Dynamic Torso Posture Compliance Control for Standing Balance of Position-Controlled Humanoid Robots

Compliance is important for humanoid robots, especially a position-controlled one, to perform tasks in complicated environments with unknown disturbances. This paper presents a dynamic torso compliance method for position-controlled humanoid robots to adapt to external disturbances when standing through the controllers based on a viscoelastic model and a double inverted pendulum. The viscoelastic model is used to realize ankle compliance by control the foot postures according to forces and torques measured by force/torque sensors mounted between the foot and ankle. And the double inverted pendulum is adopted to obtain the dynamic compliant movements of torso and calculate the desired torques of ankle compliance controller. With the proposed method, a position-controlled robot can perform impressive torso posture compliance and maintain balance on both rigid and soft ground (turf), which is validated through experiments on the BHR-5T, a position-controlled humanoid robot with high reduction ratios.