Patent GB-622927-A (GB)
Title: Improvements in or relating to electrical control systems
IPC: G05D3/14
Filed: 1946-01-11
Abstract: 622,927. Control of A.C. Motors. SPERR Y GYROSCOPE CO., Inc. Jan. 11, 1946, No. 1059. Convention date, Nov. 17, 1939. [Class 38(iii)] [Also in Group XXXVIII] In an electrical control system an alternating signal representative in amplitude and sign of the magnitude and Sense of a variable (signals 180 degrees phase displaced being regarded as of opposite signs) is demodulated to a continuous signal, representative of the variable which in turn modulates an alternating signal at a different frequency which is used to control the magnitude and sense of the speed or torque of a reversible A.C. motor, in response to the magnitude and sense of the variable, means being provided for the avoidance of angular ambiguity between the controlling and controlled quantities and for the introduction of terms dependent on the derivatives of the variable with regard to time. In Fig. 1 a hand wheel 1 is connected direct to a slow speed selsyn transmitter 4 and through 36 to 1 gearing to a high speed selsyn transmitter 3, which are of the kind having single circuit single phase A.C. rotors and three-circuit stators connected to corresponding receivers 5 and 6, the rotors of which produce an A.C. voltage dependent in magnitude and phase on the magnitude and sense of the deviation between the receiver and transmitter rotors. The receiver rotors are coupled to the controlled object 2 by mechanical followup means 13, the output of the high speed receiver 5 being zero when the controlled object 2 is in alignment with the controlling object 1, and the output of the low speed receiver 6 being zero when there is a misalignment of -2¢ degrees. The high speed voltage is limited by rectifier device 31, added to the low speed voltage, and combined with an alternating bias from transformer 12 equal in amplitude but opposite in phase to the signal voltage at the low speed zero deviation. The resulting combination signal applied to the input of the push-pull amplifier 15 is such as to ensure, in combination with the low speed zero misalignment that no 180 degree ambiguity will arise between the controlling and the controlled members. The ring demodulator 17 is fed with the amplified signal from transformer 16 and with steady A.C. from transformer 12, to produce a continuous voltage variable in magnitude and sign according to the movements of the controlling member. After removal of A.C. components by filters, the voltage is applied to a ring modulator 23 fed with steady A.C. of a different frequency, as used to drive the motor 46. The output, which is an A.C. voltage dependent in magnitude and phase on the movements of the controlling member, is fed to the amplifier 30, the anodes of which are fed with A.C. of similar frequency to the input through chokes 33 and resistances 34, 35 so that the D.C. unbalance between the anode circuits depends on the magnitude and phase of the input to the grids from the modulator. Voltage drops will appear across the chokes and resistances dependent in phase and magnitude on the deviation between the controlling and controlled members and on the rate of change of such deviation, and these voltages, together with an alternating component dependent on the deviation, are applied to the differentiating circuit 36, 37, 36, 39. The output, comprising an A.C. component dependent on the deviation and also voltages dependent on the first and second derivatives of the deviation with regard to time, is applied to the grid controlled rectifiers 40, 41 which determine the operation of the capacity type two-phase induction motor 46 driving the controlled object 2 so that its movements correspond with those of the controlling object 1. In Fig. 1a (not shown) the motor circuit is modified, while in Fig. 4 (not shown) a push-pull thermionic modulator is used instead of the ring modulator to control a reversible repulsion motor. Specification 622,991, [Group XXXVIII], is referred to.