Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-09-06
2004-04-20
Hsieh, Shih-Wen (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S030000
Reexamination Certificate
active
06722757
ABSTRACT:
This application is based on Japanese Patent Application Nos. 2001-272802 and 2001-272803, both filed Sep. 7, 2001, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printing apparatus for printing an image on a print medium by ejecting ink from a print head and to an ejection recovery device used in the ink jet printing apparatus to keep ink ejection from nozzles of the print head in good condition.
The present invention can be applied not only to general printing apparatus but also to copying machines, facsimile machines with a communication function, word processors with a printing unit and even industrial printing apparatus combined with a variety of processors.
2. Description of the Related Art
Printing apparatus with functions of a printer, a copying machine and a facsimile, composite type electronic apparatus including computers and word processors, and printing apparatus used as an output device for workstations are designed to print an image on a print medium such as paper and plastic thin films.
Of these printing apparatus, an ink jet printing apparatus, which forms an image by ejecting ink onto a print medium from a print head as a printing means, has the following advantages. That is, the print head can easily be reduced in size, which in turn enables high-speed printing of an image with an enhanced resolution; and the ink jet printing apparatus can print on plain paper without requiring a special treatment of the print medium, thus reducing the running cost. Another advantage is that since the ink jet printing apparatus employs a non-impact system, noise is low. Further, multiple ink colors can be used to form a full color image with ease. In a line type ink jet printing apparatus in which a large number of nozzles are arrayed in a direction of width of the print medium, still faster printing is possible.
Further, in an ink jet printing means (print head) employing a so-called bubble jet (tradename) system that uses a thermal energy to form bubbles in ink and ejects ink by an energy generated by the bubbles, a highly dense nozzle arrangement can be realized which comprises electrothermal transducers, electrodes, liquid paths and a top plate, all formed on a substrate by a semiconductor manufacturing process including etching, vapor deposition and sputtering. The high-density nozzle arrangement allows for a further reduction in size.
The ink jet printing apparatus, however, has a problem that an ingress of air into ink ejection nozzles may dry ink, increasing an ink viscosity and making ink ejection from the nozzles impossible. A known technique to recover the ability of the print head to eject ink is a method that draws out the ink not contributing to the image making from the tips of the nozzles by suction (recovery by suction).
A means for realizing this recovery by suction (suction-based recovery means) consists generally of a cap that can cover the nozzles of the print head air-tightly and a negative pressure generating means that can generate a negative pressure in the cap.
In his specification, the word “nozzle” is meant to include a plurality of divided liquid paths for ejecting ink supplied to a common liquid chamber in the print head and ink ejection ports or openings formed at one end of the liquid paths. The word “ink” is meant to include visually recognizable color liquids and a print quality enhancement liquid that improves a print quality of that portion of a print medium which is applied with this enhancement liquid.
FIG. 17
shows a recovery device conventionally used in the ink jet printing apparatus. The recovery device shown here includes a cap M
5001
arranged in a path on which the print head not shown is moved, a pump M
5100
as a negative pressure generating means communicating with this cap, and wiper blades M
5011
, M
5012
-
1
, M
5012
-
2
for removing ink from a nozzle forming surface of the print head.
When a PG motor E
0003
rotates in a forward direction, the cap M
5001
comes into hermetic contact with the ejection port forming surface of the print head to enclose the nozzles of the print head (capping). Next, when the PG motor E
0003
rotates in a backward direction to rotate the pump in a reverse direction, a roller is rotated while in pressure contact with the pump tube, squeezing the pump tube to generate a negative pressure.
This negative pressure acts on the nozzles of the print head through exhaust port M
5001
a
formed in the cap to discharge ink from the cap M
5001
and a plurality of suction ports M
5005
a
, M
5005
b
, M
5005
c
formed in a flow path forming member M
5005
that covers the exhaust port M
5001
a
. As a result, viscous ink and foam not suited for printing are drawn out of the ejection ports of the print head and further drawn into the suction ports M
5005
a
, M
5005
b
, M
5005
c
provided in the cap M
5001
through an ink absorber M
5002
for discharging.
Then, the PG motor is driven in the forward direction to cause the cap to part from the ink ejection port forming surface of the print head (decapping), ending a series of suction-based recovery operations.
As shown in FIG.
17
through
FIG. 20
, the multiple suction ports M
5005
a
, M
5005
b
, M
5005
c
are formed at a plurality of dispersed locations in the flow path forming member M
5005
so that the suction ports M
5005
a
, M
5005
b
, M
5005
c
are arranged one between each of different color ink nozzle columns. This arrangement is made to prevent different kinds of ink that have flowed out from different color ink nozzle columns of the print head from crossing other nozzle columns.
The conventional ink ejection recovery device described above, however, still has the following problems that need to be addressed.
A color printing capability and enhanced print quality and resolution required of the ink jet printing apparatus of recent years have increased the number of ink ejection nozzles of the print head and the number of ink colors and also reduced the size of ejected ink droplets considerably. It is therefore necessary to take sufficient care in handling the ink droplets ejected from the print head. For example, if a color ink enters nozzles of different color, these different colors will become mixed (color mixing), failing to produce a normal color printed image. Some countermeasures need to be taken to void this phenomenon.
This color mixing phenomenon easily occurs during the suction-based recovering operation on the print head. Thus, in the conventional technique, suction ports are provided between nozzle columns of different color inks to prevent color inks from getting into the nozzles assigned with different color inks, as described above. This technique has been confirmed to have an effect of alleviating the color mixing but more efforts are needed for minimizing this phenomenon.
To meet this requirement, various methods have been tried. For example, the ink suction is performed separately on nozzle columns of different ink colors by using suction caps dedicated for each color, or a single suction cap is used to draw out ink successively from nozzle columns of different colors, one color at a time. These methods, however, complicate the printing apparatus, resulting in increases in size, cost and suction-based recovery operation time.
In the method that performs the ink suction operations successively with a single cap, the ink staying near the nozzles of the print head is discharged after the suction-based recovery operation is finished until the printing is started, in order to clear the nozzles of unintended or unassigned color inks before starting the printing operation. In this method, too, there is a tendency that as the number of nozzles increases, the amount of ink discharged also increases. This in turn increases a consumption of ink.
SUMMARY OF THE INVENTION
The present invention has been accomplished with a view to overcoming the problems of the conventional techniques mentioned above. It is therefore an object of the pres
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