Dynamic behavior and modelling of the pre-sliding static friction

One of the main difficulties in dealing with positioning problems with extremely high precision is the static friction and the induced nonlinear behavior existing in the mechanism. In this research, the phenomenological study of the static friction behavior before normal slip starts is conducted for direct drive torque motor systems. It is found that the qualitative behavior of static friction is consistent. Furthermore, based on the experimental results published in the literature, the pre-sliding behavior is similar for various mechanical mechanisms including friction between two simple materials and friction of complicated systems that have many friction sources. It shows that the pre-sliding motion is mainly the combination of two kinds of motion: plastic deformation that demonstrates creep and work hardening, and nonlinear spring deformation that demonstrates hysteresis loop with special memory and wipe out effects. These behaviors are very close to those of most plastic materials. A new static friction model that consists of a plastic module and a nonlinear spring module is introduced. This model is of a simple structure and is proved to match all those qualitative behaviors. Parameter estimation and simulation algorithms are also described. Simulation results show that this model does coincide with those experimental results conducted by the authors as well as by other investigators. (C) 2000 Published by Elsevier Science S.A.