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Proceedings Paper

Large Surface Measuring Machine
Author(s): Mark Egdall; Robert S. Breidenthal
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Paper Abstract

A new surface measuring concept developed under government contract at Itek Optical Systems has been previously reported by Allen Greenleaf. The method uses four steerable distance-measuring interferometers at the corners of a tetrahedron to determine the posi-tions of a retroreflecting target at various locations on the surface being measured. A small wooden breadboard had been built and tested, demonstrating the feasibility of the concept. This paper reports the building of a scaled-up prototype surface measuring machine to allow the measurement of large aspheric surfaces. A major advantage of the device is that, unlike conventional interferometry, it provides surface measurement in absolute coordinates, thus allowing direct determination of radius of curvature. In addition, the device is self-calibrating. Measurements of a 24-inch mirror have been made with the new machine, giving repeatability of 4 µ m peak sag in the curvature and accuracy of 0.7 μm rms in the surface figure at best focus. The device is currently being used in the production grinding of large aspheric mirrors at Itek. The device is potentially scalable to other industries where highly accurate measurement of unusual surfaces is required.

Paper Details

Date Published: 22 September 1983
PDF: 7 pages
Proc. SPIE 0416, Applications of Optical Metrology: Techniques and Measurements II, (22 September 1983); doi: 10.1117/12.935919
Show Author Affiliations
Mark Egdall, Itek Optical Systems (United States)
Robert S. Breidenthal, Itek Optical Systems (United States)


Published in SPIE Proceedings Vol. 0416:
Applications of Optical Metrology: Techniques and Measurements II
Jar Jueh Lee, Editor(s)

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