GB908921A - Improvements relating to speed control arrangements for multiple motor drives - Google Patents

Abstract

908,921. Control of A.C. motors. LICENTIA PATENT - VERWALTUNGS - G.m.b.H. Jan. 19, 1961, No. 2225/61. Class 38 (3). In a multi-unit rolling mill for steel strip, plastics or paper, to establish desired differences in speed between successive stands 1, 2, the speed of each stand is adjusted as it first receives the strip 5 in accordance with the motor armature current of the preceding one. When the strip reaches a switch 6, a relay 6<SP>1</SP> closes contacts 6<SP>11</SP> momentarily so that the value of the current in the first armature 31, measured by a device 39, may be stored in a device 40. As the strip enters the rolls 2, if they are not running at exactly the correct speed, the resulting tension or compression in the strip changes the current in armature 31. This new value is signalled to a comparator 42, through contacts 7<SP>11</SP> (which close as the strip reaches a switch 7), where the difference between the new and the stored current value is used to control a generator 38 supplying the field 36 of the second stand's motor. The speed of the rolls 2 is thus adjusted, either until the current in armature 31 is restored to its original value, when the strip between the rolls will experience neither tension nor compression, or until this strip is loaded by a predetermined amount which is obtained by biasing the store 40 by a device 41; alternatively, the comparator 42 may have a predetermined zone of insensitivity. Contacts 7<SP>11</SP> re-open when the desired condition is reached. The arrangement may be applied to any number of successive stands, e.g. third rolls would be controlled by the current in armature 32. The switches 6 and 7 are spaced to avoid operation while the armature currents are unstable. The overall speed of the mill is varied by altering the voltage on bus-bars 33, 34, and the speed of each motor may be kept at the set value by tacho-generator feedback, in which case the output of comparator 42 would adjust a reference voltage. It is stated that the speed of a number of loaded stands may be further adjusted by a subsequent stand; e.g. prescribed current differentials may be established.