Patent GB-720087-A (GB)
Title: Improvements in and relating to apparatus for use as an aid to navigation
IPC: G01C21/02
Filed: 1950-12-05
Abstract: 720,087. Latitude and longitude instruments. JOHNSON, V. A. L. BRADYLL-. Dec. 5, 1951 [Dec. 5, 1950], No. 29809/50. Class 97 (2). [Also in Group XXXVII] Apparatus for determining the latitude and longitude of a position quickly comprises means for simultaneously observing stars and representations of the stars on a star map arranged for translational movement of the area of the map observable by a sidereal clock, e.g. in the form of a celestial globe rotatable about its polar axis by a sidereal clock, means for adjusting the star map in relation to a standardized position of the representations, for example the position corresponding to the star positions over the Greenwich meridian for longitude and the direction of the horizontal for latitude, so as to bring at an observational location the representations into coincidence with the images of the stars and means for indicating the movements of the map from the standardized position in two perpendicularly related directions or about two perpendicularly related axes, the measures of which movements being the latitude and longitude at the observational location with respect to Greenwich.- The globe 4, Fig. 1, internally illuminated by light from an electric lamp 26 " piped " to a sphere 25 and having transparent representations of the stars, is mounted on a stump spindle 10 ending in a plate 27 cylindrically curved about its short axis, and is adjustable, by a worm 30, Fig. 3, engaging a toothed rack on a long side, in grooves in a sector 29, Fig. 1, ending in a plate 31 with its axis of curvature at right angles to that of plate 27. The plate 31 is adjustable in a grooved sector 32 by a rack and worm mechanism operated by a wheel 13. Sector 32 forms the top of a tubular spindle 34. By means of these adjustable plates 27, 31 a change may be made of the axis about which the globe 4 rotates to allow for the earth's nutation and precession. The spindle 34 is mounted on a bracket 6 rigidly connected by an extension 6a to an annular ring 5 coaxial with the globe 4 and rotatable in a carrier ring 24 attached to frame 63 rotatable on a ring 65 which is gimbal mounted in a frame 68 secured to the vehicle. The frame 63 is power stabilized in the vertical datum as by a power-driven gyroscope so that the plane through it which represents on the globe 4 the observer's meridian is maintained in the true N.-S. direction. The ring 5 is rotated about its axis in either direction from an electric motor 41 through worm gearing 37 engaging external teeth on the ring 5, and tilts the bracket 6 and hence the globe 4 about its centre in the N.-S. plane. The globe 4 is rotated about the axis of the spindle 34 from a differential mechanism whose planetary eye 50 is secured to shaft 45 which carries at its end worm 44 which engages with toothed wheel 43 on the spindle 34. The movement of the eye 50 is the combination of the rotation of the sidereal clock 7 through gears 75, shaft 54, worm mechanism 49 engaging external teeth of ring 22 and sun-wheel 47 engaging internal teeth of ring 22 and of the rotation of electric motor 57 through worm mechanism 53, engaging external teeth of ring 23 and sun-wheel 51 engaging external teeth on boss 52 of ring 23. This output from the differential gives local sidereal time in angle and is applied between the meridian through the point on the globe which at that instant represents the first point in Aries on the globe 4 and the observer's meridian of the instrument. The various elements of the differential are so proportioned as to eliminate movement in rotation of the globe which would be caused by tilting of the globe for latitude by motor 41. Rotation of the ring 5 and hence a measure of the latitude is indicated by a scale 11 and micrometer 12 associated with the ring. Rotation of the globe about the spindle 34 and hence a measure of the longitude is indicated by a micrometer 9 and scale 8 associated with ring 23. A reflecting or refracting telescope 2 is rigidly mounted on a spherical dome 70 concentric with the globe 4 and carried on a plurality of close-fitting spherical bearings 71 carried by the support 68 so that it can be moved by hand to a desired angle. A system of lenses 20 combined with the telescope to provide an effective working area of about 40 degrees radius on the globe corresponding with a similar working area of the sky due to the telescope field. Cross-wires 3 on the carrier ring 24 indicates the zenith. The dome 70 has windows through which the scales 8 and 11 can be read. Alternatively, the telescope may be rotatably mounted on a half-ring concentric with the globe and gimbal mounted on the craft. In another alternative construction the telescope may be rigidly mounted on the frame 63 and the whole assembly being gimbal mounted and power stabilized with the telescope directed towards the zenith. The ring 5 may be mounted on the other side of the globe together with its micrometer 12 and scale 11. The intensity of illumination of the representations of the stars on the globe 4 may be controlled by an adjustable rheostat in the circuit of the lamp 26. The latitude and longitude motors 41, 57 are controlled electrically from a controller (see Group XXXVII) mounted rotatably so that it may be approximately aligned in the observer's meridian or is power stabilized in the vertical datum so that the plane through it which represents the observer's meridian is maintained in the plane of his meridian. When the control handle is moved in a plane representing a plane parallel to the observer's parallel of latitude the longitude motor 57 is controlled in magnitude and direction of movement and when the control handle is moved in a plane representing the observer's meridian, the latitude motor 41 is similarly controlled and if the handle is moved in any other direction both motors will be controlled according to the components of the movement in these two planes. The control handle may be so placed that the motors will rotate in a direction and at such speed corresponding to the rate of change of latitude and longitude as to keep the image of the star map on globe 4 in coincidence with the image of the stars in the telescope. As soon as coincidence is obtained operation of a pushbutton on the control handle stops the motors and applies dynamic braking power.