Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Reexamination Certificate
2000-07-19
2003-08-12
Williams, Hezron (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
C347S070000
Reexamination Certificate
active
06604431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field:
The present invention relates to a piezoelectric sensor, an actuator whose distortion information is detected by this piezoelectric sensor, and a disk unit used for suppressing the distortion of the actuator according to the detected distortion information. More particularly, the present invention relates to a method for fixing the piezoelectric sensor to the actuator and checking the status of the electrical connection at the fixed portion.
2. Description of the Related Art:
Conventionally, electrodes have been formed on a thin plate-like piezoelectric element by plating those electrodes with such a conductive material as gold, nickel, tin, or the like. Generally, a pair of electrodes are formed with the same material in such a case. However, among those electrode materials, there have not been any materials that excel in both wettability required for soldering and adhesion required for bonding with an adhesive.
Basically, an adhesive is required to have the following characteristics: (1) The adhesive must flow smoothly. (2) The adhesive must flow into small spaces. (3) The adhesive must get electrode materials wet properly. (4) Finally, the adhesive must be set so as to form a tough layer and keep a high adhesion. More concretely, an adhesive must be fluid once. For example, it should preferably get the object electrode material wet with a low surface tension of liquid.
For example, gold has excellent wettability, but not excellent adhesion. On the contrary, nickel has excellent adhesion, but not excellent wettability. Consequently, in case of such the conventional technique, if a lead wire is to be soldered on one electrode of a piezoelectric sensor and the other electrode is to be bonded and fixed at a predetermined member thereof, either of the work properties must be sacrificed.
Under such the circumstances, the Applicant of the present invention has invented a method for bonding a piezoelectric sensor to a distortion detecting spot of an object member and examined the idea as follows. The piezoelectric sensor was provided with two electrodes, which are plated with nickel for excellent adhesion, and bonded at a distortion detecting spot of the object member with an adhesive as shown in
FIGS. 9 and 10
. (The configurations of the piezoelectric sensor shown in
FIGS. 9 and 10
are unknown in the prior art; they are not included in any conventional techniques.)
The piezoelectric sensor
51
shown in
FIG. 9
is structured so that the top and bottom surfaces of the piezoelectric element
51
a
are placed between nickel-plated electrodes. The electrode formed on the top surface is used as an output electrode
51
b
of the piezoelectric sensor and the electrode formed on the bottom surface is used to a ground electrode
51
c
thereof. The electrode
51
c
is used as a reference potential surface of the piezoelectric sensor. The surface of the ground electrode
51
c
is bonded to a distortion detecting spot of the object member
57
with an adhesive
56
. In such a structure of the piezoelectric sensor, however, the adhesive surface of the ground electrode
51
c
is hidden completely. To avoid this, therefore, part of the ground electrode
51
c
is extended up to the top surface of the piezoelectric element and a lead
54
for taking out the reference potential is soldered at this portion.
In such a configuration, although the ground electrode
51
c
is grounded surely via the lead
54
, the lead wire must be soldered to two electrodes of both output electrode
51
b
and ground electrode
51
c
. In addition, a special process is needed for extending part of the ground electrode
51
c
up to the top surface of the piezoelectric element. And, some more measures are further needed to improve both workability and cost of the piezoelectric sensor.
The bonding method shown in
FIG. 10
is based on an idea that at least the predetermined distortion detecting spot of the object member
65
is formed with a conductive material and the predetermined spot is grounded. The piezoelectric sensor
61
is structured so that the top and bottom surfaces of the piezoelectric element
61
a
is placed between nickel-plated-electrodes. The electrode formed on the top surface is used as the output electrode
61
b
of the piezoelectric sensor
61
and the electrode formed on the bottom surface is used as the ground electrode
61
c
thereof. The electrode
61
c
is assumed as a potential surface of the piezoelectric sensor
61
. The surface of the ground electrode
61
c
is then bonded and fixed to the distortion detecting spot, which is formed with a conductive material of the object member
65
with the use of a conductive adhesive
64
.
Because the ground electrode
61
c
is grounded to the object member
65
directly in this case, the method has advantages that it is no need to solder any lead to the electrode and a general-purpose piezoelectric sensor is employable. In spite of this, the method still includes an anxiety; because the ground electrode
61
c
is possibly shorted with the output electrode
61
b
due to an adhesive extruded from the end of the bonding portion, the bonding must be done specially carefully. When in accordance with the bonding method example shown in
FIG. 10
, the higher the possibility of short-circuit becomes, the thinner the piezoelectric element becomes.
SUMMARY OF THE INVENTION
Under such the circumstances, it is an object of the present invention to provide a piezoelectric sensor that never sacrifices any of work properties, for example, even when a lead wire is to be soldered to one of a pair of electrodes of a piezoelectric sensor and the other electrode is to be bonded and fixed to a predetermined member with an adhesive.
It is another object of the present invention to make it efficient to bond the ground electrode of the piezoelectric sensor to the conductive portion of the object member with an adhesive so as to be fixed and connected electrically, thereby preventing a short-circuit that might occur between the two electrodes due to extruded and stuck adhesive.
It is further another object of the present invention to provide an easier method for testing whether or not the ground electrode is connected electrically to the conductive portion of the object member.
It is further another object of the present invention to provide a method for simplifying both wiring and assembling works for disposing the piezoelectric sensor to an actuator of a disk unit with the use of the above method.
The piezoelectric sensor, which is a first invention in this application, has a first electrode formed on a first surface of a thin plate-like piezoelectric element and a second-electrode formed on a second surface of the same piezoelectric element. The first electrode is formed with a conductive metallic material of more wetting properties than the second electrode and the second electrode is formed with a conductive metallic material of more adhesive properties than the first electrode.
For example, the first electrode may be plated with gold and the second electrode may be plated with nickel. According to the method for fixing the piezoelectric sensor, which is another invention in this application, in order to bond the piezoelectric sensor with an adhesive to an object member whose distortion is to be detected, a predetermined portion of the object member is formed with a conductive material and the second electrode of the piezoelectric sensor is bonded to the predetermined portion with a non-conductive adhesive, then pressed with a predetermined pressure so as to be hardened and connected.electrically. In this case, the adhesive may be an anaerobic photo-setting one.
The actuator, which is further another invention in this application, comprises an actuator arm held rotationally within a predetermined range and composed at least partially of a conductive material; a moving coil held at the actuator arm; a stator magnet cooperating with the moving coil to compose a voice coil motor and rotate the actuator arm; and the above pie
Satoh Kiyoshi
Soga Eiji
Tsuda Shingo
Allen Andre
Bracewell & Patterson L.L.P.
International Business Machines - Corporation
Martin Robert B.
Williams Hezron
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