Metrology

A Coordinate Measuring Machine (CMM) is a device for measuring the physical geometrical characteristics of an object. This machine may be manually controlled by an operator or it may be computer controlled. Measurements are defined by a probe (mechanical, optical, laser, white light, etc.) attached to the third moving axis of this machine.

These coordinates are used to verify and to validate the dimensions of the workpiece.

A CMM consists of:

• A table (part of the machine on which the piece to be measured is immobilized, sometimes called marble but which is not necessarily geometrically perfect).
• Three slide links enables the positioning of the measuring head at any point of space. Graduated rulers (optical or electrical) make it possible to know the position of each of the slides
• A measuring head (probe).

The measuring head is an organ whose origin coordinates are known thanks to the measurement rules of the slides. It is the interface between the machine and the part, using either a stylus (stem that triggers a contactor as soon as it comes into contact with the workpiece) for the points extraction (palping method ); Or of a contact sensor, which aspect is close to that of the probe, but which continuously measures and records the profile (scanning method).

Most measuring heads allow several orientations of the probe or of the sensor which they bear for easier accessibility to the measured surface. Usually the head orientation concerns two axis.

(source : translated from Wikipedia)