Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-07-26
2004-01-06
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323040
Reexamination Certificate
active
06674217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration member which uses a piezoelectric element, that is, an electro-mechanical energy conversion element as a driving source to form a driving vibration in an elastic member, a vibration wave driving apparatus which uses the vibration member as a driving source, and an apparatus provided with the vibration wave driving apparatus.
2. Related Background Art
As a vibration wave driving apparatus which uses, as a driving source, a vibration member for forming a driving vibration in an elastic member using a vibration source of a piezoelectric element as an electro-mechanical energy conversion element, there is a vibration wave motor as one system for relatively moving the vibration member and a contact member pressurized to contact the vibration member. The vibration wave motor serves as an actuator which can extract a large torque at a low speed, there is no cogging disposed on an electromagnetic motor, and the vibration wave motor is characterized by little rotation unevenness.
Particularly, in a traveling wave type vibration wave motor, a traveling vibration wave with a uniform vibration amplitude is generated in the elastic member, a moving member as a contact member pressurized to contact the elastic member is continuously driven, and therefore no rotation unevenness is generated in principle.
FIG. 21
is a perspective view of a vibration member of a conventional vibration wave motor.
Numeral
1
denotes an annular elastic member formed of a metal or the like,
2
denotes a piezoelectric element as an annular electro-mechanical energy conversion element, and the piezoelectric element
2
is bonded and fixed to one surface of the elastic member
1
by an adhesive.
For the piezoelectric element
2
, electrodes are formed on both surfaces of a piezoelectric member constituted of ceramic subjected to a polarization treatment, voltage applying electrodes
3
are arranged at intervals in a peripheral direction on the surface shown in
FIG. 21
, and an entire surface electrode (not shown) for covering the entire surface is disposed on the surface bonded to the elastic member
1
.
On the other hand, a wear-resistant layer of a wear-resistant friction material or the like is formed on the other surface (the surface opposite to the surface bonded to the piezoelectric element
2
) of the elastic member
1
, and a moving member (not shown) is pressurized to contact via the wear-resistant layer.
In
FIG. 17
, (
1
) to (
3
) are development diagrams showing a driving principle of a traveling wave type vibration wave motor.
In
FIG. 17
, (
1
) shows a first standing wave with a wavelength &lgr; excited in the vibration member (referred to as A phase), and (
2
) shows a second standing wave with a wavelength &lgr; excited in the vibration member (referred to as B phase). For the shown A and B phases, respective node positions (antinode positions) deviate from each other by a ¼ wavelength. By simultaneously exciting and overlapping these two standing waves with a time phase difference of 90°, a traveling wave with a uniform amplitude can be synthesized as shown in (
3
) of FIG.
17
.
For the vibration member in which the flexural traveling wave is excited in this manner, since a point apart from the neutral surface of flexural displacement performs elliptical movement, by pressing the moving member onto the top surface of the vibration member for contact in the vicinity of a vertex of elliptical movement, the moving member is driven by a friction force acting between the vibration member and the moving member.
For the piezoelectric element bonded to the elastic member constituting the vibration member for exciting the respective standing waves A, B, by forming a plurality of electrodes on a single disc by evaporation or the like and subjecting a plurality of areas to the polarization treatment, two standing waves deviating in phase from each other can be excited by a single piezoelectric element.
FIGS. 18A and 18B
show a representative polarization pattern. Respective electrode groups of A and B phases are formed via a non-driving portion with a length of a ¼ wavelength, and in each group, each electrode has a length of a ½ wavelength and the electrodes adjacent to each other are polarized in reverse directions as shown by symbols (+), (−) in FIG.
18
A.
The respective electrode groups of A and B phases are short-circuited by means such as a conductive paste and a flexible printed board, a contraction and expansion force is therefore generated in a direction crossing at right angles to a polarization direction by applying a desired voltage between the electrode and a ground electrode on the back surface, and the aforementioned two standing waves are excited at the respective voltages of the A and B phases by applying a flexural moment to the vibration member.
However, in the aforementioned conventional example, when the polarization treatment is performed in order to form adjacent polarized areas in polarization directions opposite to each other in one piezoelectric element, the following problems arise.
FIG. 19
is a developed sectional view of the piezoelectric element of a portion in which the polarization directions in the adjacent polarized areas are opposite to each other. Arrows in
FIG. 19
show electric force lines by differences of potentials applied to the respective electrodes during polarization.
As shown in
FIG. 19
, in a portion apart from a boundary (
3
) of two electrodes (
1
) and (
2
), the electric force lines run substantially in a thickness direction, and the polarization direction also runs along the direction of the electric force lines.
However, many of the electric force lines in the boundary (
3
) between the adjacent electrodes (
1
) and (
2
) run in a direction crossing at right angles to the thickness direction between the adjacent electrodes, instead of the thickness direction. Therefore, the present inventors have clarified that the polarization direction also runs in the direction crossing at right angles to the thickness direction of the piezoelectric element.
On the other hand, a flexural rigidity of the vibration member is determined mainly by the flexural rigidity of the elastic member and the rigidity of the bonded piezoelectric element.
Since the piezoelectric element is bonded to a position apart from the neutral surface of the vibration member in the thickness direction, the rigidity of the direction crossing at right angles to the vibration direction contributes to the flexural rigidity of the vibration member. For the piezoelectric element, a modulus of longitudinal elasticity is anisotropic depending on the applied polarization direction. Specifically, in
FIG. 19
, when the modulus of longitudinal elasticity of a direction parallel to the polarization direction of an area subjected to a treatment in the (ideal) polarization direction is Y
11
, and the modulus of longitudinal elasticity of a direction crossing at right angles to the ideal polarization direction is Y
33
, there is usually a relation of Y
11
>Y
33
.
Since polarization is performed substantially in the thickness direction in the vicinity of the middle of the electrodes (
1
) and (
2
), the modulus of longitudinal elasticity of the thickness direction is Y
11
. However, when the adjacent electrodes are polarized in reverse directions, the modulus of longitudinal elasticity of the direction crossing at right angles to the thickness direction is Y
33
in the boundary (
3
). Therefore, the modulus of longitudinal elasticity of the boundary of the electrodes polarized in the reverse directions indicates a smaller value than that of an electrode portion.
If there is partially a difference in the modulus of longitudinal elasticity of the elastic member, the following phenomenon occurs.
Specifically, for the standing wave excited by the elastic member, a propagation speed is determined by the flexural rigidity of each portion of the elastic member, and a line dens
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