Optical Edge Sensor, Tastauge

The Tastauge or “Probing Eye” is a touch trigger sensor for optical measuring projectors. A thin glass fiber picks up the light signal in the beam path of the projector and guides it to a photomultiplier (see Fig. 3c). When an object is moved through the beam path, each edge produces a bright-dark or a dark-bright transition. Whenever an edge transition is detected based on an electronic threshold value technique, the coordinates of the measuring axis are read out. Important here is correct determination of the threshold value based on calibrated standards. This occurs automatically in modern measuring systems.

In practice, use of the Tastauge is limited to measurements performed according to the transmitted-light technique and in two or two-and-one-half dimensions (2-D or 2 1/2-D). 2 1/2-D means that an adjustment (but no measurement) is possible in the third axis. Low contrast values such as those characteristic of reflected light may result in measuring errors, since the spot-shaped sensor permits hardly any strategies for differentiating between contamination, surface interference, and genuine probing features.