Method and apparatus for deskewing and side registering a sheet

An apparatus for deskewing and side registering a sheet having an unknown magnitude of side-to-side misregistration and an unknown initial angle of skew comprising:

• selectably controllable drive means for driving the sheet in a process direction;
• control means for selectably controlling said drive means to drive the sheet either differentially or non-differentially, said control means controlling said drive means to drive the sheet differentially to compensate for the magnitude of side-to-side misregistration and thereby induce a registration angle of skew, and further, to drive the sheet differentially to compensate for an absolute angle of skew which is defined by the sum of the initial angle of skew and the registration angle of skew;
• initial skew sensing means for measuring the initial angle of skew;
• registration skew sensing means for measuring the registration angle of skew;
• and
• means for summing the initial angle of skew and the registration angle of skew so as to determine the absolute angle of skew.

A method of registering a sheet comprising the steps of:

• driving a sheet non-differentially in a process direction;
• measuring an initial angle of skew of the sheet;
• driving the sheet differentially to induce a registration angle of skew;
• measuring the registration angle of skew of the sheet;
• summing the initial angle of skew and the registration angle of skew to determine an absolute angle of skew of the sheet;
• and
• driving the sheet differentially to compensate for the absolute angle of skew so as to register one side edge of the sheet.

An apparatus for registering a sheet comprising:

• drive means for driving the sheet in a process direction;
• control means for selectably controlling said drive means to drive the sheet either differentially or non-differentially, said control means controlling said drive means to drive the sheet differentially to induce a registration angle of skew;
• means for measuring an initial angle of sheet skew;
• means for measuring the registration angle of sheet skew;
• and
• means for summing the initial angle of sheet skew and the registration angle of sheet skew to determine an absolute angle of sheet skew, said control means driving the sheet differentially to compensate for the absolute angle of sheet skew.