Whole-Body Control and Angular Momentum Regulation using Torque Sensors for Quadrupedal Robots

Ground reaction force (GRF) plays an integral role in legged robots to control interaction with the ground. However, most techniques in whole-body controller for quadrupedal robots do not explicitly take into account actual torque or force in their control loops and instead use feed-forward force to generate joint torque at every time step. In this paper, we present a closed-loop whole-body controller using the actual joint torque feedback, which regulates angular momentum of the center of mass (CoM) for quadrupedal locomotion. Using the torque measured from each torque sensor and the torque by solving the inverse dynamics, we can compute the external joint torque induced by the contact with the ground. To fully use the computed joint torque, we discuss a feasible approach and whole-body control criterion for quadrupedal robots that have constrained support polygons because of their point-feet and certain gaits using two or less legs in contact. Based on the approach, we generate a centroidal moment pivot trajectory considering the leg dynamics, linear translation, and angular rotation of the CoM, which can stabilize the robot‘s balance by using the actual angular momentum rate change transformed from the measured joint torque. In addition, a push recovery strategy based on capture point dynamics derived from linear momentum and a foothold generation method are integrated into the controller. The proposed controller is tested on a quadrupedal robot, called AiDIN-VI, that has a torque sensor at each joint. The proposed whole-body controller enables the robot to demonstrate several gait types such as trotting, pacing, jumping, and walking on various environments, and locomotive abilities under external pushes are verified.