Abstract
Optical surfaces can be accurately figured by computer controlled optical surfacing (CCOS) that uses well characterized sub-diameter polishing tools driven by numerically controlled (NC) machines. The motion of the polishing tool is optimized to vary the dwell time of the polisher on the workpiece according to the desired removal and the calibrated tool influence function (TIF). Operating CCOS with small and very well characterized TIF achieves excellent performance, but it takes a long time. This overall polishing time can be reduced by performing sequential polishing runs that start with large tools and finish with smaller tools. In this paper we present a variation of this technique that uses a set of different size TIFs, but the optimization is performed globally - i.e. simultaneously optimizing the dwell times and tool shapes for the entire set of polishing runs. So the actual polishing runs will be sequential, but the optimization is comprehensive. As the optimization is modified from the classical method to the comprehensive non-sequential algorithm, the performance improvement is significant. For representative polishing runs we show figuring efficiency improvement from approximately 88% to approximately 98% in terms of residual RMS (root-mean-square) surface error and from approximately 47% to approximately 89% in terms of residual RMS slope error.
Highlights
Many computer controlled optical surfacing (CCOS) processes have been developed and used since 1963 [1,2,3,4,5,6,7,8]
Because the material removal process is affected by the workpiece motion and edge effects, which are the function of tool position on the workpiece, the tool influence function (TIF) is changed according to its center position on the workpiece [19]
In this paper the non-sequential optimization technique for a CCOS process utilizing multiple TIFs was developed and its performance was demonstrated. This technique benefits from the use of a wider search space than that of conventional optimization techniques
Summary
Many computer controlled optical surfacing (CCOS) processes have been developed and used since 1963 [1,2,3,4,5,6,7,8]. These CCOS processes are usually aimed at three characteristics, i) low tooling overhead, ii) deterministic material removal and iii) embedded process control intelligence [9,10] These CCOS techniques have been successfully used for fabrication of large aspheric optical surfaces, including off-axis segments [4,5,6,7,8,11]. The actual polishing runs are still to be sequential under the guidance of comprehensive optimization This new technique, which enables the ensemble of various TIFs, forms an attractive solution for the mass fabrication capability of high quality optical surfaces.
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