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Technical Briefs

Design and Experimental Evaluation of a Vertical Lift Walker for Sit-to-Stand Transition Assistance

[+] Author and Article Information
Thomas C. Bulea

Department of Biomedical Engineering,  Case Western Reserve University, 319 Wickenden Building., 10900 Euclid Ave, Cleveland, OH, 44106tcb9@case.edu

Ronald J. Triolo

Department of Orthopaedics,  Case Western Reserve University, Cleveland, OH, 44106; Department of Veterans Affairs Medical Center, 10701 East Blvd., Cleveland, OH 44106, USAronald.triolo@case.edu

J. Med. Devices 6(1), 014504 (Mar 13, 2012) (5 pages) doi:10.1115/1.4005786 History: Received June 09, 2011; Revised December 15, 2011; Published March 12, 2012; Online March 13, 2012

A walker capable of providing vertical lift support can improve independence and increase mobility of individuals living with spinal cord injury (SCI). Using a novel lifting mechanism, a walker has been designed to provide sit-to-stand assistance to individuals with partially paralyzed lower extremity muscles. The design was verified through experiments with one individual with SCI. The results show the walker is capable of reducing the force demands on the upper and lower extremity muscles during sit-to-stand transition compared to standard walkers. The walker does not require electrical power and no grip force or harness is necessary during sit-to-stand operation, enabling its use by individuals with limited hand function. The design concept can be extended to aid other populations with lower extremity weakness.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Design concept of the vertical lift assist walker. The platform moves vertically and provides a vertical lift force equal to roughly 80% of body weight. Lift force is provided through bilateral gas springs. Platform motion is guided by self aligning linear bearings, which prevent tilt and hold the platform horizontal.

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Figure 2

Pneumatic elevator components. The gas springs actuate the assembly. (a) The platform sits 34 inches from the ground in the fully compressed position. (b) In the fully extended position, the platform height is 54 inches. (c) Clevis-pin rod end attachment of gas spring to walker platform. (d) Ball-joint rod end attachment of gas spring cylinder to mounting bracket.

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Figure 3

Finite element stress analysis of the ball-headed bolt which connects the gas springs to the walker. (a) The maximum applied load depicted on a solid model of the bolt, made from plain carbon steel (yield strength of 2.2 × 10−8 N/m2 ). (b) Stress distribution under maximum load. Maximum stress was approximately 65% of yield stress. (c) Displacement of the bolt during maximum loading. Maximum displacement was 6.0 × 10−4 inches.

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Figure 4

Photographs of a sit-to-stand transition using the prototype lift assist walker. (a) Initially, the walker is locked in the seated position. (b) Upon pressing the release button, the gas springs exert 890 N (200 lbf) of force through the shoulders of the user to lift him from the chair. (c) The walker is locked in the fully extended position, capable of supporting loads in excess of 1335 N (300 lbf).

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Figure 5

The mean vertical torso position (a) and mean velocity (b) during the sit-to-stand transition, normalized in time by the lift cycle. Position is relative to the ground. The dotted lines are ±1 standard deviation.

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Figure 6

The mean lower extremity lift force exerted by the user during the sit-to-stand transition with a standard walker and prototype lift walker. The dotted lines are ±1 standard deviation.

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Figure 7

(a) The mean upper extremity vertical force exerted by the user during sit-to-stand transition with a standard walker. (b) The mean lift force exerted by the prototype lift walker during sit-to-stand transition. The dotted lines are ±1 standard deviation.

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