The figure schematically illustrates an automated electronic vision system that operates in conjunction with a scanning robot to inspect a large surface for damage. In the original application for which the system was developed, the surface comprises the panels of the space shuttle thermal radiators, with a total area of more than 1,200 ft2 (>111 m2). Typically, the whole area contains between zero and five damage sites, though occasionally it contains hundreds of damage sites, along with hundreds of nondamage sites that may look like damage sites at first glance. Heretofore, the surface was inspected by technicians using flashlights and magnifying glasses in a tedious, slow, labor-intensive process, and the inspection data were recorded manually in a form not readily accessible for review and analysis. The automated vision system performs the inspection much faster and stores results in a data base that is readily accessible for review and analysis.

The system includes a high-resolution video camera mounted on the scanning robot arm, along with two stroboscopic illuminators, about 2 ft (0.6 m) away from the surface to be inspected. The camera and illuminators operate under control by a computer, and the video output is digitized and sent to the computer. The system scans the surface in a continuous motion, viewing a square area about 5 in. (13 cm) on a side. Data are taken when the stroboscopic illuminators "freeze" the motion at intervals of 4 in. (10 cm) along the surface.

The Automated Electronic Vision System and the scanning robot together constitute an automated inspection system that can quickly find a few damage sites on a large surface.

The two illuminators are used to reveal different kinds of damage. One illuminator comprises a ring flash lamp that encircles the camera, plus an ellipsoidal reflector behind the camera and flash lamp. The camera and flash lamp lie in one focal plane of the ellipsoid, and the surface to be inspected lies midway between the two focal planes of the ellipsoid. Thus, the surface is illuminated diffusely and nearly uniformly and light reflected from the surface fills the camera lens nearly uniformly over the entire field of view. This optical arrangement provides a bright field illumination system that highlights small damage sites over an extended inspection area. This illuminator is used along with a component of image-data-analysis software to find such microscopic damage as punctures and scratches. The software implements a number of steps in which image background clutter is filtered out and each damage or nondamage site is characterized in terms of a list of specific features that include location, size, and shape. The lists of features for all sites are stored in the data base and the rest of the image data are discarded.

The other illuminator incorporates slide-projector optics and is located on a boom about 2 ft (0.6 m) to one side of the camera. This illuminator projects a grating (that is, a grid pattern in white light, not to be confused with a diffraction grating) onto the surface to be inspected. The resulting image of the grid is processed by a component of image-data-analysis software to find such macroscopic damage as large dents and tape delaminations. The software first processes the image of the grating to obtain the digital equivalent of a depth map of the surface. The depth-map data are then processed in a manner similar to that of the diffuse-illumination-image data to filter out background clutter, characterize each damage or nondamage site in terms of a list of specific features, and store the list of features in the data base.

The problem of identifying relatively few damage sites is solved relatively easily by use of this system. An initial inspection generates a nondamage portion of the data base. The computer can then compare feature data acquired in subsequent inspections with this portion of the data base to find changes indicative of damage that has occurred in the interim.

This work was done by Edward D. Huber and Rick A. Williams of Lockheed Martin Missiles & Space Co. for Kennedy Space Center. For further information, access the Technical Support Package (TSP) free on-line at under the Electronic Systems category, or circle no. 155 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).

Title to this invention, covered by U.S. Patent No. 5,608,215 has been waived under the provisions of the National Aeronautics and Space Act {42 U.S.C. 2457 (f)}. Inquiries concerning licenses for its commercial development should be addressed to

Edward D. Huber
Lockheed Martin Missiles &
Space Co., Inc.
Dept. H1-52, Bldg. 202
Advanced Technology Center
3251 Hanover St.
Palo Alto, CA 94304
(650) 424-3308

Refer to KSC-11726 , volume and number of this NASA Tech Briefs issue, and the page number.