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FIELD OF THE INVENTION The present invention relates to an electro-acoustic transducer in
which a vibrating element is formed from a film having a piezoelectric material provided with an
electrode and held in place by a capsule container at the periphery. In the prior art known
capsules, the container consists of a substrate whose periphery forms the support surface of the
periphery of the piezoelectric membrane. The container further comprises a lid whose periphery
is connected to the substrate and an internal recess which communicates with the outside
through at least 61 orifices. For example, in patent FR-A-251151O or patent FR-A-2331480, the
perimeter of the lid is in contact with the perimeter of the membrane and is interposed between
the membrane and the void perimeter of the substrate The pressure on the annular seal consists
of an inner crotch rigid annular lift which holds up. In the patents FR-A-1334235 and FR-A2275182, the void periphery of the substrate consists of a rigid annular lift forming the support
surface, and the membrane periphery is interposed between the lid and the weir The annular seal
is held in place against the annular lift. In the patent application DE-A-2123649, the membrane
is clamped in the slit of the perimeter seal which is interposed between the benefit and the
substrate. The central cavity of the substrate forms an inner cavity of the substrate with the
piezoelectric film. The inner four parts of the body form an inner lid cavity with the piezoelectric
film. The shape and size of the inner substrate cavity and the inner lid cavity substantially affect
the acoustic properties of the capsule. Also, the capsule is usually contained in an outer
container, in which case the outer surface of the lid and the wall of the container define an outer
void, the size and shape of the outer void also being the sound of the assembly! Affect the
characteristics. Thus, the capsule and the container in which the capsule is housed form a stack
of elements defining several cavities having a shape and size which greatly influence the
acoustical finish of the transducer. Such an 8% weight is usually formed in such a way that the
fixing is performed by welding, crimping or any other method by automatic means. Problems
known to be solved by the invention There are relatively large differences in the stacks formed
during manufacture in the known capsules. Because of these differences, the dimensions of the
different internal or external cavities and the contact forces of the members holding the
membrane perimeter in place vary considerably. As a result, the electro-acoustic quality of the
transducer varies considerably. Also, in known capsules, the piezoelectric membrane is held in
place by interposing at least one annular seal which is a separate member. As a result, it was
necessary to stack a relatively large number of elements for assembly, which took a considerable
amount of use for illll. .
The object of the present invention is in particular the known method and i! By providing a new
piezoelectric membrane capsule structure which makes it possible to produce capsules having
the shape and dimensions of the internal cavity precisely defined by means of automatic
assembly. To eliminate the disadvantages of As a result, according to the present invention, the
shape and size of the internal cavity and the supporting capacity of the weir which holds the
periphery of the membrane in place are very regulated and accurately determined. Related issues
are minimized. According to another object of the invention, the dispersion which occurs in the
formation of the internal cavity of the capsule is reduced to a minimum. This external cavity will
be formed later on assembling the capsule into the external container. For this purpose, the
capsule structure according to the invention provides a means of providing a known JjHI-like and
accurate fit on the inner surface of the outer container in which the capsule is fitted. According to
another object of the invention, the number of elements fitted during the assembly of the capsule
is substantially reduced. The problems normally associated with the use of known seals, usually
of irregular dimensions, which aggravate the flatness of the surface holding the piezoelectric film
in place are solved. Another object of the present invention is to be able to manufacture such a
capsule by simultaneously forming an assembly of a seal that holds the piezoelectric membrane
in place and contains the capsule and receives the wall of the outer container in a single
operation. As long as it provides means to automate. w! In order to achieve the above and other
objects, according to the present invention, the annular internal lift of the lid is formed by
"overmolding" (forming on a formed shape) Formed from an injectable elastomeric seal. In such a
structure, the seal is coupled to the lid. As a result, no leakage can occur between the seal and the
lid, and the seal at the periphery of the inner cavity of the lid and the seal between the inner
cavity of the lid and the inner cavity of the base are considerably improved. Ru. By using the
"overmolding" technique, a seal with a very flat support surface supported by the piezoelectric
film and high positioning accuracy can be obtained. As a result, the piezoelectric + g film is held
in place very accurately with respect to the lid, and the volume and shape of the internal cavity is
well defined. In particular, over-molding can compensate for any distortion in flatness that may
occur during molding of the lid. In an advantageous embodiment, the lid is manufactured by
overmolding from an injectible elastomer, which for example is the same material as the inner
seal, and forms an outer annular lift which forms an outer wall against which the wall of the
outer container in which the capsule is accommodated It consists of
The capsule is thus reliably used correctly. This means that the user will later fit the capsule in
the container in such a way that the outer seal seals around the inner capsule cavity. In one
embodiment, the inner seal and the outer seal are joined by a bridge that is made of the same
material that forms the seal and passes through the through holes in the lid spaced around the
periphery of the lid. Thus, the inner seal and the outer seal are formed by a single overmolding
operation. In the water specification, 1) Overmolding 1 is a conventional overmolding consisting
of injecting the material forming the seal into a mold containing the a-shaped lid, or 2 of the
molding of the lid and overmolding of the seal. By “one operation” is meant a pie-dioxicone in
which one operation is performed as two successive, closely-spaced steps by the same device.
These two treatment methods are well known and there is no need to make a specific adaptation
to the formation of the crucible of the present invention. In a preferred embodiment of the
invention, the lid is a continuous or non-continuous rigid perimeter defining an outer seal to form
a reference surface which limits collapse of the outer seal during insertion of the capsule into the
container. Has an external ring-shaped lift. The dimensions of the external cavity of the capsule
are therefore precisely and consistently determined. In one embodiment, the lid further defines
an inner seal to provide a continuous or non-continuous rigid perimeter inner annular lift
forming a reference surface that limits collapse of the inner seal during assembly of the
component by forming the capsule. Have. EXAMPLE In the example shown, the capsule of the
present invention is pressure-resistant. 4111111からなる。 The piezoelectric% lI may be
of a known type, for example, a thin metal or insulating film which forms the base of the film,
and a piezoelectric ceramic II which is fixed on the film and mated on both sides to form an
electrode. The electrodes are connected by means of electrical connection means, which may for
example be of known type, to output terminals such as the terminal 2 for connection to an
external electrical circuit. For example, it is approximately circular! III is suitably held within the
capsule container at its periphery. The container consists of a substrate 4 with a central cavity 5
whose periphery forms the support surface 6 of the periphery of the membrane 1. The support
surface 6 advantageously consists of a rigid annular lift on which the lower edge of the wAl is
mounted. The container further comprises a lid 7 connected to the substrate 4 at the periphery 8.
M7 and substrate 4 are preferably joined along respective peripheral contact surfaces 9 and 10,
which are precisely formed to form an assembly that can be easily reconfigured, M7 being shown
on the wall of the lid It has an internal recess 11 which is passed to the outside by a series of
orifices, such as orifices 12 spaced apart at W intervals.
The recess 11 of the lid forms an internal lid cavity. The central cavity of the substrate forms an
internal rB base cavity. The aforementioned internal spaces are separated from one another by
the piezoelectric film 1. The perimeter of the lid 7 consists of an internal annular relief 13 which
abuts on the perimeter of the membrane, i.e. on the upper perimeter of the membrane. Annular
lift 13 is formed from an injectable I-lastomer and overmolded inner seal. It is right-handed to
use the one that is commercially available from DuPont de Nemours under the trade mark of
Fulclin. For example, as shown in FIG. 2, the inner annular lift 13 which forms the inner seal is
overmolded in the groove of the inner surface of the lid by 17 identical to the inner
annular lift, e.g. The outer casing 5 comprises an outer annular relief 14 which is formed from a
material of the outer shell forming an outer seal against which the wall of the outer container in
which the capsule is accommodated abuts. G in this external container! Is indicated by a point
igtsi in FIG. The lid 7 also defines an outer seal 14 from the outside, and a continuous or noncontinuous outer stiffness forming a reference surface that contacts the wall 15 of the outer
container to limit the collapse of the outer seal 14 while the capsule is received. Turn the
surrounding annular lift 16 to the right. The outer annular lift considerably facilitates centering
during capsule fitting. The inner seal 13 and the outer seal 14 are advantageously joined with at
least one bridge material, such as a bridge 17. For this purpose, through holes or a series of
through holes which are equally spaced on the periphery as shown in FIG. The outer seal on l1il
@ is by overmolding the lid because there is a hole. The injection and distribution of material
takes place simultaneously to form the bridge 17 and the inner seal 13. In the illustrated
embodiment, the inner seal 13 and the outer seal 14 each form a continuous ring. Alternatively,
because the overmolding is used to form the seal, the inner and / or outer seals may be
discontinuous, for example to define radial passages for connectors and other elements. Such a
discontinuous configuration was' AM when using an additional seal. In fact, the positioning and
preparation of the seal is very difficult. During manufacture of the capsule according to the
invention, the lid 7 has already been formed in the mold by a first operation of forming a rigid
shell forming the main configuration of the lid and injecting the material forming the seals 13
and 14 The process or benefit which is formed by two successive, separate operations of the
second operation of overmolding the shell, or such benefit, comprises the first injection step
forming the rigid shell of the lid, the seals 13 and 14 It may be formed by a pie-die junction
technique consisting of two closely separated steps with the second step of injecting the material
to be formed.
Summarizing the above, the present invention provides an electro-acoustic capsule consisting of
a piezoelectric film supported in place along the periphery between the support surface of the
substrate and the annular inner seal of the lid. According to the invention, the inner seal of the lid
is formed from an injectable overmolded nilaston. Also, the lid also has an annular outer seal of
an overmoldable injectible elastomeric collar. .
Brief description of the drawings
FIG. 111 is a plan view of a piezoelectric capsule according to the present invention, and FIG. 2 is
a view showing a cross section along two radial directions A and B of FIG.
DESCRIPTION OF SYMBOLS 1 ... Piezoelectric film, 2 ... Output terminal, 4 ... Base | substrate, 5 ...
Central empty space, 6 ... Support surface, 7 ... Lid, 8 ... Around, 9 degrees DESCRIPTION OF
SYMBOLS 10 ... Contact surface, 11 ... Recess, 12 ... Orifice, 13.14.16 ... Uplift, 15 ... Wall, 17 ...
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