Robustness evaluation of three friction compensation methods for point-to-point (PTP) positioning systems

Friction is one of the major contributing factors to problems associated with accuracy in positioning systems. The positioning accuracy problem becomes more complicated because of variations in the friction. In this paper, three simple friction compensation methods for the point-to-point (PTP) positioning system, which are easily applied in practical applications, are compared and evaluated experimentally on an experimental rotary positioning system. The first controller is the nominal characteristic trajectory following (NCTF) controller and the other two are the PD controller with a discontinuous non-linear proportional feedback (DNPF) compensator and the smooth robust non-linear feedback (SRNF) compensator. All of the controllers are compared in terms of the effectiveness of the controller to compensate for the friction as well as robustness against inertia and friction variations. The results demonstrate that the NCTF controller is more robust against friction variation than the PD controller with the DNPF or SRNF compensator.