ASME Conference Presenter Attendance Policy and Archival Proceedings

2015;():V05AT00A001. doi:10.1115/DETC2015-NS5A.

This online compilation of papers from the ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2015) 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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

39th Mechanisms and Robotics Conference: Compliant Mechanisms and Micro/Nano Mechanisms (A. Midha Symposium)

2015;():V05AT08A001. doi:10.1115/DETC2015-46158.

Extended nonlinear analysis of compliant compound parallelogram mechanisms is conducted in this paper. The analytical nonlinear model of a compound basic parallelogram mechanism (CBPM) is first derived incorporating the initial internal axial force. The stiffness equations of compound multi-beam parallelogram mechanisms (CMPMs) are then followed. The effect of initial internal axial forces on the primary motion is further analyzed, which can be employed to consider active displacement preloading control and thermal effects etc. It is shown that negative initial internal axial force will reduce the primary stiffness, and vice versa. The criteria for which the primary stiffness may be considered “constant” is defined and the initial internal axial force driven by temperature change is also formulated. The dynamic analysis of a CMPM using nonlinear finite element analysis (FEA) is finally carried out to show the modal frequency and the forced excitation response in the primary motion direction.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A002. doi:10.1115/DETC2015-46179.

Constant torque compliant mechanisms produce an output torque that does not change in a large range of input rotation. They have wide applications in aerospace, automobile, timing, gardening, medical and healthcare devices. Unlike constant force compliant mechanisms, the synthesis of constant torque compliant mechanisms has not been extensively investigated yet. In this paper, a method is presented for synthesizing constant torque compliant mechanisms that have coaxial input rotation and output torque. The same shaft is employed for both input rotation and output torque. A synthesized constant torque compliant mechanism is modeled as a set of variable width spline curves within an annular design domain formed between a rotation shaft and a fixed ring. Interpolation circles are used to define variable width spline curves. The synthesis of constant torque compliant mechanisms is systematized as optimizing the control parameters of the interpolation circles of the variable width spline curves. The presented method is demonstrated by the synthesis of constant torque compliant mechanisms that have different number of variable width spline curves in the paper.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A003. doi:10.1115/DETC2015-46387.

Modeling large spatial deflections of flexible beams has been one of the most challenging problems in the research community of compliant mechanisms. This work presents a method called chained spatial-beam-constraint-model (CSBCM) for modeling large spatial deflections of flexible bisymmetric beams in compliant mechanisms. CSBCM is based on the spatial beam constraint model (SBCM), which was developed for the purpose of accurately predicting the nonlinear constraint characteristics of bisymmetric spatial beams in their intermediate deflection range. CSBCM deals with large spatial deflections by dividing a spatial beam into several elements, modeling each element with SBCM, and then assembling the deflected elements using the transformation defined by Tait-Bryan angles to form the whole deflection. It is demonstrated that CSBCM is capable of solving various large spatial deflection problems whether the tip loads are known or the tip deflections are known. The examples show that CSBCM can accurately predict the large spatial deflections of flexible beams, as compared to the available nonlinear FEA results obtained by ANSYS. The results also demonstrated the unique capabilities of CSBCM to solve large spatial deflection problems that are outside the range of ANSYS.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A004. doi:10.1115/DETC2015-46434.

This paper introduces a compliant mechanism reconfiguration approach that can be used to minimize the parasitic motions of a compliant mechanism. This reconfiguration approach is based on the position spaces, identified by the screw theory, of independent compliant modules in a compliant mechanism system. The parasitic motions (rotations) of a compliant mechanism are first modelled associated with the variables representing any positions of the compliant modules in the position spaces. The optimal positions of the compliant modules are then obtained where the parasitic motions are reduced to minimal values. A procedure of the compliant mechanism reconfiguration approach is summarized and demonstrated using a decoupled XYZ compliant parallel mechanism as an example. The analytical results show that the parasitic motions of the XYZ compliant parallel mechanism in the example can be dramatically reduced by the position/structure reconfiguration, which is also validated by finite element analysis. The position space of a compliant module contains a number of possible positions, thus a compliant mechanism can also be efficiently reconfigured to a variety of practical patterns such as the configuration with compact structure.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A005. doi:10.1115/DETC2015-46444.

Research on topology optimization of compliant mechanisms is extensive but the design of flexure hinges using topology optimization method is comparatively rare. This paper deals with topology optimization of flexure hinges undergoing large-displacement. The basic optimization model is developed for topology optimization of the revolute hinge. The objective function for the synthesis of large-displacement flexure hinges are proposed together with constraints function. The geometrically nonlinear behaviour of flexure hinge is modelled using the total Lagrangian finite element formulation. The equilibrium is found by using a Newton-Raphson iterative scheme. The sensitivity analysis of the objective functions are calculated by the adjoint method and the optimization problem is solved using the method of moving asymptotes (MMA). Numerical examples are used to show the validity of the proposed method and the differences between the results obtained by linear and nonlinear modelling are large.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A006. doi:10.1115/DETC2015-46481.

Numerous works have been done on modeling compliant modules or joints, and the closed-form models of many widely-used compliant modules have been developed. However, the modeling of complex compliant mechanisms with considering external forces is still a challenging work. This paper introduces a constraint-force-based method to model compliant mechanisms. A compliant mechanism can be regarded as the combination of rigid stages and compliant modules. If a compliant mechanism is at static equilibrium under the influence of a series of external forces, all the rigid stages are also at static equilibrium. The rigid stages are restricted by the constraint forces of the compliant modules and the exerted external forces. This paper defines the constraint forces of the compliant modules to be variable constraint forces since the constraint forces vary with the deformation of the compliant modules, and defines the external forces as constant constraint forces due to the fact that the external forces are specific forces exerted which do not change with the deformation of the compliant mechanism. Therefore, the force equilibrium equations for all rigid stages in a compliant mechanism can be obtained based on the variable constraint forces and the constant constraint forces. Moreover, the model of the compliant mechanism can also be derived through solving all the force equilibrium equations. The constraint-force-based modeling method is finally detailed demonstrated via examples, and validated by the finite element analysis. Using this proposed modeling method, a complex compliant mechanism can be modelled with a particular emphasis on considering the position spaces of the associated compliant modules.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A007. doi:10.1115/DETC2015-46526.

The large deflection of cantilever beams has been widely studied. A number of models and mathematical techniques have been utilized in predicting the path coordinates and load-deflection relationships of such beams. The Pseudo-Rigid-Body Model (PRBM) is one such method which replaces the elastic beam with rigid links of a parameterized pivot location and torsional spring stiffness. In this paper, the PRBM method is extended to include cases of a constant distributed load combined with a parallel endpoint force. The phase space of the governing differential equations is used to store information relevant to the characterization of the PRBM parameters. Correction factors are also given to decrease the error in the load-deflection relationship and extend the angular range of the model, thereby further aiding compliant mechanism design. Our calculations suggest a simple way of representing the effective torque caused by a distributed load in a PRBM as a function of easily calculated model parameters.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A008. doi:10.1115/DETC2015-46591.

A flexure strip has constraint characteristics, such as stiffness properties and error motions, that limit its performance as a basic constituent of flexure mechanisms. This paper presents a framework for modeling the deformation and stiffness characteristics of general three-dimensional flexure strips that exhibit bending, shear and torsion deformation. The formulation is based on a finite strain discrete spatial beam element with refinements to account for plate-like behavior due to constrained cross-sectional warping. This framework is suited for analytical calculations thanks to the accuracy of the beam element, while its discrete nature allows for easy implementation in numeric software to serve as calculation aid. As case study, a closed-form parametric analytical expression is derived for the lateral support stiffness of a parallel flexure mechanism. This captures the deteriorating support stiffness when the mechanism moves in the intended degree of freedom. By incorporating relevant geometric nonlinearities and a warping constraint stiffening factor, an accurate load-displacement and stiffness expression for the lateral support direction is obtained. This result is verified by nonlinear finite element analysis.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A009. doi:10.1115/DETC2015-46628.

This paper explores strategies for static balancing of several flexure types. First, it describes a method for determining the load-dependent stiffness behavior of compliant flexures. Load-dependent stiffness means that the stiffness changes when a flexure is subjected to force loads perpendicular to its axis of rotation. A set of non-dimensional parameters is selected to describe the loads and the resulting stiffness. Finite element models of each joint are developed, and stiffness data is gathered for a range of horizontal and vertical loading regimes. The method is verified by comparing results to an analytic model for joints where such is available, and to results in the literature. The load-dependent stiffness behavior is then examined to identify new strategies for static balancing that have not yet appeared in the literature.

Topics: Stress , Stiffness
Commentary by Dr. Valentin Fuster
2015;():V05AT08A010. doi:10.1115/DETC2015-46643.

The purpose of this paper is to introduce a new kind of actively controlled microarchitecture that can alter its bulk shape through the deformation of compliant elements. This new type of microarchitecture achieves its reconfigurable shape capabilities through a new control strategy that utilizes linearity and closed-form analytical tools to rapidly calculate the optimal internal actuation effort necessary to achieve a desired bulk surface profile. The microarchitectures of this paper are best suited for high-precision applications that would benefit from materials that can be programmed to rapidly alter their surfaces/shape relatively small amounts in a controlled manner. Examples include distortion-correcting surfaces on which precision optics are mounted, airplane wings that deform to increase maneuverability and fuel efficiency, and surfaces that rapidly reconfigure to alter their texture. In this paper, the principles are provided for optimally designing 2D or 3D versions of the new kind of microarchitecture such that they exhibit desired material property directionality. The mathematical theory is provided for modeling and calculating the actuation effort necessary to drive these microarchitectures such that their lattice shape comes closest to achieving a desired profile. Case studies are provided to demonstrate this theory.

Topics: Shapes
Commentary by Dr. Valentin Fuster
2015;():V05AT08A011. doi:10.1115/DETC2015-46650.

In this research a variable-stiffness compliant mechanism was developed to generate variable force-displacement profiles at the mechanism’s coupler point. The mechanism is based on a compliant Robert’s straight-line mechanism, and the stiffness is varied by changing the effective length of the compliant links with an actuated slider. The force-deflection behavior of the mechanism was analyzed using the Pseudo-Rigid Body Model (PRBM), and two key parameters, KΘ and γ, were optimized using finite element analysis (FEA) to match the model with the measured behavior of the mechanism. The variable-stiffness mechanism was used in a one-degree-of-freedom haptic interface (force-feedback device) to demonstrate the effectiveness of varying the stiffness of a compliant mechanism. Unlike traditional haptic interfaces, in which the force is controlled using motors and rigid links, the haptic interface developed in this work displays haptic stiffness via the variable-stiffness compliant mechanism. One of the key features of the mechanism is that the inherent return-to-zero behavior of the compliant mechanism was used to provide the stiffness feedback felt by the user. A prototype haptic interface was developed capable of simulating the force-displacement profile of Lachman’s Test performed on an injured ACL knee. The compliant haptic interface was capable of displaying stiffnesses between 4200 N/m and 7200 N/m.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A012. doi:10.1115/DETC2015-46672.

This paper presents the design and analysis a flexure-guided compliant micropositioning stage with constant force and large stroke. The constant force output is achieved by combining a bistable flexure mechanism with a positive-stiffness flexure mechanism. In consideration of the constraint of conventional tilted beam-based bistable mechanism, a new type of bistable structure based on tilted-angle compound parallelogram flexure is proposed to achieve a larger range of constant force output while maintaining a compact physical size. To facilitate the parametric design of the flexure mechanism, analytical models are derived to quantify the stage performance. The models are verified by carrying out nonlinear finite-element analysis. Results demonstrate the effectiveness of the proposed ideas for a long-stroke, constant-force compliant mechanism dedicated to precision micropositioning applications.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A013. doi:10.1115/DETC2015-46683.

Continuum robots have attracted increasing focus in recent years due to their intrinsic compliance and safety. However, the modeling and control of such robots are complex in comparison with conventional rigid ones. This paper presents the design of a pneumatically actuated continuum robot. A 3-dimensional dynamic model is then developed by using the mass-damper-spring system based networks, in which elastic deformation, actuating forces and external forces are taken into account. The model is validated by experiments and shows good agreement with the robotic prototype.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A014. doi:10.1115/DETC2015-46813.

This paper presents the concept and fabrication of a large deflection compliant Constant Velocity universal joint (CV joint). A novel compliant structure is proposed based on the 6R Hybrid spatial overconstrained linkage. Due to symmetry, its kinematic properties are such that can transfer rotational motion between two angled shafts with true constant velocity. The kinematic of the mechanism and the Pseudo-Rigid-Body model of its compliant configuration are studied and analyzed. A prototype was manufactured and experimentally evaluated. It was verified that the experimental results are consistent with the theoretical expectations.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A015. doi:10.1115/DETC2015-46827.

By employing screw theory and the freedom and constraint topology (FACT), the type synthesis for 2-DOF flexure-based sensing mechanism of superconductor gravity gradient was produced with the parameterized compliance approach. Six types of mechanism with 1R1T DOF were deduced with freedom and constraint pattern in parallel topologies. Based on the compliance analysis, one type was selected as preferred sensing mechanism with the comparison of freedom, main direction compliance, parasitic errors, precision and complexity. For reducing the parasitic and coupling errors, optimization was produced with the parameterized compliance approach. Then specific geometric properties were presented with compact structure for the measurement application. The simulations showed the results of analytical models were close to that of FEA (finite elements analysis) models and the maximum errors of compliance parameters were less than 6%. The conceptual design of 2-DOF flexure-based sensing mechanisms could reach the required functions.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A016. doi:10.1115/DETC2015-46869.

This paper proposes a novel compliant flexure-based microgripper with a second order amplifier including Scott-Russell magnification mechanism (SRMM) and lever amplifier. Both the dynamic model of the system and the Bouc-Wen hysteresis model are established and identified through using least square optimization method. For eliminating the hysteresis phenomenon of the actuator, compensation control method based on inverse dynamic model is proposed. A novel control strategy based on adaptive backstepping sliding model control (ABSMC) with compensator is presented to control the nonlinear system. Simulation results demonstrate that the performance of proposed control strategy is superior to conventional backstepping sliding mode control (CBSMC).

Commentary by Dr. Valentin Fuster
2015;():V05AT08A017. doi:10.1115/DETC2015-47064.

Contact Aided Compliant Mechanisms (CCMs) are synthesized via the Material Mask Overlay Strategy (MMOS) to trace a desired non-smooth path. MMOS employs hexagonal cells to discretize the design region and engages negative circular masks to designate material states. To synthesize CCMs, the modified MMOS presented herein involves systematic mutation of five mask parameters through a hill climber search to evolve not only the continuum topology (slave surfaces), but also, to introduce the desired rigid, interacting surfaces within some masks. Various geometric singularities are subdued via hexagonal cells though numerous V-notches get retained at the continuum boundaries. To facilitate contact analysis, boundary smoothing is performed by shifting boundary nodes of the evolving continuum systematically. Numerous hexagonal cells get morphed into concave sub-regions as a consequence. Large deformation finite element formulation with Mean Value Coordinates (MVC) based shape functions is used to cater to the generic hexagonal shapes. Contact analysis is accomplished via the Newton-Raphson iterations with load increment in conjunction with the penalty method and active set constraints. An objective function based on Fourier Shape Descriptors is minimized subject to suitable design constraints. An example of a path generating CCM is included to establish the efficacy of the proposed synthesis method.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A018. doi:10.1115/DETC2015-47217.

A static balancer is a mechanism used to force compensate mechanical systems and has been used in applications such as improving haptic feedback in surgical instruments and lowering motor loads in robotic systems. Currently no complete overview exists of all SB methods, this paper can be seen as an extension to earlier work by introducing more static balancing categories and methods. The goal is to have a comprehensive overview of state-of-the-art to aid designers in selecting the appropriate static balancer technology for mechanical systems. Existing designs are categorized based on the energy storage mechanism, e.g. elastic energy storage mechanisms. Critical design parameters are extracted from published literature to form the basis of comparison of the different categories. A performance criterium is defined to illustrate balancing capabilities as a function of system size. The three comparison parameters are: Display FormulaCompensatedForceVolume,SBStrokeVolume,EnergyVolume The comparison results show that compliant flexure balancers are the best selection for balancing systems while keeping minimal size. Theoretical calculations show that there is still ample room to improve current balancers with regard to the chosen balancer criteria.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A019. doi:10.1115/DETC2015-47240.

In this paper, the design of nonlinear softening springs using compliant mechanisms is investigated. The use of compliant structures is of great interest, because of the resulting absence of backlash and friction. We demonstrate that the existence of parallel singularities is a necessary condition for the architecture of a compliant softening spring. From this result, two original arrangements of softening springs are derived, with the introduction of traction and torsion softening springs. A synthesis is performed and the traction spring is numerically and experimentally assessed. As nonlinearity can also be obtained from material properties, the interest of using additive manufacturing with multi-material capability is investigated. Rubber-like materials exhibit a hyper-elastic behavior. Their integration in the proposed compliant architecture is shown to be of interest to customize the geometry of a softening spring according to the designer requirements.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A020. doi:10.1115/DETC2015-47267.

Pseudo-rigid-body models serve as a convenient numeric tool for the analysis of compliant elements. However, most PRB models are derived on the basis of Euler beam equations, without accounting for the effect of deformation on beam geometry. In this paper, we look at the effects of deformation on length and cross section of the beam, and try to understand these phenomena with respect to some dimensionless parameters. These effects are more pronounced for short beams of soft materials. A few PRB models listed in literature are compared against FEA results, and optimization methods are used to determine more accurate PRB models for varying beam geometry. A study of these results will guide the discussion on how the accuracy of the PRB models changes with the beam parameters. An example of a compliant mechanism which experiences significant axial loads will be used to prove the validity of these results.

Topics: Geometry
Commentary by Dr. Valentin Fuster
2015;():V05AT08A021. doi:10.1115/DETC2015-47271.

Flexure mechanisms become more and more popular because of their better performance, easy maintenance, wear-free properties and predictability of kinematic variables changes. Comparing to traditional ball bearings or linear slides, however, range of motion limits flexure mechanisms applications in existing market. This paper presents the design of a novel planar XY stage synthesizing the benefits of parallel and serial kinematic constraint. By parallel connecting two mechanisms: the vertical and horizontal subsystems, which both have degrees of freedom (DOFs) in primary moving direction but different degrees of constraints (DOCs) in rotation, this system is able to reduce three parasitic rotation angles (pitch, roll and yaw) less than one micro radium and also have motion range up to 40mm × 40mm. Analytical model and finite element analysis (FEA) are present to validate the performance of this stage and also determine appropriate operation parameters.

Topics: Design
Commentary by Dr. Valentin Fuster
2015;():V05AT08A022. doi:10.1115/DETC2015-47449.

The present work deals with the development of a hybrid manipulator of 5 degrees of freedom for milling moulds for microlenses. The manipulator is based on a XY stage under a 3PRS compliant parallel mechanism. The mechanism takes advantage of the compliant joints to achieve higher repetitiveness, smoother motion and a higher bandwidth, due to the high precision demanded from the process, under 0.1 micrometers. This work is focused on the kinematics of the compliant stage of the hybrid manipulator. First, an analysis of the workspace required for the milling of a single mould has been performed, calculating the displacements required in X, Y, Z axis as well as two relative rotations between the tool and the workpiece from a programmed toolpath. Then, the 3PRS compliant parallel mechanism has been designed using FEM with the objective of being stiff enough to support the cutting forces from the micromilling, but flexible enough in the revolution and spherical compliant joints to provide the displacements needed. Finally, a prototype of the 3PRS compliant mechanism has been built, implementing a motion controller to perform translations in Z direction and two rotations. The resulting displacements in the end effector and the actuated joints have been measured and compared with the FEM calculations and with the rigid body kinematics of the 3PRS.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A023. doi:10.1115/DETC2015-47526.

This paper presents a new concept: a Shape-Morphing Space Frame (SMSF), which is a novel application utilizing the Linear Bistable Compliant Crank-Slider Mechanism (LBCCSM). The frame’s initial shape is constructed from a single-layer grid of flexures, rigid links and LBCCSMs. The grid is bent into the space frame’s initial cylindrical shape, which can morph because of the inclusion of LBCCSMs in its structure. The design parameters consist of the frame’s initial height, its tessellation pattern (including bistable elements’ placement), its initial diameter, and the final desired shape. The method used in placing the bistable elements is a novel contribution to this work as it considers the principle stress trajectories. This paper will present two different examples of Shape-Morphing Space Frames, each starting from a cylindrical-shell space frame and morphing, one to a hyperbolic-shell space frame and the other to a spherical-shell space frame, both morphing by applying moments, which shear the cylindrical shell, and forces, which change the cylinder’s radius using Poisson’s effect.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A024. doi:10.1115/DETC2015-47694.

The mobility characteristics of compliant mechanisms are a function of the structural arrangement of the comprising segments and links, their types, as well as the load and/or displacement boundary conditions. It is hypothesized that an earlier defined concept of compliance number and stored strain energy in a compliant mechanism are strongly correlated. It therefore becomes necessary to define and better understand the characteristics of deformation mode shapes of compliant mechanisms. A compliant mechanism may exhibit a variety of mode shapes. In keeping with the classical mechanics notions, this paper systematically develops the mode shapes in compliant mechanisms, utilizing two distinct categories: i) segmental (elemental) mode shapes, and ii) mechanism (system) mode shapes. The possible mode shapes of the basic segment types are identified. Based on the energy storage capability of the segment types, segmental mode shapes are further classified into higher and lower order mode shapes. Similar identification is extended to compliant mechanisms as well, and the possible mechanism mode shapes are illustrated with the help of a few examples. Finally, the utility of this methodology in identifying an appropriate pseudo-rigid-body model (PRBM) corresponding to a given compliant mechanism is demonstrated. An experimental procedure aids in this process.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A025. doi:10.1115/DETC2015-47863.

This paper replaces the hinged pivots of an eight-bar linkage with flexure joints in order to achieve a flexure-connected linkage system that guides rectilinear movement of its end-effector. The goal is a linkage design that can be reduced in size to provide a suspension for the proof masses of a MEMS gyroscope. The symmetric design of the linkage and its long travel relative to other MEMS suspensions has the potential to provide a number of advantages, such as the reduction of quadrature error. The design presented yields 0.1% deviation over its range of movement. An example also presents the driving linkage of the MEMS gyroscope, which is also designed as flexure connected linkage.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A026. doi:10.1115/DETC2015-47914.

This paper investigates the effective use of the pseudo-rigid-body model (PRBM) of a small-length flexural pivot (SLFP), examining its very definition, and providing helpful guidelines in the context of a compound compliant beam composed of both compliant and rigid segments. Traditionally, for convenience in modeling, the pseudo-rigid-body model of the small-length flexural pivot assumes the characteristic pivot to be placed at the center of the SLFP. It is also suggested that the length of the adjacent rigid segment is ten or more times larger than the length of the compliant segment. In recent times, a growing interest has been expressed to test this assumption and learn more about its limitations. This paper investigates the performance of the PRBM of the SLFP, for initially straight and initially curved compound compliant beams by varying the compliant to rigid segment length ratio. The error, defined by comparing the PRBM deflections with those obtained from the closed-form elliptic integral method, may be assigned an acceptable value in determining the limit value of the segment length ratio. Plots of the maximum deflection that may be obtained within an error limit of 3%, for various segment length ratios of a fixed-free, compound compliant beam are provided.

Topics: Modeling , Deflection , Errors
Commentary by Dr. Valentin Fuster
2015;():V05AT08A027. doi:10.1115/DETC2015-47930.

Although work related to mechanical advantage of compliant mechanisms has been presented almost two decades ago, unlike many rigid-body mechanism systems, this performance measure has seldom been used. In great part, the reasons are attributed to, one, the relatively recent development of and a lack of familiarity with this technology and, two, the complexity of the understanding and evaluation of mechanical advantage of compliant systems. In an effort to simplify the evaluation, this work uses the pseudo-rigid-body model (PRBM) of a compliant mechanism, along with traditional notions of power conservation and angular velocity ratios using instant centers. As a first step, the inherent compliance in the mechanism is neglected in determining its mechanical advantage, followed by considerations to optimize its structural configuration for enhancing its mechanical advantage. The PRBM methodology, which offers us a way to estimate the characteristic compliance of the mechanism, now enables its inclusion in determining the mechanical advantage of the compliant mechanism. Two significant factors affecting it are i) the structural configuration of the PRBM, and ii) the energy stored in compliant elements of the mechanism. Several case studies are presented, which suggest that minimizing the latter contribution relative to that of an optimized structural configuration may improve the mechanical advantage of a compliant mechanism. Nonetheless, its effect on the mechanical advantage cannot be neglected.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A028. doi:10.1115/DETC2015-47943.

Compliant mechanisms have shown a great deal of potential, in just a few decades of its development, in providing innovative solutions to design problems. However, their use has been limited due to challenges associated with the materials. With ever increasing focus on the applications of compliant mechanisms, it is necessary to find alternatives to the existing material usage and methods of prototyping. This paper presents a methodology for the design of compliant segments and compliant mechanisms with improved creep resistance and fatigue life properties using the current state-of-the-art materials. The methodology proposes using a stronger material at the core of a softer casing. The paper provides an equivalent pseudo-rigid-body model and a closed-form elliptic integral formulation for a fixed-free compliant segment with an insert. The equivalent pseudo-rigid-body model is verified experimentally for the prediction of beam end point displacements. The paper also presents experimental results that show improvements obtained in the creep recovery properties as expected using the proposed design philosophy.

Commentary by Dr. Valentin Fuster

39th Mechanisms and Robotics Conference: Medical and Rehabilitation Robotics

2015;():V05AT08A029. doi:10.1115/DETC2015-46336.

In this research work, the authors developed and tested a low cost wearable and portable hand exoskeleton to assist people with physical disabilities in their everyday lives. Focusing on hand opening disabilities, the proposed actuated orthoses could support and enable daily gestures such as shacking hands or grasping objects. The Hand Exoskeleton System (HES) prototype is based on a cable-driven architecture applied to a single-phalanx mechanism. The preliminary prototype of the system has been successfully built and is currently under testing with a patient to verify its performance from a patient viewpoint.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A030. doi:10.1115/DETC2015-46344.

Robotic minimally invasive surgery has achieved success in various procedures; however, the lack of haptic feedback is considered by some to be a limiting factor. The typical method to acquire tool-tissue reaction forces is attaching force sensors on surgical tools, but this complicates sterilization and makes the tool bulky. This paper explores the feasibility of using motor current to estimate tool-tissue forces, and demonstrates acceptable results in terms of time delay and accuracy. This sensorless force estimation method sheds new light on the possibility of equipping existing robotic surgical systems with haptic interfaces that require no sensors and are compatible with existing sterilization methods.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A031. doi:10.1115/DETC2015-46389.

This paper examines the design, analysis and control of a novel hybrid articulated-cable parallel platform for upper limb rehabilitation in three dimensional space. The proposed lightweight, low-cost, modular reconfigurable parallel-architecture robotic device is comprised of five cables and a single linear actuator which connects a six degrees-of-freedom moving platform to a fixed base. This novel design provides an attractive architecture for implementation of a home-based rehabilitation device as an alternative to bulky and expensive serial robots. The manuscript first examines the kinematic analysis prior to developing the dynamic equations via the Newton-Euler formulation. Subsequently, different spatial motion trajectories are prescribed for rehabilitation of subjects with arm disabilities. A low-level trajectory tracking controller is developed to achieve the desired trajectory performance while ensuing that the unidirectional tensile forces in the cables are maintained. This is now evaluated via a simulation case-study and the development of a physical testbed is underway.

Topics: Robots , Cables
Commentary by Dr. Valentin Fuster
2015;():V05AT08A032. doi:10.1115/DETC2015-46393.

Assisted motor therapies play a critical role in enhancing the functional musculoskeletal recovery and neurological rehabilitation. Our focus here is to assist the performance of repetitive motor-therapy of the human lower limbs — in both the sagittal and frontal planes. Hence, in this paper, we develop a lightweight, reconfigurable hybrid (articulated-multibody and cable) based robotic rehabilitative device as a surrogate for a human physiotherapists and analyze feasibility and performance. A hybrid cable-actuated articulated multibody system is formed when multiple cables are attached from a ground-frame to various locations on the lower limbs. The combined system now features multiple holonomic cable-loop-closure constraints acting on a tree-structured multibody system. Hence the paper initially focuses on developing the Newton-Euler dynamic equilibrium equations of the cable-driven lower limbs to develop a symbolic analysis framework. The desired motion for the proposed rehabilitative exercise are prescribed based upon normative subjects motion patterns. Trajectory-tracking within this system is realized by a position-based impedance controller in task-space and a feedback-linearized PD controllers in joint-space. Careful coordination of the multiple cable-motors are now necessary in order to achieve the co-robotic control of the overall system, avoiding development of internal stresses and ensuring continued satisfaction of the unilateral cable-tension constraints throughout the workspace. This is now evaluated via a simulation case-study and development of a physical testbed is underway.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A033. doi:10.1115/DETC2015-46503.

Flexible robot arms have been developed for various medical and industrial applications because of their compliant structures enabling safe environmental interactions. This paper introduces a novel flexible robot arm comprising a number of elastically deformable planar spring elements arranged in series. The effects of flexure design variations on their layer compliance properties are investigated. Numerical studies of the different layer configurations are presented and finite Element Analysis (FEA) simulation is conducted. Based on the suspended platform’s motion of each planar spring, this paper then provides a new method for kinematic modeling of the proposed robot arm. The approach is based on the concept of simultaneous rotation and the use of Rodrigues’ rotation formula and is applicable to a wide class of continuum-style robot arms. At last, the flexible robot arms respectively integrated with two different types of compliance layers are prototyped. Preliminary test results are reported.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A034. doi:10.1115/DETC2015-46516.

A new, compact 2 degree-of-freedom mechanism 4.1 mm in diameter suitable for robotically controlled surgical operations is presented. Current commercially available robotically controlled instruments achieve high dexterity defined by three degrees of freedom and relatively confined swept volume at just under 1 cm in diameter. Current smaller diameter instruments result in high part count and large swept volumes (less dexterity). A meso-scale rolling contact gripping mechanism is proposed as an alternative. The manufacturing of the parts is made feasible by Metal Laser Sintering, which can produce parts that are difficult to replicate with traditional manufacturing methods. The resulting instrument has only 6 parts and a small swept volume. Instrument actuation and control by a surgical robotic system is demonstrated.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A035. doi:10.1115/DETC2015-46518.

This paper presents the analysis, design, and preliminary testing of a prototype prosthetic foot for use in India. A concept consisting of a rigid structure with rotational joints at the ankle and metatarsal with rotational stiffnesses provided by springs is discussed. Because literature suggests that prosthetic feet that exhibit roll-over shapes similar to that of physiological feet allow more symmetric gait, the joint stiffnesses were optimized to obtain the best fit between the roll-over shape of the prototype and of a physiological foot. Using a set of published gait data for a 56.7 kg subject, the optimal stiffness values for roll-over shape that also permit the motion required for natural gait were found to be 9.3 N·m/deg at the ankle and 2.0 N·m/deg at the metatarsal. The resulting roll-over shape has an R2 value of 0.81 when compared with the physiological roll-over shape. The prototype was built and tested in Jaipur, India. Preliminary qualitative feedback from testing was positive enough to warrant further development of this design concept.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A036. doi:10.1115/DETC2015-46661.

This paper presents the design and application of the SAFER glove in the field of hand rehabilitation. The authors present preliminary results on a new hand grasping rehabilitation learning system that is designed to gather kinematic and force information of the human hand and to playback the motion to assist a user in common hand grasping movements, such as grasping a bottle of water. The fingertip contact forces during grasping have been measured by the SAFER Glove from 12 subjects. The measured fingertip contact forces were modeled with Gaussian Mixture Model (GMM) based on machine learning approach. The learned force distributions were then used to generate fingertip force trajectories with a Gaussian Mixture Regression (GMR) method. To demonstrate the glove’s potential to manipulate the hand, experiments with the glove fitted on a wooden hand to grasp various objects were performed. Instead of defining a grasping force, contact force trajectories were used to control the SAFER Glove to actuate/assist this hand while carrying out a learned grasping task. To prove that the hand can be driven safely by the haptic mechanism, force sensor readings placed between each finger and the mechanism have been plotted. The experimental results show the potential of the proposed system in future hand rehabilitation therapy.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A037. doi:10.1115/DETC2015-46706.

In lower-limb rehabilitation programs, patients that suffer from neuromuscular disorders with manual muscle test (MMT) level 2 are able to perform voluntary muscle contraction and visible limb movement provided that a therapist assists the patient to eliminate the weight of his/her leg. In addition, the physical therapist is clinically needed to guide the patient performing a hip-only or knee-only motion during rehabilitation. The objective of this paper is to present a new assistive training device that replaces the function of the therapist in helping the MMT-level-2 patients self-training their hip and knee flexion/extension motions under an antigravity environment. First, we will present a novel reconfigurable mechanism, which can possess two working configurations for guiding the knee-only and hip-only training, respectively. Then, based on the theory of static balancing, two linear springs are attached to the device to generate an antigravity training environment in both configurations for the patient. The static balance design is verified by a numerical example with the support of software simulation. A prototype is built up and tested on healthy subjects. By using the electromyography (EMG) measurement, the myoelectric signals of four major muscles for the subject with/without the aid of the device are analyzed. The results show that the myoelectric voltages of the stimulated muscles are significantly reduced when the subject is assisted with the device. It further demonstrates that moving the fixation positions of the limb segments to other positions could distinctly reduce the assistive force from the device, which suggests multiple training modes to the patients in strengthening the training intensity. In conclusion, this paper presents a successful pioneering work on the design of rehabilitation devices via the integration of the principles of reconfigurable mechanisms and static balancing.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A038. doi:10.1115/DETC2015-46828.

In the last two decades robotic rehabilitation research provided insight regarding the human-robot interaction, helped understand the process by which the impaired nervous system is retrained to better control the hand motion, and led to the development of a number of mathematical and neurophysiological models that describe both the hand motion and the robot control. Now that this pool of knowledge is available, the respective models can be applied in a number of ways outside the robot domain, in which, machines are based on open kinematic chains with n-degrees of freedom (DOF’s) and sophisticated computer control, actuation and sensing. One such example is the use of mechanisms, closed kinematic chains which can still generate complex — yet specific — trajectories with fewer DOF’s. This paper further extends previous work on the design of such passive-active mechanisms that replicate the natural hand motion along a straight-line. The natural hand motion is described by a smooth bell-shaped velocity profile which in turn is generated by the well-established Minimum-Jerk-Model (MJM). Three different straight line 4-bar linkages, a Chebyshev’s, a Hoeken’s and a Watt’s, are examined. First, with the use of kinetostatic analysis and given the natural hand velocity and acceleration, the torque function of non-linear springs that act on the driving link is deduced. Then, given that the springs are acting, interaction with impaired users is considered and the extra actuation power that can maintain the natural velocity profile is calculated. A multibody dynamics software is employed for further assessing the mechanisms’ dynamic response under varying interaction forces. Also, different parameters like inertia are altered and the effects on internal (springs) and external (actuator) power are examined. Then, the three mechanisms are compared with respect to size, required amount of external power, ergonomic issues etc. Finally, it is investigated whether a linear fit of the non-linear spring torque can be adequate for generating the desired MJM trajectory and operate effectively in collaboration with the active part of the control.

Topics: Linkages
Commentary by Dr. Valentin Fuster
2015;():V05AT08A039. doi:10.1115/DETC2015-47010.

On the basis of robot kinematics, we have thus far developed a method for predicting the motion of proteins from their 3D structural data given in the Protein Data Bank (PDB data). In this method, proteins are modeled as serial manipulators constrained by springs and the structural compliance properties of the models are evaluated. We focus on localized instead of whole structures of proteins. Employing the same model used in our method of motion prediction, the motion properties of the localized structures and the relation between the motion properties of localized and whole structures are analyzed. First, we present a method for graphically expressing the deformation of objects with a complex shape, such as proteins, by approximating the shape as a rectangular prism with a mesh on its surface. We then formulate a method for comparing the motion properties of localized structures cleaved from the whole structure and those remaining in it by expressing the motion of the latter using the decomposed motion modes of the former according to the structural compliance. Finally, we show a method for evaluating the effect of a localized structure on the motion properties of proteins by applying forces to localized structures. In the formulations, we demonstrate applications as illustrative examples using the PDB data of a real protein.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A040. doi:10.1115/DETC2015-47055.

Advanced robotic hand prostheses are praised for their impressive robust and fine grasping capabilities generated from intricate systems. Nevertheless, a high demand remains for grasping mechanisms that are mechanically simple, lightweight, and cheap to produce, easy to assemble and low in maintenance costs. This paper presents the design of a partially compliant underactuated finger to demonstrate the feasibility of achieving these rigorous requirements. The conceptual topology of the three phalanx finger is selected based on competitive analysis. Employing Pseudo-Rigid Body Model and Finite Element Analysis, a genetic optimization problem is formulated to minimize bending stresses within compliant flexures. The result is a fully functional demonstrator capable of flexing 180° in finger rotation. The prototype is fabricated from flexible high strength nylon and requires no assembly steps beyond 3D printing. Experimental testing verifies the design method with an acceptable error of < 5%.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A041. doi:10.1115/DETC2015-47058.

A three-finger exoskeleton is designed and controlled to translate and or rotate a slender object held between the fingertips. Each finger exoskeleton comprises of three serially concatenated planar external four-bar linkages, all on one plane, except for the thumb exoskeleton, for which one linkage is out of plane. Linkages are constrained to be on the dorsal side (sagittal plane) of each finger. To design each linkage, when performing coordinated translation and rotation, trajectories of all phalanges of the index and middle fingers and the thumb are obtained through video capture and post-processing that involves coordinate transformation. Optimal kinematic synthesis for each linkage is then performed via the three accuracy point method coupled with a stochastic search algorithm. Post manufacturing, the exoskeleton is mounted on the dorsal side of the hand using Velcro bands. Fastening is accomplished on each phalanx, palm and forearm via a fixture designed to house all three exoskeletons. Nine micro-servo motors are employed for actuation. To perform coordinated translation and rotation tasks, trajectory following is accomplished using open loop position control, incorporating artificial neural network to convert known finger joint angles into the required driving link angles. Based on experimental tests conducted, the exoskeleton is found to be successful in reproducing the requisite finger motions involved in coordinated object manipulation.

Topics: Rotation , Design
Commentary by Dr. Valentin Fuster
2015;():V05AT08A042. doi:10.1115/DETC2015-47355.

A direct cardiac compression (DCC) device is an active sleeve that is surgically placed around the heart to help the failing heart to pump without contacting blood. Soft robotic techniques enable fabrication of a conformable DCC device containing modular actuators oriented in a biomimetic manner that can restore the natural motion of the heart and provide tunable active assistance. In this paper we describe the fabrication of a DCC device; the optimization of pneumatic actuators, their integration into a matrix with a modulus in the range of cardiac tissue and methods to affix this device to the heart wall. Pneumatic air muscles (PAMs) were fabricated using a modified McKibben technique and four types of internal bladders; low durometer silicone tubes molded in-house, polyester terephthalate (PET) heat shrink tubing, nylon medical balloons and thermoplastic urethane (TPU) balloons thermally formed in-house. Balloons were bonded to air supply lines, placed inside a braided nylon mesh with a 6.35mm resting diameter and bonded at one end. When pressurized to 145kPa silicone tubes failed and PET, nylon and TPU actuators generated isometric axial forces of 14.28, 19.65 and 19.05N respectively, with axial contractions of 33.11, 28.69 and 37.54%. Circumferential actuators placed around the heart reduced the cross-sectional area by 33.34% and 50.63% for silicone and TPU actuators respectively. PAMs were integrated into a soft matrix in a biomimetic orientation using three techniques; casting, thermal forming and layering. Designs were compared on an in vitro cardiac simulator and generated a volumetric displacement of up to 96ml when actuated for 200ms at 1Hz. Layering produced the lowest profile device that successfully conformed to the heart and this design is currently undergoing in vivo testing.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A043. doi:10.1115/DETC2015-47385.

An estimated 230,000 above-knee amputees in India are currently in need of prosthetic care, a majority of them facing severe socio-economic constraints. However, only few passive prosthetic knee devices in the market have been designed for facilitation of normative gait kinematics and for meeting the specific daily life needs of above-knee amputees in the developing world. Based on the results of our past studies, this paper establishes a framework for the design of a low-cost prosthetic knee device, which aims to facilitate able-bodied kinematics at a low metabolic cost. Based on an exhaustive set of functional requirements, we present a prototype mechanism design for the low-cost prosthetic knee. The mechanism is implemented using an early stance lock for stability and two friction dampers for achieving able-bodied kinematics and kinetics of walking. For early-stage validation of the prosthesis design, we carry out a preliminary field trial on four above-knee amputees in India and collect qualitative user feedback. Future iterations of the mechanism prototype will incorporate an additional spring component for enabling early stance flexion-extension.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A044. doi:10.1115/DETC2015-47448.

Our interest is in designing, fabricating and testing wearable robotic devices that assist human gait of able bodied individuals [1, 2]. Recently, we have been experimenting with Additive Manufacturing, 3D printing, using Fused Deposition Modeling technology as a method to fabricate key structural components for these robotic devices.

A key structural component for the JTAR (Joint Torque Augmentation Robot) hip exoskeleton was manufactured using 3D printing and has been destructively tested to validate design requirements, the average force required to destroy the part was 2500 N with a standard deviation of 86 N, and this level of strength provided a safety factor in excess 4 times the expected load. The 3D printed part also has been successfully demonstrated on the JTAR robot for approximately 32 kilometers of hiking with no signs of degradation. The JTAR device has been demonstrated with the 3D printed hip mechanism in various environments, including treadmills and unconstrained outdoor environments.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A045. doi:10.1115/DETC2015-47459.

The Atlantic razor clam (Ensis directus) digs 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 motion to sufficiently create soil fluidization is presented. Max force for the actuator to contract is based on force to pump fluid out of the device, and max expansion force is determined by the soil. Friction force in the device and potential considerations for increased force are presented. Data from laboratory tests are used to characterize how power is split between pumping water out of the device versus accelerating the mechanism itself. These relationships provide the optimal sizing and power needs for various size subsea burrowing systems.

Topics: Robots , Fluidization , Design
Commentary by Dr. Valentin Fuster
2015;():V05AT08A046. doi:10.1115/DETC2015-47693.

In this paper we present the design, fabrication, and testing of a robot for automatically positioning ultrasound imaging catheters. Our system will point ultrasound (US) catheters to provide real-time imaging of anatomical structures and working instruments during minimally invasive surgeries. Manually navigating US catheters is difficult and requires extensive training in order to aim the US imager at desired targets. Therefore, a four DOF robotic system was developed to automatically navigate US imaging catheters for enhanced imaging. A rotational transmission enables three DOF for pitch, yaw, and roll of the imager. This transmission is translated by the fourth DOF. An accuracy analysis was conducted to calculate the maximum allowable joint motion error. Rotational joints must be accurate to within 1.5° and the translational joint must be accurate within 1.4 mm. Motion tests were then conducted to validate the accuracy of the robot. The average resulting errors in positioning of the rotational joints were measured to be 0.28°–0.38° with average measured backlash error 0.44°. Average translational positioning and backlash errors were measured to be significantly lower than the reported accuracy of the position sensor. The resulting joint motion errors were well within the required specifications for accurate robot motion. Such effective navigation of US imaging catheters will enable better visualization in various procedures ranging from cardiac arrhythmia treatment to tumor removal in urological cases.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A047. doi:10.1115/DETC2015-47761.

This paper presents the design and development of a pneumatic soft-and-rigid hybrid actuator system that consists of half-bellow shaped soft sections in-between block shape rigid sections. The hybrid actuator architecture allows for selective actuation of each soft section (acting as a joint) with precise control over its bending motion. The soft half-bellow section is designed as a series of hollow ridges extending straight to a flat base. This geometry provides forward and backward bending motion when subjected to positive and negative pressure, respectively. Bending occurs as the ridges of the soft section expand and contract more than the flat base due to pressure variations. The rigid sections serve as connections between soft actuator sections and enhance force transfer. As a case study, a hybrid actuator system was designed as a soft robotic digit with three soft joints and four rigid connecting sections. Finite element analysis was performed to evaluate the design parameters such as number of ridges and materials for the robotic finger. The joints (from proximal to distal) were designed to have four, three, and two ridges, respectively, to generate the desired range of angular motion. Fabrication of the finger was done with silicone rubber RTV-4234-T4 and PMC polyurethane rubber using a combination of compression molding and overmolding processes. The angular and translational displacements of the robotic finger were experimentally and numerically evaluated at different pressures. The trajectory of the fingertip is comparable to those reported in literature for continuous soft actuators with a similar length. The significance of this actuator system is that both range of angular and translational motions are achieved at low pressure, less than 70kPa, as opposed to reported pressures of greater than 100kPa. The presented results show the great potential of the soft robotic finger for use in robotic, rehabilitation, and assistive device applications.

Topics: Actuators , Design , Robotics
Commentary by Dr. Valentin Fuster
2015;():V05AT08A048. doi:10.1115/DETC2015-47852.

RoboClam is a bio-inspired robot that digs into underwater soil efficiently by expanding and contracting its valves to fluidize the substrate around it, thus reducing drag. This technology has potential applications in fields such as anchoring, sensor placement, and cable installation. Though there are similar potential applications in dry soil, the lack of water to advect the soil particles prevents fluidization from occurring. However, theoretically, if the RoboClam contracts quickly enough, it will achieve a zero-stress state that will allow it to dig into dry soil with very little drag, independent of depth. This paper presents a theoretical model of the two modes of soil collapse to determine how quickly a device would need to contract to achieve this zero-stress state. It was found that a contraction time of 0.02 seconds would suffice for most soils, which is an achievable timescale for a RoboClam-like device.

Topics: Robots , Biomimetics , Soil
Commentary by Dr. Valentin Fuster
2015;():V05AT08A049. doi:10.1115/DETC2015-47871.

Recently, there has been a growing interest in moving away from traditional rigid exoskeletons towards soft exosuits that can provide a variety of advantages including a reduction in both the weight carried by the wearer and the inertia experienced as the wearer flexes and extends their joints. These advantages are achieved by using structured functional textiles in combination with a flexible actuation scheme that enables assistive torques to be applied to the biological joints. Understanding the human-suit interface in these systems is important, as one of the key challenges with this approach is applying force to the human body in a manner that is safe, comfortable, and effective. This paper outlines a methodology for characterizing the structured functional textile of soft exosuits and then uses that methodology to evaluate several factors that lead to different suit-human series stiffnesses and pressure distributions over the body. These factors include the size of the force distribution area and the composition of the structured functional textile. Following the test results, design guidelines are suggested to maximize the safety, comfort, and efficiency of the exosuit.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A050. doi:10.1115/DETC2015-48085.

This paper introduces an effective engineered rehabilitation system for understanding and inducing functional recovery of hemiparetic limbs based on the concept of timing-dependent induction of neural plasticity. Limb motor function is commonly impaired after neurologic injury such as stroke, with hemiparesis being one of the major impairments. In an emerging unique intervention for hemiparesis, named repetitive facilitation exercise, or RFE, a therapist manually applies brief mechanical stimuli to the peripheral target muscles (e.g., tapping, stretching of tendon/muscle) immediately before a patient intends to produce a movement with the muscle. The practice of this rehabilitation procedure by a skilled therapist often leads to dramatic rehabilitation outcomes. However, unskilled therapists, most likely due to the inaccuracy of the timing of peripheral stimulation in reference to the intention of movement (i.e. motor command), are unable to recreate the same rehabilitation results. Robotic rehabilitation, on the other hand, can improve the reliability and efficacy of the operation by satisfying the timing precision required by the therapy. This study demonstrates the use of a pneumatically-driven MRI-compatible robot for RFE assessment. The pressure dynamics of the system is studied for an accurate estimation on the time of response of the robot. The required temporal precision of the therapy is obtained and the use of the device is validated through experiments on a human subject.

Topics: Robotics
Commentary by Dr. Valentin Fuster

39th Mechanisms and Robotics Conference: Mobile Robots and Cable-Driven Systems

2015;():V05AT08A051. doi:10.1115/DETC2015-46369.

This paper proposes a trajectory generation technique for three-dof planar cable-suspended parallel robots. Based on the kinematic and dynamic modelling of the robot, positive constant ratios between cable tensions and cable lengths are assumed. This assumption allows the transformation of the dynamic equations into linear differential equations with constant coefficients for the positioning part, while the orientation equation becomes a pendulum-like differential equation for which accurate solutions can be found in the literature. The integration of the differential equations is shown to yield families of translational trajectories and associated special frequencies. This result generalizes the special cases previously identified in the literature. Combining the results obtained with translational trajectories and rotational trajectories, more general combined motions are analysed. Examples are given in order to demonstrate the results. Because of the initial assumption on which the proposed method is based, the ratio between cable forces and cable lengths is constant and hence always positive, which ensures that all cables remain under tension. Therefore, the acceleration vector remains in the column space of the Jacobian matrix, which means that the mechanism can smoothly pass through kinematic singularities. The proposed trajectory planning approach can be used to plan dynamic trajectories that extend beyond the static workspace of the mechanism.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A052. doi:10.1115/DETC2015-46432.

Developing reliable navigation strategies is mandatory in the field of Underwater Robotics and in particular for Autonomous Underwater Vehicles (AUVs) to ensure the correct achievement of a mission. Underwater navigation is still nowadays critical, e.g. due to lack of access to satellite navigation systems (e.g. the Global Positioning System, GPS): an AUV typically proceeds for long time intervals only relying on the measurements of its on-board sensors, without any communication with the outside environment. In this context, the filtering algorithm for the estimation of the AUV state is a key factor for the performance of the system; i.e. the filtering algorithm used to estimate the state of the AUV has to guarantee a satisfactory underwater navigation accuracy. In this paper, the authors present an underwater navigation system which exploits measurements from an Inertial Measurement Unit (IMU), Doppler Velocity Log (DVL) and a Pressure Sensor (PS) for the depth, and relies on either an Extended Kalman Filter (EKF) or an Unscented Kalman Filter (UKF) for state estimation. A comparison between the EKF approach, classically adopted in the field of underwater robotics and the UKF is given. These navigation algorithms have been experimentally validated through the data related to some sea tests with the Typhoon class AUVs, designed and assembled by the Department of Industrial Engineering of the Florence University (DIEF) for exploration and surveillance of underwater archaeological sites in the framework of the THESAURUS and European ARROWS projects. The comparison results are significant as the two filtering strategies are based on the same process and sensors models. At this initial stage of the research activity, the navigation algorithms have been tested offline. The presented results rely on the experimental navigation data acquired during two different sea missions: in the first one, Typhoon AUV #1 navigated in a Remotely Operated Vehicle (ROV) mode near Livorno, Italy, during the final demo of THESAURUS project (held in August 2013); in the latter Typhoon AUV #2 autonomously navigated near La Spezia in the framework of the NATO CommsNet13 experiment, Italy (held in September 2013). The achieved results demonstrate the effectiveness of both navigation algorithms and the superiority of the UKF without increasing the computational load. The algorithms are both affordable for online on-board AUV implementation and new tests at sea are planned for spring 2015.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A053. doi:10.1115/DETC2015-46480.

This paper presents operational space control of snake-like robots for tracking designated paths using a double layer sliding mode control algorithm. The snake robot has n links with assumed lateral sliding that leads to n+2 degrees-of-freedom (DOF) while it has only n-1 actuator at joints and therefore it is underactuated. Kinematic constraints were determined which describe the geometric relationship between the position of links’ mass center and the joints’ relative angle. The outer layer (loop) of the controller was designed to modulate the parameters of the serpenoid curve using the kinematic constraints in order to the mass center of links follow different designated paths. The inner layer of sliding mode controller was developed to guarantee tracking of the modulated serpenoidal pattern by the snake robot’s joints. In this work, Kane’s method was used to model the robot dynamics with a Coulomb friction for interaction with ground. Uncertainty with an upper bound was considered for the model parameters. To demonstrate the effectiveness of the designed controller in presence of uncertainties, the double layer controller was examined on a four links snake-like robot with uncertain model parameters in tracking of a straight line and a circular path. Simulation results are presented in support of the proposed idea.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A054. doi:10.1115/DETC2015-46655.

This paper presents a generalized method of determining the static shape conformation of a cable-driven serpentine robot. Given a set of desired cable displacements as model inputs, the model calculates the joint angles and cable tensions that result from those displacements. The model’s governing equations are derived from ensuring static equilibrium at each of the robot’s revolute joints, along with compatibility equations ensuring the joint angles result in the desired cable displacements. Elastic, actuation and gravitational loading are included in the model, and the results analyze the relative impact of each for various combinations of cable displacement inputs. In addition, the impact of elasticity and mass distribution on the accuracy of purely kinematic constant-curvature segment models is presented. In addition, the model also accommodates limits for the serpentine joint angles. The model is implemented in MATLAB, and results are generated to analyze the impact of the actuation, elastic and gravitational effects. Future work will include inertial effects in the model to make it dynamic. These models will be used as the foundation for a serpentine tail design for use on-board a mobile robot, and for task planning to enable that tail to be effectively used in various scenarios.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A055. doi:10.1115/DETC2015-46837.

Cable-driven robots have advantages which make them attractive solutions for a variety of tasks, however, the unidirectional nature of cable actuators complicates the design and often results in multiply redundant cable architectures which increase cost and robot complexity. This paper presents a stochastic optimization approach to the problem of designing a cable routing for a cable-driven manipulator to provide the desired robot workspace while minimizing the cable tensions required to perform a desired task.

Two cable routing design variants are developed for a robot leg through the application of a stochastic optimization methodology called Particle Swarm Optimization. The PSO methodology is summarized, followed by a description of the specific implementation of the methodology to the particular problem of optimizing the cable routing of a robot leg. An objective function is developed to capture all pertinent design criteria in a quantitative evaluation of each particular set of cable parameters. Finally, a description of the PSO execution is presented and the results of the two optimization problems are presented and discussed.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A056. doi:10.1115/DETC2015-46842.

Cable-driven robots are often considered an attractive solution for applications which require a low-inertia actuator capable of high accelerations, despite the added complexity of the system and increased challenges of the design. Previous research has developed various techniques for analyzing the workspace of a cable-driven robot and several methods of designing a cable routing have been demonstrated which enable a robot to perform a given task. In general, there are many choices of cable routing which satisfy the particular design requirements, and the problem is focused on how to select the best design from among the available choices.

Using techniques developed from statistical learning theory, the field of Randomized Algorithms offers explicit bounds on the estimation errors of an optimal solution, provided certain explicitly defined sample complexity requirements are satisfied. The main advantage of this approach is a quantitative understanding of the uncertainty of the result and the accuracy with respect to the true optimum to enable an informed decision regarding the sufficiency of the solution. The desired accuracy and confidence parameters for the optimal solution are tailored for the specific problem, allowing for balance between computational limitations and desire for solution quality. In this work, a summary of the randomized algorithm approach is presented, and an optimized solution to the design of a cable-driven manipulator is developed using a randomized algorithm according to specified accuracy, level and confidence parameters.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A057. doi:10.1115/DETC2015-47143.

Tensegrity structures have a great value in the academia and in industry, in particular for adjustable tensegrity structures that can sustain external forces when deployed. The main problem with the latter systems is checking their stability during deployment. One of the most famous methods for checking stability was developed 20 years ago by two mathematicians [1]. They showed that if the tensegrity structure is redundant then the check is simple. But if it is a determinate tensegrity structure then there is a need to calculate the velocities of all the joints and then after matrix multiplications a scalar is obtained. If the scalar is negative then it is concluded that the tensegrity system is unstable without knowing which element causes the problem and what should be done in order to stabilize it.

This paper proves that if the structure is a minimal rigid determinate structure, named Assur Graph, then there is a simple method for checking the stability. The proposed method suggests to remove a cable, calculate the curvature radius of one its inner joint and then conclude whether the structure is stable or not. In case that it was concluded that the system is unstable, then to shorten the cable so it becomes stable.

The main topic from the combinatorial method being used in this paper is the special properties of Assur Graphs, in particular their singular positions. It is proved that from all the determinate structures only the Assur Graphs have these special singular properties, upon which the proposed method and the proof relies on.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A058. doi:10.1115/DETC2015-47223.

Pose estimation and trajectory tracking of a spherical rolling robot is a complex problem owing to kinematics and dynamics of the system and the constraint of not being able to add range sensors like ultrasonic or infrared distance sensors on the robot. The pose estimate for the robot under study, needs to be derived purely using inertial measurement unit (IMU) and odometry from analog wheel encoders, which in turn include high uncertainties. Adding to this, the system kinematic and dynamic model to accurately predict the behavior is quite complex. In this paper we present a simplified kinematic model, sensor filtering techniques and the control strategy adopted to locate and navigate the robot to a desired waypoint autonomously. A filter block provides clean heading output from the IMU and incremental pulses from an analog wheel encoder; the pose estimator uses heading and incremental pulses to calculate its position according to the system kinematic model. A pure-pursuit algorithm generates left & right wheel velocities to keep the robot on a commanded waypoint, using the robot kinematic model and localization data. The validity of our kinematic model and performance of our waypoint tracking are verified with the ground truth using a motion capture system and onboard sensors, where the application domain is bio-inspired, micro (small scale) robotics.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A059. doi:10.1115/DETC2015-47583.

The Underactuated Lightweight Tensegrity Robotic Assistive Spine (ULTRA Spine) project is an ongoing effort to create a compliant, cable-driven, 3-degree-of-freedom, underactuated tensegrity core for quadruped robots. This work presents simulations and preliminary mechanism designs of that robot. Design goals and the iterative design process for an ULTRA Spine prototype are discussed. Inverse kinematics simulations are used to develop engineering characteristics for the robot, and forward kinematics simulations are used to verify these parameters. Then, multiple novel mechanism designs are presented that address challenges for this structure, in the context of design for prototyping and assembly. These include the spine robot’s multiple-gear-ratio actuators, spine link structure, spine link assembly locks, and the multiple-spring cable compliance system.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A060. doi:10.1115/DETC2015-47637.

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 or windmill, tank, and pipeline construction. In many cases, these mobile robots must operate in climbing configurations and on non-planar surfaces due to the unstructured nature of these manufacturing tasks. Unit operations are commonly considered in a planar context, but in practice are performed on generally non-planar surfaces. One such example is welding a seam along a non-flat ship hull; these surfaces consist of common geometric shapes such as cylinders or spheres. This paper will present a kinematic analysis of one mobile robot topology performing specified tasks on cylindrical surfaces. The analysis will define a method to determine the robot path on a work-piece surface as well as the configuration joint parameters along when the motion is prescribed in local tool space coordinates. This method assumes that the robot operates following the no-slip, pure roll conditions. The effort is motivated by a practical application of welding on steel hulls or other surfaces and the results will be compared with these empirical experiences. A discussion of how these results can be used to guide future design of mobile robot platforms for manufacturing is provided.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A061. doi:10.1115/DETC2015-47666.

The locomotion of legged robots is inherently underactuated, which creates control challenges in terms of rejecting large disturbances. A detailed understanding of how the control authority of a robot evolves over a gait trajectory has the potential to inform the design of controllers that offer superior disturbance rejection capabilities without compromising the efficiency benefits that typically accompany underactuated legged robots. Previous work has shown how the system velocities of an underactuated mechanical system can be decomposed into directions aligned with the inputs, or controlled directions, and directions orthogonal to the inputs, or uncontrolled directions, and applied that decomposition to drive wheeled robots to rest. This decomposition fundamentally provides a measure of the instantaneous control authority of the robot. This paper examines how the same techniques can be applied to inform the control of biped robots walking with periodic gaits. This problem differs from those previously studied in that it necessarily involves ground impacts and non-zero desired velocities. A representative example of a two-link planar biped walking on flat ground shows how a simple open loop controller that implements heuristics identified through the velocity decomposition to make use of the available control authority can improve disturbance rejection when added to a hybrid zero dynamics-based controller.

Commentary by Dr. Valentin Fuster
2015;():V05AT08A062. doi:10.1115/DETC2015-47867.

This paper discusses the design of a three degree-of-freedom (3-DOF) non-redundant walking robot with decoupled stance and propulsion locomotion phases that is exactly constrained in stance and utilizes adaptive underactuation to robustly traverse terrain of varying ground height. Legged robots with a large number of actuated degrees of freedom can actively adapt to rough terrain but often end up being kinematically overconstrained in stance, requiring complex redundant control schemes for effective locomotion. Those with fewer actuators generally use passive compliance to enhance their dynamic behavior at the cost of postural control and reliable ground clearance, and often inextricably link control of the propulsion of the robot with control of its posture. In this paper we show that the use of adaptive underactuation techniques with constraint-based design synthesis tools allows for lighter and simpler lower mobility legged robots that can adapt to the terrain below them during the swing phase yet remain stable during stance and that the decoupling of stance and propulsion can greatly simplify their control. Simulation results of the swing phase behavior of the proposed 3-DOF decoupled adaptive legged robot as well as proof-of-concept experiments with a prototype of its corresponding stance platform are presented and validate the suggested design framework.

Commentary by Dr. Valentin Fuster

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