Design of an Active Compliance Controller for a Bionic Hydraulic Quadruped Robot

Active compliance control is an effective method for a legged robot to decrease impact disturbances at the moment of foot-ground contact and to realize harmonic locomotion by actively adjusting the leg stiffness and damping in real-time, which will significantly improve the adaptability of the robot to the irregular terrain. However, the design of an active compliance controller remains to be a challenge when the nonlinearity of actuators must be taken into account. This paper presents an active compliance controller for a bionic hydraulic quadruped robot. The nonlinear dynamics of the hydraulic system, including the compressibility of the fluid, the friction of the hydraulic cylinders, and the flexibility of the tubing are well modeled and identified. The nonlinearity of the hydraulic actuators are compensated through friction compensation and feedback linearization. The proposed active compliance controller has been applied to a bionic hydraulic robot prototype. Experimental results indicate that the active controller can handle the impact disturbances from robot feet.