If you were to ask an assembler at a Tesla factory how they measure the diameter of a piston, the response could very well be “what’s a piston?” If the same question were asked, a traditional combustion engine assembler would likely exclaim “with calipers, of course!” If we are to probe and delve into the quality control limitations associated with contact thickness measurements, we are likely to witness that the use of such instruments results in operator-based measurement variability, limited sampling of the part being manufactured, and potential damage to the part. It is largely for these reasons that noncontact thickness metrology solutions have become a necessity for the manufacturing sector. In this article, we will demonstrate two distinct methods that effectively measure part thickness without making any contact. We will first describe the benefits of using chromatic confocal technology for one-sided measurements, then the benefits of using triangulation sensor technology for dual-sided profiles.
Chromatic confocal point sensors are widely used as direct imaging profilometers for surface texture analysis, dimensioning and tolerancing, and height measurement. These sensors are made up of a polychromatic source, optics that disperse this white light, and a confocal arrangement. When the dispersed wavelengths are projected and subsequently reflected from a measurement work piece, a single in focus wavelength returns to be decoded for distance via its confocal arrangement. If visibly transparent materials are being inspected, however, two confocal peaks are returned. The separation of these peaks corresponds to the optical thickness of the sample, which can be used in conjunction with knowledge of the material’s optical properties to determine a physical thickness. This one-sided noncontact thickness measurement technology is a key advantage for in-line thickness control of roll to roll processes.