Patent GB-704644-A (GB)
Title: Astrocompass and adapter for periscopic sextant
IPC: G01C17/34
Filed: 1951-12-05
Abstract: 704,644. Solar and stellar compasses. KOLLS- . MAN INSTRUMENT CORPORATION. Dec. 5, 1951 [April 20, 1951], No. 28539/51. Class 97(2) An astro-compass for use on a movable craft for observing a celestial body in its movement across the heavens for obtaining direction, heading or the relative bearing of another craft comprises an azimuth scale A, Fig. 2, mounted on the craft for adjustment about the scale axis, a periscope, e.g. a periscopic sextant 12, mounted with freedom to turn in azimuth relative to said scale A indicating means to show the angular position of the periscope relatively to the scale, an output device rotated in accordance with solar or sidereal time by a motor and variable transmission between the scale A and the output device adjustable in accordance with latitude of the craft and with the declination of the celestial body B to be observed. As shown in Fig. 2 the periscopic sextant employed has an adjustable index prism 16 and a vertical reference such as a liquid bubble level 36 so associated with an optical system as to be optically combined in a single field of vision in the eyepiece 13 with the images of the celestial body B observed and the azimuth scale A. The sextant is preferably mounted with freedom to move in azimuth on a base universally mounted, as by gimbal rings, on the craft for tilting about horizontal axes. The time responsive device and variable transmission may be constructed as a unit C attachable to a periscopic sextant to convert this latter into a periscopic astro-compass. As shown in Fig. 4 which is an explanatory simplified construction of the transmission between scale A and the output device of the motor, the azimuth scale 57 which is concentric with the axis of the periscope and tiltable therewith, is rotated through an idler gear 60 from a gear 61 coupled to the variable transmission. This latter comprises a bail 97 mounted for movement about a vertical axis and secured to the gear 61. A support 62 is mounted by lugs 64 depending from a fixed support plate 51 for tilt about a horizontal axis 63 and carries a perpendicularly mounted shaft 72 driven by a clockwork mechanism contained within the support 62. A driving arm 74 is mounted on and tiltable relatively to the shaft 72 and engages the bail 97 to move it about its axis. The support 62 is tilted by means of a gear sector 66 meshing with a worm gear 67 operated by means of a knob 70 in accordance with latitude which is registered on an indicator 71. The driving arm 74 is tilted relatively to the shaft 72, shown diagrammatically as by a geared sector 76 and worm 77 operated by a knob 80 through gear wheels 78, 79, in accordance with the declination of the celestial body the declination being indicated on an indicator 81. The clockwork mechanism is set by a knob in accordance with the longitude which is indicated on an indicator 141 and in accordance with local hour angle. The actual construction of the mechanism involving items 77, 76, 74 is shown in Figs. 6 and 7 and comprises a supporting gear 82, Fig. 6, driven by the clockwork mechanism through pinion 83 and provided with a central hole 84 through which extends a circular rack 85 engaged at its lower end by a pinion 86 operated by adjusting the declination knob 80, Fig. 4. The upper portion of rack 85 engages a pinion 88 mounted in a pair of brackets 90 on the gear 82. The pinion 88 also meshes with gears 91, 92 supported in brackets 90. The gears 91, 92 are connected to hub-portions 95, Fig. 7, of the forked end of the driving arm 74. A friction-clutch between the clockwork mechanism and the shaft 72, Fig. 4, enables this 'shaft to be set for the local hour angle or the Greenwich hour angle which is indicated on indicator 124, Fig. 4. Suitable gear change ratio mechanism for translating solar time into sidereal time is also provided between the driving mechanism and the friction clutch.