Patent GB-611005-A (GB)
Title: Improvements in or relating to devices for detecting or measuring rate of turn
IPC: G01C19/56
Filed: 1942-07-27
Abstract: 611,005. Rate-of-turn measuring devices. SMITH & SONS (MOTOR ACCESSORIES), Ltd., S., and MEREDITH, F. W. July 27, 1942, Nos. 10512/42, 12539/42 and 3922/43. [Class 40 (i)] [Also in Groups XX and XL (c)] A device responsive to rate-of-turn which may be used to give an indication of the rate, or to exercise control e.g. automatic control of aircraft as described in Specification 611,009, [Group XXXV], comprises a mass forced to vibrate along one axis and means which respond to vibration set up along an axis normal to said axis by a turn of the device about an axis normal to the plane containing the two first mentioned axes. A frequency of 800 cycles is suitable for automatic control. The device provides an alternative to a rate-of-turn gyroscope and avoids bearings and difficulties of balancing a rotating mass. In the form shown in Fig. 1, the device comprises a pair of tines 15 rigidly clamped at 14 to a base member 12 and forced to vibrate, in the manner of a tuning fork, in the plane containing the tines. The tines carry masses 16 of magnetic material separated by an air gap 17 and mounted in the gaps between similar poles of two electromagnets 20, 21 the cores of which are connected by a bridge 23 carrying a winding 24. The windings 22 of the electro-magnets are supplied with D.C. on which is superimposed A.C. of the natural frequency of the tines, -whereby an alternating flux is set up across gap 17 from each pole to the other pole of the same magnet to maintain the tines in vibration. There is no resultant flux in bridge 23 when the device is not turning about its vertical axis, but when a turn occurs, the tines are set in vibration in phase opposition and in a direction perpendicular to the plane containing them and at an amplitude dependent on the rate-of-turn, so that a corresponding alternating flux is set up in bridge 23. The resulting current in winding 24 is measured or used for control purposes. In the modification shown in Figs. 2 to 4, the tine 31 is integrally formed with a crossmember comprising end-pieces 32 connected by a cruciform web 33 to give torsional resilience while resisting bending stresses. The crossmember is formed with a pair of beds 34 for crystals 35 connected in an output circuit and overlaid by a plate 38 on which rest a pair of adjusting screws 37 carried by a bar 36 arranged at right-angles to the plane containing the tine and its cross-member. The ends of the crossmember of the tine and of the transverse member 36 are mounted in a rigid annular base forming an enclosure for the whole device. The tine is vibrated in the plane of the paper, Fig. 2, by the arrangement shown in Fig. 4, comprising a pair of magnets 39 in the anode circuit of valve 41 impulsed by a polarized magnet 40 connected in the grid circuit, the plane in which the tine vibrates being adjusted by potentiometer 42. The natural frequency of vibration of the tine in a plane perpendicular to the paper, Fig. 2, is less than the frequency in the plane of the paper owing to the torsional resilience of the cross-member and the flexural resilience of the transverse member 36, and this fact is used to differentiate between stray vibrations of the tine in the perpendicular plane and vibrations set up in that plane due to rotation of the device about the axis of the tine. In a further modification, shown in Fig. 5, the tine 43 is rigidly mounted on a base 162 forming part of a cylindrical member enclosing the tine and driving and controlling mechanism, and suspended at three points from a ring 62 supported by vibration dampers in an outer casing 64. Voltages for vibrating the tine in the plane of the paper, and for damping out vibration in the perpendicular plane are generated by two sets of windings on cores below screen 151 and in a cylindrical member 45 in the upper end of the device. The set shown in side elevation comprises a pair of coils 56 from which A.C. is taken to the corresponding driving unit above the screen and a pair of coils 55 fed with D.C. A similar set for generating the damping voltages is mounted at right-angles on core 58, all the D.C. windings being connected in series. The driving and damping sets mounted above the screen 151 are exactly similar to the generating sets, the D.C. windings being connected in series with those of the generating sets. The generating and driving and damping sets are radially adjustable by grub-screws 144 and circumferally by a vernier (not shown). The output of the A.C. generating winding in plane of the paper is connected after amplification to the corresponding A.C. driving windings in a direction to maintain the vibration in this plane, but the damping output of the generating set is connected after amplification to the corresponding windings in the upper set in a direction to damp-out vibration in a plane perpendicular to the paper. The driving output is maintained constant by automatic volume control. The D.C. coils may be replaced by a single D.C. coil 65 or the tine may be permanently magnetized. The output of the damping generator is a measure of the amplitude of vibration in the perpendicular plane due to rate rotation of the device about the axis of the tine; angle of turn may be obtained by an integrating watt-meter: In a modification of Fig. 5, Fig. 7 (not shown), the tine is supported at nodal points on each side of its centre point by flexible diaphragms, a central mass being carried by the tine to bring the nodes closer together. The generating unit may be at one end of the tine and the driving and damping unit at the other, or, the main generator and drive at one end and the damping generator and drive at the other. Natural damping of the tines may be reduced by mounting the devices in sealed casings. The electro-magnetic units may be replaced by condensers, piezoelectric or magneto-strictive devices. Reference has been directed by the Comptroller to Specification 601,051.