Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electrostrictive – magnetostrictive – or piezoelectric
Reexamination Certificate
1999-03-19
2001-03-20
Woo, Stella (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electrostrictive, magnetostrictive, or piezoelectric
C381S191000, C310S311000, C367S155000, C367S157000
Reexamination Certificate
active
06205226
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a piezoelectric acoustic device, and more particularly to a piezoelectric acoustic device in the form of a piezoelectric speaker, a piezoelectric buzzer or the like which is suitable for use for an electronic equipment such as a portable telephone or the like.
A piezoelectric acoustic device which has been conventionally known in the art is disclosed in U.S. Pat. No. 4,079,213 and U.S. Pat. No. 4,989,302. The conventional piezoelectric acoustic device disclosed includes a casing constituted of a combination of a first casing half and a second casing half, as well as a piezoelectric vibrator received in the casing. The piezoelectric vibrator includes a vibrating plate which is made of a metal material and has an outer peripheral portion interposedly held between the first casing half and the second casing half. Another piezoelectric acoustic device is also proposed which is constructed in substantially the same manner as that described above except that a vibrating plate is joined at an outer peripheral portion thereof to a casing by means of an adhesive.
Unfortunately, the adhesive before curing is pasty and exhibits flowability or fluidity, resulting in flowing on a metal vibrating plate while spreading inwardly in a radial direction thereof. Thus, after the adhesive is cured, it deteriorates vibration of the outer peripheral portion of the metal vibrating plate, to thereby reduce a substantial diameter of the metal vibrating plate. For example, when the adhesive spreads by 0.5 mm inwardly in the radial direction of the metal vibrating plate, the metal vibrating plate is reduced by about 1.0 mm in substantial diameter thereof.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a piezoelectric acoustic device which is capable of keeping a substantial diameter of a metal vibrating plate from being reduced.
It is another object of the present invention to provide a piezoelectric acoustic device which is capable of preventing clogging of a damping cloth member.
It is a further object of the present invention to provide a piezoelectric acoustic device which is capable of eliminating a necessity of arranging a damping cloth member as required.
In accordance with the present invention, a piezoelectric acoustic device is provided. The piezoelectric acoustic device includes a piezoelectric vibrator including a metal vibrating plate and a piezoelectric ceramic element joined to the metal vibrating plate, a casing constructed so as to receive the piezoelectric vibrator therein and formed on an inner peripheral surface thereof with an inclined joint surface section of an annular shape which surrounds an outer peripheral portion of the metal vibrating plate, and a pressure-sensitive adhesive layer formed by coating a pressure-sensitive adhesive on the inclined joint surface section. The outer peripheral portion of the metal vibrating plate is joined through the pressure-sensitive adhesive layer to the inclined joint surface section.
The term “pressure-sensitive adhesive” used herein means an adhesive which is made by dissolving a sticky or tacky material in a solvent or made of the sticky or tacky material. Also, the term “pressure-sensitive adhesive layer” used herein indicates a layer which is formed by volatilizing the solvent from the pressure-sensitive adhesive or is formed of the sticky material. The pressure-sensitive adhesive layer exhibits stickiness even when it does not contain the solvent or even when it is in a dry state, which stickiness permits joining between the outer peripheral portion of the metal vibrating plate and the inclined joint surface section. More particularly, joining between members by means of a pressure-sensitive adhesive is generally carried out by volatilizing a solvent contained in the pressure-sensitive adhesive therefrom and then subjecting the members to joining while abutting them against to each other. Thus, joining using a pressure-sensitive adhesive is distinguished from that using a curable adhesive wherein members to be joined are abutted against each other prior to drying (curing) of the curable adhesive. The pressure-sensitive adhesive suitable for use in the present invention may be prepared by dissolving a sticky material mainly consisting of acrylic resin, synthetic rubber or the like in a solvent such as toluene, ethyl acetate or the like.
The pressure-sensitive adhesive layer formed on the inclined joint surface section does not exhibit flowability or fluidity which causes the pressure-sensitive adhesive layer to radially inwardly enlarge or expand on the metal vibrating plate, unlike a paste-like curable adhesive. Also, the pressure-sensitive adhesive layer permits the metal vibrating plate to be joined to the casing while biting corners of the outer peripheral portion of the metal vibrating plate arranged at a predetermined angle on the inclined joint surface section of the casing into the pressure-sensitive adhesive layer, resulting in reducing a contact area between the outer peripheral portion of the metal vibrating plate and the pressure-sensitive adhesive layer. Also, the pressure-sensitive adhesive layer exhibits flexibility unlike a curable adhesive layer, to thereby ensure satisfactory vibration of the metal vibrating plate. Thus, the present invention prevents a reduction in substantial diameter of the metal vibrating plate.
The casing may be constituted of a first casing half made of an insulating resin material and including a first opposite wall arranged opposite to one surface of the piezoelectric vibrator and a first peripheral wall arranged so as to extend from an outer peripheral portion of the first opposite wall and a second casing half including a second opposite wall arranged opposite to the other surface of the piezoelectric vibrator and a second peripheral wall arranged so as to extend from an outer peripheral portion of the second opposite wall and fitted to the first peripheral wall of the first casing half. In this instance, the first peripheral wall and second peripheral wall are formed on an inner peripheral surface thereof with a first tapered surface section and a second tapered surface section, respectively. The first and second tapered surface sections cooperate with each other to form an annular groove for fitting the outer peripheral portion of the metal vibrating plate therein when the first and second peripheral walls are fitted to each other. The first and second tapered surface sections each are inclined so as to permit the groove to enlarge toward a central portion of the casing while directing an opening of the groove toward the central portion. One of the first and second tapered surface sections acts as the inclined joint surface section. The pressure-sensitive adhesive is coated on the inner peripheral surface of the first peripheral wall, to thereby provide the pressure-sensitive adhesive layer. The outer peripheral portion of the metal vibrating plate is held in the casing by means of a portion of the pressure-sensitive adhesive layer positioned in the groove.
In the illustrated embodiment, the first peripheral wall has an opposite surface constituting a part of an inner peripheral surface thereof and arranged opposite to an outer peripheral surface of the second peripheral wall. The opposite surface of the first peripheral wall and the outer peripheral surface of the second peripheral wall are so configured that the opposite surface is positioned outside a virtual surface defined by a locus of a distal end of the outer peripheral surface of the second peripheral wall when the first peripheral wall and second peripheral wall are fitted to each other and the pressure-sensitive adhesive layer applied to the opposite surface is prevented from being intruded into the groove.
Formation of the opposite surface of the first peripheral wall and the outer peripheral surface of the second peripheral wall into the above-
Senoo Masao
Sunahara Tadao
Yamashita Tsuyoshi
Hokuriku Electric Industry Co., Ltd.
Ni Suhan
Rankin, Hill Porter & Clark LLP
Woo Stella
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