Arrangement for Photoelectric Pick-Up of the Relative Position of Two Relatively Moving Parts of a Machine Tool

1,179,438. Position determining arrangement. VYZKUMNY USTAV OBRABECICH STROJU A OBRABENI. July 19, 1967, No.33200/67. Heading G1A. The relative position of two parts of, for example, a machine tool is determined by a scale 2, Fig. 3 of light and dark fields of equal width through which a beam from a light source 1 is transmitted and a relatively movable reading screen 4 with two side-by-side rows of narrow gaps 3 each spaced in correspondence with the scale spacing but staggered half a division with respect to one another, the beams through the two screens being separated by a further screen 6 and applied to respective photo-cells. The cells are connected in a bridge circuit and give a zero output when the slots of both rows cover dark/ light boundaries. Production of the main scale by cutting a photograph of a chess board is described.