22 September 1983 Large Surface Measuring Machine
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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.
© (1983) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mark Egdall, Mark Egdall, Robert S. Breidenthal, Robert S. Breidenthal, "Large Surface Measuring Machine", Proc. SPIE 0416, Applications of Optical Metrology: Techniques and Measurements II, (22 September 1983); doi: 10.1117/12.935919; https://doi.org/10.1117/12.935919

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