Patent GB-583861-A (GB)
Title: Improvements in electric motor control systems
IPC: H02P7/292
Filed: 1943-12-06
Abstract: 583,861. Control of D.C. motors. BEVIR, O., MORSE, H. E., WRIGHT, C. S., and LYNCH, H. J. A. Dec. 6, 1943, No. 20320. [Class 38 (iii)] In a control system for a series motor supplied from a D.C. source in which a double or tripleanode mercury vapour rectifier has one anode connected through the motor to the positive supply line, another anode connected to the same line through a resistance, and the cathode connected to the negative supply line, the motor current is maintained at a selected mean value by alternately positively pulsing the normally negatively-biassed control grids associated with each anode, a commutating condenser being connected between the anodes. In Fig. 1 (Provisional Specification) a series motor 1 is connected in series with a triple-anode mercury arc rectifier across a D.C. supply. Fields 2 and 3 for opposite directions of rotation are connected to anodes 4 and 5, respectively, while "off" anode 9 is connected to the positive supply terminal through resistance 10. Normal arc striking means 11 and 12 are provided. Rectifier 16 provides a normal negative bias for the grids. In the "off" position of controller 17, the grid of anode 9 is made positive from potentiometer 20 while anodes 4 and 5 are non-conducting. Movement of the controller in one direction alters the spring bias on relay 19 which changes over and makes anode 4 conducting to energize field 2 and rotate the motor. Operating coil 19a carrying the motor current causes relay 19 to be vibratory. The motor current is therefore intermittent and has a mean value dependent on the pressure applied to controller 17. Movement of the controller in the opposite direction controls vibratory relay 18 similarly to produce reverse rotation of the motor by energizing field 3 through anode 5. Commutating condensers 7 and 8 facilitate arc transfer from anode to anode. Four other methods of controlling the are are described in which control of the motor in both directions is effected either by adjusting a control potentiometer across a D.C. supply or by means of a variable voltage source of reversible polarity. In one, the spring bias of the vibratory relays is replaced by electromagnetic bias provided by coils in the anode circuit of a thermionic valve, the grid bias of which is varied by a control potentiometer. In another argon type gas-filled relays are used instead of vibratory relays, the difference between the voltage from a control potentiometer and the volt drop across resistance in the motor circuit being used to produce periodic operation. In a third, vibratory relays, having windings energized from a variable voltage source and windings carrying the motor current, control the rectifier through gas-filled relays which are unable to operate to transfer the arc until the commutating condensers are adequately charged. In the fourth, gas-filled relays energized from an A.C. source are arranged so that only one relay can conduct during each positive half cycle of the supply. The motor may be a servomotor, in a position control system, following changes of the control voltage which may, according to the Provisional Specification, be dependent on changes of temperature, pressure, speed, alignment &c. A booster transformer associated with the control potentiometer for the purpose of reducing lack of correspondence in such a system is shown in one arrangement. Control of two or more motors independently, motors in series or parallel and motors with multiple series fields giving a variety of torquespeed characteristics, using multiple-anode mercury arc rectifiers, is mentioned. Separate thyratrons or ignitrons may be employed in place of the multiple-anode mercury arc rectifier.