Note: Descriptions are shown in the official language in which they were submitted.
1066798
The present invention relates to a vibration
detecting device which detects mechanical vibrations
and converts them to electrical si~nals, and more
particularly the present invention provides a vibra-
tion detect$ng device suitable for a vibration detecting
device for a musical instrument such as a guitar,
violin or the like, and a method for adapting the
vibration detecting device.
It is a first ob~ect of the present inven-
tion to provide a small size vibration detecting
device which is simple in structure and can be manu- -
factured at a low cost.
It is a second ob~ect of the present in- `
vention to provide a vibration detecting device which
has a hi8h sensitivity and a flat frequency charac-
teristic and which is most suitable as a pickup for
a musical instrument such as guitar, violin or the
` like.
It is a third ob~ect of the present inven-
tion to provide a vibration detecting device which can
be used as a vibration detecting device for a musical
instrument as well as a vibration detecting device
for detecting the vibration of a mechanical apparatus.
It is a fourth ob~ect of the present inven-
tiOn to provide a method for adapting the characteristics
` of the vibration detecting device, such as the sensitivity,
rise time~ fall time or the like, in a very simple
~` manner.
me present invention relates to a vibration
detecting device for detecting the vibration of a
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machine, musical instrument or the like and provides such
a vibration detecting device having a flat frequency character-
istic and a high sensitivity particularly in a low frequency
range.
Accordingly, the invention provides a vibration
detecting system comprising at least one piezoelectric ceramic
plate having electrodes on both operative surfaces thereof,
a case housing said piezoelectric ceramic plate and having
a surface ~or receiving vibrations to be detected, an accoustic
coupling medium interleaved between the case and the operative
surfaces of said piezoelectric plate and said case said
medium extending generally parallel to said surfaces so as to
couple them accoustically to the vibration receiving surface
of said case and said coupling medium comprising a vibration
damping material adapted to damp high frequency vibrations
through said case to said plate to suppress unfavourable
resonances in the high frequency regions and flatten the
fre~uency characteristic in the low frequency region. ~ -
The above and other objects, features and advantages
of the present invention will become more apparent from the
following detailed description of the preferred embodiments
of the present invention when taken in conjunction with the
accompanying drawings, in which:
Fig. 1 is a perspective view of a prior art vibration -
; detection device. -~
Fig. 2 is a sectional view thereof.
Fig. 3 is an exploded perspective view of a vibration
detecting device in one embodiment of the present invention.
Fig. 4 is a sectional view thereof.
Figs. 5 through 7 are sectional views of other embodiments
of the present invention.
Fig. 8 is an exploded perspective view of a major part
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of a vibration detecting device in another embodiment of the
present invention.
Fig. 9 is a sectional view thereof.
Fig. 10 is a sectional view of a further embodiment
of the present invention.
Fig. 11 is a longitudinal sectional view of a vibration
detecting device in a still further embodiment of the present
invention.
Fig. 12 is a cross-sectional view thereof.
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Pigs. 13 and 14 are longitudinal sectional
views of vibration detecting devices in accordance
with still other embodiments of the present inven-
tion, respectively.
Fig. 15 is a cross sectional view of
a vibration detecting device in accordance with
still another embodiment of the present inven-
tion-
Fig. 16 is a longitudinal sectional view
thereof.
Figs. 17A and B are perspective views
showing the mounting of the vibration detecting
device on a conventional guitar.
Fig. 18A is a perspective view showing
the mounting of a prior art device shown in Figs,
17A and B, and Fig. 18B and C are perspective views
of the embodiments of the present invention. ~ -
Referring first to Figs. 1 and 2, a prior `
art vibration detecting device of the type describet
above is explained.
In Figs. 1 and 2, 1 and 2 designate piezo-
electric ceramic plates, 1', 1", 2' and 2" designate
electrodes formed on the surfaces of the piezoelectric
ceramic plates 1 and 2~ 3 designates a case, 4 a
coaxial cable~ 4' a grounding lead wire, 4" an
internal wire~ 5 a plastic plate of such material
as epoxy or phenol resin, 6 epoxy resin filled between
the case 3 and the piezoelectric ceramic plates 1,
2, and the lead wires 4', 4", 7 a lead wlre connecting
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the electrodes 1", 2' of the piezoelectric ceramic
plates 1, 2, and 8 designates solder or conductive
bonding maeerial.
When such a vibration detecting device
is attached to an ob~ect, such as a machine, musical
instrument or the like, having a vibrating plane
parallel to the electrode planes of the piezoelectric
ceramic plates 1 and 2~ it can detect the vibration ~`
of the ob~ect. Namely, since the bending~mode of
; 10 vibration is caused in the piezoelectric ceramlc
plates 1 and 2 through the vibration of the ob~ect,
an electric signal is produced between the lead
wire 4~ and the internal wire 4" connected to the
electrodes 1~ and 2" of the piezoelectric ceramic
plates. In the case of the prior art arrangement shown
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in Fi8. 2, because the epoxy or phenol resin and
the filling epoxy resin are hard, the sensitivity `
to relatively low frequency vibrations has been
low. Also, because there exists a resonance point
of the detector at a relatively high frequency, -
the vibration is propagated from the detector
` through an amplifier, a speaker, air, the musical
instrument and back to the detector when the detector
is used as a music instrument vibration detecting
device, causing howling or deterioration of quality
of sound or the emphasis of a particular sound. `
The present invention is intended to eliminate
such drawbacks of the prior art device and to provide
a vibration detecting device having a f lat requency
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characteristic and a high sensitivity in a low fre-
quency region.
One embodiment of the present invention will
now ~e described in con~unction with Fig. 3 in which
ehose parts which are common to Figs. I and 2 are
represented by the same reference numerals. Referring
to Fig. 3, the reference numerals 9, 9'~ 10 designate
vibration absorbing plates of relatively soft material,
such as cork board, resin or rubber board including
asbestos, or rubber board, which absorbs the vibra-
tion. mese are bonded together by an adhesive in
the directions of the arrows and placed in a case 3 to
complete a vibration detecting device as shown in
- Fig. 4. In Fig. 4, 3' designates a lid of the case
3 and 6 designates the adhesive material. As shown
in Fi8. 4, the interior of the case 3 is reduced at
its tip end and periphery so that the peripheries of
the vibration absorbing plates 9~ 9'~ 10 contact each
other to surround the piezoelectric ceramic plates
` 20 1 and 2.
Other embodiments of the present invention
are explained in con~unction with Figs. 5, 6 and
7.
In a embodiment shown in Fi8. 5, the
piezoelectric ceramic plate 1 is held between the
vibration absorbing plates 9~ 9' and 10, and a
shielding metal plate 11 is interleaved between
the vibration absorbing plates 10 and 91.
In an embodiment shown in Fig. 6, U-shaped
metal plates 12 are interleaved between the piezoelectric
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ceramic plates 1, 2 and the vibration absorbing plate
10.
In an embodiment shown in Fig. 7, U-shaped
metal plates 13 are interleaved between the vibration
absorbing plate 9 and the piezoelectric ceramic plate
1 and between the vibration absorbing plates 9~ and
10. me vibration detecting devices of the present
invention thus constructed offer the following
advantages.
(A) Since the piezoelectric ceramic plate or
the detecting element comprising the bonded piezo-
electric ceramic plate and metal plate is surrounded
by the vibration absorbing plate, high frequency
vibratlons are propagated only with difficulty so
that when it is used as a music instrument vibration
detecting device a soft tone is produced and the
resonance output is very small even when a resonance -
point of the detecting element is at a high frequency.
Further, the sensitivity at a high frequency is reduced
suppressing howling.
(B) Since the shape of the vibration absorbing
plate is si~ple it is possible to select the material
from the standpoint of vibration absorbing ability
without paying attention to the molding of the plate ` -
and hence a vibration detecting device of an excellent
characteristic can be provided.
(C) It is easy to assemble.
In the prior art device shown in FiP. 2,
since there exists hard epoxy resin 6 between the
vibration detecting element and the case 3~ there
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are drawbacks in that resonance occurs at a high fre-
quency while the sensitivity to low frequency vibration
is low, and the frequency characteristic is not
flat.
According to another embodiment of the
present invention, in order to eliminate the above
drawbacks of the prlor art device, resin 6 having
foaming material mixed thereto is interlesved between
the vibration detecting element and the case 3. As
the foaming mater~al~ ~'Erozeam~ used to prevent the
flow of the adhesive material may be preferably
used.
; In the above embodiment, in place of the
plastic plate 5 a molded resin plate having foaming
; 15 material mixed thereto may be used.
Accord$ng to the embodiments of the present
inventlon describet above~ the resonance at a high
frequency is prevented and the reduction of the --
sensitivity at a low frequency is also prevented so
that an advantageous result of a flat frequency
characteristic is obtainet.
Flgs. 8 and 9 show another embodiment of
the present invention, in which those parts common
to Figs. 1 and 2 are represented by the identical
reference numerals. Referring to Fig. 8, 22 designates
a metal plate formed in V-shape, and the piezoelectric ~-
ceramic plates l-land 2 are tightly bonded to outer ~ -
surfaces of the metal plate 22 by adhesive matérial.
me electrode on the bottom of the piezoelectric
ceramic plate 1 and the metal plate 22, and the
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electrode on the top of the piezoelectric ceramic plate 2 and
the metal plate 22, respectively, are electrically connected
through the adhesive material. 20 designates an envelope-like
holder comprising vibration absorbing material such as rubber
or resin including cork, asbestos or the like, formed into an
envelope shape, and a supporting member 20' is integrally formed
at a center of the envelope-like holder 20. As shown in Fig. 9,
the U-shaped metal plate 22 is housed in the envelope-like holder
20 to hold the supporting member 20' by the U-shaped metal plate.
Since a small amount of adhesive material is filled in the
envelope-like holder 20, the metal plate 22 is affixed within
the envelope-like holder 20. On a surface of the envelope-like
holder housing the metal plate 22 therein as described above,
adhesive material is applied and the envelope-like holder 20 is
placed in the case 3 and fixed thereto. 6 designates epoxy
resin filledin an opening of the case 3 and 3' designates a lid
of the case 3.
Fig. 10 shows another embodiment of the present invention
in which the piezoelectric ceramic plate l is bonded to the
inside of one piece of the U-shaped metal plate 22, the other
piece of the U-shaped metal plate 22 serving as a shielding
plate.
Figs. 11 and 12 show ànother embodiment of the present
invention, which will now be described in conjunction with the
drawings, in which l designates the piezoelectric ceramic plate,
3 the case, 4 the coaxial cable, 4' the internal wire, 4" the
grounding
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106~;798
wire and 24 the vibration absorbing material. The vibration
detecting device according to the present embodiment is formed
with grooves 7, 7', 8,8' near the periphery of the inner side
of the vibration detecting section A in the case 3.
The detecting section defined between the grooves 8
and 8' is easily vibrated at a low frequency region owing to
its thick structure. Fig. 13 shows a further embodiment of
~e present invention, in which similar references designate
the same parts as shown in Figs. 11 and 12. In the embodiment
a recess 26 is formed in the inner side of the vibration
detecting section A in the case 3 at a position corresponding
to a center of the piezoelectric ceramic plate.
Owing to the thin thickness of the recessed portion,
it is easily vibrated at a high fre~uency region. Fig. 14
shows still another embodiment of the present invention, in
which similar references designate the same parts as shown in
the previous embodiment. In the drawing, 30 and 30' designate
spacers of relatively soft material such as rubber, soft plastic,
cork orthe like, 32 designates a box-like metal foil for
shielding, to which the piezoelectric ceramic plate 1 is bonded,
the bonding surface being electrically conductive. 34, 36 and
36' deslgnate a raised portion and recessed portions. The
piezoelectric ceramic plate 1 is bonded to the inner face of ~ -
; the box-like metal foil 32 and the spacer 30 of plate or block
shape made of rubber or cork is filled in the space and bonded to
the adhesive material 24, and the vibration detecting unit -
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thus constructed is then bonded and affixed to the assembly com-
prising the case 3 having the raised portion 34 and the recessed
portions 36, 36' formed in the inner face of the vibration detect-
ing section A, the spacer 30' being fitted to the inner surface
of the case 3.
In the embodiment shown in Figs. 11 and 12, by the pro-
vision of the grooves 7, 7', 8, 8' near the periphery of the inner
surface of the vibration detecting section A of the case 3, the
sensitivity at a low frequency region can be enhanced. In this
case, when the filling adhesive material 24 is softer than the
material of the case 3, a remarkable effect is obtained in that
the sensitivity at a low frequency range is further enhanced. In
thè embodiment shown in Fig. 13, not only the overall sensitivity
is enhanced, but the sensitivity at a high frequency range is
further enhanced. This effect is remarkable when the filling
adhesive material 24 is softer than the material of the case 3.
In the embodiment shown in Fig. 14, not only the overall sensi-
tivity is enhànced but the sensitivity at a low frequency range
is further enhanced. This effect is remarkable when the material
of the spacers 30, 30' as softer than the material of the case 3.
~hile the grooves or the raised and recessed portions
~- are formed in the inner surface of the vibration detecting sectionA of the case 3, they may be formed on the outer surface of the
vibration detecting section A of the case to obtain similar result.
Further,
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a similar result is obtainable when the filling adhesive
materia ~ and the fillers such as the spacers 10, 10' are not
provided over the entire inner surface of the case 3.
Figs. 15 and 16 show another embodiment of the present
invention, in which 21 designates a piezoelectric ceramic
plate located in a case 23 of plastic or wood. Vibration
absorbing material ~ of such as rubber or plastic is bonded
to the inner wall of the case 23, and the piezoelectric
ceramic plate 21 is bonded thereon. 44 designates fillinq
material, such as epoxy resin mixed with foaming material,
filled in thevoid in the case 23, and 46 designate a shield
wire. 47 and 48 designate lead wires aoldered to the
electrodes on the surface of the piezolectric ceramic plate 21.
The case 23 is constructed such that the thickness
tl, t2 of the planes which are parallel to the plane of the
piezoelectric ceramic plate 21 are thinner than the thicknesses
dl, d2, wl, w2 of other planes.
While the piezoelectric ceramic plate 21 is intimately
contacted to the inner wall of the case 23 through the vibration
absorbing material ~r in the above embodiment, it may be
intimately contacted directly to the inner wall of the case -~
23.
According to the vibration detecting device of the
- above embodiment, since the case Gf the vibration detecting
device is constructed such that the thickness of the planes -~
;~ parallel to the plane of the
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piezoelectric ceramic plate is thinner than the other planes, the
flexing or bending vibrations on the other planes do not strongly
appear and the vibration energy does not escape and the vibration
energy on the bottom surface effectively is used to cause the
bending operation of the piezoelectric ceramic plate, resulting
in a high sensitivity. Further the amplitude at the antinode of
the vibration wave on the bottom surface of the case is not reduced
and a high sensitivity is assured. Thus, since a sufficient sen-
sitivity is obtainable from a single piezoelectric ceramic plate,
it is simple in structure and easy to manufacture. The above
effect is remarkable when the density of the case material is
higher than that of the filling material or when the material of
the filling material is more flexible than the case.
In general, in the vibration detecting device of the
type described above, there are lead wires for deriving an
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electrical signal from the vibration detecting device. In such
an instance, there has been inconvenience in that the lead wires
contact a portion of the body of an instrument player or contact
the guitar body so that the vibration of the lead wires is pro-
pagated to the vibration detecting device, creating noise. A
similar inconvenience has been encountered when the vibration -
` detecting deviceof the type described above was attached to other
musical instruments or machines.
Fig. 17A shows a guitar to which a prior art vibration
detecting device is attached. In Fig.
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17A, 51 ~esignates a guitar, and 52 designates a vibration
detecting device bonded to a frame of the guitar 1. 53 designates
a lead wire (shielded wire) having one end connected to the
vibration detecting device 52, the other end of the lead
wire 53 being connected to an amplifier. In another example of
the prior art shown in Fig. 17B, a connector 57 is fixed to
~` the guitar 51 and the vibration detecting device 52 is
connected to the connector 57 by the lead wire 53, and a
cord 58 is removably coupled to the connector 57.
Fig. 18 shows the guitars to which the vibration
detecting devices are mounted, in which Fig. 18A shows the
prior art as shown in Figs. 17A and B, and Figs. 18B and C show
the embodiments according to the present invention. In Figs.
18A, B and C, 52 designates the vibration detecting device,
53 the lead wire, and 54, 54' the retainers for the lead wire
53. The retainer 54 shown in the embod me~nt of Fig. 18B is
constructed by stamped-out portions ~t~l6~ by which the lead
wire 53 is retained, The retainer~ is bonded to the guitar,
and that port-ion of the lead wire 53 which lies between the
retainer 54 and the vibration detecting device 52 is slackened.
The retainer 54' shown in the embodiment of Fig. 18C comprises
a rubber or plastic block having an aperture therein through
which the lead wire 53 is passed for fixing.
By fi~ing the lead wire near the vibration detecting
device, the vibration occuring whenthe lead wire contacts-
with a player body or the instrument
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body does not propagate to the vibration detecting device and the
occurrence of noise is prevented.
The effect of noise suppression is further enhanced by
slackening the lead wire portion between the retainer and the
vibration detecting device. ~here the lead wire is fixed by the
stamped-out portion of the retainer of the embodiment shown in
Fig. 18B, the same effect is obtainable whether one or two stamped-
out portions are used. The material of the retainer may be metal,
rubber, plastic or adhesive tape.
While the above embodiment has been described in conjunc-
tion with the guitar, the same effect is obtainable with other
musical instruments or machines. While both the vibration detect-
ing device and the retainer are attached to a vibrating object or
guitar in the above embodiment, the same effect is obtained when
the vibration detecting device and the retainer are attached to `-
different bodies.
Where the bottom surface of the vibration detecting
device of the present invention is to be attached to a musical
instrument or the like, the sensitivity is increased as the dis-
tance from the bottom surface of the case to the piezoelectricceramic plate is shortened because the vibration of the musical
instrument is more strongly propagated. Accordingly, it has been
noticed by the inventor that the sensitivity is enhanced by
cutting away the entire region, central portion or peripheral
portion of the bottom surface of the case by grinding
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or other means. This effect is remarkable particularly when the
vibration propagating material is softer than the case material.
The same effect is obtainable when the top surface of the case is
cut away by grinding or other means, although the effect is not
considerable.
Similarly, when the bottom surface of the case is to
be attached to the musical instrument or the like, the sensitivity
is enhanced and the tracking characteristic to the vibration of
the musical instrument is also enhanced by cutting away the side
surface of the case. Namely, the sensitivity is enhanced and the
rise time and fall time are shortened. This effect is remar~able
when the vibration propagating material is softer than the case
material.
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