Patent ID: 6336701
Filing Date: 2002-01-08
Classification: B41J

Abstract:
A method for placing ink drops from a plurality of scanning ink-jet printheads onto a print medium in an ink-jet hard copy apparatus, wherein the print medium is transported along a media advance axis perpendicular to a printhead scanning axis, the printheads mounted for scanning the medium along a scanning axis and each printhead having a plurality of ink drop firing nozzles arranged as at least one column of nozzles parallel to the print medium advance axis having a predetermined nozzle packing density, a known relative alignment error between printheads, and a known nozzle spacing, and the print medium having a printing surface defined as a matrix of pixels arranged as adjacent horizontal rows and vertical columns at a resolution in the media advance axis greater than the nozzle packing density, the apparatus having a means for tracking real-time position of the printheads during scanning, the method comprising:a) providing the plurality of printheads wherein at least two printheads are provided for each colorant selectively simultaneous addressing both odd and even print rows and wherein pen-to-pen spacing is not required as an integer multiple of nozzle spacing distance; b) during a first scan of the printheads across the print medium wherein the nozzles have a real-time known positional relationship to the matrix, scan printing a first swath of columns of dots of each colorant in rows of the matrix by firing ink drop nozzles at target pixels using printhead nozzles of each of the at least two printheads of a same colorant wherein nozzles fired for each row are logically selected with respect to the known relative alignment error; c) advancing the medium in the print medium advance axis a distance in accordance with the equation d=(m*S)+S/n, whered=microstep advance distance, less than or equal to the nozzle overlap distance between printheads, m=a value of zero or any integer, S=nozzle spacing, n=an integer greater than one; d) determining a new positional relationship of the nozzles to the matrix; e) during a second scan of the printheads across the print medium, scan printing the swath of columns of dots of each colorant in rows of the matrix by firing ink drop nozzles at target pixels using printhead nozzles of each of the at least two printheads of a same colorant wherein nozzles in the new positional relationship fired for each row are logically selected with respect to the known relative alignment error; and f) repeating the advancing the medium in the print medium advance axis a distance according to the equation in step c) between each scan printing of the swath until each horizontal row of target pixels has been addressed at least once.