Quadruped posture control based on simple force distribution-a notion and a trial

Presents a standing posture controller for quadruped robots, i.e. control of the trunk's desired roll angle, pitch angle and height. The controller is based on a few simple ideas: (1) control the legs vertically using force control and horizontally using position control; (2) use simple rules to distribute leg forces; (3) the supporting surface should not have to be horizontal, planar or even static; (4) since the height is not easily defined for a legged robot, the average of the "leg heights" is used. This controller is successfully tested in both simulations and experiments. It is capable of adjusting to step changes in reference posture, as well as standing on a moving balance board. Finally, we suggest tests to benchmark posture controllers.