Laser Scanner Reverse-Engineers Automotive Panels

Paula M. Powell

Aftermarket automotive manufacturers usually must visit automaker facilities to preview new automobile models. They often are given just a couple of hours to take enough measurements to ensure that they can build products that mesh with vehicle dimensions. When engineers at Infinity Products in Minneapolis -- which makes consoles that mount DVD and VCR screens to vehicle ceilings, as well as decorative instrument panel overlays -- used a portable coordinate measuring machine to reverse-engineer parts, the limited number of data points measured meant that it often took weeks to build a computer-aided design (CAD) surface model. But switching to a portable laser scanner allowed them to collect 250,000 data points from a cubic foot of surface in about 10 s. This dropped the build time for an accurate surface model to less than a day, according to engineering manager Troy Graphenteen.

To digitize complex surface data, a Laser Design scanner uses laser triangulation to collect a 512-point strip of data 60 times per second, producing 250,000 data points per cubic foot of surface area in seconds.

Relying on laser triangulation to measure complex surfaces, the scanner projects 670-nm laser light from a class II diode laser, which has a power rating of less than 1 mW. According to Marty Schuster, CEO of Minneapolis-based scanner manufacturer Laser Design Inc., the beam is then split into a plane of laser light that scans the surface to form a profile. A two-dimensional CCD array in one of two optical sensors mounted on either side of the probe captures reflected light and records the profile shape. Scanner software determines an X-position for each pixel value.

The 9 x 9 x 3 in., tripod-mounted laser head requires only two cable connections to a laptop computer. Data capture involves pointing the unit at the target surface, setting the scanning range and brightness, and pushing the start button. A dedicated interface card translates the video image of the line into 3-D coordinates.

Schuster said that the Surveyor PS-1100 scanner used by Infinity features resolution of 0.002 in. and accuracy of 0.002 to 0.004 in. He defines resolution as the smallest change in distance that the sensor can detect, while accuracy is a function of the optical qualities of the object being scanned. For example, resolution and accuracy will be nearly the same for a matte surface.

Graphenteen noted that designers can now register scan data and generate individual surfaces in the CAD system in less than an hour. "We do a little cleanup, such as eliminating noise and outlier points in that environment, then export an STL format file and read it into Pro/Engineer or a different CAD package. So we save a week or two on this part of the process. The bottom line is that we have cut the average time required to go from measurement to production from 14 to 10 weeks."