Discrete Fourier Transform-Based Trajectory Decomposition for Parallel Tool Servo Diamond Turning of Microstructured Surfaces

Abstract Diamond turning is a mainstream technology for fabricating microstructured surfaces with high form fidelity. However, traditional systems utilizing either the slow slide servo (SSS) or fast tool servo (FTS) are constrained by inherent tradeoffs between the stroke capacity and control bandwidth of a single servo axis, restricting achievable machining performance. To address these limitations, this technical brief proposes a novel discrete Fourier transform-based parallel tool servo (DFT-PTS) diamond turning process, enabling coordinated control within a dual-stage feed drive system. In the proposed process, the initial tool trajectory is decomposed into low- and high-frequency components using the DFT and its inverse, with the low-frequency trajectory assigned to the SSS axis and the high-frequency trajectory to the FTS axis. A frequency response data-based simulation procedure is developed to determine the optimal cutoff frequency for trajectory decomposition. Experimental results on a three-axis ultra-precision machine tool equipped with a customized FTS axis show that the proposed DFT-PTS process significantly improves tracking performance. When applied to turning composite microlens arrays, the DFT-PTS process achieves a 49% reduction in peak-to-valley form error and a 52% reduction in root-mean-square form error compared with conventional geometry-based trajectory decomposition methods. These results confirm that the proposed method can simultaneously improve machining accuracy and efficiency, offering strong potential for industrial applications in ultra-precision manufacturing of microstructured optical surfaces.