Dynamic Control of a Bipedal Walking Robot actuated with Pneumatic Artificial Muscles

This paper reports on the control structure of the pneumatic biped Lucy. The robot is actuated with pleated pneumatic artificial muscles, which have interesting characteristics that can be exploited for legged machines. They have a high power to weight ratio, an adaptable compliance and they can reduce impact effects. The discussion of the control architecture focusses on the joint trajectory generator and the tracking controller which is divided in four parts: a computed torque module, an inverse delta-p unit, a local PI controller and a bang-bang pressure controller. The control design is divided into single support and double support where specifically the computed torque differs for these two phases. A full hybrid dynamic simulation model is used to evaluate the control architecture of the biped. This simulator combines the dynamical behaviour of the robot with the thermodynamical effects that take place in the muscle-valves system. The observed hardware limitations of the real robot and expected model errors are taken into account in order to give a realistic qualitative evaluation of the control performance and to test the robustness. Finally the first results of the incorporation of this control architecture in the real biped Lucy are given.