JP2682473B2 - Polarization method of piezoelectric transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a polarization process of the piezoelectric element, in particular, it relates to a method of polarization piezoelectric transformer having an output and an input unit.

[0002]

A piezoelectric device such BACKGROUND ART piezoelectric transformer, lead zirconate titanate: the (PZT PbZrTi O ₃₎ surface after firing the piezoelectric ceramic material, such as a pair of input electrodes and one pair or one output It is prepared by providing electrodes and subjecting the input part and the output part to polarization processing. In the polarization process, a constant DC voltage is applied between the input electrodes between the input electrodes and a pair of output parts or between the input and output electrodes when there is one output electrode, and the polarization direction in the ceramic crystal is fixed. Polarization is performed by aligning with.

5 to 6 show examples of DC pulse waveforms applied during polarization of a piezoelectric element having a pair of input electrodes (JP-A-61-268085 and JP-A-2-14).
3474 publication). By applying this kind of DC pulse voltage between the input electrodes, dielectric breakdown due to a high voltage is prevented and the piezoelectric characteristics are improved. The conventional example is characterized in that a direct-current pulse voltage of the same voltage with a constant cycle is applied to perform polarization in a constant direction.

It is known that a piezoelectric transformer can generally exhibit a predetermined function by performing polarization processing twice.

Further, in ceramic materials used for piezoelectric transformers and the like, in order to suppress the effect of residual strain due to an applied electric field, it has been conventionally performed to raise the processing temperature in a heating furnace or silicon oil and perform processing with a lower electric field. It is being appreciated.

FIG. 7 shows the experimental result in this case. The experimental result shown in FIG. 7 shows that a piezoelectric element having a size of 37 × 5.3 [mm] and a thickness of 1.3 [mm] was produced using a sintered body of NEPEC8 (trade name: manufactured by Tokin Co., Ltd.). Then, electrodes are provided on the upper and lower surfaces thereof, and a constant DC electric field of 1.5 [kV / mm] is applied in the thickness direction of 150 [° C.] silicon oil for 30 minutes. The measured values of (K ₃₁ , Qm) are shown. Then, this sample was held in a constant temperature bath at each predetermined temperature for 30 minutes and then allowed to stand, and the decrease in polarization degree (k ₃₁ after heat treatment / initial measurement value) was measured. The higher the temperature, the higher the temperature. , It can be seen that the degree of polarization is severely reduced. In particular, it was confirmed that when the second polarization treatment was performed at a temperature of 3/4 or more of the Curie point, the piezoelectric transformer was reduced to a level at which it was difficult to use.

The degree of polarization of the piezoelectric element is a function of temperature, electric field strength, and time during polarization and is in a proportional relationship.
Further, in order to obtain a certain degree of polarization, it is possible to perform processing with a low electric field strength when the processing temperature is high, and it is possible to prevent dielectric breakdown of the element, stress cracking during polarization, and the like. This polarization degree is a value that greatly contributes to the step-up ratio and efficiency of the piezoelectric transformer, and it is necessary to perform polarization processing to a value as high as possible.

[0008]

However, when a piezoelectric element such as a piezoelectric transformer is divided into two parts, that is, an input part and an output part, and polarization is performed twice, the polarization process of the first polarization process is performed for the second time. There is an inconvenience that the electromechanical coupling coefficient Keff and the mechanical quality coefficient Qm, which indicate the degree of polarization, are affected by the polarization process and are reduced. In particular, when the polarization treatment temperature is high, the tendency becomes remarkable.

[0009]

The object of the present invention is to improve the disadvantages of the conventional example, in particular to improve the degree of polarization of the piezoelectric element and to set the step-up ratio of the piezoelectric transformer high, and to speed up the polarization work. It is an object of the present invention to provide a method for polarizing a piezoelectric transformer.

[0010]

According to the present invention, an input portion and an output portion of a piezoelectric transformer having an input portion and an output portion are formed,
The application of different levels of the DC pulse voltage DOO
However, at this time , a configuration is adopted in which the input section and the output section are alternately applied. This aims to achieve the above-mentioned object.

[0011]

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
It will be described based on.

1 and 2, reference numeral 1 indicates a piezoelectric transformer which is a polarized sample. This piezoelectric transformer 1
Has an output electrode 2 which is an output part at the center of FIG. Reference numerals 3A and 4A indicate input electrodes. This input electrode 3
On the back side of A, 4A, the corresponding output electrodes 3B,
4B is attached.

The output electrode 2 is equipped with an output terminal 2a, and the input electrodes 3A and 4A are equipped with a common input terminal 3a. Reference numeral 5 indicates an electrode terminal (input / output common terminal) attached to the back surface side of the piezoelectric transformer 1 corresponding to the input electrodes 3A and 4A.

Each of these electrodes 2, 3A, 4A
Is connected to the pulse voltage control power supply 7 via a transfer relay 8 which is a changeover switch. This transfer relay 8, the input electrode 3A, the 4A and the output electrode 2, together with the DC pulse voltage of different levels are applied many times in succession, the input electrode 3A at this time, and 4A
The output electrode 2 and the output electrode 2 are alternately applied.

Here, the polarization method of the piezoelectric transformer 1 will be described in more detail.

[0016] First, the piezoelectric transformer element was heated in a silicone oil in 200 using a voltage applying circuit shown in FIG. 2 at a temperature of [℃], 1.0 [k V / mm] square wave DC pulse voltage (input Polarization was performed by applying a part (1.3 kV , an output part 6 kV ). More specifically, in the other im chart of FIG. 3
As such, the pulsed power supply voltage and the output portion pole voltage 10 and the input electrode voltage 9 in FIG a) is repeated a number of times alternately,
Using the relay contact, in the A state of b) in the figure , to the output part,
In the state B of FIG. 6B, the polarization state was continued for 40 minutes so that it was applied to the input portion.

Then, after washing, drying and standing, the five samples were checked, and a relatively good polarization characteristic value was obtained in which the polarization degree of the input portion and the output portion was 95% on average in one polarization. I was able to. At this time, the time ratio (duty ratio) of maintaining the high voltage and maintaining the low voltage (value of almost zero voltage) was about 70%.

As an additional examination, as a result of examining the pulse width, the time for maintaining the high voltage and maintaining the low voltage is 1 to 6.
It was confirmed that the polarization degree was almost the same in both the input and output parts when used in the second range.

Next, for comparison, the conventional polarization method
The input part and the output part were polarized separately. Same processing temperature 20
At 0 [° C.], the output part was polarized with a DC voltage of 1 [kV / mm] (6.0 kV) for 20 minutes, and then the input part was 1 [kV / m].
m] DC voltage (1.3 kV) for 20 minutes, washed, dried, left to stand, and confirmed with 5 samples. Is 90
% And the degree of polarization decreased.

Here, the element of the piezoelectric transformer (piezoelectric ceramic) is a sintered body of NEPEC8 (trade name: manufactured by Tokin Co., Ltd.) , and the length is 37 mm x 5.3 mm and the thickness is 1.3 mm. A plate-shaped element was used. The electrode was formed by using silver paste, patterning it by a thick film screen printing method, and baking it at 600 ° C. When measuring the piezoelectric characteristics, after the polarization is completed, a 0.1φ copper wire is attached to the center of the electrode by soldering at a position corresponding to the node of mechanical vibration, and then a predetermined measuring device is used. K ₃₁ eff
Alternatively, the degree of polarization was set by measuring k ₃₃ eff (the mechanical quality factor Qm also showed the same tendency although the value was different).

[0021]

[Embodiment 2] An example in which conditions are changed based on the configuration similar to the case of Embodiment 1 described above will be described below.

First, at the same processing temperature of 200 ° C.,
An attempt was made to polarize by applying a rectangular wave DC pulse voltage of 1.5 [kV / mm], but a situation occurred in which the ceramic was dielectrically broken down. Therefore, the pulse waveform is a trapezoidal wave composed of step-up, high-voltage maintenance, step-down, and low-voltage (value of almost zero voltage) maintenance shown in FIG. 4, and switching between input and output electrodes is performed in the low-voltage state, A trapezoidal DC pulse voltage of 1.5 [kV / mm] was applied and polarization was performed for 40 minutes.

After washing, drying and standing, the five samples were checked, and as a result, the input part and the output part each showed a polarization degree of 100%. Each time at this time is 0.5 seconds for boosting, 0.5 to 5 seconds for maintaining high voltage, 0.1 second for stepping down, 0.5 to maintaining low voltage.
As a result of studying the pulse width in the range of 2 seconds (total time range of 1.5 to 7 seconds), it was confirmed that a polarization degree of almost 100% was obtained in both the input and output sections. Further, regarding the boosting time, it was obtained by another examination that 0.1 second or more was required per polarization voltage of 1 [kV], but here it was set to a constant 0.5 second.

[0024]

Third Embodiment An example in which conditions are changed based on the configuration similar to the case of the first embodiment described above will be described below.

First, the piezoelectric transformer element is placed in a constant temperature bath,
After heating to a temperature higher than the Curie point (310 ° C.) of the piezoelectric element of 320 [° C.] in 25 minutes, 0.5 [kV /
mm] of the above-described DC pulse voltage of Example 2,
After cooling to 100 [° C.] in 25 minutes, polarization was performed by a method of stopping the pulse voltage. As a result of confirming 5 samples left after polarization, a polarization degree of 100% was shown in both the input part and the output part. Under the same conditions, 250 [° C], 1 [kV / m
The same result was also shown for the polarized sample by the trapezoidal DC pulse voltage of [m].

As described above, according to the above-described embodiment, by alternately applying a rectangular or trapezoidal DC pulse voltage to the input / output portion of the piezoelectric transformer, the piezoelectric characteristic (polarization degree) that can be polarized in one step is obtained. It is possible to obtain a low-cost piezoelectric transformer having good combination. Further, if polarization is performed at a temperature of 3/4 or more of the Curie point, the polarization electric field can be made relatively low, and therefore, there is an advantage that residual strain in the piezoelectric element is reduced.

Further, in the present embodiment, the three-terminal third-order vibration mode piezoelectric transformer is used, but the present invention can be applied to the polarization of the Rosen type or the four-terminal insulating structure piezoelectric transformer as it is.

[0028]

Since the present invention is constructed and functions as described above, according to the present invention, the rectangular or trapezoidal DC pulse voltage is alternately applied to the input / output portion of the piezoelectric transformer by switching, so that one step is performed. It is possible to obtain a low-cost piezoelectric transformer having good piezoelectric characteristics (degree of polarization) that can be polarized with, and the process for that is completed in one step, whereas two steps were required in the conventional example. In this respect, it is possible to provide an unprecedented excellent piezoelectric transformer polarization method capable of performing the polarization treatment more quickly.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a piezoelectric transformer used for confirmation of a polarization method in a first embodiment of the present invention.

FIG. 2 is a voltage application circuit diagram including a DC pulse voltage switching operation used in the polarization method of the embodiment shown in FIG.

FIG. 3 is a time chart showing the DC pulse voltage used in the embodiment of FIG. 2 and the switching timing.

FIG. 4 is a waveform diagram showing a trapezoidal DC pulse voltage according to the second embodiment of the present invention.

FIG. 5 is a waveform diagram showing a DC pulse voltage used for conventional two-step polarization, and FIG. 5A is a diagram showing a normal case;
FIG. 5B is a diagram showing a case where the duty ratio is small, and FIG.
FIG. 7C is a diagram showing a case where the duty ratio is large.

[6] In another waveform diagram showing a DC pulse voltage to be used in two steps polarization in the conventional example, FIG. 6 (a) shows a case where a sine wave equal to that half-wave rectification of a normal, Fig. 6B is a diagram showing a case where the time width is reduced, and FIG. 5C is a diagram showing a case where the time width is increased.

FIG. 7 is a diagram showing a decrease in the degree of polarization that occurs when the temperature is high.

[Explanation of symbols]

 1 Piezoelectric transformer 2 Output electrodes 3A, 4A Input electrode 5 Input / output common terminal 7 Pulse voltage control power supply 8 Electrode switching relay 9 Input partial pole voltage 10 Output partial pole voltage 11 Boost 12 High voltage maintenance 13 Step down low voltage

Claims (3)

(57) [Claims] To claim 1 wherein said input portion and the output portion of the input portion and the output portion are formed piezoelectric transformer, to apply a different level of the DC pulse voltage, respectively, the input at this time
A method of polarizing a piezoelectric transformer, characterized in that the voltage is applied alternately between the output part and the output part . 2. The DC pulse voltages of different levels are
Each step of boosting, maintaining high voltage, maintaining step-down, maintaining low voltage is output at the same time, and output is alternated from a single power supply terminal, and the output destination is switched when maintaining low voltage after this step-down.
Output each DC pulse voltage to the input section.
The method for polarizing a piezoelectric transformer according to claim 1 , wherein the voltage is applied alternately to the force portion . 3. A DC pulse voltage starts to be applied at a temperature of 3/4 or more of the Curie point temperature of the piezoelectric element, and thereafter, the DC pulse voltage is lowered while the temperature is lowered to a low temperature at which the piezoelectric characteristic of the piezoelectric element does not change. The method for polarizing a piezoelectric transformer according to claim 1 or 2, wherein the voltage is continuously applied.