Structure of Fuzzy Two-Degree-of-Freedom Positioning Systems

Abstract

In this paper, two types of fuzzy two-degree-of-freedom positioning systems are considered. One is a system which consists of a self-tuning fuzzy feedforward controller (STFC) and a fixed rules fuzzy feedback controller (FBC). The control rules of the STFC are automatically adjusted by a tuning law, the objective of which is to make an equivalent dynamic inverse of a nonlinear plant after tuning. The rules of the FBC are tuned in advance so that the FBC acts as a high gain feedback controller to restrain the effect of disturbance input. The other consists of the STFC and a fuzzy disturbance observer (FDO). The same rules of the STFC which provide the equivalent dynamic inverse are used in the FDO to estimate the disturbance input. To ensure the validity of the proposed systems, the responses of a positioning system with a progressive wave type ultrasonic motor (PUM) are measured. Experimental results demonstrate the effectiveness of the systems for improvement of the tracking performances and robustness.