Precision Motion Control at Low Velocities in the Presence of Friction

Abstract

The force of friction is almost always present when there is relative motion between two objects. There is currently no model of friction that describes "this force at all times. In particular slip stick friction particular is extremely important since it determines the lower bounds for any piece of machinery that must operate at velocities close to zero. At a velocity near zero, most models of friction characterize the friction force as discontinuous. I propose that the friction force is not discontinuous at zero. I have tried to generate a friction model that is continuous around a zero velocity. In order to generate the friction model, I used two computer programs: Working Model and Matlab . The software I used is able to represent simple models of friction, but when the model becomes more complex, the computer modeling programs are often at their limits. Nonetheless, it is shown that a model that captures the microscopic structural features of the contact zone exhibits the experimentally observed phenomena with relative fidelity. In particular it is shown that low velocity stick-slip oscillations are potentially enhanced by regularity of the asperities on the contacting surfaces while random appearances of these asperities reduces or potentially eliminates these oscillations. This in in my view an important result that can have applications in the design of machinery and in particular in precision motion applications.