Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-01-07
2001-12-11
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06328396
ABSTRACT:
TECHNICAL FIELD
This invention relates to inkjet printers and, in particular, to a method for reducing the time required for an inkjet printer to print a page.
BACKGROUND
Inkjet printers are well known and extremely popular. Particular inkjet printers are described, for example, in U.S. Pat. Nos. 5,648,806, 4,855,752, and 4,967,203. An inkjet printer ejects fine droplets of ink onto a print medium, principally paper, from precisely formed nozzles in one or more printheads. High quality color inkjet printers include printheads, alternatively termed pens, typically for the three subtractive primary color inks, cyan, magenta, and yellow, and a separate printhead for black ink. When printing a color image, droplets, or dots, of the three primary colors are printed in various combinations to achieve the desired color tones, or hues, to reproduce the original color image. Inkjet printers including printheads for additional color inks, for example, for seven color inks, are also known. Multiple drops of the same color may be used for a single color spot to increase the intensity of that color in the color spot.
In an inkjet printer, printing is performed as a print carriage conveying the pens is scanned across a print medium. Printing multiple drops requires multiple passes of the print carriage across the same portion of the print medium. Printing may be performed in both directions, that is as the print carriage sweeps from left to right across the medium and as it sweeps from right to left. The data to be printed on a page is typically partitioned into regions based on the nature of the content of each region. A distinct printmode, or collection of printing techniques, is used to optimize the print quality and printing speed of each region. For example, different printmodes are used for text and for graphics. Printmode parameters include, but are not limited to, the number of drops per location, which is related to the number of passes, output resolution, sweep speed, and sweep direction.
A region is printed during one or more sweeps of the carriage over the medium, and each region is completed before the next is begun. Data from two regions is never printed during the same sweep. Because the height of a given region is almost never an integral multiple of the height of a pen, a portion of the pen extends beyond the region being printed during one or more passes. The nozzles in the portion of the pen that extend beyond the current region go unused. By not using all the available nozzles at any given time, more sweeps are required to print a page than would otherwise be needed if all nozzles were utilized. The time required to print a page is directly proportional to the number of sweeps of the print carriage.
One approach to avoiding carriage sweeps with unused nozzles because of printing adjacent regions with different printmodes, is to print multiple regions with a single, “least common denominator” printmode. This approach avoids the overhead of switching between printmodes, but may result in loss of print quality when the single printmode is not optimal for some of the regions being printed. What is needed is a way to reduce the time to print a page by minimizing unused nozzles while retaining optimal print quality.
SUMMARY
A method of reducing the time required for an inkjet printer to print a page minimizes unused pen nozzles during printmode transitions.
An image to be printed by an inkjet printer is represented in terms of rows of dots, each dot printed by a pen nozzle. An algorithm for transforming the image to the representation in terms of dots depends on a global printmode, which includes factors such as type of print medium, user-specified quality, and input data format. The algorithm also depends on a regional printmode that depends on the content of the data representing the image to be printed. Consecutive rows that share a common regional printmode are termed an image region. The regional printmode may change many times on a single page.
The data representing the dots that are printed in a single sweep of a carriage carrying pens across a print medium is termed a swath. The maximum number of rows of dots in a swath is equal to the number of nozzles on a pen. According to an embodiment of the present invention, a swath contains data from more than one image region.
The process of generating a swath is divided into a cleaver process and a packer process. The cleaver processes the data representing the image to generate an intermediate output termed a cut. The process of generating a cut includes determining the direction in which the data is to be printed. The number of rows in a cut is less than or equal to the number of rows in a swath. The packer module accumulates cuts into directional buffers, that is one buffer for printing left to right and one for printing right to left. The packer adds data from the cut being processed to the appropriate directional buffer if the cut data and the directional buffer data are compatible. The data in the cut and in the directional buffer are compatible if they can be printed at the same time without loss of print quality.
If the cut is too large to fit on the selected directional buffer, or if cut data is not compatible with the directional buffer, the printer is controlled to print the contents of the directional buffer. When an instruction is issued to control the printer to print the contents of the directional buffer, the position of the data in the directional buffer on the output medium is checked against the position of the data in the second directional buffer. If the data in the second directional buffer is located higher on the output medium than the position of the data in the selected directional buffer, the contents of the second directional buffer will be printed before the contents of the first directional buffer.
REFERENCES:
patent: 4855752 (1989-08-01), Bergstedt
patent: 4967203 (1990-10-01), Doan et al.
patent: 5731823 (1998-03-01), Miller et al.
patent: 6158834 (2000-12-01), Kato et al.
patent: 6168320 (2001-01-01), Ono et al.
Osborne William S.
Smith Stephen A.
Hewlett--Packard Company
Vo Anh T. N.
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