ABSTRACT
For analyzing the system dynamics with friction, one needs first to look into the fundamental equations of motion, like those formulated in the Lagrangian mechanics. In control engineering practice, it is well known that before a visible, so to say, macroscopic motion begins, a drive actuator has to produce a certain amount of the (static) force that will be sufficient to overcome the so-called stiction in a mechanical assembly. The measured motor current reveals a relatively high oscillating pattern, which however helps additionally to overcome the stiction and adhesion by-effects. At the same time, the slope of the motor current and thus of the average input torque is relatively flat, so that the excitation dynamics is rather slow. Alternating or equal sign of the controlled output at convergence depends on the relationship between all control parameters and Coulomb friction coefficient. At the same time, the value of the Coulomb friction coefficient itself does not significantly change the principal stick-slip behavior.
