Photoelectric linear or angular measuring instrument

摘要

In a photoelectric linear or angular measuring instrument having a parallel light-beam path for measuring the relative position of two objects, a scale (5) and a scanning plate (8) can be displaced relative to one another at a specific distance from one another in the direction of a light beam, which for technical diffraction reasons must be kept within narrow tolerance limits in order to obtain optimum measuring signals. In order to permit relatively large changes in this distance, the scanning plate (8) has two scanning fields (F1, F2) which are arranged such that the optical path lengths of the light beams between the division plane (EM) of the scale (5) and the division planes (EA1, EA2) of the scanning fields (F1, F2) have a path difference of d = n . pM<2>/2 lambda (n = 1,2,3...), pM signifying the grid constant of the scale (5) and lambda the wavelength of the light. The electrical scanning signals (S1, S2) obtained with the aid of the scanning fields (F1, F2) are used to form an aggregate signal (S) which essentially remains constant even in the event of relatively large changes in distance. <IMAGE>