Patent GB-561783-A (GB)
Title: Improvements in or relating to measuring apparatus
IPC: G01B11/00
Filed: 1942-12-02
Abstract: 561,783. Optical scale-reading apparatus. KAPELLA, Ltd., TAYLOR, M. H., and CLIFFORD, T. W. Dec. 2, 1942, No. 17149. [Class 97 (i)] [Also in Group XXII] In apparatus for determining the position of a point in a reference plane and particularly suitable for setting the tool or work in a copying machine, a grid consisting of two sets of lines spaced in accordance with a system of coordinates is marked or optically projected on the plane and sub-divisions of spaces between the lines of the grid are determined by scales in a measuring microscope. As applied to a grinding or other cutting machine, the cutter D and its driving motor are carried by a fixed support D<1> and the work table C is movable on two mutually perpendicular slides A<1>, C<1> by screws and hand wheels. The reference plane is formed by the lower surface R of the work table and the grid F, consisting of a glass plate with mutually perpendicular lines, is secured to the table as close to this surface as possible. Cross lines are provided on a graticule H secured to the machine frame immediately below the grid F, an image of the grid and graticule being thrown by a lighting system I<1> onto the eye piece G<1> of a microscope G mounted in the machine frame. The operative edge of the cutter D, which may be observed by a microscope E attached to the support D<1>, is arranged vertically above the origin O, Fig. 6, of the graticule lines H<1>, H<2> so that a work piece on the table C may be set relatively to the cutter according to rectangular co-ordinate measurements by moving the table imtil the required lines of the grid F are made coincident with the lines H<1>, H<2> in the eye piece of the microscope G. The lines of the grid may be arranged onetenth of an inch apart and for readings between these lines, two scales J<1>, K<1> are provided in the eye piece of the microscope. The scales may each consist of four lines J<2> ... J<5>, K<2> ... K<5>, parallel to the respective cross lines H<1>, H<2> and are carried by slides L<1>, M<1> movable by thumscrews L<2>, M<2> along guides which are inclined to the lines H<1>, H<2>. Each line is marked with twenty-five divisions, the lines J2, K<2> being numbered 0 to 0.025, lines J<3>, K<3> 0.025 to 0.050, lines J<4>, K<4> 0.050 to 0.075 and lines J<5>, K<5> 0.075 to 0.1, and the inclination of the slides is such that in moving the scales 25 divisions each line thereon will be moved transversely through one-quarter of the space between the grid lines. The lines J<2> ... J<5> and K<2> ... K<5> are spaced apart one-quarter of a grid division and are spaced from the cross lines H<1>, H<2> so that with the zero of the first line J<2> on the cross line H<1> the line J<2> will be spaced from the line H<2> by an exact number of grid divisions and will coincide with a line of the grid, whilst movement of the scale J<1> through a number of scale divisions relatively to the line H<1> will displace the line J<2> through a corresponding number of thousandths of an inch from the originally coincident grid line. Since in the zero position of the scale J<1> the second line J<3> is already spaced from a grid line by twenty-five thousandths of an inch, the number of thousandths between twenty-five and fifty are read on this second line and the numbers between fifty and seventy-five, and between seventy-five and one hundred are read on the lines J<4> and J<5> respectively. Measurements of the second and third decimal places along the other co-ordinate directions are read similarly on the scale Kl. The intersections of the scales J<1>, K<1> are masked at H<3> to avoid confusion and the grid and scale lines may be coloured differently to assist identification. In a modified form of illumination, two lamps N, Fig. 7, are arranged at 45 degrees on opposite sides of the grid F, which may be provided with an upper whitened surface to disperse the light, and are formed as a unit N<2> with the measuring microscope G, and with this illumination the grid may be marked directly on the underside of the table P. In a further modification, an image of the grid is projected by an inclined mirror onto a screen located adjacent the lower surface of the table. The grid may be provided on a part of the machine which partakes of the table movements and the tool may consist of a milling cutter or a stylus &c. for marking the surface of the work.