Patent ID: 9688068
Date: 2017-06-27
CPC Classifications: B41J,H04N

Claim:
1. A method of determining line feed error in an image forming apparatus for printing an input image by overprinting multiple times on the same area of a print medium, wherein the image forming apparatus includes a print head having ink ejection nozzles within nozzle banks and a head sensor configured to sense information from the input image printed on a print medium, the method comprising: obtaining swaths by half-toning the input image, wherein each swath includes a correlatable noise pattern in a bottom area of the swath and height of the bottom area is equivalent to a line feed distance; printing a first swath of the swaths on the print medium while the print head moves across the print medium in a scan direction; repositioning the print head relative to the print medium on which the first swath is printed by at least one line feed distance in a feed direction which intersects the scan direction; and after the repositioning, sensing the bottom of the first swath on the repositioned print medium by the head sensor and determining the line feed error based upon information sensed from the printed first swath by the head sensor, between the time when the print head reaches an edge of the printed first swath in the scan direction and the time when the ink ejection nozzles start to print a second swath of the swaths, and then printing the second while the print head moves across the print medium in the scan direction, wherein the line feed error is determined from a vertical shift represented by a position of the head sensor before the repositioning, the line feed distance, and a position of the printed first swath in the feed direction, and wherein the second swath is printed on top of the printed first swath on the print medium while compensating for the determined line feed error by controlling the ejection of ink from the ink ejection nozzles within the nozzle banks of the image forming apparatus.