Web gap control for corrugator

A web gap control for a corrugator which processes a moving web into box blanks including a shear for severing the moving web into leading and trailing portions and a cut-off machine for cutting the web into box blanks, comprising:

• means for generating a first speed signal representative of the speed of the leading portion of the severed web,
• means for generating a second speed signal representative of the speed of the trailing portion of the severed web,
• means for generating a gap signal representative of the size of the gap between said leading and trailing portions of said severed web based on the difference between said first and second speed signals, and
• means for varying the speed of the leading portion of said severed web in response to said gap signal so that the gap between said leading and trailing portions of said severed web is maintained below an upper limit beyond which bumping occurs at the stacker conveyor.

A method of imbricating box blanks delivered successively onto a stacker conveyor, wherein a moving web is severed into leading and trailing portions and the box blanks are cut from the leading and trailing web portions, so that the box blanks cut from the trailing portion of the severed web do not disturb those cut from the leading portion of the severed web on the stacker conveyor, comprising:

• detecting the trailing edge of a first box blank at a first position relative to the stacker conveyor,
• detecting the leading edge of a second box blank at a second position relative to the stacker conveyor,
• said first and second positions being spaced apart by a preselected distance based on the desired shingle ratio for box blanks on said stacker conveyor,
• stopping the stacker conveyor when the trailing edge of said first box blank has been detected at said first position but the leading edge of said second box blank has not been detected at said second position, and
• re-starting the stacker conveyor when the leading edge of said second box blank is detected at said second position.

A web gap control for a corrugator which processes moving web into box blanks including a shear for severing the moving web into leading and trailing portions, a cut-off for cutting the leading and trailing web portions into box blanks, and a stacker conveyor for transporting the box blanks in shingled relation, comprising:

• means for generating a first web travel signal representative of the distance traveled by the trailing edge of said leading portion of said severed web,
• means for generating a second web travel signal representative of the distance traveled by the leading edge of said trailing portion of said severed web,
• means for causing said stacker conveyor to stop when the difference between said first and second web travel signals exceeds an upper limit beyond which a first box blank cut from the trailing web portion disturbs a second box blank cut from the leading web portion at the stacker conveyor, and
• means for re-starting said stacker conveyor when said difference between said first and second web travel signals falls below said upper limit.

A web gap control for a corrugator which processes moving web into box blanks including a shear for severing the web into leading and trailing portions, a cut-off for cutting the leading and trailing web portions into box blanks, and a stacker conveyor for transporting the box blanks in shingled relation, comprising:

• trailing edge detector means for detecting the trailing edge of a first box blank at a first position relative to said stacker conveyor,
• leading edge detector means for detecting the leading edge of a second box blank at a second position relative to said stacker conveyor,
• said second position being spaced apart from said first position by a preselected distance based on the shingling ratio of blanks on said stacker conveyor,
• means for stopping said stacker conveyor when the trailing edge of said first box blank is detected at said first position but the leading edge of said second box blank is not detected at said second position, and
• means for re-starting said stacker conveyor after the trailing edge of said first box blank has been detected at said first position and the leading edge of said second box blank is detected at said second position.