Cut off apparatus for cutting off corrugated fiberboard web

A cut off apparatus for cutting off a corrugated fiberboard web, said apparatus comprising:

• a preceding knife cylinder having, on a peripheral surface thereof, a preceding helical knife;
• a following knife cylinder having, on a peripheral surface thereof, a following helical knife for cutting off the corrugated fiberboard web in cooperation with the preceding knife;
• a preceding gear attached at one of axially opposite ends of the preceding knife cylinder;
• a following gear attached at one of axially opposite ends of the following knife cylinder;
• a preceding drive gear which has a meshing engagement with said preceding gear;
• a following drive gear which has a meshing engagement with said following gear;
• a preceding knife driving motor for rotationally driving said preceding drive gear;
• a following knife driving motor for rotationally driving said following drive gear, said following knife driving motor having the same rated capacity as that of said preceding knife driving motor;
• and
• a cut off control device for individually controlling said preceding knife driving motor and said following knife driving motor;
• said control device comprising:
• a speed pattern generator, to which a feeding speed of the corrugated fiberboard web and a sheet length to be cut off is to be input, for generating rotational speed patterns of the preceding knife driving motor and the following knife driving motor based on the input feeding speed and the input sheet length to be cut off and for outputting a speed instruction value;
• a comparator for comparing the speed instruction value from said speed pattern generator with a detected speed of the preceding knife driving motor or the following knife driving motor;
• an instruction torque computing unit for computing rotational torque instruction values for the preceding knife driving motor and the following knife driving motor based on a signal from said comparator;
• a cutting torque computing unit for computing cutting torque of the preceding knife driving motor and the following knife driving motor;
• a to-be-given torque pattern generator for distributing the cutting torque sent from said cutting torque computing unit, generating a to-be-given torque pattern based on the feeding speed of the corrugated fiberboard web and the sheet length to be cut off, and outputting a to-be-given torque instruction value;
• an instruction torque subtractor unit for subtracting the to-be-given torque instruction value, output from said to-be-given torque pattern generator, from the rotational torque instruction value computed by said instruction torque computing unit;
• a preceding power amplifier for controlling the preceding knife driving motor based on a computation result obtained by said instruction torque subtractor;
• an instruction torque adder for adding the rotational torque instruction value, computed by said instruction torque computing unit, to the to-be-given torque instruction value computed by said to-be-given torque pattern generator;
• and
• a following power amplifier for controlling the following knife driving motor based on a computation result obtained by said instruction torque adder.