Patent GB-474705-A (GB)
Title: Improvements in the control of the speed of electric motors and in their application to distant control systems
IPC: H02P7/26
Filed: 1936-11-19
Abstract: 474,705. Automatic control systems; electric motor control; distant control systems. SUBMARINE SIGNAL CO. (LONDON), Ltd. (Submarine Signal Co.) Nov. 19, 1936, No. 31742. [Class 38 (iv)] [Also in Groups XXXVII and XXXVIII] Speed.-A variable-speed driving system for an electric motor 81 comprises a gridcontrolled gaseous rectifier 85 in the armature circuit and means, preferably a potentiometer 90, whereby a positive potential may be applied to the grid and continuously varied to determine any desired speed, an opposing potential varying in proportion to the motor speed and operating to define that speed being included in the grid circuit. The back e.m.f. of the armature is the opposing potential as shown in Fig. 13, and in a modification a tachometer generator is used. Stoppage of the motor may be effected by reversing the armature polarity and substituting for the aforesaid grid potentials a positive potential determined by the motor speed and falling to zero as the motor stops. These arrangements are described as applied to controlling a machine operating on a continuous web which may break, such as a paper-making machine, the machine being stopped in this event. The system is also described as applied to distant control of the movement of a pointer or valve in which the speed of operation is automatically increased with the extent of movement desired. Fig. 13 shows a motor 81 driving a continuous web 122 with a photoelectric cell 127 arranged to be illuminated when the web breaks, causing relay 130 to reverse the armature connections and to connect the grid circuit across the reversed armature ; switches 129, 132 are used for automatic and manual stopping respectively. According to Fig. 1, apparatus for remote control of a pointer I and from a hand wheel 8 comprises a differential gear the element 18 of which is driven by the hand wheel and the element 20 of which is coupled through a selsyn transmission to the pointer 1 which is driven by a motor 7 ; the third element 19 of the differential is connected to an arm 67 operating a contact over potentiometer resistances 70, 71, as shown in Fig. 5, and to a cam which operates a switch 73 controlling a reversing switch for the motor 7. A flywheel 17 prevents excessive speed of the hand wheel, the position of which is indicated on a dial 13. When the hand wheel is moved to a new position the arm 67 takes a corresponding position on the potentiometer and a corresponding potential is applied to the grid of the rectifier 63 whereby the motor 7 is driven at a speed in accordance with the extent of the desired movement, the back e.m.f. of the motor operating against the potentiometer potential to determine the speed. The resulting motion of the pointer 1 operates upon the differential gear to restore the arm 67 to its initial position progressively, with consequent progressive reduction of the speed of the motor 7 and pointer 1 until they come to rest with the latter in its desired position. The Specification describes also motor control arrangements in which two rectifiers are used for full-wave control on a single-phase supply and for half-wave control in a three-phase supply; circuits for three-phase operation using three and six rectifiers are also described.