Patent GB-798107-A (GB)
Title: Gyroscopic reference apparatus
Inventor: VACQUIER VICTOR
IPC: G01C19/44
Filed: 1956-02-24
Abstract: 798,107. Gyroscopic apparatus. SPERRY RAND CORPORATION. Feb. 24, 1956, No. 5818/56. Class 97(3) [Also in Group XXXVIII] Gyroscopic apparatus for defining a vertical reference comprises a gyroscope consisting of a rotor bearing member 17, Fig. 2, containing a rotor 13 having a normally vertical axis, a supporting member 10 in which the gyroscope is mounted with freedom of angular movement about mutually perpendicular normally horizontal axes, a case 5' in which the supporting member 10 is mounted for rotation about a normally vertical axis, motive means 22 adapted when energized to rotate the supporting frame slowly but continuously about its axis and a gravitational controller for exercising control of the gyroscope to maintain the rotor axis vertical. As shown the rotor is of the electrically spun type and the member 17 is a spherical case mounted in the member 10 by a gimbal ring 19. The gimbal ring supports the rotor case 17 on a minor axis 18 and is itself supported in the member 10 on a major axis 20. The member 10 is filled with a liquid of density such that the liquid displaced by the case is equal in weight to that of the rotor and its case and the gimbal ring 19 is made to have the same net density as that of the liquid. The gimbal ring bearings are thus substantially relieved of load. The member 10 is mounted for rotation in the case 5<SP>1</SP> on bearings 20<SP>1</SP> and 21<SP>1</SP> and the motive means 22 is an electric motor which drives the member 10 through gearing. The case 5<SP>1</SP> also contains the gravitational controller which comprises a pendulum consisting of a bob 26 suspended by a filament 29 over a two-part pick-off 70 in a tube 27 containing a damping liquid 28. The pick-off comprises a centre pole 72, Fig. 5, and four outer poles. The centre pole has a winding supplied from a single phase A.C. supply and the windings on opposite pairs of outer poles 73, 73<SP>1</SP> and 74, 74<SP>1</SP> are respectively connected together. The pendulum bob varies the reluctance between the centre pole 72 and the individual poles of the two pairs of outer poles, the A.C. output of the outer poles varying in magnitude with tilt of the pendulum and reversing in phase for opposite tilts. The pick-off 70 controls a torque-applying-device 30 which is similar in construction to the pick-off in that it has a centre pole 85 and four outer poles but it acts on a curved disc 80 which is mounted on the case 17 and which is large enough to overlie the poles and is a good conductor of both electricity and magnetism. The case 5<SP>1</SP> is attached to a platform 5 (Fig. 1) which is universally gimballed on a major axis 2 and a minor axis 4 by means of a gimbal ring 3. The platform 5 is maintained level about its major axis by means of a servomotor 6 which is coupled to the gimbal ring 3 through reduction gearing 7, 7<SP>1</SP> and a gear sector 8. It is maintained level about the minor axis 4 by a servo-motor 6<SP>1</SP> mounted in the bottom of platform 5 and geared to a sector 9 secured to gimbal ring 3 through reduction gearing. The motor 6 drives a transmitter 11 and the motor 6' a transmitter 12 for transmitting the movements of the platform, but the platform can also be used directly as a horizontal reference. The motors 6 and 6<SP>1</SP> are controlled by a pick-off 42 which is similar to the pick-off 70 and the five poles of which are supported in the top of the case 5<SP>1</SP> over the gyroscope. The outputs from windings on two opposite outer poles are connected to operate the motor 6 through a phase sensitive amplifier and the outputs of the other two windings on the other outer poles are connected to operate the motor 6' through another phase sensitive amplifier. The platform is therefore stabilized from the gyroscope. The torque applying device 30 and the gravitational controller are maintained fixed in azimuth by means of a repeater system actuated from a gyrocompass and comprising a repeater motor 37 on the platform 5 which through reduction gearing orients both the tube 27 and the torque applying device 30. Alternatively a meridian resolver between the pendulum and device 30 can be used. The output of the windings on the poles 73, 73<SP>1</SP> of the pick-off 70 which are maintained in the north-south direction are fed to a phase sensitive amplifier 50 and a further amplifier 51 the output of which controls a motor 52 whose speed is closely proportional to the magnitude of the signal and hence to the extent of movement of the pendulum in the north-south direction. Since the displacement of the pendulum is proportional to the acceleration of the ship or aircraft in which the apparatus is mounted the amount of rotation of the motor shaft is a measure of the ship's or aircraft's velocity resolved in the northsouth direction. To increase the accuracy the output of the amplifier 50 is partially opposed by an eddy current speed generator 53 on the shaft of the motor. The motor shaft also drives through a large reduction gear train 54 a synchro transmitter 55 the output of which is a measure of the ship's or aircraft's velocity and which energizes through an amplifier 61 the corresponding poles 30<SP>1</SP>, 31 of the torque applying device 30 to preset the gyroscope to move it to the new true vertical position. The amount of the precession of the gyroscope is proportional to the change in position of the ship or aircraft on the earth's surface due to the velocity. The other pair of poles 74, 74<SP>1</SP> of the pickoff 70 which are maintained in the eastwest direction similarly control the poles 32, 33 of the torque applying device 30 and the output of the synchro transmitter connected to these poles is a measure of the velocity in the east-west direction. The pendulum will also correct the gyroscope for the change in direction of its vertical axis caused by the rotation of the earth. The gyroscope is given a period about 84 minutes by adjusting the torque gradients of the device 30 with respect to the gyroscopic moment of inertia, rotor speed and other constants since with this period acceleration errors disappear. To damp slow oscillations of the gyroscope a portion of the amplified signal from each pair of outer windings on the pick-up 70 is also applied to the appropriate windings of the torque applying device 30 by connecting the signal in series with the signal from the respective synchro transmitter. A switch 60 is provided for removing the damping signal when necessary. A setting knob is also provided on each of the synchro transmitters to bring the apparatus to its correct position quickly when starting up. A thermostatically controlled heater is contained in the case 5' to maintain the liquid in the member 10 and in the tube 27 at a constant temperature. In a modification the pendulum bob of the gravitational controller is mounted on a spring support so that the displacement of the pendulum is opposed both by gravity and by the resilience of the spring support; thus the displacement of the pendulum under the action of acceleration is kept small even though the apparatus is mounted in an aeroplane. A small tube also surrounds the pendulum bob support to act as a limit stop and also as a rest for the bob when the aeroplane flies upside down, to prevent. buckling of the spring support.