GB2298334A - A surface-mounted electromagnetic sound generator - Google Patents

Abstract

Coil ends 18a, 18b and terminals 8b, 10b are connected within the periphery of the magnet 20 and in a plane which is the same as that of the coil, etc. Accordingly, the magnet 20 and the structural portion at which the coil ends are connected do not overlap, as a result of which a very slender surface-mounted electromagnetic sound generator is obtained. Further, since the structural portion at which the coil ends are connected is situated on the inner side of the magnet 20, ultra-miniaturization is possible. Furthermore, the attaching portions 8b, 10b of the terminals 8, 10 are led out so as to project upwardly from a lower case 6. As a result, the structure is such that the connecting operation also is greatly facilitated. The magnet 20 may also be 'C'-shaped (Fig 24).

Description

Title SURFACE-MOUNTED ELECTROMAGNETIC SOUND GENERATOR This invention relates to an electromagnetic sound generator in which sound is generated by vibrating a vibration plate using an electromagnet. More particularly, the invention relates to a surface-mounted electromagnetic sound generator mounted directly on a substrate on the surface of which a conductor pattern has been formed.

The recent trend toward greater surface mounting of miniature electronic components has been accompanied by proposals for electromagnetic sound generators of the surface-mounted type, and these sound generators have been marketed.

An example of a conventional surface-mounted electromagnetic sound generator of this kind has been disclosed in the specification of Japanese Utility Model Application Laid-Open No. 61-116492. This electromagnetic sound generator is obtained by joining a substrate having a surface on which terminal electrodes for surface mounting have been formed, and a case which accommodates a coil and the like. Further, a surfacemounted electromagnetic sound generator also is disclosed in the specification of Japanese Patent Application Laid-Open No. 2-34900. In this electromagnetic sound generator, a case for accommodating a coil and the like is formed by a vessel and a base.

In the surface-mounted electromagnetic sound generators described above, terminals necessary for surface mounting are provided on the substrate or base, and the terminals are soldered to coil ends below a magnet or bobbin terminals of the coil are soldered to the terminals on the rear side of the base, whereby the terminals are electrically connected to the coil.

In the conventional surface-mounted electromagnetic sound generators described above, the connections between the coil ends and the terminals for surface mounting are made below the magnet or coil. As a result, the sound generators have a stacked structure in the height direction, thus making it difficult to achieve reduced thickness. Further, the connecting operation is difficult since the coil ends and the terminals must be connected in the very limited space below the magnet or coil.

Accordingly, as disclosed in the specification of Japanese Patent Application Laid-Open No. 5-80774, a surface-mounted electromagnetic sound generator has been proposed in which a resonance chamber is placed alongside a portion which accommodates a buzzer assembly such as a coil and the like, with the coil ends being connected to the terminals inside the resonance chamber.

In the case of an electromagnetic sound generator, however, the buzzer assembly and the resonance chamber are arranged side by side in a plane. As a consequence, the mounting area on a printed circuit board is enlarged and a reduction is size cannot be achieved even if the device can be reduced in thickness.

The present invention has been devised in view of the foregoing problems and its object is to provide a surface-mounted electromagnetic sound generator in which the work for connecting the coil ends to the terminals for surface mounting is facilitated and it is possible to achieve a reduction in thickness and size.

According to the present invention, there is provided a surface-mounted electromagnetic sound generator comprising: a case; a yoke accommodated inside said case; a coil attached to said yoke; a magnet placed about the periphery of said coil; a vibration plate facing to said yoke; and a terminal for surface mounting having a connecting portion integrally secured to said case and led out to the exterior of said case, and an attaching portion, which is led into a place inside the outer periphery of said magnet, to which an end of said coil is attached.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Fig. 1 is an exploded perspective view showing the structure of a surface-mounted electromagnetic sound generator according to an embodiment of the present invention; Fig. 2 is a perspective view of the surface-mounted electromagnetic sound generator shown in Fig. 1; Fig. 3 is a sectional view of the surface-mounted electromagnetic sound generator shown in Fig. 1; Fig. 4 is a plan view of the surface-mounted electromagnetic sound generator shown in Fig. 1; Fig. 5 is a plan view showing the manner in which a yoke and a coil are received in a lower case illustrated in Fig. 1; Fig. 6 is a sectional view of a lower case and the like shown in Fig. 5;; Fig. 7 is a plan view showing the manner in which a magnet is received in the lower case illustrated in Fig.

5; Fig. 8 is a sectional view of the lower case and the like shown in Fig. 7; Fig. 9 is a plan view showing the manner in which a vibration plate is received in the lower case illustrated in Fig. 7; Fig. 10 is a sectional view of the lower case and the like shown in Fig. 9; Fig. 11 is a sectional view illustrating a modification in the shape of an attaching portion of a terminal shown in Fig. 1; Fig. 12 is a sectional view illustrating a modification in the shape of an attaching portion of a terminal shown in Fig. 1; Fig. 13 is a sectional view illustrating a modification in the shape of an attaching portion of a terminal shown in Fig. 1; Fig. 14 is a sectional view illustrating a modification in the shape of an attaching portion of a terminal shown in Fig. 1;; Fig. 15 is a perspective view showing a modification in which the lower case, magnet and yoke of the surface-mounted electromagnetic sound generator illustrated in Fig. 1 have been changed; Fig. 16 is a plan view showing a surface-mounted electromagnetic sound generator, which is illustrated in Fig. 15, in a state in which the upper case and vibration plate have been removed; Fig. 17 is a sectional view of the surface-mounted electromagnetic sound generator illustrated in Fig. 15; Fig. 18 is a perspective view showing a modification in which the case of the surface-mounted electromagnetic sound generator illustrated in Fig. 1 has been changed; Fig. 19 is a plan view showing a surface-mounted electromagnetic sound generator, which is illustrated in Fig. 18, in a state in which the case and vibration plate have been removed;; Fig. 20 is a sectional view of the surface-mounted electromagnetic sound generator illustrated in Fig. 15; Fig. 21 is a perspective view showing a modification in which the case, vibration plate, magnet and yoke of the surface-mounted electromagnetic sound generator illustrated in Fig. 1 have been changed; Fig. 22 is a plan view showing the surface-mounted electromagnetic sound generator, which is illustrated in Fig. 21, in a state in which the upper case and vibration plate have been removed; Fig. 23 is a sectional view of the surface-mounted electromagnetic sound generator illustrated in Fig. 21; Fig. 24 is an exploded perspective view illustrating a surface-mounted electromagnetic sound generator according to another partial modification of the present invention; Fig. 25 is a sectional view of the surface-mounted electromagnetic sound generator shown in Fig. 24; and Fig. 26 is a plan view illustrating the surface mounted electromagnetic sound generator, which is illustrated Fig. 24, in a state in which the upper case and vibration plate have been removed.

Fig. 1 is an exploded perspective view showing the structure of a surface-mounted electromagnetic sound generator according to an embodiment of the present invention, and Figs. 2, 3 and 4 are a perspective view, a sectional view and a plan view, respectively, of the surface-mounted electromagnetic sound generator illustrated in Fig. 1. In the Figures, numeral 2 denotes a case made of plastic. The case 2 in this embodiment has a box-like external configuration the planar shape of which is rectangular and is constituted by an upper case 4 and a lower case 6. The upper case 4 has recesses 4a, which agree with terminals for surface mounting, described below. The recesses 4a are provided at four locations on the outer surface of side walls 4c, 4d of the upper case. The upper case 4 has a sound emitting opening 4b in a side wall 4e shown at the left in the drawings.The lower case 6 has a substantially plate-shaped configuration and is equipped near its outer periphery with inner side walls 6c - 6f, which position the upper and lower cases 4, 6, contiguous the inner surface of the side walls 4c - 4f of the upper case 4. The inner side wall 6e is cut away at a position corresponding to the sound emitting opening 4b and is formed so as not to cover the sound emitting opening 4b. A depression 6a conforming to a yoke, described later, is provided in the lower case 6 at the central part thereof. The depression 6a has a generally circular planar shape in which a portion of the circle is recessed in the diametric direction from the periphery.The lower case 6 is provided with a pedestal portion 6b that protrudes into the depression 6a from the direction of the sound emitting opening 4b, and a positioning projection 6g having a generally circular planar shape that rises from the edge of the depression 6a. The positioning projection 6g is cut away in the direction of the sound emitting opening 4b.

Numerals 8, 10, 12 and 14 denote terminals for surface mounting, these being insert-molded at the four corners of the lower case 6. Among these, the terminals 8, 10 each have one end portion thereof let out to the exterior of the lower case 6. These end portions are bent into the recesses 4a of the upper case 4 to form connecting portions 8a, 10a. The other end portions are led out so as to project upwardly from the surface of the pedestal portion 6b to form attaching portions 8b, 10b.

Numeral 16 denotes a yoke consisting of a disk shaped magnetic circuit board 16a a portion of which is provided with a cut-out 16b so as to conform to the depression 6a and pedestal portion 6b, and a center pole portion 16c which rises from the center of the circuit board.

Numeral 18 denotes a ring-shaped coil mounted on the outer periphery of the center pole 16c of yoke 16.

Two coil ends 18a, 18b are led out from the coil 18.

Numeral 20 denotes a ring-shaped magnet designed so that the outer diameter thereof is the same as that of the magnetic circuit board 16a of the yoke 16. The magnet 20 is formed so as to be comparatively small in thickness, with the upper end of the magnet being formed to have a ring-shaped step portion 20a. In this embodiment, the magnet 20, which is molded, consists of a material, such as an iron-chrome-cobalt magnet, that is capable of being subjected to cutting.

Numeral 22 denotes a vibration plate to which a weight 22a is attached at the center thereof. The vibration plate 22 in this embodiment is designed to have an outer diameter that conforms to the step portion 20a of the magnet 20.

The surface-mounted electromagnetic sound generator in this embodiment is assembled by incorporating the above-mentioned component parts in the lower case 6 in regular order. The assembly steps will be described on the basis of Figs. 5 through 10. First, as shown in Figs. 5 and 6, the yoke 16 is secured upon being fitted into the depression 6a of lower case 6 in which the terminals 8, 10, 12, 14 have been insert-molded. At this time the cut-out 16b of yoke 16 agrees with the pedestal portion 6b and the yoke 16 is thus positioned.

Next, the coil 18 is mounted on the center pole 16c of yoke 16. At this time the coil ends 18a, 18b are led in the direction of the attaching portions 8b, 10b of terminals 8, 10 or are placed in a state in which they are wound about the attaching portions. Next, as shown in Figs. 7 and 8, the coil ends 18a, 18b are soldered to the attaching portions 8b, 10b, after which the magnet 20 is mounted on the magnetic circuit board 16a of yoke 16. At this time the magnet 20 is positioned at the proper location by the positioning projection 6g. As shown in Figs. 9 and 10, the vibration plate 22 is placed upon the step portion 20a of the magnet 20, and the upper case 4 is placed on top to cover the components, as depicted in Figs. 3 and 4.The entire periphery of the joint between the upper case 4 and the lower case 6 is subjected to ultrasonic welding or bonding with a bonding agent to secure the upper case 4, thereby completing the device.

In the surface-mounted electromagnetic sound generator assembled as set forth above, resonance chambers 24 are formed inside the case 2 in the four corners thereof, as shown in Fig. 9, and a resonance chamber 26 is formed between the vibration plate 22 and the upper case 4, as illustrated in Fig. 3. Sound generated by vibration of the vibration plate 22 is emitted from the sound emitting opening 4b at the side upon having its sound pressure intensified by the resonance chambers 24, 26. It should be noted that the sound emitting opening 4b may be provided in any of the side walls 4c - 4f of the upper case 4 and can also be provided in an upper wall 4g of the upper case 4.

Further, the attaching portions 8b, 10b of the terminals 8, 10 in this embodiment are generally columnar in shape. However, as shown in Figs. 11 through 14, it is possible for these to be modified to a shape that makes it easier to wind the coil ends 18a, 18b about them. By thus modifying the shape of the attaching portions 8b, 10b of the terminals 8, 10, it is easier to attach the coil terminals 18a, 18b. This makes it possible to improve the operability of subsequent soldering.

The rear side of the lower case 6 in this embodiment is provided with projections 6h, 6i for positioning the surface-mounted electromagnetic sound generator when the sound generator is mounted on a mother board such as a printed circuit board.

Accordingly, positioning of the surface-mounted electromagnetic sound generator is facilitated by providing the mother board with depressions or small holes at the mounting position. As a result, the sound generator can be prevented from moving or falling off at the time of conveyance or reflow. It should be noted that the projections 6h, 6i are furnished as necessary and need not be provided.

In this embodiment, the size and shape of the resonance chambers can be changed to raise sound pressure or to minimize external dimensions merely by changing the diameter of the magnet 20 or yoke 16 or changing the size of the case without altering the basic structure. More specifically, a surface-mounted electromagnetic sound generator shown in Figs. 15 through 17 has a structure basically the same as that shown in Fig. 1. The vibration plate 22, magnet 20 and yoke 16 are changed to a vibration plate 52, magnet 50 and yoke 46 of smaller diameters, and the lower case 6 is changed to a lower case 36 having a depression 36a and a positioning projection 36g that agree with the magnet 50 and yoke 46.By making these modifications, a resonance chamber 54 surrounding the magnet 50 can be made much larger, as shown in Figs. 16 and 17, without changing the external shape or size of the case 2, as depicted in Fig. 15. Further, the surface-mounted electromagnetic sound generator shown in Figs. 18 through 20 is modified to one in which the case 2 shown in Fig. 2 is replaced by a case 62 having a larger resonance space. The case 62 is constituted by an upper case 64 and a lower case 66 obtained by extending the case 2 of Fig. 1 in the direction of the sound emitting opening. By using the upper case 64 and the lower case 66, the space between the magnet and the sound emitting opening 64b is enlarged so that this space can also be employed as a resonance chamber 74.Furthermore, a surface-mounted electromagnetic sound generator illustrated in Figs. 21 through 23 has a vibration plate 102, a magnet 100 and a yoke 96 the diameters whereof are reduced, as in the sound generator shown in Fig. 16, and has smaller case 82 comprising an upper case 84 and a lower case 86. In this surface-mounted electromagnetic sound generator, the performance of the electromagnet can be made substantially the same as that shown in Fig. 1 since the size of the coil is not changed. The result is a sound generator of minimum size that is capable of providing a sound pressure that is satisfactory for practical purposes.

Fig. 24 is an exploded perspective view illustrating a surface-mounted electromagnetic sound generator according to another partial modification of the present invention, Fig. 25 is a sectional view of the surface-mounted electromagnetic sound generator shown in Fig. 24, and Fig. 26 is a plan view illustrating the sound generator in a state in which the upper case and vibration plate have been removed. In this partial modification, the sound generator employs a generally C-shaped magnet 120 and a ring-shaped supporting frame 130 which supports the vibration plate.

The magnet 120 is provided with the generally C-shaped configuration by cutting away part of a ring. The pedestal portion 6b of the lower case 6 is set so as to be received within a cut-out 120a of the magnet.

Further, the magnet 120 is disposed inwardly of the positioning projection 6g of case 6 and is fixed to the magnetic circuit board of yoke 16. The supporting frame 130 is placed on the outer side of the magnet 120 and is positioned by the positioning projection 6g. The upper portion of the supporting frame 130 is provided with a ring-shaped step portion 130a. The vibration plate 22 is supported by the step portion 130a. In this partial modification, the coil ends 18a, 18b are attached to the attaching portions 8b, 10b of the terminals 8, 10 within the cut-out 120a of the magnet 120 on the inner side of the supporting frame 130. Accordingly, if the outer diameters of the supporting frame 130 and the magnet 20 shown in Fig. 1 are the same, it is possible to modify the magnet without changing the structure or size of the case 2 and coil 18, etc.Since the magnet 120 has a shape that is comparatively easy to machine, it is possible to use not only an iron-chrome-cobalt magnet that is capable of being subjected to cutting machining but also a ferrite magnet or the like that is easy to form by powder molding work.

It should be noted that sound pressure can be raised and size reduced by applying the changes shown in Figs. 15 through 23 also to the partial modification using the magnet 120 and supporting frame 130.

In accordance with the present invention, the coil ends and the attaching portions of the terminals for surface mounting are connected between the coil and the magnet or in the cut-out of the magnet. As a result, it is possible to provide a very slender surface-mounted electromagnetic sound generator in which there is no overlapping between the magnet or the coil and the structural portion at which the coil ends are connected.

Further, in this invention, the structural portion at which the coil ends are connected is placed inwardly of the magnet or supporting frame. As a result, a space for disposing the structural portion at which the coil ends are connected need not be provided on the outer side of the magnet or supporting frame. This makes ultra-miniaturization possible. In addition, mounting area on a mother board such as a prirtte'd circus board can be held to the minimum.

Furthermore, the coil ends in this invention are connected to the terminals at locations very close to the coil and it is unnecessary to lead the coil ends below the magnet or to the outside, as is required in the prior art. As a result, the coil ends can be introduced to the attaching portions of the terminals in a very simple manner. Further, since the attaching portions of the terminals are led out so as to project upwardly from the pedestal portion of the lower case, the coil ends can be wound about the terminals easily and the soldering operation can be greatly facilitated.

Furthermore, the size of the case and magnet, etc., can be changed at will without modifying the basic structure. As a result, the sound generator can be readily adapted to various apparatus.

Further, since the design is such that the component parts are placed in the case in regular order from above, automatic assembly is easy and it is possible to improve yield, reduce labor and achieve great mass production.

Claims (7)

CLAIMS:

1. A surface-mounted electromagnetic sound generator comprising: a case; a yoke accommodated inside said case; a coil attached to said yoke; a magnet placed about the periphery of said coil; a vibration plate facing to said yoke; and a terminal for surface mounting having a connecting portion integrally secured to said case and led out to the exterior of said case, and an attaching portion, which is led into a place inside the outer periphery of said magnet, to which an end of said coil is attached.

2. A surface-mounted electromagnetic sound generator according to claim 1, wherein said attaching portion of said terminal is led into a space between said coil and magnet.

3. A surface-mounted electromagnetic sound generator according to claim 2, wherein said vibration plate is supported by said magnet.

4. A surface-mounted electromagnetic sound generator according to claim 1, wherein said magnet has a cut-out.

5. A surface-mounted electromagnetic sound generator according to claim 4, wherein said attaching portion of said terminal is led into the cut-out of said magnet.

6. A surface-mounted electromagnetic sound generator according to claim 5, further comprising a supporting frame placed about the periphery of said magnet, and wherein said vibration plate supported by said supporting frame.

7. A surface-mounted electromagnetic sound generator substantially as hereinbefore described with reference to and as illustrated in figures 1 to 26 of the accompanying drawings.