Multi-contact Stability of Humanoids using ZMP and CWC

Abstract

We propose a method for checking the multicontact stability of humanoids simultaneously using Zero Moment Point (ZMP) and Contact Wrench Cone (CWC). The main idea of our method is to derive the friction constraints of foot contact using soft-finger contact model. Thanks to the similar definition of ZMP and the soft-finger contact model, it is able to use the friction ellipsoid computed from the soft-finger contact model at ZMP to replace the 6 dimensional wrench that computed from the friction constraints at each contact point of the foot contact. By using our proposed method, the stability of the foot rotation can be judged by using the ZMP while other factors affecting the stability of a robot can be judged by the CWC. By combining two wrench spaces, our method can be used to check the stability of humanoids which walking on the horizontal floor with hand contact with the environment.