Sensorless Contact Force Observation with Friction Distinguishment in Heavy Legged Robot Via PMSM Load Torque and IMU

This paper aims at sensorless observation of contact force and friction for the heavy-legged robot (HLR) driven by electric cylinders. It is known that the acquisition of contact force is challenging but significant for HLR due to the high self-weight. Additionally, as the main driving device, the electric cylinder contains considerable friction and disturbances, which greatly influence the accuracy of observed contact force. As a significant novelty, a method for contact force and friction observation through permanent magnet synchronous motor (PMSM) load torque observer is proposed in this paper. The proposed approximate PMSM model containing dynamics of PMSM, the electric cylinder, and the HLR is established. The motor speed is utilized to observe the friction disturbance and the external torque based on the sliding mode observer (SMO) theory. Centroidal dynamics and the information of inertial measurement unit (IMU) are introduced to distinguish the contact force included in the observation result of the proposed model. The entire algorithm is validated in the MATLAB-SIMSCAPE environment, and the observation results show that this algorithm is reliable and accurate in the utilization of HLR.