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Proceedings Paper

Miniaturised optical encoder
Author(s): John Carr; Marc P. Y. Desmulliez; Nick Weston; David McKendrick; Graeme Cunningham; Geoff McFarland; Wyn Meredith; Andrew McKee; Conrad Langton; Iain Eddie
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Paper Abstract

Optical encoders are pervasive in many sectors of industry including metrology, motion systems, electronics, medical, scanning/ printing, scientific instruments, space research and specialist machine tools. The precision of automated manufacture and assembly has been revolutionised by the adoption of optical diffractive measurement methods. Today's optical encoders comprise discrete components: light source(s), reference and analyser gratings, and a photodiode array that utilise diffractive optic methods to achieve high resolution. However the critical alignment requirements between the optical gratings and to the photodiode array, the bulky nature of the encoder devices and subsequent packaging mean that optical encoders can be prohibitively expensive for many applications and unsuitable for others. We report here on the design, manufacture and test of a miniaturised optical encoder to be used in precision measurement systems. Microsystems manufacturing techniques facilitate the monolithic integration of the traditional encoder components onto a single compound semiconductor chip, radically reducing the size, cost and set-up time. Fabrication of the gratings at the wafer level, by standard photo-lithography, allows for the simultaneous alignment of many devices in a single process step. This development coupled with a unique photodiode configuration not only provides increased performance but also significantly improves the alignment tolerances in both manufacture and set-up. A National Research and Development Corporation type optical encoder chip has been successfully demonstrated under test conditions on both amplitude and phase scales with pitches of 20 micron, 8 micron and 4 micron, showing significantly relaxed alignment tolerances with signal-to-noise ratios greater than 60:1. Various reference mark schemes have also been investigated. Results are presented here.

Paper Details

Date Published: 2 September 2008
PDF: 11 pages
Proc. SPIE 7068, Optical System Alignment and Tolerancing II, 70680M (2 September 2008); doi: 10.1117/12.793254
Show Author Affiliations
John Carr, Heriot-Watt Univ. (United Kingdom)
Renishaw plc (United Kingdom)
Marc P. Y. Desmulliez, Heriot-Watt Univ. (United Kingdom)
Nick Weston, Renishaw plc (United Kingdom)
David McKendrick, Renishaw plc (United Kingdom)
Graeme Cunningham, Renishaw plc (United Kingdom)
Geoff McFarland, Renishaw plc (United Kingdom)
Wyn Meredith, CST Global Ltd (United Kingdom)
Andrew McKee, CST Global Ltd (United Kingdom)
Conrad Langton, CST Global Ltd (United Kingdom)
Iain Eddie, CST Global Ltd (United Kingdom)

Published in SPIE Proceedings Vol. 7068:
Optical System Alignment and Tolerancing II
José M. Sasian; Richard Neil Youngworth, Editor(s)

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