Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-02-20
2004-06-08
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S331000, C310S359000, C310S366000
Reexamination Certificate
active
06747396
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric actuator for an ink jet printhead, comprising: a body of piezoelectric material having a bottom face through which the mechanical energy of the actuator is transferred to a receiving member, said body having an active part adjacent to the bottom face as well as an inactive part; a layered structure of alternating signal electrodes and common electrodes arranged in the active part in parallel with the bottom face and separated by layers of the piezoelectric material; a layered structure of alternating auxiliary electrodes and common electrodes arranged in the inactive part in parallel with the bottom face and separated by layers of the piezoelectric material; at least one signal lead electrode formed on a first side face of said body and interconnecting the signal electrodes; a ground lead electrode formed on a second side face opposite to said first side face and interconnecting the common electrodes; and an auxiliary lead electrode interconnecting the auxiliary electrodes.
An actuator of the type described hereinabove is used for pressurizing liquid ink in an ink jet printhead, so that ink droplets can be jetted-out from nozzles of the printhead. Typically, the printhead has a linear array of nozzles, and each nozzle is connected to an ink channel that is filled with ink. The ink channels are arranged in parallel with each other and are covered by a sheet-like receiving member which is bonded to the bottom face of the actuator so that it can be deformed in accordance with the expansion and retraction strokes of the actuator for compressing the ink in the ink channels. The active part of the piezoelectric body is divided into a plurality of parallel fingers associated with the respective individual ink channels and separated by dicing cuts cut into the bottom face of the body. The inactive part of the body forms a bridge-like structure which interconnects the fingers on the side opposite to the bottom face.
The signal lead electrodes are respectively associated with the individual fingers, so that an ink droplet from a selected one of the nozzles can be obtained by applying a voltage across the associated signal lead electrode and the ground lead electrode.
The inactive bridge portion of the piezoelectric body serves as a backing member which bears the reaction forces of the active actuator fingers and also facilitates the manufacturing process in that it permits the production of a plurality of fingers as a one-piece construction, by simply forming dicing cuts in the piezoelectric body. The auxiliary electrodes in the inactive part are not needed when the printhead is operating. These auxiliary electrodes are only needed in the process of manufacturing the actuator.
As is well known in the art, a piezoelectric device made for example of piezoelectric ceramic needs to be polarized during the manufacturing process in order to show the desired piezoelectric effect. This polarizing step is accompanied by an anisotropic shrinkage or expansion of the piezoelectric material. Thus, when only the active part were polarized, the piezoelectric body as a whole would behave like a bimorph element and would undesirably be distorted or even broken. This is why the auxiliary electrodes are also used for polarizing the inactive part of the piezoelectric body.
FIG. 4
illustrates an example of a printhead
10
in which a commercially available piezoelectric actuator
12
is employed.
The printhead
10
comprises a support member
14
on which a channel plate
16
is disposed. A plurality of parallel ink channels
18
are formed in the top surface of the channel plate
16
. Only one of these ink channels
18
is shown in FIG.
4
. One end of the ink channel
18
is formed as a nozzle
20
from which ink droplets are to be expelled. The rear end of the ink channel is connected to an ink supply system (not shown) which is accommodated in the support member
14
. A receiving member
22
is formed as a thin flexible sheet and is superposed on the channel plate
16
so that it covers all the ink channels
18
and the nozzles
20
.
The actuator
12
comprises a body
24
made of a piezoelectric ceramic and shaped as a parallelepiped having a bottom face
26
which is bonded to the receiving member
22
. The portion of the body
24
adjacent to the bottom face
26
is subdivided into a plurality of fingers
28
which are arranged in parallel with one another and with the ink channels
18
. Each finger
28
is disposed directly above a respective one of the ink channels
18
. However, it can be seen in
FIG. 4
that the body
24
and also the fingers
28
thereof extend beyond the ink channels
18
on the side opposite to the nozzles
20
. Only the part of the fingers
28
situated above the ink channels
18
is formed as an active part
30
of the piezoelectric actuator. This active part
30
comprises a layered structure with alternating signal electrodes
32
and common electrodes
34
. The common electrodes
34
extend only over the active part
30
, whereas the signal electrodes
32
extend over the entire length of the body
24
and, accordingly, are also present in an inactive part
36
which is offset from the ink channels
18
.
The portion of the body
24
bridging the individual fingers
28
and situated above the active part
30
forms another inactive part
38
. This inactive part
38
contains a layered structure with alternating common electrodes
34
and auxiliary electrodes
40
.
All the electrodes
32
,
34
and
40
are formed by plane rectangular sheets of conductive material arranged in parallel with the bottom face
26
of the body
24
and separated from each other by layers of ceramic material.
The signal electrodes
32
of each finger
28
are interconnected with each other by a signal lead electrode
42
formed on a rear side face of the body
24
, i.e. the side face opposite to the nozzles
20
. Similarly, all the common electrodes
34
in the active part
30
and the inactive part
38
are interconnected by a common ground lead electrode
44
formed on the front side face of the body
24
. The auxiliary electrodes
40
are interconnected by a common auxiliary lead electrode
46
formed again on the rear side face of the body
24
but separated from the signal lead electrodes
42
by a gap
48
.
The signal lead electrodes
42
and the ground lead electrode
44
are connected to respective contact electrodes
50
and
52
′ formed on the bottom face
26
of the body
24
. The contact electrode
52
extends beyond the rear ends of the ink channels
18
. All the contact electrodes
50
and
52
are electrically connected to a control circuit (not shown) via electrical leads formed on a connecting piece
54
. The connecting piece
54
is formed by a flexible foil which is sandwiched between the bottom face
26
of the body
24
and the receiving member
22
below the inactive part
36
.
When an energizing signal is supplied to one of the signal lead electrodes
42
via the associated contact electrode
50
and the connecting piece
54
, the active part
30
of the corresponding finger
28
performs an expansion stroke, so that the receiving member
22
is flexed downward and compresses the ink contained in the ink channel
18
, thereby expelling an ink droplet from the nozzle
20
.
In order to avoid losses in the mechanical energy transferred to the receiving member
22
, it is preferable that the connecting piece
54
is not provided between the active part
30
of the actuator and the receiving member
22
but is only provided in the rear of the ink channels
18
. The body
24
has been extended rearwardly beyond the ink channels
18
in order to provide a sufficient contact area between the contact electrodes
50
and
52
and the connecting piece
54
. Since the receiving member
22
cannot flex downwardly in this area because it is supported by the channel plate
16
, the part
36
of the body
24
is inactive and does not contain common electrodes
34
.
It will be noted that in the conventiona
Budd Mark
Oce--Technologies B.V.
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