How to accurately measure a thin object using 3D laser technology

SUMMARY: There are many applications for 3D laser scanners. Some legacy components were developed using non-computerized manufacturing techniques and CAD models don’t exist for them, for instance. Also, sometimes it’s necessary to reverse engineer a component for iterative design or manufacturing process improvement. Whatever the reason, generating a 3D model of a component is considerably easier, and can produce much higher quality results, when completed using a 3D laser scanner.

In the business of manufacturing not all components are going to be large enough that they can be easily inspected and measured. For these components traditional coordinate-based systems and standard mechanical measurement systems are often too imprecise and even precision instruments like a micrometer may provide inaccurate data for a variety of reasons. For these specialized conditions it is often necessary to employ a more advanced measurement system such as 3D Laser measurement. Unlike traditional measurement systems which essentially measure the gap between two remote planes, a 3D laser system scans an object’s surface using scanning laser technology. These systems can take thousands or millions of measurements across even the most complex and small surfaces which are then stored in a computer for analysis. For a very thin object there are two primary methods of scanning: geometry-based alignment and marker alignment. Either of these methods will encounter problems when scanning thin objects, but with careful planning and by following a few simple steps it is possible to produce accurate, detailed scans of even very thin objects.

Attach small spheres to the edges of the object to be scanned. Remember that the spheres must not move during scanning and that they are opaque. If the spheres move or if the laser light passes through them the scan results will be skewed. Even a slight shift in the position of the spheres can cause problems during the scanning process. Furthermore, the spheres should be 3.18mm to 6.35mm or 6.35mm to 15.9mm depending on which type of lens the scanning equipment is using.

Ensure that the object to be scanned is of a uniform, preferably white color. An object doesn’t necessarily need to be white but it will scan more quickly, and with more accurate results, if it has been spray-painted white beforehand. Be certain that the paint has dried and that the coat is even across the surface and, also, that the paint process does not move the tracking spheres.

To scan the face of the object ensures that the object scanner is angled at 45 degrees in orientation to the object to be scanned. Using measurements specific to each object, ensure that the Range viewer focuses properly on the object and that a scan is taken at every 45 degrees of the object, rotated clockwise. The best way to ensure the scans have aligned properly is to use paired point alignment.

To scan the sides of the object ensure that the object scanner is exactly horizontal in orientation to the object to be scanned and aim the Rangeviewer at each sphere individually for a scan. Be sure to scan each sphere at least once and, again align the scans using paired point alignment.

Finally, flip the object over and, ensuring that it has been painted white as well, proceed with scanning exactly as when scanning the face of the object. Similarly, using paired point alignment will ensure that the scans have aligned properly and that accurate measurements and scans are created.

Once the scans are completed and the data are loaded into a 3D image processing application the software can be used to combine the data and render a final image. In many cases the process will only take roughly half an hour though obviously larger or more complex objects will require more processing time.

Regardless of the components being scanned, a 3D scanner is one of the fastest and easiest ways to develop accurate, precise 3D models for use in engineering and manufacturing processes. Combined with some simple techniques and a little patience, 3D scanners are an invaluable compliment to any manufacturing and designing toolset.

Zac Brown is a freelance writer interested in Konica Minolta , a leading name for 3D scanner  services and other high-end scientific measurement equipments.

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