Master–Slave Coordinated Control of Fast and Slow Tool Servos for Diamond Turning of Complex-Shaped Optics

Diamond turning based on tool servos is gaining applications increasingly in the surface forming of complex-shaped optics. However, current fast/slow tool servo techniques encounter inherent limitations in terms of stroke or bandwidth, posing a significant challenge for high-precision and high-efficiency machining of structures with relatively large strokes. To handle this dilemma, this study proposes a master–slave coordinated control strategy for fast and slow cooperative tool servo diamond turning. Specifically, the slow tool servo (STS) serves as the master servo to follow the desired toolpath, while an additional fast tool servo (FTS) axis acts as the slave servo to track the motion error of the master servo in real time. To enhance the tracking performance of the slave servo, a frequency response data-based enhanced real-time iterative compensation method is developed to control the fast axis. As a validation, the ultraprecision diamond turning experiments are conducted on a three-axis lathe equipped with a custom-designed FTS. The servo motion is performed with high accuracy and a microlens array is generated with high quality, suggesting that the proposed strategy effectively eliminates the motion errors of the STS and significantly improves the form accuracy of the fabricated surfaces.