EP1156701B1 - Electroacoustic transducer with small dimensions - Google Patents

Abstract

An electroacoustic transducer of small dimensions has a cup-shaped component made of a metallizable plastic material embedded in a housing component having a housing shape and being of a non-metallizable plastic material. The cup-shaped component has an inner surface provided with a metal coating. A magnet is arranged in the cup-shaped component. A diaphragm is connected to the housing component and has an oscillation coil configured to interact with the magnet.

Description

The invention relates to electroacoustic transducers with small dimensions, in particular those with a housing having an outer diameter of 15 mm and smaller.

With the increasing miniaturization of electro-acoustic transducers for use in cordless telephones, in mobiles, in headphones, in dictation machines, integrated in computer screens and the like. more, problems arise that have not existed in the classical converter technology. A major problem is the compliance of the transducer characteristics of increasing relative tolerances with the reduction of the dimensions while maintaining or even reducing the unit costs, since, due to the high quantities, the cost issue is given much greater attention than in large-volume transducers, which are built in small numbers for special applications.

Conventional electroacoustic transducers, which operate on the electrodynamic principle, consist essentially of a pot-like, frontally open housing, in the front of a magnet system is used, which consists of the actual magnet and a multi-part yoke, wherein the yoke frontally forms an annular air gap , A front side of the magnet system attached to the housing membrane has a voice coil which projects into the air gap of the yoke and can swing there in the axial direction. The individual yoke parts are mostly: a cup-like, bottom-side arranged part, in the center of which the magnet is glued and a circular front part, whose outer periphery forms the inner circumference of the air gap (for example GB 2081052 A ).

A particular problem in the miniaturization is the centricity or eccentricity between the air gap and the voice coil, since with every eccentricity, the membrane starts to wobble and the transducer characteristic is disturbed sensitive. Due to the miniaturization of the transducers eccentricities, which are quite permissible for large-format transducers are already a serious quality problem, since the relative eccentricity at constant absolute tolerances and reduction of the components is of course greater with the Mimaturisierung. So it is with converters with one Diameter of the housing of about 15 mm already necessary to push the eccentricity in the range of a few hundredths of a millimeter, to get to the predetermined transducer characteristics without distortion.

If you consider that the tolerances of the commonly used parts: housing, magnet system, retaining rings and the like. in the normal transducer construction in the range of tenths of millimeters, in high-precision parts, as they are used today for small converter obeying the need lying in the range of five hundredths of a millimeter, it is immediately apparent that it can easily come to eccentricities even with average pairings of tolerances, which are no longer in the acceptance area. In unfavorable pairings you shoot far beyond any permissible eccentricity.

The invention now aims to solve these problems and to provide a transducer of small dimensions, in particular with an outer diameter of the housing of 15 mm or below, which achieves the required accuracy and in particular the necessary centricity cost.

According to the invention, an electroacoustic transducer is characterized in that it consists of a cup-like, at least one radially protruding projection having component made of a metallizable plastic, which is encapsulated by a housing having a non-metallizable plastic component, and that the inner surface of the cup-like component and at least a part of the surface of the radially protruding projection are provided with a metal coating.

A method according to the invention for producing such an electroacoustic transducer is characterized in that a component with the shape of the magnet pot together with the contacts of the electroacoustic transducer is made of metallizable plastic by injection molding, that then in the same injection mold, but using another top part of the injection mold, this component is encapsulated with a non-metallizable plastic in the housing mold, and that the surface area as a magnetic pot and contacts with a metal coating are verschen. The latter can be done for example by chemical activation, subsequent copper plating and eventual nickel plating.

The inventive measures to achieve a one-piece body having both the usual magnetic pot and the housing and finally the contacts themselves in one piece and, since these parts are formed and manufactured in a single mold, the inevitable according to the prior art tolerances and whose addition or interaction avoids.

The method according to the invention is particularly suitable for small-sized electroacoustic converters, since only in the case of such miniaturized converters can the metallic cross-sections which can be achieved by the copper-plating and nickel-plating be sufficient to be used as conductors.

• die Fig. 1 den Aufbau eines elektroakustischen Wandlers gemäß dem Stand der Technik in rein schematischer Darstellung vor dem Zusammenbau,
• die Fig. 2 einen erfindungsgemäßen elektroakustischen Wandler in schematischer Ansicht,
• die Fig. 3 und 4 eine erfindungsgemäße Variante,
• die Fig. 5 einen Wandler mit Radialmagnet gemäß dem Stand der Technik und
• die Fig. 6 einen erfindungsgemäßen Wandler mit Radialmagnet.

The invention will be explained in more detail below with reference to the drawing. It shows

• the Fig. 1 the structure of an electroacoustic transducer according to the prior art in a purely schematic representation before assembly,
• the Fig. 2 an electroacoustic transducer according to the invention in a schematic view,
• the 3 and 4 a variant according to the invention,
• the Fig. 5 a radial magnetic transducer according to the prior art and
• the Fig. 6 a transducer according to the invention with radial magnet.

The Fig. 1 shows the essential parts of the invention for an electroacoustic transducer in its construction according to the prior art. Shown are the lower, cup-like yoke part 1, which is usually made of soft iron sheet by deep drawing. Thus, the inner diameter is sufficiently accurate, the outer diameter, however, depends on the sheet thickness, the type of sheet and its ductility and is thus subject to tolerances. When installing the cup-shaped yoke part 1 in the housing 2 produced by injection molding, it thus comes to joint gaps and thus to eccentricity. If one chooses overlapping tolerances in order to avoid joint gaps, deformations and internal mechanical stresses occur, which are released in particular under temperature loads and deform the sensitive diaphragm (not shown) attached to the housing top, which now leads to acoustic distortions and to Tumbling of the membrane when swinging leads.

Usually, two contacts 4 for the supply wires for the (not shown) voice coil of the membrane are arranged on a projection 3 of the housing 2. These contacts 4 are usually made of sheet metal as stamped or bent parts, which are to fit accurately and not wobbling on the projection 3. Therefore, these parts must be fixed by gluing, using a glue drop with a volume of about 0.3 mm ³ . This dosage and correct placement encounters great problems in automated series production and requires human monitoring and care. Even the production and handling of the contacts themselves, in their original size their maximum dimension in the range of about 1.5 mm, is difficult.

These problems are completely avoided by the inventive measures. It is inventively manufactured in an injection mold, a component 11 which has substantially the shape of the cup-shaped yoke part 1, but on which a projection 3 corresponding projection 13 is formed integrally with. This component consists of a metallizable plastic and it is, if it is solidified in the injection mold, this not removed, but it is only the upper part of the injection mold replaced by another shell and then it is this cup-like member 11 in essential areas of a Surrounding plastic, which is not metallizable and ultimately has an outer shape which at least substantially corresponds to the shape of the housing 2 of conventional electro-acoustic transducer. This outer part 12 preferably has a location as in FIG Fig. 2 illustrated, a recess or notch 16, so that a portion 14 'of the projection 13 is connected via a lying in the region of the notch 16 free surface with the inner portion of the cup-like member 11.

Between the contact part 14 'and its counterpart 14 ", a cover 15 is provided, by means of which the surface of the projection 13 is separated into two metallizable areas, which do not have a connection which could be metallized, whereby the two contacts are electrically separated from one another. The material of the housing part 12 encloses the outside (in the Fig. 2 invisible underside) of the cup-like member 11 in its entirety.

If now the surfaces to be metallized are to be metallized, it is possible, after appropriate activation of the plastic in a bath, to use the later contacts 14 ', 14 "at the same time, in the illustrated example, via the contact 14' and the notch 16, metallize the inside of the pot-like component 11 and the small-area, exposed outer part of its jacket in the region of the notch 16.

This metallization, which comprises, for example, the application of a copper layer and the subsequent application of a nickel layer by means of electroplating processes, belong to the state of the art and require no further explanation here. It should only be pointed out that to form a functional coating, the layer thickness of the nickel layer should be at least 25 microns and preferably at least 100 microns.

The further processing of the semi-finished electroacoustic transducer thus produced, is carried out in the usual way: It is glued in the center of the cup-like member 11 of the magnet together with already glued to him disc-shaped yoke member, which is ensured by appropriate guides or gauges sufficient centricity. It is then the membrane, optionally secured with a mounting or retaining ring on the housing part 12, wherein the mounted on the diaphragm voice coil comes to lie centrally in the air gap. The supply wires of the voice coil are guided in the region of the membrane attachment from the interior of the then closed transducer and in each case with one of the two contacts 14 ', 14 "mechanically and electrically conductively connected, for example by friction welding or ultrasonic welding.

The outer sides or the lower sides of the two contacts 14 ', 14 "are used for contacting the electro-acoustic transducer in the device in which it is used.

Since the diaphragm, attached to the coil and the retaining ring of the membrane are produced in one operation, their centricity is ensured to a large extent. Since the retaining ring is fixed to the housing part 12 and this part is in excellent centricity to the pot-like part 11, the problem of eccentric arrangement of the voice coil in the air gap is best solved. Due to the one-piece design of the cup-like member 11 and the housing part 12 with each other and with the contacts 14 ', 14 ", the overall handling for such a highly miniaturized electroacoustic transducer is greatly improved compared to prior art handling.

The 3 and 4 show a possible by the inventive measures variant with a slightly different construction of the transducer as you after him Fig. 2 It receives: As is shown in exploded view in the axial direction in the manner of an exploded view, a body part 21 with corresponding partially galvanized surface with a housing part 22 overmolded, wherein the material of the housing part 22 is not galvanisierbar. The body part 21 has integrally formed a central elevation, which represents the inner yoke part 23.

In the annular gap thus formed between the inner yoke 23 and the housing part 22 a magnetized in the axial direction of the ring magnet 24 and about a likewise annular pole plate 25 is inserted and bonded to the body part 21 and the housing part 22.

By manufacturing in a single mold using a replaceable head part to achieve the best possible accuracy and avoiding any addition of tolerances, so that the insertion of the pole plate 25 in the corresponding recess of the housing part 22 does not contribute to the otherwise feared eccentricity.

In the 3 and 4 is the contact, unlike in Fig. 2 , not shown, it can be done in a similar way as there or otherwise.

In the Fig. 4 shown fitting of the pole plate 25 must not be as shown, since it can be quite advantageous to make the recess in the housing part 22 in the axial direction so large that the pole plate is seated in the axial direction exclusively on the ring magnet 24 and is glued to it and the recess in the housing part 22 only takes over the radial guidance.

Another variant is in FIGS. 5 and 6 shown; In this case, a (or more appropriately arranged) radially magnetized magnet is used. It shows the Fig. 5 the previous structure of such electroacoustic transducer according to the prior art and the Fig. 6 a variant of the invention.

How out Fig. 5 is apparent, consists of an electroacoustic transducer with radially magnetized magnet of a plurality of plate-shaped magnets which are magnetized normal to the platelet main plane, said platelets are arranged along the lateral surface of a regular polygon. The cause of the use of this arrangement is that it is extremely difficult to manufacture annular magnets with radial magnetization, so as to provide such a quasi-annular arrangement.

How out Fig. 5 1, a yoke part 33 and an outer yoke part 35 are arranged radially inside and radially outside these individual magnetic platelets, respectively. These two yoke parts are on the front side of the electroacoustic transducer, which faces a diaphragm 37 shown in this figure Air gap, in which a voice coil 38 dips. The two yoke parts are each mounted in an inner housing 31 and an outer housing 32, wherein the outer housing 32 also carries the membrane 37.

In the embodiment according to the prior art, as in Fig. 5 is shown, it is necessary to machine the two metal yoke parts 33, 35, namely by milling, since another possibility does not exist, to provide the largest possible contact between the individual magnets 34 and the sides of the yoke parts 33, 35 facing them get. In the production itself, the yoke parts are held together with their plastic housings in a centering device and the magnets 34 are then inserted into the vacant for them cavities and glued to the yoke parts. After hardening of the adhesive, the transducer is removed for mounting the diaphragm 37 from the centering device and further mounted.

The invention now makes it possible to simplify these complicated operations drastically and thus supply them in some application areas favorable magnet arrangement of a wider breadth of the application, since the converter constructed in this way are no longer covered with the previous cost. One inventive converter of this kind is in Fig. 6 A partially galvanically metallized outer housing 42 and an at least partially galvanized yoke part 41 are provided with correspondingly planar surfaces 43, 45 during injection molding, between which the platelet-shaped magnets 44 come to lie in the mounted state. The surfaces 43, 45 and the adjacent areas ( Fig. 6 upward), which finally leave the air gap between them, are galvanically coated with metal and serve as a yoke for the magnet system. In order to obtain a coating covering only part of the surface, the yoke part 41 and the housing part 42 may be produced from two different types of plastic in a two-stage injection molding process, as described with reference to FIG Fig. 2 has been described for the local variant.

For centering it is for example possible to put the two parts 41, 42 upside down on a centering ring corresponding to the air gap to be formed and then from the then upwardly projecting bottom side, thread the individual magnetic plates 44 in the pockets formed and to stick.

It was in Fig. 6 a centrally symmetrical transducer body shown, but it is of course also possible and advantageous here, the contacts, as in the embodiment of the Fig. 2 and 3 , mitauszubilden and also to galvanize, which is analogous to the training of Fig. 2 or 3 can happen and here no further explanation needs more.

In Fig. 6 is an annular groove indicated at the upper outer edge of the housing part 42, which serves to receive a mounting ring for a membrane, this annular groove can of course be designed differently, the attachment of the membrane to a housing part belongs to the prior art, by the integral production Injection molding, an extremely high centricity can be achieved without this would cause the otherwise necessary costs.

The invention is not limited to the illustrated embodiments, but may be variously modified. It is essential that at least a portion of the yoke forming parts of the magnetic system of an electroacoustic transducer not as discrete components but as a metallic coating on an injection molded plastic part of the electroacoustic transducer. It is particularly preferred that all yoke parts are made of such metallic coatings, as this the simplest and most economical way, the best possible centering can be achieved.

In an advantageous embodiment of the invention, it is provided to provide the contacts provided for contacting the electroacoustic transducer in this way and to avoid the separate production and the subsequent application of metallic contacts.

In both applications it is possible, instead of the described coppering and subsequent nickel plating, to apply a different metallic coating, provided that it has the necessary magnetic properties only when used for the yoke parts, this is especially the case when pure iron or cobalt is used used. For the creation of the contacts for contacting the electroacoustic transducer, it is of course possible to use gold or thicker copper layers, a corresponding multi-stage treatment or a separate galvanic treatment of the yoke parts and the contacts is then necessary, but due to the uncritical handling of the already finished cast transducer body no longer critical role.

Claims (4)

1. An electroacoustic transducer of small dimensions, in particular with housing with an outer diameter of 15 mm or less, characterised in that it has a cup-shaped cup component (11,21,31) consisting of a metallisable plastics material, around which is cast a housing component (12,22,23) in the form of a housing and consisting of a non-metallisable plastics material, and in that at least the inner surface of the cup component (11,21,31) is provided with a metal coating.
2. An electroacoustic transducer according to Claim 1, characterised in that the cup component (11,21,31) has at least one radially protruding projection (13), and in that at least one part of the surface (14',14") of the radially protruding projection (13) is provided with metal coating.
3. An electroacoustic transducer of small dimensions, in particular with housing with an outer diameter of 15 mm or less, with radially magnetised magnetic plates (44), characterised in that it has a yoke part (41), which is metallised in the region of its outer circumferential surface (43), and an annular housing component (42) which is separate from the yoke part and which is metallised in the region of its inner circumferential surface (45), and in that the magnetic plates (44) are disposed between the metallised circumferential surfaces (43,45).
4. An electroacoustic transducer according to Claim 3, characterised in that the yoke part (41) has at least one radially protruding projection, and in that at least one part of the surface of the radially protruding projection is provided with a metal coating.

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