A New Controller for FES-Assisted Sitting Down in Paraplegia

Abstract

A new control strategy that supports the sitting down phase in FES-assisted standing in paraplegia is proposed. It is an adaptation of a well established closed-loop On/Off controller that uses trajectories within the state space of knee angle and knee angular velocity, but defines a zone between the On and Off sub-spaces for gradual change in the stimulation levels. This new controller has been experimentally tested on two paraplegic patients and it is concluded that compared to the conventional On/Off controller it better controls the lowering of the person toward the seat, by reducing knee-end velocity and handle reaction forces. It has a certain degree of interaction with the user's voluntary effort. Keeping the system simple in respect to the required number of sensors, only the knee angle measurements are required as feedback signal making the strategy simple and, thus, particularly useful for daily standing exercises in home environments.

Keywords

• biomedical engineering
• control strategies
• neuromuscular stimulation
• paraplegia
• sitting down