Linear modelling and controller design for the single limb movement of paraplegics using FES

This paper deals with the problem of modelling and control of the knee joint dynamics. Using controlled functional electrical stimulation (FES) of the quadriceps muscle group the knee joint will be positioned at a commanded angle, subject to disturbances and displacements of the hip and ankle joints. A simple ARX-model has been estimated directly from measured input-output plant data. Further, a discrete linear pole-placement controller will be presented as solution for the tracking and regulation problems. Advantages of this approach in comparison with nonlinear controllers based on physiological models will be discussed and natural limitations are shown. A simple tuning rule for an already determined controller will be given to achieve robust stability with respect to the plant characteristics, which depend on the actual operating point. Experiments with neurologically intact subjects show encouraging results