Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-11-06
2002-06-18
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06406116
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a technique of ejecting ink to create dots and print a multi-tone image. More specifically the present invention pertains to a printing technique using a plurality of different dots created in different states with a substantially e equivalent quantity of ink.
BACKGROUND ART
A diversity of printers have widely been used as output devices to print multi-color, multi-tone images processed by the computer. One of such printers is an ink jet printer that creates dots with several color inks ejected from a plurality of nozzles provided on a print head, so as to record an image. The ink jet printer generally enables expression of only two tones, that is, a dot-on state and a dot-off state, in each pixel. The ink jet printer accordingly carries out the halftone processing, which expresses multiple tones of original image data by a distribution of dots, prior to printing an image.
Multi-valued printers that enable expression of at least trinary tones in each pixel are one of the proposed techniques to attain richer tone expression. The multi-valued printers include printers using a plurality of inks having different densities with regard to an identical hue and printers using variable quantities of ink to create dots. The variable-ink quantity printers include printers that change the frequency of ink ejection to vary the quantity of ink in each pixel and printers that vary the quantity of ink per ejection. Such multivalued printers ensure the smooth tone expression and improve the image quality.
In the ink ejection-type printers, the image quality of the resulting printed image is affected by the printing paper. This is because the state of penetration of ejected ink depends upon the printing paper. For example, in the case of plain paper, ink readily penetrates into the sheet. The plain paper is not able to sufficiently hold the ink dye in the vicinity of the sheet surface and may thus not ensure the desired density expression. In order to compensate for this potential disadvantage, the prior art technique increases the quantity of ink ejection than usual in the case of printing in a printing medium of high ink permeability, for example, the plain paper. A concrete procedure changes the contents of the halftone processing to enhance the dot recording density when such a printing medium is selected.
The prior art multivalued printer has a relatively restricted density range expressible in each pixel. The structure using a large number of different inks having different densities to express a greater number of tones disadvantageously expands the size of the print head. The printing medium generally has an upper limit in quantity of ink absorbable per unit area (hereinafter referred to as the duty restriction). The variation in quantity of ink ejected in each pixel is accordingly restricted to the upper limit. The printing medium having high ink permeability, for example, the plain paper, has a relatively low duty restriction. The prior art printing apparatus does not attain the sufficient density expression nor ensure the sufficient image quality in such printing media.
The arrangement of creating dots with the varying quantity of ink also has the restrictions by the printing speed and the print head mechanism. Under the condition of a fixed driving frequency of the print head, the printing speed is lowered with an increase in frequency of ejection per pixel. The allowable range of varying the quantity of ink ejected from each nozzle has upper and lower limits according to the nozzle diameter. With a recent trend of high printing resolution that requires very fine dots, the allowable range of varying the quantity of ink is more strictly restricted.
In the prior art technique, the area of high density is expressed by raising the dot recording density or by increasing the quantity of ink ejected in each pixel. This increases the quantity of ink ejected per unit area and may cause stains or blots.
Because of these factors discussed above, the prior art technique has a relatively restricted range of tones expressible in each pixel.
DISCLOSURE OF THE INVENTION
One object of the present invention is to extend a range of tone values expressible in each pixel and thereby improve the image quality in a printing apparatus that ejects ink to print an image. Another object of the present invention is to provide a print head that attains such a wide tone range and a method of driving the print head. Still another object of the present invention is to ensure adequate tone expression in the case of printing in a printing medium having a high penetration rate of ink.
At least part of the above and the other related objects is attained by a print head that pressurizes ink in an ink conduit, through which a supply of ink is fed from an ink tank to a nozzle, so as to cause ink to be ejected from the nozzle and create a dot.
The print head includes: a pressure variation unit that varies a pressure applied to the ink in the ink conduit; and a driving unit that controls the pressure variation unit to apply the pressure to the ink along a preset pressure waveform.
In this print head, the driving unit varies a parameter relating to a pressure reduction, so as to enable different dots to be created in different dot creation states with a substantially identical quantity of ink.
In the print head of the present invention, the driving unit varies the parameter relating to the pressure reduction, so as to enable different dots to be created in different dot creation states with a substantially identical quantity of ink.
In the print head of this configuration, varying the waveform of the pressure applied o the ink enables different dots to be created in a variety of dot creation states with a substantially identical quantity of ink. Under the condition of ejecting a fixed quantity of ink, the different dot creation states vary the density expressed. The print head of the present invention accordingly varies the density expressed in one pixel under the condition of a substantially identical quantity of ink. Printing with the print head of the present invention ensures the richer tone expression and thereby improves the image quality. This arrangement extends the expressible tone range without increasing the quantity of ink, thus reducing the occurrence of blots or stains.
The relationship between the dot creation state and the expressed density is described below. The dot creation state represents the shape of dots actually created on the printing medium when a substantially identical quantity of ink is ejected. Ejection of ink at one point in a concentrated manner and ejection of ink in a predetermined area in a diffused manner result in creating dots of different forms. The substantially identical quantity of ink does not require strict constancy in the plural dot creation states, but may be in a range that can be regarded as constant based on the quantity of ink absorbable by the printing medium. It is conventionally thought that different dot creation states express an identical density as a whole in the case of a fixed quantity of ink ejection.
As results of minute analyses, the inventors of the present invention have, however, found that different dot creation states vary the total area of dots. The variation in total area of dots naturally varies the density expressed as a whole.
The principle of varying the area according to the dot creation state is described with the comparison between the case of creating a single dot and the case of creating a split dot.
FIG. 1
shows a dot created by ejecting ink at one point in a concentrate manner. The upper row of the drawing shows a moment when an ink droplet Ip hits against a printing medium P. The ink droplet Ip penetrates in the direction of the depth of the printing medium P at a velocity Vy and in the direction of the plane at a velocity Vx. The penetration results in creating a single dot Dt having a diameter d as shown in the lower row of the drawing. The ejected ink droplet penetrates into the printing me
Katakura Takahiro
Sayama Tomohiro
Nguyen Thinh
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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