Assessment on Tracking Performance of Cascade P/PI, NPID and NCasFF Controller for Precise Positioning of XY Table Ballscrew Drive System

摘要

Nowadays, the demands in machine tools are in terms of precision positioning, low-cost tooling and robustness against variable disturbance forces. Disturbance forces in machine tools are in the form of friction and cutting forces. Disturbance forces that acting directly or indirectly towards the system would result to poor tracking performance. The goal of this research work is to assess the tracking performance of Cascade P/PI, NPID and the newly designed control strategy called Nonlinear Cascade Feedforward (NCasFF) controller. There are three different cutting force disturbances injected into the system namely at spindle speed of 1000 rpm, 2000 rpm and 3000 rpm. The tracking performance of the controller is analyzed and evaluated using Fast Fourier Transform (FFT) of the tracking error. Robustness of these controllers in compensating different cutting characteristics is compared based on reduction in the harmonics of FFT error. It is found that the NCasFF controller performs better than both NPID and Cascade P/PI controller. The average percentage error reduction between NCasFF controller and NPID controller is about 87% whereas the average percentage error reduction between NCasFF and Cascade P/PI controller is about 44% at spindle speed of 1000 rpm. The finalized design of the newly developed control strategy called NCasFF controller could be util ized for CNC machine application. The implementation of NCasFF controller in machine tools application will increase the quality of the end product and the productivity in the industry by saving the machining time. It is suggested that the range of spindle speed could be made wider to accommodate the needs for high speed machining and for the betterment of manufacturing sustainability.