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RESEARCH PAPERS

Modeling and Control Considerations for Powered Lower-Limb Orthoses: A Design Study for Assisted STS

[+] Author and Article Information
Wesley R. Eby

Systems Design Engineering, University of Waterloo, Waterloo, Canada N2L 3G1wreby@engmail.uwaterloo.ca

Eric Kubica

Systems Design Engineering, University of Waterloo, Waterloo, Canada N2L 3G1ekubica@kingcong.uwaterloo.ca

Under the assumption of bilateral symmetry, both shanks work as a single link, both thighs work as a single link, and the head, arms, and torso (HAT) act as a single link.

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Manufactured by NDI, Waterloo, ON.

J. Med. Devices 1(2), 126-139 (Sep 01, 2006) (14 pages) doi:10.1115/1.2735969 History: Received March 22, 2006; Revised September 01, 2006

Lower-limb orthotic devices may be used to aid or restore mobility to the impaired user. Powered orthoses, in particular, hold great potential in improving the quality of life for individuals with locomotor difficulties because active control of an orthosis can aid limb movement in common tasks that may even be impossible if unaided. However, these devices have primarily remained the products of research labs with the number of effective commercial applications for the laity being nearly nonexistent. This paper provides an overview of the current status of powered orthoses and goes on to discuss key issues in modeling and control of powered orthoses so that designers can have a unified framework in developing user-oriented devices. Key concepts are demonstrated for a powered knee-orthosis intended for assisting the sit-to-stand task, and both pneumatic muscle and dc motor actuators are considered in this conceptual design study. In the final analysis, we conclude that the ability to provide sit-to-stand assistance is profoundly dependent on the type of control signal employed to control the actuator from the user–orthosis interface.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Link segment model of the sit-to-stand task

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Figure 2

Schematic of the Tradition X2K knee brace. A lever arm and actuator cable lspan are modifications to the brace. Inset is a photograph of the unmodified brace.

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Figure 3

Static force–length–pressure curve for a MAS-10 with exponential best fit. The curves with markers represent the actual data, while the curves without markers represent the best fit. Utilized working area of the PMA for the powered lower-limb orthosis is shaded.

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Figure 4

Dynamic PMA model

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Figure 5

Flow diagram of PMA model

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Figure 6

Speed–tension requirement of dc motor and working ranges of various spindle radii

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Figure 7

Joint trajectories for: (a) slow; (b) natural; and (c) fast STS trials. The vertical line indicates the time of liftoff.

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Figure 8

Assistive control system

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Figure 9

Required torque versus position of the knee

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Figure 10

Reduction complexity of PMA actuated orthosis control

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Figure 11

PMA pressure controller architecture

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Figure 12

dc motor torque controller architecture

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Figure 13

Overview of the simulation setup

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Figure 14

Orthosis torques for: (a) slow, (b) natural; and (c) fast STS trials. The control signal is based on an actual STS task, and the torque is provided as soon as STS begins. The dynamics are included in the torque output of the actuators.

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