Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-08-20
2001-08-21
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S369000
Reexamination Certificate
active
06278222
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric element and piezoelectric element manufacturing method and an actuator using a piezoelectric element manufactured by said method.
2. Description of the Related Art
Actuators using a piezoelectric element have been widely used in recent years in cameras, measurement devices, and other precision mechanisms used for positioning and driving driven members because they increase the conversion efficiency for converting the supplied electrical energy to a drive force, increase the generated drive force while reducing the form-factor and weight, and allow the drive force to be easily controlled.
The piezoelectric element used as a power source in such actuators are constructed as units of multilayered piezoelectric elements, as disclosed in U.S. Pat. No. 5,589,723. This construction adds the displacement in the thickness direction generated in the piezoelectric element unit so as to take the largest possible displacement.
The piezoelectric element constructed as a plurality of layers of the piezoelectric element unit is subject to higher cost because it is manufactured by complex operations involving a process for providing electrodes on the respective surfaces of the unit elements, a process for adhering the laminate layers, and a process for connecting the leads of the electrodes of each layer.
A piezoelectric element formed as a single layer of a hollow cylinder has been proposed as another configuration of a piezoelectric element in U.S. Pat. No., 4,874,979.
The hollow cylinder piezoelectric element characteristically has a relatively high mechanical strength, but requires a higher electric field strength to increase the generated displacement. Accordingly, when there is a restriction on the voltage applied to the piezoelectric element, the electric field intensity must be increased by making the piezoelectric element thinner. This arrangement is disadvantageous in that the strength of the piezoelectric element is reduced when attempting to increase the generated displacement.
For this reason, the present inventors considered constructing a piezoelectric element by forming a ceramic material having PZT (PbZrO3.PbTiO3) as a main component into a thin sheet, attaching electrodes to both surfaces, and wrapping the sheet into a cylindrical shape, then sintering the material.
The element of this construction is subject to disadvantages such as deformation of the piezoelectric element due to the heating process during sintering.
SUMMARY OF THE INVENTION
The present invention eliminates the aforesaid disadvantages by providing an electromechanical transducer or a piezoelectric element comprising a thin sheet piezoelectric element formed of a piezoelectric ceramic having PZT (PbZrO3.PbTiO3) as a main component with electrodes formed on the surfaces thereof, said thin sheet piezoelectric element being wrapped around a shaft to form a cylinder.
This thin sheet piezoelectric element may be constructed by a laminate body comprising laminated first and second piezoelectric elements having an electrode formed on one surface, respectively.
This shaft may be a hollow shaft or solid shaft, and may be a burned shaft formed of the same material as the first and the second piezoelectric elements. The shaft also may be formed by a high melting point material.
This shaft may be constructed by adhering a plurality of members via an adhesive which thermally decomposes at a temperature below the burning temperature of the piezoelectric element.
The plurality of members comprising the shaft may be a plurality of individual disk-shaped plates separated relative to the displacement direction of the piezoelectric element and formed of a high melting point material, this shaft being formed by stacking the plurality of disk-shaped plates in the axial direction and adhering these plates using an adhesive which thermally decomposes at a temperature below the burning temperature of the piezoelectric element so as to form a cylindrical or circular column-like shaft.
The plurality of members comprising the shaft may be a plurality of individual cylindrical or circular column-like segments separated relative to the displacement direction of the piezoelectric element and formed of a high melting point material, this shaft being formed by gluing the plurality of segments using an adhesive which thermally decomposes at a temperature below the burning temperature of the piezoelectric element so as to form a cylindrical or circular column-like shaft.
Alternatively, the shaft may be constructed by coating the surface of a high melting point material with a coating agent which thermally decomposes at a temperature below the burning temperature of the piezoelectric element.
This piezoelectric element is manufactured by a process for forming electrodes on the surface of a first and a second piezoelectric element comprising a piezoelectric ceramic having a thin sheet of PZT (PbZrO3.PbTiO3) as a main component, a process for forming a cylindrical body by superimposing the first and second piezoelectric elements such that the surface having an electrode of the first piezoelectric element confronts the surface without an electrode of the second piezoelectric element, and wrapping these elements around a shaft to form a cylindrical body, a process for burning the formed cylindrical body at a predetermined temperature, and a process for polarizing the burned cylindrical body by applying a predetermined voltage between the electrodes.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.
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Katsuragi Hiroji
Matsui Naoki
Dougherty Thomas M.
McDermott & Will & Emery
Minolta Co. , Ltd.
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