Actively-compliant locomotion control on rough terrain: Cyclic jumping and trotting experiments on a stiff-by-nature quadruped

This paper is authored to describe a control framework that is designated for realizing cyclic, actively-compliant and dynamically-balanced jumping and trotting quadruped locomotion over rough terrain. In order to succeed in exhibiting such locomotion abilities, two controllers are synthesized: i) Active Compliance Control via force feedback, ii) Angular Momentum Control via gyro sensing. The first controller computes the joint displacements that are associated with ground reaction force errors, using Jacobian transpose and admittance blocks. Together with position constraints, these joint displacements are simultaneously fed-back to local servo controllers; allowing the robot to perform the given locomotion task in an actively-compliant manner. The second controller, in the meantime, evaluates gyro sensor information to calculate the required compensation torque about center of mass, which is necessary to regulate upper torso rotational motion. Afterwards, it updates the orientation input in accordance with this compensation torque. Using the proposed framework, the overall control performance is tested via cyclic jumping and trotting motion experiments, conducted over rough terrain with a stiff-by-nature quadruped robot. Results turn out to be positive; the robot demonstrates successful jumping and trotting cycles in a repetitive, actively-compliant and dynamically-balanced fashion.