A push recovery strategy for a passively compliant humanoid robot using decentralized LQR controllers

This paper presents a control scheme that is directed towards the performance of push recovery on the compliant humanoid robot, COMAN. The novelty offered by this work is related to the use of a decentralized controller based on an initial Limited Quadratic Regulator (LQR) design on a humanoid robot in addition to the regulation of the actual joint positions instead of the motor positions. Moreover, the ankle-knee strategy is examined through the use of a compliant double inverted pendulum model. A key feature of the propounded approach lies in the controller´s ability to regulate the system´s inherently compliant dynamics through considering not only the motor-related variables but also those of the link-side, appearing after the passive compliant element. Consequently, this leads to a control method that is capable of stabilizing the robot by means of increasing the damping on the link, which is essential given the system´s oscillatory behaviour once it has been perturbed.