Patent GB-726625-A (GB)
Title: Navigation instrument
Inventor: CLARET RENE
IPC: G01C21/02
Filed: 1953-07-21
Abstract: 726,625. Automatic alignment control systems. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AERONAUTIQUES. July 21, 1953, No. 20149. Class 38 (4). [Also in Groups XXXVIII, XXXIX and XL (b)] In an instrument for celestial navigation a pair of stars of known angular separation is employed for the positional determination of a body, (Groups XL (b) and XXXVIII). To maintain a pair of telescopes aligned each with one of the stars a photo-electric automatic control system is provided, a further two photo-electric automatic control systems also being provided; one maintaining a reference platform horizontal and the other maintaining a collimator " looking at " a fixed point so as to indicate the heading and inclination of a craft containing the instrument. As shown, Fig. 1, a pair of stars A, B of known angular separation AB is employed for the positional determination of a body where zenith is the point Z. Further data required are the angle BAP between the meridian plane of star A and the great circle of arc AB and the declination SA of star A. The direction of the celestial poles PP<SP>1</SP> is determined by rotating the plane TAB about the line TA through an angle equal to dihedral angle BAP thereby determining the meridian plane of star A, and rotating the line TA in the meridian planes through an angle equal to the complement of the declination #A, thereby defining the direction of the celestial poles PP<SP>1</SP>. The direction 3 of the vertical at the observers' position together with the polar axis gives the meridian plane of the position. The angle between the meridian planes of A and Z, i.e. AH AZ  (the Local Hour Angle of A) is used to determine the longitude by means of the known relation between it and longitude L, Greenwich sidereal time (Tso) and right ascension AR A  ; L=Tso-ARA-AHAZ. Latitude is the complement of the angle formed between the vertical TZ and the polar axis. General arrangement (Fig. 2).-A pair of telescopes 24, 37 are initially set and maintained pointing at stars A, B respectively by a photo-electric automatic control system to be described later. Telescope 24 is carried on an axle 6 which may be rotated by a servo motor 81 the stator of which is fixed to a forked member 9 carrying axle 6. This forked member may in turn be started by a servo motor 82. These two motors together maintain telescope 24 directed at star A. On the same shaft as fork 9 is a fork 16 always parallel to fork 9 and carrying a further fork 28. This fork is linked to telescope 24 by a bar 25 and its axis 1<SP>1</SP> is thus always maintained parallel to the axis 1 of primary telescope 24. Fork 28 carries a further fork 32 on an axle 36 of which is mounted the secondary telescope 37 (Fig. 3). Telescope 37 may be pivoted about its axle 36 so that its axis 2 makes the angle AB with axis 1<SP>1</SP>. Rotation of shaft 31 by servo motor 83 the stator of which is fast with fork 28 causes axis 2 to describe a cone about axis 1<SP>1</SP> until the telescope is aligned on star B. The semi-angle of this cone, which is the angular separation of stars A and B is set by rotating telescope 37 on its axle 36 in which position it is locked by a nut which clamps against fork 32. Angle AB is indicated by a scale and pointer 40. On the other end of shaft 31 is a fork 41 the position of which is so adjustable by means of a clamp that the plane of fork 41 can be set making an angle with fork 32 equal to the dihedral angle BAP (see Fig. 1). This angle is initially set and indicated on scale 44. When the two telescopes are aligned with their stars the polar axis of the celestial sphere is contained in the line perpendicular to the plane of fork 41. Pivoted to fork 41 is a further fork 58 (Fig. 5) which is arranged by clamp 53 to make with fork 41 an angle equal to the complement of the declination this angle being indicated on scale 54. Fork 58 carries the stator of servo-motor 84 and angular position transmitter 184 the shaft 62 of which carries a vertical finder 60 (see Fig. 5 and below) which by means of servo-motors 84 and 85 maintains itself horizontal thus defining the line TZ (Fig. 1). When the axis settings referred to are made and the telescopes are aligned with their stars, remote position transmitter 184 controls a receiver which indicates the Local Hour Angle of the primary star while angular position transmitter 185 carried on the shaft of servo 85 measures the angle between the polar axis and the vertical thus indicating the complement of the latitude. To indicate the heading and inclination of the aircraft a collimating device 73 is maintained by a photo-electric system driving servomotors 86, 87 described below directed at a fixed point in the vehicle. Angular position transmitters 186, 187 indicate transmitter heading and inclination readings at a distance. Modifications, (Fig. 16).-In a modified arrangement (Fig. 16), the two telescopes 321, 322 are each arranged to receive an image of stars A and B respectively through the same lens 301. The two telescopes are mounted in a housing 307 which with the attached cylindrical member 308 may be rotated and pivoted so as to direct telescope 321 at star A. Telescope 322 is initially set at angle AB to telescope 321 by means of toothed quadrant 345 and scale 352 and maintains itself on star B through a photo-electrically controlled servo system which controls the rotation of the housing about its axis. Telescope 321 is so geared as to remain still while the housing rotates around it. Shaft 353 corresponds to shaft 31 of Fig. 3 and the operation is thereafter the same as in the previous embodiment. In the arrangement of Fig. 23, telescope 521 is maintained " looking at " an image of star A formed on plate P by spherical mirror 544. A pair of servomotors 581, 582 moves the telescope in two directions while a further motor 583 moves telescope 522 in a cone with shaft 551 of telescope 521 as axis, the rotation of telescope 522 is transmitted to sprocket 566 by a perforated tape 569. Shaft 562 corresponds to shaft 31 of Fig. 3, and the arrangement is otherwise the same. Indicating arrangements (Fig. 13, not shown). A single unit comprises 4 self synchronous receivers, one indicating latitude fed from transmitter 185, one indicating heading (transmitter 186) one inclination of the vehicle (transmitter 187) and one combining its readings of Local Hour Angle in a differential gear with the movement of a chromometer giving Greenwich sidereal time to indicate longitude and a scale which is adjustable to take account of the right ascension of star A. Telescope details and photo-electric control of telescope alignment (Fig. 8).-The telescope used in the first of the embodiments above described (Fig. 8), comprises a casing 101 an objective 102 and a catadioptric magnifier 103 supported by arms 104. The magnifier comprises a divergent lens with a reflecting coating on its convex face presented to mirror 102. An enclosed mirror 107 receives light reflected by the magnifier and directs it to the apex of a pyramid 122 each face of which has associated with it a photo-electric cell (only two are shown). When telescope and star are aligned the cells are all equally illuminated. Divergence of the image illuminates one or one pair of cells more than the others controlling servomotors 81, 82 (Fig. 2). The circuit diagram for this arrangement is shown in Fig. 10. Photocells 118-121 are associated with the primary telescope and cdntrol servo motors 81, 82 while two cells 124, 125 only are necessary for the secondary telescope which has only one degree of freedom and is controlled by motor 83. The output signals of cells 118, 120 on opposite faces of the pyramid are fed to the input of a balanced D-C amplifier 131 while cells 119, 121 feed amplifier 132. The D-C amplifiers are connected to balanced magnetic amplifiers 134, 135, 136, the outputs of which are loaded with the primaries of transformers 137, 138, 139, each feeding one winding of one of twophase servomotors 81, 82, 83. The magnetic amplifiers are of known type, each consisting of two balanced stages 167, 168, each stage comprising two transductors 153, 154 and 155, 156. Each transductor comprises an A.C. winding 259, a self-existing winding 251 traversed by D.C. current derived from a bridge-type rectifier and a pair of oppositelyacting control windings 158, 163, each carrying the anode current of one of valves 151, 152. The D.C. current in the cores acts additionally with the control current in the case of cores 153, 154 and subtractively in the cores of transductors 155, 156, thus controlling the resultant alternating current in the two halves of transformer primary 137 to drive servomotor 81 and re-align the telescope with the star. In the modified telescope adopted in the embodiments described with reference to Figs. 16 and 23, the device for maintaining the telescope aligned with the star is shown in Figs. 18 and 19. A hollow shafted continuously rotating motor 388 carries a cup 391 closed by a half blackened lens 392 focusing light from the star on to a photo-electric cell 400. Leads from the cell pass through the hollow shaft. The motor also drives a magnet 403 which produces a reference alternating voltage in coil 404. The output of the cell is brought to terminals 402; of coil 408 to terminals 406. The circuit arrangement for controlling the motors positioning the primary telescope is shown in Fig. 20. The reference AC is amplified and used to energize winding 408 of two phase motor 381 directly and winding 410 of motor 382 after passing through a phase-shifting network 414 giving a 90-degree phase change. If the image of the star lies on the axis of pole 407 but not at the centre of the cell, since axis 407 is maintained parallel with the axle supporting the casing 306 (Fig. 16), there will be an error in elevation which will be corrected by motor 382. If the image is not