CMM vs. White Light Scanners

The CMM has long been the king of accuracy in 3D dimensional metrology – but when will non-contact measurement replace it? White light scanners are well placed, but it will be some time before they can rival the accuracy of a CMM.

CMM 3D accuracy is often one or two microns – an order of magnitude better than the per–point accuracy of most white light scanners. However, their measurement speed is slow. A white light scanner makes millions of measurements in seconds; a CMM would manage perhaps a dozen in the same time.

In many applications the accuracy of the CMM is simply not required. An accuracy of 10's of microns measured in seconds is usually adequate – especially if it means that this measurement can be performed on every part.

Gathering a point cloud on a complex surface – such as a body panel, a gas turbine blade, or a wing section – is a slow undertaking. In many cases, the ideal solution may even be a combination – if some dimensions need the CMM's accuracy, then use white light to ensure the freeform shape, the complex curves that define the part's efficiency and form are correct – and then use the CMM for the last few, painstaking points.

The CMM may still hold the edge on polished metals, but even then, newer scanners – such as Phase Vision's Quartz DBE family – excel in this area. However the CMM reigns supreme on translucent material such as glass – a real problem for optical systems.

In summary, a CMM is ideal where the application requires a small number of extremely accurate measurements, or is on a very difficult surface like glass or mirrors; while the white light scanner wins out on freeform measurement, or where speed is of the essence.