Patent GB-666056-A (GB)
Title: Improvements in or relating to electronic control systems for direct current electric motors
IPC: H02P7/292
Filed: 1949-09-20
Abstract: 666,056. Control of D.C. motors. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. Sept. 20, 1949. [Oct. 15, 1948] No. 24162/49. Class 38 (iii). [Also in Group XXXVIII] An electronic motor control system for operating a direct-current-motor in response to the polarity and magnitude of an error voltage comprises two grid-controlled electronic tubes so connected between a source of alternating current and the armature circuit of the motor as to cause in said armature circuit the flow of current in one direction during one half cycle of the alternating voltage and in the opposite direction during the next half cycle ; grid control circuits for said tubes adjusted to cause the flow of armature current in both directions for equal time intervals in the absence of an error voltage; and circuit means for applying an error voltage to said grid control circuits so as to advance the firing- point of one tube and retard the firing-point of the other tube as a function of said error voltage, the grid control circuits for the tubes including circuit elements for applying an alternating biasing voltage of a predetermined phase relation with respect to the line voltage, and additional circuit elements for superimposing a direct error voltage on said alternating biasing voltage. As shown, an armature A is a soft iron structure of an error measuring device E wherein the magnetic pick-up measures the displacement between the ring SR and the position of the armature A. indicative of the position of the precession axis of a gyroscope, for example, the displacement between a gyroscope and a gun-sighting station represented by the ring SR. Movement of the primary member A of the follow-up device from the symmetrical position shown causes an error signal to appear at 17, 18, the amplitude and phase sense of the signal depending on the degree and direction of the movement, and the signal after amplification at 20 is applied to a phase sensitive rectifier comprising four diodes connected as shown to a load resistor 29, 30, biasing transformer winding 21, and input transformer windings 23, 35. The resulting voltage modified by an anticipating network 80, 81 to prevent hunting is applied to a D.C. amplifier 84, the output of which feeds resistors 57, 65, 62 in series. Resistors 57, 62 are included in the grid circuits of thyratrons 1, 2 with separate A.C. anode supplies and A.C. biasing arrangement such that normally one tube conducts for the second half of one half cycle of the supply and the other for the second half of the next half cycle. When the bias is modified by the error signal, one thyratron conducts for more and the other for less than 90 degrees and consequently the motor the armature of which is common to both anode circuits runs in one direction or. the other at a speed which depends on the error signal. The Specification, as open to inspection under Sect. 91, comprises also a reference to dynamic braking being produced by the shunting effect of one of the thyratrons when the error signal disappears. This subject-matter does not appear in the Specification as accepted.