Sound Producing Device

The present invention relates to a sound producing device equipped with a so-called ceramic sound producer for producing acoustic signals to report to the user the working condition of an electric apparatus, such as a microwave oven, which incorporates said device.

Recently, electric apparatuses, such as microwave ovens, having an electronic control device in the form of a combination of a microcomputer and a keyboard have been put to practical use. Concurrently therewith, buzzers and other sound producing devices are being used in large quantities.

The sound producing property of such sound producing device depends largely on the arrangement of the sound producer and resonance box and also varies greatly with the way they are assembled. Thus, in order to stabilize the sound producing property, it has been necessary to arrange the sound producer and resonance box so that the sound producing property does not vary with the way they are assembled.

For example, a conventional buzzer 1 of this type used in a microwave oven, as shown in FIGS. 1-5, comprises a resonance case 2, a sound producer 3, and input lead wires 4 and 5 connected to the electrode plates of the sound producer 3 to obtain electric signals from the outside. As for the sound producing principle of this type of sound producing devices, there are two types, the separate excitation type wherein both ON- and OFF-signals are applied to the lead wires 4 and 5, and the self-excitation type wherein the piezoelectric property of a ceramic sound producer is utilized to apply only ON-signals thereto to cause vibration. The conventional example is of the separate excitation type.

The sound producer 3 is built up of a metal electrode plate 6 and a ceramic electrode plate 7 which are bound together by an adhesive agent 8. The peripheral edge of the metal electrode plate 6 of the sound producer 3 is fixed to the peripheral edge of an opening 9 at one end of the resonance case 2 by an adhesive agent 10, as shown in FIG. 5. In this condition, if an oscillation waveform is applied to the input lead wires 4 and 5, the ceramic electrode plate 7 of the sound producer 3 is deflected according to the frequency of the ocillation wave and produces a sound. The sound pressure is determined when the resonance frequency dependent on the volume of the resonance case 2 and on the inner diameter of a sound release hole 12 formed in the other end surface 11 of the resonance case 2 coincides with the frequency of the oscillation waveform applied from the outside. In addition, the resonance frequency f of the resonance case 2 is ##EQU1## where f is the resonance frequency; C is the velocity of sound; A is the radius of the sound release hole 12; D is the support diameter of the sound producer 3; H is the depth of the resonance case 2; K is a constant; and L is the depth of the sound release hole 12.

This conventional sound producing device has the following drawbacks which have been serious problems.

(1) If the amount of the adhesive agent 10 fixing the sound producer 3 and the resonance case 2 to each other is too small, there is formed a clearance between the resonance case 2 and the sound producer 3, producing a dissonance which disturbs the sound. Further, if the amount of the adhesive agent 10 is too large, as shown in FIG. 5, the adhesive agent 10 intrudes into the resonance case 2, changing the support diameter D of the sound producer 3, so that, as is clear from equation 1, the resonance frequency f changes and the sound pressure decreases. Thus, what is required is uniform application of a proper amount, but this is difficult to attain and hence the performance has been unstable.

(2) As shown in FIG. 6, a sound producing device 13 comprises a control-purpose printed circuit board 14, the conventional buzzer 1 electrically connected on said board, and oscillation circuit parts 15 for vibrating said buzzer 1 disposed around the latter. However, a large installation space is required, increasing the size of the control-purpose printed circuit board 14.

The present invention eliminates the drawbacks of the sound producing device described above, and provides a sound producing device having stabilized performance and high qualitative reliability, wherein in forming a resonance box of synthetic resin material, a ceramic sound producer is embedded in the resonance box to be integral with the latter.

In the sound producing device of the invention, one wall surface constituting the resonance box is provided with an electronic circuit associated with the sound producing device, so that there is a practical advantage that the space for the electronic circuit of the sound producing device is reduced to a great extent.

FIG. 1 is an external perspective view of a conventional sound producing device; FIG. 2 is a side view, in section, of said device;

FIG. 3 is a plan view of the sound producer of said device;

FIG. 4 is a side view of the same;

FIG. 5 is an enlarged sectional view of the principal portion of the same;

FIG. 6 is an external perspective view of a printed circuit board having said device attached thereto;

FIG. 7 is an exploded perspective view of a sound producing device according to an embodiment of the present invention;

FIG. 8 is a side view, in section, of said device;

FIG. 9 is an exploded perspective view looking at the front of said device;

FIG. 10 is a plan view of the sound producer of said device;

FIG. 11 is a side view of the same;

FIG. 12 is an external perspective view of said device looking at the rear thereof; and

FIG. 13 is a side view, in section, of the same.

An embodiment of the invention will now be described with reference to FIGS. 7 through 13. In the figures, the metal electrode plate 6, ceramic electrode 7 and adhesive agent 8 constituting the sound producer 3 are the same in arrangement as the prior art shown in FIG. 3. A resonance frame 16 is a frame made of synthetic resin, and the numeral 17 denotes an input terminal integral with the metal electrode plate 6. The resonance frame 16 has a sound producer holding wall 18 wherein mating dies are put together in opposite directions A and B to embed the periphery of the metal electrode plate 6 of the sound producer 3 and fix it in position. Substantially the middle of this sound producer holding wall 18 is provided with a substantially circular opening 21 to allow vibration of the sound producer 3. In an opening 20 opposed to the sound producer holding wall 18 of the resonance frame 16 having the sound producer 3, a printed circuit board 22 of insulating material with the same shape as the opening 20 in the resonance frame 16 is positioned to cover the opening 20. Opposed inner lateral surfaces of the resonance frame 16 are provided with projecting locking bars 19, while the printed circuit board 22 is provided with notches 23 adapted to receive said projecting locking bars 19 so as to facilitate assembly operation. The printed circuit board 22 is fitted in the resonance frame 16 and the front ends of the projecting locking bars 19 are fused, thereby building the resonance box. Further, substantially the middle of the printed circuit board 22 is provided with a circular sound release hole 12, whereby the sound produced by vibration of the sound producer 3 is effectively released from the resonance box. The printed circuit board 22 forming part of the resonance box has mounted thereon oscillation circuit parts 15 necessary for the oscillation circuit to vibrate the sound producer 3; predetermined oscillation is effected by applying a predetermined electric input to input terminal 26 fixed to the printed circuit board 22. An electrode lead wire 24 soldered to the ceramic electrode plate 7 of the sound producer 3 extends through a lead hole 25 for a lead wire in the printed circuit board 22 and is soldered to a solder lead on the printed circuit board 22 and thereby connected to the oscillation circuit. Further, the electrode lead wire 24, when connected, is somewhat slackened so as not to interfere with vibration of the sound producer 3. The lead wire for supplying power to the metal electrode plate 6 is in the form of an integral input terminal 17 which is integral with the metal electrode plate 6, as shown in FIG. 10. Since the sound producer 3 is fixed to the resonance frame 16 in such a manner that said integral input terminal 17 projects in the same direction as input terminals 26 fixed to the printed circuit board 22, it has the function of supplying power through the integral input terminal 17 and the input terminals 26 as well as the function of attachment to other printed circuit boards. In addition, the integral input terminal 17 may be provided on the ceramic electrode plate 7.

The operation of the aforesaid arrangement is substantially the same as in the conventional arrangement. Thus, when an oscillation waveform is applied between the integral input terminal 17 of the metal electrode plate 6 and the electrode lead wire 24, the ceramic electrode plate 7 is deflected, and this deflection is amplified by the metal electrode plate 6, producing a sound through the sound release hole 12.

Since the present embodiment is so arranged that the oscillation circuit parts 15 mounted on the printed circuit board 22 are stored in the resonance box, it has the effect of making the sound producing device itself compact.

According to the present embodiment, a number of effects enumerated below can be obtained.

(1) Integral formation of the sound producer 3 and resonance box 16 ensures that support points for the sound producer 3 are kept unchanged, and nonuse of an adhesive agent makes it no longer necessary to manage to provide for uniform application of adhesive agents, eliminating the possibility of the sound being disturbed by non-uniform application of adhesive agents and of the sound pressure dropping owing to a shift in resonance frequency; thus, it is possible to stabilize the performance.

(2) Integral attachment of the printed circuit board 22 constituting the oscillation circuit to the resonance box 16 reduces the size of the sound producing device and saves space.

(3) Integral formation of the metal electrode plate 6 of the sound producer 3 with the input electrode projecting therefrom eliminates the need to separately connect an input lead wire, thus facilitating assembly and increasing strength.

(4) The lead wire connected to the ceramic electrode plate 7 of the sound producer 3 extends through the printed circuit board 22 constituting the oscillation circuit and is soldered on the copper foil surface. As a result, the number of lead wires for take-out wiring in the conventional arrangement is reduced by one, thus facilitating assembly.

(5) If the resonance box is provided with a sound release hole 12, this would complicate the mold for the resonance box. In contrast, formation of the sound release hole 12 in the printed circuit board constituting the oscillation circuit simplifies the molding of resin into the resonance box, reduces the cost of the mold, facilitates formation of the sound release hole 12, and improves the performance of the sound producing device itself and reduces its cost.

As has been described so far, according to the present invention it is possible to provide a compact sound producing device which has improved sound producing performance and stabilized quality. Thus, it is possible to provide a sound producing device adapted for control by electronic circuits, which finds a broad range of uses in the field of electric apparatuses including microwave ovens.