Fast and Compliant Whole Body Control for Gear-Driven Torque Sensorless Quadruped Robot Trotting

This study demonstrates a dynamic quadruped trotting using fast and compliant whole body control (WBC) for electrically actuated quadruped robots with large reduction-ratio harmonic gear. Currently the torque control plays a dominant role in achieving dynamic control of quadruped robots. However, due to the complex friction of harmonic gear, torque-controlled actuation without joint torque sensors for the robot equipped with large-reduction-ratio harmonic gears tends to result in the poor locomotion performance, including poor position tracking, low bandwidth in torque control, and large latency. In our previous work, the joint output torques are estimated to increase the torque control accuracy. In this study, a fast whole body control method based on quadratic programming (QP) along with the virtual leg compliance (VLC) model is applied to the locomotion controller to further enhance the robot balance while dynamic trotting. The hybrid force and position control is adopted in the low-level controller, to realize the variable stiffness control during fast locomotion phase changing within the whole control loop. An upgraded quadruped robot platform, Pegasus II, is developed to validate the controller performance in the experiments.