Inverse dynamics control with acceleration optimization on a force-controlled bipedal robot

This paper presents an acceleration-based inverse dynamics method to control the floating base of a force-controlled bipedal robot. The desired accelerations of the floating base are derived by PD control in operational space and then used to calculate the accelerations of the joints. Given kinematic constraints to the feet, a relationship between the accelerations of the floating base and the desired external forces needed for those accelerations is obtained. The desired external forces are constrained by ZMP, friction and unilateral vertical forces, which introduces corresponding constraints on the accelerations. If the desired accelerations do not satisfy the constraints, quadratic programming is applied to determine optimal accelerations, which will satisfy the constraints. These optimal accelerations are used instead of the desired ones when calculating inverse dynamics. Our controller guarantees the desired external forces satisfy their constraints. The effectiveness of the proposed methods is demonstrated by tracking desired trajectories and recovering from disturbances on a force-controlled bipedal robot in simulation.