Patent GB-824173-A (GB)
Title: Improvements in control systems for electric reel motors
IPC: B21B37/54
Filed: 1956-01-26
Abstract: 824,173. Control of D.C. motors. IGRANIC ELECTRIC CO. Ltd. Jan. 26, 1956 [Feb. 7, 1955], No. 2600/56. Class 38 (3). In a system for controlling a reel motor 19 similar to that described in Specification 772,021, the inertia-compensating field winding 31 of the exciter 23 is supplied from magnetic amplifying means of the push-pull type comprising a pre-amplifier stage 63, an intermediate power stage 50 and a compensating stage 36. A voltage proportional to the speed of the mill motor 14 is developed by tachometer generator 78 so that a potential varying in accordance with the rate of change of strip speed is applied to the input control windings of amplifier 63 through resistor 77 and capacitor 79. When the motor 14 is accelerating, a voltage appears across terminals 64, 65, whereby an output voltage appears across terminals 51, 52 of amplifier 50 to which the input terminals 43, 44 of amplifier 36 will be subjected. Thus the section 31a of the inertia-compensating winding is energized. When the motor reaches a steady speed, the amplifiers 63, 50 and 36 are turned off due to the blocking action of the capacitor 79. Deceleration of the motor 14 reverses the current in the input control windings of the amplifier 63 so that an output voltage is developed across terminals 65, 66, and section 31b is energized. Ballast resistors 48, 49 are connected between the common and other two input terminals of the compensating stage, and the intermediate power stage comprises rheostats 61, 62 for adjusting the negative feedback in each push-pull section. The pushpull section 36a of the amplifier 36 comprises A.C. power windings 82, 85 supplied from transformer 80 and connected through resistors and rectifiers to the field winding section 31a. Amplifier section 36a is also provided with input control winding sections 93a, 93b connected in series with winding sections 95a, 95b of amplifier section 36b across terminals 43, 45. Bias feed-back windings 98a, 98b oppose windings 93a, 93b and are connected to a source 46, 47 of direct-current, the ampere-turns developed in windings 98a, 98b, being dependent upon the setting of adjustable resistor 97, the voltage across output terminals 35, 40 and the value of resistor 96. The construction of amplifier section 36b is similar to that of the section 36a. In addition, the amplifier 36 is provided with control winding sections 105a, 105b and 106a, 106b which are adapted to compensate for the changes in inertia of the reel as material is being wound thereon. For this purpose these winding sections are connected between slides 108a, 111a of ganged rheostats 108, 111, forming part of a compound rheostat set additionally including a rheostat 112 having its resistance element connected across lines 114, 115, which are subjected to a voltage proportional to the rate of change of strip speed. The sliders of rheostats 108, 111, 112 are mechanically coupled to an arm 122 so that the sliders are moved in unison as the coiling on reel 13 progresses. Assuming the slider of rheostat 108 to be uncoupled from those of rheostats 111, 112, then the latter will provide a voltage at the output of amplifier 36 which varies inversely with the reel diameter. The resistance elements of these rheostats are so arranged that concurrent adjustment of the sliders results in a predetermined pattern of potential variation across windings 105a-106b which causes the output of amplifier 36 to be modified in such a manner that the exciter 23 compensates for the fixed inertia of the reel and associated driving apparatus, and the continuously changing inerta effect of the strip coiled on the reel. The rheostat set 116, 117, provides for adjustment of the pattern of potential variation for different strip widths or for different weights per unit area of the strip material. Rheostat 120 has a slider adjusted in common with the sliders of rheostats 116, 117, and is so formed that there is no change of load resistance across conductors 114, 115, caused by any adjustments of the rheostats 116, 117, 120. The compound rheostat set comprising rheostats 111, 112, is also preferably of the type described in Specification 684,882. Assuming rheostats 116, 117, 120 to be set in their extreme clockwise positions and rheostats 111, 112 in their extreme counter-clockwise positions, then the rheostat 108 would provide an output voltage tor the amplifier 36 which varies with the reel diameter. An impulse transformer may be substituted for capacitor 79. In a modification the tachometer generator, field winding 31, and the magnetic amplifiers are replaced by apparatus connected to bus-bars subjected to a voltage selected in accordance with the average rates of acceleration and deceleration of the mill motor, Fig. 4 (not shown), a reversing switch being changed over in accordance with the acceleration or deceleration of the motor. Exciter 23 has two inertia compensating windings each connected in series with compound rheostats adjusted in accordance with the reel diameter, and a further rheostat set compensates for the width and weight per unit area of the strip being coiled.