JPS5946432B2 - bimorph piezoelectric element - Google Patents

Description

[Detailed description of the invention] The present invention relates to bimorph piezoelectric elements.

It is generally known that a bimorph piezoelectric element is a device in which a pair of piezoelectric ceramic elements are laminated together and a deflection voltage is applied to the elements to bend the elements in the longitudinal direction.

Each piezoelectric ceramic element constituting this bimorph piezoelectric element is made of a polycrystalline material with a high dielectric constant, and this material exhibits piezoelectric properties when polarized by the polarity of an applied voltage. A polarized material is said to have a ``direction of polarization,'' and exhibits unique mechanical properties when a voltage is applied to it. For example, a thin and long piezoelectric ceramic element is connected to a substrate (for example, a metal plate).
When a voltage is applied to the piezoelectric ceramic element in the same direction as the polarization direction, the thin and long piezoelectric ceramic element will shrink in the longitudinal direction. At this time, the substrate does not change at all, so the stacked piezoelectric ceramic elements end up bending together with the substrate. A known method for increasing this bending effect is to stack and bond two piezoelectric ceramic elements and apply a voltage to each piezoelectric ceramic element, which causes the polarization direction of one element to be opposite to the polarization direction of the other element. It is to do so. A push-pull effect is achieved in which a pair of laminated elements bends more than a single element. Furthermore, by reversing the applied voltage, the bending of the element can be reversed. Applications of bimorph piezoelectric elements that require large deflections in both directions include, for example, video tape recorders (VTRs).

That is, in a VTR, the information on the videotape is contained in tracks of the tape, and for best reproduction of the information contained in that track, the video head must be centered over the track being read. Electronic techniques for sensing the position of the video head with respect to the tracks of this VTR and aligning the video head with the tracks are known. In a VTR using such a technique, a video head is installed at one end of a bimorph piezoelectric element. A bimorph piezoelectric element is provided so that the deflection voltage properly positions the video head with respect to the track being read. In order to center the video head on the track, a deflection voltage that changes over time is applied. As the deflection voltage, AC signals with a wide range of frequencies such as sine waves, triangular waves, square waves, sawtooth waves, etc. are used, and the bimorph piezoelectric element responds to such deflection voltages and at the same time produces a deflection different from the deflection voltage, resulting in unnecessary vibrations. occurs.

For example, in a bimorph piezoelectric element made by gluing together two piezoelectric ceramic elements with a width of 8u and a thickness of 0.3n (length: 17 mm), the frequency of this unnecessary vibration is approximately 1 KHz, and such unnecessary vibration should be removed or removed as much as possible. It is preferable to attenuate it. As a method for removing or damping the unnecessary vibrations of the bimorph piezoelectric element mentioned above, an attempt has been made to limit the unnecessary vibrations by holding the bimorph piezoelectric element between dead rubbers and butts. However, such clamping with dead rubber butts has the drawback of limiting the range in which the bimorph piezoelectric element can be deflected, thereby limiting the dynamic deflection range of the bimorph piezoelectric element. In other words, the vibration of the bimorph piezoelectric element itself corresponding to the deflection voltage is removed and attenuated, and the range of deflection is limited, making it difficult to provide a faithful response. The present invention has been made in view of the above points, and an object of the present invention is to provide a bimorph piezoelectric element that can eliminate or attenuate unnecessary vibrations without limiting the deflectable range of the bimorph piezoelectric element. .

Another object of the present invention is to provide a bimorph piezoelectric element that is inexpensive and has good responsiveness without requiring a special circuit for the drive circuit of the bimorph piezoelectric element. FIG. 1 is a schematic diagram showing the structure of a bimorph piezoelectric element according to the present invention.

In FIG. 1, piezoelectric ceramic elements 110 and 120 are piezoelectric ceramic elements made of, for example, PZT-based or ternary material. Electrodes 21, 22, 23, and 24 are electrodes obtained through normal manufacturing processes. The elastic layer 4 is for removing or damping unnecessary vibrations of the bimorph piezoelectric element. Adhesive layer 3 is for bonding these elements together. FIG. 2 shows the response characteristics of the bimorph piezoelectric element according to the present invention having the structure shown in FIG. 1 when a sawtooth wave deflection voltage is applied. In FIG. 2, waveform A represents the deflection voltage, and waveform B represents the response of the bimorph piezoelectric element. The present invention relates to a bimorph piezoelectric element formed by laminating and bonding a plurality of piezoelectric ceramic elements, in which an elastic layer is provided between the piezoelectric ceramic elements to control unnecessary vibrations, and in particular, the elastic layer has a Young's modulus of 1. ×10-4~5
It is said that excellent properties can be obtained by using a material with a yield of 0.10 N/m.

The material of the elastic body used in the present invention is appropriately selected depending on the material, shape, etc. of the piezoelectric ceramic element, but in practice, the Young's modulus of thin lead sheets, solder sheets, elastic rubber, etc. (It is preferable to use N/m substances.

The present invention will be explained in detail below using examples.

In the above embodiment, the length of the piezoelectric ceramic element is 17 mm and 14 m7! T1 width 8mm, thickness 0.
Ceramics with a thickness of 31 nm and a Young's modulus of 8 x 1010 (N/M2) are used, and the elastic layer has a length of 17 mm, a width of 8 fins, a thickness of 0.1 mm, and a Young's modulus of about 7 x 108 (N/M2).
The polyethylene film sheet of 2) was used. Further, the deflection voltage used had a frequency of 30 Hz. Next, as a comparative example, FIG. 4 shows the relationship between the deflection voltage and the response of the bimorph piezoelectric element for a bimorph piezoelectric element having the structure shown in FIG. 3 under the same conditions except for the elastic layer 4 in FIG. Ta. Note that waveform A shows the deflection voltage, and waveform B shows the response of the bimorph piezoelectric element. As is clear from this result, by using the present invention, unnecessary vibrations are almost eliminated and an ideal bimorph piezoelectric element can be obtained. In the above example, a polyethylene film sheet was used as the elastic layer, but the effect varies depending on the size, thickness, etc. of the inserted material, so it is necessary to select the shape that will improve the properties the most. It is also possible to create a partial gap in the elastic layer or insert a honeycomb structured elastic layer.A bimorph piezoelectric element with an elastic layer inserted as described above has a deflectable range of the element. This method makes it possible to remove or attenuate unnecessary vibrations without any restrictions, and provides a bimorph piezoelectric element with good responsiveness at low cost without adding a special circuit to the drive circuit of the bimorph piezoelectric element. made it possible to do so.

The structure of the bimorph piezoelectric element has been explained using a structure for a VTR, so a cantilever support method was considered, but the effects of the present invention are not limited to cantilever support bimorph elements. In addition, bimorph piezoelectric elements can be used not only in VTRs, but also as deflection elements in devices that apply optical systems, such as video discs, and the improved response of bimorph devices makes it easy to incorporate them into these devices. do. It goes without saying that the present invention is not limited to a push-pull type device in which a plurality of piezoelectric ceramic elements are stacked and bonded, but can also be used in a bimorph piezoelectric device in which piezoelectric ceramic elements are stacked and bonded on a metal substrate to obtain the same effect. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of the structure of the bimorph piezoelectric element according to the present invention, FIG. 2 is a diagram showing the response of the bimorph piezoelectric element according to the present invention to deflection voltage, and FIG. FIG. 4 is a schematic diagram showing an example of the structure of a conventional bimorph piezoelectric element, and FIG. 4 is a diagram showing the response of the conventional bimorph piezoelectric element to a deflection voltage.

110, 120...Piezoelectric ceramic element, 21
, 22, 23, 24... Electrode, 3...
Adhesive layer, 4...Elastic layer.

Claims (1)

[Scope of Claims] 1. A bimorph piezoelectric element formed by laminating and bonding a plurality of piezoelectric ceramic elements, characterized in that an elastic layer for controlling unnecessary vibrations is provided between the piezoelectric ceramic elements. 2 In claim 1, the elastic layer has a Young's modulus of 1 x 10^-^4 to 5 x 10^1^0 (N/m^
A bimorph piezoelectric element characterized by using the substance of 2).