Chromatic focus sensors

In order to have the broadest possible spectrum available, a white light source is used for illumination. This is why these sensors are sometimes not quite accurately referred to as white light sensors. The best focused light colour has the strongest intensity at the measurement points. This is determined using an integrated spectrometer and the detected colour is assigned the corresponding distance value. With increasing magnification of the lenses, the sensitivity of the sensors increases and the measuring range decreases.

As with all focussing sensors, the sensitivity of the sensor is highest when the aperture of the lenses used is very large. However, high aperture requirements reduce the working distance, which leads to an increased risk of collision. A relatively large working distance with a large aperture can be achieved with large but expensive lenses. The measurement of surfaces is possible with both diffusely reflective and reflective behaviour, as direct reflection does not interfere, as is the case with triangulation methods, for example.

The arrangement of a series of optical fibers makes it possible to implement the same principle as a line sensor. These sensors combine high measuring speed with low measurement uncertainty. In addition to the wave length of the reflected light, the intensity is also analysed to create a raster image of the workpiece surface. The subsequent evaluation with the image processing software allows measurements "in the image" of geometric features, e.g. to determine the workpiece coordinate system. The application possibilities for chromatic sensors correspond to those of the Foucault sensor. Some object surfaces, such as functional optical surfaces, and layer thicknesses can be measured better or more accurately. The disadvantages are the shorter working distance, the separate mounting location and the higher costs.