Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-11-27
2004-08-10
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S068000
Reexamination Certificate
active
06773085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording apparatus used in a printer or in a facsimile machine for example, and to an ink jet recording method.
2. Description of the Related Art
Conventionally, there is known an ink jet recording apparatus that records characters and images on a recording medium using a ink jet head which ejects ink from a plurality of nozzles. In such an ink jet recording apparatus, the nozzles of the ink jet head are provided in a head holder so as to oppose the recording medium, and this head holder is mounted on a carriage to be scanned in a direction orthogonal to a conveying direction of the medium to be recorded.
A schematic exploded view of an example of a head chip of such an ink jet head is shown in
FIG. 13 and a
sectional view of main parts of the same is shown in FIG.
14
. As shown in
FIGS. 13 and 14
, a plurality of chambers
102
are provided in parallel with each other in a piezoelectric ceramic plate
101
, and each chamber
102
is separated by side walls
103
. An end portion in a longitudinal direction of each chamber
102
is extended to an end surface of the piezoelectric ceramic plate
101
and the other end portion is not extended to the other end surface, making the chamber
102
become gradually shallower. In addition, electrodes
105
for applying a driving electric field are formed on surfaces on opening-side of both the side walls
103
in each chamber
102
along its longitudinal direction.
A cover plate
107
is bonded to the piezoelectric ceramic plate
101
on the opening side of the chambers
102
by using adhesive
109
. The cover plate
107
includes a common ink chamber
111
to be a recessed portion communicating with the other end portion of each chamber
102
where it is shallower, and an ink supply port
112
that is bored from the bottom portion of this common ink chamber
111
in a direction opposite to the chamber
102
.
In addition, a nozzle plate
115
is bonded to an end surface of a bonded body of the piezoelectric ceramic plate
101
and the cover plate
107
in which the chambers
102
are opened, and nozzle openings
117
are formed in the nozzle plate
115
at positions opposing the respective chambers
102
.
Note that, a wiring substrate
120
is fixed to the surface of the piezoelectric ceramic plate
101
which is on the side opposite from the nozzle plate
115
and on the side opposite from the cover plate
107
. Wiring
122
connected to each electrode
105
by bonding wires
121
and the like is formed on the wiring substrate
120
, and a driving voltage can be applied to the electrodes
105
via this wiring
122
.
In a head chip configured in this way, when each chamber
102
is filled with ink from the ink supply port
112
and a predetermined driving electric field is caused to act on the side walls
103
on both sides of the predetermined chamber
102
via the electrode
105
, the side walls
103
are deformed to change the volume of the predetermined chamber
102
, whereby the ink in the chamber
102
is ejected from the nozzle opening
117
.
For example, as shown in
FIG. 15
, when ink is to be ejected from the nozzle opening
117
corresponding to a chamber
102
a
, a positive driving voltage is applied to electrodes
105
a
and
105
b
within the chamber
102
a
, and electrodes
105
c
and
105
d
which face the electrodes
105
a
and
105
b
, respectively, are grounded. This causes a driving electric field to act on side walls
103
a
and
103
b
in a direction towards the chamber
102
a
, and if this is orthogonal to the polarization direction of a piezoelectric ceramic plate
101
, the side walls
103
a
and
103
b
deform towards the chamber
102
a
due to a piezoelectric thickness shear effect to reduce the volume of the chamber
102
a
while increasing the pressure. Thus, ink is ejected from the nozzle opening
117
.
In such a head chip, although the time required from when vibration of the side walls caused by ink ejection stops until when the ink pressure in the chamber becomes zero to be ready for next ink ejection depends upon the length of the chamber, the shape of the nozzle opening, and the like, since the chamber is low in sealing property, the sound pressure is repeatedly reflected within the chamber, thus requiring a considerable amount of time for completely attenuating it. Therefore, a problem occurs in that it is difficult to increase the speed of continuous ejection, that is, to increase the printing speed.
Since the time required until the sound pressure attenuates largely varies depending upon the shape of the nozzle opening, in particular, a problem occurs in that it is difficult to control the amount of ejection according to the shape of the nozzle opening.
The chamber is composed of a boundary portion communicating with the common ink chamber, and a pump portion extending from the nozzle opening to the boundary portion, which is driven to eject ink, and the contraction time during which the chamber pressure attenuates depends upon the length of the pump portion, i.e., upon the distance from the nozzle opening to the boundary portion. However, the problem is that, when the pump length is shortened in order to reduce the contraction time, ink ejection characteristics are deteriorated, resulting in unnormal printing operation.
A driving electric field generated in the side walls on both sides of the chamber by one-time ejection consists of a preliminary driving electric field which causes the chamber volume to temporarily increase, and an ejection driving electric field which causes the chamber volume to temporarily decrease subsequently to the preliminary driving electric field. The driving time ratio of the preliminary driving electric field to the ejection driving electric field is AP to 2N×AP (N denotes a natural number, and AP denotes a periodic time that is determined by the pump length and the pressure propagating speed within ink, i.e., a time required from a positive pressure peak to a negative pressure peak). That is, as the preliminary ejection driving generates a negative pressure in the chamber, and the ejection driving electric field generates a positive pressure in the chamber; after the positive pressure has been generated by the ejection driving electric field, the chamber volume is returned to the original volume, thereby causing a negative pressure to be generated in the chamber, and a positive pressure peak generated after 2N×AP after generation of an ejection driving electric field is cancelled by this negative pressure, thus preventing ink leakage or ejection failure.
Therefore, if the driving time ratio of the preliminary driving electric field to the ejection driving electric field is AP to (2N−1)×AP, that is, if the ejection driving electric field is an odd-numbered multiple, a negative pressure peak generated at a period of 2AP after a time AP elapses since an application of ejection driving electric field coincides with the timing of generation of a negative pressure caused by the chamber volume returning to the original volume, thus extraordinarily increasing the negative pressure to thereby cause contamination of air bubbles into the chamber or degradation in the ejection performance. Therefore, the driving time ratio of the preliminary driving electric field to the ejection driving electric field is set to AP to 2N×AP, so that a positive pressure peak generated at a period of 2AP after a time 2AP elapses after an application of ejection driving electric field is cancelled by a negative pressure generated when the chamber volume returns to the original volume. The time involved in ejection using both the preliminary driving electric field and the ejection driving electric field becomes at least 3AP, thus requiring a long ejection time and further requiring the time for contraction of the pressure in the chamber for next ejection. Therefore, a problem occurs in that it is difficult to increase the speed of continuous ejection, in particular.
SUMMA
Adams & Wilks
Nguyen Judy
SII Printek Inc.
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