PID control design for rehabilitation by quasi-isometric training in paraplegia: a simulation study

This paper reports simulation results about the design of a PID controller of Functional Electrical Stimulation (FES) to be used for quasi-isometric exercises in rehabilitation of paraplegics. The simulations refer to a specific experimental device developed at the Fondazione Don Gnocchi, mainly used in standing up and sitting down using FES. This is a seesaw, with the patient on one side and a weight on the other side. The patient is seated so that its posture can be fully known in real-time by continuously monitoring the knee joint angle. The design of feedback controllers for such a device is currently based on nonlinear strategies. These are necessary when aiming to standing and sitting control. However, there is a strong demand by rehabilitation physiotherapists for easy-to-tune controllers, even though these could be used only in specific conditions. So, a PID linear controller has been designed and tested by means of simulations. The controller tuning is performed by using four different methods specifically designed for unstable systems with delay. Comparison of the performnce obtained with each controller is provided.