Experimental Study on Linear State Feedback Control of Humanoid Robots with Flexible Joints

Abstract This paper reports on an experimental study on use of static full state linear feedback for link tracking control of a compliant humanoid leg, cCub. Passive elasticity is used in pitch joints of the cCub legs, offering many benefits in terms of safe interaction as opposed to rigid robots. However, the elasticity makes the link tracking problem more challenging in particular tasks when the robots joints are under large gravitational forces or external disturbances, such as going up the stairs. Therefore, this study explores the experimental results of applying LQR control, formulated using Linear Matrix Inequality in discrete time and implemented on a humanoid robot. A summary of the theory used and a numerical simulation are presented. The proposed LQR controller provides a systematic way of designing the feedback gains with desired closed loop dynamics and it is shown to have good tracking performance in the experiments.