A Bond Graph Approach to the Analysis of Prosthesis for a Partially Impaired Hand

[+] Author and Article Information
Anand Vaz

Department of Mechanical Engineering,  SLIET, Longowal, District Sangrur, Punjab 148106, Indiaanandvaz@ieee.org

Shinichi Hirai

Department of Robotics,  Ritsumeikan University, Noji-higashi 1-1-1, Kusatsu, Shiga 525-8577, Japanhirai@se.ritsumei.ac.jp

J. Dyn. Sys., Meas., Control 129(1), 105-113 (Mar 07, 2006) (9 pages) doi:10.1115/1.2397160 History: Received April 26, 2004; Revised March 07, 2006

A system dynamics approach, based on bond graphs, is presented for the analysis of prosthetic devices for a partially impaired hand. The partial impairment implies that the hand has lost one or more fingers but retains the ability of its remaining natural fingers. It is shown that the existing natural joints can be used for the actuation of prosthetic finger joints and enable performance of tasks that would not have been possible otherwise. This is a challenging task as motion has to be transmitted from the remaining natural joints to the prosthetic joints. The joint axes move with respect to each other during performance of tasks and do not have any fixed relative orientation. In this work, basic concepts for the actuation of the prosthesis required for such tasks are developed systematically. Based on these concepts, Bowden cable based joint actuation mechanisms for transmission of motion from natural joints to corresponding prosthetic joints are presented and analyzed. The analysis of dynamics of the resulting under-actuated prosthesis with joint actuation mechanism is based on bond graph models that are systematically developed. Using these models, system equations are derived and numerical simulations performed for the analysis. One- and two-joint actuated prototypes of the prosthesis have been presented and effectively demonstrate the proposed concepts.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Skeletal link structure of the first three fingers during hand writing

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Figure 2

Joint actuation using Bowden cable string-tube combination

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Figure 3

Configurations for joint actuation. (a) Like configuration. (b) Unlike configuration.

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Figure 4

Modularity of joints. Modularity allows extension of more DOF to the mechanism.

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Figure 5

Bond graph representing Bowden cable based joint actuation

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Figure 6

Actuation of an active joint and its bond graph. (a) The active joint is connected to a natural finger which provides required torque for joint actuation. (b) Bond graph model of dynamics for the active joint.

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Figure 7

Bond graph for the Bowden cable based joint actuation. Elastic and internal damping properties of the string-tubes, and friction between the string and tube are considered.

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Figure 8

Time history of joint angles and their rates for active and passive joints. Opening and closing of the joints in unlike configuration is shown. (a) Joint angles θA and θP. (b) Joint angle rates θ̇A and θ̇P.

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Figure 9

Tension in strings during actuation. (a) Tension in string 1. (b) Tension in string 2. No pretension is applied in this case.

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Figure 10

Plot of tensions with extensions in the absence of initial pretension. (a) Tension versus extension for string 1. (b) Tension versus extension for string 2.

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Figure 11

Plot of string tensions with time during actuation. Initial pretension of 10N is considered. (a) Tension versus time for string 1. (b) Tension versus time for string 2.

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Figure 12

Graphs of tensions versus extensions during actuation with a pretension of 10N. (a) Tension versus extension for string 1. (b) Tension versus extension for string 2.

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Figure 13

Power transactions. The distribution of input power for actuation of the finger joints and the power losses in bearings.

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Figure 14

Plot of tensions with extensions in the absence of initial pretension. Hysteresis can be observed. (a) Tension versus extension for string 1. (b) Tension versus extension for string 2.

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Figure 15

One-joint actuated prosthetic mechanism demonstrating the unlike configuration. (a) Opening movement. (b) Closing movement. No tubing is used in this device. The joint axes are fixed.

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Figure 16

Photograph of the Bowden cable string-tube arrangement

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Figure 17

Two-joint actuated Bowden cable based mechanism with unlike configuration. Photographs show intermediate frames during motion taken at equal intervals. Passive joints are actuated by corresponding active joints. The joint axes for the second active and passive joints are not fixed.




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