Patent GB-587925-A (GB)
Title: Improvements in and relating to dynamic compasses
IPC: G01C17/00
Filed: 1940-01-01
Abstract: 587,925. Magnetic compasses; gyroscopic apparatus. JAEGER-AVIATION. Jan. 1, 1940, No. 71. Convention date, Jan. 4, 1939. [Classes 97 (ii) and 97 (iii)] [Also in Group XXXV] In a compass of the type in which the magnetic needle is maintained in oscillation by impulses imparted to it when it is in the immediate vicinity of the N-S reference line of the compass, the difference in the times of the half-swings on either side of the position of rest of the needle which occurs when this position does not coincide with the N-S reference line is used to control the indicating means. The apparatus may be applied to a telecompass, a drift indicator, or to the control of a gyroscopic compass or a gyroscopic or other automatic pilot. A number of forms are described in which the needle oscillations are maintained, and the comparison of the times of the halfswings is effected, by mechanical, electrical or pneumatic means. As shown in Fig. 1, the magnetic needle 1 carries a pin 2 through which it receives impulses from a pivoted fork 3 which is driven by an escapement mechanism (not shown) and carries a wheel 4 meshing with a wheel 5 coaxial with the pivotal axis of the fork. The wheel 4 is brought by the oscillation of the fork alternatelyinto mesh with oppositely-rotating wheels 6, 7. If the needle 1 lies in the magnetic meridian a-b, the wheel 4 contacts the wheels 6, 7 for equal times, and is given only a very small oscillating movement. If, due to a rotation of the apparatus the needle at the time of impulse lies in a direction such as c-d or e-f, the times of the halfswings and hence the periods of contact of the wheel 4 with the wheels 6, 7, are unequal, so that the wheel 4 is driven in a corresponding direction and rotates the wheel 5. An index 8 indicates the rotation of the wheel 5, the apparatus in this form serving to indicate the drift of an aircraft or ship from a rectilinear path. By the addition of a spring 10 which tends to restore the index to zero the index will indicate divergence from course. In a modification, Fig. 2 (not shown), a further wheel meshes with the wheel 5 and with the interior of a gear ring concentric with the wheel 5 and fixed in relation to the craft, causing the whole device to rotate until the needle 1 lies in the magnetic meridian, so providing a compass indication. In the form shown in Fig. 3, a contact 21 carried by the needle 20 engages contacts 23, 24 and alternately closes the circuits of the windings 25, 26 of a relay 27 which reverses at each half period the direction of the current from a source 31 to a polarized amperemeter having a long period of oscillation in relation to that of the needle, the oscillation of which is maintained by windings 28, 29 which are alternately energized at the same times as the relay windings 25, 26 respectively. When the mean position of the needle is in the magnetic meridian, the relay contacts are closed for equal times, and the amperemeter remains at zero. When the system is rotated, the times are unequal, and the meter indicates the deviation from the chosen direction. The index 34 of the meter may close the reversing contacts 35, 36 of a motor 37 which rotates a wheel 39 on the shaft of which, the system is mounted, so returning the system to the N-S position to provide a compass indication. In a modification, Fig. 4 (not shown), the needle operates a single contact in the circuit of an electromagnet causing a pawl and ratchet to drive a cam wheel which operates a pusher reversing the connections to the meter. Another form, Fig. 9 (not shown), comprises a lever escapement which maintains the oscillation of the needle, the pallets and the escapement wheel forming contacts which reverse the current through the amperemeter. Forms are also described,-Figs. 6, 7 (not shown), in which a forked lever which maintains the oscillation of the needle is operated by an escapement driven by an air or other fluid jet and a vane wheel. A blade carried by the lever interrupts alternately two jets which are directed either into two manometric capsules differentially operating an indicator, or to opposite sides of a vane wheel which by its rotation may restore the system to the N-S position. In a modification, Fig. 8 (not shown), the oscillation of the needle is maintained by a jet directed on to a pivoted blade carried by it. The indicating apparatus may be used to control the application of precession torques to a gyroscope, the orientation of which is thereby controlled by the magnetic needle.