Integral Control Action in Precise Positioning Systems with Friction
Chapter, Peer reviewed
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For high precision positioning systems a fast and accurate settling to the reference state is most significant and, at the same time, challenging from the control point of view. Traditional use of an integral coaction in feedback can attain a desired reference tracking at steady-state motion, but can fail in case of precise positioning. Most crucial is that this is independent on how accurate the integral control part is tuned. This paper addresses the feedback control action in precise positioning systems with friction. Analyzing the closed-loop control dynamics with nonlinear friction in feedback it is shown why the integral action cannot efficiently cope with Coulomb friction which becomes time-varying at motion onsets and reversals. The latter leads to the reduced control performance expressed in desired immediate stop at the reference position. The nature of presliding friction as functional of positioning control error, in vicinity to the reference position, and not as function of the time argument, is postulated as main disturbing factor that limits efficiency of the integral control coaction. The conclusions drawn in performed analysis are also reinforced by the demonstrated numerical examples of a controlled motion with nonlinear friction.