Contact vs. Non–Contact Measurement

There is a very clear split within dimensional measurement systems – whether they use a mechanical contact, or some form of optical procedure:

• Contact techniques use a mechanical probe of some form, either touched onto the surface to be measured, or dragged across it.
• Non–Contact approaches use some form of radiation (usually light) to perform measurements.

Contact techniques (usually CMM or mechanical arms) are not affected by the optical characteristics of the surface, but can affect the surface to be measured – for example, soft materials such as many silicones or rubbers will distort when probed. Fibrous material will be displaced by the probe tip; while materials such as titanium and aluminium can actually be scored by the effects of the tip – a fact which surprises many people. Due to the need for physical contact, these approaches tend to be relatively slow.

In contrast, non–contact techniques (laser or white light scanners / fringe projection) are usually very fast and should not affect the surface being measured, as the only impact they have on the surface is the light used in the measurement. However, light itself can be affected by the surface, and this in turn affects the quality of the measurement – for example, clear / translucent materials such as glass components are very challenging, as are shiny surfaces (such as mirrors, or highly polished metal).

Suppliers in each area are working to improve their offerings, but nonetheless, there are many applications which by their nature must use either a contact or non–contact approach.

Phase Vision's products are all non–contact, using advanced optical techniques to provide accurate measurement – even on challenging surfaces.