Overcoming inherent performance limitations in industrial motion stages with reset control

Abstract

Linear time-invariant controllers are undoubtedly the most popular type of regulators used in industrial applications, with the overwhelming majority of companies employing them. The reason is mainly given by their simple design methods. In particular, frequency domain predictive performance analysis and stability methods allow the use of loopshaping techniques. Nevertheless, inherent limitations affecting linear controllers pose constraints on their performance that can only be overcome through the adoption of nonlinear control schemes. Promising findings in recent literature suggest that with reset control, a nonlinear control technique, it is possible to overcome these limitations. At the same time, reset control could also potentially allow the use of straightforward design techniques, thus making it suitable for industrial applications. The main goal of this work is to bring together the different concepts scattered in literature, in order to initialize the construction of a general framework for the design and analysis of reset controllers suitable for an industrial setting. Tuning guidelines for different structures using two classes of reset controllers, the first order reset element and the proportional Clegg integrator, were presented. Two frequency domain methods, namely open-loop higher order sinusoidal input describing functions (HOSIDFs) and pseudosensitivities computed through analytically derived (approximate) closed-loop HOSIDFs, were effectively applied to predict steady-state performance. Stability was (when possible) analysed through the frequency domain Nyquist stability vector method, which could also be implemented in the design process. The frequency domain analysis methods allowed the use of loopshaping techniques similar to LTI control for the design of reset controllers. The controllers, implemented digitally on an ASM Pacific Technology wire bonding machine, show that through reset control a significant decrease in the root mean square of the settling error compared to an equivalent LTI controller could be achieved. The existing frequency domain analysis methods, its straightforward implementation and the increase in performance achieved in experiments validate the potential of reset control as a suitable alternative to LTI control for industry. Nevertheless, limitations in the explored reset control structures still exist and further work is required in order to achieve the full potential that this technique has to offer.