Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-05-17
2001-05-08
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S132000, C347S234000, C358S448000
Reexamination Certificate
active
06229555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic machine, and, more particularly, to a method and apparatus for minimizing visual artifacts resulting from laser scan process direction position errors.
2. Description of the Related Art
In an in-line color electrophotographic imaging process, latent images are formed on a plurality of photosensitive drums, which are in turn developed using a predetermined color of toner. The developed images are then transferred to a sheet of media (such as paper) which travels past the drums. The image in each color is created one line at a time, and the lines are oriented at right angles to the direction of travel of the sheet of media. The individually-generated images combine to form a full-color image. In a typical multi-color laser printer, for example, the sheet of media passes through four color developing stations in series, with the colors being black, magenta, cyan and yellow.
It is recognized that in order for the multi-color laser printer to print accurately, the laser beams for all four colors must be in alignment, both in the scan direction (across the page) and the process direction (feed direction of the print medium). However, providing proper alignment of even a single laser printhead in relation to the sheet of media in the process direction can be difficult. This problem is compounded with the addition each printhead, since the plurality of printheads must be in registration so that the individual images generated by each printhead can be superimposed correctly when combined. During printer assembly an attempt is made to optically align the laser printheads both individually and collectively, but the ability to provide precise alignment is limited by several factors, including component tolerances. In addition, it is possible for a precisely aligned printing system to drift out of alignment due to component aging and/or the influences of printing environment factors, such as the internal temperature changes of the printer that cause distortion of the laser beam optical scan path.
What is needed in the art is a method and apparatus for minimizing visual artifacts resulting from laser scan process direction position errors, such as printhead skew and laser beam optical scan path distortion.
SUMMARY OF THE INVENTION
The present invention provides method and apparatus for minimizing visual artifacts resulting from laser scan process direction position errors, such as printhead skew and laser beam optical scan path distortion.
One aspect of the invention relates to an electrophotographic machine having defined therein a process direction. The electrophotographic machine includes a photoconductive device having an image forming surface, a printhead unit, and a controller. The printhead unit generates a laser beam, and includes optics for scanning the laser beam to form a plurality of scan lines extending across the photoconductive device in a scan direction which traverses the process direction. Adjacent scan lines of the plurality of scan lines are separated by a scan line separation distance. The controller is electrically coupled to the printhead unit for controlling the power of the laser beam during the scanning of an adjacent pair of scan lines to form a synthesized dot having a center which lies at a synthesized position between the adjacent pair of scan lines.
One method of the invention is directed to minimizing visual artifacts resulting from laser scan process direction position errors in an electrophotographic machine, wherein the electrophotographic machine includes a photoconductive device having an image forming surface. The method includes the steps of defining with respect to the surface of the photoconductive device a plurality of pixel locations which form a pixel grid; generating a laser beam; scanning the laser beam to form a plurality of scan lines extending across the photoconductive device in a scan direction which traverses the process direction, wherein adjacent scan lines of the plurality of scan lines are separated by a scan line separation distance; and controlling the power of the laser beam during the scanning of an adjacent pair of scan lines to form a synthesized dot which lies at a synthesized position between the adjacent pair of scan lines, and wherein the synthesized position substantially corresponds to one pixel location of the plurality of pixel locations.
An advantage of the present invention is that the scan path of the laser beams of a multicolor electrophotographic machine can be corrected for printhead skew and optical scan path distortion, both during and after an initial printhead alignment.
Another advantage of the invention is the ability to synthesize the position of dot formation on the photoconductive drum in the process direction.
REFERENCES:
patent: 5719680 (1998-02-01), Yoshida et al.
patent: 4-317254 (1992-11-01), None
patent: 8-184772 (1996-07-01), None
patent: 11-352744 (1999-12-01), None
Hadady Craig Eric
Ravitz Cary Patterson
Lexmark International Inc.
Pendegrass Joan
Sanderson Michael T.
Taylor & Aust P.C.
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