High precision feed particularly useful for UV ink jet printing on vinyl
An apparatus ( 30, 40, 50 ) and a method of ink jet printing are disclosed that use a system for feeding a substrate longitudinally relative to a support area and a system for moving a printhead parallel to the direction of substrate feed. Indexing between transverse scan rows of a printhead ( 20 ) is carried out initially by the substrate feed system ( 16 ) and the actual feed distance is measured using an encoder or other substrate position measurement device ( 26 ). A controller ( 25 ) determines the amount of any error that occurs between the actual and the desired feed distances. The controller ( 25 ) then sends signals to move the printhead ( 20 ) to compensate for any error in the feed system feed. Compensating adjustments are then made to the next subsequent substrate indexing step so that the printhead tends to move back toward its home or zeroed position with its next correction and does not walk away from this home position as a result of cumulative movements. For printers that have bridges ( 17 ) moveable relative to the machine frame ( 11 ) on which the printhead ( 20 ) is carried, printhead motion is achieved by moving the bridge, for example, by actuating a linear servo bridge motion system ( 31 ). For fixed bridge roll-to-roll printers, the printhead ( 20 ) can be caused to shift longitudinally on the bridge ( 17 ) to make the correcting movements.
1. An ink jet printing apparatus comprising:
a frame;
a bridge extending transversely across the frame and defining a position of a printing station relative to the frame;
a feed system configured to advance a substrate longitudinally relative to the frame through the printing station;
a printhead moveable transversely across the bridge to print a row of an image across the substrate at the printing station;
a motion system connected to the bridge and configured to move the printhead longitudinally relative to the frame;
a controller operable to activate the feed system to index the substrate longitudinally a predetermined distance through the printing station;
a web position measurement device mounted to the bridge and operable to measure, and communicate to the controller a signal corresponding to, an actual distance moved by the substrate through the printing station during the indexing of the substrate;
the controller being operable to activate the motion system, in response to the signal to move the printhead longitudinally, relative to the indexed substrate, a correction distance corresponding to the predetermined distance less the actual distance moved by the substrate during the indexing of the substrate;
the bridge having a carrier transversely moveable thereon;
the printhead being longitudinally moveable relative to the carrier;
the carrier having a motor mounted thereon and connected to the printhead, the motor being operable to move the printhead relative to the carrier along the longitudinal direction of the substrate in response to the activation of the motion system to adjust the longitudinal position thereof relative to the substrate at the printing station; and
the controller being operable to activate the motion system to operate the motor to move the printhead longitudinally relative to the bridge to thereby move the printhead longitudinally the correction distance relative to the substrate.
2. The apparatus of claim 1 wherein:
the web position measurement device includes an encoder responsive to the motion of the substrate relative thereto and operable to generate the signal corresponding to an actual distance moved by the substrate through the printing station during the indexing of the substrate.