Patent GB-716129-A (GB)
Title: Improvements in and relating to automatic tension control for electric reel motor control systems
Inventor: BARANY THOMAS ERNEST
IPC: G05D15/01
Filed: 1951-09-04
Abstract: 716,129. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. July 7, 1952 [Sept, 4, 1951], No. 20862/51. Class 38(3) [Also in Group XXXV] In an automatic tension control system for a Ward-Leonard drive for a reel-motor in a strip rolling mill, the generator field is controlled to provide substantially constant armature current, and the motor field is controlled to maintain a constant armature voltage for a given strip speed. Inertia compensation is provided during acceleration and deceleration, in accordance with the strip width and reel diameter. The system comprises a main generator 4 supplying the motor 1; a generator exciter 5 and pilot exciter 12; a motor exciter 6, having a field 7a controlled by a rheostat 8 driven by a Ward- Leonard set 9, 10; and a pilot generator 2 providing an output proportional to strip speed. Current control. The pilot exciter 12 is energized by a field 13a in accordance with the current in the main Ward- Leonard loop. The difference between the pilot exciter voltage and a reference voltage from a tension adjusting potentiometer 15 energizes the main exciter field 5a since the excitation has to be substantially proportional to strip speed, basic excitation is provided by field 5c energized from the pilot generator thereby reducing the gain required in the pilot exciter. Field 13c prevents overspeeding if the strip breaks and field 13d provides inertia compensation, as described below. Motor voltage control. The rheostat drive generator 10 is energized in accordance with the difference between the strip speed (field 11a) and the motor voltage and IR drop (field 11b, 11d). For a given strip speed, the voltage of the motor tends to decrease during the wind, (as the reel diameter increases) and the rheostat control increases the motor exciter energization. To reset the field control rheostat after a wind switch 19 is opened, and the rheostat motor energized by hand control to make a complete revolution to the low voltage starting position. Overspeed control. If the strip breaks removing the load from the motor, the constant current control tends to drive the main generator to saturation. This causes a reversal of the rheostat generator output, which passes through rectifier 18 to the generator pilot exciter field 13c to oppose the current control while rectifier 17 prevents the rheostat drive motor from operating in reverse to reduce the motor voltage, whereby there is only a small increase in speed of the reel motor. Inertia control. The field 13d is supplied with a voltage proportional to the mill acceleration (i.e. strip acceleration) and the magnitude is controlled by a preset " strip width" compensating rheostat 20 shunted by a " reel diameter " compensating rheostat linked to the motor field control rheostat to provide a movement substantially proportional to the reel diameter. Stalled current limiting. Switch 24 is closed when the reel is stalled. and if the tension setting (rheostat 15) is greater than the stalled current setting (rheostat 22) current flows through rectifier 23 to reduce the reference voltage.