GB588608A - Improvement in electro-optical function synthesizers - Google Patents

Abstract

588,608. Photo electric calculating- apparatus. DOLL, H. G, May 16, 1944, No. 9375. Convention date, Oct. 19, 1943. [Class 40 (iii)] [Also in Group XIX] Apparatus for solving a function such as the sum, difference, product, or quotient of two variables comprises an optical screen having light-transmitting properties over its area which vary from point-to-point in accordance with the value of the function for the particular coordinates at each point, the screen being used to modify a light beam. which controls photoelectric apparatus. In Fig. 1, 15 is the optical screen having axes of reference x, y with respect to which the function is plotted. A tight beam 12 passes from a source 13 through lens 14 on to the mirror 10 of a galvanometer G1 mounted to swing about an axis parallel to the y-axis, thence on to the mirror 11 of a galvanometer G2 mounted to swing about an axis parallel to the x-axis, and then through screen 15 and lens 16 on to photo-cell 17. The ampli.- fied output of the cell is fed to indicator D to afford the required input. Chopper 6 modulates the beam at carrier frequency to enable A.C. couplings to be used in the transmission circuit to D which is fed from rectifier 32, 33. Currents proportional to the abscissµ are fed to G1 and currents proportional to the ordinates are fed to G2. The mirrors 10, 11 may be mounted on mechanically movable elements if desired. Fig. 3 shows a screen used for solving. the function Z =y/x. This comprises a number x of sector-shaped regions which are shaded by cross-patching to reduce the light transmission as required, the mesh of the cross-hatching being fine in relation to the cross-section of the beam. If accurate evaluation is required, the shading of the screen must vary continuously. Fig. 6 (not shown) and Fig. 7, show arrangements for giving solutions for positive and negative values of all the variables in which the outputs of two cells are combined differentially. In Fig. 7, cells 17, 17<1>, which receive the beam for positive and negative values of the function respectively, are disposed in a bridge circuit of which the output is applied to amplifier 50 arranged in a further bridge circuit feeding indicator D. Baffle 39 prevents stray light falling on either photo-cell. Instead of using two galvanometers to deflect the beam, a cathode-ray tube may be used and the beam derived from the spot on the screen, the spot being moved in accordance with deflecting potentials or currents proportional to the variables to be evaluated applied to the deflecting elements bf the tube. Carrier modulation may be effected by control of the cathode-ray beam. In Fig. 9 the screen 15 is uniformly illuminated and is imaged on the target 89 of an iconoscope 84 so that a signal representative of the desired solution appears across the output resistor 99. To obtain readings for positive and negative values of the fuction, the part of the screen portraying positive values may be illuminated with light interrupted at one frequency and the negative part of the screen may be illuminated by light interrupted at another frequency, the two carrier outputs being separated and combined differentially to operate the indicator. Instead of an iconoscope, a television transmission tube of. the dissector type may be employed.. Where three variables are to be combined, a solution involving only two variables is first derived and the result combined with the third variable. Alternanatively, where a cathode-ray tube is employed, the cathode-ray beam may be modulated in accordance with the value of the third variable.