A hand-held optoelectronic shop tool measures cavities of the order of 6 in. (15 cm) in length and width, 2 to 4 in. (5 to 10 cm) in depth, with nominally flat side walls, and either curved or flat outer and inner surfaces. The system is called the Tile Cavity Measurement System (TCMS) because in the initial application for which it was developed, the cavities are those created by removal of space shuttle insulating tiles. In that application, the data acquired by the system are used in computer-aided design (CAD) and in computer-aided manufacturing (CAM) of new tiles to fit in the cavities. The system can also be used to measure other cavities of similar size and shape.

The hand-held optoelectronic shop tool (see figure) contains a white-light projector that illuminates the surfaces of the cavity with a pattern of stripes. Two high-resolution video cameras mounted on opposite sides of the projector are aimed toward the sidewalls and inner surfaces of the cavity to facilitate viewing the cavity sidewalls from different angles. The reason for using two cameras is simply that one camera would not suffice to view all cavity surfaces. The combined field of view of the cameras is an area of about 10 in. (25 cm) square, which includes the side walls and inner surface of the cavity plus the surrounding outer-surface area. The projector and cameras are connected by a 30-ft (9-m) cable to a mobile workstation, which includes a computer, video display, and the control and interface electronics. The projector and cameras operate under control by the computer, and the outputs of the cameras are digitized and sent to the computer for analysis.

Using a Hand-Held Shop Tool that contains a camera and a projector, the technician measures a tile cavity in less than 1 second. Previously, it was necessary to make and use a plaster model in a tedious, messy process that took as long as 30 hours and yielded marginal accuracy.

The projector and cameras are mounted on a rigid frame, which includes a shroud that keeps out background light and also serves to stabilize the tool against the cavity outer surface during measurements. The hand-held unit is equipped with handles and a pistol grip for positioning and control. On the pistol-grip handle are menu-selection thumb buttons and a trigger switch to initiate the measurement. A small color video monitor attached to the pistol-grip handle displays menus, video images of the measurement scene, and data.

The projector system includes a solenoid-operated translation stage with a striped pattern mounted on it. In operation, the video cameras acquire a set of four images of the pattern, each translated 1/4 of the stripe width. The entire measurement of a cavity takes less than 1 second. The shifted-stripe-pattern data are then processed by established phase-shifted-fringe-measurement techniques to obtain data from which the cavity surfaces are reconstructed in three dimensions. The data are stored and transferred to other computers in International Graphics Exchange Specification (IGES) format. The data can also be printed.

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 www.techbriefs.com under the Electronic Systems category, or circle no. 102 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. 5,561,526 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-11727, volume and number of this NASA Tech Briefs issue, and the page number.

NASA Tech Briefs Magazine

This article first appeared in the June, 1998 issue of NASA Tech Briefs Magazine.

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