Patent GB-803411-A (GB)
Title: Polar co-ordinate navigation systems
IPC: G06G7/78
Filed: 1955-02-07
Abstract: 803,411. Navigational instruments. MINISTER OF NATIONAL DEFENCE OF HER MAJESTY'S CANADIAN GOVERNMENT. Feb. 7, 1955 [Nov. 10, 1954], No. 3623/55. Class 97(2) Apparatus for solving navigational problems in polar co-ordinates comprises, as shown schematically in Fig. 2, a resolver 20 into which are continuously set a distance factor ("ground miles") analogous to a cumulative distance travelled and as a second input a directional factor which represents the angle between the direction being travelled and the direction to a datum point, the resolving means being arranged to deliver a first output analogous to the change of range to the datum point which is indicated cumulatively on a counter 23 and fed to a divider 21 as a divisor, and a second output analogous to the change of distance travelled normally to the direction of the datum point which is fed to the divider as dividend. The output of the divider is analogous to the change of direction of the datum point and is subtracted in the device 22, from a factor ("track") representing direction being travelled, the difference being fed as the directional factor to the resolver 20. While the cumulative output of the divider is indicated as by the double pointer, shown on a dial 24. The "track" may be separately indicated by the single pointer so that, in the case of an aircraft, the pilot can fly to the datum point by heading the aircraft to align the pointers and flying until the counter 23 indicates zero. The Specification describes the mathematical basis of the operation of the device. In the embodiment shown in Fig. 5 the ground miles are received as a selsyn input at 210 and applied to a shaft 211 which through a servo system including a motor 213, drives a shaft 39. The resolver system comprises two ball and disc integrators 31, 32 having their discs on the shaft 39 with  their ball carriages operated from the shaft 45 through cranks 33 and 34 which produce sine and cosine functions. The range output from the integrator 31 is fed to a servo system, with motor 109, the output of which drives a counter 72 and a stop transmitter 227 connected to a motor 230 which produces a further indication on a repeater panel 225 for the pilot. The range shaft also drives a leadscrew, not shown, which sets the ball carriag of the further ball and disc integrator 35 which functions as the divider. A further servo system is provided comprising a motor which drives the disc and thence the roller to keep it in synchronism with the output from the roller of the integrator 32. The bearing output is subtracted, in a differential 37, from the track input on the shaft 68, the difference being fed to the shaft 45 as the directional input to the resolver system. The track input is received as a selsyn signal which is applied electrically to an amplifier 223 which drives an induction motor 224. Track and bearing are repeated by selsyn transmitters 226 and 228, with receivers 229, 231 on the dial assembly of the repeater panel. The control system for the range servomotor, which is typical also of those for the bearing and ground miles motors, is represented diagrammatically in Fig. 5 as a differential 201 and contact system 202 and is shown in detail in Fig. 4A. The output on the roller 40 of the integrator 31 is fed to a leadscrew on which is a pinion 102 in driving engagement with an elongated pinion 104 driven by the servomotor 109. An input on the leadscrew displaces a member 307 which actuates a contact system to cause the motor to run. The member 307 displaces one or other of the contacts 107a, 107b from engagement with a central contact connected to a positive supply line and moves it into engagement with a contact 108a or 108b respectively. This completes the circuit of the motor 109 to cause it to run in the sense needed to re-centre the member 307. A device to prevent hunting comprises a resistance 301 and a switch 300 which is operated by a cam 306 on the shaft 45 in accordance with the sign of the sine function applied to the integrator i.e. according to whether range is increasing or decreasing, the resistance being brought into the motor circuit if the motor overshoots and reverses direction. A certain amount of input from the integrator is stored on the leadscrew while the motor is following up but if this causes a very large displacement of the contact 108a or 108b it engages an outer contact 308 or 309 which energizes a relay to open the circuit of the ground miles motor 213, the input to the ground miles servo being meanwhile stored on its leadscrew. The leadscrew by which the motor 109 sets the ball carriage of the integrator 35 is provided with upper and lower limit switches shown in Fig. 4A as 313 and 317 to stop the operation of the motor 109 when the limit is reached. The upper limit switch also lights a warning lamp 316 and energizes the solenoid 314 to open the circuit of the ground miles motor 213. In order to be able to reset the range manually in accordance with information from an alternative source a switch 312 is provided having contacts 312B, 312C by which the motor 109 may be directly energized to run in the required direction while a clutch 204 is opened by a solenoid 322S energized through contacts 312A. The instrument also contains parts for use in accordance with what is called "alternative base operation" whereby information as to range and bearing is furnished with reference to a new datum point. This is achieved by setting into the instrument at high speed, a range corresponding to the distance between the old and new datum points. The required bearing and range are preset by hand on a synchro in the instrument and on a dial 220. On operating a lever, not shown, the track servo is switched to operate from the hand-set synchro and the ground miles motor is declutched from the remainder of its servo system and runs until the preset distance has been set into the computer, when the dial 220 will have been run back to zero to operate a contact to stop the motor. The distance appears however on the counter 219 and remains as a setting by which, in conjunction with the bearing setting, the instrument may be restored to work with the original datum. The instrument also contains an arrangement for feeding false data into the computer at low ranges where high rates of change of bearing would be required. Less stringent performance requirements are thereby obtained with some loss of accuracy. The ground miles and track information is obtained from an instrument, as described in Specification 803,412, to which are fed true air speed, heading and wind data. By feeding in, insteady of wind data, data received by radio, of the course and speed of another aircraft, the instrument above described can be caused to operate with the other aircraft as a datum and the pilot is thus enabled to fly so as to intercept the other aircraft.