JP7606851B2 - Driving method, driving circuit, and displacement driving device - Google Patents

Description

The present invention relates to a driving method, a driving circuit, and a displacement driving device for a dielectric element.

In panels that use tactile technology, such as electronic touch panels, technology that makes it feel as if buttons are on the panel and technology that allows you to know the location of buttons by touch without having to look at the panel while driving are attracting attention.

In these technologies, the vibration devices used to generate haptics include electromagnetic eccentric motors, LRAs (Linear Resonant Actuators), and piezoelectric actuators. Piezoelectric actuators have the characteristic of fast response speed, can handle a wide range of drive frequencies, and can express a variety of haptics, so they are attracting particular attention as next-generation haptic module components (for example, Patent Document 1).

JP 2001-197762 A

Conventionally, the drive amplitude of a piezoelectric actuator is smaller than that of an electromagnetic type, and in order to increase the drive amplitude, it is necessary to increase the drive voltage of the piezoelectric element. However, bipolar drive is limited by the coercive electric field, and there is a problem of depolarization when the drive voltage amplitude is increased above the coercive electric field. Also, unipolar drive in the polarization direction is not affected by the coercive electric field, but there are problems such as loss of reliability when the drive voltage amplitude is excessively increased and the displacement decreasing depending on the number of drives.

Furthermore, while PZT (lead zirconate titanate), a representative piezoelectric material, has excellent piezoelectric properties, there are also plans to replace it with lead-free materials due to environmental considerations. This is an environmental concern. On the other hand, lead-free piezoelectric materials require regulated substances such as Bi and Sb, and expensive materials such as Li, Ta, or Nb, which poses a cost problem.

In view of the above circumstances, the object of the present invention is to provide a driving method, driving circuit, and displacement driving device that can maximize the amount of displacement of a dielectric element without compromising reliability.

In order to achieve the above object, a driving method according to one embodiment of the present invention provides a dielectric element having a ceramic that exhibits electric field induced strain, a positive electrode including a plurality of positive internal electrodes provided inside the ceramic and a positive external electrode provided on a surface of the ceramic and connected to the plurality of positive internal electrodes, and a negative electrode including a plurality of negative internal electrodes provided inside the ceramic facing the plurality of positive internal electrodes via the ceramic and a negative external electrode provided on the surface of the ceramic and connected to the plurality of negative internal electrodes , the driving voltage waveform having a predetermined driving frequency is applied between the positive electrode and the negative electrode, wherein a first driving maximum voltage which is one peak voltage of the driving voltage waveform is a voltage between 0.37 and 0.84 times the breakdown voltage of the ceramic at the driving frequency, and a second driving maximum voltage which is the other peak voltage of the driving voltage waveform is a voltage between 0.1 and 0.8 times the coercive electric field of the ceramic in the polarity opposite to that of the first driving maximum voltage, is applied between the positive electrode and the negative electrode.

According to this driving method, by applying a voltage to the opposite side of the main driving side within a range that does not exceed the coercive electric field, it is possible to increase the driving voltage amplitude and prevent a decrease in the deformation characteristics due to the imprint effect. Therefore, it is possible to maximize the displacement of the dielectric element without compromising driving stability or driving reliability. Furthermore, with this driving method, ceramics that exhibit electric field induced strain can be used as the material for the dielectric element, and there is no need to use materials with high piezoelectricity or high ferroelectricity, making it possible to reduce the environmental burden and cost burden.

The ceramic may have a coercive field of less than 1 kV/mm or a Curie temperature of less than 300°C.

The driving voltage waveform may be a sine wave, a triangular wave, a Haversine wave, a Gaussian wave, or a burst wave of any of these.

In order to achieve the above object, a drive circuit according to one embodiment of the present invention generates a drive voltage waveform having a predetermined drive frequency and is applied between the positive electrode and the negative electrode of a dielectric element having a ceramic that exhibits electric field induced strain, a positive electrode including a plurality of positive internal electrodes provided inside the ceramic and a positive external electrode provided on the surface of the ceramic and connected to the plurality of positive internal electrodes, and a negative electrode including a plurality of negative internal electrodes provided inside the ceramic facing the plurality of positive internal electrodes via the ceramic and a negative external electrode provided on the surface of the ceramic and connected to the plurality of negative internal electrodes, wherein a first drive maximum voltage which is one peak voltage of the drive voltage waveform is a voltage between 0.37 and 0.84 times the breakdown voltage of the ceramic at the drive frequency , and a second drive maximum voltage which is the other peak voltage of the drive voltage waveform is a voltage between 0.1 and 0.8 times the coercive electric field of the ceramic in the polarity opposite to that of the first drive maximum voltage, and applies the drive voltage waveform between the positive electrode and the negative electrode.

The ceramic may have a coercive field of less than 1 kV/mm or a Curie temperature of less than 300°C.

In order to achieve the above object, a displacement driving device according to one aspect of the present invention comprises a dielectric element, an object to be driven, and a driving circuit.
The dielectric element has a ceramic that exhibits electric-field-induced strain , a positive electrode including a plurality of positive internal electrodes provided inside the ceramic and a positive external electrode provided on a surface of the ceramic and connected to the plurality of positive internal electrodes, and a negative electrode including a plurality of negative internal electrodes provided inside the ceramic facing the plurality of positive internal electrodes via the ceramic, and a negative external electrode provided on the surface of the ceramic and connected to the plurality of negative internal electrodes .
The dielectric element is joined to the object to be driven.
The drive circuit generates a drive voltage waveform that is applied between the positive electrode and the negative electrode and has a predetermined drive frequency, wherein a first drive maximum voltage that is one peak voltage of the drive voltage waveform is a voltage between 0.37 and 0.84 times the breakdown voltage of the ceramic at the drive frequency, and a second drive maximum voltage that is the other peak voltage of the drive voltage waveform is a voltage between 0.1 and 0.8 times the coercive electric field of the ceramic at the drive frequency and has a polarity opposite to that of the first drive maximum voltage, and applies the drive voltage waveform between the positive electrode and the negative electrode.

The ceramic may have a coercive field of less than 1 kV/mm or a Curie temperature of less than 300°C.

The dielectric element and the driven object may form an actuator.

In order to achieve the above object, a driving method according to one embodiment of the present invention provides a piezoelectric element having a piezoelectric body made of a piezoelectric material, a positive electrode including a plurality of positive internal electrodes provided inside the piezoelectric body and a positive external electrode provided on a surface of the piezoelectric body and connected to the plurality of positive internal electrodes, and a negative electrode including a plurality of negative internal electrodes provided inside the piezoelectric body facing the plurality of positive internal electrodes via the piezoelectric body and a negative external electrode provided on the surface of the piezoelectric body and connected to the plurality of negative internal electrodes, the method comprising: applying, between the positive electrode and the negative electrode, a driving voltage waveform having a predetermined driving frequency, wherein a first driving maximum voltage which is one peak voltage of the driving voltage waveform is a voltage between 0.37 and 0.84 times the breakdown voltage of the piezoelectric body at the driving frequency, and a second driving maximum voltage which is the other peak voltage of the driving voltage waveform is a voltage between 0.1 and 0.8 times the coercive electric field of the piezoelectric material in a polarity opposite to that of the first driving maximum voltage, between the positive electrode and the negative electrode.

The driving voltage waveform may be a sine wave, a triangular wave, a Haversine wave, a Gaussian wave, or a burst wave of any of these.

In order to achieve the above object, a drive circuit according to one embodiment of the present invention generates a drive voltage waveform having a predetermined drive frequency, which is applied between the positive electrode and the negative electrode of a piezoelectric element having a piezoelectric body made of a piezoelectric material, a positive electrode including a plurality of positive internal electrodes provided inside the piezoelectric body and a positive external electrode provided on a surface of the piezoelectric body and connected to the plurality of positive internal electrodes, and a negative electrode including a plurality of negative internal electrodes provided inside the piezoelectric body facing the plurality of positive internal electrodes via the piezoelectric body and a negative external electrode provided on the surface of the piezoelectric body and connected to the plurality of negative internal electrodes, wherein a first drive maximum voltage which is one peak voltage of the drive voltage waveform is a voltage between 0.37 and 0.84 times the breakdown voltage of the piezoelectric body at the drive frequency, and a second drive maximum voltage which is the other peak voltage of the drive voltage waveform is a voltage between 0.1 and 0.8 times the coercive electric field of the piezoelectric material in a polarity opposite to that of the first drive maximum voltage, and applies the drive voltage waveform between the positive electrode and the negative electrode.

In order to achieve the above object, a displacement driving device according to one aspect of the present invention includes a piezoelectric element, a vibrating body, and a driving circuit.
The piezoelectric element has a piezoelectric body made of a piezoelectric material, a positive electrode including a plurality of positive internal electrodes provided inside the piezoelectric body and a positive external electrode provided on a surface of the piezoelectric body and connected to the plurality of positive internal electrodes, and a negative electrode including a plurality of negative internal electrodes provided inside the piezoelectric body opposite the plurality of positive internal electrodes via the piezoelectric body, and a negative external electrode provided on the surface of the piezoelectric body and connected to the plurality of negative internal electrodes .
The vibrating body is joined to the piezoelectric element.
The drive circuit generates a drive voltage waveform that is applied between the positive electrode and the negative electrode and has a predetermined drive frequency, wherein a first drive maximum voltage, which is one peak voltage of the drive voltage waveform , is a voltage between 0.37 and 0.84 times the breakdown voltage of the piezoelectric body at the drive frequency, and a second drive maximum voltage, which is the other peak voltage of the drive voltage waveform, is a voltage between 0.1 and 0.8 times the coercive electric field of the piezoelectric material in the opposite polarity to the first drive maximum voltage, and applies the drive voltage waveform between the positive electrode and the negative electrode.

The piezoelectric element and the vibrating body may form a piezoelectric actuator, and the vibration of the vibrating body may generate a tactile sensation in the vibrating body.

As described above, the present invention provides a driving method, driving circuit, and displacement driving device that can maximize the amount of displacement of a dielectric element without compromising reliability.

1 is a schematic diagram of a displacement driving device according to a first embodiment of the present invention; 4 is a cross-sectional view of a piezoelectric element included in the displacement driving device. FIG. A driving voltage waveform generated by a driving circuit provided in the displacement driving device. 1 shows a driving voltage waveform generated by a driving circuit included in the displacement driving device. 1 shows a bipolar drive drive voltage waveform, which is a dynamic voltage waveform of a conventional piezoelectric element. 1 shows a driving voltage waveform for unipolar driving, which is a dynamic voltage waveform of a conventional piezoelectric element. FIG. 5 is a schematic diagram of a displacement driving device according to a second embodiment of the present invention. 4 is a cross-sectional view of a dielectric element provided in the displacement driving device. FIG. 1 is an example of a PE hysteresis loop for a dielectric material typically required for piezoelectric actuators. 2 is an example of a PE hysteresis loop of the dielectric material constituting the dielectric element. 5A to 5C are schematic diagrams illustrating a method for measuring the displacement of a piezoelectric actuator according to an example and a comparative example of the present invention.

(First embodiment)
A displacement driving device according to a first embodiment of the present invention will be described below. The displacement driving device includes a vibration generating device.

[Configuration of the displacement driving device]
1 is a schematic diagram of a displacement driving device 100 according to this embodiment. As shown in the figure, the displacement driving device 100 includes a piezoelectric actuator 101 and a driving circuit 102. The piezoelectric actuator 101 is a unimorph type piezoelectric actuator composed of a vibrating body 103 and a piezoelectric element 104.

The vibrating body 103 provides a tactile sensation to a user who touches the vibrating body 103. The vibrating body 103 can be a plate-shaped member made of metal, glass, or resin material, such as a liquid crystal panel or the housing of an electronic device. There are no particular limitations on the shape or size of the vibrating body 103.

The piezoelectric element 104 is bonded to the vibrating body 103 and generates vibrations. FIG. 2 is a cross-sectional view of the piezoelectric element 104. As shown in the figure, the piezoelectric element 104 includes a piezoelectric body 111, a positive electrode 112, and a negative electrode 113. The piezoelectric body 111 is made of a piezoelectric material such as PZT (lead zirconate titanate).

The positive electrode 112 includes a positive internal electrode 114 and a positive external electrode 115. The positive internal electrode 114 is made of a conductive material and is provided in multiple layers in the piezoelectric body 111. The positive external electrode 115 is made of a conductive material, is formed on the surface of the piezoelectric body 111, and is connected to the positive internal electrode 114.

The negative electrode 113 includes a negative internal electrode 116 and a negative external electrode 117. The negative internal electrode 116 is made of a conductive material and is provided in multiple layers in the piezoelectric body 111. The negative external electrode 117 is made of a conductive material, is formed on the surface of the piezoelectric body 111, and is connected to the negative internal electrode 116.

As shown in FIG. 2, the positive internal electrodes 114 and the negative internal electrodes 116 are arranged alternately and face each other via the piezoelectric body 111. The positive external electrodes 115 and the negative external electrodes 117 are provided at a distance on the front and back surfaces of the piezoelectric element 104. As shown in FIG. 1, the positive external electrode 115 is connected to the positive wiring 105, and the positive external electrode 115 functions as a positive terminal. The negative external electrode 117 is connected to the negative wiring 106, and the negative external electrode 117 functions as a negative terminal.

In the piezoelectric element 104, when a voltage is applied between the positive electrode 112 and the negative electrode 113, the piezoelectric body 111 deforms due to the inverse piezoelectric effect, generating vibration. As shown in FIG. 2, the piezoelectric element 104 may have a layered structure in which the positive electrodes 112 and the negative electrodes 113 are alternately layered with the piezoelectric body 111 interposed therebetween, or may have another structure. The piezoelectric element 104 may be bonded to the vibrating body 103 by a resin or the like. Two or more piezoelectric elements 104 may be bonded to the vibrating body 103.

The drive circuit 102 is connected to the piezoelectric element 104 via a positive electrode wiring 105 and a negative electrode wiring 106, and supplies a drive signal to the piezoelectric element 104. Specifically, the drive circuit 102 generates a drive voltage waveform, which will be described later, and supplies it between the positive electrode 112 and the negative electrode 113.

The displacement driving device 100 has the above-described configuration. The displacement driving device 100 can be installed in various electronic devices such as smartphones and haptic function devices.

[Drive voltage waveform]
The drive voltage waveform generated by the drive circuit 102 will be described. The drive voltage waveform generated by the drive circuit 102 has a first drive maximum voltage, which is one of the peak voltages, that is a voltage between 0 V and the breakdown voltage (dielectric breakdown voltage) of the piezoelectric body 111 at the drive frequency. The other peak voltage of the drive voltage waveform, which is a second drive maximum voltage, is a voltage between 0.1 and 0.8 times the coercive electric field of the piezoelectric material in the opposite polarity to the first drive maximum voltage.

Figure 3 shows the drive voltage waveform generated by the drive circuit 102. As shown in Figure 3, in this drive voltage waveform, one peak voltage and the other peak voltage have opposite polarities, with the peak voltage on the positive side being the first drive maximum voltage Vp+ and the peak voltage on the negative side being the second drive maximum voltage Vp-.

The breakdown voltage of the piezoelectric body 111 at the frequency of the drive voltage waveform (drive frequency) is the breakdown voltage BV, and as shown in FIG. 3, the breakdown voltage BV on the positive side is BV+. Furthermore, the coercive field of the piezoelectric material that constitutes the piezoelectric body 111 is the coercive field Ec. As shown in FIG. 3, the coercive field Ec on the positive side is the coercive field Ec+, and the coercive field Ec on the negative side is the coercive field Ec-.

The drive voltage waveform generated by the drive circuit 102 has a first drive maximum voltage Vp+ that is greater than 0 V and less than the breakdown voltage BV+. Furthermore, the second drive maximum voltage Vp- is 0.8 to 0.1 times the coercive electric field Ec-. In other words, the first drive maximum voltage Vp+ and the second drive maximum voltage Vp- satisfy the following (Equation 1) and (Equation 2).

0V<Vp+<BV+ (Formula 1)
0.8Ec-≦Vp-≦0.1Ec- (Formula 2)

In order to increase the amount of displacement of the piezoelectric element 104, it is preferable that Vp+>Ec+.

Although FIG. 3 shows a drive voltage waveform with a positive polarization direction (>0V), the polarization direction may be negative (<0V). FIG. 4 shows a drive voltage waveform generated by the drive circuit 102 with a negative polarization direction.

As shown in Figure 4, in this drive voltage waveform, one peak voltage and the other peak voltage have opposite polarities, with the negative peak voltage being the first drive maximum voltage Vp- and the positive peak voltage being the second drive maximum voltage Vp+. Also, as shown in Figure 4, the breakdown voltage BV on the negative side is BV-. As shown in Figure 4, the coercive field Ec on the positive side is the coercive field Ec+ and the coercive field Ec on the negative side is the coercive field Ec-.

The drive voltage waveform generated by the drive circuit 102 has a first drive maximum voltage Vp- that is greater than the breakdown voltage BV- and less than 0 V. Furthermore, the second drive maximum voltage Vp+ is 0.1 to 0.8 times the coercive electric field Ec+. In other words, the first drive maximum voltage Vp- and the second drive maximum voltage Vp+ satisfy the following (Equation 3) and (Equation 4).

BV-<Vp-<0V (Formula 3)
0.1Ec+≦Vp+≦0.8Ec+ (Formula 4)

In order to increase the amount of displacement of the piezoelectric element 104, it is preferable that Vp-<Ec-.

The drive circuit 102 generates the drive voltage waveform shown in FIG. 3 or FIG. 4, and supplies the drive voltage waveform between the positive electrode 112 and the negative electrode 113 via the positive electrode wiring 105 and the negative electrode wiring 106. Note that the drive voltage waveform generated by the drive circuit 102 is not limited to the sine wave shown in FIG. 3 and FIG. 4, and may be any waveform in which the first drive maximum voltage and the second drive maximum voltage satisfy the above conditions. Specifically, the drive voltage waveform generated by the drive circuit 102 may be a sine wave, a triangular wave, a Haversine wave, a Gaussian wave, or a burst wave of these.

[Effects of the displacement drive device]
The drive voltage waveform generated by the drive circuit 102 will be described in comparison with a conventional drive voltage waveform. Figure 5 is a graph showing a drive voltage waveform for bipolar drive, which is a conventional drive voltage waveform. As shown in the figure, in bipolar drive, |Vp+|=|Vp-|, and in order to prevent depolarization, it is necessary to make |Ec|>|Vp|. Therefore, if the coercive electric field Ec of the piezoelectric material is small, the drive voltage amplitude Vp-p cannot be increased, and the displacement of the piezoelectric actuator cannot be increased.

Figure 6 is a graph showing the drive voltage waveform of unipolar drive, which is a conventional drive voltage waveform. In Figure 6, the drive voltage waveform is entirely on the positive side of 0 V, but the entire drive voltage waveform may be entirely on the negative side of 0 V. As shown in the figure, in unipolar drive, by continuing to drive with a voltage biased to the positive or negative side, the dielectric constant during driving decreases due to the imprint effect, and continued driving deteriorates the displacement characteristics.

In contrast, the drive voltage waveform (see Figures 3 and 4) generated by the drive circuit 102 according to this embodiment can increase the drive voltage amplitude Vp-p by swinging the voltage in a range that does not exceed the coercive electric field Ec in the opposite direction to the main driving side, and can prevent the deterioration of the deformation characteristics due to the imprint effect. Therefore, the displacement of the piezoelectric element 104 can be maximized without compromising the drive stability or drive reliability.

As mentioned above, the second drive maximum voltage Vp is preferably between 0.1 and 0.8 times the coercive electric field Ec. However, if the second drive maximum voltage Vp is less than 0.1 times the coercive electric field Ec, the imprint effect occurs as with unipolar drive. Also, if the second drive maximum voltage Vp exceeds 0.8 times the coercive electric field Ec, depolarization and a decrease in insulation occur. Therefore, the second drive maximum voltage Vp is preferably between 0.1 and 0.8 times the coercive electric field Ec.

Second Embodiment
A displacement driving device according to a second embodiment of the present invention will now be described. The displacement driving device includes a vibration generating device.

[Configuration of the displacement driving device]
7 is a schematic diagram of a displacement driving device 200 according to this embodiment. As shown in the figure, the displacement driving device 200 includes an actuator 201 and a driving circuit 202. The actuator 201 is a unimorph type piezoelectric actuator composed of an object to be driven 203 and a dielectric element 204.

The driven object 203 is, for example, a vibration plate, and presents a tactile sensation to a user who touches the driven object 203. The driven object 203 can be a plate-shaped member made of metal, glass, or resin material, for example, a liquid crystal panel or the housing of an electronic device. There are no particular limitations on the shape or size of the driven object 203.

The dielectric element 204 is joined to the driven object 203 and drives the driven object 203. The dielectric element 204 can, for example, generate vibrations in the driven object 203. FIG. 8 is a cross-sectional view of the dielectric element 204. As shown in the figure, the dielectric element 204 includes a dielectric 211, a positive electrode 212, and a negative electrode 213. The dielectric 211 is made of a dielectric material, specifically, a ceramic that exhibits electric field-induced strain.

As long as the ceramics exhibits electric field induced strain, it may have a coercive field Ec of less than 1 kV/mm or a Curie temperature Tc of less than 300° C. An example of such a material is BT (BaTiO ₃ ) (see the examples). Although a ferroelectric is preferable as the dielectric material constituting the dielectric 211, it may also be a material close to a paraelectric as long as it exhibits electric field induced strain.

The positive electrode 212 includes a positive internal electrode 214 and a positive external electrode 215. The positive internal electrode 214 is made of a conductive material and is provided in multiple layers in the dielectric 211. The positive external electrode 215 is made of a conductive material, is formed on the surface of the dielectric 211, and is connected to the positive internal electrode 214.

The negative electrode 213 includes a negative internal electrode 216 and a negative external electrode 217. The negative internal electrode 216 is made of a conductive material and is provided in multiple layers in the dielectric 211. The negative external electrode 217 is made of a conductive material, is formed on the surface of the dielectric 211, and is connected to the negative internal electrode 216.

As shown in FIG. 8, the positive internal electrodes 214 and the negative internal electrodes 216 are arranged alternately and face each other via the dielectric 211. The positive external electrodes 215 and the negative external electrodes 217 are provided at a distance on the front and back surfaces of the dielectric element 204. As shown in FIG. 7, the positive external electrode 215 is connected to the positive wiring 205, and the positive external electrode 215 functions as a positive terminal. The negative external electrode 217 is connected to the negative wiring 206, and the negative external electrode 217 functions as a negative terminal.

In the dielectric element 204, when a voltage is applied between the positive electrode 212 and the negative electrode 213, the dielectric 211 is deformed by electric field-induced strain. As shown in FIG. 8, the dielectric element 204 may have a laminated structure in which the positive electrode 212 and the negative electrode 213 are alternately laminated with the dielectric 211 interposed therebetween, or may have another structure. The dielectric element 204 may be bonded to the driven object 203 by a resin or the like. Two or more dielectric elements 204 may be bonded to the driven object 203.

The drive circuit 202 is connected to the piezoelectric element 204 via a positive electrode wiring 205 and a negative electrode wiring 206, and supplies a drive signal to the piezoelectric element 204. Specifically, the drive circuit 202 generates a drive voltage waveform, which will be described later, and supplies it between the positive electrode 212 and the negative electrode 213.

The displacement driving device 200 has the above-described configuration. The displacement driving device 200 can be installed in various electronic devices such as smartphones and haptic function devices.

[Drive voltage waveform]
The driving voltage waveform generated by the driving circuit 202 will be described. The driving voltage waveform generated by the driving circuit 202 can be the same as that in the first embodiment. That is, the driving voltage waveform generated by the driving circuit 202 can be such that when the polarization direction is on the plus side (>0 V), the above formulas 1 and 2 are satisfied (see FIG. 3), and when the polarization direction is on the minus side (<0 V), the above formulas 3 and 4 are satisfied (see FIG. 4).

The drive circuit 202 generates the drive voltage waveform shown in FIG. 3 or FIG. 4, and supplies the drive voltage waveform between the positive electrode 212 and the negative electrode 213 via the positive electrode wiring 205 and the negative electrode wiring 206. Note that the drive voltage waveform generated by the drive circuit 202 is not limited to the sine wave shown in FIG. 3 and FIG. 4, and may be any waveform in which the first drive maximum voltage and the second drive maximum voltage satisfy the above conditions. Specifically, the drive voltage waveform generated by the drive circuit 202 may be a sine wave, a triangular wave, a Haversine wave, a Gaussian wave, or a burst wave of these.

[Effects of the displacement drive device]
In the displacement driving device 200, the driving circuit 202 generates the above-mentioned driving voltage waveform (see Figs. 3 and 4) and supplies it to the dielectric element 204. As in the first embodiment, by applying a voltage in a range that does not exceed the coercive electric field Ec also in the opposite direction to the main driving side, it is possible to increase the driving voltage amplitude Vp-p and prevent a decrease in the deformation characteristic due to the imprint effect. Therefore, it is possible to maximize the displacement of the piezoelectric element 204 without impairing the driving stability and driving reliability.

In addition, in the displacement driving device 200, by using the driving voltage waveforms as described above (see Figures 3 and 4), it is possible to expand the conditions of the dielectric material forming the dielectric 211. The dielectric material generally required for a piezoelectric actuator must have a Curie temperature Tc of 300°C or higher, a coercive electric field Ec of 1 kV/mm, and must have reflow resistance and bipolar drive resistance. Figure 9 shows an example of a P-E hysteresis loop of a dielectric material generally required for a piezoelectric actuator, with the horizontal axis representing the electric field (P) and the vertical axis representing polarization (E).

However, in the displacement driving device 200, by using the driving voltage waveform as described above, it is possible to use ceramics with a coercive electric field Ec of less than 1 kV/mm or a Curie temperature Tc of less than 300°C as the material for the dielectric 211, so long as the material exhibits electric field-induced distortion. Furthermore, the material for the dielectric 211 does not need to have high ferroelectricity as shown in Figure 9. Figure 10 is an example of a P-E hysteresis loop of the dielectric material that constitutes the dielectric 211, with the horizontal axis representing the electric field (P) and the vertical axis representing polarization (E).

Dielectric materials commonly used in piezoelectric actuators require polarization processing by DC polarization. This polarization processing is prone to differences in the degree of polarization, i.e., differences due to the degree of rotation of the polarization phase, which can easily cause variations in the displacement characteristics, and requires a polarization device with a complex mechanism to align the degree of polarization, which also places a heavy burden on process costs. In contrast, the displacement drive device 200 uses ceramics, which exhibits electric field-induced strain, as the material for the dielectric 211, making polarization processing unnecessary. This is because electric field-induced strain is exhibited regardless of the presence or absence of polarization.

In this way, when ceramics that exhibit electric field-induced strain are used as the material for the dielectric 211, it is assumed that the dielectric 211 is unpolarized, so there is no need for a high coercive electric field Ec. In addition, since there is no concept of depolarization, there is no problem even if the dielectric 211 is exposed to high temperatures during the manufacturing process, and there is no problem even if the Curie temperature Tc is less than 300°C. Preliminary polarization may also be performed on the piezoelectric element 204 for performance testing, etc.

As described above, in the displacement driving device 200, a material that does not have high piezoelectricity or high ferroelectricity can be used as the material for the dielectric 211, making it possible to select a dielectric material that has a lower environmental impact and cost burden than the dielectric materials generally required for piezoelectric actuators. Furthermore, since the dielectric element 204 does not require polarization processing, complex and expensive polarization devices and polarization processing processes are not required, making it possible to improve production tact time and reduce production equipment costs. In addition, since no inspection is required to check the degree of polarization, it is also possible to reduce the inspection process.

A unimorph type piezoelectric actuator 101 (see FIG. 1) according to the first embodiment was fabricated. The vibrating body 103 was a plate made of stainless steel, with a length of 40 mm, a width of 15 mm, and a thickness of 0.3 mm. The piezoelectric element 104 had a length of 30 mm, a width of 15 mm, and a thickness of 0.3 mm, and was bonded to the vibrating body 103 with a resin adhesive. The coercive electric field Ec of the piezoelectric material constituting the piezoelectric body 111 was 1.1 kV/mm, and the breakdown voltage of the piezoelectric element 104 was 9.5 kV/mm.

Figure 11 is a schematic diagram showing a method for measuring the displacement of a piezoelectric actuator. As shown in the figure, fixed parts 302 and 303 are provided on a fixed substrate 301, and both ends of the vibrating body 103 are fixed to the fixed parts 302 and 303, respectively. The free length of the vibrating body 103 is shown as free length L. The bending displacement of the center part (1/2L) of the vibrating body 103 was measured by a laser Doppler vibrometer (LDV) 304. The following [Table 1] shows the measurement results.

In Example 1, the drive waveform is a sine wave, the drive frequency is 100 Hz, the first drive maximum voltage Vp+ is 3.5 kV/mm, the second drive maximum voltage Vp- is -0.8 kV/mm, and Vp-p is 4.3 kV/mm. The first drive maximum voltage Vp+ is a voltage between 0 V and the breakdown voltage (9.5 kV/mm). The second drive maximum voltage Vp- is a voltage between 0.1 and 0.8 times the coercive electric field Ec- (-1.1 kV/mm).

The displacement measured by the laser Doppler vibrometer 304 was 26.5 μm. Furthermore, when the displacement was measured after 20M cycles of continuous operation under high humidity conditions of 40°C and 90% RH, the displacement reduction rate was -1%, and very high characteristic stability was obtained. Thus, in Example 1, both the displacement amount and characteristic stability were good.

In Example 2, the drive waveform is a sine wave, the drive frequency is 100 Hz, the first drive maximum voltage Vp+ is 5 kV/mm, the second drive maximum voltage Vp- is -0.8 kV/mm, and Vp-p is 5.8 kV/mm. The first drive maximum voltage Vp+ is a voltage between 0 V and the breakdown voltage (9.5 kV/mm). The second drive maximum voltage Vp- is a voltage between 0.1 and 0.8 times the coercive electric field Ec- (-1.1 kV/mm).

The displacement measured by the laser Doppler vibrometer 304 was 32.8 μm. Furthermore, when the displacement was measured after 20 M cycles of continuous operation under high humidity conditions of 40°C and 90% RH, the displacement reduction rate was -2%, indicating high characteristic stability. Thus, in Example 2, both the displacement amount and characteristic stability were good.

In Example 3, the drive waveform is a sine wave, the drive frequency is 100 Hz, the first drive maximum voltage Vp+ is 8 kV/mm, the second drive maximum voltage Vp- is -0.8 kV/mm, and Vp-p is 8.8 kV/mm. The first drive maximum voltage Vp+ is a voltage between 0 V and the breakdown voltage (9.5 kV/mm). The second drive maximum voltage Vp- is a voltage between 0.1 and 0.8 times the coercive electric field Ec- (-1.1 kV/mm).

The displacement measured by the laser Doppler vibrometer 304 was 45.4 μm. Furthermore, when the displacement was measured after 20 M cycles of continuous operation under high humidity conditions of 40°C and 90% RH, the displacement reduction rate was -4%, indicating high characteristic stability. Thus, in Example 3, both the displacement amount and characteristic stability were good.

In Comparative Example 1, the drive waveform is a sine wave, and the drive frequency is 100 Hz. The first drive maximum voltage Vp+ is 3.5 kV/mm, the second drive maximum voltage Vp- is 0 kV/mm, and Vp-p is 3.5 kV/mm. The first drive maximum voltage Vp+ is a voltage between 0 V and the breakdown voltage (9.5 kV/mm). The second drive maximum voltage Vp- is not a voltage between 0.1 and 0.8 times the coercive electric field Ec- (-1.1 kV/mm), but a voltage greater than 0.1 times.

The displacement measured by the laser Doppler vibrometer 304 was 23.1 μm. Furthermore, when the displacement was measured after 20M cycles of continuous operation under high humidity conditions of 40°C and 90% RH, the displacement reduction rate was -7%, indicating low characteristic stability. Thus, in Comparative Example 1, the amount of displacement was good, but the characteristic stability was insufficient.

In Comparative Example 2, the drive waveform is a sine wave, and the drive frequency is 100 Hz. The first drive maximum voltage Vp+ is 1 kV/mm, the second drive maximum voltage Vp- is -1 kV/mm, and Vp-p is 2 kV/mm. The first drive maximum voltage Vp+ is a voltage between 0 V and the breakdown voltage (9.5 kV/mm). The second drive maximum voltage Vp- is not a voltage between 0.1 and 0.8 times the coercive electric field Ec- (-1.1 kV/mm), but a voltage less than 0.8 times.

The displacement measured by the laser Doppler vibrometer 304 was 16.8 μm. Furthermore, when the displacement was measured after 20 M cycles of continuous operation under high humidity conditions of 40°C and 90% RH, the displacement reduction rate was 0%, and high characteristic stability was obtained. Thus, in Comparative Example 2, although the characteristic stability was good, the amount of displacement was insufficient.

In Comparative Example 3, the drive waveform is a sine wave, and the drive frequency is 100 Hz. The first drive maximum voltage Vp+ is 8 kV/mm, the second drive maximum voltage Vp- is 0 kV/mm, and Vp-p is 8 kV/mm. The first drive maximum voltage Vp+ is a voltage between 0 V and the breakdown voltage (9.5 kV/mm). The second drive maximum voltage Vp- is not a voltage between 0.1 and 0.8 times the coercive electric field Ec- (-1.1 kV/mm), but a voltage greater than 0.1 times.

The displacement measured by the laser Doppler vibrometer 304 was 41.3 μm. Furthermore, when the displacement was measured after 20 M cycles of continuous operation under high humidity conditions of 40°C and 90% RH, the displacement reduction rate was -12%, indicating low characteristic stability. Thus, in Comparative Example 3, the amount of displacement was good, but the characteristic stability was insufficient.

In Comparative Example 4, the drive waveform is a sine wave, and the drive frequency is 100 Hz. The first drive maximum voltage Vp+ is 10 kV/mm, the second drive maximum voltage Vp- is 0 kV/mm, and Vp-p is 10 kV/mm. The first drive maximum voltage Vp+ is not a voltage between 0 V and the breakdown voltage (9.5 kV/mm), but a voltage greater than the breakdown voltage. The second drive maximum voltage Vp- is not a voltage between 0.1 and 0.8 times the coercive electric field Ec- (-1.1 kV/mm), but a voltage greater than 0.1 times.

In Comparative Example 4, a breakdown occurred in the piezoelectric body 111, and no displacement was measured by the laser Doppler vibrometer 304.

As described above, in Examples 1 to 3, good results were obtained for both the displacement amount and characteristic stability. On the other hand, in Comparative Examples 1 to 4, good results were not obtained for both the displacement amount and characteristic stability. Therefore, by setting the first maximum driving voltage to a voltage between 0V and the breakdown voltage, and the second maximum driving voltage to a voltage between 0.1 and 0.8 times the coercive electric field, it is possible to realize a displacement driving device that is excellent in both the displacement amount and characteristic stability.

The dielectric element 204 (see FIG. 8) according to the second embodiment was produced. The dielectric element 204 is a 3216 shape in which 10 layers of 26 μm dielectrics are alternately laminated with the positive internal electrode 214 and the negative internal electrode 216. The dielectric elements 204 made of various dielectric materials were produced, and the dielectric elements 204 were driven by the above driving voltage waveform (driving voltage -2V to +104V, driving frequency 10Hz, see FIG. 3). Using a laser Doppler vibrometer, a laser was irradiated from above the dielectric element 204 (Z direction, see FIG. 8), and the amount of expansion and contraction displacement in the thickness direction (Z direction) of the dielectric element 204 was measured. Furthermore, the amount of displacement in the polarization direction/electric field strength/number of layers was calculated as the amount of displacement d33 ^* . The following [Table 2] is a table showing the configuration and measurement results of the dielectric element 204.

The "Material" in the above [Table 2] is the dielectric material constituting the dielectric 211 of the dielectric element 204 in each example. The following [Table 3] is a table showing the composition of BT1 in Examples 4 and 5 and the composition of BT2 in Example 6. The following [Table 4] is a table showing the composition of LNKN1 in Example 7. The composition of PZT1 in Example 8 is PZT-PZN (Pb(Zr _1/2 Ti _1/2 )O ₃ -Pb(Zn _1/3 Nb _2/3 )O ₃ ).

The dielectric elements 204 of Examples 4, 7, and 8 were polarized at 25°C, 3.5 kV/mm, and 15 min, and displacement measurements were performed. On the other hand, the dielectric elements 204 of Examples 5 and 6 were subjected to displacement measurements in an unpolarized state.

As shown in Table 2 above, both LNKN1 according to Example 7 and PZT1 according to Example 8 are materials with a Curie temperature Tc of 300° C. or higher and a coercive field Ec of 1 kV/mm or higher. In Example 7, the displacement d33 ^* was 190 pm/V, and in Example 8, the displacement d33 ^* was 450 pm/V.

On the other hand, BT1 and BT2 according to Examples 4-6 are materials having a Curie temperature Tc of less than 300° C. and a coercive electric field Ec of less than 1 kV/mm. In Examples 4 and 5, the displacement d33 ^* was 370 pm/V, and in Example 6, the displacement d33 ^* was 390 pm/V. Therefore, even though the material had a Curie temperature Tc of less than 300° C. and a coercive electric field Ec of less than 1 kV/mm, a displacement comparable to that of a material having a Curie temperature Tc of 300° C. or higher and a coercive electric field Ec of 1 kV/mm or higher was obtained.

In addition, from Examples 4-6, even when the dielectric element 204 was in an unpolarized state, a displacement amount equivalent to that in a polarized state was obtained. Therefore, the dielectric element 204 does not require polarization processing.

100, 200... Displacement driving device 101... Piezoelectric actuator 102, 202... Driving circuit 103, 203... Drive target 104... Piezoelectric element 105, 205... Positive electrode wiring 106, 206... Negative electrode wiring 111... Piezoelectric body 112, 212... Positive electrode 113, 213... Negative electrode 114, 214... Positive electrode internal electrode 115, 215... Positive electrode external electrode 116, 216... Negative electrode internal electrode 117, 217... Negative electrode external electrode 201... Actuator 204... Dielectric element 211... Dielectric

Claims (13)

a dielectric element including: a ceramic that exhibits electric-field-induced distortion; a positive electrode including a plurality of positive internal electrodes provided inside the ceramic and a positive external electrode provided on a surface of the ceramic and connected to the plurality of positive internal electrodes; and a negative electrode including a plurality of negative internal electrodes provided inside the ceramic facing the plurality of positive internal electrodes via the ceramic and a negative external electrode provided on the surface of the ceramic and connected to the plurality of negative internal electrodes, the driving method comprising: applying, between the positive electrode and the negative electrode, a driving voltage waveform having a predetermined driving frequency, wherein a first driving maximum voltage which is one peak voltage of the driving voltage waveform is a voltage between 0.37 and 0.84 times a breakdown voltage of the ceramic at the driving frequency, and a second driving maximum voltage which is the other peak voltage of the driving voltage waveform is a voltage between 0.1 and 0.8 times a coercive electric field of the ceramic in a polarity opposite to that of the first driving maximum voltage, between the positive electrode and the negative electrode. 2. The driving method according to claim 1,
The ceramic has a coercive electric field of less than 1 kV/mm or a Curie temperature of less than 300° C. The driving method according to claim 1 or 2,
The driving method, wherein the driving voltage waveform is a sine wave, a triangular wave, a Haversine wave, a Gaussian wave, or a burst wave thereof. a positive electrode including a plurality of positive internal electrodes provided inside the ceramic and a positive external electrode provided on a surface of the ceramic and connected to the plurality of positive internal electrodes; and a negative electrode including a plurality of negative internal electrodes provided inside the ceramic facing the plurality of positive internal electrodes via the ceramic and a negative external electrode provided on the surface of the ceramic and connected to the plurality of negative internal electrodes. A drive circuit generates a drive voltage waveform having a predetermined drive frequency, which is applied between the positive electrode and the negative electrode, wherein a first drive maximum voltage which is one peak voltage of the drive voltage waveform is a voltage between 0.37 and 0.84 times a breakdown voltage of the ceramic at the drive frequency, and a second drive maximum voltage which is the other peak voltage of the drive voltage waveform is a voltage between 0.1 and 0.8 times a coercive electric field of the ceramic in a polarity opposite to that of the first drive maximum voltage, and applies the drive voltage waveform between the positive electrode and the negative electrode. 5. A drive circuit according to claim 4,
The ceramic has a coercive electric field of less than 1 kV/mm or a Curie temperature of less than 300° C. a dielectric element including: a ceramic that exhibits electric field induced strain; a positive electrode including a plurality of positive internal electrodes provided inside the ceramic and a positive external electrode provided on a surface of the ceramic and connected to the plurality of positive internal electrodes; and a negative electrode including a plurality of negative internal electrodes provided inside the ceramic facing the plurality of positive internal electrodes via the ceramic and a negative external electrode provided on the surface of the ceramic and connected to the plurality of negative internal electrodes ;
a driving object to which the dielectric element is bonded; and
a drive circuit that generates a drive voltage waveform that is applied between the positive electrode and the negative electrode and has a predetermined drive frequency, wherein a first drive maximum voltage that is one peak voltage of the drive voltage waveform is a voltage between 0.37 and 0.84 times the breakdown voltage of the ceramic at the drive frequency, and a second drive maximum voltage that is the other peak voltage of the drive voltage waveform is a voltage between 0.1 and 0.8 times the coercive electric field of the ceramic in the opposite polarity to the first drive maximum voltage, and applies the drive voltage waveform between the positive electrode and the negative electrode. The displacement drive device according to claim 6,
The ceramic has a coercive electric field of less than 1 kV/mm or a Curie temperature of less than 300° C. The displacement drive device according to claim 6 or 7,
The dielectric element and the object to be driven constitute an actuator. a positive electrode including a plurality of positive internal electrodes provided inside the piezoelectric body and a positive external electrode provided on a surface of the piezoelectric body and connected to the plurality of positive internal electrodes; and a negative electrode including a plurality of negative internal electrodes provided inside the piezoelectric body facing the plurality of positive internal electrodes via the piezoelectric body and a negative external electrode provided on the surface of the piezoelectric body and connected to the plurality of negative internal electrodes, the method comprising: applying, between the positive electrode and the negative electrode , a driving voltage waveform having a predetermined driving frequency, wherein a first driving maximum voltage which is one peak voltage of the driving voltage waveform is a voltage between 0.37 and 0.84 times a breakdown voltage of the piezoelectric body at the driving frequency, and a second driving maximum voltage which is the other peak voltage of the driving voltage waveform is a voltage between 0.1 and 0.8 times a coercive electric field of the piezoelectric material in a polarity opposite to that of the first driving maximum voltage, between the positive electrode and the negative electrode. The driving method according to claim 9,
The driving voltage waveform is a sine wave, a triangular wave, a Haversine wave, a Gaussian wave, or a burst wave thereof.
Drive method. a positive electrode including a plurality of positive internal electrodes provided inside the piezoelectric body and a positive external electrode provided on a surface of the piezoelectric body and connected to the plurality of positive internal electrodes; and a negative electrode including a plurality of negative internal electrodes provided inside the piezoelectric body facing the plurality of positive internal electrodes via the piezoelectric body and a negative external electrode provided on the surface of the piezoelectric body and connected to the plurality of negative internal electrodes. A drive circuit generates a drive voltage waveform having a predetermined drive frequency and is applied between the positive electrode and the negative electrode of a piezoelectric element having a piezoelectric body made of a piezoelectric material, a plurality of positive internal electrodes provided inside the piezoelectric body and facing the plurality of positive internal electrodes via the piezoelectric body, and a negative external electrode provided on the surface of the piezoelectric body and connected to the plurality of negative internal electrodes, the drive circuit generating a drive voltage waveform having a predetermined drive frequency and a first drive maximum voltage which is one peak voltage of the drive voltage waveform, which is a voltage between 0.37 and 0.84 times a breakdown voltage of the piezoelectric body at the drive frequency, and a second drive maximum voltage which is the other peak voltage of the drive voltage waveform, which is a voltage between 0.1 and 0.8 times a coercive electric field of the piezoelectric material in a polarity opposite to that of the first drive maximum voltage, and applying the drive voltage waveform between the positive electrode and the negative electrode. a piezoelectric element including: a piezoelectric body made of a piezoelectric material; a positive electrode including a plurality of positive internal electrodes provided inside the piezoelectric body and a positive external electrode provided on a surface of the piezoelectric body and connected to the plurality of positive internal electrodes; and a negative electrode including a plurality of negative internal electrodes provided inside the piezoelectric body facing the plurality of positive internal electrodes via the piezoelectric body and a negative external electrode provided on the surface of the piezoelectric body and connected to the plurality of negative internal electrodes ;
a vibration body to which the piezoelectric element is bonded;
a drive circuit that generates a drive voltage waveform that is applied between the positive electrode and the negative electrode and has a predetermined drive frequency, wherein a first drive maximum voltage that is one peak voltage of the drive voltage waveform is a voltage between 0.37 and 0.84 times the breakdown voltage of the piezoelectric body at the drive frequency, and a second drive maximum voltage that is the other peak voltage of the drive voltage waveform is a voltage between 0.1 and 0.8 times the coercive electric field of the piezoelectric material in the opposite polarity to the first drive maximum voltage, and applies the drive voltage waveform between the positive electrode and the negative electrode. The displacement drive device according to claim 12,
The piezoelectric element and the vibrating body constitute a piezoelectric actuator, and a tactile sensation is generated on the vibrating body by vibration of the vibrating body.

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