Robust Impedance Control for Rehabilitation Robot

In this study, a novel robust impedance control for a lower-limb rehabilitation robotic system using voltage control strategy is used. Most existing control approaches are based on control torque strategy, which require the knowledge of robot dynamics as well as dynamics of patients. This requires the controller to overcome complex problems such as uncertainty and nonlinearity involved in the dynamics of the system, robot and patients. Conversely, the voltage-based control approaches is free from the system dynamics. In addition, it considers the actuator dynamics. The performance of voltage-based approaches is demonstrated by experimental result in robotic applications. Compared with a torque control scheme, it is simpler, less computational and more efficient. Nevertheless, uncertainty of actuator dynamics results in challenges for the voltage control strategy applications. The present paper, presents a novel robust impedance control based on the voltage control strategy. To overcome uncertainties, the adaptive fuzzy estimator is designed based on the voltage-based strategy. The proposed control is verified by a stability analysis. To illustrate the effectiveness of the control approach, a 1-DOF lower-limb rehabilitation robot is designed. Both torque-based impedance control and the voltage-based impedance control are compared through a therapeutic exercise. It is shown that the voltage-based impedance control perform better than the traditional torque-based impedance control. Simulation and experimental results both shows that the proposed voltage-based robust impedance control is superior to voltage-based impedance control in presence of uncertainties.