JPS6125228B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in bimorph piezoelectric elements. Recently, bimorph piezoelectric elements have been developed as an application of piezoelectric ceramic elements.This bimorph piezoelectric element is made by laminating and bonding a pair of piezoelectric ceramic elements, and a deflection voltage is applied to each of the piezoelectric ceramic elements. It is known that it can be bent in the longitudinal direction.

A piezoelectric ceramic element is made of a polycrystalline material with a high dielectric constant, and exhibits piezoelectric properties that are polarized depending on the characteristics of an applied voltage. The above-mentioned materials that are polarized are said to have direction of polarization and exhibit unique mechanical properties when a voltage is applied. For example, when a thin and long piezoelectric ceramic element is bonded to a substrate made of metal or the like and a voltage is applied to the piezoelectric ceramic element in the same direction as the polarization direction, the piezoelectric ceramic element will shrink in the longitudinal direction. At this time, since the substrate does not change at all, the connected piezoelectric ceramic element eventually bends together with the substrate. A method to increase the effect of this bending is to connect two piezoelectric ceramic elements and apply a voltage to each element, so that this voltage becomes the polarization direction of one element and the opposite polarization direction of the other element. It is to do so. A pair of elements coupled in this manner, ie, a bimorph piezoelectric element, can be bent more than a single piezoceramic element, achieving a so-called push-pull effect. Furthermore, the bending can be reversed by reversing the polarity of the applied voltage.

Applications of such bimorph piezoelectric elements include those that require large deflections in both directions, such as video tape recorders (VTRs).
In a VTR, the information on a videotape is contained in a track 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. The bimorph piezoelectric element is used for this positioning, that is, alignment of the video head and the tape track.

FIG. 1 is a perspective view showing the schematic structure of a conventional bimorph piezoelectric element used for such applications. A piezoelectric ceramic element 3 having electrodes 1 and 2 attached to both main surfaces, and a piezoelectric ceramic element 6 having electrodes 4 and 5 attached to both main surfaces, respectively, are laminated with an adhesive 7 interposed therebetween. ing. Furthermore, the piezoelectric ceramic elements 3 and 6 are connected in parallel, with their respective polarization directions aligned. The thus combined bimorph piezoelectric element has one end,
That is, the right side of the lower surface of the electrode 5 is fixed within the scanning drum of the VTR. Further, the video head is fixed to the other end of the bimorph element, that is, to the left side of the upper surface of the front electrode 1 or to the left side of the lower surface of the electrode 5. Thus, the electrodes 1, 5 and the electrodes 2, 4 have the same polarity, and a power supply line is connected to each electrode 1, 2, 3, 4, 5,
By applying a predetermined deflection voltage to the piezoelectric ceramic elements 3, 6, the video head is properly positioned with respect to the track.

Incidentally, as the deflection voltage, a sine wave, a triangular wave, a rectangular wave, a sawtooth wave, etc., which are AC signals having a frequency over a wide band, are used. When such a deflection voltage is applied to a bimorph piezoelectric element, the element responds to the deflection voltage and at the same time produces a deflection different from the deflection voltage, generating unnecessary vibrations. For example, when a sawtooth wave as shown in FIG. 2a is applied to a bimorph piezoelectric element, the element is deflected in accordance with the sawtooth wave as shown in FIG. 2b, and generates unnecessary vibrations. Furthermore, in a bimorph piezoelectric element made by gluing two piezoelectric ceramic elements 17 mm long, 8 mm wide, and 0.3 mm thick, the frequency of this unnecessary vibration is approximately 1 kHz. It is preferable to eliminate or attenuate such unnecessary vibrations as much as possible. As a method of removing or damping the unnecessary vibrations of the bimorph piezoelectric element mentioned above, an attempt has been made to control the unnecessary vibrations by holding the bimorph piezoelectric element between debt rubber pads. However, such clamping with dead rubber pads has the disadvantage 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 was made in consideration of the above circumstances, and
The purpose is to provide a bimorph piezoelectric element that can eliminate or attenuate unnecessary vibrations without limiting the range of deflection, and that does not require a special drive circuit and is inexpensive and has good responsiveness. It's about doing.

First, an overview of the present invention will be explained. As a means for eliminating the unnecessary vibrations, the inventors formed an elastic body between the piezoelectric ceramic elements 3 and 6, and attempted to absorb the unnecessary vibrations with this elastic layer. Experiments were conducted using a relatively small element using a polyethylene film sheet for the elastic layer, and the result was that the unnecessary vibrations were significantly reduced. Here, as the unnecessary vibration removal effect, the reciprocal of the time until the unnecessary vibration wave reaches a peak value of 10% of the peak value of the first waveform was used. That is, the cut-off level of the unnecessary vibration liquid shown in FIG. /
Let it be T. The unnecessary vibration removal effect (1/T) with respect to the length l in the longitudinal direction of the element was measured and was as shown by curve A in FIG. 3. As is clear from this curve A, in the case of an element using a polyethylene film sheet as the elastic layer, when the length l is short, the unnecessary vibration removal effect (1/
T) is large, but if the length l is long, the unnecessary vibration removal effect (1/T) will be small. Therefore, although it is possible to significantly attenuate the unnecessary vibrations in a small-shaped element, it is not possible to significantly attenuate the unnecessary vibrations in a large-shaped element. Therefore, the present inventors formed the elastic layer with various materials and repeated experiments, and in order to find a material that has a large unnecessary vibration removal effect (1/T) even when the length l is long, I did a lot of research. As a result of the research, it was found that Sn (tin) and Pb (lead) are excellent as materials for the elastic layer, and in particular, an alloy sheet of Sn and Pb was found to be the most excellent. By the way, when the elastic layer was formed with an alloy sheet of Sn and Pb and the unnecessary vibration removal effect (1/T) was measured, curve B in Figure 3 was obtained.
It became like this. In other words, when the length l is short, the unnecessary vibration removal effect (1/T) is small, but when the length l becomes long, the unnecessary vibration removal effect (1/T) becomes significant and is sufficiently large compared to polyethylene film sheets. It became.

The present invention focuses on this point, and achieves the above object by using an alloy of Sn and Pb as the elastic layer.

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 4 is a perspective view showing a schematic configuration of an embodiment of the present invention. In the figure, numeral 10 is a first piezoelectric ceramic element made of PZT or ternary material;
Electrodes 11 and 12 are attached to both main surfaces of 0, respectively. Moreover, the second piezoelectric ceramic element 20
Similarly to the above element 10, electrodes 21,
22 are attached to each. These first and second piezoelectric ceramic elements 10, 20
is an elastic layer 30 made of an alloy sheet of Sn and Pb.
They are sandwiched and laminated with adhesive 40. That is, the electrode 12 on the lower surface side of the first piezoelectric ceramic element 10 is attached to the upper surface of the elastic layer 30 via the adhesive 40, and the electrode 21 on the upper surface side of the second piezoelectric ceramic element 20 is attached to the upper surface of the elastic layer 30 via the adhesive 40. Elastic layer 3 through
It is attached to the bottom surface of 0. Note that the Sn content of the Sn and Pb alloy sheet forming the elastic layer 30 was 98%.

With such a configuration, unnecessary vibrations generated in response to an AC deflection voltage can be avoided by the elastic layer 3 as described above.
Since it is absorbed at 0, unnecessary vibrations can be removed or significantly damped. For example, the length, width, and thickness of the first piezoelectric ceramic element 10 are set to 30 [mm], 12 [mm], and 0.3 [mm], and the second
The length, width, and thickness of the piezoelectric ceramic element 20 are 35 (mm), 12 [mm], and 0.3 [mm], respectively, and the elastic layer 3 is
The length, width, and thickness of 0 are 30 [mm] and 12, respectively.
[mm], 0.2 [mm], and the frequency is 30 as the deflection voltage.
When using a sawtooth wave of [Hz], Figure 5 a, b
The results shown are obtained. That is, the response to the sawtooth wave as shown in FIG. 5a has almost no unnecessary vibration components, as shown in FIG. 5b. As is clear from this result, the unnecessary vibrations are significantly attenuated.

Therefore, according to this embodiment, unnecessary vibrations can be removed or significantly damped without using a dead rubber pad or the like as in the conventional case, that is, without limiting the deflectable range. Furthermore, according to this embodiment, the third
As is clear from the figure, this is particularly effective when the shape (length l) is large. Moreover, the elastic layer 30
is made of an alloy sheet of Sn and Pb, so
The operating temperature range is expanded (~
200℃). Further, by simply forming the elastic layer 30 with an alloy sheet of Sn and Pb, there is no need to add a special drive circuit, and there are advantages such as being able to be realized at low cost.

FIG. 6 is a perspective view showing a schematic configuration of another embodiment. Note that the same parts as in FIG. 4 are given the same reference numerals, and detailed explanation thereof will be omitted. This embodiment differs from the previously described embodiments in that the adhesive 40
The first and second
The piezoelectric ceramic elements 10 and 20 are attached. That is, the elastic layer 30 is placed between the first and second piezoelectric ceramic elements 10 and 20.
After the elastic layer 30 is inserted, the elastic layer 30 is pressurized and heated. Since the elastic layer 30 is an alloy sheet of Sn and Pb, it is melted by the above heating. Thus, the first and second piezoelectric ceramic elements 1
0 and 20 are welded and laminated.

Of course, even with such a configuration, the same effects as in the previous embodiment can be achieved. Furthermore, the first and second piezoelectric ceramic elements 10 and 20
Since it is directly attached to the elastic layer 30 made of an alloy sheet of Sn and Pb, that is, a conductive sheet, there is an advantage that the connection between the electrodes 12 and 21 is unnecessary and the manufacturing process can be simplified.

Note that this invention is not limited to each of the embodiments described above. For example, the size, thickness, etc. of the piezoelectric ceramic element may be determined as appropriate according to specifications. Similarly, the size and thickness of the elastic layer may be appropriately determined depending on the size and thickness of the piezoelectric ceramic element used. Furthermore, in order to increase the effect of eliminating unnecessary vibrations, it is also possible to partially form gaps in the elastic layer or to form the elastic layer into a honeycomb structure.

Furthermore, the present invention is not limited to a push-pull type in which a plurality of piezoelectric ceramic elements are stacked and bonded, but may be applied to a structure in which piezoelectric ceramic elements are stacked and bonded on a metal substrate. Furthermore, in addition to VTRs, it can also be used as a deflection element for devices that use optical systems, such as video disks. In addition, various modifications can be made without departing from the spirit of the invention.

As detailed above, according to the present invention, a bimorph that can eliminate or attenuate unnecessary vibrations without limiting the deflectable range, and that can be realized at low cost without requiring a special drive circuit. A piezoelectric element can be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the schematic structure of a conventional bimorph piezoelectric element, and FIGS. 2a and 2b illustrate the operation of the above device, respectively. FIG. Figure b is a diagram showing the response of the element, Figure 3 is a diagram for explaining the gist of the invention, Figure 4 is a perspective view showing a schematic configuration of an embodiment of the invention, and Figures 5 a and b are 5A is a signal waveform diagram showing the deflection voltage, FIG. 5B is a diagram showing the response of the element, and FIG. 6 is a perspective view showing the schematic configuration of another embodiment. It is a diagram. 10, 20... piezoelectric ceramic element, 30...
Elastic layer, 40...Adhesive, 11, 12, 21,
22...electrode.

Claims (1)

[Claims] 1. A bimorph piezoelectric element formed by laminating and bonding a plurality of piezoelectric ceramic elements, characterized in that an alloy of lead and tin is used as an elastic layer between the piezoelectric ceramic elements to suppress unnecessary vibrations. .