Apparatus and method for combined deskewing and side registering

A combination sheet deskew and side registration apparatus for deskewing and side-registering a sheet having an initial skew of unknown magnitude and direction and unknown side registration along a process direction, said apparatus comprising:

• selectably controllable drive means for driving sheets in the process direction;
• initial skew sensing means for detecting the initial random skew of sheets entering the apparatus;
• side edge sensing means, removed from said initial skew sensing means, for sensing a side edge of a sheet;
• and
• control means for selectably controlling said drive means for driving said sheet differentially and non-differentially, said control means controlling said drive means for differential driving first in response to initial sensing by said initial skew sensing means to remove initial skew and induce alignment skew, and later in response to subsequent sensing by said side edge sensing means to remove alignment skew.

A method of combined sheet deskew and side registration comprising the ordered steps of:

• feeding in a process direction a sheet with an initial random skew of unknown magnitude and direction into engagement with a sheet driver including at least two spaced apart independently controllable sheet drivers for selectively providing differential and non-differential driving of said sheet;
• driving said sheet non-differentially in only said process direction with said sheet driver until said sheet reaches an initial skew sensing means including spaced apart first and second sheet sensors;
• measuring said initial random skew of said sheet with said initial skew sensing means;
• driving said sheet differentially with said sheet driver to both compensate for said initial random skew and induce a known alignment skew of a fixed magnitude and direction;
• driving said sheet non-differentially in only said process direction with said sheet driver until said sheet reaches side edge sensing means including a third sheet sensor removed from said initial skew sensing means;
• driving said sheet differentially with said sheet driver to compensate for said alignment skew so that said sheet is deskewed and side registered to a lateral position transverse to said process direction;
• and
• driving said sheet non-differentially in said process direction with said sheet driver.

A method of combined sheet deskew and side registration in a deskewing and side registration arrangement, including a sheet path;

• two spaced apart sheet drivers, each sheet driver differentially drivable by one of first and second sheet driver motors, said sheet driver motors controllably driven by a controller delivering control pulses to said sheet driver motors;
• and first, second and third sensors, said first and second sensors comprising an initial sheet skew detector, and said third sheet sensor comprising a sheet side edge detector;
• the method comprising the ordered steps of:
• advancing a sheet non-differentially along said sheet path with said sheet drivers;
• detecting the lead edge of said sheet with one of said first and second sensors;
• counting control pulses from said controller until said lead edge is detected by said other of said first and second sensor to derive an initial skew sheet skew measurement of direction and magnitude measured in control pulses;
• advancing said sheet along said sheet path with said sheet drivers differentially by delivering a differential number of control pulses to said first and second sheet driver motors, said differential number equal to the initial skew measurement plus the number of control pulses required to skew the sheet to a selected alignment skew;
• advancing the sheet non-differentially along the sheet path with said sheet drivers, maintaining said alignment skew until said third sensor, removed from said first and second sensors, detects the sheet side edge;
• advancing said sheet differentially along the sheet path with said sheet drivers by delivering a differential number of control pulses to said first and second sheet driver motors, said differential number equal to the the number of control pulses required to deskew the sheet from the selected alignment skew;
• advancing a sheet non-differentially along said sheet path with said sheet drivers.