Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-03-20
2004-09-14
Liang, Leonard S (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S019000, C347S085000, C347S005000, C347S086000, C347S101000, C347S106000, C347S107000
Reexamination Certificate
active
06789876
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to inkjet printers and, more particularly, to an improved large-format digital color inkjet printer including a group of sensors and subassemblies that cooperate to produce high quality graphic images using a plurality of different colors of ink and different types of print media at speeds several times faster than similar conventional inkjet printers. In addition, the use of cooperating elements permit the manufacture of complex, large-format digital color inkjet print engines that are less expensive to fabricated, operated, and serviced. The present invention finds use in large-format digital color printing and imaging, where successful repeatable printing requires precise placement of droplets of ink, toner or other marking material on a print medium such as paper, vinyl, film, or similar substrate.
BACKGROUND OF THE INVENTION
Inkjet printers are well known. Large-format inkjet printers generally move a scanning carriage containing one or more print-head in a transverse or horizontal direction across a print medium, while incrementally advancing—or “stepping”—a print medium in a lengthwise or vertical direction in-between successive printing passes, or scans, of a reciprocating carriage. Inkjet printing involves placing large quantities of tiny ink droplets formed by one or more ink-emitting (or “jetting”) nozzles onto predetermined locations on a print medium or substrate. The ink droplets solidify or dry on the print medium forming small dots of color. A quantity of these small colored dots when viewed at a nominal distance will be perceived as a continuous-tone visual image. To increase the rate of print production, a print-head typically employs numerous jetting nozzles per color of ink ganged together in a suitable arrangement to create a band or “swath” of printed area that is much wider than otherwise would be obtainable from a single jetting nozzle. Usually, several linear arrays of jetting nozzles are disposed in a print-head in an orientation parallel to the direction of media travel (X-axis) and perpendicular to the direction of carriage travel (Y-axis). Both text and graphic images may be printed with inkjet printing.
The printed image from an inkjet printer is made up of a grid-like pattern of potential dot locations, called picture elements or “pixels”. A pixel generally refers to a coverage area that is defined by the incremental advance accuracy of the media (positioning resolution) of the media drive system along the X-axis, and the maximum number of colored dots the print-head can produce (marking resolution) along the Y-axis. Pixel density is often referred to as print resolution; while pixel density is often the same for both travel axes, this need not be the case for every inkjet printer. Print resolution is often conceived of as a performance measure of an inkjet printer. The print resolution of an inkjet print engine tends to vary as needed for the particular imaging application; hence, the print resolution necessary for printing a billboard, such as are commonly viewed from hundreds of feet away, may be on the order of 6-12 pixels per inch. For many smaller-format documents commonly viewed from 1-6 feet away, the inkjet printing industry has produced printer with a print resolution of between 200 and 2600 pixels per inch (40,000-6,760,00 pixels per square inch) and a maximum media width of 18 inches. While the aforementioned upper range of print resolution may be acceptable for smaller-format documents, such as photo-reproduction or color-matching images, which have an optimum viewing distance of less than 1-8 feet, the use of higher print resolution in large-format devices becomes problematic for a number of reasons.
One reason, which tends to obviate any others, is that employing higher print resolution in larger-format images tends to be counter-productive due to the large amount of image data that must be processed. In digital printing, example, for every doubling of print resolution there is a concomitant quadrupling of the number of required pixels for the same printed area (e.g., 100×100 dpi=10,000 pixels per sq. in.; 200×200 dpi=40,000 pixels per sq. in., etc.). Each pixel requires at least one memory location to represent it: hence, each time print resolution doubles the number of memory locations required to render the same size image quadruples. Data inflation not only affects how much expensive on-line memory is needed to render an image, but also influences various other aspects of printer design and manufacture. For example, higher print resolution requires a fast I/O system to handle the large amount of image data that must be transferred from a rendering device to the print heads, as well as a fast processor and optimized software to quickly render a large image for printing. Higher print resolution also requires large off-line storage devices such as hard-disks and CD-ROM drives to store a rendered image, as well as large data buffers to stage the rendered image data to the print heads. Each of these outcomes tends to increase the cost of manufacture for large-format, graphics-quality inkjet printers.
The problem of data inflation is further exacerbated by the use of process color printing. Inkjet printers generally use one or more of several different types of ink and potential combinations of colors of ink. Color inkjet printers of the prior art typically use the four subtractive primary colors: cyan, magenta, yellow and black (“CYMK”). Color blending of these four ink colors is achieved through two mechanisms. First, the inkjet printer may deposit multiple colors of ink on the same pixel location. Upon combining one or more of the CMYK ink colors at a given pixel location, a particular color combination is formed, either in a dot-on-dot or a dot-next-to-dot pattern. The particular color combination produced by depositing multiple ink colors at a particular pixel location may be affected by the order of printing the various colors, as well as the homogeneity (or lack thereof) of ink mixing. Second, when viewed at a distance, the eye will blend colors from adjacent pixel locations. Thus, for instance, a number of exclusively magenta and yellow colored dots may be laid down in an area of a printed image, with no pixel location receiving two colors of ink. Rather than perceiving individual magenta and yellow dots, the eye will blend the adjacent dots to perceive an orange color. In practice, ink blending at particular pixel locations and perception blending across pixel locations are used to create various colors and shades in a printed image. Usually, a substantial number of the pixel locations in a printed image will be left blank, allowing the perceived visual image to have the correct shades or tones (lightness/darkness values) across the image. Through both forms of color blending, inkjet printers using only four colors of ink can visually reproduce continuous-tone, graphics-quality color images.
However, for every individual color used to render an image, a separate pixel grid—or color plane—must be rendered and staged in either on-line or off-line memory, or both, for transmission to the print-head. Consequently, the amount of memory needed to render and store image data correspondingly increases for each additional color of ink used to print an image. For example, a 36×42-inch image will comprise 1512 square inches of printed area. At a print resolution of 600 dpi, this image area constitutes a pixel grid having 544,320,000 discreet grid locations, or pixels (i.e., 1512×600×600=544,320,000). For each color used to print an image, a separate color plane must be rendered that controls whether a drop of ink of a particular color will—or will not—be deposited at each specific pixel grid location. Thus, to render a CMYK image at 600 DPI requires four separate color planes and generates 2,177,280,000 (c.f, 544,320,000×4=2,177,280,000) bits of total image data. As print resolution increases, or as the number of process color
Anderson Kerry R.
Barclay Aaron G.
Bigaoutte Richard J.
Campion Kevin R.
Gonier Larry W.
Carmody & Torrance LLP
Liang Leonard S
LandOfFree
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