Tolerance control with high resolution 3D measurements

The use of a laser range sensor in the 3D digitalization process for inspection tasks allows very significant improvement in acquisition speed and in 3D points density but does not attain the accuracy obtained with a Coordinate Measuring Machine (CMM). Inspection consists in verifying the accuracy of a part related to a given set of tolerances. It is thus necessary that the 3D measurements be more accurate than the tolerance range. In the 3D capture of a part, several sources of error can alter the measured values. So, we have to find and model the effect of the most influential parameters affecting the accuracy of the range sensor in the digitalization process. This model is used to provide a sensing plan to acquire completely and accurately the geometry of an object. The sensing plan is composed of the set of viewpoints, each of which defines the exact position and orientation of the camera relative to the part. The 3D cloud obtained from the sensing plan is registered with the CAD model of the part and then segmented according to the different surfaces. Segmentation results are used to check tolerances of the part. We propose in this paper a methodology for geometrical inspection that uses the segmented 3D data related to the surface of interest and the CAD model of the part.