Power Efficiency-Based Stiffness Optimization of a Compliant Actuator for Underactuated Bipedal Robot

Introducing compliant actuation to robotic joints can obtain better disturbance rejection performance and higher power efficiency than conventional stiff actuated systems. In this paper, inspired by human joints, a novel compliant actuator applied to underactuated bipedal robot is proposed. After modeling the stiffness of the compliant actuator, this paper gives the configuration of the bipedal robot actuated by compliant actuators. Compared with the elastic structure of MABEL, the compliant element of our robot is simplified. Based on the dynamics of the compliant actuator-driven bipedal robot, a feedback linearization controller is presented to implement position control of the compliant actuator for power efficiency analysis and stiffness optimization. Co-simulations of MATLAB and ADAMS are performed under the defined control trajectory by altering actuator stiffness. The simulation results indicate that, compared with the actuator maintaining very high stiffness like a rigid actuator, the power efficiency of the compliant actuator is improved, and the stiffness optimized to 375 N•m/rad can reach the highest power efficiency.