Automatic optical focusing device

Claim 1

An auto-focusing device, particularly for positioning reflective objects under investigation in a measuring apparatus, comprising about an optical axis in mutual optical alignment, a light source for emitting a narrow spectral band radiation, means for producing a plurality of images of said light source, said plurality of images serving as an illumination beam, a first and a second lens, a first beam splitter being for folding said optical axis at right angles to itself, an objective lens being arranged subsequently to said beam splitter in the folded optical axis, said objective lens having an object plane and an image plane, said first beam splitter having a beam splitting face inclinedly arranged by 45° relative to said optical axis and to said folded optical axis, said first and said second lens being for directing said illumination beams for illuminating said object plane via said first beam splitter and said object lens, a reflective object to be measured, said reflective object being for producing a focusing beam and an imaging beam, said objective lens being for imaging said reflective object into said image plane for evaluation, said beam splitting face being for transmitting said imaging beam and for reflecting said focusing beam to propagate in opposite direction to said illumination beam, a deviating means being inserted into said focusing beam between said second and said first lens, said deviating means being for directing said focusing beam at right angles to said optical axis, means for producing a first beam portion and a second beam portion, from said focusing beam, said means for producing said first and said second beam portion being arranged subsequently to said deviating means in said focusing beam, a first aperture being arranged in said first beam portion, a second aperture being arranged in said second beam portion, a first detector unit, a second detector unit, said first aperture being for producing two first individual images from said plurality of images transfered by said first beam portion, first means for producing a first interference pattern by superimposing said two individual images in said first detector unit, said second aperture being for producing two second individual images from said plurality of images transfered by said second beam portion, second means for producing a second interference pattern by superimposing said two second individual images in said second detector unit, an evaluation unit being connected to said first and said second detector unit, on the one hand, and to an adjustment means, on the other hand, incorporated in said objective lens for performing adjustment movements of the latter along said folded optical axis, said first detector unit and said second detector unit being for producing signals indicative of an actual focus position of said objective lens, and of the direction of defocusing, if any, said signals being compared to a focused position value stored in said evaluation unit, said evaluation unit being for feeding an adjustment signal to said adjustment means when said objective lens being out-of-focus.