Joint Compliance Control of Biped Robot Considering Position Tracking and Task Priority

In this work, we propose a joint force control framework for the stable motion of a humanoid biped robot. In motion planning, nonlinear centroid dynamics is used to generate gait on uneven terrain, which overcomes the limitation of a linear inverted pendulum (IP) model on centroid height. The motion control layer combines multipriority inverse kinematics (MPIK) and multipriority dynamic control (MPDC). The MPIK uses a multipriority inverse kinematics numerical iteration algorithm to calculate joint position command. The MPDC uses a multipriority iterative optimization method based on the task-space dynamics model on the forward path, which does not need preallocation or preoptimization of contact force, does not explicitly control the movement of center of mass (CoM), and tries its best to complete high-priority tasks. Finally, a stable joint compliance force control framework is built, and the introduction of kinematic error information ensures the accurate position tracking of the force control system. The results show that the control strategy completes the task of climbing stairs well and shows a certain antidisturbance ability in standing still and variable speed walking. The maximum disturbance in the sagittal plane can reach 50 N·s (achieved solely by adjusting the position of the pressure center and without using the step stability strategy).