Research Papers

A Method for the Autonomous Control of Lower Limb Exoskeletons for Persons With Paraplegia

[+] Author and Article Information
Michael Goldfarb

Department of Mechanical Engineering,
Vanderbilt University,
Nashville, TN 37235

Manuscript received August 16, 2011; final manuscript received April 29, 2012; published online October 11, 2012. Assoc. Editor: Jahangir Rastegar.

J. Med. Devices 6(4), 041003 (Oct 11, 2012) (6 pages) doi:10.1115/1.4007181 History: Received August 16, 2011; Revised April 29, 2012

This paper describes a control method for a lower limb powered exoskeleton that enables a paraplegic user to perform sitting, standing, and walking movements. The different maneuvers are commanded by the user based on postural information measured by the device. The proposed user interface and control structure was implemented on a powered lower limb orthosis, and the system was tested on a paraplegic subject with a T10 complete injury. Experimental data is presented that indicates the ability of the proposed control architecture to provide appropriate user-initiated control of sitting, standing, and walking. The authors also provide a link to a video that qualitatively demonstrates the user's ability to independently control basic movements via the proposed control method.

© 2012 by ASME
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Fig. 1

Powered lower limb orthosis

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Fig. 2

Functional schematic of embedded system

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Fig. 3

Finite state machine for sitting, standing, and walking

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Fig. 4

Commanded trajectories corresponding to transition states (a) S7 and S11, (b) S8 and S9, and (c) S10 and S12

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Fig. 5

Schematic indicating estimated stride length (Xh) and center of pressure (Xc), both estimated based on the configuration of the orthosis

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Fig 6

Schematic indicating the use of center of pressure (Xc) estimate for purposes of sit-to-stand and stand-to-sit transitions

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Fig. 7

Photographic sequences showing standing, a left step, and a right step

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Fig. 8

Joint angles and controller state during the third TUG test

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Fig. 9

Data excerpted from Fig. 8. Top row: finite state corresponding to a sequence of steps. Middle row: center of pressure estimate (Xc, blue/bottom) and center of pressure threshold (Xĉ, red/top). Bottom row: step length estimate (Xh).

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Fig. 10

Finite states corresponding to each of the three TUG tests



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