High Resolution position coder

Abstract

Coder of position of a first element in displacement relatively to a second element, the latter including an optical system provided with at least one coherent light source emitting a beam intended to interfere, after collimation in a diaphragm, with the second element and at least one photodetector with contiguous cells in a line for detection of the light signal after interference. The second element includes a succession of primary coding cells provided with diffraction holograms each defining therein a single location, the cells interfering in succession with the light beam in the course of their relative displacement. The diffracted signal is sent to the photodetector or photodetectors for measurement of absolute position. The coder includes a series of secondary coding cells provided with diffraction holograms interfering successively with the light beam. The said cells are provided with an identical hologram diffracting the incident light into aligned diffraction light spots, the said hologram including a modulation, in the form of a stripe or a plurality of identical stripes arranged in parallel, which modulates the diffracted signal by orientating it at each instant perpendicularly to the tangent to the said stripe progressively as the collimated beam is displaced relatively to the cell, the position of the centre of the diffraction spot of order 0 remaining unchanged. At least one relative position photodetector is provided so orientated as to correspond to the displacement of a diffraction light spot produced by the secondary coding cell.

Dependencies are inferred from the claim text.