Singular Perturbation-based Variable Impedance Control of Robots with Series Elastic Actuators

Compared with constant-impedance controllers, variable impedance control allows variation of the desired stiffness and damping in continuous manner, which gives more flexibility and abilities to robots in completion of complex tasks. But, variable impedance controller is seldom designed for robots with series elastic actuators (SEAs) in robot-environment interaction. This paper proposes a variable impedance controller for SEAs-driven robots based on the singular perturbation approach. Constraints on impedance profiles ensure the stability of the desired impedance dynamics. Based on the singular perturbation approach, the robot dynamics is formulated into a fast time scale subsystem at the actuator and a quasi-steady state subsystem. The proposed controller is composed of a control term to stabilize the fast subsystem and a variable impedance control term for the quasi-steady system. The stability of the closed-loop control system is proved according to the Tikhonovs theorem and the Lyapunov theory. Simulation results illustrate the effectiveness of the proposed controller.