Disturbance compensating control of a biped walking machine based on reflex motions

A control system that utilizes the concept of reflex control in animals is proposed for a biped walking machine with consideration of compensation of external disturbances. A walking machine was modeled as a sequential machine, and a series of single-reflex motions was synthesized for it. A hierarchical three-level control system was constructed. As disturbances, two types of external forces were considered: "impulsive" force with a large magnitude and short action-time and "continuous" force with a small magnitude and long action time. Appropriate state variables for rapid and reliable sensing of each disturbance were investigated and the thresholds of their values used as the triggers for changing the gait from a periodic gait to a disturbance compensation one were determined. Motions of disturbance compensation gaits were determined by combining some single-reflex motions. A control system for an experimental biped walking machine whose mass is 18 kg, total height is 0.66 in, step length is 0.25 m and walking cycle is 133 steps/min was constructed and tested. The proposed control system enabled the walking machine to successfully avoid tumbling when it was subjected to the two external forces and return to a periodic gait.