Analysis of Linear Feedback Position Control in Presence of Presliding Friction

Abstract

In various servo applications, the design of a precise positioning control constitutes a trade-off between the fast transient response and the short settling time for the required accuracy. Mostly, neither 'universal' control gains can be found to be equally suitable for both of these objectives. In this study, the design of a cascaded precise positioning control is analyzed in the presence of nonlinear friction. The nonlinear friction strongly impacts the reference settling and can deteriorate the positioning control performance. Two common cascaded structures, and that P-PI and PI-PI, are analyzed by exposing the closed-loop dynamics of the control system with friction in details. It is shown that a more 'traditional' integral control part is less useful when compensating for the nonlinear friction at the reference position settling. Furthermore, we show how the settling performance can be improved by applying a feed-forward friction observer. This can be included as a plug-in after designing the surrounding cascaded feedback control and without re-tuning. The proposed control strategy is evaluated experimentally on a standard industrial linear positioning axis, with a relatively high reference speed of +/−500 mm/s and narrow positioning error band of +/−0.01 mm.

Friction-resilient position control for machine tools—Adaptive and sliding-mode methods compared

“…The design of a more general nonlinear friction observer was provided in Ruderman and Iwasaki (2015), especially for motion control applications. The performance limitations of the cascaded P-PI motion controls with respect to nonlinear friction rejection at micro-positioning were discussed in Ruderman and Iwasaki (2016); Ruderman (2016). The authors demonstrated that zero steady-state positioning error is nearly impossible with linear controllers.…”

To stick or to slip: A reset PID control perspective on positioning systems with friction

“…In 1902, Stribeck showed a continuous, velocity-dependent decrease from static to Coulomb friction levels [76], commonly present in lubricated contacts and widely known as the Stribeck effect. Further developments have led to dynamic friction models to accommodate for presliding effects (see, e.g., [5,74]), such as the Dahl model [32], the LuGre model [26], or the ones in [77,4].…”

Online friction parameter estimation for machine tools

“…Gearbox lubricants introduce viscous friction, while heat losses in the drive (eg, due to eddy currents), may change viscosity under operation. Static friction (stiction) significantly contributes to the degrading of the linear axes positioning, especially during motion onsets and axes reversals . Sufficient knowledge of the occurring frictional phenomena not only facilitates better control loops but may also infer information about the levels of equipment wear.…”