Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-12-03
2002-10-29
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000
Reexamination Certificate
active
06471316
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for driving a print head of an ink-jet printer.
2. Description of the Related Art
In a print head driving method in a conventional drop on-demand type ink-jet printer, a drive voltage signal is applied to a print head every time a print instruction is issued, and ink drops are discharged from a nozzle to carry out a print operation.
FIG. 1
is a diagram showing an example of the structure of the print head of an ink-jet printer. As shown in
FIG. 1
, the print head
12
is composed of an ink discharging nozzle
14
, an ink pressure increasing room
16
, an actuator
18
, and a drive signal generating circuit
19
. The ink pressure increasing room
16
is connected to the nozzle
14
. The actuator
18
receives a pulse drive voltage signal and applies a pressure to ink in the ink pressure increasing room
16
in accordance with the magnitude of a drive voltage signal. The drive signal generating circuit
19
generates the drive voltage signal which should be applied to the actuator
18
.
The print head
12
is subjected to a repetitive reciprocating motion in a print region along a paper (not shown). In this state, the pulse drive voltage signal is generated by the drive signal generating circuit
19
and is repeatedly supplied to the actuator
18
. As a result, the ink in the ink pressure increasing room
16
is pressurized so that ink drops are discharged from the nozzle
14
to the paper. The supply and non-supply of the pulse drive voltage signal generated by the drive signal generating circuit
19
to the actuator
18
are controlled so that a print operation to the paper is carried out.
FIGS. 2A
to
2
C are waveform diagrams showing the waveform of the drive voltage signal, the displacement of ink meniscus at the nozzle tip section and the velocity of an ink meniscus at the nozzle tip section, respectively. In
FIGS. 2A
to
2
C, the horizontal axis indicates time and a vertical axis indicates voltage in
FIG. 2A
, the displacement of the meniscus in
FIG. 2B
, and the meniscus velocity in
FIG. 2C
, respectively.
When the drive voltage signal is supplied to the actuator
18
as shown in
FIG. 2A
, the drive voltage signal increased rapidly between a point A and a point B, and ink
20
in the ink pressure increasing room
16
is also pressurized rapidly by the actuator
18
. At this time, the meniscus velocity in the nozzle tip section is rapidly increased between a point X and a point Y in FIG.
2
C. The ink meniscus
22
,
21
changes from the original state shown in
FIG. 3A
to the state shown in
FIG. 3B
, and the discharge of ink drop from the tip section of the nozzle
14
is started. Thus, an ink pillar
24
is first formed. At this time, the displacement quantity of the meniscus
22
becomes large rapidly as shown in FIG.
3
B.
After that, the drive voltage signal is settled to a constant value between the point P and a point C in FIG.
2
A. As a result, the pressure of the meniscus
22
decreases and the velocity of the ink meniscus in the nozzle tip section starts to decrease between a point Y and a point Z in FIG.
2
C. Thus, the difference in meniscus velocity between the ink pillar
24
discharged from the nozzle
14
and the ink within the nozzle becomes large. For this reason, as shown in
FIG. 3C
, the ink pillar
24
is cut off from the ink within the nozzle
14
and an ink drop
26
is discharged from the nozzle
14
.
It should be noted that the drive voltage signal is sometimes decreased depending on a printer, instead of keeping constant between the point B and the point C shown in FIG.
2
A. In the case, the drive voltage signal is decreased at the timing earlier than the velocity of the ink meniscus. However, the basic operation is the same.
After the ink drop
26
is discharged, the position of the meniscus
22
in the tip section of nozzle
14
is recessed to the side of the nozzle proximate by a quantity equivalent to discharged ink drop, as shown in FIG.
3
D.
After that, the recessed meniscus
22
tries to return to the original position by surface tension in the tip section of the nozzle
14
and vibrates (refill phenomenon). Also, the recessed meniscus
22
undergoes influence of the remaining vibration of the pressure wave by the actuator
18
. Thus, the meniscus vibrates. The vibration attenuates gradually and the meniscus
22
returns to the original position as shown in
FIG. 2B
, and FIG.
3
A. Also, the velocity of ink meniscus attenuates gradually and becomes a zero, as shown in FIG.
2
C. Such an operation is repeated every time the drive voltage signal is supplied to the actuator
18
and the print operation is carried out.
By the way, the ink meniscus in the nozzle section vibrates for a time as mentioned above, when the drive voltage signal is once supplied and the ink drop is discharged. Therefore, the ink drop can be next discharged at the timing of Q in
FIG. 2A
or after that. That is, the next discharge of the ink drops is after the vibration of the ink meniscus
22
has been settled. However, it is impossible to print at high speed, because the supply period of the drive voltage signals becomes long in the above-mentioned condition. For this reason, it could be considered that the drive voltage signal is supplied to the actuator
18
before the timing of Q and ink drops are discharged.
For example, as shown in
FIG. 2B
, the position of the ink meniscus returns to the original position at the timing of A in FIG.
2
A. Therefore, it is effective to supply the drive voltage signal at this timing. However, at the timing of O, the ink meniscus is moving with some velocity as shown in FIG.
2
C. Therefore, when the drive voltage signal is supplied at this timing, the velocity of the ink meniscus is equal to an addition of the above remaining velocity and a velocity determined in response to the new drive voltage signal. This is different from the desired velocity and causes the degradation of the print quality.
On the other hand, as shown in
FIG. 2C
, the ink meniscus stops at the timing of P. In this case, if the following drive voltage signal is supplied, there is no problem with respect to the meniscus velocity of the ink. However, as shown in
FIG. 2B
, because the ink meniscus is displaced largely, the quantity of discharged ink drop is different from the desired quantity and still causes the degradation of the print quality.
To solve these problems, various methods are conventionally proposed, in which after the drive voltage signal is once supplied, a preliminary drive voltage signal is supplied to control the ink meniscus and makes high-velocity print possible.
Also, various methods are proposed in which a quantity of ink discharged from the nozzle
14
is increased through the once drive of the actuator
18
so that the discharge efficiency of ink is improved.
Hereinafter, three representative methods will be described.
In the first conventional method, the ink meniscus
22
at the tip section of the nozzle
14
is returned to an initial state, i.e., the state before the ink drops are discharged, as soon as possible. The repetition period of the supply of the drive voltage signal is made small. For this purpose, the drive voltage signal is supplied to restrain the remaining vibration of the meniscus
22
after supply of the drive voltage signal. For example, the first conventional method is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 5-338150) and Japanese Laid Open Patent Application (JP-A-Showa 59-10495).
FIG. 4A
is a waveform diagram showing the waveform of the drive voltage signal and the preliminary drive voltage signal in the first conventional driving method.
FIG. 4B
is a waveform diagram showing the drive voltage signal and the preliminary drive voltage signal which are repeatedly supplied to the actuator
18
in the first conventional driving method.
As shown in
FIG. 4A and 4B
, in the first conventional driving method, every time the drive voltage signal
28
is supplied to the actuator
Dickstein , Shapiro, Morin & Oshinsky, LLP
NEC Corporation
Vo Anh T. N.
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