Patent GB-1352878-A (GB)
Title: Automatic control system for crop shear
IPC: B23D36/00
Filed: 1971-04-19
Abstract: 1352878 Controlling shears GENERAL ELECTRIC CO 19 April 1971 [16 March 1970] 21989/71 Heading B3U [Also in Division G4] A computer 49 (Fig. 3) calculates the position (x, Fig. 5, not shown) at which a motor driven rotary crop shear 19, 20 must be started to crop an approaching slab 10 at a predetermined crop  line. In the embodiment described a hot metal slab is cropped at head and tail crop lines. Initially the shear is positioned in its park position by feeding to motor 24, via switch S 4  closed by a relay R1, the difference signal from an amplifier 44 receiving at its input a reference voltage V r  and a feedback signal 46 from a park sensing potentiometer 45 driven with the crop shear by the motor, the amplifier output drop ping to zero when the shear is correctly parked. Computer 49 computes two quantities, the distance (DT, Fig. 5, not shown) of the head crop line from a fixed cut point detector 32 and the distance (DM) of the head crop line from the detector when the shear is started. When these two quantities are equal the switch S4 is opened and a switch S1 closed so that the motor 24 accelerates the shear blades until they acquire a velocity determined by the signal from a head speed sensor 26 measuring the speed of movement of the slab and fed via a speed adjustment potentiometer 41. Initially the shear is accelerated at a fixed rate until a predetermined velocity is attained when the speed limit action of a regulator 33 becomes effective to reduce the acceleration by an amount dependent on the acceleration of the slab. The potentiometer 41 is used to adjacent the ratio of the speed of the shear blade to the speed of the slab at the instant it is cut. When the slab is cropped a switch S5 is actuated resulting in relay R1 being actuated to open switch S1 and close park switch S4 so that the shear is returned to its park position. The process is then repeated for the tail crop line, the speed being sensed by a tail speed sensor 29, the output from which is fed to a second speed adjustment potentiometer 42. Computer operation.-The computer concontinuously computes the time t c  the shear blades will take to move from their parked position to their cut position in terms of the instantaneous slab velocity V o , acceleration or deceleration a o  of the slab and multiplier K o  (represented by the potentiometer position) by determining the area under the velocity curve of Fig. 4 (not shown) and equating this to the known distance d c  that the blades move. Then since the distance travelled by the slab in the time t c  is V o t c  + ¢a o t c <SP>2</SP> = D-DM where D is the known distance between the cut position and the cut point detector 32 the time at which the crop shear is started may be computed. Simultaneously the computer computes the distance DT of the crop line from the cut point detector, the movement of the shear blades being started when DM = DT. Alternatively the time required for the crop line to move from its instantaneous position to the shear may be computed and compared with the time t c , the shear being operated when the times are equal.