Photoelectric position-measuring arrangement having a plurality of shiftable grids

Claim 1

A photoelectric position-measuring arrangement for measuring length or angles which includes first, second and third grids which are shiftable with respect to one another, which grids diffract the light eminating from a light source into partial-beams and bring the diffracted partial-beams into interference wherein the intensity modulations arising from the interference from the partial-beams are transduced by photodetectors into electrical signals which are phase shifted with respect to one another, wherein the improvement comprises: a first grid, a second grid, and a third grid, the first grid disposed such that light from the light source impinges the first grid at an angle α relative to the grid normal (0) and is diffracted by the first grid, the second grid disposed to receive the partial-beams diffracted by the first grid, the third grid disposed to receive partial-beams diffracted by the second grid; the first grid being configured such that only the partial-beam of the zero diffraction order and the partial-beam of the first diffraction order lying closest to the grid normal (0) are diffracted at the second grid, whereby only these two beams contribute to the signal formation, and the first grid being further configured such that the partial-beams obtain a constant phase displacement of an amount θ; the second grid being configured such the partial-beams incident thereon are resolved only into partial-beams of their first diffraction orders, the second grid being further configured such that the partial-beams lying closest to the grid normal (0) are brought into interference by diffraction on the third grid; the third grid being identically configured to the first grid; and the photodetectors being disposed such that the interfering partial-beams from the third grid impinge thereon.