The First Aspheric Form and Texture Results From a Production Machine Embodying the Precession Process

D. D. Walker, D. Brooks, R. Freeman, A. King, G. McCavana, R. Morton, D. Riley, J. Simms

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

89 Citations (Scopus)


We report on progress developing the 'Precession Process', that has recently been embodied for the firsttime in a fully-productionised aspheric polishing machine. We describe how the process uses inflatedpolishing tools of continuously-variable size and hardness. Despite the rapid tool-rotation needed togive high removal rates, the method produce well-behaved and near-Gaussian tool influence-functions,by virtue ofthe precession ofthe spin axis.

We then describe how form-errors are controlled. The method takes influence-function data and anerror-map as input, together with, uniquely, weighting factors for height and slope residuals andprocess-time. A numerical optimisation of the cost function with variable dwell-time, tool-path andtool-size is then performed. The advantages of this new technique are contrasted with conventional deconvolutionmethods. Results of form-control on aspheric surfaces are presented, with an interpretationin terms of spatial frequencies. We draw particular attention to control of form at the centre andperiphery of a work-piece.

Finally, we describe how Precession processing gives multi-directional rubbing of surfaces, and wepresent the superb texture achieved on samples.

Original languageEnglish
Title of host publicationOptical Manufacturing and Testing IV
EditorsH. Philip Stahl
Number of pages10
ISBN (Print)9780819441652, 0819441651
Publication statusPublished - 27 Dec 2001
Externally publishedYes
EventInternational Symposium on Optical Science and Technology - San Diego, United States
Duration: 29 Jul 20013 Aug 2001

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceInternational Symposium on Optical Science and Technology
Country/TerritoryUnited States
CitySan Diego
Internet address


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