Patent GB-474718-A (GB)
Title: Improvements in and connected with the ascertaining and the indicating of the speed and position of vehicles (including aircraft, submarines, ships); and with the automatic correction of the latitude-speed-course error of gyro-compasses
IPC: G01P15/14
Filed: 1937-01-22
Abstract: 474,718. Speed, distance, and position indicators; counting-apparatus. HOLT, C. F. Jan. 22, 1937, No. 1888. [Classes 106 (i) and 106 (iii)] [Also in Group XX] Ground speed, distance, and position of an aircraft or other vehicle are indicated and recorded by devices actuated by accelerometers associated with integrating mechanism, an automatic correction being applied to the gyro - compass orientation to eliminate error due to change of latitude. A vertical spindle supported on gimbals and orientated by a gyro-compass supports (a) an upper platform 3 carrying the east-west accelerometer and its integrating mechanisms together with the speed and distance meters, and (b) a lower platform carrying below it the north-south accelerometer and its integrating mechanisms. The compass correction device and the clock for driving the time elements are mounted between the platforms. The accelerometer comprises a weight 8 mounted on rollers 7 to run on east-west grooved rails 5 on the platform 3 and constrained by tensioned springs 9. Adjustably connected to the weight 8 is a roller frame 12 guiding a radius bar 14 having its other end pivoted on the platform and carrying a sharp-edged wheel 19. This wheel engages frictionally a time-driven cylinder 20 which is mounted so that it may be moved axially by the varying inclination of the wheel 19 and radius bar 14, the axial position of the cylinder 20, as given by a pointer 36 on a scale 32, representing the ground speed at that instant. The axial displacements of the cylinder 20 are transferred either to a second sharp-edged wheel cooperating with a time-driven cylinder or preferably to an integrating planimeter wheel 40 engaging frictionally a time-driven disc 44 at variable distances from its axis depending on the actual speed, the distance travelled east-west being finally shown on a meter 47 driven by the gears 33, 46a. Similar devices associated with the lower platform give northsouth speed and distance indication on meters 48, 49 respectively. In order to eliminate error introduced by change of latitude and to orientate the platform to the true geographical meridian, an arm attached to the gyro-compass spindle is slotted to engage a pin adapted to rotate the platforms and the whole instrument relatively to the gyro-compass card, the rotation thus applied being compounded of motions fed from the integrating mechanism. A motion proportional to the component of ground speed eastwards or westwards and a motion proportional to the component northwards or southwards of the absolute distance travelled, are compounded by the motions of slides &c., and the slide partaking of this last motion is provided with a slot in the form of a cosine curve which constrains the pin referred to above so that its displacement is proportional to the algebraic sum of the component of ground speed east or west and the peripheral speed of the earth at the latitude of the vehicle. The platforms are maintained horizontal against the tilting effect of moving masses forming part of the instrument by precessional forces developed by twin gyroscopes. A distance meter, Fig. 16, of known counter type wherein a series of discs 108 display numerals at casing apertures 96, is provided with devices for zeroizing and for bringing a reversed set of numerals into the display position when the vehicle crosses the meridian in the opposite direction at a later stage in its journey. For zeroizing, a grip 107 draws axially through the hollow shaft 101 a trip rod 103 having projections engaging cam-surfaces formed within the hubs of the discs 108, which are thus first drawn out of gear with the star-wheels 91 and then turned to zero. For reversing the distance-indicating direction, the discs 108 are each provided with a second set of numerals alongside the first, reversed in direction and coloured differently, and these numerals are brought into the display position by shifting axially the internal mechanism of the meter by a bell-crank reversing lever 113 which is brought into operation when projections on a trip rod 111 engage slots in the rims of the discs 108 in the zero position. The lever 113 brings a slotted ratchet wheel 117 into the path of a striker 116 on the cam-shaft 87, and the lever 113 is thus moved axially, taking with it the internal mechanism of the meter. The slotted wheel 117 is then automatically positioned to receive the striker 116 if the vehicle should re-cross the initial meridian later on.