Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-03-08
2003-10-07
Vo, Anh T. N. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S010000
Reexamination Certificate
active
06629741
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording apparatus and in particular, to an ink jet recording head drive method for recording characters and images by discharging ink droplets from a nozzle and an apparatus thereof.
2. Description of the Related Art
Conventionally, there is known a drop-on-demand type ink jet apparatus in which an electro-mechanical converter such as a piezoelectric actuator is used to generate a pressure wave (accoustic wave), which serves to eject an ink droplet from a nozzle connected to a pressure generation chamber. This type of ink jet recording head drive method is disclosed, for example, in Japanese Patent Publication (examined) 53-12138. This type of ink jet recording head is shown in
FIG. 25
as an example.
Referring to
FIG. 25
, a pressure generation chamber
100
is connected to a nozzle
101
for discharging ink and an ink supply path
103
for introducing ink from an ink tank (not depicted) via a common ink chamber
102
. Moreover, at the bottom of the pressure generation chamber
100
, a diaphragm
104
is provided. When discharging an ink droplet, this diaphragm
104
is displaced by a piezoelectric actuator
105
(electro-mechanical converter) provided outside the pressure generation chamber
100
, so as to generate a volume change of the pressure generation chamber
100
, thus generating a pressure wave in the pressure generation chamber
100
. This pressure wave ejects a portion of ink from the pressure generation chamber
100
outside via the nozzle
101
and the ink droplet
106
flies to a recording medium such as a recording paper to form a recording dot. The formation of recording dot is repeatedly performed according to an image data, so as to record a character and an image on the recording paper.
In order to obtain a high quality image using this type of ink jet recording head, it is necessary to set the diameter of the ink droplet
106
very small. That is, in order to obtain a smooth image without feeling of the respective droplets, it is necessary to make the recording dot (pixel) as small as possible. For this, the diameter of the ink droplet ejected should be set very small. Normally, when the dot diameter is equal to or smaller than 40 micrometers, the image quality is remarkably improved. The ink droplet diameter and the dot diameter depend on the ink droplet flying speed (droplet speed), ink characteristic (such as viscosity and surface tension), the type of the recording paper. Normally, the dot diameter is twice as much as the ink droplet diameter. Accordingly, in order to obtain a dot diameter of 40 micrometers or less, the ink droplet should have a diameter of 20 micrometers or less. It should be noted that in the explanation below, the droplet diameter represents a total ink amount ejected by one eject operation (including a satellite shown by
106
′ in
FIG. 25
) which is preceded by a corresponding spherical droplet.
In order to reduce the ink droplet diameter, the nozzle
101
should have a reduced diameter. However, considering technical limits and reliability such as a problem of clogging, the nozzle diameter practically has a lower limit of 25 micrometers. It is difficult to obtain an ink droplet of the 20 micrometers level only by reducing the nozzle diameter. To cope with this, an attempt has been made to reduce the ink droplet diameter through the recording head drive method and several effective methods have been suggested.
As a drive method for discharging a very small droplet by the ink jet recording head, for example, Japanese Patent Publication (unexamined) 55-17589 discloses a drive method for temporarily expanding the pressure generation chamber immediately before eject and an ink surface formed by reserved ink in a nozzle opening (hereinafter, referred to as meniscus) is pulled into the pressure generation chamber and then ejected. FIG.
26
(
a
) shows an example of a drive voltage waveform used in this type of drive method. It should be noted that the relationship between the drive voltage and operation of the piezoelectric actuator
105
varies depending on the structure of the actuator
105
and polarization direction. In the explanation given below, it is assumed that increase of the drive voltage decreases the volume of the pressure generation chamber
100
while decrease of the drive voltage increases the volume of the pressure generation chamber
100
.
The drive voltage waveform of FIG.
26
(
a
) consists of a first voltage change process
1
for expanding the pressure generation chamber
100
so as to pull the meniscus from the nozzle opening into the pressure generation chamber
100
and a second voltage change process
2
that compresses the pressure generation chamber
100
, so as to eject an ink droplet.
FIG. 27
schematically shows motion of the meniscus
3
at the nozzle opening when the drive voltage waveform of FIG.
26
(
a
) is applied. In the initial state when a reference voltage is applied, the meniscus
3
is flat as shown in FIG.
27
(
a
). When the pressure generation chamber
100
is expanded by the first voltage change process
1
immediately before eject, the meniscus
3
is pulled backward as shown in FIG.
27
(
b
). That is, the center of the meniscus
3
is recessed than the peripheral portion and a U-shaped meniscus
3
is formed. After the U-shaped meniscus
3
is formed, the pressure generation chamber
100
is compressed by the second voltage change process
2
, so that a slender liquid column
4
is formed at the center of the meniscus
3
as shown in FIG.
27
(
c
). Subsequently, the tip end of the liquid column
4
is separated to form an ink droplet
106
as shown in FIG.
27
(
d
). Here, the ink droplet
106
has a diameter almost identical to the diameter of the liquid column
4
, which is smaller than the diameter of the nozzle
101
. Accordingly, this drive method enables to eject the ink droplet
106
having a smaller diameter than that of the nozzle
101
. Hereinafter, the drive method for discharging a very small droplet by operating the meniscus
3
immediately before eject, that is the configuration of the ink droplet
3
reserved in the nozzle opening will be referred to as the meniscus control method.
As has been described above, by using the meniscus control method, it is possible to eject an ink droplet having a diameter smaller than the diameter of the nozzle. However, when using the drive voltage waveform as shown in FIG.
26
(
a
), practically, the droplet diameter has a lower limit of 25 micrometers and it is impossible to satisfy the high quality image requirement.
The applicant of the present invention discloses in Japanese Patent Application 10-318443, a drive voltage waveform as shown in FIG.
26
(
b
) as a drive method enabling to eject a further smaller droplet. This drive voltage waveform consists of a first voltage change process
1
for pulling a meniscus
3
toward the pressure generation chamber
100
immediately before eject, a second voltage change process
2
for compressing the volume of the pressure generation chamber
100
so as to form a liquid column for eject, a third voltage change process
5
for separating an ink droplet
106
quickly from the tip end of the liquid column
4
, and a fourth voltage change process
6
for suppressing the residual pressure wave remaining after eject of the ink droplet. That is, the drive waveform of FIG.
26
(
b
) includes the third voltage change process
5
for early separation of the ink droplet
106
and the fourth voltage change process
6
for suppressing reverberation in addition to the conventional meniscus control method as shown in FIG.
26
(
a
). This enables to obtain a stable eject of the ink droplet
106
having a diameter in the order of 20 micrometers.
When discharging a very small droplet using the aforementioned meniscus control method, the greatest problem is to assure a stable eject. That is, the ink droplet diameter and eject speed of the ink droplet ejected by the meniscus control method greatly depend
Ishiyama Toshinori
Okuda Masakazu
Dickstein , Shapiro, Morin & Oshinsky, LLP
Dudding Alfred
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