Active profiling and polishing for efficient control of material removal from large precision surfaces with moderate asphericity

Sug Whan Kim, David Walker, David Brooks

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

We present the development of an active fabrication technology for controlling material removal on large precision surfaces of moderate departure from a sphere. The underlying philosophy was established as an efficient solution to the challenging problem of fabricating secondary mirrors of up to nominally 2.5 m in diameter for modern 8 m class telescopes and beyond. The facility described comprises a CNC profiler, two contact profilometers, and a full size active polisher. The trial work-piece was a convex surface of 830 mm in diameter on a zero-expansion ceramic ('Cervit') blank - a 1/3 scale hyperbolic mirror for a proposed 2.5 m diameter f/7 secondary mirror for the 8 m Gemini telescope. Using software error-correction from profilometric metrology data, a factor of 2 improvement in generating the convex aspheric profile was achieved. An active loose-abrasive polishing process is also described, in which a full-size tool is configured to deliver variable, edgeless, sub-diameter removal-footprints. Real-time monitoring of process variables is described, and approximately 10% convergence in each polishing pass is reported.

Original languageEnglish
Pages (from-to)295-312
Number of pages18
JournalMechatronics
Volume13
Issue number4
Early online date17 Jan 2002
DOIs
Publication statusPublished - May 2003
Externally publishedYes

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