Friction Modeling in Dynamic Robot Simulation

This paper discusses the importance of appropriately modeling friction for the simulation and control of high performance robot systems. Incorporating Coulombtype friction in the dynamic equations introduces two difficulties in the forward dynamic so-lution. We show that the differential equations become discontin-uous in the highest order derivative terms. In addition, the load dependency of this type of friction generally causes the equations to be implicit in the joint accelerations. For the important case of load-dependent transmission friction, the equations are shown to be explicit. Techniques for the forward solution are described through the example of a roller screw transmission. Experimen-tal and simulation results are used to show the importance of load-dependent friction in a particular robot. Implementational issues are discussed as well as implications for robot control.