Control of a Heavy Weight Biped Robot in the Frontal Plane

The advantage of legged locomotion in rough terrain and in confined spaces has been investigated extensively in recent years. It is anticipated that in the next decade or so, the prophecy that anthropomorphic biped robots will work side-by-side with humans will be realised. Recent successes in Japan have advanced the field substantially. However, little research has been conducted into the realisation of an industrial scale materials handling biped robot. Such a device presents challenges in terms of the magnitude of dynamic forces produced and of the systems required to control it in real-time. A 500kg, self-contained biped robot, called Roboshift, has been built to explore these challenges and to identify the significant aspects of control. This paper identifies issues associated with the control of the biped in the frontal plane. Results from balancing trials are presented which demonstrate the effect of ankle torque on the control of the biped. A model is then presented which demonstrates the effect of control forces and of geometry on the response of the biped in frontal sway. It is shown how the stiffness produced by control torque, a function of the gain of the control system and the response of the joint, affects the dynamic characteristics of the system.