In this study, a novel variable impedance control for a lower-limb rehabilitation robotic system using voltage control strategy is proposed. Most existing control approaches are based on control torque strategy, which require the knowledge of robot dynamics as well as dynamic of patients. This requires the controller to overcome complex problems such as uncertainties and nonlinearities involved in the dynamic of the system, robot and patients. Conversely, the voltage-based control approaches is free from the system dynamic. In addition, it considers the actuator dynamic. Compared with a torque control scheme, it is simpler, less computational and more efficient. Furthermore how impedance parameters must be selected is a serious question in control system design for rehabilitation robots. To resolve these problems this paper, presents a variable impedance control based on the voltage control strategy. Variable impedance parameters based on interval type-2 fuzzy logic (IT2Fl) is proposed to effectively control the system. 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. Voltage-based impedance control are simulated through a therapeutic exercise. Simulation results show that the proposed voltage-based variable impedance control is superior to voltage-based impedance control in therapeutic exercises.

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