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Properties
While other measuring devices, such as height gauges, can measure an object's geometry, CMMs can measure multiple geometrical facets and even produce detailed three-dimensional (3-D) measurements. A variety of CMMs, in differing sizes, configurations and measuring accuracy, are used for different applications. All CMMs have a probe to measure objects, using either mechanical, laser, optical or white lights. An automated CMM enables repetitive and automatic inspection of high volumes of objects, useful for factory processes.
Mechanical CMMs
Used to gather a high number of points in bores and surfaces of parts, mechanical scanning probes give an accurate picture of roundness, cylindricity and flatness. Most modern CMMs use an electronic touch trigger probe, consisting of either a fixed or moving probe head, the touch probe itself and a stylus for contact with the object. Many mechanical CMMs have a fixed vertical or horizontal arm. Using multiple CMMs with a fixed arm configuration prevents waiting for arms to move, enabling the rapid inspection of high volume parts.
Noncontact CMMs
Using optical, laser or white light, noncontact CMMs can measure profiles of delicate surfaces, coated objects and soft parts because the probe doesn't physically touch the part. Lasers provide high levels of accuracy, able to measure to within a thousandth of an inch. Lasers are also able to construct 3-D images of an object. Software enables video cameras to act as measuring devices, while white light scanning uses the interference of light beams (interferometry) to measure objects without contact.
Uses
The type of CMM device needed depends on the size, shape, quantity and frequency of objects that need measuring. Horizontal arm units using mechanical measuring are often deployed in auto parts factories for rapid inspection of large quantities of parts. Video systems used to inspect flat parts, such as sheet metal, can do so quicker than other CMMs. While lasers can digitize odd-shaped parts in minutes, taking thousands of measurements per second.