Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-08-30
2002-03-26
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06361154
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink-jet head for use in an ink-jet printer, and more particularly, it relates to improvement of a vibration plate of a piezoelectric actuator used for discharging ink in an ink-jet head.
Recently, ink-jet printers are widely used in offices and households. Various systems have been proposed for ink-jet heads used in the ink-jet printers in order to meet recent demands for low noise and high print quality. In general, the systems for the ink-jet heads can be roughly divided into the following two systems:
In a first system, part of an ink passage and an ink chamber is formed into a pressure chamber by using a piezoelectric actuator having a piezoelectric device, and a pulse voltage is applied to the piezoelectric device so as to deform the piezoelectric actuator. Thus, the pressure chamber is deformed to have a smaller volume, thereby generating a pressure pulse within the pressure chamber. By using the pressure pulse, ink drops are jetted through a nozzle hole communicating with the pressure chamber.
In a second system, an exothermic resistance is provided in an ink passage, and a pulse voltage is applied to the exothermic resistance so as to generate heat therein. Thus, ink contained in the passage is boiled with vapor bubble generated. By using the pressure of the vapor bubble, ink drops are jetted through a nozzle hole.
The present invention relates to an ink-jet head of the first system, and hence, this system will be further described in detail.
FIGS. 11 through 13
show an exemplified conventional ink-jet head of the first system, and the ink-jet head comprises a head body
101
including a plurality of pressure chamber concaves
102
each having a supply port
102
a
for supplying ink and a discharge port
102
b
for discharging ink. The concaves
102
of the head body
101
are arranged along one direction at predetermined intervals.
The head body
101
includes a pressure chamber part
105
forming the side walls of the concaves
102
, an ink passage part
106
forming the bottoms of the concaves
102
and including plurality of thin plates adhered to one another, and a nozzle plate
113
. Within the ink passage part
106
, an ink supply passage
107
communicating with the supply port
102
a
of each concave
102
and an ink discharge passage
108
communicating with the discharge port
102
b
of each concave
102
are formed. Each ink supply passage
107
communicates with an ink supply chamber
110
extending in the direction of arranging the concaves
102
, and the ink supply chamber
110
communicates with an ink supply hole
111
formed in the pressure chamber part
105
and the ink passage part
106
and connected with an external ink tank (not shown). In the nozzle plate
113
, nozzle holes
114
respectively connected with the ink discharge passages
108
are formed.
On the upper surface of the pressure chamber part
105
of the head body
101
, a piezoelectric actuator
121
is disposed. The piezoelectric actuator
121
includes one flat vibration plate
122
that covers all the concaves
102
of the head body
101
so as to form pressure chambers
103
together with the concaves
102
. The vibration plate
122
also works as a common electrode shared by all piezoelectric devices
123
described below. Also, the piezoelectric actuator
121
includes the piezoelectric devices
123
disposed on the vibration plate
122
respectively correspondingly to the pressure chambers
103
and individual electrodes
124
respectively disposed on the piezoelectric devices
123
for applying a voltage to the piezoelectric devices
123
.
When a pulse voltage is applied between the vibration plate
122
serving as the common electrode and each individual electrode
124
, each piezoelectric device
123
shrinks in a lateral direction perpendicular to a thickness direction, but the vibration plate
122
and the individual electrode
124
do not shrink. Therefore, a portion of the vibration plate
122
corresponding to the piezoelectric device
123
is deformed into a convex projecting toward the pressure chamber
103
due to so-called the bimetal effect. This deformation causes a pressure within the pressure chamber
103
, and owing to the pressure, ink contained in the pressure chamber
103
is jetted from the nozzle hole
114
through the discharge port
102
b
and the ink discharge passage
108
.
In the ink-jet head for jetting ink by using the piezoelectric actuator as described above, various improvements have been recently made so as to meet strict demands for compactness and light weight, a low driving voltage, low noise, low cost, and high controllability in jetting ink. In order to attain further compactness and higher performance, the vibration plate, the piezoelectric devices and the like can be formed from thin films easily subjected to refined processes.
When the vibration plate and the piezoelectric devices are simply made from thin films with keeping the shape and the structure of the conventional piezoelectric actuator, however, there is a fear of occurrence of cracks and film peeling in the vibration plate and the piezoelectric devices in manufacture of the ink-jet head. As a result, the productivity of the ink-jet head is disadvantageously lowered. Accordingly, an ink-jet head that is not only compact but also can be easily manufactured with good productivity is desired.
The present invention was devised under these circumstances. An object of the invention is, in an ink-jet head for jetting ink contained in a pressure chamber by using a piezoelectric actuator, changing the structure of a vibration plate of the piezoelectric actuator so as to make compact the ink-jet head by forming a vibration plate and piezoelectric devices from thin films as well as to improve the productivity as far as possible by suppressing occurrence of cracks and the like in the vibration plate and the piezoelectric devices.
SUMMARY OF THE INVENTION
In order to achieve the aforementioned object, according to the invention, vibration plates are separately provided correspondingly to one or plural pressure chambers, or a portion of a vibration plate corresponding to each pressure chamber is bent into a convex projecting in an opposite direction to the pressure chamber.
Specifically, the ink-jet head of this invention comprises a head body including plural pressure chamber concaves each having a supply port for supplying ink and a discharge port for discharging ink; and a piezoelectric actuator including mutually electrically connected vibration plates that cover the concaves of the head body in order to form pressure chambers together with the concaves and are separately provided correspondingly to one or plural pressure chambers; piezoelectric devices respectively provided on surfaces of the vibration plates opposite to the pressure chambers correspondingly to the pressure chambers; and individual electrodes respectively provided on surfaces of the piezoelectric devices opposite to the vibration plates for applying a voltage to the piezoelectric devices together with the vibration plates, wherein the vibration plates are deformed in a manner that volumes of the pressure chambers are decreased by applying a voltage to the piezoelectric devices through the vibration plates and the individual electrodes, whereby ink contained in the pressure chambers is discharged through the discharge ports.
In this manner, the vibration plates are separately provided correspondingly to one or plural pressure chambers. Therefore, the separated vibration plates can be prevented from affecting one another in their internal stress and strain, and hence, the internal stress caused in each vibration plate can be reduced as compared with the case where one vibration plate covers all the concaves of the head body. As a result, the internal stress caused in the piezoelectric device and the individual electrode disposed on the surface of the vibration plate opposite to the pressure chamber can be also reduced. Accordingly, even when the vibration p
Kanno Isaku
Takayama Ryoichi
Tomita Kenji
Watanabe Osamu
Matsushita Electric - Industrial Co., Ltd.
Nguyen Judy
Nixon & Peabody LLP
Robinson Eric J.
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