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STIL dimensional sensors are based on two distinctive proprietary technologies:
Each has its own advantages, and together they open the way to numberless metrological applications and to outstanding measurement possibilities.
Both technologies use a confocal optical setup, which means that at any given instant the photodetector “sees” a single point. This point is illuminated by a small, perfectly focused spot, and the system is completely insensitive to ambient light. The “classical” confocal setup is characterized by an excellent lateral resolution and a very high signal-to-noise ratio. It has a single drawback: a very small depth of focus, requiring vertical scanning.
The two technologies developed by STIL SA combine the confocal setup with new optical principles (color coding for CCS, spectral interferometry for CSI) which extend its depth of focus, eliminating the need for vertical scanning. As a result these innovating technologies share all the advantages of the “classical” confocal setup, but not its drawback.
Chromatic Confocal sensing (STIL patent) was invented in 1995 and has since been worldwide acknowledged as an accurate and reliable technique for non-contact distance and thickness measurement. It is one of the very few non-contact techniques for 3D metrology recommended by the ISO 25178 international standard.
Setup:
A chromatic lens L generates the image of a point white-light source W as a continuum of monochromatic images located on the optical axis (“Chromatic coding”). A sample is located inside the color-coded segment and its surface scatters the incident light beam.
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The backscattered light passes through the chromatic lens L in the opposite direction, and arrives at a pinhole P which filters out all wavelengths except a single wavelength, λM. The collected light is analyzed by a spectrometer S. The sample position (point M) is directly related to the detected wavelength. Advantages:
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Confocal Spectral Interferometry (STIL pending patent) is a state-of-the-art technology which combines the high signal-to-noise of the Confocal Setup with the exceptional precision and resolution of Spectral Interferometry.
Setup:
The light from a white-light point source W passes through an interferometric objective L and a reference plate R before it reaches the sample surface. The superposition of the light beams reflected from the sample
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surface and from the reference plate generates an interference phenomenon. The reflected beams pass through the interferometric lens L in the opposite direction, and arrive at a pinhole P which filters out all light rays except those originating from the object point M. The spectrometer S measures the channeled spectrum of the interference signal. The thickness of the air gap between the sample and the reference plate can be extracted with sub-nanometric resolution from the spectral phase of this spectrum. Advantages:
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