Virtual Reference Feedback Tuning for Knee Joint Position Control Using Functional Electrical Stimulation

This paper deals with design of a feedback controller for knee joint movement of paraplegics using functional electrical stimulation of the paralysed quadriceps muscle group. The applied controller design approach, Virtual Reference Feedback Tuning (VRFT), is directly based on open loop measured data and fits the controller in such a way that the closed loop meets a model reference objective. Omitting the system identification step reduces the time required for controller design significantly. The controller will also not be affected by system identification errors. In the case of a controlled neuroprosthesis, the time spent to adjust the controller represents an important issue since rapid fatigue of electrically stimulated muscles and the interest in the well-being of the patient do not allow long lasting open loop tests for identification data collection and time consuming modelling procedures. However, due to the day-to-day change of the neuro-musculoskeletal system, an update of the controller parameters dependent on currently measured open loop Input/Output data is highly to recommend. In this sense, VRFT gives an useful alternative to model-based control as the determination of a suitable controller in less time is guaranteed. © 2001 EUCA.