Patent GB-405251-A (GB)
Title: Improvements in or relating to electrical positional or follow-up control systems
IPC: G05D3/12
Filed: 1932-07-23
Abstract: 405,251. Control of motors. SPERRY GYROSCOPE CO., Inc., Manhattan Bridge Plaza, Brooklyn, New York, U.S.A.-(Assignees of Wittkuhns, B. A. ; 12, Norwood Avenue, Summit, New Jersey, and Watkins, F. M. ; 191, Puritan Avenue, Forest Hills, New York, both in U.S.A.) July 23, 1932, No. 20860. Convention date, April 1. [Class 38 (iii).] Following movement of control member.- In a positional or follow-up control system comprising a receiving element driven by a reversible commutator electric motor, the number of revolutions and direction of which are controlled in accordance with the number of rotations and direction of a regulating member supplied with alternating current, an electromotive force inductively produced and proportional to the relative displacement of the sending and receiving elements as to amount and direction so shifts in the opposite sense the phases of the alternating current grid potentials on two or more grid-glow tubes supplied with alternating current that the plate currents of the tubes determine the number of revolutions and direction of rotation of the motor. A gridglow tube is defined as a three-element tube containing a cathode, an anode and a control electrode or grid and an inert gas or vapour at sufficient pressure to support an arc. The principle upon which the invention is based is described with reference to Fig. 1. The centretapped secondary winding of a transformer 1 is connected to two circuits each consisting of a condenser 7 or 9 in series with a transformer winding 8 or 10. The windings 8, 10 are oppositely wound on a single core so that when equal currents flow through them, they have no inductance. The primary windings 11, 12 are connected in series to the alternating current source. By varying the current through windings 11, 12 by means of a reversing switch 13 and a rheostat 14, the apparent resistances of the windings 8, 10 can be varied in opposite directions, and in consequence the phase of the voltages between the points 18 or 19 and the centre-tapping 17 of the transformer 1 are varied oppositely. The potentials at the points 18, 19 are applied to the grids of grid-glow tubes 5, 6, the plate circuits of which are connected through oppositely wound field windings 23<1>, 24<1>, to the armature 201 of a motor. The direction of rotation of the motor is determined by the stronger of the two fields. As applied to the control of a searchlight 46, Fig. 2, four gridglow tubes 31-34 are connected to operate in pairs in full wave fashion, the arrangement being such that flow of current in transformer primary windings 37, 38 causes the motor 20, which has two separate commutator windings, to rotate in the appropriate direction. The transmitting element consists of a selsyn 47 operated by a handle 50 and electrically connected with a similar selsyn 45 coupled with the searchlight. Movement of the rotor of the selsyn 47 disturbs the current equilibrium so that a voltage is induced in the winding 51 connected to the transformer windings 37, 38. Rotation of the searchlight by the motor 20 restores selsyn 45 to the position where no voltage is induced in the coil 51. As applied to a follow-up system on a compass, Fig. 3, the motor 201 is coupled with the phantom element 56 of the compass which carries cored windings 59, 60. Windings 57, 58 carried by the sensitive element are supplied with alternating current. Potentials induced in the windings 59, 60 are applied to the grid of an amplifying valve 61, the plate current of which flows through the primary windings of transformers 66, 67 energizing the grids of the tubes 5<1>, 6<1>. In order to prevent the motor from stopping before reaching perfect alignment, a mechanical oscillation is produced by making the amplifier act also as a low frequency oscillator. This is effected by closely coupling the grid and plate circuits of the amplifier 61 through a transformer 68. One of these circuits is tuned to the desired frequency or to such a frequency as will produce with the supplied frequency an oscillation of the desired low frequency, and the amplitude is regulated by a rheostat 69. In a modification, the oscillation is not created in the amplifier but the output from the grid-glow tubes feeds a transformer tuned on the primary and/or secondary sides to the required oscillation which is superimposed on the signal. All the windings 57-60 may be carried on the follow-up member, the sensitive element having an unwound core. In the preferred form of the invention, Fig. 5, an oscillatory circuit consisting of a condenser 73 and a choke 74 is interposed between the two sides of the input windings 59<1>, 601 and the input of the amplifier 61<111> so as to determine the frequency of the desired low speed oscillations. The output of the amplifier 61<111> supplies through a transformer 75 having a centre tapped secondary winding, the grids of valves 76, 77 acting in push-pull fashion, the plates of which are supplied with alternating currents of opposite phase through the transformers 67<1>, 681. The phase of the low frequency oscillations is adjusted by connecting a variable resistance 82 and condenser 83 across the secondary winding of the feed-back transformer 70<1> this circuit being connected by a wire 84 to the grid-cathode circuit of the valve 61<111>. A variable resistance 87 short-circuits more or less of the feed-back impulse thereby adjusting the amplitude of the tremors.