A comprehensive error correction/prediction system for tool-servo driven diamond turning of freeform surfaces

Slow tool servo (STS) is widely used to fabricate freeform optical elements. However, it is still difficult to obtain nanometer-level form accuracy in a short time due to characteristic error factors such as the tool trajectory error and the dynamic follow-up error of machine tools. In this study, we proposed a new machining flow, which included error factor modification and error prediction, to improve the form accuracy in machining freeform surfaces by STS. Comprehensive error analysis and modelling was performed to identify all the main error factors, some of which have never been taken into account by previous researchers. Numerical simulation was then carried out to clarify the relationship between these error factors and the form error of the finished surface. Using the proposed error correction/prediction system, fabrication of micron-level sinusoidal wave grids was attempted on single-crystal silicon. The form accuracy was successfully improved to the nanometer-level.