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Proceedings Paper

Holographic Real Image Measurement Using A Computer Controlled,Closed Circuit Television System
Author(s): D G. Wright
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Paper Abstract

A hologram of an intricate mechanical assembly can be used to project a three dimensional image which can be examined optically. Any part of the image can be observed provided that the corresponding part of the mechanical assembly was illuminated during the construction of the hologram and was visible from any part of the 'window' formed by the holographic plate. Accurate reconstruction from a carefully processed holographic plate yields an image which is within ± 1% of the size of the original object. When measured markers are included with the object, adjustments can be made to make the reconstruction more accurately 1:1 and image accuracies approaching 0.1 % have been achieved. A three axis computer controlled measurement system is employed to move a television camera throughout the image volume. The accuracy of the system is better than 5pm and the repeatability of the measurements is 50 μm within a volume measuring 600 mm x 300 mm x 300 mm. The television camera utilises an 18 mm image tube which gives a monitor image representing an area of 8.7 mm by 6.7 mm with each scan line representing a distance of 11.6 μm. The form of any part of the mechanical assembly is known and a processing system can produce a mask to compare with the acquired image. The difference between the two can be evaluated and the camera position can be changed until the difference is a minimum. The image is adjusted to be within 1 pixel of the mask and accurate measurements of the position, in three dimensions, of selected parts of the structure determined in this manner. The paper will include an analysis of the causes of loss in measurement precision and discuss modifications which could lead to improved performance.

Paper Details

Date Published: 17 November 1986
PDF: 7 pages
Proc. SPIE 0654, Automatic Optical Inspection, (17 November 1986); doi: 10.1117/12.938275
Show Author Affiliations
D G. Wright, Marchwood Engineering Laboratories (England)

Published in SPIE Proceedings Vol. 0654:
Automatic Optical Inspection
Lionel R. Baker; H. John Caulfield, Editor(s)

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