Improvements in and relating to automatic electric control systems for rotary shears

摘要

426,236. Rolling-mill plant. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. June 8, 1934, No. 17046. Convention date, June 8, 1933. [Class 83 (iv)] [See also Group XXXVII] An electrically driven machine operating upon strip material, such for example, as a rotary shear for cutting lengths from bars of metal, comprises means responsive to the position of the end of the material with reference to the operative element, for example, the shear blades, to cause temporary variation in the speed of the machine to change the relative position so that the first and every piece cut off shall be of the same length. Shear blades 16, 17 are driven by a motor 10, the speed of which is varied as described by changing the strength of the field 98. The last finishing stand 22 and pinch rolls 25 are driven at equal speeds by the aid of a variable field resistance 49 and tachometer comparison means 46; the ratio between this speed and the speed of the shear is adjusted to determine the length of cut by a variable gear 26 between the pinch rolls and the shear motor 10. The relative angular positions of the shear motor 10 and the motor 23 driving the finishing rolls are compared by a differential receiving device 78 comprising a three phase rotor in a three phase stator. The rotor of this device is energized from the three phase stator of a position sending device 76 coupled to the shear motor 10 and having a single phase rotor energized from a source 72 ; the stator is energized from the three phase stator of a position determining device 55 having a three phase rotor excited from a stationary device 70 similar to the device 76. The rotor of the device 55 is held by electromagnetic means 56 in a definite position so long as there is no strip material under treatment. Material entering operates a flag switch 86 and a relay 90 is thereby operated to de-energize the electromagnetic means 56 and to energize a clutch 60 coupling the rotor of the position determining device 55 to the motor 23 to drive it at the speed of the shear. This drive is attained through variable-speed gearing 63 assisted by comparison means 80, 82 and pointer 84 which is stationary when the speed is correctly adjusted. If at the moment of presentation of the end of the material to the flag switch the shear blades are in correct position to cut the desired length from the strip the single phase rotor of a device 125 is held by the device 78 in non-inducing relationship to its single phase stator ; a disagreement in the relative positions of the strip and the shear blades will cause the device 125 to generate a single phase E.M.F. proportional to the difference and this is applied through the transformer 123 to the grids of valves 112, 118 so that, according to Specification 251,301, [Class 38 (ii)], one or other is rendered conducting to an extent depending on the sense and degree of the positional disagreement. Thus oppositely wound fields of a generator 102 are selectively excited and the field of the shear motor 10 varied to change the speed of the shear in such a manner that normal speed is resumed when positional agreement has been attained. When the strip leaves the flag switch the relay 90 is de-energized and operates after a time delay to de-energize the clutch 60 and valve circuits and to energize the means 56 by which the position determining device is held in its original position. An adjustment of the correcting means is obtained by manual rotation of the rotor of the device 70. In a modification adapted for use when the distance between the finishing rolls and the shear is insufficient to give the necessary time for correction, the last finishing stand and the shear are driven by the motor 10, and rolls at sufficient distance from the shear are driven by the motor 23. The current rise in the motor 23 as the strip is introduced actuates a relay controlling the relay 90 and a separate time delay opening relay arranged in the circuit of the latter. The variable speed coupling between the motor 23 and the elements 60 and 82 is constituted by a dynamo on the shaft of the motor 23 and a variable field motor driving the elements referred to.