Design and Optimization of a Cable Driven Upper Arm Exoskeleton

Abstract

This paper outlines the design of a wearable upper arm exoskeleton that can be potentially used to assist and train arm movements of stroke survivors or subjects with weak musculature. In the last 10 years, a number of upper arm training devices have emerged. However, due to their size and weight, their use is restricted to clinics and research laboratories. Our proposed wearable exoskeleton builds upon our research experience in wire driven manipulators and design of rehabilitative systems. The exoskeleton consists of three main parts: (i) an inverted U-shaped cuff that rests on the shoulder, (ii) a cuff on the upper arm, and (iii) a cuff on the forearm. Six motors mounted on the shoulder cuff drive the cuffs on the upper arm and forearm with the use of cables. In order to assess the performance of this exoskeleton prior to use on humans, a laboratory test-bed has been developed where this exoskeleton is mounted on a model skeleton, instrumented with sensors to measure joint angles. This paper describes the design details of the exoskeleton and addresses the key issue of parameter optimization to achieve a useful workspace based on kinematic and kinetic models. The optimization results have also been motivated from activities of daily living.

Dynamics and control of a 4-dof wearable cable-driven upper arm exoskeleton

“…All six originate at the shoulder cuff, where the motors are mounted. The attachment points at the shoulder are adjustable both radially and angularly to allow optimal positioning of the motors [15]. Four of the wires terminate at the bicep cuff, and are responsible for the three degrees-of-freedom at the shoulder (plane of elevation, angle of elevation, internal/external rotation).…”

“…Unlike rigid links, cables can only be effective while in tension, so the location of the cables becomes very important. Briefly, the cable positions were selected by optimizing the area of the static workspace [15]. The static workspace was calculated by setting q && and q & equal to 0 in (1), and then determining the total number of feasible points where the arm can be in equilibrium under gravity.…”

Design considerations for an active soft orthotic system for shoulder rehabilitation

“…However, pneumatics are an expensive and complicated actuation method for a device to be used in the home. Agrawal et al created a system of six shouldermounted motors and cables to actuate the arm in multiple DOF [9], [10]. This system's kinematics have been optimized to achieve a useful range of motion, however it is not adjustable to anatomical variations or easily wearable.…”

Optimal Design of a 3-DOF Cable-Driven Upper Arm Exoskeleton

“…Based on workspace analysis, Mustafa et al and Yang et al proposed a six-cable parallel manipulator to implement the rotation of upper arm and gave several sets of available dimension parameters [19,20]. Mao and Agrawal optimized the upper arm part of the proposed cable-driven arm exoskeleton [21,22]. However, due to analysis complexity, existing research on optimal design is based on limited design options and fails to illustrate the relationship between design parameters and manipulator performances.…”