Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-03-19
2002-10-08
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06460967
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid jetting device, and in particular, to a liquid jetting device wherein a liquid is jetted from a liquid jetting section, and a jetted trace of the liquid is recorded on a recording medium such as paper, cloth, nonwoven fabric and a plastic film, as, for example, in an ink jet printer.
In the case of an ink jet printer used for cloth, for example, a drop of ink (liquid) is jetted from a nozzle of a liquid jetting section, namely, of a print head onto a web (recording medium) on a platen so as to print a pattern. In the case of a color print, a print head has thereon ink heads which are respectively for the four primary colors of cyan, magenta, yellow and black, for example, and a combination of ink dots jetted from various ink heads expresses various colors and patterns. Combinations of colors of ink dots and patterns formed by them are specified by image forming data supplied from the control unit (computer). Density of ink dots constituting a pattern is usually between several hundred dpi to more than one thousand dpi.
Ink is supplied to a print head directly from an ink tank or through an ink tube. When letting ink run through a path from the ink tank to the print head initially, a pressure difference which makes the pressure on the part of the ink tank to be higher relatively than that on the part of the tip of the print head is given between the ink tank and the tip of the print head, to feed ink forcibly. The pressure is generated by suction or pressurization caused by a pump. Even when a nozzle of a print head is clogged with foreign substances such as dust or air bubbles, the foreign substances are ejected out of the nozzle together with ink by force feeding. The force feeding of ink of this kind for ejection of foreign substances is also conducted under the pressure which is the same as that in initial ink running.
When the pressure which is the same as that in initial ink running is used in force feeding of ink for ejection of foreign substances, air bubbles have failed to be ejected out sufficiently, depending on their size and location, which has been a problem.
To be concrete, an air bubble which is produced in an ink tube and is relatively large is easily fed forcibly by a high pressure, but when it fragments into small air bubbles, they are hardly moved. When such air bubbles are deposited in an ink manifold of an ink head, they affect ink jet operations, while when air bubbles which are further smaller are stuck to an inner wall of a jetting channel (nozzle) of the ink head, the jetting direction of ink loses its accuracy.
The diameter of the nozzles of the print heads capable of making a print having such a high dot density mentioned above is extremely small, and jetting failure caused by adhesion of dyes or pigments of the ink tends to occur, requiring cleaning of the print head on a timely basis.
As an example of a conventional liquid jetting device equipped with a cleaning unit for the print heads, there is described a device in TOKKAIHEI 4-185450, for example. In this device, a cleaning roller made of porous material is brought into contact with a print head, and thereby smudges on the nozzle plane are absorbed when the cleaning roller is rotated on the nozzle plane by travel of the print head.
Further, as another example of a conventional liquid jetting device equipped with a cleaning unit for a print head, there is described, for example, a device in TOKKAIHEI 6-079880. In this device, a cleaning blade made of porous material is caused to hold a cleaning liquid and is brought into contact with the print head, so that the front surface of the print head is wiped by the cleaning blade as the print head travels along its limited path.
In the aforesaid example of the conventional jetting device, the print head is brought into contact with a cleaning roller or a cleaning blade whose position is fixed so as to clean the ink jetting plane by utilizing sucking action or wiping action based on traveling of the print head. However, the traveling speed of the print head is the same as the main scanning speed in the course of printing, or it can not be changed greatly even if it is changed. Therefore, the desired cleaning needs to be conducted within a given range of traveling speed, requiring hard work in selection of materials and shapes of a cleaning roller or the cleaning blade, or in selection of the cleaning liquid, which has been a problem.
In particular, in the conventional device described in TOKKAIHEI 4-185450, the cleaning effect is insufficient because smudges stuck on the nozzle plane can not be scraped off, though smudges on the nozzle plane can be absorbed, due to utilization of rotations of a cleaning roller on the print head surface. In the conventional device described in TOKKAIHEI 6-079880, on the other hand, a mechanism for supplying a cleaning liquid and a mechanism for absorbing smudges are complicated, and sufficient effect of cleaning is not always obtained, because the same contact surface of the cleaning blade is always used.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the problems mentioned above, and its object is to materialize a liquid jetting device wherein foreign substances and air bubbles contained in a liquid are appropriately removed and a liquid jetting section is cleaned appropriately.
The object stated above can be attained by the following structures.
(A) A liquid jetting apparatus, comprises
a head provided with a liquid jetting section;
a feeding means for feeding a liquid to the head;
a control section for controlling the liquid jetting section to jet the liquid such that a jetting trace of the liquid is recorded on a recording medium; and
a liquid ejecting means for varying a pressure in the head by plural steps so as to eject the liquid in the head from the liquid jetting section.
Here, as the liquid ejecting means for varying a pressure in the head in plural steps so as to eject the liquid in the head from the liquid jetting section, it may be permissible to be able to merely vary the pressure in the head by plural steps. The liquid ejecting means includes a case that the pressure steps in the head are changed differently in accordance with an objective of liquid ejection, the property of foreign material, and the kind of liquid and a case the pressure is varied by plural pressure steps by only a single ejecting action.
(B) A liquid jetting apparatus, comprises:
a head provided with a liquid jetting section;
a feeding means for feeding a liquid to the head;
a control means for controlling the liquid jetting section to jet the liquid such that a jetting trace of the liquid is recorded on a recording medium;
a wiping means for wiping the liquid jetting section of the head, the wiping section being rotatable and having an outer peripheral surface at least on which a wiping member having a liquid-absorbing characteristic is provided;
a driving means for rotating the wiping means; and
a cleaning liquid feeding means for feeding a cleaning liquid to the wiping means.
Further, the object stated above can be attained by the following structures as a preferable embodiment. (Item
1
) A liquid jetting device to jet a liquid from a liquid jetting section and to record a jetted trace of the liquid on a recording medium, wherein there is provided a liquid ejecting means in which the pressure is varied in plural steps to eject the liquid from the liquid jetting section.
In the invention of Item
1
, the liquid ejecting means can conduct liquid ejection which is in conformity with properties of foreign substances, by varying the pressure in plural steps. Incidentally, air bubbles are included in the category of foreign substances. (Item
2
) The liquid jetting device described in Item
1
, wherein the liquid ejecting means stated above is provided with a pressure releasing means.
In the invention of Item
2
, the pressure releasing means gives the time constant for increase or decrease of pressure. (Item
3
) The liquid jetting device des
Maekawa Yoshikazu
Makita Masahiro
Nishikawa Takuo
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
Tran Huan
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