Practical high-precision motion control system based on nominal characteristic trajectory following control and simple feedforward element design methods

Abstract

A practical design for a high-precision motion control system was formulated without an accurate dynamic model. The designed control system consisted of a nominal characteristic trajectory following (NCTF) control system—which can be easily designed without an accurate mechanical model—and time-invariant feedforward (FF) elements determined using a learning controller (LC). Specifically, an improved FF element design method, in which the LC was used to procedurally determine all the FF elements from the results of only four experiments, was used to enhance the motion control performance of the NCTF control system. To verify the effectiveness of the proposed framework, the NCTF control system was designed for a ball screw mechanism. This system was combined with the time-invariant FF element that is designed using the improved FF element design method. The performance of this system was compared with those of the conventional NCTF control system and the NCTF control system with the LC used as the FF element. The effectiveness of the improved FF element design method and combination of the determined FF elements and NCTF control system was experimentally demonstrated. Moreover, the enhancement in the position resolution of the FF element, which could compensate for the position-dependent factor in motion control, was verified. The average maximum error of this control system for the sinusoidal input with an amplitude of 0.2 mm and a frequency of 1 Hz is 0.209 μm, which is less than half the error of the other control systems.