Patent GB-486679-A (GB)
Title: Improvements in or relating to navigating instruments
IPC: G01C21/02
Filed: 1937-01-29
Abstract: 486,679. Electric control systems. GROVES, W. W. (Clark, J. C.) Jan. 29, 1937, No. 2660. [Class 40 (i)] [Also in Groups XX, XIX, and XL] A navigating instrument comprises a finder which is automatically maintained directed towards a celestial body, e.g. the sun, by means actuated by radiation from the body. The instrument may include a resolving unit whereby there may be continuously shown on a panel not only the latitude and longitude of the supporting craft but also the distance and great circle course to an objective of known latitude and longitude. The finder unit, Figs. 1 and 2, comprises a tube 65 automatically rotated about an axis 314 in a ring 395 in accordance with the declination of the observed object, e.g. the sun, by a motor 320. The ring 395 pivots about an axis 211 in a ring 118 which pivots about a horizontal axis 117 in arms 116 upstanding from a frame 95. The latter is mounted for rotation about a vertical axis in a ring 87 and is driven by a motor 94 to maintain the axis 117 lying east and west. The ring 87 carries by means of a frame 90 the motor 94, a magnetic compass 135 controlling the motor 94, and a motor 104 which compensates for magnetic deviation. A ring 85 supporting the ring 87 on pivots 86 is pivoted on a perpendicular horizontal axis in standards 84 rising from the base 82 of the casing 83. A glass dome 89 closing the casing 83 at the top compensates by its refraction for the refraction due to the earth's atmosphere. The tube 65 carries at the top an infra red transmitting filter 66, an internally reflecting diaphragm 68 with a square aperture 67, and a partially parabolic reflector 71 with an open end 72, and centrally at the bottom a square reflector 75. When the tube 65 is pointing directly at the sun, light therefrom passes to the reflector 75 which reflects it straight out again. Mis-alignment of the tube causes the light to fall on one or more of four light sensitive cells 76, 81, surrounding the reflector 75. One pair of opposite cells controls a motor 123 driving the ring 395 about the axis 211 and the other pair controls a motor 121 carried by the ring 118 and driving the latter about the east-west axis 117 by means of a cord 127, so that the tube 65 is automatically directed on the sun. The arrangement is such that the angular position of the motor 121 corresponds to the latitude of the instrument and that of the motor 123 to the longitude plus a displacement depending on the time of operation and corresponding to the diurnal motion of the sun, i.e. 360‹ in 24 hours. A motor (not shown), similar to the motor 320 may be provided to compensate for the equation of time. In a modification the magnetic compass 135 is replaced by a sun compass comprising a light sensitive device driven by clockwork so as to follow the sun when the device is properly orientated. A pair of photo-electric cells when out of alignment with the sun varies the grid potential of a thermionic valve, in the anode circuit of which is a relay controlling the operation of the motor 94, which drives the finder and the sun compass in azimuth. The photo-electric cells 76, 81, may form the sun compass in which case they are connected to the motor 94 and the motor 123 in alternation. The resolving unit, Figs. 6 and 7, comprises a fixed bracket 19 supporting the bracket 34 for rotation about the normally horizontal axis 32 by the motor 33. The bracket 34 carries a spindle 3 on which is rotatably mounted a motor 36 rigidly carrying a yoke 37. The yoke 37 pivotally supports at 29 a motor 38 having pivotal bearings 39 for a secondary yoke 42. The latter is pivotally connected at 44 to a bracket 43 which is driven about a horizontal axis by the motor 45 fixed to a bracket 46, rotated in turn about a vertical axis by the motor 47. The motor 33 moves in step with the latitude motor 121 of the finder unit and the axis of the motor 36 and yoke 37 represents the earth's radius to the terrestrial position of the instrument. The motor 45 is adjusted in accordance with the latitude of a predetermined destination and the motor 47 in accordance with the difference of longitude between the destination and the present position. The motor 47 is in circuit with the motor 123 and also with an electric clock so that when the supporting craft is stationary each impulse from the motor 123 is cancelled by an opposite impulse from the clock. When the craft moves over the earth the resultant movement of the motor 47 represents the longitude movement. The axis 44 of the yoke 42 then represents the earth's radius to the destination. A cable 63 resiliently attached to the yoke 42 passes over a pulley 56 on an arm 55 projecting from the yoke 42 at right-angles to its axis, pulleys 57 on the yoke 37, round a pulley carried by an insulating disc 50 on the spindle of the motor 38 and back to an anchorage on the yoke 37. The tension of the cable 63 causes the yoke 37 to move into the plane containing the axes of the yokes 37 and 42 and representing the great circle course between the present position. and destination. Consequential adjustments of the motors 36 and 38 represent respectively the compass course giving the great circle to the destination and the distance from the present position to the destination. To cause the motor 36 to drive through the required angle it is controlled by a contact 8 resiliently attached by spring 9 to the bracket 34 and working between contacts 6 on an insulating disc 5 secured to the spindle of the motor. Similarly the motor 38 is controlled by a contact lever 53 resiliently attached by spring 54 to the yoke 42 and working between a pair of contacts on the insulating disc 50. The indicator unit. A distance indicator 146, Fig. 9, comprising a dial 147 graduated in degrees and a dial 148 graduated in fractions of a degree is driven by a motor 10, Fig. 4, synchronized with the motor 38 of the resolving unit. The motor 10 comprises a pair of electromagnets 12 adapted to rock a lever 15 in one or other direction. The lever 15 carries a pair of pawls 24 adapted to engage and drive a gear wheel 22 one tooth in one or other direction each time an electromagnet is energized. A pinion 26 freely pivoted eccentrically on the gear wheel 22 engages simultaneously an internally toothed gear 27 fixed to the casing of the motor and a rotatable gear 28 having one more tooth than the gear 27 so that the gear 28 is moved on one tooth for each complete revolution of the gear 22. The degrees scale 147 rotates with the gear 28 and the minutes scale 148 with the gear 22. The energizing current to the electromagnets is intermittently interrupted by an electric clock which also has a dial 161 on the panel 140. A course indicator 141 comprises dials 142 and 143 and a pointer 144. A motor 172, Fig. 10, is fixed to a casing 171 and drives the casing of a motor 174 driving in turn the casing of a motor 176. The dial 143 is carried by a hollow spindle 177 fixed to the casing of motor 174 and driven by the motor 172 which synchronizes with the motor 104. The dial 142 is carried by the casing of motor 176 and is driven by both motors 172 and 174 which synchronize with the motor 36 of the resolving unit. Pointer 144 is driven by the three motors 172, 174 and 176 which synchronize with the motor 94. Thus the pointer 144 indicates deviations from the great circle course to the destination, the dial 142 indicates the compass course to the destination and the dial 143 indicates the deviation of the compass. A longitude indicator comprises dials 151, 152, indicating degrees and minutes of longitude of the destination and driven by a motor whose movements are communicated to the motor 47, and also dials 153, 154, indicating minutes and degrees of longitude of position and driven by a motor driven in accordance with the difference between the movements of the motor 123 and the clock 161. A latitude indicator 155 comprises dials 156, 157, indicating the latitude of the destination and driven by a motor synchronizing with the motor 45 and dials 158, 160, indicating the latitude of position and driven by a motor synchronizing with the motors 121 and 33. The latitude and longitude of position may be recorded on a time driven chart by pens which are adjusted by motors synchronizing respectively with the motors 33 and 47. A photo-electric cell 88, Fig. 1, in the centre of the mirror 75 of the finder is adapted, when the sun disappears, e.g. below the horizon, to disconnect the motor 123 from the photoelectric cells 76, 81, and couple it with the clock circuit. Simultaneously the. motor 47 is disconnected from the clock circuit. Thus when the cell 88 is de-energized, the finder rotates about the axis 211 at a speed equal to the speed of the earth's rotation and the resolving unit and indicating unit remain at the setting corresponding to the position of the craft when the sun ceased to shine. When the sun shines again the original circuits are automatically restored, the finder picks up the sun again, and the resolving and indicating units are moved on to the setting corresponding to the new position of the craft. If desired the motors 121 and 123 may be disconnected from the resolving and indicating units and the finder tube 65 adjusted from a position pointing at the sun to a position pointing at a fixed star. When the circuits are restored the finder 65 will follow the fixed star.