Insight into aspheric misfit with hard tools

Mapping the island of low mid-spatial frequencies

David Walker, Wu Hsing-Yu, Guoyu Yu, Hongyu Li, Wang Zhang, Chunlian Lu

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

This paper addresses computer numerical control (CNC) polishing of aspheric or freeform optics. Prior CNC grinding of the asphere tends to produce mid-spatial frequencies (MSFs) at some level. Precessions polishing can rectify these, but the very ability of the bonnet tooling to adapt to the local asphere enables it to do so, at least in part, to similar spatial frequencies in the MSFs. To accelerate smoothing, hard tools can, in principle, be used, but aspheric misfit is often assumed to preclude this. In this paper, we explore new insight into the role of abrasive particle size in accommodating misfit. First, we report on a glass-bending rig to produce a continuous range of complex surfaces, while withstanding process forces. Then, we describe how this was used to evaluate the triangle of misfit, abrasive size, and MSFs produced for hard rotating tools. This has revealed a regime in which such tools can be used without introducing significant new MSFs, as evidenced by manufacture of prototype off-axis aspheric segments for the European Extremely Large Telescope project.

Original languageEnglish
Pages (from-to)9925-9931
Number of pages7
JournalApplied Optics
Volume56
Issue number36
DOIs
Publication statusPublished - 13 Dec 2017

Fingerprint

aspheric optics
Polishing
Abrasives
numerical control
abrasives
Bending (forming)
polishing
Telescopes
Optics
tooling
Particle size
grinding
precession
smoothing
triangles
prototypes
telescopes
optics
glass

Cite this

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title = "Insight into aspheric misfit with hard tools: Mapping the island of low mid-spatial frequencies",
abstract = "This paper addresses computer numerical control (CNC) polishing of aspheric or freeform optics. Prior CNC grinding of the asphere tends to produce mid-spatial frequencies (MSFs) at some level. Precessions polishing can rectify these, but the very ability of the bonnet tooling to adapt to the local asphere enables it to do so, at least in part, to similar spatial frequencies in the MSFs. To accelerate smoothing, hard tools can, in principle, be used, but aspheric misfit is often assumed to preclude this. In this paper, we explore new insight into the role of abrasive particle size in accommodating misfit. First, we report on a glass-bending rig to produce a continuous range of complex surfaces, while withstanding process forces. Then, we describe how this was used to evaluate the triangle of misfit, abrasive size, and MSFs produced for hard rotating tools. This has revealed a regime in which such tools can be used without introducing significant new MSFs, as evidenced by manufacture of prototype off-axis aspheric segments for the European Extremely Large Telescope project.",
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Insight into aspheric misfit with hard tools : Mapping the island of low mid-spatial frequencies. / Walker, David; Hsing-Yu, Wu; Yu, Guoyu; Li, Hongyu; Zhang, Wang; Lu, Chunlian.

In: Applied Optics, Vol. 56, No. 36, 13.12.2017, p. 9925-9931.

Research output: Contribution to journalArticle

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