Concept and Takagi-Sugeno descriptor tracking controller design of a closed muscular chain lower-limb rehabilitation device

The authors consider the kinematic concepts of a new lower-limb rehabilitation device in closed muscular chain. The proposed control structure is based on a trajectory generator and a continuous non-linear tracking controller. The human efforts applied to this device are considered as external disturbances to the system´s dynamics and as inputs to the trajectory generator and allow safe voluntary control of the system by the user. A H_∞ control structure based on a Takagi-Sugeno descriptor model is proposed to track the desired trajectories and to attenuate external disturbances. Stability conditions are given in terms of linear matrix inequalities using a fuzzy Lyapunov function. Finally, the simulation results of the proposed control structure for the new rehabilitation device during isokinetic movements illustrate the efficiency of the proposed approach.