Quadrant glitch compensation using friction model-based feedforward and an inverse-model-based disturbance observer

Accurate tracking is essential for machine tools. Both friction forces and cutting forces contribute to positioning and tracking errors. This paper considers contour tracking errors caused by friction forces only. The complex non-linear behaviour of friction at motion reversal causes a unique tracking error known as quadrant glitch. Compensation of quadrant glitches is desired to minimize surface contour error that is visible in circular tracking test. This paper analyzed, simulated and experimentally validated three different friction compensation strategies on a machine tool linear drive: (i) feedforward based on two friction models proposed in the literature, (ii) an inverse- model-based disturbance observer, and (iii) the combination of friction model feedforward and disturbance observer. The considered friction models are a simple static friction model and the recently developed Generalized Maxwell-slip friction model. The combination of feedforward based on the Generalized Maxwell-slip friction model and the disturbance observer yield the smallest tracking error and glitches.