Task-space Whole-body Control with Variable Contact Force Control for Position-controlled Humanoid Adaptation to Unknown Disturbance

Whole-body control is beneficial for improving the disturbance adaptation of humanoid robots, since it can simultaneously optimize desired joint torque, joint acceleration, and contact force while considering whole-body dynamics and other physical limits. However, the lack of torque feedback information prevents the position-controlled humanoids from utilizing whole-body control directly, because it enhances the difficulty of guaranteeing desired contact force which is important for maintaining stability. In this paper, a whole-body control that integrates task-space inverse dynamics and variable contact force control is proposed for position-controlled humanoids to enhance the robot’s adaptability toward the unknown disturbance. The task-space inverse dynamics generates the desired joint acceleration and contact force with the consideration of whole-body dynamics and other limits to track the references. The variable contact force control modifies references related to Center of Mass (CoM) and end effectors to ensure reasonable contact force tracking performance, thereby assuring good tracking performance of CoM and momentum to maintain robot stability. Simulations and experiments of balancing and walking under unknown disturbance have been successfully conducted on a position-controlled humanoid robot, BHR-7P3, with the proposed method.