Optimal control of ankle joint moment: Toward unsupported standing in paraplegia

Hunt, K.J., Munih, M., Donaldson, N. and Barr, F.M.D. (1998) Optimal control of ankle joint moment: Toward unsupported standing in paraplegia. IEEE Transactions on Automatic Control, 43(6), pp. 819-832.

Abstract

This paper considers part of the problem of how to provide unsupported standing for paraplegics by feedback control. In this work our overall objective is to stabilize the subject by stimulation only of his ankle joints while the other joints are braced, Here, we investigate the problem of ankle joint moment control. The ankle plantarflexion muscles are first identified with pseudorandom binary sequence (PRBS) signals, periodic sinusoidal signals, and twitches. The muscle is modeled in Hammerstein form as a static recruitment nonlinearity followed by a linear transfer function. A linear-quadratic-Gaussian (LQG)-optimal controller design procedure for ankle joint moment was proposed based on the polynomial equation formulation, The approach was verified by experiments in the special Wobbler apparatus with a neurologically intact subject, and these experimental results are reported. The controller structure is formulated in such a way that there are only two scalar design parameters, each of which has a clear physical interpretation. This facilitates fast controller synthesis and tuning in the laboratory environment. Experimental results show the effects of the controller tuning parameters: the control weighting and the observer response time, which determine closed-loop properties. Using these two parameters the tradeoff between disturbance rejection and measurement noise sensitivity can be straightforwardly balanced while maintaining a desired speed of tracking. The experimentally measured reference tracking, disturbance rejection, and noise sensitivity are good and agree with theoretical expectations.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: UNSPECIFIED
• Authors: Hunt, K.J., Munih, M., Donaldson, N., and Barr, F.M.D.
• Subjects: R Medicine > R Medicine (General)
• College/School: College of Science and Engineering > School of Engineering > Systems Power and Energy
• Journal Name: IEEE Transactions on Automatic Control
• Publisher: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
• ISSN: 0018-9286
• Copyright Holders: © Copyright IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
• First Published: First published in IEEE Transactions on Automatic Control 43(6):819-832
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher