Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-12-13
2003-05-13
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S023000
Reexamination Certificate
active
06561622
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an ink-jet recording apparatus having an ink-jet recording head capable of jetting ink from nozzles to form dots on a recording medium according to printing data. In particular, this invention is related to an ink-jet apparatus which can recover nozzles' ability to jet ink by discharging ink with no relation to a printing operation from the nozzles.
BACKGROUND OF THE INVENTION
As shown in
FIG. 15
, a general ink-jet recording head has: a plurality of nozzles
40
(although only one nozzle is shown in
FIG. 15
) and a plurality of pressure chambers
41
communicating with the nozzles
40
respectively. A piezoelectric vibrating member
42
is mounted on an outside surface of each elastic wall which partly defines each of the pressure chambers
41
. The piezoelectric member
42
expands or contracts depending on a printing signal. Thus, a pressure in each of the pressure chambers
41
is changed to jet ink
44
from the pressure chamber
41
through the nozzle
40
as an inkdrop
45
.
In recent apparatuses for printing color images, plural color types of ink may be used as the ink
44
, which may include yellow ink, magenta ink, cyan ink as well as black ink. The nozzles
40
are arranged for each of the color inks.
In the above recording head, the ink
44
in the nozzles
40
may dry up to clog the nozzles
40
therewith while the recording head remains stopped after a printing operation. Then, the nozzles are sealed by a capping unit except while the recording head is in the printing operation. However, solvent of the ink
44
in the nozzles
40
may gradually evaporate to increase a viscosity of the ink
44
if the nozzles are sealed for a long time. In the case, it may be difficult to start a printing operation immediately. In addition, there may be some troubles, for example that quality of printed images may deteriorate.
During the printing operation, the nozzles
40
frequently jetting inkdrops
45
are scarcely clogged with the ink
44
because new ink
44
is supplied thereinto in succession. However, even during the printing operation, the nozzles
40
rarely jetting inkdrops
45
, for example the nozzles arranged at an upper end portion or a lower end portion, are liable to be clogged with the ink
44
because the ink
44
in such nozzles
40
is liable to dry to increase the viscosity thereof.
To solve the above problems, a “flushing operation” or a “cleaning operation” is carried out by forcibly discharging the clogging ink
44
from the nozzles
40
in no relation to the printing operation, to recover the ability of the nozzles
45
to jet inkdrops. The above flushing or cleaning operation may be carried out when power supply starts to be given to the recording apparatus or when a first printing signal is inputted to the recording apparatus, as a preparatory step before the printing operation.
In the flushing operation, a driving signal in no relation to the printing data is supplied to the piezoelectric vibrating members
42
to jet the clogging ink
44
having a relatively increased viscosity from the nozzles
40
. The cleaning operation is carried out when the ability of the nozzles to jet inkdrops is not sufficiently recovered by the flushing operation. In the cleaning operation, a suction pump applies a negative pressure to the nozzles
40
to forcibly suck the clogging ink
44
having a relatively increased viscosity from the nozzles
40
.
The degree of the increasing viscosity of the ink
44
in the nozzles
40
, i.e., the degree to which the nozzles
40
are clogged becomes worse depending on the length of the capping time for which the recording head remains sealed by the capping unit or the length of the total printing time until the recording head is sealed by the capping unit.
Therefore, as shown in
FIG. 16
, whether the flushing operation or the cleaning operation should be carried out is determined by the combination of the capping time and the total printing time. The flushing operation is carried out when the capping time or the total printing time is relatively short (see a flushing area in FIG.
16
). The cleaning operation is carried out when the capping time or the total printing time is relatively long (see a cleaning area in FIG.
16
).
As described above, the apparatuses for printing color images use the plural color types of ink including the black ink, the yellow ink, the cyan ink, the magenta ink or the like. The plural color types of ink have different evaporating rates of the solvent thereof. Thus, the respective degrees of the increasing viscosity of the respective types of ink are different even when the capping time and the total printing time are the same. That is, the nozzles may have a different ability to jet ink respectively, even when the nozzles are used in the same condition.
In addition, in the case of the above conventional apparatus, there is a uniform boundary condition for the cleaning operation or the flushing operation. Thus, the cleaning operation may be carried out for the nozzles jetting ink having a relatively low rate of increasing viscosity, even when the ability of the nozzles to jet ink can be recovered by the flushing operation. This may waste ink.
To the contrary, the rate of increasing viscosity of the ink may be too high to recover the ability of the nozzles to jet ink by the flushing operation. In the case, as shown in
FIG. 17
, a meniscus of the ink in the flushing operation may become unstable and dented deeply and obliquely to take an air bubble in the nozzle
40
.
In addition, the nozzles are used for printing with different frequencies respectively. For example, in the apparatus for printing color images which uses the plural types of ink including the black ink, the yellow ink, the cyan ink, the magenta ink or the like, the nozzles for the respective color ink are used with different frequencies respectively. When a nozzle is used with a low frequency, i.e., when inkdrops are jetted from a nozzle at a low frequency, the ink in the nozzle is liable to dry and the viscosity of the ink is liable to increase. Thus, the degrees of the increasing viscosity of ink are different depending on the frequencies of using the nozzles even when the printing time is the same. That is, the nozzles may have a different ability to jet ink respectively, even when the printing time is the same. In the case of the above apparatus, the uniform condition for the cleaning operation or the flushing operation is defined in no relation to the frequencies of using the nozzles. Thus, the cleaning operation may be carried out for the nozzles whose ability to jet ink can be sufficiently recovered by the flushing operation. This may waste ink.
To the contrary, the rate of increasing viscosity of the ink jetted from the nozzles used with only a low frequency may be too high to recover the ability of the nozzles to jet ink by the flushing operation. In the case, as shown in
FIG. 17
, a meniscus of the ink in the flushing operation may become unstable and dented deeply and obliquely to take an air bubble in the nozzle
40
.
On the other hand, the volume of the ink removed in the cleaning operation is larger than that in the flushing operation because the ink is forcibly sucked by the suction pump in the cleaning operation. Thus, it is preferable that the flushing area is as large as possible. That is, it is preferable that the flushing operation is carried out for the conditions of as highly an increasing viscosity as possible of the ink to recover the ability of the nozzles to jet ink. This can reduce the volume of the ink removed to solve the clogging and increase the volume of the ink saved to use for the printing operation. This can also reduce the volume of the wasted ink.
Of course, regarding the cleaning operation, it is also requested that conditions for the cleaning operation be set to reduce the wasted ink.
SUMMARY OF THE INVENTION
The object of this invention is to solve the above problems, that is, to provide an ink-jet recording apparatus that can carry out an effic
Kanaya Munehide
Suzuki Kazunaga
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