JPS6230396Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a piezoelectric buzzer that generates a sound by vibrating the back cover of the outer case of a watch.

Nowadays, alarm functions have become commonplace as a feature that should be added to digital wristwatches, and as digital wristwatches become cheaper, it has become urgent to supply cheap buzzers. As an example, a piezoelectric buzzer as shown in Fig. 1 was proposed in Utility Model Application No. 135574/1983. This is a piezoelectric buzzer having a structure in which a piezoelectric element 1 is directly attached to a back cover 3 of an exterior case, and because the number of parts is small and the structure is simple, it can be manufactured at a low cost. Therefore, a buzzer structure in which a piezoelectric element is attached to the back cover is ideal for low-cost digital wristwatches.

By the way, by changing the outer case material from conventional metals such as stainless steel to plastics such as polycarbonate, the material cost and processing cost of the back cover can be reduced, but there are the following problems.

First, it is not easy to attach the piezoelectric element. When attaching the piezoelectric element to the back lid, an epoxy adhesive is used and the piezoelectric element is left at a constant temperature of 100°C or higher for a short period of time to adhere. Therefore, when the back cover is made of metal, there is no thermal deformation of the back cover due to being left at high temperatures, and there is no change in the appearance of the back cover after pasting the piezoelectric element. However, if the back cover is made of plastic, the back cover will undergo thermal deformation unless it is a special type. For this reason, bonding must be performed at low temperatures, resulting in a very long bonding time and poor mass production.

Second, the piezoelectric element becomes more susceptible to cracking. Plastic has a smaller Young's modulus than metal, and when the back cover was pressed, it deformed greatly and cracked the piezoelectric element. When the piezoelectric element cracks, the electrodes separate, the displacement of the piezoelectric element decreases, and the sound pressure decreases. To prevent this, as shown in Figure 2, the back cover 3 and piezoelectric element 1 are
A possible structure is that a metal plate 2 is interposed between the piezoelectric element and the piezoelectric element to increase the rigidity of the piezoelectric element and prevent cracking. However, this structure cannot avoid the problem of thermal deformation of the plastic during bonding as described above.

The object of the present invention is to solve the above-mentioned problems and provide a piezoelectric buzzer using a plastic back cover that is easy to manufacture.

Figure 3 shows an embodiment of the present invention, in which 1 is a piezoelectric element, 2
is a metal plate, and 3 is a plastic back cover. The piezoelectric element 1 is fixed to a holding portion 2b of the metal plate 2, which has a larger diameter than the piezoelectric element, with an adhesive or the like. Usually, electrodes are formed on both sides of the piezoelectric element, but the holding portion of the metal plate can also be used as one electrode of the piezoelectric element. The piezoelectric element 1 and metal plate 2 are molded inside a plastic back cover 3.
A portion 2a of the metal plate 2 protrudes to the outside of the back lid 3. This protrusion can serve as an input terminal for a piezoelectric element drive signal, and is used to add spring properties and improve electrical conduction. metal plate 3
It will be even better if it is made of a conductive material such as brass, phosphor bronze, or beryllium copper. In order to drive the piezoelectric element 1, a drive signal must also be input to the surface electrode, as is well known. For this purpose, the piezoelectric element electrode 4
A part of the upper back cover mold is removed by a hole 3c so that the drive signal output terminal 5 comes into contact with the electrode 4. The behavior of the piezoelectric element 1 when it is driven will be explained. When the piezoelectric element 1 is alone, it only expands and contracts in the radial direction, but when it is bonded to the metal plate 2, it vibrates perpendicular to the plane due to the bimetallic effect. Therefore, during driving, the back lid 3 deforms as shown in FIG. 4. The upper mold part 3a of the piezoelectric element 1 and the lower mold part 3b of the metal plate 2
receives force from the vibrations of the piezoelectric element 1 and the metal plate 2, deforming them upward and downward, respectively, and generating vibrations.
At this time, if the respective boundary surfaces A and B with the mold part are not bonded, the mold parts 3a and 3b will not be deformed at the same time, so the mold part will be more easily deformed, and the sound pressure will increase.

According to the structure of the present invention, there is no need for the labor-intensive work of gluing the piezoelectric element or metal plate to the diaphragm of the back lid, etc., and the piezoelectric buzzer can be molded at the same time when the back lid is injection molded, which greatly reduces the number of man-hours. becomes. In addition, as mentioned above, the vibrating part can cause vibration independently on the inner and outer surfaces of the back cover, so even if the vibrations on the outer surface of the back cover are suppressed when the arm is attached, there will still be vibrations on the inner surface, resulting in a decrease in sound pressure. will also decrease.

As described above, the present invention provides a piezoelectric buzzer that can reduce manufacturing costs by reducing the number of man-hours.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a piezoelectric buzzer in which a piezoelectric element is attached to the back cover. FIG. 2 is an explanatory diagram of a piezoelectric buzzer in which a metal plate is interposed between a piezoelectric element and a back cover. FIG. 3 is an explanatory sectional view of an embodiment of the present invention. FIG. 4 is an explanatory diagram of the behavior of the piezoelectric buzzer of the present invention. 1... Piezoelectric element, 2... Metal plate, 3... Back cover, 4... Electrode.

Claims (1)

[Scope of utility model registration request] It consists of a plastic back lid 3 that is attached to a storage case of an electronic device, and a piezoelectric element 1 with a metal plate 2 pasted on one surface.The metal plate 2 and the piezoelectric element 1 are attached to the back lid. The metal plate 2 has a holding portion 2b having a larger diameter than the piezoelectric element, and a portion 2a protruding from the inner surface of the back lid as a conduction path for one pole of the piezoelectric element. The back cover 3 has a hole on the inner surface for exposing the other pole of the piezoelectric element and establishing electrical conduction, and the piezoelectric element and the metal plate have a peripheral part of the piezoelectric element molded. A piezoelectric buzzer characterized in that the buzzer is fixed and the center portion is held in a non-adhesive manner to the back cover.