Piezoelectric actuator having an array of drive columns

Details Piezoelectric actuator having an array of drive columns Piezoelectric actuator having an array of drive columns

1999-02-10

2001-04-24

Budd, Mark (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S366000, C310S367000

Reexamination Certificate

active

06222303

ABSTRACT:

BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a piezoelectric actuator having an array of drive columns and, more particularly, to a piezoelectric actuator that is especially suitable for ink jet printers, that can be fabricated with improved positional accuracy and increased integration density, and that can be stably driven. The present invention also relates a method for fabricating such a piezoelectric actuator.
(b) Description of the Related Art
In ink jet printers, a piezoelectric actuator is generally used in the ink jet head of the ink jet printers for ejecting liquid ink therefrom. A conventional piezoelectric actuator for such an ink jet head is proposed in, for example, Patent Publication No. JP-A-96-156272. FIGS. 1A and 1B show the proposed piezoelectric actuator.
For fabrication of the piezoelectric actuator, a plurality of elongate piezoelectric plates
88
of a stacked structure are first bonded onto a substrate
84
along electrode plates
86
and
87
formed thereon, as shown in FIG.
1
A.
Subsequently, a plurality of slits extending in a direction perpendicular to the longitudinal direction of the elongate piezoelectric plates
88
are formed in the piezoelectric plates
88
and on the surface portion of the substrate
84
at a predetermined pitch. Thus, a plurality of rows
91
are formed each having a plurality of stacked piezoelectric elements (or drive columns)
89
and
90
. Subsequently, the electrode plates
86
and
87
are subjected to patterning to form a plurality of external signal electrodes
93
each corresponding to one of the piezoelectric elements
89
, as shown in FIG.
1
B.
Surface electrodes are then provided on the opposite side surfaces of each of the piezoelectric elements
89
and
90
. The piezoelectric element has therein a plurality of layered internal electrode films including a plurality of signal electrodes and a plurality of common electrodes alternately disposed with each other. Each surface electrode of the piezoelectric elements connects the signal electrodes or common electrodes together. The surface electrode connecting the internal common electrodes together is connected via conductive material to an external common electrode
82
formed on the substrate
84
, whereas the surface electrode connecting the internal signal electrodes together is connected via conductive material to an external signal electrode
93
formed on the substrate
84
. Further, a support member
94
is disposed on and bonded to the substrate
84
, the support member
94
having an opening for encircling each row of the piezoelectric elements
89
and
90
so that the top surface of the support member
94
is flush with the top surfaces of the piezoelectric elements
89
and
90
. Each of the stacked piezoelectric elements
89
and
90
has a displacement output surface at the top thereof far from the substrate
84
, and, due to the longitudinal piezoelectric effect, outputs a displacement in the same direction as the direction of the stacking.
In the conventional technique as described above, a plurality of piezoelectric elements are obtained after separation of the elongate piezoelectric plate by using slits extending in the transverse direction of the elongate piezoelectric plate. Thus, each piezoelectric element has a rectangular planar shape, and an ink chamber and a nozzle for ejecting liquid ink in association with the piezoelectric element should conform to the rectangular shape of the piezoelectric element. A pattern of external electrodes for each row of the piezoelectric elements is located on either side of the piezoelectric plates. This prevents a higher integration of the actuator unit, such as provision of three or more rows of piezoelectric elements on a single actuator unit, resulting in a difficulty in increasing the number of nozzles per unit area, as well as in a low productivity.
Further, since the material of the substrate differs from that of the piezoelectric element, it generates differences in the thermal expansion coefficient and in workability between the substrate and the piezoelectric element during machining of the slits.
Furthermore, a bonding process must be performed twice; i.e., when the piezoelectric plate is bonded onto the substrate and when the support member is bonded onto the substrate. In addition, when the piezoelectric plates are positioned relative to the external electrode patterns on the substrate before being bonded to the substrate, a positional deviation is often caused between the piezoelectric plates.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a piezoelectric actuator having a compact structure and including a plurality of piezoelectric elements formed with a higher integration and a higher positional accuracy.
It is another object of the present invention to provide a method for forming such a piezoelectric actuator.
The present invention provides a piezoelectric actuator comprising a base, an array of drive columns arranged on the base, each of the drive columns having a top surface for outputting a displacement force, and an external common electrode and an external signal electrode for each of the drive columns, each of the drive columns being formed in a unitary body with an underlying portion of the base by a first block of a plurality of green sheets made of a piezoelectric material and stacked together, the green sheets including first green sheets each having thereon a common electrode pattern in electrical contact with the external common electrode and second green sheets each having thereon a signal electrode pattern in electrical contact with the external signal electrode, the base having additionally a second block of third green sheets stacked between adjacent two of the first block.
The present invention also provides a method for manufacturing a piezoelectric actuator comprising the steps of: forming a plurality of green sheets made of piezoelectric material and each having thereon a common electrode pattern; forming a plurality of second green sheets made of piezoelectric material and each having thereon a signal electrode pattern; forming a plurality of third green sheets made of piezoelectric material; stacking the first through third green sheets such that the first green sheets and the second green sheets form a plurality of first block, the third green sheets form at least one second block, and the first blocks and second block are stacked alternately to form a stacked body; forming at least one first groove on the second block and at least one second groove intersecting the first groove to leave a plurality of drive columns separated by the grooves; forming an external common electrode and an external signal electrode for each of the drive columns, the external common electrode being in electric contact with corresponding common electrode patterns, the external signal electrode being in electric contact with corresponding signal electrode patterns.
In accordance with the piezoelectric actuator of the present invention or formed by the method of the present invention, the piezoelectric actuator has a compact size because of the unitary body of the base and the plurality of drive columns fabricated with a reduced cost and positional accuracy.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.


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patent: 5912526 (1999-06-01), Okawa et al.
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