Locomotion Control of Quadruped Robots With Online Center of Mass Adaptation and Payload Identification

Most of the controllers for quadruped robots are based on the planning of their centers of mass (CoM), with the assumption that the CoM locates at the geometrical center of the robot trunk. However, this assumption rarely meets the fact of the robot prototype and introduces apparent influences to the system. This article proposes a CoM estimation and adaptation method for quadruped robots in dynamic trot gait based on the model predictive control (MPC) of the trunk. The influences of the CoM offset on the robot states are inherently analyzed. The CoM components on the horizontal plane are taken into consideration and estimated based on the speed errors and the contact force differences, which are compensated to the robot controller. In the case of payload changes, the identification method for the mass of payload is proposed based on the estimated CoM. Simulation results verify that with the proposed approach, the robot successfully adapts to the CoM payload changes while the locomotion is not interrupted, and the state errors are significantly reduced.