Abstract: The machining accuracy and efficiency of optical micro-structured surfaces depend on the tracking performance of fast tool servo (FTS) systems. Therefore, a feedforward compensation method based on repetitive controller (RC) is proposed to address this issue. For this method, the precise tracking of aperiodic reference trajectories is achieved for FTS systems by the online learning and offline compensation of the segmented tracking errors. The comparative tracking experiments are conducted on a self-developed monoaxial FTS system, and the experimental results show that the RMS tracking errors of the two degree-of-freedom control method are reduced by 94.47% and 93.83% via using the proposed method when tracking the random uniform B-spline curve and the muti-frequency sinusoidal curve, respectively. Furthermore, the grid surface and the compound eye lens array are machined under a high spindle speed with the proposed feedforward compensation method by integrating the FTS system into an ultraprecision lathe. The maximum contour error of the obtained two types of surfaces are 93.59 nm and 134.73 nm, respectively, and the surface roughness of both two surfaces is less than 5 nm. The results provide a novel method and a new idea for FTS systems to achieve the high efficiency and high precision machining of optical micro-structured surfaces.

Key words: fast tool servo, precision motion control, optical micro-structured surface, ultra-precision turning, repetitive control