THE EFFECT OF FRICTION ON THE FORWARD DYNAMICS PROBLEM

This article discusses the numerical solution of the forward dynamic equations of an n-degree-of-freedom manipulator with friction. Also discussed are the modeling and experimental identification of friction. It is shown that the inclusion of Coulomb-type friction in the dynamic equations introduces two difficulties in the forward dynamic solution. The differential equations are shown to be discontinuous in the highest-order derivative terms. In addition, the load dependency of this type of friction typically causes the equations to be implicit in the joint accelerations. For the important case of load-dependent transmission friction, the equations can 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.