A model reference adaptive controller to control the knee joint of paraplegics

Muscle, paralyzed as a result of spinal-cord injury, may be activated to contract with the technique of Functional Neuromuscular Stimulation (FNS). This technique thus has the potential for restoring abnormal or absent skeletal movement. The translation of such externally induced contraction into functional movements of the lower limbs of paralyzed individuals may be considerably improved by the incorporation of a controller into a feedback loop closed around the leg joints. This work describes the design and implementation of a model reference adaptive controller (MRAC) to control the unloaded leg joint of paraplegics. Using this type of control algorithm, adequate tracking of reference angular input trajectories was achieved in spite of significant nonlinearities and nonstationarities in the open-loop plant dynamics. The basic MRAC algorithm is given, along with modifications made to it in order to overcome motor unit recruitment nonlinearities and a constraint on the rate of change of the control signal to the muscles. This work has particular significance for the design and implementation of closed-loop orthoses for FNS assisted standing and walking of paraplegic individuals.