Joint kinematic configuration influence on the passivity of an impedance-controlled robotic leg

摘要

Although the design of legged robots may be dependent on the application, all of them share the need to safely deal with physical interaction with the environment in every step they take. Impedance controllers have been applied with success to handle contact, and some authors applied the concept of passivity to guarantee stability during the interaction. Whereas previous studies on the passivity of legged robots considered aspects such as inner force loop gains and actuation bandwidth influence on the Z-width (i.e. the range of renderable passive impedances), they did not take into account the role of the kinematic configuration of the leg on the stability of the interaction. Thus, in this work we present a systematic analysis of the effects of joint positions on the passivity conditions of a robotic leg and show that this is a very relevant aspect that may seriously affect the stability and passivity of an impedance controller. By analyzing a linearized model of the leg via its Nyquist plots and the respective Z-width diagrams, we were able to determine what joint configurations within the leg workspace are more suitable to physically interact with the environment or people.