Patent GB-618328-A (GB)
Title: Improvements in or relating to turn responsive apparatus
IPC: G01C19/56
Filed: 1946-10-17
Abstract: 618,328. Indicating rate of turn and angular acceleration of a body. SPERRY GYROSCOPE CO., Inc. Oct. 17, 1946, No. 30980. Convention date, Oct. 17, 1945. [Class 40 (i)] [Also in Group XX] Apparatus responsive to the turning of a body about an axis comprises a member elastically coupled to the body so as to be capable of torsional movement relative to the body about that axis, means for cyclically varying the moment of inertia of the member about that axis and means responsive to the variations of relative angular displacement of the member and the body about that axis. As shown in Fig. 1, a tuned fork 11 is connected by an elastic constraining portion 12 having a low torsional stiffness, but a high resistance to bending forces to a base 13, about an axis 24. The tuned fork 11 is maintained in vibration at its natural frequency by means of a pair of vibrational pick-up devices 16, 17 attached to the prongs 14, 15 and connected in series to the input circuit of an amplifier 18 whose output either directly or through a rectifier 19 controls the tuned fork exciter 21. The vibrational pick-ups may be of the Rochelle salt crystal type. The output of the pick-ups 16, 17 is also connected to an amplifier 29 whose output voltage is rectified at 32 and used for automatic gain control of the amplifier 18. A further vibration pick-up 23, which may comprise a Rochelle salt crystal unit, has a stator portion rigidly connected with the base 13 and a relatively movable portion connected through a stiff rod 25 to the tuned fork 11 at the junction of the prongs 14, 15. As the base 13 rotates about the axis 24, the fork is angularly displaced relatively to the base because of its torsional connection therewith, and this angular displacement varies as the moment of inertia of the fork 11 varies due to its vibration about the axis 24. The axial pick-up 23 produces an alternating voltage corresponding to this periodic variation in the relative angular displacement between the fork 11 and the base 13, but which varies in magnitude and phase relation. to the phase of the output of the pick-up devices 16, 17 according to the rate and direction of rotation of the base 13 about axis 24. The output of the pick-up 23 is, after amplification at 26, connected to the input circuit of a phase-sensitive detector 27 which is supplied with a reference phase input signal from the output voltage of pick-up 16, 17 as amplified at 29. The D.C. output of the detector 27 is supplied to a galvanometer 28 functioning as a rate-of-turn indicator. In addition, the output of the pick-up 23 comprises a direct current voltage component whose sense and magnitude is proportional.to the angular acceleration of the base 13 about the axis 24. This direct voltage is amplified in a D.C. amplifier 33 and indicated on a galvanometer 34. The outputs of the phasesensitive detector 27 and the D.C. amplifier 33 may be used for control purposes. The fork 11 may be replaced by mass systems whose moment of inertia is periodically varied by magnetostriction or piezo-electric methods.