Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1997-03-31
2001-02-20
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06189993
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method and apparatus for liquid ink printing and more particularly to a printing system for printing images having different grayscales through control of printhead carriage velocity and the number of drops deposited per pixel.
BACKGROUND OF THE INVENTION
Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based, or thermal, have at least one printhead from which droplets of liquid ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of ink conduits or channels. Power pulses cause the droplets of ink to be expelled as required from orifices or nozzles at the ends of the channels.
In a thermal ink-jet printer, the power pulse is usually produced by a heater transducer or a resistor, typically associated with one of the channels. Each resistor is individually addressable to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in the associated channel and initially bulges toward the channel orifice followed by collapse of the bubble. The ink within the channel then retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel orifice and towards the recording medium whereupon hitting the recording medium a dot or spot of ink is deposited. The channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink.
The ink jet printhead may be incorporated into either a carriage type printer, a partial width array type printer, or a page-width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated, at a constant speed, to print one swath of information (equal to the length of a column of nozzles), at a time, on a stationary recording medium, such as paper, fabric, or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. This procedure is repeated until the entire page is printed. In contrast, the page width printer includes a stationary printhead having a length sufficient to print across the width or length of the recording medium at a time. The recording medium is continually moved past the page width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page width ink-jet printer is described, for instance, in U.S. Pat. No. 5,192,959, herein incorporated by reference.
Printers typically print information received from an image output device such as a personal computer. Typically, this received information is in the form of a raster scan image such as a full page bitmap or in the form of an image written in a page description language or a combination thereof. The raster scan image includes a series of scan lines consisting of bits representing pixel information in which each scan line contains information sufficient to print a single line of information across a page in a linear fashion. Printers can print bitmap information as received or can print an image written in the page description language once converted to a bitmap consisting of pixel information.
Information printed by a printer can be printed having the grayscale of the received information. The printer can also modify the received bitmap and print the information at a grayscale different than the one received. In either event, it is typical that grayscale printing is performed either by controlling the number of drops per pixel, by controlling the size of the white space between pixels, or both. One known method of improving image quality through grayscale control is to print pixels on a higher resolution grid in both the scan direction and the paper advance direction. Such methods require multiple passes of the printhead so that more drops are placed within a given region of the print medium. These methods also require small and very accurate paper advance steps for accurate placement of the drops on a high resolution grid. Because such methods require multiple passes of the printhead, print speed may be undesirably reduced. In addition, accurate paper advance steps may increase the cost of the printing system as such systems typically require advanced electronic controllers and expensive encoders which can be cost prohibitive.
Various methods and apparatus for printing images with scanning carriage type liquid ink printers have been developed. The following references describe these and other methods and apparatus for liquid ink printing.
U.S. Pat. No. 4,965,593 to Hickman describes a dot printer wherein the spacing of ink jet nozzles of a print head are spaced by an amount greater than the pixel spacing of the printing medium such that adjacent pixels are not printed until the deposited colorant has time to dry.
European Patent Application Publication No.623 473 to Holstun et al, describes increased print resolution in the carriage scan axis of an ink-jet printer. The increased print resolution is achieved by moving the carriage of an ink-jet cartridge in the carriage scan direction to provide a first resolution in that direction which is twice the second resolution in a print media advance direction. Two smaller drops of ink are fired onto each square pixel in a single pass of the cartridge so as to provide, for example, a 600 dpi resolution in the carriage scan axis with a 300 dpi resolution in the media advance direction.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided a liquid ink printing system for printing, from print data, an image on a recording medium, moving in a first direction along a path, including pixel locations being deposited with liquid ink drops. The printing system includes a printhead, located adjacent the path, including a plurality of drop ejectors, for depositing the liquid ink drops, an electromover, for moving the recording medium along the path, and a print driver, operatively coupled to the electromover and to the printhead, for controlling a plurality of relative velocities between the recording medium and the printhead, each of the plurality of relative velocities being associated with one of a plurality of grayscales.
Pursuant to another aspect of the present invention, there is provided a method of printing with a liquid ink printhead including drop ejectors ejecting ink drops at a drop ejection frequency at a plurality of pixel locations having a predetermined resolution on a recording medium moving along a path to form an image including a plurality of dots. The steps include examining an image quality selection, determining, as a function of the examined image quality selection, a relative velocity between the recording medium and the printhead for printing the image, and printing the image with the printhead ejecting ink drops on the recording medium with the relative velocity between the recording medium and the printhead being determined in said determining step.
REFERENCES:
patent: 4631548 (1986-12-01), Milbrandt
patent: 4965593 (1990-10-01), Hickman
patent: 5216445 (1993-06-01), Hirsaswa et al.
patent: 5245359 (1993-09-01), Ito et al.
patent: 5412410 (1995-05-01), Rezanka
patent: 623473 A2 (1994-09-01), None
Arthur David J.
Barlow John
Stewart Jr. Charles W.
Xerox Corporation
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