Patent GB-565351-A (GB)
Title: An electromagnetic course-indicating navigation instrument
IPC: G01C17/30
Filed: 1943-01-22
Abstract: 565,351. Gyroscopic apparatus. AGA-BALTIC AKTIEBOLAG. Jan. 22,1943, No. 1153. Convention date, April 21, 1942. [Class 97 (iii)] [Also in Group XXXVI] In a course-indicating navigation instrument of the induction type two magnetic circuits polarized in opposite directions are provided, each comprising a rotating part of such a form that during rotation of that part the magnetic field of the circuit is subject to periodical changes, at least one part of each of the magnetic circuits carrying a winding for induction of a voltage dependent on the periodical changes of the magnetic field, these two windings being connected to an instrument for indicating equal voltages, and the rotating parts of the two magnetic circuits are formed by a rotor part common to the two circuits. A hollow shaft 37, Fig. 4, is flanged at its lower end to form a plate 40 to which an airtight case 41 is attached. Within this is a gyroscope and an A.C. generator utilising the earth's magnetism as its field. The gyroscope is driven by vacuum produced by a suction-pump connected by a connection 42 to the hollow shaft 37, so as to transmit the vacuum to the inside of the case 41. Air is admitted to drive the gyroscope through a filter 43 connected to a chamber 44, which carries one of the bearings 45, Fig. 5, of the outer gimbal ring 46. Openings 47 in the bearing 45, a channel 48 in the steel spindle 49 of the ring 46, and a channel 50 in the ring 46 allow air to pass to the inner gimbal ring 52. The air passes through openings 53 in the bearing 51 and a channel 55 in the stub axle 54 of the inner ring 52 to a jet 56 in the ring 52. Air from this jet impinges on a turbine wheel 57 which is also the rotor of the gyroscope. The air then passes to an annular channel 58 in the inner gimbal ring 52, this channel being connected to the interior of the case 41 by channels having an exit 59, Fig. 4. The generator 61 is built in one side wall of the turbine 60 and contains four radial magnet cores 62, 63, 64, 65, each of which is surrounded by a winding 66, 67, 68, 69. These four cores are in one plane and a substantially square magnetic member 70 rotates between the cores, its corners being chamfered so that they pass the polepieces with a constant air gap. Magnetic paths are thereby closed as shown by dotted lines 71, 72. The two pairs of cores are oppositely polarized by two permanent magnets (not shown) which are adjustable by screws 75, of which one is shown in Fig. 4. Each of the pairs of windings are connected in series, the two series circuits being connected to three slip-rings 76, 77, 78 with which brushes 79, 80, 81 engage. The brushes 76, 77, 78 are connected to two rectifiers, the rectified voltages being connected in series opposition and their difference being passed to a moving coil instrument which gives a zero reading when the magnets have a predetermined direction with regard to the earth's field. The position of the magnets 62, 65 with relation to the longitudinal direction of the vessel is adjustable by means of a worm wheel 83 and a worm 84 in order to set any particular course. The worm 84 is rotatable by a crank or wheel on the instrument panel. In a modification the difference in the output voltages of the rectifiers drives a differential motor which controls the magnets until these have assumed a position corresponding to the new voltage zero, and also operates a scale formed as a compass dial. The same motor may be used for automatic steering by means of a servomotor. The rotor part may be hexagonal, in which case the magnets are arranged alternately at angles of 60 degrees and 120 degrees apart.