CMM

Ref : http://en.wikipedia.org/wiki/Coordinate-measuring_machine

A coordinate-measuring machine (CMM) is a device for dimensional measuring. It is a mechanical system designed to move a measuring probe to determine the coordinates of points on the surface of a workpiece. These machines are used to measure the sizes and positions of features on mechanical parts. Oftentimes these parts have tolerances as small as .0001". The machine uses an X-Y-Z grid to determine its position on a worktable. The probe is used to touch different spots on the part being measured. The machine then uses the X,Y,Z coordinates of each of these points to determine size and position. There are newer models that have probes that drag along the surface of the part taking points at specified intervals. This method of CMM inspection is more accurate than the conventional touch-probe method and most times faster as well. The next generation of scanning, known as laser scanning, is advancing very quickly. This method uses laser beams that are projected against the surface of the part. Many thousands of points can then be taken and used to not only check size and position, but to create a 3D image of the part as well. This "point-cloud data" can then be transferred to CAD software to create a working 3D model of the part. The laser scanner is often used to facilitate the "reverse engineering" process. This is the process of taking an existing part, measuring it to determine its size, and creating engineering drawings from these measurements. This is most often necessary in cases where engineering drawings may no longer exist or are unavailable for the particular part that needs replacement.