A disturbance observer for robust position tracking control and ground contact detection of a Cheetaroid-I leg

Quadruped robot systems are being intensively investigated by as a new means of transportation systems with multi-purposes. As the operation conditions of such systems, such as a payload, gait speed, and so on, are demanding, the control of the robotic legs is challenging. In addition, the dynamics of such systems is subjected to large disturbances and parameter variations due to the ground contact and the complicated mechanical structure. In this paper, a robust control algorithm based on a disturbance observer (DOB) is proposed for the control of legs of a quadruped robot, Cheetaroid-I. The DOB enables rejecting disturbances caused by the ground contact, payload, etc, and detecting the ground contact without force sensors. The proposed method is verified by experimental results.