Print cartridge alignment in paper axis

A method for aligning an operation of printhead cartridges along a media scan axis in a swath printer having (a) a carriage that is movable along a horizontal carriage scan axis in first and second carriage scan directions, (b) independently controlled first and second ink jet printhead cartridges supported by the movable carriage for printing onto a print media that is selectively movable along a vertical media scan axis, each printhead cartridge having a plurality of ink jet nozzles arranged in alignment with the vertical axis such that the nozzles of each cartridge are spaced apart along the vertical axis, the cartridges being positioned relative to each other such that the ink jet nozzles of the first and second printhead cartridges may overlap along the vertical axis, and (c) an optical sensor supported by the movable carriage for imaging a horizontal line and providing an output indicative of a vertical position of said line within a vertical operating range of the optical sensor, the method comprising the steps of:

• (A) causing the first and second printhead cartridges to print three non-overlapping horizontal test line segments in a single carriage scan, wherein a first line segment is printed with a selected nozzle of the first printhead cartridge and wherein a second and a third line segment are printed with selected nozzles of the second printhead cartridge;
• (B) determining with the optical sensor, respective vertical positions of the horizontal test line segments;
• (C) determining a vertical distance between the first and second horizontal test line segments and the vertical distance between the second and third horizontal test line segments;
• (D) calculating a media advance mechanism compensation factor by dividing (a) a nominal distance between the selected nozzles of the second printhead by (b) the vertical distance between the second and third horizontal test line segments;
• (E) multiplying the vertical distance between the first and second test line segments by the media advance mechanism compensation factor to provide a cartridge position correction factor;
• and
• (F) adjusting an operation of the first and second printhead cartridges along the vertical by enabling selected nozzles and adjusting the position of the first and second printhead cartridges relative to each other on a basis of the position correction factor so that the enabled nozzle of the first cartridge and the enabled nozzle of the second cartridge that are closest along the vertical axis are vertically apart by substantially one nozzle pitch.

A method for aligning operation of printhead cartridges along a media scan axis in a swath printer having (a) a carriage that is movable along a horizontal carriage scan axis in first and second carriage scan directions, (b) independently controlled first and second printhead cartridges supported by the movable carriage for printing onto a print media that is selectively movable along a vertical media scan axis, each printhead cartridge having a plurality of ink jet nozzles arranged in alignment with the vertical axis such that the nozzles of each cartridge are spaced apart along the vertical axis, and (c) an optical sensor supported by the movable carriage for imaging a horizontal line and providing an output indicative of a vertical position of said line within a vertical operating range of the optical sensor, the method comprising the steps of:

• (A) causing the first and second printhead cartridges to print three non-overlapping horizontal test line segments in a single carriage scan, wherein a first line segment is printed with a selected nozzle of the first printhead cartridge and wherein a second and a third line segment are printed with selected nozzles of the second printhead cartridge;
• (B) moving the print media to a predetermined vertical start location such that the sensor is vertically displaced from all of the horizontal test line segments;
• (C) horizontally moving the carriage to horizontally align the optical sensor with a nominal center of a selected one of the horizontal test line segments;
• (D) incrementally moving the print media by a predetermined amount so that a series of vertical locations in a vertical region that includes the selected horizontal test line segment are sensed by the optical sensor, whereby the selected horizontal test line segment is scanned along the media axis relative to the optical sensor which remains stationary;
• (E) reading the optical sensor output for each of the series of vertical locations sensed by the optical sensor to produce a series of position samples for the scanned horizontal test line segment;
• (F) determining a vertical position of the scanned horizontal test line segment from the series of position samples;
• (G) performing the steps (b) through (F) for each remaining horizontal test line segment;
• (H) determining a vertical distance between the first and second horizontal test line segments and a vertical distance between the second and third horizontal test line segments;
• (I) calculating a media advance mechanism compensation factor by dividing (a) a nominal distance between the selected nozzles of the second printhead by (b) the vertical distance between the second and third horizontal test line segments;
• (J) multiplying the vertical distance between the first and second test line segments by the media advance mechanism compensation factor to provide a cartridge position correction factor;
• (L) enabling selected nozzles of each print cartridge on a basis of the cartridge position correction factor such that the enabled nozzles of each print cartridge do not overlap along the horizontal axis;
• and
• (M) adjusting positions of the first and second printhead cartridges relative to each other so that the enabled nozzle of the first cartridge and the enabled nozzle of the second cartridge that are closest along the vertical axis are vertically apart by substantially one nozzle pitch.