Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2003-05-08
2004-11-02
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06811247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet head and an ink jet recording apparatus applicable, for example, to a printer or a facsimile machine.
2. Description of the Related Art
An ink jet recording apparatus has been known which records characters and images on a recording medium by using an ink jet head having a plurality of nozzles for ejecting ink. In such an ink jet recording apparatus, the nozzles of the ink jet head are provided in a head holder so as to be opposed to the recording medium, and the head holder is mounted on a carriage, with which scanning is performed in a direction perpendicular to the direction in which the recording medium is transported.
FIG. 11
is an exploded perspective view of an example of such an ink jet head. As shown in
FIG. 11
, a plurality of grooves
132
are arranged side by side in a piezoelectric ceramic plate
131
, and the grooves
132
are separated from each other by partition walls
133
. One longitudinal end portion of each groove
132
extends to one end surface of the piezoelectric ceramic plate
131
, whereas the other end portion thereof does not extend to the other end surface, and its depth gradually decreases. Further, on the opening side surfaces of the partition walls
133
on both sides of each groove
132
, electrodes
134
for applying a drive electric field are formed so as to extend in the longitudinal direction.
Further, attached to the opening side of the grooves
132
of the piezoelectric ceramic plate
131
is an ink chamber plate
136
defining a common ink chamber
135
communicating with the shallow end portions of the grooves
132
.
Further, fixed to the ink chamber plate
136
is a flow passage substrate
138
which seals one side of the common ink chamber
135
and which has a communication hole
137
communicating with an ink supply passage for supplying ink to the common ink chamber
135
.
Provided in the flow passage substrate
138
is an ink sump
139
constituting a part of the ink flow passage for supplying ink from the communication hole
137
to the common ink chamber
135
.
A nozzle plate
140
is attached to the end surface of the joint unit formed by the piezoelectric ceramic plate
131
and the ink chamber plate
136
where the grooves
132
are open, and nozzle openings
141
are formed at the positions of the nozzle plate
140
opposed to the grooves
132
.
In this ink jet head, constructed as described above, the grooves
132
are filled with ink from the communication hole
137
, and when a predetermined drive electric field is applied to the partition walls
133
on both sides of a predetermined groove
132
through the electrodes
134
, the partition walls
133
are deformed to change the volume of the predetermined groove
132
, whereby the ink in the groove
132
is ejected from the corresponding nozzle opening
141
.
In this ink jet head, the diameter of the nozzle openings
141
is very small, so that even if the volume of each groove
132
is varied, it is impossible to eject ink from the nozzle openings
141
in a satisfactory manner unless back pressure is generated in each groove
132
from the common ink chamber
135
side.
In view of this, in the conventional ink jet head, a mesh-like filter
142
formed, for example, of stainless steel (SUS), is provided between the ink sump
139
and the common ink chamber
135
. Due to this filter
142
, back pressure is generated in the grooves
132
to eject ink droplets from the nozzle openings
141
.
The ink sump of the conventional ink jet head, however, includes a region where ink does not flow easily. For example, in a region such as a corner of the ink sump, the ink supplied to the ink sump does not flow easily, with the result that bubbles stay in that region. When bubbles stay in such a region, the volume of the ink sump changes, resulting in a deficiency in the ink supply to the ink chamber. In particular, when, for example, an ink with poor bubble permeability such as a water-color ink is used, bubbles are likely to be generated in the ink, with the result that the deficiency in ink supply is gradually aggravated.
It is general practice to remove the bubbles thus accumulated in the ink sump through a so-called cleaning operation in which the bubbles are sucked from the nozzle opening side. However, even by this cleaning operation, it is difficult to substantially remove the bubbles staying in the portion of the ink sump on the upstream side of the filter, which do not pass through the filter.
In an ink jet head in which bubbles cannot be removed from a region where ink does not flow easily, bubbles staying in the ink sump may pass through the filter to be ejected together with ink during printing, thereby causing a printing failure. Thus, such an ink jet head is to be disposed of, resulting in a poor yield rate.
Further, when the size of the ink droplets is large or the number of nozzle openings is large, that is, when the amount of ink ejected per unit time is large, the amount of bubbles existing, in particular, in the ink sump, is large, so that the area of the ink flow passage is substantially reduced, resulting in the deficiency in the ink supply to the ink chamber being gradually aggravated.
It might be possible to accelerate the ink flow by narrowing the flow passage of the ink sump to thereby prevent the bubbles in the ink sump from staying. This, however, would involve a substantial reduction in the filter size, resulting in a deficiency in the ink supply to the common ink chamber. Further, even by adopting this method, it is impossible to completely remove the bubbles staying in the portion of the ink sump on the upstream side of the filter through the above-mentioned cleaning operation.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problem in the prior art. It is an object of the invention to provide an ink jet head and an ink jet recording apparatus in which it is possible to reliably prevent ink bubbles from staying in the ink sump and the interior of the head chip and in which it is relatively easy to remove the bubbles.
According to a first aspect of the present invention for solving the above-mentioned object, there is provided an ink jet head including: a plurality of grooves arranged side by side so as to communicate with nozzle openings; an ink chamber for supplying ink to each of the grooves; an ink sump provided so as to communicate with the ink chamber; and ink storage unit communicating with the ink sump through ink supply passages,
characterized in that there is provided an air duct establishing communication between a region in the ink sump which is substantially free from interference with an ink flow from the ink supply passages to the ink chamber and in which bubbles easily gather and an air region of the ink storage means.
According to a second aspect of the present invention, in the first aspect of the present invention, the ink jet head is characterized in that the ink chamber is provided so as to extend over the direction in which the grooves are arranged side by side, that the ink chamber and the ink sump communicate with each other over the direction in which the grooves are arranged side by side, that the ink supply passages are provided on both sides of the ink sump with respect to the direction in which the grooves are arranged side by side, and that the air duct is provided between the ink supply passages.
According to a third aspect of the present invention, in the first or second aspect of the present invention, the ink jet head is characterized in that the ink sump is equipped with a tapered portion gradually diverging from at least one of the openings of the ink supply passages and the air duct toward the ink chamber.
According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, the ink jet head is characterized in that the ink sump is equipped with a filter situated in the vicinity of the border between the ink sump and the ink chamber.
A
Denda Masaki
Koseki Osamu
Makishima Tomiharu
Nakamura Yuji
Sekiya Yasuhito
Adams & Wilks
Gordon Raquel Yvette
SII Printek Inc.
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