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Research Papers

Design and Preliminary Evaluation of a Passive Spine Exoskeleton

[+] Author and Article Information
Haohan Zhang

Department of Mechanical Engineering,
Columbia University,
New York, NY 10027
e-mail: hzhang2347@columbia.edu

Abhijit Kadrolkar

Department of Mechanical
and Industrial Engineering,
University of Massachusetts Amherst,
160 Governor's Drive,
Amherst, MA 01003
e-mail: akadrolk@umass.edu

Frank C. Sup, IV

Department of Mechanical
and Industrial Engineering,
University of Massachusetts Amherst,
160 Governor's Drive,
Amherst, MA 01003
e-mail: sup@umass.edu

1Corresponding author.

Manuscript received March 23, 2015; final manuscript received September 14, 2015; published online November 16, 2015. Assoc. Editor: Carl Nelson.

J. Med. Devices 10(1), 011002 (Nov 16, 2015) (8 pages) Paper No: MED-15-1150; doi: 10.1115/1.4031798 History: Received March 23, 2015; Revised September 14, 2015

This paper presents a design of a passive spine exoskeleton which implements a “push–pull” external assistive strategy. The spine exoskeleton was designed for reducing the risk of back injury. It applies a pulling force on thoracic region and a pushing force on lumbar region during spine flexion/extension. The design was inspired by previous simulation work, where the results highly supported benefits of the push–pull strategy on reducing the back muscular efforts and bending moment for the sagittal spine flexion/extension. A passive physical prototype was designed and constructed to test the push–pull strategy on human subjects. Three subjects were able to repeat the identical dynamic spine flexion and extension tasks with the spine exoskeleton prototype. The surface electromyography showed a reduction of up to 24% at lumbar and 54% at thoracic level muscle for the human subjects wearing the exoskeleton suit to accomplish the same static tasks without any external assistance. The muscle force and intervertebral bending moment were estimated to be reduced by up to 479 N and 36 N · m, respectively.

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Figures

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Fig. 1

Inverted pendulum model with the push–pull external assistive strategy. The blocks denote the segments of human body; the ellipse connecting pelvis to the thorax represents the erector spinae; F1 and F2 represent the external assistances proposed by the push–pull strategy; and the gravitational force and the ground reaction force are labeled.

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Fig. 2

(Left) Customized opensim full-body musculoskeletal model with markers locations and (right) implementation of push–pull in opensim. The thorax part and pelvic part are welded on the torso and pelvis, respectively, and the cam is pin jointed on the pelvis where the joint locates at the geometric center of the bottom cylinder. The pin joint rotation is coupled with the hip flexion.

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Fig. 3

Solid model of passive spine exoskeleton: (a) dummy user wearing exoskeleton, (b)zoomed-in detail view, and (c) the cable-tension mechanism of applying the spring pushing force on the human lumbar region

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Fig. 4

Model of static analysis for subject flexion with sEMG sensor attached

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Fig. 5

(a) and (b) Configurations of the subject wearing the exoskeleton spine prototype and (c) sEMG sensor distributions on the back of subject

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Fig. 6

Representative data comparison with/without exoskeleton suit from a single participant doing dynamic test: (a) comparison of the average of normalized muscle sEMG signals at lumbar level during all trials; (b) comparison of the average of normalized muscle sEMG signals at thorax level during all trials; (c) comparison of angle reading from sensor channel 8; and (d) comparison of linear accelerations reading from sensor channel 7

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Fig. 7

Representative sEMG data comparison from a single participant undertaking static tests: (a)–(c) comparison of normalized muscle sEMG at lumbar level at positions 1 (barely flexion) to 3 (full-range flexion) and (d)–(f) comparison of normalized muscle sEMG at thorax level at positions 1–3

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