Optimal dimensional synthesis of force feedback lower arm exoskeletons

This paper presents multi-criteria design optimization of parallel mechanism based force feedback exoskeletons for human forearm and wrist. The optimized devices are aimed to be employed as a high fidelity haptic interfaces. Multiple design objectives are discussed and classified for the devices and the optimization problem to study the trade-offs between these criteria is formulated. Dimensional syntheses are performed for optimal global kinematic and dynamic performance, utilizing a Pareto front based framework, for two spherical parallel mechanisms that satisfy the ergonomic necessities of a human forearm and wrist. Two optimized mechanisms are compared and discussed in the light of multiple design criteria. Finally, kinematic structure and dimensions of an optimal exoskeleton are decided

Mechanical design optimization for multi-finger haptic devices applied to virtual grasping manipulation

This paper describes the design of a modular multi-finger haptic device for virtual object manipulation. Mechanical structures are based on one module per finger and can be scaled up to three fingers. Mechanical configurations for two and three fingers are based on the use of one and two redundant axes, respectively. As demonstrated, redundant axes significantly increase workspace and prevent link collisions, which is their main asset with respect to other multi-finger haptic devices. The location of redundant axes and link dimensions have been optimized in order to guarantee a proper workspace, manipulability, force capability, and inertia for the device. The mechanical haptic device design and a thimble adaptable to different finger sizes have also been developed for virtual object manipulation

Kinematic design of a two contact points haptic interface for the thumb and index fingers of the hand.

This paper presents an integrated approach to the kinematic design of a portable haptic interface for the thumb and index fingers of the hand. The kinematics of the haptic interface was selected on the basis of constructive reasons, design constraints, and usability issues, and in order to guarantee the best level of performance with the lowest encumbrance and weight over the workspace of the hand. The kinematic dimensioning was the result of a multi-objective optimization of several performance parameters, such as minimum required torque at actuators and maximum reachable workspace, with the simultaneous fulfillment of design constraints, such as satisfactory mechanical stiffness at the end effector, global kinematic isotropy over the workspace, and limited bulk of the device. A geometric interpretation of singularities based on screw theory was formulated to point out both hand postures and movements associated with weaker performance. The results of the paper were used to build the prototype of a new portable haptic interface with two contact points, whose main design features are also specifically presented

HEXOSYS II - Towards realization of light mass robotics for the hand

This research presents a prototype of a direct-driven, optimized and light-mass hand exoskeleton that is designed to fit over the dorsal side of the hand, thus retaining palm free for interaction with real/virtual objects. The link lengths of the proposed Hand EXOskeleton SYStem (HEXOSYS) TT have been selected based on an optimization algorithm. In an attempt to make the design human hand compatible, the actuators of HEXOSYS II have been chosen as a result of series of experiments on human hands of various sizes. The system based on an optimum under-actuated mechanism provides 3 DOF/finger. The resultant motion of the exoskeleton allows the wearer to perform flexion/abduction as well as passive abduction/adduction. Simple and under-actuated mechanisms together with compact mechanical design lead to realize a light mass robotic system. The first prototype of HEXOSYS II has been fabricated. Comprising of four fingers, which are enough to accomplish most of our daily life activities, the system weighs 600 grams. © 2011 IEEE

Design optimization and control of a parallel lower-arm exoskeleton

Wearable force feedback robotic devices, haptic exoskeletons, are becoming increasingly common as they find widespread use in medical and virtual reality (VR) applications. Allowing users to mechanically interact with computationally mediated environments, haptic exoskeletons provide users with better “immersion” to VR environments. Design of haptic exoskeletons is a challenging task, since in addition to being ergonomic and light weight, such devices are also required to satisfy the demands of any ideal force-feedback device: ability withstand human applied forces with very high stiffness and capacity to display a full range of impedances down to the minimum value human can perceive. If not properly designed by taking these conflicting requirements into account, the interface can significantly deteriorate the transparency of displayed forces; therefore, the choice of the kinematic structure and determination of the dimensions of this kinematic structure have significant impacts on the overall performance of any haptic display independent of the control algorithm employed. In this thesis, we first propose a general framework for optimal dimensional synthesis of haptic interfaces, in particular for haptic interfaces with closed kinematic chains, with respect to multiple design objectives. We identify and categorize the relevant performance criteria for the force feedback exoskeletons and address the trade-offs between them, by applying a Pareto-front based multi-objective design optimization procedure. Utilizing a fast converging gradient-based method, the proposed framework is computational efficient. Moreover, the approach is applicable to any set of performance indices and extendable to include any number of design criteria. Subsequently, we extend this framework to assist the selection of the most appropriate kinematic structure among multiple mechanisms. Specifically, we perform a rigorous comparison between two spherical parallel mechanisms (SPMs) that satisfy the ergonomic necessities of a human forearm and wrist and select the kinematic structure that results in superior performance for force-feedback applications. Utilizing the Pareto optimal set of solutions, we also assign dimensions to this mechanism to ensure an optimal trade-off between global kinematic and dynamic performance. Following the design optimization phase, we perform kinematic and dynamic analyses of the SPM-based exoskeleton in independent coordinates to facilitate efficient simulation and real-time implementation of model based controllers. We decide on the hardware components considering human wrist torque and force limits, safety and ergonomy constraints, and present the CAD model of a prototype of the exoskeleton. Finally, we implement model based task-space position and impedance controllers in simulation and present the results of them

Haptic Guidance for Extended Range Telepresence

A novel navigation assistance for extended range telepresence is presented. The haptic information from the target environment is augmented with guidance commands to assist the user in reaching desired goals in the arbitrarily large target environment from the spatially restricted user environment. Furthermore, a semi-mobile haptic interface was developed, one whose lightweight design and setup configuration atop the user provide for an absolutely safe operation and high force display quality