Friction modeling in dynamic robot simulation

The importance of appropriately modeling friction for the simulation and control of high-performance robot systems is discussed. Incorporating Coulomb-type friction in the dynamic equations introduces two difficulties in the forward dynamic solution. It is shown that the differential equations become discontinuous 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. Experimental 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