Patent GB-541176-A (GB)
Title: Improvements in or relating to flying shears for cutting metal sheets
IPC: B23D36/00
Filed: 1940-02-12
Abstract: 541,176. Automatic control systems. THOMAS & CO., Ltd., R., and GRANT, W. K. Feb. 12, 1940, No. 2628. [Class 38 (iv)] [Also in Group XXII] Constantly driven flying shears for cutting up strip have the speed of the strip varied by controlling the speeds of the motors driving the trim shear, feed rollers, and levellers (group motors) to increase the range of lengths cut at the bottom end of the range. For example a shear that by means of a known gear box 55, Fig. 1A cuts length from 42 inch to 21 ft. in increments of fractions of an inch has the range extended below 42 in. down to a few inches by controlling the speeds of the group motors by a Ward-Leonard control. In cutting the longer lengths the rheostat controlling the flying shear motor 16 is ganged with the rheostats controlling the group motors but in cutting the shorter lengths the ganged rheostat for the motor 16 is out of circuit and replaced by a rheostat with control independent of the group motors control. The motor 16 is run at a speed e.g. 1200 revs. per min. corresponding to the maximum cutting speed e.g. 300 ft. per min. of the flying shears and the gear box 55 is set for its maximum length of cut of 42 inch. If now a length of cut of 14 inch is desired the speed of the group motors is reduced to feed the strip at 100 ft. per min. and the speed of the leveller motor 12 e.g. 400 r.p.m. is transmitted by chain 6 and gears 7 to the shaft 39 of a differential gear 4. The motor 16 is coupled by a chain 29 to a positive infinitely variable gear 13 that may be set by distant control from the operator's bench 8 so that the speed of the output shaft 18 is also 400 r.p.m. and in the opposite direction to that of the shaft 39. Should there be any small error in the setting the casing of the differential will rotate in one direction or other driving by a chain 20 a magnetic clutch 23 transmitting (when excited) to a rheostat 22 controlling the motor 16. Limit switches on the rheostat cut out the clutch coils when the limit of adjustment in either direction is reached. A friction driven limit switch 24 operated by the chain 20 puts the correct rheostat limit switch in series with the coil, that operates the contacts for the clutch coils, according to the direction of rotation of the casing 4. The motor 5 that controls the variable gear 13 actuates also limit switches 45, 46 that control forward and reverse rotation of the motor. In a second form the mechanical connection between the motor 12 and the differential gear is replaced by an electrical link an A.C. generator on the motor shaft being connected to a synchronous motor driving the differential gears. In a third form the differential gear is dispensed with, A.C. generators driven by the motor 12 and the variable gear are connected to the stator and rotor respectively of a synchronous motor controlling the rheostat 22. The motor then rotates at a speed equal to the difference on the speeds of the two generators. In a fourth form a synchronous motor on which both motor and " stator " rotate is employed.