Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-04-10
2001-07-10
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000
Reexamination Certificate
active
06257688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ink jet recording apparatus ejecting ink from a nozzle onto a recording medium such as recording paper, thereby executing recording.
2. Description of the Related Art
Ink jet recording apparatuses of the shear mode type using a piezoelectric ceramic material are known as those of the drop-on-demand type. For example, Japanese patent publication No. 63-247051 (1988) discloses one of such ink jet recording apparatuses.
FIGS. 9A
to
10
show a recording head used in the ink jet recording apparatus of the shear mode type.
FIG. 9A
is a sectional view taken along a plane crossing the length of an ink chamber of the recording head. The recording head
21
includes a cover plate
201
and a base plate
202
opposed to the cover plate
201
. A plurality of shear mode wall actuators
203
are provided between the cover plate
201
and the base plate
202
. Each of the shear mode wall actuators
203
is polarized in the directions of arrows F
3
and F
4
in FIG.
9
A. An ink chamber
205
and an air chamber
212
are alternately formed between each shear mode wall actuator
203
and the adjacent one. Each shear mode wall actuator
203
has membrane electrodes
204
and
214
formed on opposite side faces thereof respectively.
FIG. 9B
is a sectional view taken along the length of the recording head
21
. A nozzle plate
207
is mounted to front ends of the shear mode wall actuators
203
. The nozzle plate
207
is formed with nozzles
206
communicating with the ink chambers
205
respectively. A manifold
209
is mounted to rear ends of the shear mode wall actuators
203
. The manifold
209
has a filler
208
preventing ink in an ink channel
213
from penetrating the air chamber
212
. The manifold
209
distributes the ink from an ink tank or ink supply into the ink chambers
205
. The electrodes
204
and
214
are covered with respective insulating layers (not shown) so as to be insulated from the ink. The electrodes
214
facing the respective air chambers
212
are connected to an earth line
211
. The electrodes
204
formed in the respective ink chambers
205
are connected to a head driver IC
83
for applying actuator drive signals to the electrodes
204
and
214
.
The following describes the relationship between the timing for application of the drive pulse signal to the recording head and the pressure induced in the vicinity of the nozzle
206
in the ink chamber
205
by the application of the drive pulse signal. In the above-described construction, a drive pulse signal is supplied to the recording head when one record data, for example, one dot of record data is recorded. The drive pulse signal corresponding to one record data is composed of two drive pulses (multipulse). The above-mentioned drive pulse signal has a drive frequency of 10.8 kHz, for example (ejection interval of 93 &mgr;sec).
The head driver IC
83
applies a first drive pulse
110
a
with a waveform as shown in
FIG. 11
to the electrode
204
. An electric field with a direction of arrows F
1
in
FIG. 10
is then induced in the left-hand side shear mode wall actuator
203
, and an electric field with a direction of arrows F
2
is induced in the right-hand side shear mode wall actuator
203
. Consequently, both shear mode wall actuators
203
are subjected to piezoelectric sliding deformation so that the volume of the ink chamber
205
is increased. Pressure is decreased in the vicinity of the nozzle
206
in the ink chamber
205
such that meniscus
230
is withdrawn into the ink chamber
205
(at time T
1
), as shown in FIG.
12
B. This state is maintained for a one-way propagation time T of pressure wave in the ink chamber
205
(pulse width of the first drive pulse
110
a
). This effects supply of the ink from the ink channel
213
during the maintenance of the above-described state.
The one-way propagation time T is required for the pressure wave in the ink chamber
205
to propagate in the direction of length of the ink chamber
205
. The one-way propagation time T depends upon the length L (see
FIG. 9B
) of the ink chamber
205
and sound speed a in the ink in the ink chamber
205
, that is, T=L/a. According to the theory of pressure wave propagation, the pressure in the ink chamber
205
is changed to positive pressure upon elapse of the time T from the time of application of the drive pulse
110
a
. The drive voltage applied to the electrode
204
of the ink chamber
205
is returned to zero in synchronism with the change to the positive pressure (at time T
2
).
Then, each shear mode wall actuator
203
is returned to the former state (see FIG.
9
A), whereupon pressure is applied to the ink. Since pressure resulting from the return of each shear mode wall actuator
203
to the former state is added to the above-mentioned positive pressure, a relatively high pressure is induced in the vicinity of the nozzle
206
of the ink chamber
205
. Consequently, the meniscus
230
is ejected as ink droplets
232
from the nozzle
206
at a predetermined speed, as shown in FIG.
12
A. After the ejection, another meniscus comes out of the opening of the nozzle as shown in FIG.
12
A.
Subsequently, a second drive pulse
110
b
is applied to the electrode
204
upon elapse of the one-way propagation time T from the fall of the first drive pulse
110
a
, that is, at time T
3
so that ink droplets are ejected. The second drive pulse
110
b
has the same peak value (amplitude) as the first drive pulse
110
a
and a pulse width equal to the one-way propagation time T. The drive pulse signal
110
is thus applied to the recording head
21
in synchronism with input of the record data so that the ink droplets are ejected onto a recording medium such as recording paper, whereby recording is executed.
The viscosity of the ink used in the ink jet recording apparatus changes according to an ambient temperature.
FIG. 8
shows the relationship between the ambient temperature of the ink and the ink viscosity. For example, the viscosity of the ink is about 3 mPa·s at the temperature of 25° C. However, the viscosity changes to about 6 mPa·s at 10° C. and about 2 mPa·s at 40° C. as shown in FIG.
8
.
SUMMARY OF THE INVENTION
The inventor conducted an experiment to examine an influence of the changes in the ambient temperature upon the ejecting performance of the recording head. The results of the experiment show that the volume of a portion of the meniscus
230
standing up above the opening edge of the nozzle
206
is decreased as the viscosity of the ink is increased, with the result that the volume of the ejected ink droplet is decreased. On the other hand, the volume of the meniscus portion standing up above the nozzle opening edge is increased as the ink viscosity is decreased, so that continuous application of the pulses to the electrodes results in spray of ink such that normal dots cannot be formed on the recording medium.
More specifically, the recording density is reduced since the volume of the ink droplet is decreased with decrease in the ambient temperature. The increase in the ambient temperature causes the spray of ink and accordingly, reduces the recording quality. The inventor obtained from the results of the experiment a graph of the relationship between the ambient temperature and the recording density.
FIG. 7
shows the graph as curve P.
FIG. 7
shows that a normal recording is executed in a range between the recording densities k
1
and k
2
. Accordingly, when the ambient temperature is lower than 15° C. or higher than 35° C., the recording density becomes abnormal with the result of reduction in the recording quality.
Therefore, an object of the present invention is to provide an ink jet recording apparatus which can prevent reduction in the recording quality even when the ambient temperature of the apparatus changes.
The present invention provides an ink jet recording apparatus comprising a recording head having a nozzle and, when a drive pulse signal is supplied thereto, driven to eject, from the nozzle,
Barlow John
Brother Kogyo Kabushiki Kaisha
Hallacher Craig A.
Oliff & Berridg,e PLC
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