Patent GB-985975-A (GB)
Title: Improvements relating to analogue computors
IPC: G01C21/22
Filed: 1961-02-08
Abstract: 985, 975. Analogue computers. MINISTER OF NATIONAL DEFENCE OF H.M. CANADIAN GOVERNMENT. Feb. 8, 1961 [Feb. 15, 1960], No. 4703/61. Heading G4G. A computer providing analogue outputs to control the position of a projector in terms of E.W. and N.S. miles to project a display of aircraft position on to either a Mercator or a grid chart comprises analogue storage devices for information of aircraft ground position in terms of latitude, longitude, and cartesian grid co-ordinates (including Mercator) and switches to select transmission of Mercator or grid chart information as required, the reception and storage of the information not selected being meanwhile continued. Computer system. The four storage units 12, 13, 14, 15 described in more detail below for the E.W. and N.S. Mercator and grid sections respectively, are each provided with a pair of input signals corresponding to:- (unit 12) change in longitude and R sin # (derived from a resolver 80 where R is range from aircraft to target, # is bearing); (unit 13) secant of change in latitude and R cos #; (unit 14), change in X miles and R sin #; (unit 15) change in Y miles and R cos #, so that the outputs on lines 36, 37, 38, 39 represent the aircraft position in terms of latitude and longitude and grid coordinates at right angles respectively. Selection is made by switches 30, 31 the input to those storage units from which an output is not required being however continued. A secant generator 11 (see below) is included, since for the Mercator projection there is a secant relationship between the latitude and longitude co-ordinates. Switches 90, 91 control switches 93, 94 and 98, 99 respectively which apply input to motors 24 of the storage units to slew the projector (not shown) to the desired position to bring the aircraft to the centre of the chart being used. To locate an object switches 96, 101 are operated to store its position as a "datum" point in a datum storage unit 16, and the displacement of this position from the centre of the chart to be used is set into resolver 80 and switches 142, 143, 96 and 110 operated to move potentiometer wipers 123, 136 of unit 16 to compensate for this displacement. The compensated datum point can then be displayed at the centre of the chart by selecting the input to motors 24. To display a detected object, the range and bearing of said object are fed to resolver 80 and through switches 142, 143 to potentiometers 45, 55 of, for example, the storage units 12, 13 thereby adding R sin #, R cos # to the longitude and latitude outputs on 36, 37 thus causing the aircraft position as projected on the chart to be displaced by an amount corresponding to the range and bearing of the object, thus enabling the navigator to plot the position of this object. Switches 142, 143 are then released and the projector is returned to normal latitude and longitude outputs. Storage units 12, 13, 14, 15. All are similar and only 12 will be described. This comprises as a storage element a coil spring 22 tensioned to store and uncoiled to read out the stored information. A step-by-step motor 20 converts the electrical input into a mechanical input for spring 22, a differential 23 being supplied with the output of spring 22 and from motor 24, and drives the potentiometer wiper 33 which determines the output. Datum storage unit 16 consists essentially of a closed servo-loop comprising, for example, an amplifier 95 and a motor 122 which drives the wiper of potentiometer 125 to balance the voltage from 36 applied to potentiometer 125 the wiper 123 thus "storing" the input until switches 96,120 are released. Secant generator 11. An analogue of the cosine of the change in latitude derived from a latitude resolver 10, is applied to potentiometer 66 the wiper of which is driven by a motor 70 until the wiper voltage is balanced against that from a ratio potentiometer 69 so that the motor position is the analogue of the cosine reciprocal i.e. the secant of the change in latitude. The motor 70 operates a variable transformer to transmit this secant function as an electric analogue input over line 75 to the resolver 80 which may be of the type described in Specification 985, 977.