GB544938A - Improvements in or relating to optical scale-reading apparatus - Google Patents

Abstract

544,938. Measures of length. KAPELLA, Ltd., and WARMISHAM, A. Oct. 29, 1940, No. 15819. [Class 106 (ii)] [Also in Group XX] Scale-reading apparatus comprises an optical system for projecting an image of the scale into a plane containing a first reference line at right angles to the length of the scale and also containing a second reference line parallel to the scale and vernier scale extending at right angles to the scale, the first reference line and one of the other markings being carried by a graticule movable in a direction slightly inclined to the reference line. Superposed images of the markings may replace the actual markings in the plane of the image of the scale to be read and the superposed images may be projected on to a screen or viewed through a lens system. As shown in Fig. 1, a vertical scale B is lighted by a source D in conjunction with a condenser D<SP>1</SP> and mirror D<SP>3</SP> and a condenser D<SP>2</SP> and mirror D4, these elements being contained in one compartment A<SP>1</SP> of a casing A having a vertical wall C in which is a vertical slot-like aperture. The imaging system comprises two equal collimating lenses E<SP>1</SP>, E2 and an objective E, optically associated as described in Specification 498,419, [Group XX], and arranged in conjunction with prisms E<SP>3</SP>, E4 to produce an image in the focal plane of an eyepiece F, all these elements being housed in a second compartment A<SP>2</SP>. Fixed and movable graticules G, H, respectively, are arranged in the image plane, the graticule G carrying a vertical line G<SP>1</SP>, Fig. 3, and the graticule H carrying a horizontal line H<SP>1</SP> and scale H<SP>2</SP> and being carried by a block H<SP>3</SP> reciprocable along an inclined guide H4 by a spring and a screw operated by an external knob. The graduations of the scale H<SP>2</SP> and the inclination of the guide are chosen so that the scale serves as a vernier, the scale comprising, for example, 25 divisions and being raised one division of the image of the scale B m a complete traverse of the line G<SP>1</SP>, the measurement being thus effected in thousandths of an inch if the divisions of the scale B are fortieths of an inch. Modifications of the optical system are described in which the collimating lenses E<SP>1</SP>, E<SP>2</SP> are of unequal focal lengths, or the erecting prisms E3, E<SP>4</SP> are replaced by a lens system similar to and in tandem with the lenses E<SP>1</SP>, E, E2, or, for reading inaccessible scales, the microscope eyepiece is replaced by a telescope system, bowden wire or other remote control means being provided for the graticule H.