Patent GB-742980-A (GB)
Title: Turn responsive apparatus
Inventor: BARNABY ROLAND EMSLEY
IPC: G01C19/56
Filed: 1953-12-23
Abstract: 742.980. Electric indicating systems. SPERRY CORPORATION. Dec. 23, 1953. No. 35731/53. Class 40(1) The invention relates to a rate-of-turn measuring device, e.g. as disclosed in Specifications 618,328 and 730,783 in which an electrically vibrated tuning fork is connected by a torsional constraining element to a base support, torsional vibrations being developed in the element proportionally to the rate of turn of the support as a result of the fork vibrations, and measured electrically. The invention provides improved means for maintaining the fork tines 10, 11, Fig. 1, in vibration in the plane X-X<SP>1</SP>, Y-Y<SP>1</SP>, and for preventing or compensating for spurious vibrations. Mounting of the fork. Figs. 1, 2, 3. The fork is rigidly secured by a coupling cylinder 29 to a torsion rod 27 resiliently secured in an evacuated casing 13. Figs. 2, 3 by two sets of four equiangularly-spaced radial spokes 28. The casing 13 is rigid and mounted by shock-absorbing rings 17 in the craft whose rate of turn is to be measured. The coupling cylinder 29 has a series of bosses equispaced around the periphery of its lower face which are brazed to the top face of the torsion rod 27. The coupling cylinder is disposed in an axial recess in the heel 12 of the fork and may be similarly secured to a surface 30 - of the heel lying in a nodal plane with respect to the tine vibrations. Alternatively, the coupling cylinder, Fig. 7 (not shown), may be screwed into the recess in the fork heel until its upper surface lies in the nodal plane and then secured by brazing. Maintaining the fork vibrations. The tines 11, 10 carry at their free ends, Fig. 8, pole pieces 22, 23, shaped, Fig. 9, so that, in the normal position of the tines the air-gap between the adjacent pole faces 25 is much less than the air-gap between the adjacent pole faces 24, the pole faces 25 being, however, smaller in area than the pole faces 24. The poles 25 are embraced by an A.C. energized coil 17 mounted in a bracket 22 rigid with the casing 13 and the pole pieces 22, 23 are polarized by a permanent magnet 26 producing a diametral field coaxial with the coil 17. The coil 17 which maintains the tines in oscillation at their natural frequency is energized by an oscillating drive and reference amplifier 18 which is controlled as to frequency and phase by the coil output. Fig. 11 (not shown). Measuring rate of turn, Fig. 1. As the casing 13 turns about the axis Y-Y<SP>1</SP> of the fork, the torsional oscillations developed in the torsion rod 27 are detected by series connected electromagnet pick-offs 34, 35 co-operating with a diametral armature 45-46 on the rod 27, and passed through a parasitic elimination filter 40, and amplifier 39, and a phase detector 43 to a rate-of-turn meter or other utilization apparatus 44. The phase detector compares the amplified rate-of-turn signal with a reference signal derived from the oscillator-amplifier 18 to determine the sense of the rate of turn. The output of the amplifier 39 is also fed back to further coils 59, 60 co-operating with the armature 45-46 to damp the torsional oscillations. Spurious torsional vibrations due to unbalance of the fork tines, Fig. 10b (not shown), are compensated by injecting in series opposition to the pick-off signal, a signal derived from pick-offs 49-52 responsive to vibrations of the fork at its heel, the compensating signal being injected through a mixing circuit 55.