The simulation of Coulomb friction in mechanical systems

Coulomb or dry friction occurs in mechanical systems when nonlubricated surfaces come into sliding contact. The force resulting from Coulomb friction has a magnitude dependent on the contact force and a direc tion opposite to the relative velocity. If the re lative velocity is zero, the Coulomb friction assumes the value, within bounds, to maintain zero velocity. This, of course, presents the opportunity for a variety of equilibrium configurations. This paper presents an overview of the common tech niques for the digital simulation of Coulomb fric tion. All these techniques use the relative velocity to determine the friction force and are therefore flawed since they cannot predict multiple equilibrium positions. By means of an example, this paper shows that modeling Coulomb friction as a function of posi tion rather than of velocity allows multiple equili bria and offers features that are useful in modeling high-friction, low-mass systems.