Neuroprosthesis for standing-up and sitting-down: experimental results

In this study different closed-loop control strategies for standing-up (SU) and sitting-down (SD) were experimentally tested on two paraplegics by applying Functional Electrical Stimulation (FES) to the quadriceps muscle. The motion is supported by a seesaw construction. The control strategies studied include on-off control, PID control, PID control with feedforward on the basis of an inverse dynamic model (IDM), and "patient-driven motion reinforcement" (PDMR). Satisfactory control behaviour was observed in the on-off and PID controllers. However, during standing they show a tendency towards instability. The PDMR controller is able to coordinate FES and upper body and significantly reduce upper body effort. A disadvantage of the IDM-based and PDMR controllers is that cumbersome parameter adjustment is required prior to the experiments.