A laser catches what the eye can't see in a truck lamp. Every truck more than 80 inches wide is required to carry clearance and ID lamps of this sort. They are amber in front, red in the rear. Down each side, amber rows must end in red. The National Highway Traffic Safety Administration calls them "conspicuity lights," because they're supposed to make a truck conspicuous for safety's sake. 
Incandescent and LED lamps are used to mark trucks and trailers, just as they serve as taillights or to signal brakes and turns. LEDs generally cost more to buy, but tend to make up for it over time. They burn cooler than traditional glowing-filament lamps and draw less power from an electrical system. LEDs are expected to outlast the truck, so they eliminate the cost of replacements. Breault Research Organization of Tucson, Ariz., had the job of developing the optical part to mate with the LED in the new lamp. The company came up with an injection-molded component to disperse light and meet tight size and weight constraints. Reading beams of light at thousands of hertz, a laser scanner builds a point cloud describing the surface of an object. 
When the initial prototype came back, though, it did not meet requirements, even though optical simulation showed that it should. Measurements indicated that it did meet dimensional specifications. "Even though our design analysis had predicted that the component would work, test results showed that it was not putting out light in all the right places," said John Koshel, manager of optical design at Breault Research. Although the crew at Breault knew something wasn't right, they couldn't put a finger on the cause. They couldn't put a probe on it, either. Contact with a coordinate measuring device might damage the plastic and compound the problem. Some features seemed too fine for a probe to trace. Breault's engineers sent the prototype of the lamp to Laser Design Inc., which operates a laser scanning service bureau in Minneapolis as a sideline to its main business, which is making and marketing scanning systems.
Laser Design used a model called Surveyor, which has a movement envelope of 16 by 20 by 16 inches. The system emits beams of light and records them as they reflect off as many as 15,000 points per second. As it computes the travel of each beam, the scanner builds a point cloud representing the surface of an object. According to Larry Carlberg, sales coordinator for Laser Design's service bureau, the scan is accurate within 10 to 30 micrometers. Computer software converts the cloud into a model of the piece as it was built. When a program compares the as-built version with the original 3-D CAD model, color-coding will show where the two differ. When Laser Design's technicians sent their results to Koshel, he found small ripples in a critical area of the lamp's surface. Although at 0.001 inch they fell within design tolerance, the ripples pitched a critical slope 7 degrees away from the desired value.


