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RESEARCH PAPERS

Design of a Passive Gravity-Balanced Assistive Device for Sit-to-Stand Tasks

[+] Author and Article Information
Abbas Fattah

Mechanical Systems Laboratory, Department of Mechanical Engineering,  University of Delaware, Newark, DE 19716fattah@me.udel.edu

Sunil K. Agrawal1

Mechanical Systems Laboratory, Department of Mechanical Engineering,  University of Delaware, Newark, DE 19716agrawal@me.udel.edu

Glenn Catlin, John Hamnett

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

1

Corresponding author.

J. Mech. Des 128(5), 1122-1129 (Oct 10, 2005) (8 pages) doi:10.1115/1.2216732 History: Received March 31, 2005; Revised October 10, 2005

A sit-to-stand assist device can serve the needs of people suffering from muscle weakness due to age or disabilities that make sit-to-stand a difficult functional task. The objective of this paper is to design a passive gravity-balancing assist device for sit-to-stand motion. In our study, it has been shown that the contribution to the joint torques by the gravitational torque is dominant during sit-to-stand motion. On the basis of this result, a gravity balanced assistive device is proposed. This passive device uses a hybrid method to identify the center-of-mass of the system using auxiliary parallelograms first. Next, appropriate springs are connected to the device to make the total potential energy of the system due to the gravity and the springs constant during standing up. A demonstration prototype with the underlying principles was fabricated to test the feasibility of the proposed design. The prototype showed gravity balancing and was tested by the authors. This prototype will be modified appropriately for clinical testing.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 5

Spring attachments of the 3 DOF human body

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Figure 1

A 3-DOF planar model of the human body

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Figure 2

Joint angles for standing up motion, θa (ankle), θk (knee), θh (hip), from experiment (19) and simulation

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Figure 3

(a) Ankle joint torques, (b) knee joint torques, (c) hip joint torques. Total: Solid; inertial: Dotted; gravitational: Dashed; and passive: Dashdot

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Figure 4

The 3 DOF human body and device with auxiliary parallelograms to determine the c.m. of the body

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Figure 6

Joint torques with gravity balancing and without gravity balancing

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Figure 7

Spring extensions (a) and spring forces (b) for the preliminary design. x and fPC: Solid line; x1 and fO1S1: Dashed; x2 and fS3C: Dashdot; x3 and fO2S2: Dotted.

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Figure 8

Schematic model of the new design

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Figure 9

Spring extensions (a) and spring forces (b) for the new design. x and fPC: Solid line; x1 and fO1S1: Dashed; x2 and fS3C: Dashdot; x3 and fO2S2: Dotted.

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Figure 10

(a) Auxiliary parallelograms for the preliminary design, (b) auxiliary parallelograms for the new design

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Figure 11

Photograph of the new prototype of the assistive design

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Figure 12

Photographs of the new prototype with the subject in sit and stand positions

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