FES standing up in paraplegia: a comparative study of fixed parameter controllers

A computer model was developed as a test bed to aid the development and testing of FES controllers for assisting the sit to stand maneuver. Here, the authors illustrate its use by comparing the performance of two basic open-loop techniques used clinically and three experimental closed-loop control strategies. The simpler open loop control described by Kralj and Bajd (1989), was robust with a rapid response which can produce undesirable large terminal velocities in the knee joints. A variant of the scheme, often used in clinical practice was to linearly increase the stimulus intensity. This could be more convenient for the subject but unfortunately also deteriorated the control performance. The closed-loop controllers can reduce the terminal angular velocities of the knee joints. The phase-plane on-off controller, although easy to design, elongated the standing up time and resulted in increased arm forces. The PID controller was robust, but in order to optimize its performance, gain scheduling was required for the different phases of the motion. The fuzzy logic controller was able to accommodate considerable changes in the system dynamics. It produced a smooth motion with a superior trajectory following capability