Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-03-01
2002-06-18
Sircus, Brian (Department: 2839)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S328000, C310S800000
Reexamination Certificate
active
06407481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device using a piezoelectric/electrostrictive film, and more particularly relates to the structure of a piezoelectric/electrostrictive device for improving an operational characteristic of a piezoelectric/electrostrictive device in an element for converting electrical energy into mechanical energy such as mechanical displacement, mechanical force, and vibration, and for converting in reverse. Concretely, the present invention relates to a piezoelectric/electrostrictive device to be preferably utilized in a variety of sensors, such as transducers, a variety of actuators, frequency-region functional components (filters), transformers, vibrators and resonators for communication and motive power, oscillators, discriminators, ultrasonic sensors and acceleration sensors, angular velocity sensors and impact sensors, mass sensors, or the like, and moreover to be applied to unimorph- and bimorph-type elements used for servo displacement elements described in “From Foundation up to Application of Piezoelectric/Electrostrictive Actuator” written by Kenji Uchino (edited by Japan Industrial Technique Center and published by MORIKAWA SHUPPAN), and to be preferably employed to a variety of actuators used for mechanisms for displacement and positioning adjustment and angle adjustment of a variety of precision components, or the like, of an optical apparatus and a precision apparatus, or the like.
2. Description of the Related Art
Recently, there has been a requirement for a displacement control element for adjusting an optical-path length or a position in sub-micron order in optical and magnetic recording fields and precision machining fields. Responding to the requirement, development has been progressed of a piezoelectric/electrostrictive actuator or the like which is an element utilizing a displacement based on the reverse piezoelectric effect or the electrostrictive effect caused when an electric field is applied to a piezoelectric/electrostrictive material such as a ferroelectric substance or the like.
In a magnetic recording field represented by a hard disk, among the above mentioned fields, particularly a storage capacity has been remarkably increased in these years, and this is because an attempt has been made to increase the recording density per se by increasing the number of recording tracks for more effective use of recording mediums, in addition to the improvement of a recording method of write/read.
So far, such attempt has been made mainly on the improvement of a voice coil motor, however, an attempt is introduced as a new technique, for example, in a preprint manuscript of “1997 International Conference on Solid-State Sensors and Actuators” of “TRANSDUCERS '97”, pp. 1081-1084, that an electrostatic-type micro-actuator fabricated by micro-machine processing of Si or Ni is applied to the tracking system of a hard-disk magnetic head.
Moreover, Japanese Unexamined Patent Publication No. 10-136665 discloses a piezoelectric/electrostrictive actuator
101
, as shown in
FIG. 26
, wherein a fixing portion
103
and a movable portion
104
and at least one beam portion
102
constituted therewith are integrally formed by arranging at least one hole on a plate-shaped body composed of a piezoelectric/electrostrictive material, a displacement generating portion is constituted by providing an electrode layer
105
such that an expansion and a contraction is caused in a direction connecting the fixing portion
103
with the movable portion
104
on at least a part of the at least one beam portion
102
, and a displacement of the movable portion
104
relative to the fixing portion
103
generated by the expansion or the contraction of the displacement generating portion becomes an arc-shaped displacement or a rotational displacement in-plane of the plate-shaped body.
However, with a conventional art for positioning a recording head primarily using a voice coil motor, it is difficult to accurately position the recording head so as to accurately trace tracks thereof by increasing the number of the tracks, in order to respond to the further increase in capacity.
Further, although the above-described art using the electrostatic-type micro-actuator is an art to obtain a displacement by a voltage applied between a plurality of plate-shaped electrodes formed by the micro-machining, structurally, it is difficult to raise a resonant frequency, and as the result, a problem is immanent that vibrations are hardly attenuated when operated at a high speed. Furthermore, in view of the principle of displacement, there is a feature that the linearity of the voltage-displacement property is inferior, and from a viewpoint of an accurate positioning, there are many problems to be solved. Furthermore, the process of micro-machining per se is problematical in the fabrication cost.
Moreover, since the piezoelectric actuator
101
disclosed in Japanese Unexamined Patent Publication No. 10-136665 has a piezoelectric operating portion (a portion where a displacement is caused by distortion of a piezoelectric film) of a monomorph structure, an axis of the main distortion of a piezoelectric body naturally becomes coaxial or parallel with an axis of the main displacement of the piezoelectric operating portion, thus there is a problem that a displacement generated at the piezoelectric generating portion per se is small, and a displacement of a movable portion is also small. Furthermore, the piezoelectric actuator
101
per se is heavy, and as described in the official gazette of Japanese Unexamined Patent Publication No. 10-136665, it is likely to be influenced by harmful vibrations for operation, for example, residual vibrations and vibrational noises, for example, when operated at a high speed, making it necessary to suppress the harmful vibrations by filling a hole with a filler. However, the use of such filler is likely to unfavorably influence upon a displacement of the movable portion. Further, since the piezoelectric actuator
101
is constituted unavoidably with a piezoelectric/electrostrictive material per se which is inferior in mechanical strength, there is also a problem that the actuator is likely to be subjected to limitation of a shape and a use application due to the strength of the material.
SUMMARY OF THE INVENTION
The present invention is made in view of the problems of a piezoelectric/electrostrictive device described above, and it is the object of the present invention is to produce a piezoelectric/electrostrictive device which is made capable of performing precise operation at a high speed with a low power, and is roughly classified into three categories as described hereinafter. It should be noted that “piezoelectric” of a piezoelectric element, a piezoelectric film, and piezoelectric ceramics used in the present invention includes meanings of both “piezoelectric” and “electrostrictive”.
According to the present invention, provided as a first piezoelectric/electrostrictive device is characterized in that a connecting plate, a diaphragm, and a substrate are mutually joined together such that a joining direction of the connecting plate with the substrate and a joining direction of the connecting plate with the diaphragm are mutually intersected to form a cross, and the diaphragm is straddled between the connecting plate and the substrate, a piezoelectric element is arranged on at least a part of at least one surface of the diaphragm, and the diaphragm is convexly curved in a direction perpendicular to two directions by which said cross is formed.
In this first piezoelectric/electrostrictive device, a fixing plate is also preferably joined with an end of the connecting plate. Other devices, parts, or the like of a magnetic head or the like may also be preferably fixed to a tip or the like of the connecting plate. Further, a larger displacement is also made obtainable by a structure wherein a connecting plate and a fixing plate are alternately joined to be a meandering shape, and a diaphragm with a piezoelec
Kimura Koji
Takeuchi Yukihisa
Yamamoto Kazuhiro
Burr & Brown
NGK Insulators Ltd.
Zarroli Michael C.
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