High precision optical measurement with smart photosensors

The smart integrating photosensor is described. A scale (linear or circular code and incremental track) is displayed on a specially designed detector by means of a simple telecentric imaging system. The arrangement is also realised in the reflective illumination mode. The code track detector is capable of 20-bit resolution. If a bit on the scale has length X, a length of 220 times X can therefore be encoded. The resolution of this system is X. Now it's the turn of the incremental detector. It is designed in such a way that the image of the incremental track is converted into four quasi harmonic-free photo current signals offset by 90/spl deg/ during the scanning process. Signals of this quality are converted by electronic interpolators into digital signals whose resolution is limited by the detector noise. It has been proved that the incremental system achieves a resolution of X/256.