Patent GB-638506-A (GB)
Title: Improvements in and relating to electric control systems for dynamo electric machines
IPC: B65H23/18
Filed: 1946-12-24
Abstract: 638,506. Automatic motor control systems. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 24, 1946, No. 37811. Convention date, Dec. 28, 1945. [Class 38 (iv)] Relates to a motor control system wherein the variations in the tension and speed of a strip of material wound from one reel on to another are maintained within narrow limits. As shown, a strip 1 of material is unwound from a reel 2 on to a reel 5 driven by a motor 6, the strip passing through idler rollers 4 which drive a tachometer generator 41 in accordance with the speed of the strip. Back tension on the reel 2 is controlled by a generator 10 driven by the reel and feeding energy into a generator 7 which supplies the armature of the motor 6. Compensation of the variations of strip speed and tension due to the varying diameters of the reeled material during the winding operation is effected by varying the excitation of the field windings 6a, 10a by amplidyne generators 23, 34. The generator 23 is provided with two opposed field windings 23c, 23d, the former of which is excited by a difference voltage dependent on the field circuit of generator 10 and a reference voltage at a tapping of resistance 25 connected across supply mains 14, 15, and the latter in accordance with a difference voltage dependent on the armature current of generator 10 (resistance 30) and a similar reference voltage tapped from a resistance 28 across the mains. The amplidyne 34 has two field windings 34b, 34c excited in a similar manner but in this case excitation of the winding 34c is dependent on the voltage of tachometer generator 41. To maintain the strip speed and tension within narrow limits non-linear resistances 33, 43 are shunted across the windings 23c, 34b in order that large voltage changes produce only relatively small changes on excitation. Blocking rectifiers 32, 42 are also provided to de-energize the windings 23a, 34c when the signal voltages from 30 and 41 fall below the reference voltages. In order to effect rapid retardation when winding is stopped, braking resistors 45, 47 are provided for short circuiting the armatures of the machines 6, 10. During acceleration or deceleration the strip tension is maintained substantially the same as that during normal winding by switching in a resistance 48 in series with the resistance 30 or a resistance 27 in the reference voltage circuit. To compensate for the varying reel diameters during operation, the amplidyne 34 provides excitation for the motor 6 through a range, the minimum and maximum of which corresponds to the empty and full conditions of the reel 5. Similar conditions of excitation are provided by the amplidyne 23 in accordance with the speed of the generator 10 and reel 2. The operation of the system is started by depressing a switch 49 to operate and lock-up the relay 50 over contacts 50c. Relay 50 pulls up contactors 51, 52 which connects generator 7 to the machines 6, 10 and interrupts the dynamic braking circuits 45, 47 normally maintained closed by relays 44, 46. Release of relays 44, 46 operates relays 31, 38 to complete the circuits of field windings 23a, 34b and motor 6 is driven at low speed due to the inclusion of resistance 13 in the field winding of the generator 7. Operation of the switch 22 to the " fast " position pulls up relay 20 to start a motor 19 coupled to the slider 13a and cut out resistance 13 to accelerate the motor 6 to the desired speed when the switch 22 is restored to neutral position. Reduction of speed can be brought about in a similar manner by operation of the switch 22 into the " slow " position. The winding operation is stopped by depressing a button 54 to release the relay 50 and the contactors 51, 52, and complete the braking circuits of the machines 6, 10.