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Research Papers

Variable Geometry Stair Ascent and Descent Controller for a Powered Lower Limb Exoskeleton

[+] Author and Article Information
Andrew Ekelem

Department of Mechanical Engineering,
Vanderbilt University,
2400 Highland Avenue Olin Hall Room 101,
Nashville, TN 37212
e-mail: ekelem90@gmail.com

Gerasimos Bastas

Department of Physical Medicine
and Rehabilitation,
Vanderbilt University,
Nashville, TN 37212
e-mail: gerasimos.bastas@vanderbilt.edu

Christina M. Durrough

Pi Beta Phi Rehabilitation Institute,
Vanderbilt Bill Wilkerson Center,
1215 21st Avenue South, Suite 9211,
Nashville, TN 37232
e-mail: christina.m.durrough@vanderbilt.edu

Michael Goldfarb

Mem. ASME
Department of Mechanical Engineering,
Vanderbilt University,
2400 Highland Avenue Olin Hall Room 101,
Nashville, TN 37212
e-mail: michael.goldfarb@vanderbilt.edu

1Corresponding author.

Manuscript received August 4, 2017; final manuscript received June 26, 2018; published online July 30, 2018. Assoc. Editor: Elizabeth Hsiao-Wecksler.

J. Med. Devices 12(3), 031009 (Jul 30, 2018) (10 pages) Paper No: MED-17-1278; doi: 10.1115/1.4040699 History: Received August 04, 2017; Revised June 26, 2018

This paper describes a control approach for a lower limb exoskeleton intended to enable stair ascent and descent of variable geometry staircases for individuals with paraplegia resulting from spinal cord injury (SCI). To assess the efficacy of ascent and descent functionality provided by the control approach, the controller was implemented in a lower limb exoskeleton and tested in experimental trials on three subjects with motor-complete SCI on three staircases of varying geometry. Results from the assessments indicate that subjects were able to capably ascend and descend step heights varying from 7.6 to 16.5 cm without changing control settings; the controller provided for step time consistency highly representative of healthy subjects (9.2% variation in exoskeleton step time, relative to 7.7% variation in healthy subjects); and the exoskeleton provided peak joint torques on average 110% and 74% of the healthy-subject peak joint torques during stair ascent and descent, respectively. Subject perceived exertion during the stair ascent and descent activities was rated between “light” and “very light.”

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References

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Figures

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Fig. 1

Configuration parameters used in the controller

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Fig. 2

State machine for ascent

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Fig. 3

State machine for descent

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Fig. 4

Indego Exoskeleton. Photograph courtesy of Parker Hannifin.

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Fig. 5

Stair geometries used in controller assessment

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Fig. 6

Photographic sequence of ascent states

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Fig. 7

Joint angle trajectories corresponding to stair ascent for 90 steps from three subjects on stair 1 (dark), and 63 steps on stair 3 (light). The trajectories start from state 2 and the vertical lines mark the state transitions.

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Fig. 8

Average ascent joint torques are shown for three subjects for 90 steps on stair 1. Dashed lines are plus and minus one standard deviation. The plots begin in state 2 and vertical lines mark state transitions.

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Fig. 9

Average ascent joint powers are shown for three subjects for 90 steps on stair 1. Dashed lines are plus and minus one standard deviation. The plots begin in state 2 and vertical lines mark state transitions.

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Fig. 10

Photographic sequence of descent states

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Fig. 11

Joint angle trajectories corresponding to stair descent for 89 steps from three subjects on stair 1 (dark) and 63 steps on stair 3 (light). The trajectories start from state 2 and the vertical lines mark the state transitions.

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Fig. 12

Average descent joint torques are shown for three subjects for 89 steps on stair 1. Dashed lines are plus and minus one standard deviation. The plots begin in state 2 and vertical lines mark state transitions. Positive torques correspond to extensive moments.

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Fig. 13

Average descent joint powers are shown for three subjects for 89 steps on stair 1. Dashed lines are plus and minus one standard deviation. The plots begin in state 2 and vertical lines mark state transitions.

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Fig. 14

Average time per step of each user for 36 steps, and the average of the group with plus/minus one standard deviation bars

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Fig. 15

Average angle measurements and plus/minus one standard deviation bars for the right hip (RH) and right knee (RK) at the transition point from the state 3 of ascent where stair tread contact is made for stair 2 and stair 3, corresponding to step heights of 7.62 cm and 15.24 cm, respectively. Stair 1 is omitted due to similarity in height to stair 3.

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