GB482262A - Improvements in optical scale-reading apparatus - Google Patents

Abstract

482,262. Optical scale-reading apparatus. KAPELLA, Ltd., and REASON, R. E. Sept. 24, 1936, No. 28845/37. Divided out of 482,202. [Class 97 (i)] Apparatus for reading a divided scale comprises an optical system for forming at least one of two juxtaposed representations of the scale which are of different pitch and move in opposite directions relatively to the optical system when the scale reading changes, so that the two representations can be viewed simultaneously and one serves as a vernier for reading in conjunction with the other. In the form shown in Fig. 3, particularly intended for reading a straight scale, a transparent support A<1> carried by a body whose movements relatively to a fixed base are to be measured bears two scales A, B of different pitches. An inverted image b of the scale B is formed alongside the scale A by a concave reflector F<1>, the scale B being illuminated by rays from a lamp F<2> reflected by a mirror F<3> and passing through a lens F<4>. The scale A and image b are viewed through a microscope or eyepiece E. A separate digit scale may be marked on the support A<1> so that it is seen in the eyepiece ; the scale A and image b then act together as a vernier to give the fractional reading, the approximate reading being obtained from the digit scale. Figs. 5 and 6 show a form, also intended especially for reading a straight scale, in which two images, one inverted and one erect, of a single scale A are observed. The rays forming the two images are separated by an apertured mask G<2> in the focal plane of a field lens G<1>. The images are formed by objectives H, H<1> the scale lying in the focal plane of the objective H so that the rays are parallel between the objectives. A biprism H2 and field lens H3 are disposed in the image plane to form superposed images of the mask apertures G3, G<4>. The rays traversing the aperture G<3> pass through a reversing prism J to invert one image in a direction parallel to the length of the scale, and the rays traversing the aperture G<4> pass through a telescope K which produces a slightly magnified image. The support A<1> may also carry a digit scale D which is imaged by the part of the system forming the larger image. In a modification the support A<1> carries two scales of slightly different pitches, one being imaged by rays passing through the aperture G3 and the other by rays passing through the aperture G4, the telescope K being dispensed with. Fig. 8 shows one form for use with a circular scale. Scales A, B of different pitches are marked on a transparent angularly-movable disc L in diametrically opposite positions at equal radii and are obliquely projected by similar lenses M<2> carried by a fixed part M to form juxtaposed images near the axis of rotation of the disc. The rays are deflected parallel to the axis by reflectors M<3> and are observed through an eyepiece M<4>. A digit scale D is provided adjacent the scale A.