Adaptive control of second page printing to reduce smear in an inkjet printer

In a sheet fed inkjet printer in which liquid ink is applied to a sheet of print medium in a succession of horizontal swaths and including a print head having a plurality of vertically displaced print nozzles, sheet feeding means for advancing said sheet vertically past said print head, carriage means for slewing said print head horizontally across successive said horizontal swaths at respective vertically displaced portions of the sheet, print means for printing an image on said sheet by selectively applying dots of said ink to said sheet through selected ones of said nozzles as said print head is slewed by said carriage means, densitometer means responsive to said print means for determining a location of a densely printed area of said sheet and a density of said location, and stacking means for stacking successive sheets after said sheets have been printed, the improvement comprising:

• throughput enhancement means for reducing a time said print head is traversing across blank portions of said sheet to thereby establish a variable throughput rate determined by a sum of (a) an intra-sheet printing time between an initial positioning of the print head adjacent a top portion of the sheet before a first horizontal swath has been printed and a final positioning of the print head at a bottom portion of the sheet after a last horizontal swath has been printed and (b) an inter-sheet feeding delay equal to a second elapsed time between said final positioning. of a preceding sheet and the initial positioning of said sheet;
• and
• anti-smear means responsive to at least a density determined by said densitometer means relating to a densely printed area of said preceding sheet for determining a required delay before the print head is enabled by the throughput enhancement means to either traverse blank portions of said sheet at a higher slew rate, or skip such areas altogether, to thereby maintain said variable throughput rate below a value where the next sheet will come into contact with a densely printed area of the preceding sheet in said stacking means before the ink in said densely printed area of the preceding sheet has dried such that the preceding sheet is not subject to being smeared by such contact with said sheet.

A method for reducing smearing of an image on a first sheet by contact with a second sheet in a sheet fed printer in which liquid ink is applied to each sheet across a succession of horizontal swaths including one or more swaths having one or more printed areas and possibly also including blank lines, comprising the steps:

• locating one or more of said printed swaths of said first sheet having at least one densely printed area;
• calculating a respective delay interval following the application of said ink to said one or more swaths required for all the ink applied to said densely printed area to dry sufficiently to avoid smearing when contacted by said second sheet, said delay interval being a function of the density of said densely printed area of said first sheet;
• searching the swaths included in the second sheet for any of said blank lines, and
• causing the print head to vertically traverse across said blank lines at an enhanced throughput rate only if a leading edge of the second sheet will not be output in contact with said densely printed area of the first sheet before said delay interval has elapsed.