Closed loop control of FES supported standing up and sitting down using virtual reference feedback tuning: a simulation study

This work is focused on the design of closed-loop controllers for FES-supported standing up and sitting down. This task is a difficult one, due to the lack of stability of the considered system and to the highly nonlinear dynamic behaviour. In this paper, a control strategy based on two nested control loops is presented. The inner loop is based on a PID controller, designed on the basis of a set of local models for the considered plant. Each model represents the behaviour of the system about a given operating point in closed loop. The outer loop is also based on a PID controller designed using the VRFT strategy, that allows a fast and easy tuning of the controller starting from a single I/O data set. Finally, a nonlinear control law has been implemented exploiting the features of the VRFT method. Simulation results show that the proposed technique is effective in controlling a paraplegic patient in FES-based standing up and sitting down.