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Research Papers

Design and Optimization of a Cable Driven Upper Arm Exoskeleton

[+] Author and Article Information
Sunil K. Agrawal, John J. Gangloff, Elizabeth Brackbill, Ying Mao, Vivek Sangwan

Department of Mechanical Engineering, Mechanical Systems Laboratory, University of Delaware, Newark, DE 19716

Venketesh N. Dubey

School of Design, Engineering and Computing, Bournemouth University, Fern Barrow, Poole, BH12 5BB, UK

J. Med. Devices 3(3), 031004 (Aug 31, 2009) (8 pages) doi:10.1115/1.3191724 History: Received January 06, 2009; Revised May 28, 2009; Published August 31, 2009

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.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Model of the exoskeleton on a skeleton arm

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Figure 2

Exoskeleton fitted on a plastic arm with cable driven cuffs

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Figure 3

Shoulder cuff design with adjustable motor placement

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Figure 4

Parameters for kinematic modeling

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Figure 5

Zero configuration and axis of rotation (a) as viewed from the back and (b) from the side of a human model

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Figure 6

Flow chart of optimization process; the whole arm is split into shoulder and elbow joint cables. Initially, positive tension is ensured in the elbow cables and then later at the shoulder.

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Figure 7

A sketch of a feasible region for m for a 3DOF shoulder joint driven by four cables

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Figure 8

Cable attachment points on shoulder and upper arm cuffs with optimization parameters as shown with respect to the local coordinate frame and the sense of rotation on the plane of the cuffs

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Figure 9

Feasible workspace at the initial setting: (a) qualitative (darker and better) and (b) quantitative (gray, feasible; black, infeasible points) obtained by testing the feasibility conditions for a unit arm placed at the coordinate frame passing through (ArmX, ArmY, and ArmZ) end positions

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Figure 10

Upper and lower bounds of an attachment point on the shoulder cuff

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Figure 11

Optimized workspace due to the joint motion at the shoulder: (a) qualitative and (b) quantitative (gray, feasible; black, infeasible points; 7830 feasible points achieved out of 8000 possible points)

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Figure 12

Exoskeleton workspace: (a) initial setting and (b) optimized result (gray, feasible; black, infeasible points), 8390 feasible points achieved out of 10,000 possible points

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Figure 13

Optimization results for cable attachment points from the initial to the final configuration; the top plate shows the model in the initial configuration represented by the left hand line diagram. The optimized arrangement is shown in the right hand line diagram reflected into the new model setting—the central line is the arm in the extended position and black lines represent the cuffs.

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Figure 14

Workspace for ADL: (a) initial setting, (b) global optimization, and (c) ADL specific optimization

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Figure 15

Schematic of the implementation architecture on the exoskeleton in (a) hardware and (b) software

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Figure 16

(a) Joint angle: simulation (dashed) versus experiment (solid). (b) Wrist point coordinates in base frame: simulation (dashed) versus experiment (solid)

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