Active/passive compliance control for a hydraulic quadruped robot based on force feedback

In the realm of quadruped robot locomotion, compliance control is imperative to handle impacts when negotiating unstructured terrains. Usually, passive devices such as the spring are used to implement compliance contact with environments. However, the impact energy cannot be totally absorbed by the spring. Active compliance control is another good solution to deal with the impacts by changing the end-effector stiffness and damping, but it also has intermediate requirements for the actuator, because the impact duration is too short. In order to achieve a better compliance performance, the position based active compliance control is combined with the passive compliance control by strengthening their advantages and making up the shortfalls. We first implement this method on a hydraulic actuator, and then similar experiments are carried out on a quadruped robot leg, the controller has same effect on both platform. Conclusions about compliance controller designing can be received by analyzing the one degree of freedom actuator system model. All the work lays a solid foundation for the quadruped robot compliance control designing.