Contact Dynamics

Abstract

This chapter describes the contact dynamics. It is essential for humanoid robot motion since it largely influences the whole behavior of the robot in the following manner. The actuation forces are propagated in the body structure and act to the external world via the contact points. Then, the reaction force accelerates the robot itself. The contact points are not permanently connected to the world but can make relative movements to it, due to which the overall system dynamics discontinuously varies. It is necessary to understand the contact dynamics in order to describe and predict correctly how the contact points move with respect to the contact forces. The contact forces are resulted from nanoscopic molecular interactions. For humanoid robots, however, those interactions are typically approximated in microscopic or macroscopic scales by various models, some of which are presented in this chapter. They are useful not only for understanding the robot behavior but also for some practical purposes. While a rather detailed model is acceptable in simulation and analysis, a macroscopic model based on the relationship between momentum and impulse is preferred for planning and control. Which model is to be chosen depends on properties of the objects to contact, available computation time, spatiotemporal scale of the phenomenon to study, and so forth.