Software for coordinate measuring machines

Coordinate measuring machines (CMMs) are based on a simple principle. Using high-precision measuring rules placed on the machine's various guideways, the coordinates of a probe are determined and brought into contact with the surface of a part to be measured.

The software associated with measuring machines performs numerous functions: it teaches and executes inspection routines, numerically controls probe movements along predefined trajectories, statistically processes measurement results obtained on a series of parts, and digitally compensates for the 21 geometric defects of the machine [1] . Of all these functions, we shall limit ourselves in this article to those linked to measurement processing, i.e. those which determine the coordinates of the points of contact between the probe and the surface to be measured, and which, by mathematical processing of the coordinates, enable dimensional measurements to be made and the characteristics of the geometric tolerances of the parts to be verified.

We will therefore assume that the geometry of the measuring machine and its measuring system are flawless, i.e. that the coordinates are expressed in an orthonormal reference frame with maximum accuracy with respect to the macro-geometric defects of the parts to be measured. In addition, to simplify this presentation, we assume in all our examples that the CMM is a gantry-type measuring machine without a fourth axis. The reader can easily transpose this presentation to other machine structures.