Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-04-13
2001-05-15
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S011000, C347S010000
Reexamination Certificate
active
06231150
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese patent application No. 9-111866 filed on Apr. 14, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ink-jet printing control for printing by ejecting ink droplets onto print media, and more particularly to an ink-jet printing control which is capable of providing stable performance of ink droplet ejection.
2. Description of Related Art
Among conventional ink-jet printing apparatuses, there is a drop-on-demand arrangement of a shear mode type using piezoelectric ceramic material as disclosed in Japanese Unexamined Patent Publication No. 63-247051. A printing head used in this kind of ink-jet printing apparatus is shown in
FIGS. 8A and 8B
.
Referring to
FIGS. 8A and 8B
, a printing head
21
is provided with a cover plate
201
and a base plate
202
which is provided facing the cover plate
201
. A part between the cover plate
201
and the base plate
202
is formed with piezoelectric material so that partitions are provided by a plurality of shear mode actuator walls
203
polarized in arrow directions F
30
and F
40
indicated in
FIG. 8A
, and an ink channel
205
and an air channel
212
are arranged alternately between each pair of shear mode actuator walls
203
. One side of each shear mode actuator wall
203
has a film electrode
204
, and the other side thereof has a film electrode
214
.
As shown in
FIG. 8B
, the front end of the shear mode actuator wall
203
is provided with a nozzle plate
207
which has nozzles
206
each of which is connected with the ink channel
205
, and the rear end of the shear mode actuator wall
203
is provided with a manifold part
209
which has a filler part
208
for preventing intrusion of ink from a common ink passage
213
into the air channel
212
. The manifold part
209
is used for distributing ink from an ink reservoir (not shown) to each ink channel
205
. Each of the electrodes
204
and
214
is covered with an insulating layer (not shown), and the electrode
214
facing the air channel
212
is connected with the ground
211
. The electrode
204
forming the ink channel
205
is connected with a head driver IC (integrate circuit)
83
which applies an actuator drive signal to the electrodes
204
and
214
.
In the printing head
21
structured as mentioned above, when the head driver IC
83
applies the actuator drive signal
110
having a pulse width T shown in
FIG. 10
to the electrode
204
, piezoelectric thickness slip deformation occurs on each shear mode actuator wall
203
to increase a volume of the ink channel
205
. For instance, as shown in
FIG. 9
, when a positive drive voltage is applied to the electrode
204
of the ink channel
205
, electric fields are produced on the shear mode actuator wall
203
in arrow directions F
10
and F
20
, causing piezoelectric thickness slip deformation to occur on upper walls
203
a
and lower walls
203
b
of the shear mode actuator wall
203
so that the volume of the ink channel
205
is increased. At this step of operation, pressure in the ink channel
205
including a vicinal part of the nozzle
206
is decreased. This state is maintained during the pulse width T which corresponds a period of one-way propagation time T of a pressure wave in the ink channel
205
. Thus, ink is supplied from the common ink passage
213
thereinto.
The one-way propagation time T of the actuator drive signal
110
indicates a period of time required for the pressure wave in the ink channel
205
to complete propagation in the longitudinal direction of the ink channel
205
. Using length ‘L’ (
FIG. 8B
) of the ink channel
205
in the longitudinal direction thereof and acoustic velocity ‘a’ in ink in the ink channel
205
, ‘T’ is expressed as follows; T=L/a.
Based on the principle of pressure wave propagation, pressure in the ink channel
205
is reversed to become positive after a lapse of time T following application of the drive voltage. At the timing of pressure reversal, the drive voltage being applied to the electrode
204
of the ink channel
205
is reset to zero (0) V. Thus, the shear mode actuator wall
203
is restored to normal (FIGS.
8
A and
8
B), applying pressure to ink. At this step of operation, the positive pressure is added to pressure which has been produced by restoration of the shear mode actuator wall
203
to normal, so that relatively high pressure is generated in the vicinity of the nozzle
206
in the ink channel
205
, thereby ejecting ink from the ink channel
205
to the outside through the nozzle
206
.
In actual use, the printing head
21
is mounted on a carriage which is electrically driven by a motor to move transversely across the printable medium during the printing operation. As the motor speed changes greatly at the time of starting and ending an energization of the motor, the moving speed of the printing head
21
relative to the printable medium changes correspondingly. Further, the moving speed of the printing head
21
changes, even during the constant speed rotation of the motor, due to other causes such as friction between the carriage and a carriage shaft supporting the carriage movably thereon. As a result, even if the drive pulse signal
110
is applied at a fixed driving interval (fixed frequency), the actual driving interval varies when the transverse moving speed of the printing head relative to the printable medium changes.
According to measurement of the ink ejection speed against the driving interval of the drive pulse signal
110
, as shown in
FIG. 7
, the ink ejection speed changes between the highest speed (9.00 m/s) at a driving interval of 110 &mgr;s and the lowest speed (6.25 m/s) at another driving interval of 125 &mgr;s. Thus, the maximum change in the ink ejection speed is 2.75 m/s.
The above variation in the driving interval of the actuator drive pulse signal
110
thus causes variations in the ink ejection speed of the printing head
21
due to a residual pressure wave vibration in the ink chamber
205
. This results in degradation in the printing quality.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ink-jet printing control which is capable of delivering stable ejection of ink droplets to ensure satisfactory printing quality.
It is a further object of the present invention to provide an ink-jet printing control which is capable of suppressing variation in ink ejection speed against variation in driving interval of a drive pulse signal.
According to the present invention, a drive pulse signal applied to an actuator of a printing head for each ink ejection operation includes a first drive pulse and a second pulse. The first drive pulse changes a volume of an ink channel to eject ink from the ink channel. The second drive pulse has a wave height equal to that of the first drive pulse and a pulse width equal to approximately 0.20 to 0.40 times the one-way propagation time T of pressure wave in the ink channel. The second drive pulse is applied to the actuator so that it ends within a range of approximately 2.60 to 2.80 times the one-way propagation time T from a fall time of the first drive pulse signal. Thus, residual pressure wave oscillation in the ink channel can be suppressed to ensure stable ink droplet ejection, thereby making it possible to attain satisfactory quality of printing.
REFERENCES:
patent: 4879568 (1989-11-01), Bartky et al.
patent: 4887100 (1989-12-01), Michaelis et al.
patent: 4992808 (1991-02-01), Bartky et al.
patent: 5003679 (1991-04-01), Bartky et al.
patent: 5028936 (1991-07-01), Bartky et al.
patent: 5359350 (1994-10-01), Nakano et al.
patent: 5600350 (1997-02-01), Cobbs et al.
patent: 5680163 (1997-10-01), Sugahara
patent: 63-247051 (1988-10-01), None
Barlow John
Brother Kogyo Kabushiki Kaisha
Dudding Alfred
Oliff & Berridge PLC.
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