JPS5936479B2 - Electromagnetic acoustic transducer - Google Patents

Description

[Detailed description of the invention] The present invention biases the diaphragm by the magnetic flux of a permanent magnet,
This relates to the improvement of electromagnetic acoustic transducers such as buzzers, which use an alternating current to flow through a coil and vibrate a diaphragm using the alternating magnetic flux. An object of the present invention is to provide an electromagnetic acoustic transducer that is so small that it can be stored inside the device and that can produce a predetermined sound volume.

Conventionally, as shown in FIG. 1, a bar magnet 2 is provided protruding from the center of a cylindrical bottomed yoke 1, a coil 3 is fitted around its outer periphery, and the outer periphery of a diaphragm 4 is fixed to the upper surface of the yoke 1 to generate vibrations. A buzzer in which an iron piece 5 fixed at the center of a plate 4 is opposed to the top surface of a bar magnet 2 is known, but the magnetic flux from the coil 3 is
Generally, the magnetic permeability of the magnet is extremely poor compared to that of the yoke, so the magnetic efficiency due to coil excitation becomes extremely poor, making it unsuitable for small buzzers.

Therefore, as shown in FIG. 2, a yoke T is provided protrudingly from the center of the cylindrical bottomed yoke 6, a coil 8 is fitted on the outer periphery of the yoke T, and further between the coil 8 and the cylindrical portion 6a of the cylindrical bottomed yoke 6. A buzzer in which a magnet 9 is arranged and fixed in an annular shape, an outer peripheral part of a diaphragm 10 is fixed to the upper surface of a cylindrical bottomed yoke 6, and an iron piece 11 fixed at the center of the diaphragm 10 is opposed to the upper end of the central yoke T. was considered, but part of the magnetic flux emitted from the magnet 9 forms a closed magnetic path passing through the cylindrical portion 6a of the cylindrical bottomed yoke 6, and this magnetic flux does not act on the iron piece 11, so the magnetic efficiency is correspondingly poor. On the other hand, if the gap between the magnet and the diaphragm is made smaller in order to increase the biasing force caused by the magnet, in this structure, only the magnetic flux passing through the cylindrical part 6a will increase, but the magnetic flux passing through the iron piece 11 and the yoke 1 will increase. Since there is no magnetic effect, the magnetic efficiency will not be improved as a result, and since the magnet 9 is arranged in a ring shape outside the coil 8, the magnet will be large, and in the case of an ultra-small buzzer, the magnetomotive force will be reduced. The drawback is that it is expensive due to the use of rare earth magnets such as samarium cobalt. The present invention eliminates the drawbacks of the conventional magnet by arranging a center yoke with a magnetic gap around the outer periphery of a rod-shaped permanent magnet. Next, each embodiment of the present invention shown in the accompanying drawings will be described in detail.

FIG. 3 shows a first embodiment, in which an annular gap 21 is provided on the outer periphery of a rod-shaped permanent magnetic holder 20 to form an annular center yoke 22, a coil 23 is wound around the outer periphery of the annular center yoke 22, and a coil 23 is wound around the outer periphery of the annular center yoke 22. The outer yoke 24 and the center yoke 22 are connected by a bottom yoke 25.
4. The outer periphery of the diaphragm 26 is fixed at the upper end, and the iron piece 21 fixed at the center is connected to the bar-shaped permanent magnet 20 and the center yoke 22.
The iron piece 2T is opposed to the upper end with a predetermined gap, and the outer diameter of the iron piece 2T is approximately equal to or somewhat larger than the outer diameter of the center yoke 22. Next, the effect will be explained.

The magnetic flux from the upper end of the bar-shaped permanent magnet 20 forms a closed magnetic path from the iron piece 2T through the center yoke 22 to the lower end of the bar-shaped permanent magnet 20, and since the iron piece 2T is attracted to the center yoke 22, the diaphragm 26 is biased efficiently. Ru. When the coil 23 is excited with an alternating current, the magnetic flux is transferred to the center yoke 22, the iron piece 2? A closed magnetic path is formed from the diaphragm 26, the external yoke 24, and the bottom yoke 25 to the center yoke 22, and the iron piece 21 is intermittently attracted to the center yoke 22 to generate sound. This method has the advantage that the smaller the gap between the center yoke 22 and the iron piece 2T, the greater the biasing force due to the magnet, and at the same time the magnetic efficiency due to the coil is improved. FIG. 4 shows a second embodiment, in which a rod-shaped permanent magnet 20 is fitted and fixed in an annular bushing 28 made of a non-magnetic material, and a center yoke 22 is arranged on the outer periphery of the bushing 28 and is integrally integrated with the annular bushing 28 concentrically. A coil 23 is inserted between the outer cylinder 29 and the center yoke 22 formed in
, and fix the outer periphery of the diaphragm 26 to the upper end of the outer cylinder 29.
An iron piece 2T is fixed at the center as in the first embodiment.

A bottom plate 30 is made of a non-magnetic material and connects the bush 28 and the outer cylinder 29.

FIG. 5 shows a third embodiment, in which the unit of the second embodiment shown in FIG. 4, except for the outer cylinder 29 and the diaphragm 26, is placed inside a bottomed cylindrical case 31 made of non-magnetic material. The outer periphery of the diaphragm 26 is fixed to the upper end of the case 31 by fitting. FIG. 6 shows a fourth embodiment, in which a bushing 32 made of non-magnetic material is fitted into the annular gap 21 of the first embodiment shown in FIG. Fitted into a bottomed cylindrical case 33, an annular step 33a is provided inside the upper end of the case 33, the outer circumference of the diaphragm 26 is fixed to the upper end of the case 33, and an annular closed magnetic path plate made of a magnetic material is fitted to the annular step 33a. The outer periphery of 34 is fixed.

FIG. T shows a fifth embodiment, in which the rod-shaped permanent magnet 20 in the first embodiment shown in FIG.
The movable yoke 35 is screwed onto the inner surface of the annular center yoke 22 and attached so that it can move up and down, and the iron piece 2T of the diaphragm 26 and the movable yoke 35 and The gap with the upper end of the rod-shaped permanent magnet 20 can be finely adjusted.

FIG. 8 shows a sixth embodiment. In the second embodiment shown in FIG. 4, a bush 36 made of a non-magnetic material separated from the bottom plate 30 is screwed onto the inner surface of the center yoke 22 and moved up and down. The gap between the iron piece 2T of the diaphragm 26 and the upper end of the rod-shaped permanent magnet 20 can be finely adjusted.

FIG. 9 shows an embodiment of the present invention, in which a bush 32 made of a non-magnetic material is fitted around the outer periphery of a rod-shaped permanent magnet 20 to form a magnetic gap, and an annular center yoke 22 is arranged on the outer periphery of the bush 32. The electromagnetic drive unit 3T, which has a coil 23 wound around its outer periphery, an annular external yoke 24 arranged around its outer periphery, and is integrally connected by a bottom yoke 25, is mounted in a bottomed cylindrical case 38 made of a non-magnetic material. An annular gap 39 is formed between the outer surface of the electromagnetic drive unit 3T and the inner surface of the case 38.
A self-excited electric circuit component 40 is housed in the case 38, and the outer periphery of the diaphragm 26 is fixed to the upper end of the case 38.

According to this embodiment, the diaphragm 26 can be made larger, the frequency can be lowered, and since it is compact and self-excited, it is easy to install.
FIG. 10 and FIG. 11 show an embodiment showing the coil end treatment of the present invention, in which a notch 25a is formed in the diaphragm support member 25,
A circuit board 41 is disposed in the notch 25a, and a through hole 44 is formed in the conductors 42 and 43, which are formed at the bottom of the cutout and serve as coil electrodes, to pass from the coil mounting side to the bottom of the circuit board. Lead the terminal lead wire 23a and connect the conductors 42, 4
Solder to 3.

By adopting such a coil terminal processing structure, the coil terminal lead wire 23a can be processed with good workability over the shortest distance. In the various embodiments described above, the center yoke and the outer yoke do not necessarily have to be annular, and a plurality of them may be arranged in an annular shape, or two may be arranged symmetrically.

Furthermore, in the embodiment shown in FIG. 9, the outer yoke and the bottom yoke may be omitted, or they may be made of non-fitting material.In short, a magnetic gap may be provided on the outer periphery of the rod-shaped permanent magnet. It is sufficient if there is a center yoke, a coil is wound around its outer periphery, and a diaphragm is placed on top. If the diaphragm is made of a non-magnetic material, an iron piece is always required, but if the diaphragm is made of a magnetic material, the iron piece is not necessarily necessary but is optional. It may be raised and formed into a predetermined height and shape. According to the present invention, the magnetic flux of the bar-shaped permanent magnet and the coil can both pass through the center yoke to form a closed magnetic path, and the magnetic flux due to coil excitation does not pass through the permanent magnet with extremely low magnetic permeability, so magnetic efficiency is extremely high. Furthermore, because the magnetic flux generated by the magnet and the magnetic flux generated by the coil do not intersect on the iron piece, making it difficult to apply demagnetizing force to the magnet, stable characteristics can be obtained without any change in characteristics over a long period of time.

In addition, only one permanent magnet needs to be placed around a bar-shaped permanent magnet, so even if an expensive rare earth magnet with good magnetic efficiency is used as a magnet, it can be manufactured at a lower cost than conventional magnets, and the overall cost is much lower. Even though it is ultra-compact with an outer diameter of 8mm and a thickness of 2.5m, it can produce a volume that is practically acceptable for use in watches, thin pocket phones, etc. It is suitable as a notification buzzer. Although this embodiment has been described as a sounding device, it can also be applied directly to an acoustic-to-electrical converter such as a microphone.

[Brief explanation of the drawing]

1 and 2 are front views of each comparative example of a conventional device, and FIGS. 3 to 8 are front sectional views of each of the first to sixth embodiments of the present invention,
FIG. 9 is a front sectional view showing an embodiment of the present invention, FIG. 10 is a front sectional view of the embodiment showing coil terminal processing of the present invention, and FIG. 11 is a bottom view of FIG. 10. 20... Bar-shaped permanent magnet, 21... Annular gap, 22... Center Yokazuhisa 23...
...Coil, 26...Diaphragm, 28...
・Butsuyu, 38... Case, 39...
- Annular cavity part, 40...Baku excitation type electric circuit component.

Claims (1)

[Claims] 1. A center yoke is arranged around the outer periphery of a rod-shaped permanent magnet, a coil is wound around the outer periphery of the center yoke, a predetermined gap is formed between the upper end of the rod-shaped permanent magnet and the center yoke, and a diaphragm is arranged. An electromagnetic acoustic transducer.