of 3%.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A047. doi:10.1115/DETC2014-35651.

This paper presents the design and simulation results of a passive prosthetic ankle prosthesis that has mechanical behavior similar to a natural ankle. The presented design achieves active behavior with powered push-off to propel the body forward. The design contains a conventional compression spring network that allows coupling between two degrees of freedom. There is a translational degree of freedom along the leg and a rotational degree of freedom about the ankle joint. During a standard gait cycle, potential energy from the person’s weight is stored in the spring network from deflection along the leg. The energy is released by the spring network as rotation of the foot. With this design, capping the allowable leg deflection at 15 millimeters produces 45% of the rotational work that a natural ankle will produce. This is based on simulation using published average kinetic and kinematic data from gait analyses.

Commentary by Dr. Valentin Fuster

38th Mechanisms and Robotics Conference: Mechanism Analysis and Synthesis

2014;():V05AT08A048. doi:10.1115/DETC2014-34171.

In this paper, a new type of the offshore wind turbine installation equipment is proposed, which has 6 sets of intelligent legs. Each intelligent leg consists of two-UPS and one-UP. Based on the theory of the parallel mechanism, the mechanism of this offshore wind turbine installation equipment with 6 sets of intelligent legs is constructed. We take a set of the intelligent leg for analysis and conducted kinematic analysis and dynamic analysis on the offshore wind turbine installation equipment. Finally, by studying the fuzzy reliability of the kinematic accuracy of a branch, the reliability model of the whole mechanism of the installation equipment combined with the characteristics of installation process is established, and the calculation of the fuzzy reliability of the kinematic accuracy of the whole mechanism is carried out.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A049. doi:10.1115/DETC2014-34207.

The full rotatability of a linkage refers to a linkage in which the input may complete a continuous and smooth rotation without the possibility of encountering a dead center position. Full rotatability identification is a problem generally encountered among the mobility problems that may include branch (assembly mode or circuit), sub-branch (singularity-free) identification, range of motion, and order of motion in linkage analysis and synthesis. In a complex linkage, the input rotatability of each branch may be different while the Watt six-bar linkages may be special. This paper presents a unified and analytical method for the full rotatability identification of Watt six-bar linkages regardless of the choice of input joints or reference link or joint type. The branch of a Watt without dead center positions has full rotatability. Using discriminant method and the concept of joint rotation space (JRS), the full rotatability of a Watt linkage can be easily identified. The proposed method is general and conceptually straightforward. It can be applied for all linkage inversions. Examples of Watt linkage and a six-bar linkage with prismatic joints are employed to illustrate the proposed method.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2014;():V05AT08A050. doi:10.1115/DETC2014-34210.

This paper introduces a new 6DOF parallel manipulator with a ‘3-3’-PSS structure for the space docking test system. The objective of the paper is to present a design method for determine the geometrical parameters of the 6-DOF manipulator according to a prescribed workspace and required performances. By the study of the relationships between the geometrical parameters and the performance indices of the manipulator, a new method is presented for finding all the appropriate parameters on the contour maps of the performance indices. With this method, the smallest manipulator whose workspace involves the prescribed workspace and whose performances fit the requirements could be found.

Topics: Design , Manipulators
Commentary by Dr. Valentin Fuster
2014;():V05AT08A051. doi:10.1115/DETC2014-34213.

Singularity analysis of multi-DOF (multiple-degree-of-freedom) multiloop planar linkages is much more complicated than the single-DOF planar linkages. This paper offers a degeneration method to analyze the singularity (dead center position) of multi-DOF multiloop planar linkages. The proposed method is based on the singularity analysis results of single-DOF planar linkages and the less-DOF linkages. For an N-DOF (N>1) planar linkage, it generally requires N inputs for a constrained motion. By fixing M (M<N) input joints or links, the N-DOF planar linkage degenerates an (N-M)-DOF linkage. If any one of the degenerated linkages is at the dead center position, the whole N-DOF linkage must be also at the position of singularity. With the proposed method, one may find out that it is easy to obtain the singular configurations of a multiple-DOF multiloop linkage. The proposed method is a general concept in sense that it can be systematically applied to analyze the singularity for any multiple-DOF planar linkage regardless of the number of kinematic loop or the types of joints. The velocity method for singularity analysis is also used to verify the results. The proposed method offers simple explanation and straightforward geometric insights for the singularity identification of multiple-DOF multiloop planar linkages. Examples are also employed to demonstrate the proposed method.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2014;():V05AT08A052. doi:10.1115/DETC2014-34216.

In this paper, we revisit the classical Burmester problem of the exact synthesis of a planar four-bar mechanism with up to five task positions. A novel algorithm is presented that uses prescribed task positions to obtain “candidate” manifolds and then find feasible constraint manifolds among them. The first part is solved by null space analysis, and the second part is reduced to finding the solution of two quadratic equations. Five-position synthesis could be solved exactly with up to four resulting dyads. For four-position synthesis, a limited number of solutions could be selected from the 1 many through adding an additional linear constraint equation without increasing the computational complexity. This linear constraint equation could be obtained either by defining one of the coordinates of the center/circle points, by picking the ground line/coupler line, or by adding one additional task position, all of which are proved to be able to convert into the same form as in (23). For three-position synthesis, two additional constraints could be imposed in the same way to select from the 2 many solutions. The result is a novel algorithm that is simple and efficient, which allows for task driven design of four-bar linkages with both revolute and prismatic joints, as well as handling of different kinds of additional constraint conditions in the same way.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A053. doi:10.1115/DETC2014-34242.

This article presents the kinematic analysis of a new class of mechanical devices called planar Reconfigurable Motion Generators (RMGs) for multi-phase motion generation tasks having only a slight change in the desired motion. The concepts of configuration matrices and state vectors are introduced as a novel way to represent planar RMGs. The kinematic analysis of a planar RMG in it’s initial configuration to determine the associated adjustable link lengths and angles is discussed. The adjustable link lengths are used to determine the link vector and state vector of a RMG. Future work will involve the application of configuration matrices and state vectors to aid in both systematic analysis and synthesis of RMGs.

Topics: Generators
Commentary by Dr. Valentin Fuster
2014;():V05AT08A054. doi:10.1115/DETC2014-34320.

Differential evolution (DE) and Pareto front theory are used to optimize stiffness in three directions and workspace of a 3UPU manipulator. Stiffness of the mechanism in each direction is analyzed, and it comes to the fact when stiffness in x and y directions increase, stiffness in z direction will decrease and therefore, the sum of stiffness in x and y and stiffness in z are optimized simultaneously by applying DE, but those two objectives are not in the same scale, a normalization of objectives is therefore considered. Furthermore, workspace volume of the mechanism is analyzed and optimized by using DE. By comparing landscapes of stiffness and workspace volume, one finds stiffness in z has same trend with workspace volume whereas stiffness in x and y and workspace volume conflicts. By employing Pareto front theory and DE, the sum of stiffness in x and y and workspace volume are optimized simultaneously.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A055. doi:10.1115/DETC2014-34486.

A single-line symbolic notation is proposed for description of an arbitrary mechanism or a multibody system. The kinematics is represented by a sequence of elementary transformations; each of those being marked by a reserved alphabetic character. Force and constraint links between the bodies are also defined by reserved characters. The parameters of the system, such as identifiers of degrees of freedom, inertia parameters and others, are assigned default names if not specified. However, user-defined names, parameters and functions can be placed instead, if needed. The proposed description in its shortest form is suitable for academic purpose to identify only the essential properties of a multibody system. In an extended form, by explicit mentioning names of variables and parameters and other data like initial conditions, this description can serve as input data for multibody analysis software. Examples from academic area and technical applications are given to show the applicability of the proposed description.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A056. doi:10.1115/DETC2014-34593.

The Accurate calculation of the workspace and joint space for 3 RPS parallel robotic manipulator is a highly addressed research work across the world. Researchers have proposed a variety of methods to calculate these parameters. In the present context a cylindrical algebraic decomposition based method is proposed to model the workspace and joint space. It is a well know feature that this robot admits two operation modes. We are able to find out the set in the joint space with a constant number of solutions for the direct kinematic problem and the locus of the cusp points for the both operation mode. The characteristic surfaces are also computed to define the uniqueness domains in the workspace. A simple 3-RPS parallel with similar base and mobile platform is used to illustrate this method.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A057. doi:10.1115/DETC2014-34638.

The duality (known also as symmetry) between serial chain manipulators and fully parallel mechanisms is well known in the literature. This paper takes this idea one step further, by introducing a systematic method that transforms mechanical systems into other and different mechanical systems so that the wrench screws in the original system gives rise to the relative twist screws in the second system. The mathematical foundation of this work relies on using the BB graph, a variant of graph representation widely used in mechanisms, possessing both the topology and geometry of the original system. From the dual graph of the latter it is possible to construct the dual system at a specific configuration. Relying on the equivalence between the dual systems, it is proved that if the screw system of a mechanism is at the singular position, so is that of its dual. This idea is demonstrated by showing the dual system of a Bricard mechanism, which is a 6/6 Stewart Platform in the singular position. The paper also shows that the cyclohexane molecule is dual to the 6/3 Stewart platform at the singular position, providing another perspective of the known mobility of this molecule.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A058. doi:10.1115/DETC2014-34654.

Currently, the small satellite mechanisms that are used to deploy sensors and antennae in space have been restricted to simple one arm pin jointed members or telescopic mechanisms. This means, to deploy multiple sensors, multiple actuators and controllers are required. However, simple rigid link mechanisms, like the 6-bar hexagonal mechanism described in this paper, give the freedom to incorporate a greater number of sensor platforms in one deployable structure and also helps reduce the number of actuators. In fact, by the use of boom technology, the entire mechanism can be deployed by a single tape-spring boom. Further, to make these structures more robust and stiffer at the joints, rotational springs can be used. In this paper, an attempt is made to study the stiffness and stability of such mechanisms at their equilibrium points. Also since the positions and orientations of the sensor platforms are critical, it is shown through a few examples how these parameters can be adjusted just by tweaking the preloads of the rotational springs. The tape-spring boom — which is bi-stable in nature — offers further stiffness to the structure in its deployed state. It is well known now and also well established by the theory of mechanics of materials that by arranging multiple tape springs in certain orientations within the boom; a boom can be obtained with significant axial and flexural stiffness in its deployed state. Through modal analyses at equilibrium and by looking at the characteristics of the Hessian of the potential energy function, it is also shown how this significantly rigid boom affects the stiffness and stability of the structure. Herein, the force method of matrix analysis for deployable structures is used for analyses. This paper also discusses the possibilities of the system failing due to insufficient actuation force by the boom — the condition where the boom does not reach its second stable position.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A059. doi:10.1115/DETC2014-34713.

There are two established approaches to represent constraints: the body-bar (BB) and the bar-joint (BJ) graph that can be used in machine theory. They are referred to as topological graphs as they describe the relation between members of a mechanism. It is known, however, that in many cases these graphs are not unique. Hence any method for kinematic analysis or mobility determination that is based on these topological graphs is prone to failures.

In this paper a generalized and unified concept for the representation of constraints in mechanisms is introduced. It is first shown in which situations BB and BJ representations fail to correctly represent the mechanism. The novel constraint graph is then derived starting from the most general model of constrained rigid bodies. It is shown how BB and BJ graphs result as special cases. Therefore the new graph representation is called the ‘mixed graph’. It is further shown how this novel mixed constraint graph allows for computation of the correct generic (topological) mobility, and thus overcomes the problems of BB and BJ representations.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A060. doi:10.1115/DETC2014-34795.

The progress of the 21st century advanced and integrated manufacturing technology highly relies on the development of higher performance robotic system for rapidly adapting to the dramatic change of manufacturing environment and performance-critical applications. Based on this scenario, this research is focused on system configuration, performance analysis and multi-objective optimization of a new hybrid parallel robotic manipulator with two rotations and three translations. The structure design and the kinematic analysis are conducted. The key performance indices including local/global stiffness, local/global dexterity and workspace are modeled, visualized and optimized. The proposed method provides a unique viewpoint for the design optimization of multi-axis machine center based on system hybridization.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A061. doi:10.1115/DETC2014-34838.

A deployable mechanism is a mechanism that is designed to be repeatedly expanded and contracted without failure. Most deployable mechanisms are over-constrained mechanisms with a mobility of one. Although many deployable mechanisms had been proposed and employed in application in the past decades, few generalized methodologies for the synthesis of both planar and spatial deployable mechanisms are available. In this paper, a systematic methodology, based on the Cardanic motion of planar linkage, for the synthesis of both the spatial and planar deployable mechanisms is presented. By using the characteristics that some of the coupler points of Cardanic linkages are able to move along a straight line, a building unit mechanism that utilizes such a linkage can be extended or retracted as desired. Once the boundary conditions of the building unit mechanisms are obtained, design of an entire deployable mechanism, planar or spatial, can be fulfilled. After the design is achieved, motion of the synthesized mechanism is simulated in Pro/Engineer, and the prototype of a planar model is manufactured for the justification of this method.

Topics: Linkages , Design
Commentary by Dr. Valentin Fuster
2014;():V05AT08A062. doi:10.1115/DETC2014-34850.

Metamorphic transformation is a fundamental and key issue in the design and analysis of metamorphic mechanisms. It is tedious to represent and calculate the metamorphic transformations of metamorphic parallel mechanisms using the existing adjacency matrix method. To simplify the configuration transformation analysis, we propose a new method based on block adjacency matrix to analyze the configuration transformations of metamorphic parallel mechanisms. A block adjacency matrix is composed of three types of elements, including limb matrices that are adjacency matrices each representing a limb of a metamorphic parallel mechanism, row matrices each representing how a limb is connected to the moving platform, and column matrices each representing how a limb is connected to the base. Manipulations of the block adjacency matrix for analyzing the metamorphic transformations are presented systematically. If only the internal configuration of a limb changes, the configuration transformations can be obtained by simply calculating the corresponding limb matrix. A 3-URRRR metamorphic parallel mechanism, which has five configurations including a 1-DOF translation configuration and a 3-DOF spherical motion configuration, is taken as an example to illustrate the effectiveness of the proposed approach to the metamorphic transformation analysis of metamorphic parallel mechanism.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A063. doi:10.1115/DETC2014-34881.

The motion of gait is a cyclical activity that requires the coordination between locomotion mechanism, motor control and musculoskeletal function. The basic assumption is that one stride is the same as the next. From a simplified kinematics point of view, the human gait can be considered as a TRS serial chain with six degrees-of-freedom driven by the pelvis rotational and tilting motion during walking. This paper presents a dimensional synthesis procedure for the design of two degrees-of-freedom of spatial eight-bar linkages by mechanically constraining a TRS serial chain. The goal is to develop a methodology for the design of under-actuated lower limb walking devices or passively driven exoskeleton systems.

The dimensional synthesis process starts with the specification of the links of a TRS chain according to the gait anthropometric data. We show the various ways how four TS constraints can be used to constrain the links of the this chain to obtain a two degrees-of-freedom spatial eight-bar linkage. We formulate and solve the design equations as well as analyze the resulting eight-bar linkage from the data we obtained from an optical motion capture system. An example demonstrates our results.

Topics: Chain
Commentary by Dr. Valentin Fuster
2014;():V05AT08A064. doi:10.1115/DETC2014-34924.

This article introduces a reconfigurable four-bar mechanism. The mechanism uses a rotational-translational variable joint to switch between a RRRR four-bar and a RRRP1 four-bar. The ability to transition between two types of four-bar mechanisms allows the reconfigurable four-bar mechanism to complete a rigid body guidance task not possible by either a RRRR four-bar mechanism or a RRRP four-bar mechanism. The reconfigurable mechanism reduces the number of required actuators in the mechanism.

Topics: Actuators , Switches
Commentary by Dr. Valentin Fuster
2014;():V05AT08A065. doi:10.1115/DETC2014-34932.

Camus’ concept of Auxiliary Surface (AS) is extended to the case of involute gears with skew axes. In the case at hand, we show that the AS is an orthogonal helicoid whose axis a) lies in the cylindroid and b) is normal to the instant screw axis of one gear with respect to its meshing counterpart; in general, the helicoid axis is skew with respect to the latter. According to the spatial version of Camus’ Theorem, any line attached to the AS, in particular any generator g of AS itself, can be chosen to generate a pair of conjugate flanks with line contact.

While the pair of conjugate flanks is geometrically feasible, as they always share a line of contact and the tangent plane at each point of this line, there are poses where the flanks even have a common Disteli axis. Then there is a G2-contact at the striction point and the two surfaces penetrate each other.

The outcome is that the surfaces are not realizable as tooth flanks. Nevertheless, this is a fundamental step towards the synthesis of the flanks of involute gears with skew axes.

Topics: Gears
Commentary by Dr. Valentin Fuster
2014;():V05AT08A066. doi:10.1115/DETC2014-34934.

A polygon-scaling mechanism is a single DOF (degree-of-freedom) mechanism for scaling a polygon. This paper presents a tetragon-elements based synthesis method of polygon-scaling mechanisms. According to movable conditions of radial scaling elements, four basic tetragon elements (rhombus element, parallelogram element, kite element and general tetragon element) are proposed. For a given polygon, these four types of elements can be selected based on the characteristics of target polygons to construct polygon-scaling mechanisms in a straightforward manner. Using this synthesis method, some planar 1-DOF scaling mechanisms are obtained with the characteristics of retracting and deploying. Their 3D models are also presented to proof the validity of the proposed method. Finally, a table of tetragon elements with the characteristics of their associated polygon-scaling mechanisms is summarized using which polygon-scaling mechanisms can be easily constructed.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A067. doi:10.1115/DETC2014-34951.

The present paper deals with the formulation of specific algorithms for the kinematic synthesis of quasi-homokinetic four-bar linkages, slider-crank mechanisms included, which are based on the fundamentals of kinematics, as the centrodes, the inflection circle, the cubic of stationary curvature, Freudenstein’s theorem, the Euler-Savary equation and Chebyshev’s theory.

These algorithms are aimed to obtain in a given range of motion, a quasi-constant transmission ratio between the driving and driven links, thus producing a quasi-homokinetic behaviour. In particular, the infinitesimal Burmester theory and the Chebyshev optimality criterion are applied to propose a compact closed-form solutions, which are validated through several significant examples.

Topics: Kinematics , Linkages
Commentary by Dr. Valentin Fuster
2014;():V05AT08A068. doi:10.1115/DETC2014-35029.

A bending moment and a tension/compression force are two types of commonly used load patterns in loading test for mechanical components. A great number of simulator types available for the two loads have been reported widely. However, current types mainly focus on the single load pattern and only one-dimensional bending moment can be achieved. With the increasing demand of the mechanical part performance, it is urgent to build a more complex testing environment. In this situation, a novel compound load simulator capable of outputting single multi-dimensional load and compound load patterns gradually catches the attention of the researchers. The development of parallel mechanism (PM) supplies a new direction to the field of simulators, whereas there is still shortage of effective types and design principles. In this paper, type synthesis of the compound load simulators outputting the bending moment and tension/compression force is introduced. First of all, the relationship between load patterns and degree-of-freedom (DOF) of parallel mechanism is derived. Based on the derivation, the DOF correspondence with a two-dimensional pure bending moment is two-dimensional rotation and that with a tension/compression force is one-dimensional translation. Furthermore, a typical 3-PRS PM as a representative of the PM with 2R1T DOF is studied and the analysis reveals that there is parasitic motion during its two-dimensional rotation. The undesired parasitic motion will bring additional load to the part, such as shear force. Then the special characteristics of PM meeting the requirement of outputting pure bending moment are proposed. Finally, a graphical approach is utilized to synthesize the effective types of the compound simulator.

Topics: Stress , Compression , Tension
Commentary by Dr. Valentin Fuster
2014;():V05AT08A069. doi:10.1115/DETC2014-35155.

This paper deals with the dimensional synthesis of a novel parallel manipulator for medical applications. This parallel mechanism has a novel 2T2R mobility derived from the targeted application of needle manipulation. The kinematic design of this 2T2R manipulator and its novelty are illustrated in relation to the percutaneous procedures. Due to the demanding constraints on its size and compactness, achieving a large workspace especially in orientation, is a rather difficult task. The workspace size and kinematic constraint analysis are considered for the dimensional synthesis of this 2T2R parallel mechanism. A dimensional synthesis algorithm based on the screw theory and the geometric analysis of the singularities is described. This algorithm also helps to eliminate the existence of voids inside the workspace. The selection of the actuated joints is validated. Finally, the dimensions of the structural parameters of the mechanism are calculated for achieving the required workspace within the design constraints of size, compactness and a preliminary prototype without actuators is presented.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A070. doi:10.1115/DETC2014-35263.

In this paper we present an algorithm that automatically creates the linkage loop equations for planar 1-DoF linkages of any topology with rotating joints, demonstrated up to 8-bars. The algorithm derives the linkage loop equations from the linkage graph by establishing a cycle basis through a single common edge. Divergent and convergent loops are identified and used to establish the fixed angles of the ternary and higher links.

Results demonstrate the automated generation of the linkage loop equations for the five distinct 6-bar mechanisms, Watt I-II and Stephenson I-III, as well as the seventy one distinct 8-bar mechanisms.

The resulting loop equations enable the automatic derivation of the Dixon determinant for linkage kinematic analysis of the position of every possible assembly configuration. The loop equations also enable the automatic derivation of the Jacobian for singularity evaluation and tracking of a particular assembly configuration over the desired range of input angles.

The methodology provides the foundation for the automated configuration analysis of every topology and every assembly configuration of 1-DoF linkages with rotating joints up to 8-bar. The methodology also provides a foundation for automated configuration analysis of 10-bar and higher linkages.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2014;():V05AT08A071. doi:10.1115/DETC2014-35265.

This paper seeks to advance the design of planar shape-changing mechanisms used in a variety of applications, such as morphing extrusion dies and airfoils. The presence of defects is a limiting factor in finding suitable single-degree-of-freedom (DOF) mechanisms, particularly when the number of shapes to achieve is large and/or the changes among those shapes are significant. This paper presents a new method of designing multi-DOF mechanisms to aid in avoiding these defects. The primary method uses a building-block approach similar to the current one-DOF synthesis procedure and is compared to alternative strategies that seek to leverage the use of multiple single-DOF subchains. While more complex in terms of determining the actuation pattern, the primary method offers a larger design space in which to find solutions. In all cases a genetic algorithm is employed to search the design space. Two example problems involving four prescribed shapes demonstrate the benefits of using multi-DOF mechanisms in terms of shape matching and mechanical advantage.

Topics: Design
Commentary by Dr. Valentin Fuster
2014;():V05AT08A072. doi:10.1115/DETC2014-35371.

This paper uses coupler-path synthesis to design four-bar linkage modules that constrains the movement of links in an nR serial chain. The goal is to formulate a general procedure for path-synthesis of a robotic system using four-bar linkages. A desired end-effector trajectory is transformed into a secondary trajectory that is used for nine-point synthesis of a constraining four-bar linkage. This procedure constrains an nR chain to become a 4n-2 bar linkage. An example presents the constraint of a 2R chain to a six-bar that has a prescribed trajectory for an end-effector point.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A073. doi:10.1115/DETC2014-35374.

A synthesis technique for designing novel vehicle suspension linkages based on the Watt I six-bar is presented. The goal is to maintain near vertical alignment of the wheels to the road during cornering. The complete suspension is analyzed as a symmetric planar 12-bar linkage with ground pivots located at the contact patches. The design procedure specifies the vehicle chassis orientation and the tire camber angles of the vehicle when cornering. As well, two task positions of the wheels with respect to the chassis are specified for suspension movement in straightaways. The result is 18 design equations with 18 unknowns that have a total degree of 2,097,152, though only 336 roots. An example design is presented.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A074. doi:10.1115/DETC2014-35494.

This paper presents a design methodology for lower-mobility parallel manipulators based on classification of wrench systems into four main classes. Wrench systems are represented in a three-dimensional projective space ℙ3 using wrench graphs where it is easy to incorporate geometric constraints to have simple singularity conditions using Grassmann-Cayley algebra (GCA). The main idea of the approach is to design a PM with an overall (constraint and actuation) wrench system that complies with a given wrench graph for which singularity conditions have been predetermined. The main advantage of this methodology is that the singularity conditions are already known a priori and consequently, it gives an opportunity to avoid such conditions at the design stage and make them unreachable. In the worst case scenario, where none of singularity conditions cannot be avoided, one can have a PM with known singular configurations which are always difficult to determine for already designed manipulators. As illustrative examples, two different five degrees-of-freedom (dof) mechanisms have been designed based on some of the defined wrench graphs giving 3T2R motion pattern. The first mechanism has some avoided singularities and the second one is free of singularity.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A075. doi:10.1115/DETC2014-35510.

The interaction between human and passive, constraint-based path generating mechanisms has been scarcely studied. When it comes to rehabilitation robots, output trajectories and/or forces are achieved mainly as a result of actuation on all joints, since they form an open kinematic chain. On the other end, there exists a wide range of mechanisms that can trace complex trajectories primarily due to mechanical constraints in their topology and structure. Probably the simplest example is the four bar linkage, a widely used 1-DOF mechanism. It consists of a driving link, a driven link, and a coupler which connects the two. As the input link rotates, each point on the coupler link traces a unique trajectory in space, called a coupler curve. Ideally, the linkage dimensions can be chosen so that a near-natural hand trajectory is generated for a specific task. As a first step, in this work a straight line generating four-bar mechanism, namely the Chebyshev’s linkage is considered for generating a natural bell-shaped velocity profile, as prescribed by the Minimum-Jerk-Model. Initially the mechanism is synthesized for producing a straight line trajectory of a desired length. Kinematic and kinetostatic analysis is performed in order to determine the required input torque necessary for achieving the desired spatio-temporal profile. The main objective is to determine whether this input torque can approximated by a series of linear torsional springs that can be installed on the pivoted side of the input link.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2014;():V05AT08A076. doi:10.1115/DETC2014-35523.

This paper formulates a methodology for designing planar eight-bar linkages for five task positions, by adding two RR constraints to a user specified 6R loop. It is known that there are 32 ways in which these constraints can be added, to yield as many as 340 different linkages. The methodology uses a random search within the tolerance zones around the task specifications to increase the number of candidate linkages. These linkages are analyzed using the Dixon determinant approach, to find all possible linkage configurations over the range of motion. These configuration trajectories are sorted into branches. Linkages that have all the five task configurations on one branch, ensure their smooth movement through the five task positions. The result is an array of branch-free useful eight-bar linkage designs. An example is provided to illustrate the results.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2014;():V05AT08A077. doi:10.1115/DETC2014-35571.

Two degree-of-freedom (DOF) manipulators have been widely applied in pointing devices. Besides the commonly used gimbal platforms, two different kinds of parallel platforms base on parallel manipulators are presented as real applications in this paper. In a situation, a pointing device acquires and tracks a remote target via optical sensors amounted on the device. As the authors’ recent research, there are image distortions caused by deflected camera axis while the pointing device changing its attitudes. The paper refers the phenomena to the self-motion characteristics as the 2-DOF platforms rotate around the fixed platform axis. Basic image distortion principles of the three platforms are illustrated and discussed. Relationship between the self-motion and revolution are analyzed via the graphic approach and simulated on the software. Results indicate that these different phenomena are due to the different inherent characters of the platform’s freedom lines and freedom disks. Conclusions revealed in this paper would help the engineers with the type selections and applications, especially for the remote virtual reality devices which can provide realistic images for the human eyes. This work will facilitate the image processing and improve the measuring accuracy for the pointing devices.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A078. doi:10.1115/DETC2014-35595.

Minimizing the bearing reactions in statically balanced linkages reduces the loads experienced by the frame; and making the bearing reactions constant in all configurations makes the linkages run smoothly. Current techniques for static balancing of a linkage using only springs and no auxiliary bodies have free parameters to be chosen by the designer. We describe methods that utilize these free parameters to impose additional conditions that make the magnitude of all bearing reactions constant in all configurations. We also show additional conditions that also minimize the constant bearing reactions. The conditions required for constant bearing reactions for a statically balanced planar 1R crank and a statically balanced planar 2R linkage are derived in this paper. These results are then generalized for any planar linkage with revolute joints.

The main contribution of this paper is in overcoming inherent disadvantages of static balancing using only springs. One disadvantage is concerned with large bearing reactions that vary with the configuration of the linkage. The second disadvantage is large pre-load in the balancing springs. The former is addressed in this paper and the latter was addressed in a prior work. In this paper, we show that simultaneous minimization of constant bearing reactions and pre-loads is not always possible. Hence, we discuss a tradeoff between the two as a practical way to regulate bearing reactions and spring loads. Practical examples of linkages are used to illustrate the application of the proposed methods.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A079. doi:10.1115/DETC2014-35654.

A series of Joint Torque Augmentation Robot (JTAR) devices were created to assist the hip joint in walking. Both passive and active assistance approaches were developed. The active device has been demonstrated in an unconstrained outdoor environment.

Topics: Torque , Robots
Commentary by Dr. Valentin Fuster
2014;():V05AT08A080. doi:10.1115/DETC2014-35668.

In a novel compliant parallel mechanism, a motor and spring are arranged in a parallel fashion and are connected to a movable lever arm. The motor pushes and pulls on one attachment point and the spring stores and releases energy at a second attachment point. In a non-obvious choice, we do not attach the output link to the commonly thought of end-effector, but to the third link in the planar, parallel mechanism. The new mechanism allows the transmission ratio of the motor to be a function of the output angle and the force applied at the spring. For example, if there are no loads on the spring, the overall gear ratio is lowered, and the output speed can be increased. Conversely, if there are loads on the spring, the overall gear ratio is increased, and the output torque can be increased.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A081. doi:10.1115/DETC2014-35675.

This paper presents a methodology for the Jacobian analysis of parallel manipulators with multiple end-effectors (PMxE). The end-effector velocity state of a PMxE is described by one twist of a principal end-effector with respect to the base and a set of relative twists of the remaining end-effectors with respect to the principal end-effector The twist of each terminal link with respect to the principal end-effector is then expressed as a linear function of the relative twists, which enables an extension of the generalized Jacobian analysis to PMxE. The presented methodology is detailed for parallel manipulators with two end-effectors, where a planar 6-RRR manipulator with a 2-RRR internal closed-loop is used as an example.

Commentary by Dr. Valentin Fuster

38th Mechanisms and Robotics Conference: Mobile Robots and Cable-Driven Systems

2014;():V05AT08A082. doi:10.1115/DETC2014-34060.

Driving simulators (DS) are an indispensable developmental tool in the automotive industry. Versatile areas of application all profit from the high degree of reproducibility and safety of DS. The upcoming demands for advanced driver assistance systems (ADAS) with respect to urban traffic situations result in increasing DS requirements in regard to motion envelope and system dynamics [1]. To fulfill those increased requirements, modern-day DS show up to 12 degrees of freedom (DOF) whilst comprising multiple drive mechanisms. These improvements come with the disadvantage of creating a complex system with increased moving mass of about 80 t. Thus, a link between moving mass and motion envelope is caused, limiting either motion envelope or system dynamics.

Mobile dynamic DS solve the core problem of the increased moving mass. The proposed design of a Wheeled Mobile Driving Simulators (WMDS) shows three self-propelled and active steerable wheels that allow translational motion and yaw [2]. The main idea is based on the assumption that a wheeled system, whose propulsion is limited by friction forces, is suitable to simulate dynamics of vehicles that are also limited by tire friction forces. An additional system provides cabin tilt. Avoiding the conventional rail systems, which mainly cause the moving mass increase, results in a light weight concept [3]. The design and construction of the WMDS are carried out at the Institute of Automotive Engineering (Fahrzeugtechnik Darmstadt: FZD), Germany since 2010.

This paper shows the evaluation of a suitable design — by the standards of modern product development — in general for mobile dynamic DS and specifically for WMDS. Furthermore, this paper shows the selection of the individual components and overall properties as well as limitations of the prototype.

Topics: Design
Commentary by Dr. Valentin Fuster
2014;():V05AT08A083. doi:10.1115/DETC2014-34080.

We evaluate and compare the stiffness properties of 6 different configurations of tensile trusses. More specifically, given a constant structural envelope and amount of homogeneous isotropic linear elastic cable material, the stiffness properties of the configurations are analyzed with constant cross-sectional area cables. The configurations include: (1) a Stewart platform, (2) Stewart platform with full spine, 3 cable tie-offs, and slip joint, (3) 6-loop dual-reeved system with partial spine, (4) 4-node/4-loop dual-reeved system, (5) double Stewart platform, and (6) 3D extension of a 2D 2 cable system. In each case, we use analytical results for the evaluation of the stiffness matrix, with some new stiffness matrix results being presented. Of the 6 competing configurations considered, no one configuration was uniformly better than all others, but both the double Stewart platform and the Stewart platform with full spine, 3 cable tie-offs, and slip joint performed quite well, of course given free, massless, rigid body material.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A084. doi:10.1115/DETC2014-34365.

To investigate novel mobile robots is still of its fantasy. In this paper, we proposed a novel hybrid 3-RPR mechanism with scalable platforms for self-crossing locomotion. The hybrid mechanism is constructed by replacing the lower and upper rigid platforms of over-constrained 3-RPR parallel mechanism (PM) each with a scalable planar 3P mechanism. Through the contraction and expansion of the two scalable platforms, the mechanism can achieve a novel locomotion, which is called self-crossing locomotion (SCL). By actuating three limbs, the mechanism can also achieve inchworm locomotion and combined locomotion of SCL and inchworm locomotion. The mobility and kinematic analysis of the mechanism are then dealt with. As a demonstration, the pipe-climbing gaits with the above modes of locomotion are planned. According to the gaits analysis, the mechanism can adapt to a wide range of pipe diameters and overcome bigger fracture in pipe. The specific mechanical design is introduced and the prototype is fabricated to verify the feasible of the mechanism.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A085. doi:10.1115/DETC2014-34419.

This paper proposes a trajectory planning technique for planar three-degree-of-freedom cable-suspended parallel robots. Based on the kinematic and dynamic modelling of the architecture, force constraints that can guarantee that cables remain under tension are obtained. Periodic parametric trajectories that extend beyond the static workspace are designed. The trajectories involve combined translations and rotations. Substituting the trajectories into the force constraints, interval arithmetics is used to search for global conditions on the trajectory parameters which ensure that the trajectories are feasible. Special frequencies related to combined rotational and translational motions are exposed which can be used to better exploit cable-suspended robots. Moreover, it is observed that the special frequencies related to the translation are akin to the natural frequency of pendulum-like systems. The proposed trajectory planning approach can be used to plan combined rotational and translational dynamic trajectories that can extend beyond the static workspace of the mechanism, thereby opening novel applications and possibilities for cable-suspended robots.

Topics: Robots , Cables
Commentary by Dr. Valentin Fuster
2014;():V05AT08A086. doi:10.1115/DETC2014-34467.

Serial multi-body systems can be driven by cables routed through the links to achieve the desired range of motion. Placement and routing of the cables alter the performance characteristics of the manipulator. There are possible applications for such mechanisms where low moving inertia is required. One of the challenges in the design of cable-driven mechanisms is to keep cables in tension during the motion. In this article, the addition of springs and its impact on workspace is investigated. A 2-link cable-driven robot is used to illustrate changes in Wrench Feasible Workspace (WFW) as springs are added between the serial manipulator and the ground or between the links.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A087. doi:10.1115/DETC2014-34522.

Variable-stiffness modules add significant robustness to mechanical systems during forceful interactions with uncertain environments. Traditionally, most existing variable stiffness modules tend to be bulky by virtue of their use of solid components making them less suitable for mobile applications. In recent times, pretensioned cable-based modules have been proposed to reduce weight. While passive, these modules depend on significant internal tension to provide the desired stiffness and stiffness modulation capability tends to be limited. In this paper, we present design, analysis and testing of a cable based active variable stiffness module that can be realized to achieve a large stiffness range. Controlled changes in structural parameters (independent of cable length actuation) now permits independent modulation of the perceived stiffness with desired tension. This capability is now systematically evaluated on a hardware-in-the-loop experimental setup and results are analyzed.

Topics: Cables , Stiffness , Tension
Commentary by Dr. Valentin Fuster
2014;():V05AT08A088. doi:10.1115/DETC2014-34541.

This paper presents and analyzes a novel architecture for a fully constrained cable-based robot that is used in warehousing tasks. A mobile platform is connected to a static box by a set of twelve cables; the cables arrangement allows the mobile platform to achieve stiff positions with constant orientation along with large planar motions. The mechanical analysis of the robot includes inverse and forward kinematics, as well as static analysis and stiffness models. In addition, a workspace analysis describes the feasible boundaries for the suspended and fully constrained cases. Then, the stiffness attributes for both cases are analyzed and discussed. Simulation results show that the proposed robot meets the warehousing requirements of large workspace, high stiffness, and low force input.

Topics: Robots , Cables , Stiffness
Commentary by Dr. Valentin Fuster
2014;():V05AT08A089. doi:10.1115/DETC2014-34591.

Walking robots have been studied a lot over last several decades due to their good adaptability in different complex environments. The walking robot in this paper is designed for the research on emergency rescue missions in nuclear plants. Unlike other mobile robots, it apply parallel mechanism for its legs. This paper mainly focus on the kinematic performance of the parallel leg mechanism. Section 2 gives a brief introduction of our robot and the kinematic model. Then section 3 analyze the workspace of the leg tip. After that the payload and velocity capability are discussed respectively and it turns out that the mechanism has very good payload performance but the velocity is relatively low. Next the isotropic characteristic is studied in the whole workspace. Then the experiments indicate that the robot can successfully finish walking and manipulating tasks.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A090. doi:10.1115/DETC2014-34656.

The operational workspace of a cable-driven serial robot is largely dictated by the choice of cable placement and routing. As robot complexity increases with additional cables and degrees of freedom, the problem of designing a cable architecture can quickly become challenging.

This paper builds upon a previously described methodology to identify and analyze optimal cable configurations, expanding the approach to a 3-DoF robot leg driven by four cables. The methodology is used to analyze configuration trends in the routing and placement of the cables which achieve the desired range of motion for the robot. The results of the analysis are used to inform the design of a cable architecture which is shown to be capable of controlling the robot through the desired task.

Topics: Robots , Cables , Design
Commentary by Dr. Valentin Fuster
2014;():V05AT08A091. doi:10.1115/DETC2014-34672.

The optimal architecture of a cable-based robot for warehousing applications is the main topic of this paper. This study is limited to two types of redundant planar symmetrical configurations with crossed and non-crossed cables. The design problem is divided in two main stages. First, the feasible workspace is optimized for a maximum size and rectangular-type shape of each of the redundant planar architectures. A set of four parameters is selected to fully define the geometry of the mobile platform and the location of its anchor points. In the second design stage, an optimized spatial architecture is obtained for a maximum stiffness by selecting a new set of six parameters which defines the transversal anchor points on both the mobile and static platforms. Based on these optimal parameters, a prototype is fully modeled and built for further experimentation.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A092. doi:10.1115/DETC2014-34690.

This paper presents an evolution on the configuration of a novel micro aerial vehicle (MAV) design, the Omnicopter MAV. The first generation Omnicopter prototype has an actuation system with eight degrees of freedom (DOFs) consisting of 5 brushless direct current (BLDC) motors and 3 servo motors. It is composed of a carbon fiber rod built airframe, 2 central counter-rotating coaxial propellers for thrust and yaw control, and 3 perimeter-mounted electric ducted fans (EDFs) with servo motors performing thrust vectoring. During the development of the second generation prototype, we simplified and 3D printed the frame to increase stiffness, robustness and manufacturability, and reduced the actuation DOFs from 8 to 7 by removing the top propeller and using just the bottom one for yaw control to improve performance. Flight controller and control allocator designs and test flight results for this new configuration are presented in this paper.

Topics: Design , Aircraft
Commentary by Dr. Valentin Fuster
2014;():V05AT08A093. doi:10.1115/DETC2014-34804.

Walking robots in practice are energy autonomy, so the high power density drive technology is crucial in robotics. In this paper, two approaches are proposed to increase power density of a novel hydraulic quadruped robot. One is that, a hybrid actuator is invented to make the simplest hydraulic system for robot. The structure and feature of the actuator is described in detail. The other is to reduce installed capacity by optimizing flow requirement. The factors that contribute to flow rate are analyzed. The experiment results show that the quadruped robot with the simplest hydraulic system works stably and reliably.

Topics: Robots , Power density
Commentary by Dr. Valentin Fuster
2014;():V05AT08A094. doi:10.1115/DETC2014-35061.

This paper presents an omnidirectional drive system. The design presented here involves a spinning hemispherical wheel mounted on a gimbal. The wheel operates at its singularity point when in the “neutral” or static position. As the gimbal is tilted, the wheel provides a thrust vector to the vehicle. The tilt determines the effective radius of the wheel, which in turn determines the amount of power that can be transmitted for motion. The paper presents the design and kinematic and inverse kinematics analysis of a singularity drive mechanism.

Vehicles can have single or multiple singularity drive mechanisms to achieve increasing levels of maneuverability. From a control standpoint, each singularity drive is kinematically decoupled from other drives on the same vehicle. Vehicles with one, two and three singularity drive mechanisms are introduced and some experimental results are presented.

Topics: Kinematics
Commentary by Dr. Valentin Fuster
2014;():V05AT08A095. doi:10.1115/DETC2014-35069.

There has been continuous research and development to add more actuators into robotic hands to increase their dexterity. However, dexterous hands require complex control and are more costly to build. Therefore, many researchers and commercial enterprises have begun developing under-actuated robotic hands with fewer actuators and passive mechanical adaptation to not only reduce complexity and cost, but to also achieve better grasp performance in unstructured settings. This paper presents the design and analysis of the Valkyrie hand — a four fingered, tendon-driven, and under-actuated robotic hand that balances dexterity and simplicity with total 14 joints, and six degrees of actuated freedom. A derivation is provided of general dynamic and static equations for the analysis of a tendon driven mechanism, based on Euler-Lagrange formulation. The equations were used to evaluate the design parameters’ impact on the hand grasp shape and closing effort, and also validated against a design case study.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A096. doi:10.1115/DETC2014-35109.

As mobile robotic systems advance, they become viable technologies for automating manufacturing processes in fields that traditionally have not seen much automation. Such fields include shipbuilding, windmill, tank, and pipeline construction. Some of the manufacturing tasks in these fields 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 consider the metrics that can be used in evaluating mobile robot designs for welding tasks based on kinematic and dynamic characteristics. The approach is based on a representation of the weld task and robot capabilities as a pair of n-dimensional subsets in the Euclidean n-space, where the weld task is considered a repetitive pattern constructed along the weld seam and both kinematic and dynamic characteristics are considered for the robot. The motivation is to allow different mobile manipulator designs to be measured using a direct geometric comparison of the capabilities of the robot to the requirements of the task. Three mobile welding platforms having different topological kinematic arrangements and will be evaluated based on this 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.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A097. doi:10.1115/DETC2014-35185.

A novel simplified analytical three-spheres intersection algorithm is presented for use with forward pose kinematics solutions of a four-cable-suspended robot (the method is applicable to various other cable-suspended robots with equal pole heights and three cables intersecting in one point). It is required that the vertical center heights of all three spheres are equal (otherwise one can use the existing more-complicated algorithm). We derive this new algorithm and show that the multiple solutions, algorithmic singularity, and imaginary solutions do not cause any trouble in practical implementation. The algorithmic singularity of the original three-spheres intersection algorithm regarding equal Z heights is eliminated with the new algorithm. The new algorithm requires significantly less computation compared with the original algorithm. Examples are presented to demonstrate the new three-spheres intersection algorithm for a 4-cable robot.

Commentary by Dr. Valentin Fuster
2014;():V05AT08A098. doi:10.1115/DETC2014-35330.

This paper presents a general solution to the direct static problem of a planar body suspended from two cables. First, the conditions for static equilibrium are stated and a mathematical formulation of the problem is derived. A twelfth degree univariate polynomial is then obtained using the resultant of two intermediate polynomials. It is shown that up to twelve real solutions can be obtained, thereby confirming that the polynomial is of minimal degree. Since the condition used in the derivation is necessary but not sufficient, the roots must be tested a posteriori for validity. Simple mathematical conditions are provided that allow such a verification. Finally, two examples are provided to illustrate the results and highlight the importance of the proposed root validation procedure.

Topics: Cables
Commentary by Dr. Valentin Fuster
2014;():V05AT08A099. doi:10.1115/DETC2014-35501.

This paper proposes a real-time robust localization scheme for mobile robots in indoor environments, based on the recognition of omnidirectional artificial landmarks captured by a single onboard camera. Considering the need of omnidirectional recognition and the disturbance of lighting condition, we encode the landmark identity with nested circles in black and white. The recognition algorithm consists of a global and a local recognition layers. The global recognition is a fast overall recognition process, including light detection, image clustering, region of interest (ROI) extraction, and ROI identification. If the number of identified ROIs does not meet the requirement of the localization algorithm, the local recognition will process those unidentified ROIs through adaptive ROI expansion and template cutting. Based on the landmark recognition, the absolute position and orientation of the camera in the environment are estimated using the geometric mapping between the image and global frames. The proposed approach is tested via experiments in a real indoor environment, and the result reveals high localization robustness and consistency to the lighting condition.

Topics: Mobile robots
Commentary by Dr. Valentin Fuster

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