A decentralized Strategy for Control of unsupported standing in paraplegia based on discrete-time direct adaptive controllers

In this paper, we present a decentralized control strategy which is based on discrete-time adaptive control, for control of the ankle joint in paraplegic subjects using functional electrical stimulation. Agonist-antagonist co-activation is used to control the ankle movement. To achieve this purpose, first, the human is modeled as a single segment inverted pendulum which rotates about the ankle joint. Second, the nonlinear relationship between inclination angle and center of pressure is modeled. Finally, two discrete-time adaptive controllers are used to stabilize the upright posture. Each muscle-joint complex is considered as a subsystem, and separated controllers are designed for each one. Each controller operates individually on its associated subsystem, with no exchange of information between them. Center of pressure and velocity of center of pressure are considered as two inputs for each controller, and the output of each controller is used to generate a suitable moment at the ankle joint i.e., there are two moments produced by each controllers. The results of this study show that the proposed control strategy is an effective method in paraplegic subjects using functional electrical stimulation.