Patent GB-772021-A (GB)
Title: Improvements in and relating to control systems for electric motors
IPC: B21B37/54
Filed: 1954-07-26
Abstract: 772,021. Control of D.C. motors. IGRANIC ELECTRIC CO., Lt.d. July 26, 1954 [July 27, 1953], No. 21744/54. Class 38(3) A length of material such as a strip of steel passes through mill work rolls 11, 12 and is coiled on a reel 13, the rolls being driven by a direct-current motor 14 which is supplied from generator 17. The windup reel is driven by a direct-current motor 19 having a field winding 19a and being supplied from generator 21. An exciter 23 acts as a current regulator for the motor 19 and its output is adapted to vary the excitation of winding 19a by opposing the voltage of source 15- A rectifier 24 limits the bucking-action of the exciter 23 which has a reference field winding 27 and an opposing signal field winding 29 energized in accordance with the armature current of the motor 19. When the strip is advancing at a steady speed, the motor 19 is thus regulated to provide constant horsepower output and strip-tension is kept at a steady value. In order to maintain the tension constant during accelerating periods of the motor 14, means are provided to increase the torque of the motor 19 to overcome the inertia of the reel 13 and that of the armature of the reel motor. The output of the exciter 23 is therefore suitably modified in relation to the rate of change of speed of motor 14 and the change in diameter of the coil on reel 13. For this purpose, sections 31a, 31b. of an inertia-compensating winding 31 of the exciter 23 are supplied from generators 35, 38, driven by motors 41, 42, the generators having field windings 45, 47, which are energized by exciters 43, 44, also driven by the motors. The field windings 49, 50, of the exciters 43, 44, are energized, in accordance with the rate-ofchange of speed of the motor 14, through tachometer generator 57, transformer 58, and an amplifier 59 of the type described in Specification 684,881. A potentiometer 54 provides a voltage dependent upon the diameter of the coil, such voltage being applied across the field winding 51 of motor 41 and across the armature of motor 42 so that the speed of the motor 41 is inversely proportional to the coil diameter, whilst the speed of the motor 42 is directly proportional thereto. The input to the winding 31a is thus proportional to the rate-of-change of speed of the motor 14 as well as being inversely proportional to the square of the coil diameter, and is arranged to effect a recalibration of the regulator to compensate for the fixed inertia of the motor 13 and other parts of the machinery. The winding 31b however, is excited in accordance with the square of the coil diameter and the strip acceleration and affords compensation for the changing inertia of the coil with increase in diameter. Rheostats 36, 39 are adjustable to compensate for changes in the width of the strip material 10. In a modification. Fig. 2 (not shown) the system comprises rheostats the resistances of which are complementally former, as described in Specification 684,882, so that for any positioning of the adjusting slide wires the equivalent resistance of each rheostat set in the circuit will be constant. For correct inertia compensation, it is necessary to deduct from the inertia of the fixed parts, the inertia of a solid disc of diameter equal to that of the empty reel and a thickness equal to the width of the strip. This deduction is effected by means of potentiometer rheostat 36.