Patent ID: 7748708
Filing Date: 2010-07-06
Classification: B65H

Abstract:
1. A method of aligning a sheet in a printing device in process, lateral and skew directions, comprising: receiving a sheet by a device comprising a plurality of drive rolls, wherein each drive roll has a velocity; selecting a first reference frame fixed with the drive rolls and a corresponding reference state vector for the sheet, wherein the reference state vector for the sheet comprises coordinates of a point on the sheet, an angle of the sheet, and angular velocities of the drive rolls; identifying a desired trajectory for the sheet with respect to the first reference frame; identifying a cart comprising the drive rolls and a virtual body having dimensions relating to the drive rolls, wherein the sheet serves as a surface on which the cart rides, wherein a direct relationship exists between the motion of the cart with respect to the sheet and the motion of the sheet with respect to the drive rolls; selecting a second reference frame fixed with the sheet and a corresponding reference state vector for the cart, wherein the reference state vector for the cart comprises coordinates of a point on the cart, an angle of the cart, and angular velocities of the drive rolls; determining a desired cart trajectory based on the desired trajectory for the sheet and the second reference frame; adjusting the velocity of at least one drive roll based on the reference state vector for the cart and the desired cart trajectory; and repeating the determining and adjusting a plurality of times so that the sheet tracks the desired trajectory for the sheet.