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ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V05AT00A001. doi:10.1115/DETC2017-NS5A.
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This online compilation of papers from the ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

41st Mechanisms and Robotics Conference: Awards

2017;():V05AT08A001. doi:10.1115/DETC2017-67440.

We present a design technique for generating rigidly foldable quadrilateral meshes, taking as input four arrays of direction angles and fold angles for horizontal and vertical folds. By starting with angles, rather than vertex coordinates, and enforcing the fold-angle-multiplier condition at each vertex, it is possible to achieve arbitrarily large and complex panel arrays that flex from unfolded to flatly folded with a single degree of freedom. Furthermore, the design technique is computationally simple, reducing for some cases to a simple linear programming problem. The resulting mechanisms have applications in architectural facades, furniture design, and more.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A002. doi:10.1115/DETC2017-67992.

This paper presents a new mechanics-based framework for the qualitative analysis and conceptual design of mechanical meta-materials. The methodology is inspired by recent advances in the insightful synthesis of compliant mechanisms by visualizing a kinetostatic field of forces that flow through the mechanism geometry. The framework relates load flow behavior in the microstructure geometry to the global behavior of the materials, such as auxetic (negative poisson’s ratio), high bulk modulus, and high shear modulus. This understanding is used to synthesize and demonstrate novel planar microstructures that exhibit negative poisson’s ratio behavior. Furthermore, the paper identifies three unique classes of qualitative design problems for planar mechanical microstructures that can be potentially solved using this framework.

Topics: Design , Metamaterials
Commentary by Dr. Valentin Fuster

41st Mechanisms and Robotics Conference: Compliant Mechanisms (A. Midha Symposium)

2017;():V05AT08A003. doi:10.1115/DETC2017-67270.

This paper mainly deals with the determinate design/synthesis of a class of symmetrical and monolithic flexure mechanisms. Each is composed of 6 identical in-plane wire beams with uniform square cross sections. These flexure stages can provide three out-of-plane tip-tilt-piston motions for applications in high-precision or miniaturisation environments. A generic symmetrical structure is proposed as first with a group of defined parameters considering constraint and non-interference conditions. Normalised static analytical compliance entries for the diagonal compliance matrix of a generic structure are derived and symbolically represented by the parameters. Comprehensive compliance analysis is then followed using the analytical results, and quick insights into effects of parameters on compliances in different directions are gained. Case studies without and with actuation consideration are finally discussed. As a second contribution, a physical prototype with three actuation legs is monolithically fabricated (using CNC milling machining), kinematically modelled and experimentally tested, which shows that the desired out-of-plane motion can be generated from the in-plane actuation.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A004. doi:10.1115/DETC2017-67346.

Most examples of structure controlled Tunable Stiffness Mechanisms (TSM) systems have two predefined settings of stiffness, e.g. bi-stiffness behavior, or they have a low range in tunable stiffness. In this research, this problem of control is overcome though optimization of a novel concentric circular tapered spring beam design with the novel design concept of changing the mode of deformation from bending to axial or shear. A Monte Carlo (MC) function is used with an analytical model — the unit load method of virtual work, to determine the optimum shape of two concentric tapered beams where the minimum stiffness is set, and the objective is to achieve linear and/or large stiffness change control. Three optimum designs were 3D printed, tested, and the stiffness vs. loading angle of control was validated with excellent correlation. The optimum design was obtained by changing the dominant loading modes.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A005. doi:10.1115/DETC2017-67357.

Radiofrequency ablation (RFA) is a common cancer treatment modality for patients who are ineligible for open surgery. There is a need for RFA electrodes that generate heating zones that closely match the geometry of typical tumors, especially for endoscopic ultrasound-guided (EUS) RFA. In this paper, the procedure for optimization of an RFA electrode is presented. First, a novel compliant electrode design is proposed. Next, a thermal ablation model is developed to predict the ablation zone surrounding an RFA electrode in biological tissue. Then, a multi-objective genetic algorithm is used to optimize two cases of the electrode geometry to match the region of destructed tissue to a spherical tumor of specified diameter. This optimization procedure is applied to an EUS-RFA ablation of pancreatic tissue. For a target 2.5cm spherical tumor, the optimal design parameters of the compliant electrode design were found. After simulating 40 generations of 50 designs per generation, both cases converged to optimal solutions. The objective functions were useful for simple electrode designs. For more complex electrode designs, the objective functions were unable to direct the design toward a 2.5cm sphere. The results of the optimization demonstrate how computational models combined with optimization can be used for systematic design of ablation electrodes. The optimization procedure may be applied to RFA of various tissue types for systematic design of electrodes that generate spherical ablation zones.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A006. doi:10.1115/DETC2017-67431.

The use of pseudo-rigid-body models in the analysis and design of compliant mechanisms has opened up the possibility of using various types of flexible elements within the same framework. In this paper, an idea for combining initially curved and straight beams within compliant mechanisms is developed to create a set of equations that can be easily used to analyze various designs and topologies. A pseudo-rigid-body model with three revolute joints is derived to approximate the behavior of initially-curved compliant beams, to go with another model previously presented for straight beams. The general kinematic and static equations for a single-loop mechanism are shown. Finally, this setup is used for the early-stage design of a compliant constant force mechanism to illustrate its application and comparisons with Finite Element Analysis for validation.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A007. doi:10.1115/DETC2017-67441.

Although reconfigurable rigid-body mechanisms have been extensively studied over two decades, their compliant counterparts have not received the similar attention yet. This paper aims to design a reconfigurable compliant four-bar mechanism with multiple operation modes. A planar equilateral four-bar mechanism is considered at its constraint singularity. The multiple operation modes of this linkage are kinematically exploited to design a reconfigurable compliant four-bar mechanism, which generates rotational or translational motions based on two actuated joints. Simulation is conducted to investigate the comprehensive kinematics of the reconfigurable compliant mechanism. A 3D printed prototype of the novel reconfigurable compliant mechanism at hand is presented.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A008. doi:10.1115/DETC2017-67458.

Braided pneumatic actuators (BPAs) are attractive for use in bio-robots because they offer many muscle-like properties, especially when compared to most other commercially available robotic actuators. Unfortunately, the same properties that make these actuators similar to muscles make them more difficult to control. One such actuator manufactured by Festo, the MXAM-10-AA, is frequently utilized in robotics because of its commercial availability, durability, and force capability. Although models for BPAs exist, the properties that make this actuator more durable also make its behavior less like other braided pneumatic actuators, especially for shorter actuator lengths. Length specific models that do exist for Festo fluidic muscles have numerous parameters that can only be found experimentally by taking hundreds to thousands of data points and performing a lengthy optimization process to fit parameter values for each actuator in the system. This lack of generalizability makes it difficult to build a new robot and begin testing new control systems without significant startup time and cost. The key contribution of this work is the development of a generalizable actuator model that accounts for the geometry and limitations of the actuator at shorter lengths. This empirical model relates internal pressure, strain, stretching or contracting state, and applied force on the MXAM-10-AA actuator. The model is scalable to different length actuators by measuring their resting length at zero pressure and their minimum contraction length at maximum air pressure, and can be used for feedforward length control. The model is evaluated on a robot leg with three joints and 6 actuators, each with different length. The developed controller, using the actuator model, controls the joints to within ± 3 degrees of the desired position for different desired torques only using internal actuator pressure feedback. We also demonstrate control speed by cycling a joint over 40 degrees of rotation at varying frequencies.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A009. doi:10.1115/DETC2017-67465.

In this paper, we introduce a new computational tool called the Boundary Learning Optimization Tool (BLOT) that rapidly identifies the boundary of the performance capabilities achieved by a general flexure topology if its geometric parameters are allowed to vary from their smallest allowable feature sizes to the largest geometrically compatible feature sizes for a given constituent material. The boundaries generated by the BLOT fully define a flexure topology’s design space and allow designers to visually identify which geometric versions of their synthesized topology best achieve a desired combination of performance capabilities. The BLOT was created as a complementary tool to the Freedom And Constraint Topologies (FACT) synthesis approach in that the BLOT is intended to optimize the geometry of the flexure topologies synthesized using the FACT approach. The BLOT trains artificial neural networks to create sufficiently accurate models of parameterized flexure topologies using the fewest number of design instantiations and their corresponding numerically generated performance solutions. These models are then used by an efficient algorithm to plot the desired topology’s performance boundary. A FACT-synthesized flexure topology is optimized using the BLOT as a case study.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A010. doi:10.1115/DETC2017-67512.

Short beams are the key building blocks in many compliant mechanisms. Hence, deriving a simple yet accurate model of their elastokinematics is an important issue. Since the Euler-Bernoulli beam theory fails to accurately model these beams, we use the Timoshenko beam theory to derive our new analytical framework in order to model the elastokinematics of short beams under axial loads. We provide exact closed-form solutions for the governing equations of a cantilever beam under axial load modeled by the Timoshenko beam theory. We apply the Taylor series expansions to our exact solutions in order to capture the first and second order effects of axial load on stiffness and axial shortening. We show that our model for beam flexures approaches the model based on the Euler-Bernoulli beam theory when the slenderness ratio of the beams increases. We employ our model to derive the stiffness matrix and axial shortening of a beam with an intermediate rigid part, a common element in the compliant mechanisms with localized compliance. We derive the lateral and axial stiffness of a parallelogram flexure mechanism with localized compliance and compare them to those derived by the Euler-Bernoulli beam theory. Our results show that the Euler-Bernoulli beam theory predicts higher stiffness. In addition, we show that decrease in slenderness ratio of beams leads to more deviation from the model based on the Euler-Bernoulli beam theory.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A011. doi:10.1115/DETC2017-67618.

A method is presented to optimize the shape and size of a passive prosthetic foot using the Lower Leg Trajectory Error (LLTE) as the design objective. The LLTE is defined as the root-mean-square error between the lower leg trajectory calculated for a given prosthetic foot by finding the deformed shape of the foot under typical ground reaction forces and a target physiological lower leg trajectory obtained from published gait data for able-bodied walking. In previous work, the design of simple two degree-of-freedom analytical models consisting of rigid structures, rotational joints with constant stiffness, and uniform cantilevered beams, have been optimized for LLTE. However, prototypes built to replicate these simple models were large, heavy, and overly complex. In this work, the size and shape of a single-part compliant prosthetic foot keel made out of nylon 6/6 was optimized for LLTE to produce a light weight, low cost, and easily manufacturable prosthetic foot design. The shape of the keel was parameterized as a wide Bézier curve, with constraints ensuring that only physically meaningful shapes were considered. The LLTE value for each design was evaluated using a custom MATLAB script, which ran ADINA finite element analysis software to find the deformed shape of the prosthetic keel under multiple loading scenarios. The optimization was performed by MATLAB’s built-in genetic algorithm. After the optimal design for the keel was found, a heel was added to structure, sized such that when the user’s full weight acted on the heel, the structure had a factor of safety of two. The resulting optimal design has a lower LLTE value than the two degree-of-freedom analytical models, at 0.154 compared to 0.172, 0.187, and 0.269 for the two degree-of-freedom models. At 412 g, the optimal wide curve foot is nearly half the mass of the lightest prototype built from the previous models, which was 980 g. The design found through this compliant mechanism optimization method is thus far superior to the two degree-of-freedom models previously considered.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A012. doi:10.1115/DETC2017-67677.

The human foot modulates its stiffness in different anatomical regions in order to attain greater efficiency and performance. The purpose of this study is to develop an adaptable robotic foot by biomimicking the human foot’s arch, horizontal tie and its ability of varying its stiffness. In this research we describe the design, modeling, development and optimization of the robotic foot with a novel Tunable Stiffness Mechanism (TSM) which acts as a horizontal tie. The TSM is made up of two concentric helical springs and the tunable stiffness feature is obtained by changing the parallel/series configuration of these springs. A flexible fiberglass composite arch is selected, and Multiobjective Design Optimization (MDO) is used to maximize the stiffness range and effectiveness of the system. Analytical modeling results closely match the experimental validation of both the tunable axial stiffness behavior of the TSM and tunable stiffness foot.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A013. doi:10.1115/DETC2017-67700.

This paper develops a new design of a compliant prosthetic ankle-foot 2.0. The ankle-foot is a composite made of glass-fiber reinforced plastic (GFRP). The finite element analysis is used to evaluate the structural behavior of the ankle-foot, including the deformation, stress and strain energy. The Taguchi method is used to build a special orthogonal array. By using a differential evolution algorithm, the geometric parameters of the ankle-foot are determined. The result indicated that the optimal strain energy is improved approximately 155%. The maximum energy strain of 93.914 mJ is recognized. The results also revealed that the prosthetic ankle-foot is becoming more flexible due to the compliant ankle. Lastly, the prosthetic ankle-foot was proved to be effective for a human body up to 100 kg.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A014. doi:10.1115/DETC2017-67812.

In this paper a first iteration of a new scoliosis brace design and correction strategy is presented using compliant shell mechanisms to create both motion and correction. The motion profile of the human spine was found using a segmented motion capture approach. The brace was designed for a case study using a conceptual ellipsoid design approach. The force controlled correction profile was re-invented using a two fold zero and positive stiffness profile. These force generators were built and validated to prove their zero stiffness characteristic. The kinematic part of the brace was detail designed with the correct order of magnitude and validated through their force-deflection characteristic. The end result was a first iteration of a new brace validated and analysed on some critical components which can form the basis for a future biomechanical study.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A015. doi:10.1115/DETC2017-67853.

This paper introduces a pseudo-rigid-body-model (PRBM) approach for analyzing the kinematics of a planar dual-backbone continuum robot. Unlike common load-displacement PRBM studies, the presented PRBM approach is tailor-made for the displacement-displacement analysis of compliant mechanisms, where the relationship between the lengths of the “backbone” wires and the pose of the robot is to be explored. Based on a PRB 3R modelling, the forward kinematics of the robot can be formulated as a nonlinear system of eight equations. To validate the accuracy and efficiency of the approach, a series of case studies are performed via ANSYS simulation and experiments. The results show that 1) the computation time for solving forward kinematics via the PRB 3R approach is less than 0.16% of that via ANSYS simulation; 2) the maximum percentage position errors of the PRB 3R model are 0.47% and 1.96% in the x- and y-directions, respectively; and 3) the maximum percentage orientation error of the PRB 3R model is 2.23%, as compared with ANSYS simulation results. As a result, the proposed PRBM approach delivers a satisfied compromise between accuracy and efficiency for the kinematic analysis of the planar dual-backbone continuum robot.

Topics: Kinematics , Robots
Commentary by Dr. Valentin Fuster
2017;():V05AT08A016. doi:10.1115/DETC2017-67970.

For soft robots to be utilized in medical devices, locomotion, industrial automation, and a number of other fields, they require accurate and computationally efficient models that capture both the kinetic behavior and inherent non-linearity. Fiber reinforcement enables soft robots to create useful motions, such as rotation, but poses additional complexity in modeling. The purpose of this paper is to present a constitutive model that relates the kinematic behaviour of a pneumatic fiber-reinforced soft actuator with its torsional loading. This model has the advantage of requiring minimal experimental parameter determination, being inclusive of torsional loads, without requiring large-scale computing systems. Experimental data in multiple kinematic configurations shows agreement between the models moment prediction and the moments that the actuators generate.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A017. doi:10.1115/DETC2017-68019.

Dynamic performance is of great importance to compliant mechanisms which are employed in dynamic applications, especially if the dynamic problems in DOC (degree of constraint) directions are to be met. An investigation on the dynamic characteristics of a 2R compliant mechanism is presented. Based on the substructure techniques, the in-plane dynamic model of the preceding compliant mechanisms is developed. The natural frequencies and sensitivities are then analyzed. The numerical result verifies the validity of the proposed method. Finally, optimal design of compliant mechanism is investigated.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A018. doi:10.1115/DETC2017-68097.

In the present paper, we take the input and output decoupling into account and propose a 2-DOF parallel nanopositioner, which is composed of lever amplification mechanisms, compound parallelogram mechanisms and novel crosshair flexures. In order to demonstrate the decoupling performance improvement of the crosshair flexures, the stiffness model of the crosshair flexures and the kinetostatics model of the nanopositioner are established based on Castigliano’s theorem and the compliance matrix method. Accordingly, the input and output decoupling compliance matrix models are derived to demonstrate the excellent decoupling property of the crosshair flexures based nanopositioner, which is further verified by finite-element analysis and experimental results. The open-loop experiments on the prototype stage demonstrate the maximum stroke of the nanopositioner is up to 65μm and the cross axis coupling errors are less than 1.6%.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A019. doi:10.1115/DETC2017-68113.

A method for decoupling joint stiffness and joint position for simple mechanisms was developed. This method was then demonstrated on a powered ankle prosthesis. Linear and circular mechanisms were fit to the resulting data to simplify the required actuator output. The resulting performance of desired ankle moment with corresponding ankle angle was shown to be highly correlated with able bodied walking data.

Topics: Prostheses , Stiffness
Commentary by Dr. Valentin Fuster
2017;():V05AT08A020. doi:10.1115/DETC2017-68142.

This paper mainly concentrates on the design and analysis of the annulus with zero thermal expansion coefficient (ZTE) aiming to solve the heat generation and deformation in high speed bearing. First, a fork-like lattice cell inspired by the basic triangular cell is put forward and further applied to construct an annulus. The stretch-dominated lattice cell utilizes the Poisson’s contraction effect to achieve the tailorable thermal expansion coefficient (CTE). The thermal behaviors differences between the continuous interfaces and lattice cells will lead to the internal stress. Thus, the CTE of the annulus consisting of the lattice cell can be tailored to zero even negative values through the offset between the thermal-strain and force-strain. Then a theoretical model is established with some appropriate assumptions to reveal the quantitative relations among the geometrical parameters, material properties and equivalent CTEs thoroughly. The prerequisites for realizing a zero CTE are further derived in terms of material limitations and geometric constraints. Finally, FEA method is implemented to verify and analyze the thermal behaviors of annulus. The proposed annulus design characterized by the CTE tunability, structure efficiency and continuous interfaces is hopefully to be applied in the high speed bearings, adapters between the shaft and collar and fastener screws.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A021. doi:10.1115/DETC2017-68205.

Although energy-based methods have advantages over the Newtonian methods for kinetostatic modeling, the geometric nonlinearities inherent in deflections of compliant mechanisms preclude most of the energy-based theorems. Castigliano’s first theorem and the Crotti-Engesser theorem, which don’t require the problem being solved to be linear, are selected to construct the energy-based kinetostatic modeling framework for compliant mechanisms in this work. Utilization of these two theorems requires explicitly formulating the strain energy in terms of deflections and the complementary strain energy in terms of loads, which are derived based on the beam constraint model. The kinetostatic modeling of two compliant mechanisms are provided to demonstrate the effectiveness of using Castigliano’s first theorem and the Crotti-Engesser theorem with the explicit formulations in this framework. Future work will be focused on incorporating use of the principle of minimum strain energy and the principle of minimum complementary strain energy.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A022. doi:10.1115/DETC2017-68423.

A method is presented to analyze stress in ambient-temperature, fixed-free compliant segments subjected to end load or displacement boundary conditions. The analysis method outlined herein relies on key outputs from the pseudo-rigid-body models (PRBMs). Simplified equations for stress are presented for both homogeneous and metallic-reinforced segments. Stresses in both the polymer compliant segment and the metallic reinforcing element are addressed to enable a comprehensive stress analysis method. The stress analysis method is exemplified by using two design cases: one, a homogeneous compliant segment, and two, a compliant segment reinforced with a spring steel element. The results showed that introducing a metallic reinforcement increases the flexural rigidity, but does not reduce the bending stress in the casing unless the cross-sectional thickness is reduced. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A023. doi:10.1115/DETC2017-68425.

A method based on the pseudo-rigid-body model (PRBM) is presented for the analysis of stress in metallic-reinforced, small-length flexural pivot (SLFP) compliant segments, subjected to end loads or displacement boundary conditions. The analysis method provides the designer with a tool to ensure that stress levels are maintained that are appropriate for the intended application and materials of construction. Simplified equations for stress are presented for both homogeneous polymer and metallic-reinforced composite segments, where the reinforcement shares a neutral axis with a polymer casing. The method is exemplified with two case studies, one, a homogeneous compliant segment, and, two, the segment reinforced with spring steel. The introduction of metallic reinforcement increases the flexural rigidity, but does not reduce the bending stress in the casing of a small-length flexural pivot unless the cross-sectional thickness is reduced. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A024. doi:10.1115/DETC2017-68426.

A method is provided and validated for redesigning compliant segments to improve their fatigue, creep, and stress relaxation performance. The method reduces the bending stress in the polymer portion of the compliant segment without the need for overall mechanism redesign, by introducing metallic reinforcement and by matching the force-deflection response of the redesigned segment to that of the baseline segment. An example redesign case study is presented and validated with experimental testing using a unique deflection testing device designed for fixed-free compliant mechanisms. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

Commentary by Dr. Valentin Fuster

41st Mechanisms and Robotics Conference: Dynamics and Control of Robotic Systems

2017;():V05AT08A025. doi:10.1115/DETC2017-67130.

It is difficult for a space robot to perform autonomous relative navigation of a non-cooperative space target using only a single line-of-sight measurement. To solve this problem, a decentralized-centralized relative navigation method based on multiple space robots in a leader-follower formation is proposed. All the leader and follower robots observe the same space target and combine their estimates to obtain an improved estimate of the target motion. The relative navigation filter of each leader and follower robot is independently implemented based on non-dimensional invariant sets of Hill-Clohessy-Wiltshire (HCW) equations. The invariant sets of relative motion between the follower and leader space robots are known due to their mutual cooperation, and are used in this research as state equality constraints to improve the estimate of the target motion. Numerical simulations show the feasibility of the proposed method, and the results indicate that the constrained state estimation accuracy of the space target is improved compared to unconstrained state estimation.

Topics: Robots , Navigation
Commentary by Dr. Valentin Fuster
2017;():V05AT08A026. doi:10.1115/DETC2017-67328.

Variation occurs in many closed loop multi-body dynamic (MBD) systems in the geometry, mass, or forces. Understanding how MBD systems respond to variation is imperative for the design of a robust system. However, simulation of how variation propagates into the solution is complicated as most MBD systems cannot be simplified into to a system of ordinary differential equations (ODE). This paper investigates polynomial chaos theory (PCT) as a means of quantifying the effects of uncertainty in a closed loop MBD system governed by differential algebraic equations (DAE). To demonstrate how PCT could be used, the motion of a two link slider-crank mechanism is simulated with variation in the link lengths. To validate and show the advantages and disadvantages of PCT in closed loop MBD systems, the PCT approach is compared to Monte Carlo simulations.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A027. doi:10.1115/DETC2017-67543.

Six-legged robots are reliable locomotive machines with actuation redundancy. This paper analyzes the force and velocity capacities of a six-legged high-payload robot geometrically and numerically. The full-body Jacobian between the body platform and the actuation is first of all computed. A geometric computation approach is then proposed to obtain the robot velocity/force polytopes in the platform operational space. System physical constraints of joint torques and velocities are taken into account so that the task space capacities could be quantitatively given. Besides, several capacity indices are also investigated, including the maximum velocity/force magnitude, the maximum velocity/force along a given direction and the maximum isotropic velocity/force. At last, the robot capacities are numerically analyzed with different supporting legs. The results verify high payload capacity of the robot and clarify the influence of different gait parameters on the task space performance. Our method is proposed in a general and convenient framework, and therefore it is beneficial for the quantitative performance evaluation of any multi-legged walking machine with actuation redundancy.

Topics: Machinery
Commentary by Dr. Valentin Fuster
2017;():V05AT08A028. doi:10.1115/DETC2017-67546.

In this paper the functional redundancy of a spherical parallel manipulator performing a pointing task is exploited to optimize its posture upon minimizing dynamic index. A general method to derive the inertia matrix reduced to the mobile platform via screw theory is presented. This matrix encases geometrical and inertial information of all the bodies and it allows a simple computation of dynamic indices due to its feature of being dependent only on the pose of the robot. The indices are used to compute the objective function of the optimization problem, while the orientation of the pointing task constitutes the constraint equations. The posture-optimization is used as a redundancy-resolution and it is extended to any pointing direction. Optimal postural maps are obtained and then used to drive the optimal planning of pointing trajectories by using Bézier curves. To this aim, a higher level optimization problem than previous one is solved and inverse dynamic simulations are conducted to verify the results.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A029. doi:10.1115/DETC2017-67721.

This paper presents a design process based on an advanced flexible robots modeling tool associated with realistic actuators models and pre-defined control architecture. This process implements dedicated feasibility and performance indicators, which are used to evaluate a design and its sensitivity on the considered parameters. The proposed approach is illustrated with theoretical and experimental results obtained with the YAKA robot.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A030. doi:10.1115/DETC2017-67754.

Being different from uncontrolled and unpowered biped, an underactuated compass-gait bipedal robot is the one actuated at the ankle. Energy is inputted to control the gait of biped. Based on kinetic energy shaping, controlling and anti-controlling of chaotic gait are investigated in this paper. In order to provide energy at proper instant, the energy shaping function is modified as Display Formulaksinθ1+θ0θ.12. This modification permits of taking the characteristic of gait of the biped into consideration by taking the best initial phase as initial phase, i.e. Display Formulaθ0=θ0*. The results of simulation show that the control scheme Display Formulaksinθ1+θ0θ.12 is efficient in controlling and anti-controlling chaotic gait.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A031. doi:10.1115/DETC2017-67766.

This paper presents a computational method for formulating and solving the dynamical equations of motion for complex mechanisms and multibody systems. The equations of motion are formulated in a preconditioned form using kinematic substructuring with a heuristic application of Generalized Coordinate Partitioning (GCP). This results in an optimal split of dependent and independent variables during run time. It also allows reliable handling of end-of-stroke conditions and bifurcations in mechanisms, thereby facilitating dynamic simulation of paradoxical linkages such as Bricard’s mechanism that has been known to cause problems with some multibody dynamic codes. The new Preconditioned Equations of Motion are then solved using a recursive formulation of the Schur Complement Method combined with Sparse Matrix Techniques. In this fashion the Preconditioned Equations of Motion are recursively uncoupled and solved one kinematic substructure at a time. The results are demonstrated using examples.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A032. doi:10.1115/DETC2017-67949.

In this paper, we present new Pseudo-Rigid-Body (PRB) models for clamped-free cantilever beams and pinned-free compliant links for predicting natural frequency in dynamics analysis. In recent decades, PRB models have been extensively studied for predicting statics and kinematics of 2D or 3D beams subject to large deformation under tip loads. However, few studies focus on their accuracy for predicting dynamic analysis. Not like in statics and kinematics, the mass distribution of PRB model plays an important factor in dynamics of compliant beams. In this paper, we introduce mass property parameters to the PRB models. By comparing with the continuous model, we search for the optimal set of mass property parameters for minimizing the error of natural frequency. To demonstrate the procedure, we study two cases: clamped-free cantilever beams and pinned-free compliant links both have an end mass. The results show that the natural frequency of the optimized PRB model well agrees with that from the continuous beam model. The modified PRB model will significantly simplify the dynamics modeling in compliant mechanisms.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A033. doi:10.1115/DETC2017-68011.

The paper introduces a new, intrinsically discrete, path planning and collision-avoidance problem, with multiple robots and multiple goals. The issue arises in the operation of the novel Swing and Dock (SaD) locomotion for a material handling system. Its agents traverse a base grid by sequences of rotations (swings) around fixed pins. Each agent must visit an array of goal positions in minimal time while avoiding collisions. The corresponding off-line path-planning problem is NP-hard. We model the system by an extended temporal graph and introduce two integer linear programming (ILP) formulations for the minimization of the makespan, with decision variables on the nodes and the edges, respectively. Both optimizations are constrained and favor idling over detours to reduce mechanical wear. The ILP formulations, tailored to the SaD system, are general enough to be applicable for many other single- and multi-agent problems over discretized networks. We have implemented the ILPs with a gurobi solver. Computational results demonstrate and compare the effectiveness of the two formulations.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A034. doi:10.1115/DETC2017-68074.

Series Elastic Actuators (SEA) have been in development for multiple decades. In spite of this, few design guidelines exist and stiffness selection for the compliant element still remains a trial-and-error process. In this paper, we experimentally validated the unlumped model first proposed by Orekhov for Rotary SEA (RSEA) and outlined a design methodology for selecting the spring stiffness based on the open loop force control bandwidth of unlumped model for series elastic actuators. We modified the unlumped model to apply to Rotary SEAs. Through experimental system identification, we demonstrated that our new unlumped model for RSEA is a valid model of actuator dynamics. Additionally, we recommended design guidelines for RSEA to achieve desired force control bandwidth based on the pure torque source assumption. An example of the design process was given and actuator performance was verified through dynamic simulations in ADAMS.

Topics: Actuators , Design
Commentary by Dr. Valentin Fuster
2017;():V05AT08A035. doi:10.1115/DETC2017-68272.

A novel theoretical framework for the identification of the balance stability regions of biped systems is implemented on a real robotic platform. With the proposed method, the balance stability capabilities of a biped robot are quantified by a balance stability region in the state space of center of mass (COM) position and velocity. The boundary of such a stability region provides a threshold between balanced and falling states for the robot by including all possible COM states that are balanced with respect to a specified feet/ground contact configuration. A COM state outside of the stability region boundary is the sufficient condition for a falling state, from which a change in the specified contact configuration is inevitable. By specifying various positions of the robot’s feet on the ground, the effects of different contact configurations on the robot’s balance stability capabilities are investigated. Experimental walking trajectories of the robot are analyzed in relationship with their respective stability boundaries, to study the robot balance control during various gait phases.

Topics: Stability , Robots
Commentary by Dr. Valentin Fuster
2017;():V05AT08A036. doi:10.1115/DETC2017-68312.

Skid steer mobile robots (SSMR) are platforms with simplistic mechanical drives readily adapted for a variety of applications. Skid Steer robots require slipping when navigating general paths. This slipping behavior is a function of surface conditions (friction) as well as robot motion and forces (system dynamics). Slipping affects motion along the path as well as drive torques and power consumption and is therefore an important consideration in robot design. Slipping can be characterized through the instant centers of rotation of the contact patches of the left and right tracks, and it has been shown that these are functions of the system dynamics. Therefore, prediction of system dynamics is needed to better evaluate robot slipping behavior during run time. In this paper, these instant center locations are called the slip parameters. In particular, the paper looked at two alternative models for the slip parameters, one a kinematic estimate assuming constant slip behavior for a class of tasks and the other a dynamic estimate which predicts slip parameters to lie on continuous, closed curves that vary in size relative to payload conditions. Each of these models for slip parameters have been presented in the previous literature, but this paper experimentally tests the slipping for track-based SSMR’s and compares these results to the kinematic and dynamic estimates. This paper will evaluate the validity of each model through real-time tracking and will improve understanding of slip behavior during typical manufacturing tasks. The paper will then present guidelines for the design of SSMR systems based on knowledge of ICR behavior.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A037. doi:10.1115/DETC2017-68540.

This paper presents the kinematics and dynamics of a spherical robot with a mechanical driving system that consists of four cable-actuated moving masses. Four cable-pulley systems control four tetrahedrally-located movable masses and the robot functions by shifting its center of mass to create rolling torque. The cable actuation decreases overall mass and, therefore, allow for less energy expenditure, as compared to other moving mass mechanisms that translate the masses by powered-screws. Additionally, the design allows the center of mass for the static (spherical shell, electronics, motors etc.) and dynamic mass (moving masses) to be at the geometric center at any given time, therefore has potential for tumbleweeding when needed. The derived equations of motion are verified by means of simulations.

Topics: Robots , Cables , Design
Commentary by Dr. Valentin Fuster

41st Mechanisms and Robotics Conference: Mechanism Synthesis and Analysis

2017;():V05AT08A038. doi:10.1115/DETC2017-67174.

Schoenflies-motion generators (SMGs) are 4-degrees-of-freedom (dof) manipulators whose end effector can perform translations along three independent directions, and rotations around one fixed direction (Schoenflies motions). Such motions constitute the 4-dimensional (4-D) Schoenflies subgroup of the 6-D displacement group. The most known SMGs are the serial robots named SCARA. Pick-and-place tasks are typical industrial applications that SMGs can accomplish. In the literature, 3T1R parallel manipulators (PMs) have been also proposed as SMGs. Here, a somehow novel 3T1R PM is presented and studied. Its finite and instantaneous kinematics are analyzed in depth, and analytic and geometric tools that are useful for its design are presented. The proposed SMG has a single-loop not-overconstrained architecture with actuators on or near the base and can make the end effector perform a complete rotation.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A039. doi:10.1115/DETC2017-67203.

The paper presents a simple and effective kinematic model and methodology, based on Ting’s N-bar rotatability laws [2629], to assess the extent of the position uncertainty caused by joint clearances for any linkage and manipulators connected with revolute or prismatic pairs. The model is derived and explained with geometric rigor based on Ting’s rotatability laws. The significant contribution includes (1) the clearance link model for P-joint that catches the translation and oscillation characteristics of the slider within the clearance and separates the geometric effect of clearance from the input error, (2) a simple uncertainty linkage model that features a deterministic instantaneous structure mounted on non-deterministic flexible legs, (3) the generality of the method, which is effective for multiloop linkages and parallel manipulators.

The discussion is carried out through symmetrically constructed planar eight-bar parallel robots. It is found that the uncertainty region of a three-leg parallel robot is enclosed by a hexagon, while that of its serial counterpart is enclosed by a circle inscribed by the hexagon. A numerical example is also presented. The finding and proof, though only based on three-leg planar 8-bar parallel robots, may have a wider implication suggesting that based on kinematics, parallel robots tends to inherit more position uncertainty than their serial counterparts. The use of more loops in parallel robots cannot fully offset the adverse effect on position uncertainty caused by the use of more joints.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A040. doi:10.1115/DETC2017-67284.

A family of reconfigurable parallel robots can change motion modes by passing through constraint singularities by locking and releasing some passive joints of the robot. This paper is about the kinematics, the workspace and singularity analysis of a 3-PRPiR parallel robot involving lockable Pi and R (revolute) joints. Here a Pi joint may act as a 1-DOF planar parallelogram if its lockable P (prismatic) joint is locked or a 2-DOF RR serial chain if its lockable P joint is released. The operation modes of the robot include a 3T operation modes to three 2T1R operation modes with two different directions of the rotation axis of the moving platform. The inverse kinematics and forward kinematics of the robot in each operation modes are dealt with in detail. The workspace analysis of the robot allow us to know the regions of the workspace that the robot can reach in each operation mode. A prototype built at Heriot-Watt University is used to illustrate the results of this work.

Topics: Kinematics , Robots
Commentary by Dr. Valentin Fuster
2017;():V05AT08A041. doi:10.1115/DETC2017-67302.

Large-scale forging manipulator is the indispensable equipment in the operations of automated forging. Because of the increasing demand of forging manipulator, large and medium-sized enterprises pay more and more attention to the forging operation in production. Lower freedom parallel mechanism is obtained by using the constraint-synthesis method based on the screw theory, then a mechanism of forging manipulator is designed including raising and lowering, pitching, lateral swing, lateral movement, forth or back and clamp rotation. The new type forging manipulator is a hybrid serial-parallel mechanism. The degree of freedom of the parallel mechanism is calculated by using the modified Grübler-Kutzbach criterion, and then the degree of freedom of the machine is determined. Through closed geometric method, the kinematic position analysis is performed, and the correctness of the theoretical analysis results is verified.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A042. doi:10.1115/DETC2017-67322.

Mathematical modeling is an important part of the engineering design cycle. Most models require application specific input parameters that are established by calculation or experiment. The accuracy of model predictions depends on underlying model assumptions as well as how uncertainty in knowledge of the parameters is transmitted through the mathematical structure of the model. Knowledge about the relative impact of individual parameters can help establish priorities in developing/choosing specific parameters and provide insight into a range of parameters that produce ‘equally good’ designs. In this work Global Sensitivity Analysis (GSA) is examined as a technique that can contribute to this insight by developing Sensitivity Indices, a measure of the relative importance, for each parameter. The approach is illustrated on a kinematic model of a metamorphic 4-bar mechanism. The model parameters are the lengths of the four links. The results of this probabilistic analysis highlight the synergy that must exist between all four link lengths to create a design that can follow the desired motion path. The impact of individual link lengths, however, rises and falls depending on where the mechanism is along its motion path.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A043. doi:10.1115/DETC2017-67468.

Presented in this paper is a method for force analysis of a single-input multiple-output (SIMO) linkage array that is designed for curve morphing applications, such as morphing airfoils. Different from the existing force methods, this method is developed to determine the force of a single actuator at the front that is needed to resist the forces on each loop for the entire multiloop linkage system. The proposed method is based on a full force model of a single loop four-bar linkage. When this model is applied to a multiloop system, two force sources are considered for each loop, namely the external point force on the coupler and the internal transition torque from the proceeding loop. As a result, a recursive method is proposed to compute the force from the last loop through intermediate loops to the first loop. The force vector of the first loop represents the required force of the single actuator needed to counteract the forces experienced by all the coupler forces. A number of simulations are performed and compared with FEM results to prove its effectiveness.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2017;():V05AT08A044. doi:10.1115/DETC2017-67469.

The classic Burmester problem is concerned with computing dimensions of planar four-bar linkages consisting of all revolute joints for five-pose problems. In the context of motion generation, each pose can be seen as a constraint that the coupler of a planar four-bar mechanism needs to interpolate or approximate through. We define extended Burmester problem as the one where all types of planar four-bars consisting of dyads of type RR, PR, RP, or PP (R: revolute, P: prismatic) and their dimensions need to be computed for n-geometric-constraints, where a geometric constraint can be an algebraically expressed constraint on the pose, or location of the fixed or moving pivots or something equivalent. In addition, we include both linear and non-linear and exact and approximate constraints. This extension also includes the problems where there is no solution to the classic Burmester problem, but designers would still like to design a four-bar that may come closest to capturing their intent. Such problems are representative of the problems that machine designers grapple with while designing linkage systems for a variety of constraints, which are not merely a set of poses.

Recently, we have derived a unified form of geometric constraints of all types of dyads (RR, RP, PR, and PP) in the framework of kinematic mapping and planar quaternions, which map to generalized manifolds (G-manifolds) in the image space of planar displacements. The given poses map to points in the image space. Thus, the problem of synthesis is reduced to minimizing the algebraic error of fitting between the image points and the G-manifolds. We have also created a simple, two-step algorithm using Singular Value Decomposition (SVD) for the least-squares fitting of the manifolds, which yields a candidate space of solution. By imposing two fundamental quadratic constraints on the candidate solutions, we are able to simultaneously determine both the type and dimensions of the planar four-bar linkages.

In this paper, we present 1) a unified approach for solving the extended Burmester problem by showing that all linear- and non-linear constraints can be handled in a unified way without resorting to special cases, 2) in the event of no or unsatisfactory solutions to the synthesis problem certain constraints can be relaxed, and 3) such constraints can be approximately satisfied by minimizing the algebraic fitting error using Lagrange Multiplier method. In doing so, we generalize our earlier formulation and present a new algorithm, which solves new problems including optimal approximate synthesis of Burmester problem with no exact solutions.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2017;():V05AT08A045. doi:10.1115/DETC2017-67527.

Equivalent four-bar linkage has been proved to be a simple and general approach for the identification of the singularity (dead center position) of single-DOF complex planar linkages. Based on the concept of equivalent four-bar linkage, this paper proposes the concept of equivalent five-bar linkage and extend this concept to analyze the singularity (dead center position) of three different topologies of two-DOF seven-bar planar linkages for the first time. The five links chosen from the two-DOF seven-bar linkage compose one equivalent five-bar linkage. A singular position may happen when the three passive joints of one equivalent five-bar linkage become collinear. When the equivalent five-bar linkage is at the singular position, the whole two-DOF seven-bar planar linkage must be also at the position of singularity. The propose method offers another geometric insights for the singularity analysis of two-DOF seven-bar planar linkages and other multiple-DOF planar linkages.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2017;():V05AT08A046. doi:10.1115/DETC2017-67549.

This paper presents the contribution of Offer Shai to mechanical engineering and design. Over a period of three decades Shai has created an impressive research program that is founded on solid mathematical grounds — combinatorial representations of systems. On this foundation he made contributions that ranged from inventing new concepts in mechanics (e.g., face force), new ways to characterize systems (e.g., singularity positions), new ways to create building blocks to model discrete systems (e.g., Assur graphs and their synthesis), and new methods in design (e.g., infused design). This paper summarizes some of these contributions in an attempt to describe the breadth and depth and attract researchers to continue develop his ideas.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A047. doi:10.1115/DETC2017-67565.

The kinematic synthesis of planar linkage mechanisms has traditionally been broken into the categories of motion, path and function generation. Each of these categories of problems has been solved separately. Many problems in engineering practice require some combination of these problem types. For example, a problem requiring coupler points and/or poses in addition to specific input and/or output link angles that correspond to those positions. A limited amount of published work has addressed some specific underconstrained combinations of these problems. This paper presents a general graphical method for the synthesis of a four bar linkage to satisfy any combination of these exact synthesis problems that is not over constrained. The approach is to consider the constraints imposed by the target positions on the linkage through the poles and rotation angles. These pole and rotation angle constraints are necessary and sufficient conditions to meet the target positions. After the constraints are made, free choices which may remain can be explored by simply dragging a fixed pivot, a moving pivot or a pole in the plane. The designer can thus investigate the family of available solutions before making the selection of free choices to satisfy other criteria. The fully constrained combinations for a four bar linkage are given and sample problems are solved for several of them.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A048. doi:10.1115/DETC2017-67768.

For many fully parallel robots, the number of legs is generally equal to the number of degrees of freedom, with one actuated joint per leg. However, another subset of robots exists in which there are fewer legs and more actuated joints per leg. This paper presents a method of mounting rotary actuators on the fixed platform such that no actuator mass is added to the moving links. Examples of 6-DOF parallel robot variants are given based on this technique, with inverse kinematics, and the scope of extensibility to other topologies is briefly described.

Topics: Robots , Actuators
Commentary by Dr. Valentin Fuster
2017;():V05AT08A049. doi:10.1115/DETC2017-67832.

In this paper we present a computational approximate synthesis procedure for the planar RR chain. Our approach is based on a grid search and takes an arbitrary amount of user-defined task positions for the two outer bodies of the chain and restrictions for both joints into account. The result of this synthesis approach is not only one optimal solution, but a list of several possible solutions which are ranked according to their performance. The approach aims at being used in building block-based synthesis procedures of more complex linkages. The method shall later be included into a CAD-integrated design tool for planar linkages.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A050. doi:10.1115/DETC2017-67905.

Mixed-position synthesis of linkages has been used to define local contact conditions and for better adjusting a mechanism to its desired trajectory. In this work, multiple velocities are defined at a configuration in order to fully specify the subspace of twists of the end-effector at that point, and also to specify lower-dimensional subspaces of twists. This is applied to the spatial 3R chain, for which the equations are developed in detail.

Topics: Chain
Commentary by Dr. Valentin Fuster
2017;():V05AT08A051. doi:10.1115/DETC2017-68116.

This paper introduces several complexity-based criteria for walking robots at the preliminary design stage. The motivation lies in filtering optimal leg types or body layouts to reduce cost at later iterative-design stage. Several qualitative or semi-quantitative criteria are proposed for walking robot designers. For different type-synthesis results of robot legs, three criteria are proposed named the uncertainty of the end-effector, the complexity of control and the complexity of movement. For different layouts of robot bodies, two kinematic criteria are proposed named the complexity of translation and the complexity of rotation. These criteria could together judge the kinematic performance or potential for a walking robot with the least structure parameters at the conceptual-design stage. Several prototypes in the researchers’ lab are evaluated with the criteria, and the results are compared with the experimental data to proof the validity.

Topics: Robots , Design
Commentary by Dr. Valentin Fuster
2017;():V05AT08A052. doi:10.1115/DETC2017-68214.

This paper synthesizes 4C and RCCC linkages based on the solution region methodology, that is an extension of the synthesis of spherical 4R linkages. The synthesis of spatial RCCC linkages is significantly more complicated than 4C linkages, because they are composed of an RC and a CC dyads. For the four positions problem, there are infinite solutions of the CC dyad, but there is no solution for the RC dyad theoretically. We first synthesize the spherical 4R linkages by setting up spherical 4R linkage solution region using four orientations of four given positions. So the directions of the kinematic pairs for a 4C linkage can be determined by picking a point on the spherical 4R linkage solution region. Then we use the directions of the 4C linkage and the points of four given positions to determine the spatial solution lines for 4C linkages. Next we establish a 4C linkage solution region using the solution lines. Each point on a 4C linkage solution region corresponds to a 4C linkage that visits the four positions. Different point on a spherical 4R linkage solution region corresponds to a different solution region for 4C linkages. Thus, we find the linkage solution on the solution region, which has no sliding displacement between input and fixed links through the four positions. The solution is an RCCC linkage that visits the four positions. Finally, we find all RCCC linkages on many different 4C linkage solution regions and establish the RCCC linkage solution region.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2017;():V05AT08A053. doi:10.1115/DETC2017-68318.

Numerical algebraic geometry is the field that studies the computation and manipulation of the solution sets of systems of polynomial equations. The goal of this paper is to formulate spherical linkages analysis and design problems via a method suited to employ the tools of numerical algebraic geometry. Specifically, equations are developed using special unitary matrices that naturally use complex numbers to express physical and joint parameters in a mechanical system. Unknown parameters expressed as complex numbers readily admit solution by the methods of numerical algebraic geometry. This work illustrates their use by analyzing the spherical four-bar and Watt I linkages. In addition, special unitary matrices are utilized to solve the five orientation synthesis of a spherical four-bar linkage. Moreover, synthesis equations were formulated for the Watt I linkage and implemented for an eight orientation task. Results obtained from this method are validated by comparison to other published work.

Topics: Linkages , Geometry , Algebra
Commentary by Dr. Valentin Fuster
2017;():V05AT08A054. doi:10.1115/DETC2017-68372.

A novel 3-UPU parallel mechanism with two rotational and one translational (2R1T) degrees of freedom (DOFs) is analyzed in this paper. The base and moving platform of this mechanism are always symmetric about a middle symmetry plane. The moving platform can rotate continuously about any axis on the middle symmetry plane, so there exists no parasitic motion during the rotation. Using the kinematic influence coefficient theory and the imaginary mechanism method, the first and second order influence coefficient matrix (namely Jacobian matrix and Hessian matrix) of this mechanism are derived. The relations between the velocity and acceleration of the moving platform and the actuated links are obtained. In order to verify the correctness of the theory, two numerical examples are enumerated and varified by the 3D model simulation. The singularities of this mechanism is discussed and the singular configurations of the mechanism, including one kind of limb singularity and two kinds of platform singularities, are obtained.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A055. doi:10.1115/DETC2017-68388.

This paper presents a design and manufacturing methodology for a mechanical system that draws trigonometric curves assembled from a series of links connected by gears. We demonstrate this technique using 11 gear-coupled links that trace a butterfly curve. The equation of a butterfly curve is converted to the relative rotations of the links of a coupled serial chain assembled so it operates with one input. We present a procedure to determine the adjustments to the gear ratios and link dimensions necessary for practical manufacture of the mechanism. The results are demonstrated by a working prototype.

Topics: Chain , Design , Gears
Commentary by Dr. Valentin Fuster

41st Mechanisms and Robotics Conference: Medical and Rehabilitation Robotics

2017;():V05AT08A056. doi:10.1115/DETC2017-67192.

It has been shown previously that for slow to normal walking speeds the ankle joint behaves similar to a passive mechanism from foot flat to push off. Thus a passive ankle mechanism was developed in order to mimic able-bodied gait in amputees. The ankle device is shown to be capable of matching the ground slope during heel strike, efficiently storing breaking energy from the user during rollover then releasing that energy to assist in push off, and raising the toe during swing phase to reset the system for the next heel strike. Mechanism functionality was verified through lab testing. Human testing was done through an ankle-bypass system on able-bodied subjects to verify device safety and functionality.

Topics: Prostheses , Testing , Safety
Commentary by Dr. Valentin Fuster
2017;():V05AT08A057. doi:10.1115/DETC2017-67351.

Practical and effective biped robots are trending toward reality with increasing interest in the technology and recent major innovations in nonlinear control theory. The development of underactuated techniques transitioned biped robot walking to a more elegant human-like motion. When disturbances are encountered, maintaining postural balance becomes a proven challenge that limits the practicality of these machines. This paper offers a solution to this issue by showing that an underactuated five-link reaction wheel-equipped planar biped robot can be posturally balanced successfully and efficiently with feedback control laws derived from the system’s zero dynamics and through task space optimization. The zero dynamics controller is shown to exhibit better performance compared to the task space controller in terms of settling time and total system work.

Topics: Robots , Wheels
Commentary by Dr. Valentin Fuster
2017;():V05AT08A058. doi:10.1115/DETC2017-67373.

This paper presents the design and integration of a two-digit exoskeleton glove. The proposed glove is designed to assist the user with grasping motions, such as the pincer grasp, while maintaining a natural coupling relationship among the finger and thumb joints, resembling that of a normal human hand. The design employs single degree of freedom linkage mechanisms to achieve active flexion and extension of the index finger and thumb. This greatly reduces the overall weight and size of the system making it ideal for prolonged usage. The paper describes the design, mathematical modeling of the proposed system, detailed electromechanical design, and software architecture of the integrated prototype. The prototype is capable of recording information about the index finger and thumb movements, interaction forces exerted by the finger/thumb on the exoskeleton, and can provide feedback through vibration. In addition, the glove can serve as a standalone device for rehabilitation purposes, such as assisting in achieving tip or pulp pinch. The paper concludes with an experimental validation of the proposed design by comparing the motion produced using the exoskeleton glove on a wooden mannequin with that of a natural human hand.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A059. doi:10.1115/DETC2017-67394.

Pneumatically powered prostheses have the ability to restore function and improve the quality of life by providing external power, thus decreasing human effort. However, such prostheses are expensive because they use high performance servo valves and complex control systems. To overcome this limitation, a pneumatic actuator is retrofitted with cheap solenoid valves and controlled by pulse width modulation for continuous control. High fidelity control is achieved by using a negative displacement configuration in which pressure is released on one side to create motion. The performance of the system is demonstrated using a series of position, force control experiments and ability to withstand external impulses. The pneumatic system is cheap, has high repeatability, and accuracy. The main limitation is that the speed of response is much slower than a positive displacement system but better design of the solenoid valve and use of predictive control has the potential to alleviate this issue.

Topics: Force control , Knee
Commentary by Dr. Valentin Fuster
2017;():V05AT08A060. doi:10.1115/DETC2017-67470.

This paper presents a novel six-bar Sit-to-Stand (STS) linkage mechanism integrated in a multi-functional assistive device1, that helps improve mobility of individuals with lower extremity weaknesses. The six-bar linkage follows the J-shaped trajectory of the shoulder-joint and maintains orientation of the supporting bar for the comfort and ergonomics. An overall goal was to design a device that is comfortable to the user during STS transformation, compact, light-weight, portable and one that requires minimum number of external actuators. By following the natural posture and movement of certain joints, a biomechanically correct STS motion is achieved. A natural motion ensures minimum stresses on joints and muscles and if the user can move their legs, they can undergo ambulation therapy and stimulate functional neural pathways. Dynamic analysis is done on the mechanism to design a frame and to select actuators for lifting a person weighing 300lbs. The device was tried by individuals with lower extremity weaknesses and the results showed that it lifts users well and also helps balance and stabilize them during ambulation.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A061. doi:10.1115/DETC2017-67599.

This paper describes the first stages of hardware development and preliminary assessment for a powered lower limb orthosis designed to provide gait assistance and rehabilitation to children with walking impairments, such as those associated with cerebral palsy and spina bifida. The design requirements, including range of motion, speeds, torques, and powers, are investigated and presented based on a target user age range of 6–11 years old. A three stage joint actuator is designed, built, and tested against the design requirements. The 0.6 kg actuator produced 4.2 Nm continuous torque and 17.2 Nm peak torque, and was able to run up to a speed of 480 deg/s. Backdrivability was characterized in terms of rotational friction, which was measured at 1.1 Nm. Finally, a 5.1 kg prototype orthosis was developed consisting of a hip segment, left and right thigh segments, and left and right shank segments, with four identical actuator prototypes installed in the thigh segments to actuate the hips and knees. Control electronics and a basic control structure were implemented to test the joint tracking capability of the orthosis against a predefined set of trajectories which were representative of pediatric gait patterns. Fitted to a dummy, the controlled limb successfully tracked the desired trajectories with a root-mean-square error of 9% and 4% of full scale for the hips and knees, respectively. With the dummy loaded with additional weight to representing a 32 kg child, the limbs also successfully tracked the trajectories with a root-mean-square error of 15% and 6% of full scale for the hips and knees, respectively.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A062. doi:10.1115/DETC2017-67607.

Remote manipulation during robot-assisted surgery requires proficiency in perception, cognition, and motor skills. We aim to understand human motor control in remote manipulation of robotic surgical instrument and attempt to measure motor skills. Three features, smoothness, normalized jerk score, and two-thirds power law coefficient, estimating the motor skills of surgeons were analyzed. These features were calculated through segments, extracted from continuous end-effector trajectories during suturing, knot-tying, and needle-passing surgical tasks, performed by 8 right-handed subjects on bench-top models using da vinci surgical kit control system. Each subject repeated each task five times. Totally 1567 segments were extracted, 413, 437, and 717 segments performed by experts, intermediates, and novice subjects, respectively. Dynamic change of kinematic properties was analyzed to evaluate the relationship between considered features and motor skill level. Results show smoothness is significantly correlated with normalized jerk score and both features are significant measures of expertise levels. Also, results show the power law is violated by many end-effector trajectories and there is no relationship between obeying two-thirds power law, smoothness and jerk. We conclude trajectory is improved from non-smooth and jerky in novices to smooth in expert surgeons. This property may be used for motor skill evaluation. It is unlikely that obeying two-thirds power law be a valid property of all end-effector trajectories. However, power law coefficient may be a discriminant feature for levels of expertise. The results are also applicable in a home-based monitoring platform, to monitor motor functioning improvement of stroke patients during rehabilitation process.

Topics: Engines , Robots , Motors , Surgery
Commentary by Dr. Valentin Fuster
2017;():V05AT08A063. doi:10.1115/DETC2017-67616.

Imaging plays an important role in all clinical processes. One challenge in medical image data processing is detection and tracking objects and instruments, which faces complications arising from the developed medical image acquisition systems and also the nature of in-vivo medical images. Special properties of the in-vivo bio images such as noise, specular highlights, inhomogeneity, heterogeneity, varying luminosity, and background change, in addition to the changes of camera, out of camera view tools, and multiple moving tools (instrument tools, surgical suture, cutting instrument, tissue movement) make object detection and tracking in the biomedical image processing complicated. In this study, the k-means clustering method in combination with the level set active curve model are used to develop a platform for low-cost tracking of surgical tools in robotic surgery videos. After removing the image background, the smoothed image is used as input to the numerical method. This model tracks the robot tools even when the camera view changes, the tool is lost, the tissue is bleeding and moving, and the luminosity of the images changes. The developed model is validated using video frames of real and simulated robotic surgeries. The accuracy of model in tracking da vinci robot end-effectors for a video with 12000 frames, recorded at Roswell Park Cancer Institute, is 93%. Accuracy of proposed framework is compared to those for existing numerical models, DRLSE and Chan-Vese. The results show that proposed surgical robot tool tracking model is more efficient than existing computational models.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A064. doi:10.1115/DETC2017-67837.

The paper presents the design of a lower leg orthotic device based on dimensional synthesis of multi-loop six-bar linkages. The wearable device is comprised of a 2R serial chain, termed the backbone, sized according to the wearer’s limb anthropometric dimensions. The paper is a result of our current efforts in proposing a systematic process for the development of 3D printed customized assistive devices for patients with reduced limb mobility, based on anthropometric data and physiological task.

To design the wearable device, the physiological task of the limb is obtained using an optical motion capture system and its dimensions are set such that it matched the lower leg kinematics as closely as possible. As a next step a six-bar linkage is synthesized and ensured that its motion is as close as possible to the physiological task. Next, the 2R backbone is replaced by the wearer’s limb to provide the skeletal structure for the multi-loop wearable device. During the final stage of the process the 2R backbone is relocated to parallel the human’s limb on one side, providing support and stability. The designed device can be secured to the thigh of the user to guide the lower leg without causing any discomfort and to ensure a natural physiological gait trajectory. This results in orthotic device for assisting people with lower leg injuries with compact size and better wearability.

Topics: Linkages , Design , Orthotics
Commentary by Dr. Valentin Fuster
2017;():V05AT08A065. doi:10.1115/DETC2017-67842.

This paper proposes a novel methodology for the design of series elastic actuators in parallel-actuated platforms which have full six degrees-of-freedom in position and orientation. Series elastic actuators can potentially contribute to lower power consumption and provide a better human-machine interface for the user. This is an important consideration in the use of a robotic spine exoskeleton for human subjects, which motivates this work. In the study of parallel-actuated systems with full six degrees-of-freedom, the effect of compliance in series with actuators has not been adequately studied from the perspective of kinematics and wrench capabilities. These analyses are performed in this paper with the goal to improve the design of the robotic spine exoskeleton (ROSE) and its human usage.

Commentary by Dr. Valentin Fuster
2017;():V05AT08A066. doi:10.1115/DETC2017-67947.

Historically, users of prosthetic ankles have relied on actively operated systems to provide effective slope adaptability. However, there are many drawbacks to these systems. This research builds upon work previously completed by Hansen et al. as it develops a passive, hydraulically operated prosthetic ankle with the capability of adapting to varying terrain in every step. Using gait cycle data and an analysis of ground reaction forces, the team determined that weight activation was the most effective way to activate the hydraulic circuit. Evaluations of the system pressure and energy showed that although the spring damper system results in a loss of 9J of energy to the user, the footplate stores 34J more than a standard prosthesis. Therefore, the hydraulic prosthetic provides a 54% increase in stored energy when compared to a standard prosthesis. The hydraulic circuit manifold prototype was manufactured and tested. Through proof of concept testing, the prototype proved to be slope adaptable by successfully achieving a plantarflexion angle of 16 degrees greater than a standard prosthetic foot currently available on the market.

Commentary by Dr. Valentin Fuster

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