| CPC B41J 11/0095 (2013.01) [B41J 2/0057 (2013.01); B41J 13/223 (2013.01); B41J 2203/01 (2020.08)] | 20 Claims |
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1. A digital printing system, comprising:
an intermediate transfer member (ITM), including a flexible belt, the ITM being operable to have an ink image formed on a surface thereof;
an impression station configured to transfer the ink image from the surface of the ITM to a substrate, the impression station comprising:
a rotatable impression cylinder having an impression cylinder gap housing one or more grippers operable to grasp and hold a gripper edge of the substrate, being a leading edge of the substrate as it passes through the digital printing system, for conveying the substrate along an axis of rotation of the rotatable impression cylinder during the transfer of the ink image, wherein a trailing end of the gripper edge separates between the gripper edge and a remaining portion of the substrate and coincides with a gripper bottom line of the grippers, and wherein a leading end of the gripper edge is opposite the trailing end of the gripper edge; and
a rotatable pressure cylinder operative to rotate synchronously with the rotatable impression cylinder and in an opposing direction thereto to enable the transfer of the ink image as the surface of the ITM on which the ink image has been formed passes between the rotatable pressure cylinder and the rotatable impression cylinder; and
an image quality control system comprising:
an imaging device operable, during advancement of the substrate on the rotating impression cylinder, to capture a digital image including a region of interest (ROI) that is associated with at least a portion of the one or more grippers and at least a portion of the substrate, a top edge of the ROI being associated with the at least a portion of the one or more grippers and at least a portion of the gripper edge, and a bottom edge of the ROI being associated with at least a portion of the remaining portion of the substrate; and
a controller configured to:
determine a dark-bright transition point for each column of pixels of a plurality of distinct columns of pixels in the ROI, giving rise to dark-bright transition points for the plurality of distinct columns of pixels, wherein each column of pixels of the plurality of distinct columns of pixels extends from a top end of the top edge of the ROI to a bottom end of the bottom edge of the ROI;
determine the leading end of the gripper edge by fitting the dark-bright transition points to a gripper edge model;
subsequently determine the gripper bottom line of the grippers by fitting the dark-bright transition points that are more than a threshold number of pixels from the leading end of the gripper edge, being secondary dark-bright transition points, to a grippers model;
compare the leading end of the gripper edge to the gripper bottom line of the grippers;
determine, based on the compare, that at least one criterion of one or more criteria that are indicative of a proper relation between the leading end of the gripper edge and the gripper bottom line of the grippers is not met, being indicative of an error in a position of the substrate relative to the grippers; and
perform one or more actions, based on determining that the at least one criterion is not met.
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