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.

I. Introduction

Importance of robotic systems has risen in the modern society. Their applications have been extended to not only industrial automation, but also the daily life of humans [1]. Many researchers are making their best efforts to develop robot systems that can replace the role of humans in hazardous and dangerous environments, in particular the disastrous areas by a nuclear accident [2]. Considering the required dexterousness and agility of robot systems, legged locomotion systems are being intensively investigated. In particular, quadruped robots are receiving great attention as a new means of transportation for various purposes, such as military, welfare, and rehabilitation systems. The use of four legs enables a robustly stable gait; compared to the humanoid robots, the quadruped robots are particularly advantageous in improving the locomotion speed, the maximum payload, and the robustness toward disturbances [3] [4] [5].