Patent GB-1196262-A (GB)
Title: Improvements in or relating to Navigation Apparatus
Inventor: ANDERSON EDWARD WILLIAM
IPC: G01C17/30
Filed: 1966-07-07
Abstract: 1,196,262. Navigation computers. SMITHS INDUSTRIES Ltd. 7 July, 1967 [7 July, 1966], No. 30577/66. Heading G4G. [Also in Division G1] In navigation apparatus, to compensate for the distortion of the earth's magnetic field by the presence of the vehicle or craft carrying the apparatus, two magnetic field detecting systems 1, 2 (Fig. 2), are employed, spaced along the length of a non-magnetic boom 3 extending rearwardly of the vehicle, each producing two signals indicative of the magnitude of the local field along two perpendicular directions. These two signals are then combined, in pairs, to produce two signals indicative of the magnitude of the earth's field along the two directions which are also indicative of the direction of travel of the vehicle relative to magnetic north and east directions. Two pairs of flux gates, 1, 2, see also Fig. 3 (not shown), with the axes of their cores 4, 5 arranged parallel and perpendicular to the axis of the boom produce output signals whose amplitudes are indicative of H cos # m  + x, H sin # m  + y and H cos # m +X, H sin # m +Y, respectively, whose x, y and X, Y, are the components of the local field, at the two positions, due to the presence of the vehicle and # m  is the angle between the direction of the vehicle and magnetic north. The two signals from flux gates 2 are then multiplied by factors x/X and y/Y, respectively, by potentiometers 10, 12 and the corresponding signals from the two pairs of flux gates are compared in amplifiers 11, 13 to produce signals corresponding to H(1- x/X) . cos # m  and H(1 - y/Y) . sin # m . For the vehicle where x/X = y/Y, these two signals are proportional to cos # m  and sin # m , respectively. Alternatively one of the two signals may be multiplied or divided by the factor to provide signals proportional to cos # m  and sin # m .  These two signals are then converted in unit 15 to signals proportional to cos # and sin #, where # is the angle between the vehicle direction and true north, the sliders of potentiometers 17, 19 being set to a position proportional to tan M, where M is the angle between true north and magnetic north, i.e. # m +M=#. Finally these two signals are fed to a compass 21, driven by a two-phase synchro torque receiver or a synchro resolver. The signals may also be used to determine the distance travelled by the vehicle along a northerly and easterly direction by integrating the two components V cos #, V sin #, of the velocity V, derived by a pick-off 26 coupled to the transmission of the vehicle. This may be done, Fig. 4 (not shown), by integrating the output of amplifiers whose input signals are proportional to cos # and sin # and whose gains are controlled in proportion to V. Alternatively, Fig. 5 (not shown), a signal proportional to V may be intermittently integrated for periods of time proportional to cos # and sin # respectively; In a modification the unit 15 may involve a resolver having a pair of perpendicular rotor windings rotatable with respect to a pair of perpendicular stator windings, the rotor being set to an angular position with respect to the stator which depends on the angle M. Provision is also made for applying a manually variable magnetic field to one or both of the pairs of flux gates to modify the magnetic field produced by the vehicle. In place of two flux gates at each position, three may be used, displaced from each other by 120 degrees in azimuth.