Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-10-12
2004-04-27
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S047000
Reexamination Certificate
active
06726312
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet head for use in a printer and particularly, to a head for transferring ink to an ink discharge orifice while minimizing loss of a discharging pressure applied to the ink, an inject head for feeding ink without being affected by the pressure for ejection of the ink and minimizing the blockage with the ink, and a technique for forming such a head through sintering a ceramic or glass assembly.
The present invention also relates to a structure of a driver with a piezoelectric/electrostrictive element for use with such an ink jet head and a method of fabricating the same.
The present invention relates to an ink discharge opening provided in such an ink jet head.
2. Introduction to the Invention
Ink jet printers have widely been used as computer output devices. The ink jet printers are small in the overall size and low in the cost while reproducing high-quality printed images.
One of the key technologies of ink jet printers is a head. The action of a common ink jet head includes applying a pressure in a pressurizing chamber where a liquid ink for printing is stored and ejecting the ink in the form of droplets from a discharge orifice onto printing paper. Means for applying the pressure are mainly the displacement of a piezoelectric element and the pressurizing in an ink chamber by generation of tiny air bubbles with the use of a heater for ejection of ink. The former exhibits less consumption of power and thus is favorable for further reducing the overall dimensions.
Characteristic examples of the former model are disclosed in Japanese Patent Laid-open Publications (Heisei)6-40030 and (Heisei)8-238763.
As shown in
FIGS. 18 and 19
, a technique disclosed in Publication (Heisei)6-40030 has an ink orifice member
102
made of a plurality of layers joined to one over the other and provided with an ink discharge orifice
100
which is communicated at the rear to an ink pressurizing chamber
104
. The ink pressurizing chamber
104
is defined by an ink pump member
112
which comprises a joint plate
108
having an opening
106
provided therein for communication and a spacer plate
110
which both are made of green layers of a ceramic material joined to one over the other and sintered together to form a solid and a closure plate
114
bonded to the back of the ink pump member
112
.
A piezoelectric/electrostrictive element and a pair of electrodes are disposed on the outer surface of the closure plate
114
. More particularly, the piezoelectric/electrostrictive element
146
is sandwiched between the lower electrode
114
and the upper electrode
142
. Denoted by
116
is an ink feed chamber for feeding ink via an ink feed orifice
118
and the opening
120
to the pressurizing chamber
104
. In that arrangement, the pressurizing chamber
104
is provided in the ceramic solid and exhibits higher sealing effects. However, the ink orifice member
102
comprises an ink discharge orifice plate
122
and an ink feed orifice plate
124
joined by a passage plate
126
to each other using an adhesive. The ink orifice member
102
is then bonded by the adhesive to the ink pump member
112
. Accordingly, the sealing between the plates is not perfect and may thus cause leakage of the ink. Also, the ink discharge orifice plate
122
is made of a metallic material. Even if the bonding between the plates of different materials is negligible, the metallic material is clearly limited by a stress generated during drilling of the nozzle on decreasing the distance between openings and may hence interrupt the higher density processing.
A shock wave generated by the closure plate
114
is propagated throughout the ink and reflected on the plate
108
arranged in parallel with the oscillating closure plate
114
, thus creating interference and diminishing its pressing force. The ink discharge orifice is designed to sharply become narrower towards the opening and may develop reflection of the shock wave thus declining the pressure.
FIG. 20
is a cross sectional view of an ink head disclosed in Publication (Heisei)8-238763. The ink head has an ink pump member
112
fabricated by a set of a closure plate
114
, a spacer plate
110
, an ink feed orifice plate
124
, and a reinforcement plate
123
of a ceramic material joined and sintered to a solid form which is thus improved in the sealing effect as compared with the previous ink head disclosed in (Heisei)6-40030. However, the ink pump member
112
is not bonded by an adhesive to a passage plate
126
and an ink discharge orifice plate
122
, hence being unfavorable in the sealing effect. As apparent, the conventional head fails to have a specific structure for propagating the shock wave to the nozzle without loss to effectively transfer the pressure for efficient ejection of ink.
The ink head shown in
FIG. 18
has the ink feed orifice
118
arranged facing the closure plate
114
and thus receiving directly the shock wave, whereby the feed of ink will be disturbed. The ink in a common ink jet head of a printer is pressurized for producing a high-speed jet by the piezoelectric/electrostrictive action of a piezoelectric element. The pressure generated is propagated as a shock wave throughout the ink. When the shock wave runs in its forward direction and is reflected on the opposite wall of the ink pressurizing chamber, its reflection now moves in the opposite direction and thus interferes with the coming shock wave running in its forward direction, hence diminishing the pressing force and declining the ejection of the ink from the discharge orifice. As the pressurizing chamber of a conventional ink jet head in a printer has its bottom wall arranged in parallel with the oscillating side of the piezoelectric element, the shock wave from the oscillating side is propagated through the ink and reflected on the bottom wall to offset its pressing force thus decline the effectiveness of propagation of the pressure. Also, as the ink discharge orifice
100
is provided in a conical shape becoming narrower towards the opening, the shock wave creates more reflections on the inner wall of the conical orifice
100
and offsetting its energy. Such a conventional structure fails to avoid loss of the shock wave and decrease loss of the pressure.
While the ink heads are critically demanded for minimizing the overall dimensions and speeding up the ejection of ink, the shock wave has to be generated at higher frequency and its waveform will be acute. Its propagation hence depends largely on the shape of not only the pressurizing chamber but also the ink discharge orifice
100
which has to be carefully designed for not diminishing the energy of the shock wave. Both the ink heads shown in
FIGS. 18 and 19
are unsuccessfully designed where the ink discharge orifice
100
becomes narrower towards the tip or the opening. This only contributes to the accumulation of ink to be discharged according to the Bernoulli theorem. If the ink is dried and solidified in the ink discharge orifice close to the ink pressurizing chamber during the printing action, its solids having a greater size than the diameter of the ink discharge orifice may be trapped thus blocking up the orifice.
The ink pressurizing chamber
104
is squared at each corner and may often trap air bubbles of which the elasticity diminishes the energy of the pressure. Also, as the ink jet heads are located in an array close to each other, the action of one may possibly be affected by the action of another.
The ink feed orifice
118
is also located to face against the forward direction of the shock wave and its ink feeding action may be interrupted by the shock wave. If the ink is dried while being in the stand-by state before the printing, its solids will hardly be removed. The oscillating action of one ink jet head may affect the action of another. It is however essential for every ink jet printer producing high density prints without reducing the printing speed to have a higher density type of the ink jet head. For the higher
Fujimura Tadamasa
Kajiura Nobutaka
Suganuma Toshiharu
Armstrong Westerman & Hattori, LLP
Kabushiki Kaisha Giken
Nguyen Judy
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