Systematic modeling and rapid control for diamond machining of periodical optical surface

Abstract

Spiral path based fast tool servo diamond turning technique is currently considered to be an efficient method for precision machining of micro-lens arrays. However, due to the inherent structural and methodological drawbacks, such as tracking bandwidth limitation, the system nonlinearity, it is still a great challenge for controllable fabrication of micro-lens arrays especially with complex geometry. To extend both the capability and accuracy, two aspects involving cutting method and control strategy are proposed in this paper. Firstly, the concept of the fast servo-assisted rotary cutting approach is introduced. Due to the unique diamond cutting approach, the fast servo trajectory features the characteristic of quasi-periodicity, and accordingly an advantageous terminal sliding mode repetitive control strategy is designed to realize high closed-loop tracking bandwidth and robustness against the variant system uncertainties and force disturbances during the cutting process. Then, the effectiveness is verified by the experiments on the diamond machine with respect to tracking accuracy, characteristic parameters as well as surface form error. Through comprehensive characterization and comparisons, the proposed diamond machining system with the controller is demonstrated to be able to substantially improve the machining performance of complex periodical optical surfaces.