Positioning Error
Sheet positioning error refers to the misalignment of the paper edge relative to the mechanical clamps of a printing press or die cutter. A gripper margin deviation occurs when the sheet travels too far into the gripper mechanism or stops before reaching the front lay guides. This variance shifts the margin area where the sheet is gripped, causing the printed image to be positioned incorrectly on the stock.
Accurate adjustment of the feeder timing ensures that every sheet rests consistently against the front stops before the grippers close.
Feed Adjustment
Mechanical wear on the feed board or incorrect suction timing on the delivery head can disrupt the uniform flow of paperboard sheets. If the suckers release the sheet too early, it can rebound from the front guides, which produces a varying gripper margin. Vacuum pressure must be monitored closely to ensure the sheet is transferred securely to the swinging gripper.
Static electricity can also cause sheets to stick together, which delays their arrival at the front guides and results in a shortened gripper margin.
Layout Impact
Inconsistent sheet margins complicate subsequent converting steps like blanking and folding. If the printed image is out of register with the die-cut lines, the final packages will show uneven margins or unprinted borders. Monitoring the sheet lay during the run prevents these alignment failures from ruining whole pallets of printed stock.
