Patent GB-708716-A (GB)
Title: Improvements in or relating to machines for acting at spaced points on strip material
Inventor: NICHOLSON GEORGE GALLOWAY
IPC: B23D36/00
Filed: 1950-07-25
Abstract: 708,716. Control of D.C. motors. DAVY & UNITED ENGINEERING CO., Ltd. June 20, 1951 [July 25, 1950], No. 18554/50. Class 38(3) In a control system for acting at spaced points on a continuously running strip of material by means of a tool arranged to undergo cyclic movements, the time period of each movement and the intervals between the movements are both functions of the velocity of the strip. In a shearing machine, Fig. 1, shear elements 1, 2 are geared together at 5 and rotated at equal speeds in opposite directions by an electric motor 6 so as to act on opposite faces of, and cut repeatedly, a running length of strip material S emerging from a rolling-mill M. The positions of the cuts are controlled by adjustable electronic timing relays 51. 52, 53, 54 utilizing a " bootstrap" circuit as in Fig. 2 (not shown), and producing delays inversely proportional to voltage applied. This voltage is obtained from a tachometer generator 166 driven at a speed corresponding to the speed of the strip so that the lengths cut are substantially independent of strip speed. On starting up, the beginning of the strip approaching the machine closes contacts 50a by means of a photocell or mechanical switch 50 and starts timing relay 51 which after an interval corresponding to a predetermined movement of the strip energizes a relay 17 to start shear motor 6. Motor 6 is supplied from a constant speed DC. generator 13 the field winding 13a of which is energized by an amplifying exciter 15. When relay 17 operates to start the motor, a field winding 15b of exciter 15 is energized in accordance with the difference between the voltage of generator 13 and the voltage obtained through a potentiometer 18 from a second tachometer generator 16a also driven at a speed corresponding to the speed of the strip. Motor 6 thus accelerates up to the speed, corresponding to the speed of the strip, at which the cut takes place. During acceleration the armature current of motor 6 is limited to a value corresponding to the speed of the strip by the energization of an exciter field winding 15c in opposition to field winding 15b when the voltage across a resistor 20 exceeds that obtained through a potentiometer 21 from tachometer generator 16b. Rectifiers 22, 23 ensure such current limitation during acceleration or deceleration so that the time of each is independent of strip speed. When motor 6 starts, switches 7 are closed by the shear and contact 7b starts timing relay 54 which, ultimately, initiates deceleration by deenergizing a relay 19 to reduce the voltage from potentiometer 18. After 330 degrees rotation of the shear, switches 7 are opened and contact 7a deenergizes relay 17 to stop motor 6 by connecting exciter field 15b across its armature. Timing relay 51 remains energized during the continued passage of the strip but one or other of contacts 8a, 8b is opened by switches 8 at the end of each alternate revolution of the shear and the other is closed at the beginning of the next revolution so that timing relays 52, 53 operate in turn to govern the lengths of cuts after the first.