JP2009219258A - Piezoelectric vibrator, piezoelectric actuator and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric vibrator having a driving efficiency higher than conventional devices. <P>SOLUTION: The piezoelectric vibrator 70A has piezoelectric elements 21 and a reinforcing plate 30 laminating the piezoelectric elements 21 and reinforcing the piezoelectric elements 21. The reinforcing plate 30 is formed mainly of titanium (Ti), and the elastic modulus of the reinforcing plate 30 is a value from 30 GPa to 100 GPa. Accordingly, since the elastic modulus of the reinforcing plate 30 is smaller than that of conventional stainless steel, super-invar or the like, the disturbance of vibrations of the piezoelectric elements 21 by the reinforcing plate 30 is reduced largely, and the major-axis length A of the elliptical locus R1 of the piezoelectric vibrator 70A is expanded. Consequently, a force propelling the driving of a body to be driven is increased, the body to be driven with a larger load can be driven at high speed even by the same power and the driving efficiency can be improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezoelectric vibrating body, a piezoelectric actuator, and an electronic apparatus that include a piezoelectric element and a reinforcing plate that is laminated with the piezoelectric element to reinforce the piezoelectric element.

In recent years, a piezoelectric actuator has been used as a drive source in order to reduce the size and thickness of electronic devices. Further, there is a further need for a piezoelectric actuator that can drive a driving object with a higher load, continuously drive the driving object, and increase the driving speed of the driving object.
The piezoelectric actuator has a piezoelectric vibrating body and a driven body (for example, a rotor), and the driven body is driven by the vibration of the piezoelectric vibrating body. The piezoelectric vibrating body includes a reinforcing plate and a plate-like piezoelectric element laminated on the reinforcing plate. Conventionally, stainless steel (SUS) has been widely used for this reinforcing plate.

In order to increase the driving efficiency of such a piezoelectric actuator, it is necessary to increase the amplitude of the piezoelectric vibrating body.
The reinforcing plate of the piezoelectric vibrating body is provided to support the piezoelectric element and secure the necessary strength of the piezoelectric vibrating body. Conversely, it also prevents the piezoelectric element from vibrating. Therefore, in order to increase the amplitude of the piezoelectric vibrating body, it is conceivable to use a reinforcing plate that has a necessary strength and is made of a material that is less rigid than the conventional one. For example, a reinforcing plate (Patent Document 1) made of Super Invar (32Ni-5Co-Fe), which has a lower elastic modulus (Low Young's modulus) than conventional SUS and is a low thermal expansion material, and a low thermal expansion material like this Super Invar. A reinforcing plate made of 42 alloy (42Ni—Cr—Ti—Fe) has been proposed. The physical property values of SUS, Super Invar, and 42 alloy are shown below.

International Publication No. 96/14687

However, even with Super Invar and 42 alloy, the rigidity of the reinforcing plate still acts as a resistance that hinders the vibration of the piezoelectric element, and the first problem is that the driving efficiency of the piezoelectric vibrating body cannot be sufficiently increased. there were.
In general, lead zirconate titanate (PZT (registered trademark)) or the like is used for the piezoelectric element bonded to the reinforcing plate. Generally, the thermal expansion coefficient of PZT is much lower than that of metal (about 2.3). × 10 ^-6 / ° C). For this reason, even if a reinforcing plate having a sufficiently low elastic modulus is used, if the difference in coefficient of thermal expansion between the reinforcing plate and the piezoelectric element is large, warping or peeling may occur due to thermal stress due to changes in the surrounding temperature. There was a second problem.
Further, even if a reinforcing plate having a sufficiently low elastic modulus is used, if the hardness of the reinforcing plate is low, the reinforcing plate is likely to be worn or damaged due to contact with the driven body or the like. was there.

A first object of the present invention is to provide a piezoelectric vibrating body, a piezoelectric actuator, and an electronic device that can obtain higher driving efficiency than conventional ones.
A second object is to provide a piezoelectric vibrator, a piezoelectric actuator, and an electronic device that are unlikely to be warped or peeled off due to thermal stress.
A third object is to provide a piezoelectric vibrating body, a piezoelectric actuator, and an electronic device that are resistant to wear and breakage and have excellent durability.

The piezoelectric vibrating body of the present invention is a piezoelectric vibrating body including a piezoelectric element and a reinforcing plate that is laminated with the piezoelectric element to reinforce the piezoelectric element, and the reinforcing plate is made of titanium (Ti) as a main component. The elastic modulus of the reinforcing plate is 30 GPa or more and 100 GPa or less.
Here, the piezoelectric vibrating body is used for a so-called piezoelectric actuator that drives driven bodies that are in contact with each other by the vibration of the piezoelectric vibrating body.
According to this configuration, since the elastic modulus (Young's modulus) of the reinforcing plate is smaller than that of conventional stainless steel, super invar, etc., the obstruction of the piezoelectric element due to the reinforcing plate is greatly reduced, and the piezoelectric vibration The body amplitude is enlarged.

FIG. 6 is a schematic diagram showing an example of a vibration locus of a piezoelectric vibrating body that mainly excites bending vibration among the piezoelectric vibrating bodies according to the present invention. As shown in this figure, the vibration locus of the contact portion (protrusion portion 33) formed on the reinforcing plate by the bending vibration of the piezoelectric vibrating body shows an elliptic locus R1. Here, the contact portion is a portion that contacts a driven body such as a rotor, and is a portion that generates a frictional force between the driven body and drives the driven body by the frictional force.
The inventor manufactured a plurality of piezoelectric vibrators using reinforcing plates having different elastic moduli, and measured the major axis length of the elliptical locus of each piezoelectric vibrator. The graph in FIG. 7 shows the relationship between the elastic modulus of the reinforcing plate and the major axis length of the elliptical locus. Here, the major axis length is the representative length of the elliptical locus shown in FIG. 6 (the length indicated by the arrow A in the figure) and indicates the magnitude of the distortion of the piezoelectric vibrator. The major axis length was measured with a laser Doppler displacement meter, the laser was irradiated from the laser Doppler displacement meter parallel to the major axis length direction with respect to the contact portion, and the displacement of the contact portion was measured. It is calculated from this displacement.
As shown in FIG. 7, when the elastic modulus is in the range of 30 to 100 GPa, the major axis length is about 0.85 to 0.9 μm, whereas when the elastic modulus exceeds 100 GPa, the reinforcing plate is made of the piezoelectric element. Vibration is hindered and the long axis length is reduced. On the other hand, when the elastic modulus is less than 30 GPa, the long axis length becomes small due to a decrease in Q value (vibration attenuation) of the piezoelectric actuator.
As described above, by using the reinforcing plate having an elastic modulus of 30 GPa or more and 100 GPa or less, the amplitude of the piezoelectric vibrator can be efficiently increased.

The graph of FIG. 8 shows the relationship between the drive frequency and the major axis length of the elliptical locus when, for example, rubber metal (registered trademark) is used as the material mainly composed of Ti of the present invention. In addition, in the same figure, the major axis length of the elliptical locus when the conventional SUS is used is shown for comparison. The elastic modulus of rubber metal is 60 GPa, the elastic modulus of SUS is 170 GPa, and the driving frequency indicates the frequency of the driving voltage applied to the piezoelectric actuator.
As shown in FIG. 8, the major axis length (amplitude) of rubber metal was larger than the major axis length of SUS at all driving frequencies. The driving frequency has a correlation with the consumption current of the piezoelectric actuator. In an actual piezoelectric actuator, in order to suppress current consumption as much as possible, the drive frequency is set within a range of approximately 554 kHz to 560 kHz. In this driving frequency range (range indicated by fw in FIG. 8), the maximum amplitude in rubber metal (L1 in the graph) is about twice the maximum amplitude in SUS (L2 in the graph). It was.

From the above, when the piezoelectric vibrating body of the present invention is used as an actuator, the force for driving the driven body is increased by increasing the amplitude of the piezoelectric vibrating body. Therefore, a driven body having a larger load can be driven at a higher speed even with the same input power, so that the driving efficiency can be improved and the first object can be achieved. On the other hand, since it becomes possible to drive a driven body with a predetermined load even if the input power is reduced, it is possible to reduce the electric capacity of a power source such as a battery, and to reduce the size of various devices on which a piezoelectric vibrator is mounted and Thinning can also be promoted.
In addition, the moving direction of the driven body (rotation direction in the case of a rotor) is not limited to one direction, and the rotor may be driven in both the rightward rotation and the leftward rotation, for example.
Further, the driven body is not limited to the rotor, and may be driven linearly.
The piezoelectric actuator is, for example, a driving device such as a date dial or a pointer of a watch, a zoom mechanism or an autofocus mechanism in a lens module of a camera, an inkjet head or paper feeding mechanism of a printer, a piezoelectric buzzer, a driving device in a movable toy, Can be used for

In the piezoelectric vibrating body of the present invention, it is preferable that a thermal expansion coefficient of the reinforcing plate is 0 × 10 ⁻⁶ / ° C. or more and 10 × 10 ⁻⁶ / ° C. or less.
Here, lead zirconate titanate (PZT (registered trademark)) or the like is used for the piezoelectric element bonded to the reinforcing plate. Generally, the thermal expansion coefficient of PZT is much lower than that of metal (about 2. 3 × 10 ⁻⁶ / ° C.). For this reason, if the difference in coefficient of thermal expansion between the reinforcing plate and the piezoelectric element is large, warpage, peeling, and the like may occur due to thermal stress due to changes in the surrounding temperature. According to the present invention, since the thermal expansion coefficient of the reinforcing plate is 0 × 10 ⁻⁶ / ° C. or more and 10 × 10 ⁻⁶ / ° C. or less, conventional SUS (thermal expansion coefficient: 17 × 10 ⁻⁶ / ° C.) In comparison with the above, it is possible to suppress the occurrence of warpage or peeling due to thermal stress, thereby achieving the second object.
The conventional super invar shows a relatively small coefficient of thermal expansion as shown in Table 1, but the reinforcing plate of the present invention has a low elastic modulus in addition to a low coefficient of thermal expansion, so that the driving efficiency can be improved. It is superior to conventional low thermal expansion materials.

  Here, the piezoelectric vibrator has a characteristic that, as the electromechanical coupling coefficient (k value) is larger, the propulsive force obtained with the same input power is larger and the conversion capability from electrical energy to mechanical energy is higher. The k value is calculated by the following equations (1) and (2). When the vibration mode is the same, the k value increases as the distance (Δf) between the resonance frequency (fr) and the anti-resonance frequency (fa) increases, and the conversion capability as a piezoelectric actuator increases. That is, as Δf is larger, output efficiency for driving a driven body such as a rotor is improved.

Where fs: series resonance frequency of the piezoelectric vibrator
Δf: interval between resonance frequency and anti-resonance frequency
fa: Anti-resonance frequency
fr: resonance frequency
a, b: coefficients corresponding to vibration modes of the piezoelectric vibrator

FIG. 9 is a graph showing the temperature characteristics of the impedance of the piezoelectric vibrator by frequency in an example in which rubber metal is used for the reinforcing plate among the piezoelectric vibrators according to the present invention. The horizontal axis indicates the drive frequency, and the vertical axis indicates the impedance. FIG. 10 is a graph showing the temperature characteristics of the impedance when the conventional SUS is used for the reinforcing plate as a comparative example for each frequency as in FIG.
In these figures, two resonance points where the impedance with respect to the driving frequency is minimum appear, and two anti-resonance points where the impedance is maximum appear. Of the resonance points, the lower frequency is the resonance point of longitudinal vibration, and the higher frequency is the resonance point of bending vibration. Of the anti-resonance points, the lower frequency is the anti-resonance point of bending vibration, and the higher frequency is the anti-resonance point of longitudinal vibration. Here, Δf (the range of the arrow in the figure) indicates the difference between the drive frequency at the resonance point of longitudinal vibration and the drive frequency at the anti-resonance point of longitudinal vibration.
The inventor measured the impedance for each temperature of high temperature (60 ° C.), normal temperature (24 ° C.), and low temperature (−10 ° C.), and obtained the results shown in FIGS. As a result, almost no change in Δf due to temperature was observed in FIG. 9, but in FIG. 10, Δf was larger at a higher temperature than at normal temperature and decreased at a lower temperature. In actual measurement, when the temperature is changed, the position (frequency) at which the impedance characteristic is generated changes, so that the resonance point of the longitudinal vibration of each temperature characteristic does not match. However, the graphs of FIGS. 9 and 10 are graphs in which the resonance points of the longitudinal vibration are made to coincide for each temperature characteristic in order to make it easy to compare Δf of each temperature.

From the relationship of the formula (1) and the formula (2), the driving performance of the piezoelectric vibrating body is improved when the temperature is increased, but the driving performance is decreased when the temperature is decreased. That is, the driving performance of the piezoelectric vibrating body changes depending on the temperature condition. As the piezoelectric vibrator, it is desirable that a stable driving performance can be obtained regardless of a temperature change. Therefore, it is desirable that the amount of shift of Δf with respect to normal temperature is as small as possible. According to this aspect, it can be seen that the shift amount of Δf is smaller in rubber metal than in conventional SUS.
Therefore, the inventor manufactured a plurality of piezoelectric vibrators using reinforcing plates having different thermal expansion coefficients, measured the shift amount of Δf at a low temperature (−10 ° C.) with respect to the normal temperature (24 ° C.), and the result of FIG. Got. The graph in FIG. 11 shows the relationship between the thermal expansion coefficient and the shift amount of Δf. The horizontal axis represents the thermal expansion coefficient of the reinforcing plate (hereinafter referred to as α), and the vertical axis represents the shift amount of Δf.
As shown in FIG. 11, when α is 10 × 10 ⁻⁶ / ° C. or less, the shift amount of Δf is between about 0.22 kHz and about 0.26 kHz, whereas α is 10 × 10 ⁻ It has been found that when the temperature exceeds ⁶ / ° C., the shift amount of Δf with respect to α increases rapidly, and the difference in driving performance of the piezoelectric vibrator increases. That is, Δf at a low temperature (−10 ° C.) is remarkably lowered with respect to Δf at normal temperature (24 ° C.). This shows that α is desirably 10 × 10 ⁻⁶ / ° C. or less.
According to this configuration, since α of the reinforcing plate is 10 × 10 ⁻⁶ / ° C. or less, the shift amount of Δf is relatively small as shown in FIG. 11, and further obtained by Equations (1) and (2). Since the change in the k value is small, the difference in driving performance with respect to the temperature change, that is, the variation in vibration is reduced, and the positioning accuracy of the driven body is improved. The thermal expansion coefficient is more preferably 0 × 10 ⁻⁶ / ° C. or more and 6 × 10 ⁻⁶ / ° C. or less.

In the piezoelectric vibrating body of the present invention, it is preferable that the reinforcing plate has a hardness of 200 Hv or more.
The hardness of the reinforcing plate is more preferably 300 Hv or more.
Here, for example, as shown in FIGS. 12A and 12B, when the driven body is the rotor 9 </ b> A, the piezoelectric vibrating body 9 </ b> B contacts the entire circumference of the side surface of the rotor. The same portion of 9C always becomes a contact portion, and wear tends to proceed. As a result of this wear, the contact portion with the rotor 9A that was initially in line contact (FIG. 12A) becomes surface contact with the progress of wear (FIG. 12B), and the piezoelectric vibrator 9B is driven. Performance will be degraded.
The inventor manufactured a plurality of piezoelectric vibrating bodies (experimental materials) using reinforcing plates having different hardnesses, and measured the wear volume of the contact portion of each piezoelectric vibrating body.
The graph of FIG. 13 shows the relationship between the hardness of the reinforcing plate and the wear volume of the contact portion. The horizontal axis indicates the hardness of the contact portion of the reinforcing plate, and the vertical axis indicates the wear volume of the contact portion after the rotor is driven to a predetermined rotational speed. Here, the contact portion 9C in the initial state (shaded portion in FIG. 12A) is sketched with a projector to determine the area, and the initial volume is determined by multiplying the area by the thickness of the reinforcing plate. Moreover, the volume after abrasion is calculated | required similarly to the initial volume about the contact part 9C (shaded part of FIG.12 (B)) after driving to a predetermined rotation speed. The difference between these volumes was defined as the wear volume.
As shown in FIG. 13, it was found that when the hardness of the reinforcing plate is less than 200 Hv, the wear volume of the contact portion increases rapidly. Accordingly, it is desirable that the hardness of the reinforcing plate is 200 Hv or more.
According to this configuration, since the hardness of the reinforcing plate is 200 Hv or more, when the piezoelectric vibrating body is used as an actuator, the contact portion of the reinforcing plate is pressed against a driven body (for example, a rotor), and the contact portion is pressed. Since the driven body is driven by the generated frictional force, wear at the contact portion with the driven body can be reduced, driving efficiency can be maintained even under long-term continuous driving conditions, and the quality is stabilized. It becomes possible. Therefore, a piezoelectric vibrator having excellent durability can be obtained, and the third object can be achieved.

In the piezoelectric vibrating body of the present invention, it is preferable that the hardness of the reinforcing plate is equal to or lower than the hardness of the driven body driven by the vibration of the piezoelectric vibrating body.
Here, when the hardness of the reinforcing plate is larger than the hardness of the driven body, the contact portion on the driven body side may be worn. For example, when the driven body is a rotor and the width dimension of the contact portion of the reinforcing plate is smaller than the width dimension along the rotation axis of the rotor side surface, the side surface of the rotor will be worn like a heel. .
FIG. 14 is a schematic diagram for explaining that wrinkle-like wear (portion indicated by a two-dot chain line in the figure) occurs on the side surface of the rotor 9A due to the contact portion 9C. When such wrinkle-like wear occurs, the contact portion may become inconsistent with the inner surface of the wrinkle caused by the wear due to variations in the vibration of the piezoelectric vibration member and variations in the position of the contact portion depending on the support method of the piezoelectric vibration member. There is a possibility that the drive performance of the piezoelectric actuator will deteriorate due to contact with necessity.
On the other hand, according to the configuration of the present invention, since the hardness of the reinforcing plate is smaller than the hardness of the driven body, the wear of the driven body is suppressed and the driving performance of the piezoelectric actuator is maintained. In other words, even if there are variations in the vibration of the piezoelectric vibrating body or in the contact portion position due to the support method of the piezoelectric vibrating body, the wear of the driven body is suppressed, so the above unnecessary contact occurs. Therefore, the driving performance of the piezoelectric actuator can be maintained.

In the piezoelectric vibrating body of the present invention, the reinforcing plate is formed to contain zirconium (Zr) and niobium (Nb). For example, 58 to 59% by mass of Ti, 36 to 37% by mass of Nb, and 2 to 2 of Ta. 3% by mass, titanium alloy containing 2-3% by mass of Zr and 0.1-1% by mass of O, or 64 to 66 at% of Ti, 16 to 18 at% of Zr, and 17 to 19 at% of Nb It is preferably formed of a titanium alloy.
According to this configuration, the reinforcing plate is made of a material mainly containing Ti and containing Zr and Nb. For example, rubber metal (registered trademark of Toyotsu Material Co., Ltd.), biosoft titanium (trademark of Unix Co., Ltd.) ) Etc. The component of rubber metal is Ti58.5-Nb36.3-Ta2.03-Zr2.88-O0.31 (mass%), and the component of biosoft titanium (hereinafter referred to as BS-Ti) is Ti65-Zr17- Nb18 (at%). Therefore, the drive performance of the piezoelectric vibrator can be improved by using these materials.

In the piezoelectric vibrating body of the present invention, it is preferable that the reinforcing plate is formed by heat treatment at 200 ° C. or higher and 450 ° C. or lower.
Here, the graph of FIG. 15 shows a change in hardness due to heat treatment when, for example, biosoft titanium (BS-Ti) and rubber metal are used as the material mainly containing Ti according to the present invention. The heat treatment conditions are 400 ° C. and 10 hours in an N ₂ atmosphere. However, other heat treatment conditions are not limited to this embodiment as long as the heat treatment temperature is 200 ° C. or higher and 450 ° C. or lower.
As shown in FIG. 15, the hardness of both BS-Ti and rubber metal increased by heat treatment.
In the graph of FIG. 13 described above, the result of measuring the wear volume of the contact portion using rubber metal before and after heat treatment is shown. As shown in FIG. 13, the wear volume of the rubber metal before the heat treatment is about 10 × 10 ⁻⁴ mm ³ , and the wear volume of the rubber metal after the heat treatment is about 5 × 10 ⁻⁴ mm ³ . Almost reduced to half.
When the hardness after heat treatment was measured using the heat treatment temperature of BS-Ti as a parameter, a hardness exceeding 300 Hv was obtained in the range of the heat treatment temperature of 200 to 450 ° C., and the hardness was maximum at 300 ° C. . There was little change in hardness between 200 ° C. and 450 ° C., and when the temperature was below 200 ° C. or above 450 ° C., the hardness decreased rapidly. Similarly, when the elastic modulus (Young's modulus) after heat treatment was measured, it was found that an elastic modulus of about 55 GPa to 65 GPa was obtained in the range of the heat treatment temperature of 200 ° C to 450 ° C. At 200 ° C. to 450 ° C., the change in elastic modulus was relatively small. When the temperature was lower than 200 ° C. or higher than 450 ° C., the elastic modulus decreased rapidly and the degree of change in elastic modulus due to temperature increased. Therefore, the heat treatment temperature is preferably 200 ° C. or higher and 400 ° C. or lower.
According to this configuration, since the reinforcing plate is formed by heat treatment at 200 ° C. or higher and 400 ° C. or lower, the hardness of the reinforcing plate is increased and wear can be further reduced.

The piezoelectric actuator according to the present invention includes the piezoelectric vibrator and a driven body that is driven by vibration transmitted from the piezoelectric vibrator.
According to this configuration, since the above-described piezoelectric vibrator is provided, the above-described functions and effects can be enjoyed.

The electronic apparatus of the present invention includes the piezoelectric actuator.
According to this configuration, since the above-described piezoelectric vibrator is provided, the above-described functions and effects can be enjoyed.
Here, examples of the electronic device include a wristwatch, a pocket watch, a digital camera, a digital video, a portable printer, a portable information device, and a cellular phone.

The electronic device of the present invention is preferably a timepiece including a timekeeping unit and a time information display unit that displays information timed by the timekeeping unit, and the timed information display unit is driven by the driven body.
According to this configuration, it is possible to display time information such as time and calendar by driving a gear or the like using the piezoelectric vibrator as an actuator. According to the piezoelectric vibrator described above, the amplitude is greatly enlarged, so that a heavy member with a large load can be driven, and continuous driving such as a second hand having a high driving speed, and quick return of a pointer are possible. Etc. are also possible. In addition, since the amplitude is increased and the drive efficiency with the same input power is improved, the applied voltage can be lowered and a small and thin battery with a small battery capacity can be used, so the watch can be further reduced in size and thickness. It becomes.
In addition, advantages of the piezoelectric actuator, that is, not affected by magnetism, high responsiveness, etc. can be realized.

  As described above, according to the present invention, it is possible to provide a piezoelectric vibrating body, a piezoelectric actuator, and an electronic device that can obtain high driving efficiency.

[First Embodiment]
[1. overall structure]
FIG. 1 is a plan view of a timepiece as an electronic apparatus in the present embodiment.
The timepiece of the present embodiment is an analog display type wristwatch (watch) provided with a movement 2 as a timekeeping portion and a dial plate 3, hour hand 4, minute hand 5 and second hand 6 as a timekeeping information display portion.
A substantially rectangular window portion 3A is provided at the 3 o'clock position of the dial plate 3, and printing is performed on the date wheel 74 by rotation of the date wheel 74 provided on the back side of the dial plate 3 from the window portion 3A. The days are displayed sequentially.

  The timepiece is configured as an electronic timepiece (quartz timepiece), and a driving mechanism for the hour hand 4, the minute hand 5, and the second hand 6 is omitted from illustration, but a circuit board incorporating a quartz vibrator, a coil, a stator, A stepping motor having a rotor and a driving wheel train are respectively incorporated in the movement 2.

[2. Structure of date display device]
2 is a plan view of the movement 2 of FIG. 1 as viewed from the side on which the dial 3 is provided, and FIG. 3 is an enlarged perspective view of the piezoelectric vibrating body 70A in FIG. The movement 2 incorporates a date display device 7 for displaying the date from the window 3A (FIG. 1).
The date display device 7 uses a piezoelectric actuator 70 having a piezoelectric vibrating body 70A and a rotor 78 as a drive source, and transmits date driving intermediate wheels 71 and 72 and a date driving wheel 73 that transmit the driving force while decelerating, and a date driving wheel 73. And a date wheel 74 that rotates.
The piezoelectric actuator 70, the date driving intermediate wheels 71 and 72, the date driving wheel 73, and the date dial 74 are provided on the front side (the dial 3 side) of the main plate 75, respectively.
On the other hand, on the back side of the base plate 75, a driving wheel train for driving the hour hand 4, the minute hand 5, the second hand 6, and the like, a battery, and the like are provided.

The intermediate date wheel 71 is engaged with a rotor pinion 78A above the rotor 78, and the intermediate date wheel 71 rotates in conjunction with the rotation of the rotor 78.
The intermediate date wheel 72 is composed of a large diameter part 721 and a small diameter part 722. The intermediate wheel 71 is meshed with the large diameter portion 721. The small diameter portion 722 has a disk shape slightly smaller in diameter than the large diameter portion 721 and is fixed to the large diameter portion 721 so as to be concentric. A single notch 722A is formed on the outer peripheral surface of the small diameter portion 722.

The date driving wheel 73 is a gear having five teeth, and the rotation shaft 731 is loosely inserted into a hole 75 </ b> A formed in the base plate 75. The hole 75 </ b> A is formed in a long hole shape along the circumferential direction of the date indicator 74. The rotary shaft 731 is urged toward the upper right in FIG. 2, that is, toward the date driving intermediate wheel 72 by a leaf spring 732 fixed to the main plate 75. Then, as the intermediate date wheel 72 rotates once, the teeth of the intermediate date wheel 73 fit into the notch 722A of the intermediate date wheel 72 and rotates by one tooth, so that the date driving wheel 73 is fed by one tooth. The date displayed from the window 3A (FIG. 1) is changed.
The date indicator driving wheel 73 meshes with the internal teeth 741 of the date indicator 74, and the urging action of the leaf spring 732 prevents the date indicator 74 from swinging.

The date wheel 74 is a ring-shaped gear having numbers “1” to “31” printed on the circumference thereof, and is arranged on the outer peripheral portion of the movement 2.
In such a date display device 7, the piezoelectric actuator 70 operates at the change of day (24:00), the rotor 78, the date turning intermediate wheels 71 and 72 are sequentially rotated, and the date turning wheel 73 is engaged with the notch 722A. Thus, the date wheel 74 rotates for one day.

[3. Structure of piezoelectric actuator]
(Configuration of rotor)
The rotor 78 constituting the piezoelectric actuator 70 is made of stainless steel (SUS301) or the like and is rotatably held by the rotor support 780. The surface hardness of the rotor 78 is approximately 500 Hv. The rotor support 780 is formed in a U-shaped cross section sandwiching the front and back of the rotor 78, and is pivotally supported by the ground plane 75 around the pin 781. Further, the rotor support 780 is provided with another pin 782, and when a pressing spring 783 as a pressing means wound around the shaft 75B of the ground plate 75 comes into contact with the pin 782, the counterclockwise in FIG. It is pressed around (to the piezoelectric vibrating body 70A side).

(Configuration of piezoelectric vibrator)
FIG. 3 shows a piezoelectric vibrating body 70A constituting the piezoelectric actuator 70, and the piezoelectric vibrating body 70A is formed in a substantially rectangular plate shape as a whole.
The piezoelectric vibrating body 70 </ b> A includes two rectangular plate-shaped piezoelectric elements 21 and 21 and a reinforcing plate 30 that reinforces the piezoelectric elements 21 and 21. The piezoelectric elements 70 and 21 are laminated and bonded to the front surface and the back surface of the reinforcing plate 30, respectively, so that the piezoelectric vibrating body 70A is configured.
The reinforcing plate 30 uses the aforementioned rubber metal or BS-Ti.

[4-1. Configuration of piezoelectric element]
In this embodiment, lead zirconate titanate (PZT (registered trademark)) is used for the piezoelectric elements 21 and 21. In addition, quartz, lithium niobate, barium titanate, lead titanate, and metaniobic acid are used. Lead, polyvinylidene fluoride, lead zinc niobate, lead scandium niobate, and the like can also be used.
An electrode surface formed by plating, sputtering, vapor deposition, or the like is formed on the surface of each piezoelectric element 21. This electrode surface is divided by grooves 230 formed by etching or the like, so that five electrodes 231 to 235 are formed on the surface of each piezoelectric element 21. These electrodes 231 to 235 are similarly arranged in each piezoelectric element 21. For example, on the back side of the electrode 235 arranged on the front body surface in the front side piezoelectric element 21 in FIG. An electrode 235 is arranged on the body surface on the back side. That is, the respective electrodes of the front side piezoelectric element 21 and the back side piezoelectric element 21 coincide with each other in plan view.
On the other hand, the surface opposite to the surface on which the electrodes 231 to 235 are formed in each of the piezoelectric elements 21 on the front side and the back side is in contact with the reinforcing plate 30. That is, the reinforcing plate 30 also functions as an electrode for each piezoelectric element 21.
An electrode may be formed over the entire surface of the piezoelectric elements 21 and 21 on the side where the reinforcing plate 30 is laminated. In this case, the electrode and the reinforcing plate 30 are electrically connected.

[4-2. Reinforcement plate configuration]
As shown in FIG. 3, the reinforcing plate 30 includes a rectangular reinforcing plate body 31 in which the piezoelectric elements 21 and 21 are laminated on the front surface and the back surface, and both side surfaces on the long side of the reinforcing plate body 31. A pair of support portions 32, 32, a projecting portion 33 which is a contact portion provided continuously on the short side of the reinforcing plate body 31, and a projecting portion for ensuring a vibration balance with respect to the projecting portion 33. 34, which are integrally formed.
The reinforcing plate 30 of the present embodiment is made of rubber metal having Ti as a main component and an elastic modulus of 60 GPa. Rubber metal has a coefficient of thermal expansion (α) of 0 and a hardness of approximately 330 Hv. The hardness of the reinforcing plate 30 is not more than the hardness of the rotor 78 described above (approximately 500 Hv).
Here, the material of the reinforcing plate is not limited to this, and any material having at least Ti as a main component and an elastic modulus of 30 GPa or more and 100 GPa or less may be used. The material used for the reinforcing plate may be, for example, biosoft titanium (BS-Ti) having an elastic modulus of 60 GPa and a thermal expansion coefficient of 5.8 × 10 ⁻⁶ / ° C. The physical properties of rubber metal and BS-Ti are shown below. In addition, physical properties of SUS301 are also shown for comparison.

Thus, rubber metal and BS-Ti have a smaller elastic modulus than conventional SUS and Super Invar, and have the same thermal expansion coefficient as Super Invar. Further, the hardness is smaller than SUS but higher than Super Invar.
The graph of FIG. 13 shows that a piezoelectric vibrator 70A having a projection 33 having a radius r = 0.3 mm and a thickness t = 0.1 mm rotates a rotor 78 having a diameter φ = 4 mm to drive a distance corresponding to 10000 m. It is the experimental result which measured the wear volume of the projection part 33 at the time of making it. The rotor 78 was made of the same SUS as described above and had a hardness of about 500 Hv. In this experiment, the protrusion 33 is pressed against the rotor 78 in the range of 1 gf (9.8 mN) to 50 gf (490 mN). Within such a pressure range, it can be sufficiently used as a watch driving source, and there is no problem in durability.

The length and width of the reinforcing plate body 31 are the same as the length and width of the piezoelectric element 21, respectively. Piezoelectric elements 21 and 21 are joined to the reinforcing plate body 31 with an epoxy adhesive.
Each support portion 32 has a connecting portion 321 provided continuously to the reinforcing plate body 31 and a fixing portion 322 fixed to the ground plate 75 with screws 15 (FIG. 2), and is not laminated with the piezoelectric element 21. The piezoelectric element 21 is supported in a state of protruding from the outer edge portion of the piezoelectric element 21. A fixing hole 322A through which the screw 15 is inserted and a positioning hole 322B are formed in the fixing portion 322.
The connecting portion 321 may be formed narrow so as to apply a spring force to the reinforcing plate body 31. The projection 33 is elastically pressed against the rotor 78 by the spring force, and the rotor 78 is rotationally driven by the vibration excited by the piezoelectric vibrating body 70A. The structure for applying the spring force is not limited to the above, and any structure may be used.

The protrusion 33 is set in a relative position with the rotor 78 so as to come into contact with the outer peripheral surface of the rotor 78 (FIG. 2) with a predetermined force, and between the protrusion 33 and the side surface of the rotor 78. By generating an appropriate frictional force, the vibration of the piezoelectric vibrating body 70 </ b> A is transmitted to the rotor 78.
In the present embodiment, a protrusion 34 as a counter is provided on the side not in contact with the rotor 78 with the same shape and mass as the protrusion 33.

[5. Electrical configuration of piezoelectric vibrator]
FIG. 4 shows the electrical connection of the piezoelectric vibrating body 70A. The piezoelectric vibrator 70A is provided with a lead substrate (not shown), and the electrodes 231 to 235 and the reinforcing plate 30 provided on the piezoelectric element 21 are connected to the drive circuit 28 via the lead substrate. .
The reinforcing plate 30 is connected to the GND as a common electrode for each of the piezoelectric elements 21 and 21, and is connected between the electrodes 231 to 235 of one piezoelectric element 21 and the reinforcing plate 30 by the drive circuit 28, and of the other piezoelectric element 21. An AC voltage is applied between each of the electrodes 231 to 235 and the reinforcing plate 30. The electrodes 231 to 235 are selectively used as will be described later. However, the same electrodes provided in the piezoelectric elements 21, that is, the electrodes 231 and 231, the electrodes 232 and 232, the electrodes 233 and 233, and the electrode 234, respectively. , 234 and electrodes 235 and 235 are simultaneously applied with the same potential.

A single-phase drive voltage is applied to the piezoelectric vibrating body 70A by the drive circuit 28.
Here, the frequency of the drive voltage (drive frequency) is determined in consideration of the resonance point of longitudinal vibration and the resonance point of bending vibration in the piezoelectric vibrating body 70A.
FIG. 5 shows the relationship between the drive frequency and the impedance in the piezoelectric vibrating body 70A. As shown in FIG. 5, there are two resonance points where the impedance is minimum and the amplitude is maximum with respect to the drive frequency. Of these, the lower one is the resonance point of longitudinal vibration and the higher one is bending vibration. Resonance point.
That is, when the piezoelectric vibrating body 70A is driven between the longitudinal resonance frequency fr1 of the longitudinal vibration and the bending resonance frequency fr2 of the bending vibration, the amplitudes of both the longitudinal vibration and the bending vibration are secured, and the piezoelectric actuator 20 is driven with high efficiency. . Note that, by making the longitudinal resonance frequency fr1 and the bending resonance frequency fr2 close to each other, it is possible to set a driving frequency at which both the amplitude of the longitudinal vibration and the amplitude of the bending vibration become larger.

[6. Action of piezoelectric vibrator]
FIG. 6 shows the vibration behavior of the piezoelectric vibrating body 70A. In the present embodiment, by applying a potential to each of the electrodes 231, 233, 235 and the reinforcing plate 30 provided in the piezoelectric element 21, it vibrates in a mixed mode in which longitudinal vibration and bending vibration are combined, and the protrusion 33 Draws an elliptical trajectory R1 and drives the rotor 78 (FIG. 2) in a predetermined direction. At this time, the electrodes 232 and 234 to which no potential is applied are used as vibration detection electrodes.
By such rotation of the rotor 78, the rotor pinion 78A integral with the rotor 78 is also rotated, the date indicator intermediate wheel 71 is rotated along with the rotation of the rotor pinion 78A, and the date indicator 74 of the date display device 7 is driven. The

[7. Method of joining piezoelectric element and reinforcing plate]
First, an adhesive is uniformly applied between the piezoelectric element 21 and the reinforcing plate 30. Next, in order to solidify the adhesive, the heating tank is set to 80 ° C., and the piezoelectric element 21 and the reinforcing plate 30 are heated under pressure for 2 hours. At this time, the piezoelectric element 21 and the reinforcing plate 30 expand according to their respective thermal expansion coefficients. Then, the adhesive is cured in the expanded state, and the piezoelectric element 21 and the reinforcing plate 30 are held firmly.

[Effects of this embodiment]
According to this embodiment, the following effects can be achieved.
(1) Since the elastic modulus of the reinforcing plate 30 is smaller than the elastic modulus of conventional SUS and Super Invar and is 60 GPa, the obstruction of the vibration of the piezoelectric element by the reinforcing plate 30 is alleviated and is generated by the expansion and contraction of the piezoelectric element 21. The amplitude can be expanded by the maximum vibration energy to be obtained. Accordingly, since the driving force for driving the rotor 78 increases, the rotor 78 having a predetermined load can be driven even if the input power is reduced. It is possible to promote downsizing and thinning of various devices on which the vibrator is mounted. In the case of a rotor having a larger load than the conventional one, it can be driven with the same input power as the conventional one, and the driving efficiency can be improved.

(2) Since the thermal expansion coefficient α of the reinforcing plate 30 is 0, PZT showing a thermal expansion coefficient (about 2.3 × 10 ⁻⁶ / ° C.) much lower than that of the metal is bonded to the reinforcing plate 30. However, compared with the conventional SUS (thermal expansion coefficient: 17 × 10 ⁻⁶ / ° C.), it is possible to suppress the occurrence of warpage or peeling due to thermal stress.

(3) Since the thermal expansion coefficient α of the reinforcing plate 30 is 0, 5.8 (× 10 ⁻⁶ / ° C.), the shift amount of the interval Δf between the resonance frequency and the antiresonance frequency (as shown in FIG. 11 described above) (Due to temperature change) is relatively small, and the change in k value is small. Therefore, the variation in vibration with respect to the temperature change is reduced, and the positioning accuracy of the driven body is improved.

(4) Since the hardness of the reinforcing plate 30 is 330 Hv, wear of the protrusions 33 of the reinforcing plate 30 that are in contact with the rotor 78 can be reduced, and the drive is performed even under long-term continuous driving conditions. Efficiency can be maintained and quality can be stabilized.

(5) Since the hardness of the reinforcing plate 30 is equal to or less than the hardness of the rotor 78, even if there is a variation in vibration of the piezoelectric vibrating body 70A, a variation in the position of the projection 33 due to the support method of the piezoelectric vibrating body 70A, etc. Since wear of 78 is suppressed, unnecessary contact does not occur, and the driving performance of the piezoelectric actuator 70 can be maintained.

(6) Since the piezoelectric element 21 and the reinforcing plate 30 are heated at 80 ° C. in order to solidify the adhesive, the internal stress is conventionally applied to the reinforcing plate made of SUS when actually used (for example, at room temperature). The vibration characteristics of the piezoelectric element 21 are deteriorated.
The graph of FIG. 16 shows the relationship between the temperature and the dimensional change of the piezoelectric element (PZT), BS-Ti, and SUS.
As shown in FIG. 16, the dimensional difference between the conventional SUS reinforcing plate and the piezoelectric element at 80 ° C. is the size indicated by La in the graph. On the other hand, the BS-Ti reinforcing plate has a thermal expansion coefficient lower than that of SUS, so that the dimensional difference becomes the size indicated by Lb, and the influence of vibration characteristics on the piezoelectric element can be reduced. Further, when the drying temperature is set to 150 ° C., the drying time is about 10 minutes, and the productivity can be improved. Even in this case, the dimensional difference is the size indicated by Lc, and is smaller than the dimensional difference La of the SUS reinforcing plate, so that the influence on the vibration characteristics on the PZT can be reduced.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, a configuration is shown in which durability can be improved while maintaining a predetermined elastic modulus by applying heat treatment to the reinforcing member.
In the present embodiment, only the configuration in which heat treatment is performed on the reinforcing plate of the piezoelectric vibrator is different from the first embodiment, and other configurations are configured in the same manner as in the first embodiment.
That is, the reinforcing plate made of rubber metal or BS-Ti is formed by heat treatment at 400 ° C. for 10 hours in an N ₂ atmosphere. The physical property values before and after the heat treatment are shown below.

According to this embodiment, in addition to the effects substantially the same as the effects (1) to (6), the following effects can be achieved.
(7) By heat-treating the reinforcing plate, the hardness of the reinforcing plate increases from 330 Hv before processing to 550 Hv, or from 340 Hv to 450 Hv, and the wear of the protrusion 33 can be further reduced. Further, although the elastic modulus is somewhat increased by the heat treatment, as described in the graph of FIG. 7, since the elastic modulus is 100 GPa or less, the amplitude of the piezoelectric vibrating body 70A is maintained.

[Modification of the present invention]
It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
The coefficient of thermal expansion of the material of the reinforcing plate described in the above embodiments is not limited, and the coefficient of thermal expansion of the material of the reinforcing plate is 0 × 10 ⁻⁶ / ° C. or more and 10 × 10 ⁻⁶ / If it is below ℃, the effect of the present invention will be obtained.
Further, the hardness of the material of the reinforcing plate described in the above embodiments is not limited, and the effect of the present invention can be obtained if the hardness of the material of the reinforcing plate is 200 Hv or more. The upper limit of the hardness is preferably not more than the hardness of the rotor. For example, if the rotor is made of SUS301 (hardness 500 Hv), the hardness of the reinforcing plate may be 500 Hv or less.
Further, the heat treatment conditions for the reinforcing plate described in the second embodiment are not limited, and the heat treatment conditions for the reinforcing plate are at least 200 ° C. or higher and 450 ° C. or lower. An effect is obtained.

In each of the embodiments described above, the piezoelectric vibrating body having a rectangular shape in plan view is shown. However, the shape of the piezoelectric vibrating body is not limited to this, and a longitudinal vibration or a bending vibration such as a trapezoid, a parallelogram, and a rhombus is excited. Various shapes can be employed.
Further, in the piezoelectric vibrating body in each of the embodiments, the piezoelectric elements are laminated one by one on the front and back of the reinforcing plate, but not limited to this, a plurality of piezoelectric elements are laminated on each of the front and back of the reinforcing plate, Piezoelectric elements may be laminated only on one side of the reinforcing plate.
The electrode arrangement for driving the piezoelectric element and the shape thereof are not limited to those described above, and can be appropriately selected depending on the situation. For example, in the first embodiment and the like, the electrode formed on the piezoelectric element is divided into five parts. However, the present invention is not limited to this, and a rectangular piezoelectric element may be formed with four electrodes vertically and horizontally. The number of electrodes formed on the piezoelectric element is arbitrary, and may be three or less, four, five, six or more. When piezoelectric elements are stacked on the front and back surfaces of the reinforcing plate, the number and shape of electrodes formed on the front-side piezoelectric element are the same as the number and shape of electrodes formed on the back-side piezoelectric element. Or different.

  In each of the above embodiments, the driven body is driven by transmitting the vibration of the piezoelectric vibrating body to the rotor. However, the present invention is not limited to this. For example, the vibration of the piezoelectric vibrating body is transmitted in a straight line. The drive body to drive may be sufficient. For example, the linearly driven drive body may be provided on a slider or guided by a plurality of rollers.

In each of the above embodiments, a wristwatch is illustrated as an application example of a piezoelectric vibrator, but the present invention is not limited to this, and the present invention can also be applied to a pocket watch, a table clock, a wall clock, and the like. In these various timepieces, for example, it can be used as a mechanism for driving a mechanism doll or the like.
In addition to the watch, the piezoelectric vibrator of the present invention can be used as appropriate for a camera zoom and autofocus mechanism, a film winding mechanism, a printer paper feed mechanism, and a mechanism for driving toys such as vehicles and dolls. . The piezoelectric vibrating body of the present invention can be widely used in various electronic devices such as a timepiece, a camera, a printer, a toy, and a portable information terminal and a telephone.

Although the best configuration for carrying out the present invention has been specifically described above, the present invention is not limited to this. That is, the invention has been illustrated and described primarily with respect to particular embodiments, but may be configured for the above-described embodiments without departing from the scope and spirit of the invention. Various modifications and improvements can be made by those skilled in the art in terms of materials, quantity, and other detailed configurations.
The description limiting the shape, material, etc. disclosed above is an example for easy understanding of the present invention, and does not limit the present invention. The description by the name of the member which removes a part or all of the limitation is included in the present invention.

1 is an external view of a wristwatch according to a first embodiment of the present invention. The top view of the date display apparatus in the said embodiment. The perspective view of the piezoelectric vibrating body in the said embodiment. The figure which shows the electrical connection of the piezoelectric vibrating body in the said embodiment. The graph which shows the relationship between the drive frequency and impedance in the piezoelectric vibrating body in the said embodiment. The figure which shows operation | movement of the piezoelectric vibrating body in the said embodiment. The graph which shows the relationship between the elastic modulus of the said piezoelectric vibrating body of this invention, and the long-axis length of an elliptical locus. The graph which shows the relationship between the drive frequency of the said piezoelectric vibrating body, and the major axis length of an elliptical locus. The graph which shows the temperature characteristic of the impedance of the said piezoelectric vibrating body. The graph which shows the temperature characteristic of the impedance of the conventional piezoelectric vibrating body. The graph which shows the relationship between the thermal expansion coefficient of a piezoelectric vibrating body, and the shift amount of (DELTA) f. The figure which shows the state of abrasion of the contact part of the said piezoelectric vibrating body. The graph which shows the relationship between the hardness of the reinforcement board of the said piezoelectric vibrating body, and a wear volume. The figure which shows the state of abrasion of the contact part of the conventional to-be-vibrated body. The graph which shows the hardness change by the heat processing of the said piezoelectric vibrating body. The graph which shows the relationship between the temperature of the said piezoelectric vibrating body, and a dimensional change.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Piezoelectric element, 30 ... Reinforcing plate, 33 ... Protruding part (contact part), 70 ... Piezoelectric actuator, 70A ... Piezoelectric vibrator, 78 ... Rotor (driven body).

Claims (10)

A piezoelectric vibrator comprising a piezoelectric element and a reinforcing plate that is laminated with the piezoelectric element to reinforce the piezoelectric element,
The reinforcing plate is formed mainly of titanium (Ti),
The elastic modulus of the reinforcing plate is 30 GPa or more and 100 GPa or less. The piezoelectric vibrating body according to claim 1,
The piezoelectric vibration member, wherein the reinforcing plate has a thermal expansion coefficient of 0 × 10 ⁻⁶ / ° C. or more and 10 × 10 ⁻⁶ / ° C. or less. In the piezoelectric vibrating body according to claim 1 or 2,
The piezoelectric vibrating body, wherein the reinforcing plate has a hardness of 200 Hv or more. The piezoelectric vibrating body according to claim 3,
A piezoelectric vibrator having a hardness of the reinforcing plate equal to or less than a hardness of a driven body driven by vibration of the piezoelectric vibrator. In the piezoelectric vibrating body according to any one of claims 1 to 4,
The reinforcing plate is formed by containing zirconium (Zr) and niobium (Nb). The piezoelectric vibrating body according to claim 5,
The reinforcing plate is a titanium alloy containing 58 to 59% by mass of Ti, 36 to 37% by mass of Nb, 2 to 3% by mass of Ta, 2 to 3% by mass of Zr, and 0.1 to 1% by mass of O. Or a piezoelectric vibrator formed of a titanium alloy containing 64 to 66 at% Ti, 16 to 18 at% Zr, and 17 to 19 at% Nb. In the piezoelectric vibrating body according to claim 5 or 6,
The reinforcing plate is formed by heat treatment at 200 ° C. or higher and 450 ° C. or lower. The piezoelectric vibrating body according to any one of claims 1 to 7,
And a driven body that is driven when vibration is transmitted from the piezoelectric vibrating body.   An electronic apparatus comprising the piezoelectric actuator according to claim 8. The electronic device according to claim 9 is a timepiece including a timekeeping portion and a timekeeping information display portion that displays information timed by the timekeeping portion, and the timekeeping information display portion is driven by the driven body. Electronic equipment characterized by

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