A new, noncontact surface measurement technology based on holographic imaging techniques offers advantages over traditional methods for mapping the shape of complex objects.
Successful introduction of products requires form, figure and functionality to be defined in the design process and verified in the manufacturing process. Traditional metrology methods rely on devices such as dial indicators, coordinate measuring machines (CMMs), laser scanners, and contact and noncontact surface profilometers to handle this task. But one problem with these devices is their limited ability to measure only one or, at best, two of the three parameters. In many metrology labs, in fact, it is common practice to use three different devices taking three separate measurements to check the three quality parameters.
Based on holographic imaging techniques, a new technology is able to measure form, figure and functionality simultaneously. Frequency modulated holographic speckle interferometry -- which grew out of military technology developed to map the shape of satellites from the ground -- has now been made practical for mapping the shape of complex parts in the factory. It is already being successfully used in applications including transmission and car corner components -- such as brake rotors, wheels and hubs -- ignition coils and disk drive read-write heads. The new technique relies on a specialized method of interferometry. Interferometers have traditionally been used in the optical industry for assessing the grinding and polishing of glass lenses. Interferometers today are generally amplitude-modulated devices and are sensitive to temperature changes and vibration. This is why the use of interferometers has generally not spread outside the optics and electronics industries, where environmental conditions can be accurately controlled. The new approach, by contrast, relies on frequency-modulated interferometry, which is able to filter out noise from the measurement, enabling it to be used on the manufacturing floor.