JP6140507B2 - Ultrasonic motor - Google Patents

Description

  The present invention relates to a traveling wave type ultrasonic motor. Specifically, the present invention relates to a technology for improving a piezoelectric body constituting a stator of a traveling wave type ultrasonic motor.

  As is well known, a traveling wave ultrasonic motor (hereinafter referred to as an ultrasonic motor) generates a traveling wave in a circumferential direction on a stator having an annular piezoelectric body and an elastic body, and generates a frictional force. The rotor is rotated by transmitting to the rotor. Compared with a motor using an electromagnet, it has characteristics such as low speed, high torque, high speed response, retention of torque during stoppage, quietness, and no magnetic noise.

  FIG. 1 is a diagram showing a basic configuration of an ultrasonic motor. In this drawing, the polarization polarity of an annular piezoelectric body 1 constituting the stator and the arrangement of electrodes are shown by a plan view. In the following, the surface of the piezoelectric body shown in this figure is a front surface, and the front surface side is an upper side. The elastic body constituting the stator is attached to the back side of the piezoelectric body 1.

  The piezoelectric body 1 is made of piezoelectric ceramics integrally formed in an annular shape, and here, an example in which the piezoelectric body 1 is divided into two regions (A-phase region 10a and B-phase region 10b) in which the central angle of the ring is θ1 is shown. . Individual electrodes (hereinafter referred to as drive electrodes) are formed on the upper surface of each phase region (10a, 10b), and a common ground electrode is formed on the back surface of the piezoelectric body 1 for the A phase and the B phase. ing. When the elastic body is conductive, the elastic body itself becomes a ground electrode.

  The A phase and B phase regions (10a, 10b) are further divided into a plurality of regions (hereinafter, polarization regions: 11a, 12a, 11b, 12b), and each polarization region (11a, 12a, 11b, 12b) is piezoelectric. The body 1 is polarized in the thickness direction (the normal direction of the paper). And in each area | region (10a, 10b) of A phase and B phase, the direction of the polarization polarity of an adjacent polarization area | region (11a-12a, 11b-12b) is a reverse direction. In the following, the polarization polarity from the front side to the back side of the drawing is represented by “+”, and the opposite direction is represented by “−”. Further, for example, the polarization polarity belongs to the A phase region 10a and the polarization polarity is +. This polarization region 11a is designated as “A +”. That is, the piezoelectric body 1 has four types of polarization regions “A +”, “A−”, “B +”, and “B−”.

  Here, with respect to the piezoelectric body 1 divided into four types of polarization regions (11a, 12a, 11b, 12b), driving electrodes formed in any one of the A-phase region 10a and the B-phase region 10b It is assumed that a drive signal composed of a high frequency voltage is applied between the ground electrodes. In the A-phase and B-phase regions (10a, 10b), the polarization polarities of the adjacent polarization regions (11a-12a, 11b-12b) are opposite, so each polarization region (11a, 12a, 11b, 12b) This corresponds to 1/2 wavelength (1 / 2λ) of the drive signal. Each polarization region (11a, 12a, 11b, 12b) undergoes bending vibration in the circumferential direction when a drive signal is applied, and the frequency of the drive signal includes the piezoelectric body 1 and is inherent to the stator. If it is equal to the frequency, the stator resonates and a standing wave is generated.

  In order to generate a traveling wave in the circumferential direction using this standing wave, as is well known, polarization regions (11a-12a, 11b-) corresponding to a pair of + pole and −pole adjacent on the circumference are known. 12b), the A-phase region 10a and the B-phase region 10b are shifted by 1 / 4λ using the fact that the arc corresponding to 12b) corresponds to one wavelength (λ). A high frequency voltage having a temporal phase difference of 90 ° is applied to each region of the phase region 10b. As a result, standing waves generated in both the A-phase region 10a and the B-phase region 10b cause mutual interference to generate traveling waves.

  Since the A-phase region 10a and the B-phase region 10b are relatively shifted by 1 / 4λ, generally, the polarization regions (11a, 12a, 11b, 12b) are all disposed in the annular piezoelectric body 1. It is arranged so that there is no gap across the area. Specifically, as shown in FIG. 1, gap portions (13, 14) where drive electrodes are not formed are provided at two locations on the circumference. One gap portion 13 is a region corresponding to a central angle θ2 corresponding to ¼λ, and the other gap 14 corresponds to a central angle θ3 (= 3 × θ2) corresponding to 3 / 4λ. In many ultrasonic motors, a grounding electrode is formed in the gap (13, 14) and connected to the grounding electrode formed on the back surface of the piezoelectric body 1. Thereby, both the wiring from the driving electrode and the wiring from the grounding electrode formed corresponding to the polarization regions (11a, 12a, 11b, 12b) can be drawn from the front surface. Alternatively, in order to detect the vibration state of the piezoelectric body 1 by the driving signal, an electrode called a “feedback electrode” having the same shape as the polarization region (11a, 12a, 11b, 12b) is provided in the center of the gap 14 There is also. In this case, the ultrasonic motor is configured to control the driving signal based on the detection result of the voltage signal generated between the feedback electrode and the ground electrode.

  The basic structure and principle of the ultrasonic motor are described in Non-Patent Documents 1 and 2 below. Further, in Patent Document 1 below, the gap portion 14 corresponding to 3 / 4λ in the piezoelectric body 1 shown in FIG. 1 is divided into two regions corresponding to 3 / 8λ, and two regions corresponding to 3 / 8λ are provided. A polarization region of the phase and the B phase is added to oscillate a wider region of the piezoelectric body. Patent Document 2 describes an ultrasonic motor in which an A-phase region and a B-phase region are each divided into two, and these regions are alternately arranged on the circumference at equiangular intervals through a gap.

Japanese Patent No. 2694142 JP 2000-333477 A

Shinwa Shoji Co., Ltd., “Ultrasonic Motor Catalog”, [online], [Search February 20, 2013], Internet <URL: http://www.shinwa-syoji.com/others/img/motor. pdf> The Ceramic Society of Japan, “Ceramics Archives“ Ultrasonic Motor ””, [online], [Search February 20, 2013], Internet <URL: http://www.ceramic.or.jp/museum/ contents / pdf / 2007_6_02.pdf>

  As is well known, there are “amplitude” and “phase” as indices for evaluating the performance of an ultrasonic motor. The amplitude is an index for evaluating the performance of torque, and the phase is an index for evaluating the resonance performance of the ultrasonic motor. Since the ultrasonic motor is driven using the resonance phenomenon, there is a principle problem that when the motor diameter is reduced, the amplitude is reduced and the torque performance is deteriorated. That is, it is difficult to achieve downsizing while maintaining the torque characteristics. On the other hand, the phase depends on the piezoelectric constant and mechanical quality factor of the piezoelectric material constituting the piezoelectric body.

By the way, PbTiO ₃ —PbZrO ₃ (hereinafter referred to as “PZT”) ceramics are well known as a piezoelectric material forming an annular piezoelectric body that is a main part of an ultrasonic motor. PZT is excellent in piezoelectric characteristics such as an electromechanical coupling coefficient and a piezoelectric constant, and this PZT is widely used not only for ultrasonic motors but also for piezoelectric elements such as sensors and filters. On the other hand, there is a demand for “lead-free” industrial products in consideration of recent environmental problems. Since PZT contains lead, it is necessary to replace PZT containing lead (Pb) with another piezoelectric material not containing lead in the future.

As the piezoelectric material (lead-free piezoelectric material) containing no lead, for example, the general formula _{K x Na (1-x)} NbO 3 compounds and barium titanate expressed by _(Ba n TiO ₃₎ based piezoelectric material well known. However, at present, there is no lead-free piezoelectric material having piezoelectric characteristics (relative permittivity, piezoelectric constant, mechanical quality factor, etc.) that can replace PZT. In particular, the piezoelectric constant and mechanical quality factor are insufficient, and the phase tends to be low. Therefore, sufficient resonance characteristics cannot be obtained with the conventional configuration and structure shown in FIG. Of course, whatever the material constituting the piezoelectric body is, it is very significant to improve the resonance performance of the ultrasonic motor.
Accordingly, an object of the present invention is to provide an ultrasonic motor that is excellent in torque performance and resonance performance, is small and can cope with environmental problems.

The present invention for achieving the above object is an ultrasonic motor comprising a piezoelectric body in which a + polarization region and a -polarization region having opposite polarities are arranged so as to form a ring,
Either the A phase electrode or the B phase electrode to which the high frequency signals of the A phase and the B phase are shifted from each other by 90 ° is formed on the surfaces of the + polarization region and the − polarization region, and the + and − The polarization region is divided into any of four types of polarization regions of A phase + region, A phase-region, B phase + region, and B phase-region,
The A phase + region and the A phase-region have a polarization region in which the center angle of the ring corresponds to an angle corresponding to ½ wavelength, and n in a ring shape so that the polarization polarity is alternately reversed. (Where n is a natural number equal to or greater than 2), from the A-phase polarization pattern arranged for the wavelength, a 1/2 wavelength polarization region constituting the pattern , and a 1/4 wavelength that divides the polarization region into two equal parts A region for a total of n / 2 wavelengths is selected and arranged from the region of minutes,
The B phase + region and the B phase − region are obtained by rotating the A phase polarization pattern at an angle corresponding to a quarter wavelength from the B phase polarization pattern, and the A phase + region and the A phase − region. Is selected and arranged from the polarization region in a position that does not overlap with both,
Of the four types of polarization regions, at least one type of polarization region is disposed at a point-symmetrical position with respect to the center of the ring at an angle corresponding to a half wavelength .
The ultrasonic motor is characterized by this.

And one specific polarization region belonging to one phase of the A phase or the B phase is ½ at four positions at equal angular intervals of 90 ° on the ring. Arranged at an angle of wavelength,
The + polarization region and the -polarization region belonging to the other phase of the A phase or the B phase are at an angle of ¼ wavelength and 90 ° on the ring in a region where the specific polarization region is not arranged. Are arranged at equiangular intervals,
It can also be set as the ultrasonic motor characterized by this.

Alternatively, the + polarization region and the -polarization region belonging to one phase of the A phase or the B phase are 2 in positions that are point-symmetric with respect to the center of the ring at an angle corresponding to ½ wavelength. Placed in place,
One polarization region of the + polarization region and the-polarization region belonging to the other phase of the A phase or the B phase is disposed at two rotationally symmetric positions at an angle corresponding to ½ wavelength.
It can also be set as the ultrasonic motor characterized by this.
Furthermore, the ultrasonic motor may be characterized in that a + polarization region and a -polarization region belonging to one of the A phase and the B phase are adjacent to each other.
In addition, an ultrasonic motor characterized in that the angle corresponding to the 1/4 wavelength is 22.5 ° can be provided.

  According to the present invention, an ultrasonic motor excellent in torque characteristics and resonance characteristics can be provided. Thereby, the miniaturization of the ultrasonic motor can be achieved. It can also be expected to provide an environmentally friendly ultrasonic motor that enables the use of lead-free piezoelectric materials.

It is a figure which shows an example of arrangement | positioning of the polarization area | region of the piezoelectric material which comprises the stator of the conventional ultrasonic motor. It is a figure for demonstrating arrangement | positioning of the polarization area | region of the piezoelectric material in an ultrasonic motor. It is a figure which shows arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on the comparative example of this invention. It is a figure for demonstrating arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on the Example of this invention. It is a figure which shows arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on 1st Example of this invention. It is a figure which shows the phase characteristic and amplitude characteristic of the ultrasonic motor which concern on a 1st Example. It is a figure which shows the complex impedance characteristic of the piezoelectric material in the ultrasonic motor which concerns on a 1st Example. It is a figure which shows arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on 2nd Example of this invention. It is a figure which shows arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on 3rd Example of this invention. It is a figure which shows arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on the 4th Example of this invention. It is a figure which shows the phase characteristic and amplitude characteristic of the ultrasonic motor which concern on a 2nd-4th Example. It is a figure for demonstrating other arrangement | positioning of the polarization area | region of the piezoelectric material in an ultrasonic motor. It is a figure which shows arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on the 2nd comparative example of this invention. It is a figure which shows arrangement | positioning of the polarization area | region of the piezoelectric material of the ultrasonic motor which concerns on the 5th Example of this invention. It is a figure which shows the phase characteristic and amplitude characteristic of the ultrasonic motor which concern on a 5th Example.

=== Technical thought of the present invention ===
As described above, the traveling principle of the traveling wave ultrasonic motor that is the subject of the present invention is such that the annular piezoelectric bodies driven by the A-phase and B-phase drive signals are shifted from each other by ¼λ. By doing so, two standing waves whose phases are shifted are caused to interfere with each other to generate a traveling wave. FIG. 2 shows the concept of the polarization polarity and the arrangement of the driving electrodes in the piezoelectric body 1 of the ultrasonic motor. FIG. 2A shows an arrangement state (hereinafter referred to as A phase polarization) of the polarization region (11a, 12a) of the virtual piezoelectric body 1a driven by a drive signal of one of the A phase and the B phase (here, A phase). (B) is an arrangement state of the polarization regions (11b, 12b) of the virtual piezoelectric body 1b driven by the drive signal of the other phase (B phase) (hereinafter referred to as B phase polarization). Also referred to as pattern 1b). In the figure, the A + region 11a, the A− region 12a, the B + region 11b, and the B− region 12b, which are the above four types of polarization regions, are indicated by different hatchings.

  In the A-phase and B-phase polarization patterns (1a, 1b) shown in FIGS. 2A and 2B, the polarization regions (11a, 12a, 11b, 12b) are arranged at equiangular (= α) intervals. ing. Here, an example is shown in which the central angle corresponding to 1 / 2λ is set to 45 °. Moreover, the polarization polarity is reversed in adjacent polarization regions (11a-12a, 11b-12b).

  Next, a high frequency signal having a phase difference of 90 ° is applied to the piezoelectric body 1a having the A phase polarization pattern and the piezoelectric body 1b having the B phase polarization pattern, thereby generating standing waves in the respective piezoelectric bodies (1a, 1b). In addition, a traveling wave is generated by synthesizing the standing wave. For this purpose, as shown in FIGS. 2A and 2B, the polarization pattern (1a, 1b) of one phase is reduced to ¼λ with respect to the polarization pattern (1b, 1a) of the other phase. What is necessary is just to shift so that it may be in the state rotated by the corresponding 22.5 degrees. In an actual ultrasonic motor, since the piezoelectric body constituting the stator is a single ring-shaped piezoelectric ceramic integrally formed, an appropriate polarization region (11a, 12a) is selected from the A-phase polarization pattern 1a and the B-phase polarization pattern 1b. , 11b, 12b) are selected and arranged on a ring in one piezoelectric body. In the conventional ultrasonic motor, the arrangement of the polarization regions (11a, 12a) in the A-phase polarization pattern 1a is adopted for one semicircle that bisects the circle, and the B-phase polarization is adopted for the other semicircle. The arrangement of the polarization regions (11b, 12b) in the pattern 1b is adopted, and the adopted polarization regions (11a, 12a, 11b, 12b) are arranged in an annular shape to form one piezoelectric body.

  FIG. 3 shows the polarization regions (11a, 12a, 11a, 12a, and 12b) of the piezoelectric body 100 in the conventional ultrasonic motor based on the A-phase and B-phase polarization patterns (1a, 1b) shown in FIGS. It is a figure for demonstrating arrangement | positioning of 11b and 12b). In the A-phase polarization pattern 1a shown in FIG. 2A, an angle corresponding to 1 / 8λ (here 11) with respect to a line segment 20 obtained by extending one of the boundary lines of adjacent polarization regions (11a-12a). When the circle is bisected by the line segment 21 shifted by .25 °), the polarization region (11a, 12a) of the A-phase polarization pattern 1a is adopted for one semicircle 30a, and the other semicircle 30b is adopted. The polarization region (11b, 12b) of the B-phase polarization pattern 1b shown in FIG. 2 (B) is employed.

  A part of the polarization region (11a, 12a, 11b, 12b) belonging to the A-phase and B-phase polarization patterns (1a, 1b) is divided by a circular bisector 21 and originally corresponds to 1 / 2λ. Polarized regions (11a, 12a, 11b, 12b) arranged at an angle cannot be arranged as they are. In the example shown here, for the polarization region 114 in which the polarization patterns (1a, 1b) of the A phase and the B phase are both separated by the bisector 21, the polarization region 114 is divided into two parts and the polarization of each phase is divided. It is assigned to the area (12a (114a), 12b (114b)). Further, a portion where only the polarization region (reference numeral 15b in FIG. 2B) of the B-phase polarization pattern 1b is divided is formed as a gap 113 without forming a driving electrode in the divided B-phase polarization region 15b. . In any case, in the conventional piezoelectric body 100, the A-phase region 10a in which only the A-phase polarization region (11a, 12a) is arranged is formed in one region 30a obtained by dividing the ring into two, and the other semicircle is formed. A B-phase region 10b in which only the B-phase polarization regions (11b, 12b) are arranged in the region 30b is formed. The vibration corresponding to the A phase and the B phase is generated in each phase region (10a, 10b) formed in one region (30a, 30b) obtained by dividing the ring into two parts. A standing wave is generated over the entire circumference of the ring by exciting the other phase region (10b, 10a) and the region of the gap 113 by the vibration generated in the region (10a, 10b). become. That is, the vibration generated in the half part of the ring is transmitted to the other half-circle region at a distant position.

  However, as described above, when an annular piezoelectric body made of a piezoelectric material with low phase characteristics is used, such as when the piezoelectric body is composed of a lead-free piezoelectric material, etc., it is generated in a half region of the ring. It becomes difficult to resonate the entire piezoelectric body by vibration. Further, since vibration is generated only in a half region of the ring, the amplitude of the vibration is attenuated in a region where the vibration does not occur. That is, there is a limit to the improvement in torque characteristics. This becomes more prominent as the size of the piezoelectric body is reduced.

  Therefore, the present inventor separated the polarization region (11a, 12a) corresponding to the A phase and the polarization region (11b, 12b) corresponding to the B phase for each half region (30a, 30b) of the annular piezoelectric body. Rather than disposing them, it is not necessary to transmit the vibrations generated in the individual polarization regions (11a, 12a, 11b, 12b) to far regions, if the dispersive arrangements are made over the entire circumference of the ring. We thought that attenuation could be reduced. Further, it was considered that a standing wave can be efficiently generated over the entire circumference of the ring even if the phase performance of the piezoelectric material itself is low. The present invention has been made as a result of intensive studies based on such considerations.

=== Embodiment of the Invention ===
The ultrasonic motor according to the embodiment of the present invention is characterized by the polarization polarity and the electrode arrangement in the annular piezoelectric body, and has excellent torque characteristics and resonance characteristics. Schematically, as shown in FIGS. 2A and 2B, the polarization regions (11a and 12a, 11b and 12b) are divided at equal angular intervals and the polarization polarity is alternately reversed. When the virtual A-phase polarization pattern 1a arranged in an annular shape and the B-phase polarization pattern 1b rotated relative to the A-phase polarization pattern 1a by 1 / 4λ are superimposed, For the portion where the polarization region (11a, 12b) and the B-phase polarization region (11b, 2b) overlap, one of the polarization regions (11a, 12a, 11b, 12b) is selected and disposed on the actual piezoelectric body. Is.

  Specifically, when the A-phase polarization pattern and the B-phase polarization pattern are superimposed, one of the polarization regions can be employed for each angle corresponding to 1 / 4λ. FIG. 4 shows polarization regions that can be adopted for each angle of 1 / 4λ when the A and B phase polarization patterns shown in FIGS. 2 (A) and 2 (B) are superimposed. As shown in this figure, one of the polarization regions belonging to the A phase and the B phase can be selected at an angle of 22.5 ° corresponding to 1 / 4λ. The technical idea of the present invention is to disperse the A-phase and B-phase polarization regions (11a, 12a, 11b, 12b) over the entire circumference of the annular piezoelectric body. That is, by eliminating the gaps (113, 114) provided in the piezoelectric bodies (1, 100) shown in FIGS. 1 and 3, vibrations are generated in all regions of the ring. As a result, it is not necessary to excite the gaps (113, 114) by vibrations in other regions, and the vibrations of the piezoelectric body can be used efficiently. In addition, the same kind of polarization regions (11a, 12a, 11b, 12b) are arranged in a rotationally symmetric position with respect to the center of the annular piezoelectric body, that is, on a specific shape disposed on the annular piezoelectric body. By rotating the polarization region of a kind by 360 ° / m around the center of the ring (where m is a natural number), the ring is divided into two equal parts by placing it at a position that overlaps the same kind of polarization region. When divided into two regions, the same type of polarization region (11a, 12a, 11b, 12b) is present in both regions, and furthermore, synchronous vibrations are generated at rotationally symmetric positions at equiangular intervals. Can be made. Thereby, a stable standing wave can be generated.

  Therefore, in the ultrasonic motor according to the embodiment of the present invention, the polarization region corresponding to 1 / 4λ or 1 / 2λ selected from the A-phase polarization pattern 1a and the B-phase polarization pattern 1b shown in FIG. And at least one polarization region (11a, 12a, 11b, 12b) of the four types of polarization regions (11a, 12a, 11b, 12b) described above is rotationally symmetric with respect to the center O of the ring It is characterized by having a piezoelectric body arranged at the position. In order to arrange the same type of polarization regions (11a, 12a, 11b, 12b) at rotationally symmetric positions, the A-phase polarization pattern 1a and the B-phase polarization pattern 1b have polarization regions. It is assumed that there are 2λ or more.

  In the following, as shown in FIG. 2, among the arrangement of the polarization regions based on the polarization patterns (1a, 1b) of the A phase and the B phase where the angle corresponding to 1 / 2λ is 45 ° (n = 4), Some specific examples of the arrangement of the polarization regions based on the technical idea of the present invention will be given as examples of the present invention.

== first embodiment ===
<Arrangement of polarization region in piezoelectric body>
As a first embodiment of the present invention, first, a piezoelectric body in which all of the four types of polarization regions (11a, 12a, 11b, 12b) are uniformly distributed is cited. FIG. 5 shows the arrangement state of the polarization regions (11a, 12a, 11b, 12b) of the piezoelectric body 101 according to the first embodiment. As shown in this figure, the polarization regions (11a, 12a, 11b, 12b) are arranged at intervals of 22.5 ° corresponding to 1 / 4λ along the entire circumference of the annular piezoelectric body 101. . Specifically, for the A-phase polarization pattern shown in FIG. 2A, the polarization regions (11b, 12a) are selected for each angle of 22.5 ° corresponding to 1 / 4λ, and the B-phase polarization pattern is selected. For 1b, the polarization regions (11b, 12b) located at positions that do not overlap with the polarization regions (11a, 12a) cut out from the A-phase polarization pattern 1a are selected. Then, polarization regions (11 a, 12 a, 11 b, 12 b) selected from these phase patterns (1 a, 1 b) are arranged on one piezoelectric body 101. That is, each polarization region (11a, 12a, 11b, 12b) is arranged in an annular shape at equal intervals at an angle of 1 / 4λ (22.5 °), and adjacent polarization regions (11a-11b, 11a- 12b, 12a-11b, 12a-12b), the A-phase and B-phase driving electrodes are alternately formed. As a result, all types of polarization regions (11a, 12a, 11b, 12b) are dispersed and arranged at four positions every 90 °, and any one quarter-λ polarization region (11a, 12a, 11b, 12b). When focusing on, the same polarization region (11a, 12a, 11b, 12b) is always arranged at a position that is rotationally symmetric with respect to the center O of the ring.

<Performance evaluation>
In order to evaluate the performance of the ultrasonic motor according to the first embodiment, the piezoelectric body 100 shown in FIG. 4 (hereinafter also referred to as a comparative example) and the piezoelectric device according to the first embodiment shown in FIG. A high frequency signal was applied to the body (hereinafter also referred to as the first embodiment) 101, and the characteristics were compared. 6A and 6B are diagrams showing the characteristics of the first embodiment 101 and the comparative example 100. FIG. 6A shows the phase with respect to the frequency of the drive signal, and FIG. 6B shows the frequency of the drive signal and the piezoelectric body. The relationship with the amplitude in the thickness direction of (100, 101) is shown. In the phase characteristic curve 200 of the comparative example 100 and the phase characteristic curve 201 of the first example 101 shown in FIG. 6A, the phase in the vicinity of the resonance frequency (about 104.4 KHz) is seen. The phase is improved by about 30 ° with respect to Comparative Example 100. Further, from the amplitude characteristic curve 210 of the comparative example and the phase characteristic curve 211 of the first example 101 shown in (B), it can be confirmed that the amplitude is improved by about 40% in the first example 101.

  Furthermore, the complex impedance characteristics of the first example 101 and the comparative example 100 were also evaluated. As is well known, the complex impedance of the piezoelectric body corresponds to the complex impedance when the piezoelectric element is expressed by an equivalent circuit. Therefore, when a drive signal having a frequency lower than the resonance frequency is applied to the piezoelectric body, the coil component in the complex impedance becomes large as in the equivalent circuit. That is, the phase difference between the applied voltage and the generated current is 0 ° or less, and the phase difference is −90 ° at a frequency that is not affected by resonance. Then, as the frequency approaches the resonance frequency, the phase difference increases, and in an ideal piezoelectric body, the phase difference becomes 0 ° when driven at the resonance frequency.

  On the other hand, when the drive frequency is made higher than the resonance frequency, the phase difference increases toward 90 ° due to the influence of the capacitor component in the equivalent circuit. Note that when the drive frequency approaches the anti-resonance frequency from the resonance frequency, the phase difference decreases again toward -90 °, so that the phase difference has a certain maximum value as shown in FIG. In an ultrasonic motor, this maximum value is a phase characteristic and is one of the indices.

  Here, FIG. 7 shows the impedance characteristics of the first example 101 and the comparative example 100. As shown in FIG. 7, in the complex impedance characteristic curve 220 of the comparative example 101, a peak 222 is seen in the vicinity of 65 KHz, which is different from the resonance frequency. On the other hand, the complex impedance characteristic curve 221 of the first embodiment 101 has lost its peak around 65 kHz. Further, in the first embodiment 101, a sharp peak 223 appears in the vicinity of the resonance frequency, which matches the evaluation result of the phase characteristic shown in FIG.

=== Second to fifth embodiments ===
The piezoelectric body 101 according to the first embodiment is arranged in an annular shape in a state where all of the four types of polarization regions (11a, 12a, 11b, 12b) are uniformly dispersed. there were. As shown in FIGS. 6 and 7, the ultrasonic motor using the piezoelectric body 101 according to the first embodiment is extremely different from the conventional ultrasonic motor using the piezoelectric body 100 according to the comparative example. It will have excellent properties. Therefore, if the piezoelectric body 101 of the first embodiment is configured using a lead-free piezoelectric material, the ultrasonic wave is friendly to the environment and has performance comparable to a conventional ultrasonic motor using PZT. A motor may be obtained.

  However, the technical idea of the present invention is that when an annular piezoelectric body is equally divided into two regions by dividing it into two regions, the same kind of polarization region exists in both regions, It is to generate a synchronized vibration in both divided areas.

  By the way, in the conventional technical idea, since the polarization region is assumed to be designed with a region corresponding to 1 / 2λ as a basic unit, there are regions where the A phase and the B phase overlap (for example, reference numerals 113 and 114 in FIG. 3). In other words, the polarization region of the A phase or the B phase cannot be dispersed and arranged on the annular piezoelectric body. On the other hand, in the piezoelectric body 101 according to the first embodiment based on the technical idea of the present invention, a polarization region corresponding to 1 / 4λ, which is a half region of 1 / 2λ, is adopted as a basic unit for partitioning. Nevertheless, the characteristics are improved as compared with the comparative example 100 based on the conventional technical idea. In other words, it becomes possible to disperse and arrange the A phase and the B phase by using 1 / 4λ as a basic unit, and the effect of the dispersive arrangement can reduce the loss by using 1 / 4λ as a basic unit of partitioning. We were able to confirm that it was over. Therefore, in the following, specific examples for verifying the effectiveness of the technical idea of the present invention in which the polarization patterns of the A phase and the B phase are dispersedly arranged on an annular piezoelectric body will be described as second to fifth embodiments. I will give you.

<Second embodiment>
FIG. 8 shows the arrangement of the polarization regions (11a, 12a, 11b, 12b) of the piezoelectric body 102 according to the second embodiment of the present invention. In the piezoelectric body 102 in the second embodiment, the A-regions 12a corresponding to ½λ are arranged at two positions that are rotationally symmetric with respect to the center O of the ring. That is, one A-region 12a corresponds to an angle of 45 °, and two A-regions 12a each having a region corresponding to an angle of 45 ° are arranged at positions that are rotationally symmetric with respect to the center O of the ring. Yes.

<Third embodiment>
FIG. 9 is a diagram showing the polarization regions (11a, 11b, 12b) of the piezoelectric body 103 according to the third embodiment of the present invention. In the third embodiment, the A + region 11a and the A− region 12a included in the A-phase polarization pattern 1a shown in FIG. 2A are divided into 1 / 4λ regions, and the 1 / 4λ is obtained. The A + region 11a and the A- region 12a occupying the corresponding angle of 22.5 ° are arranged at equal angular intervals of 90 °. Further, from the B-phase polarization pattern 1b shown in FIG. 2B, only the B + region 11b is selected by 4λ. That is, all the B + regions 11b in the B-phase polarization pattern 1b are selected, and are equally arranged at four positions every 90 °. The B-region 12b is not selected.

<Fourth embodiment>
FIG. 10 is a diagram showing the polarization region of the piezoelectric body 104 according to the fourth embodiment of the present invention. In the fourth embodiment, two A + regions 11a and A− regions 12a corresponding to ½λ in the A-phase polarization pattern 1a shown in FIG. 2A are selected, and each of the two selected locations is selected. The A + region 11a and the A- region 12a are arranged at positions that are rotationally symmetric. Further, from the B-phase polarization pattern 1b shown in FIG. 2B, the B + regions 11b corresponding to ½λ are arranged at two rotationally symmetric positions. The B-region 12b is disposed in the remaining region.

<Characteristics of the second to fourth embodiments>
The phase characteristics and amplitude characteristics of the piezoelectric bodies (102 to 105) according to the second to fourth examples were evaluated. FIG. 11 shows the characteristics of the piezoelectric bodies of the second, third, and fourth embodiments (hereinafter also referred to as the second embodiment 102, the third embodiment 103, and the fourth embodiment 104). FIG. 11A shows the phase with respect to the frequency of the drive signal, and FIG. 11B shows the amplitude in the piezoelectric thickness direction with respect to the frequency of the drive signal. 11A and 11B also show the characteristic curves (200, 210, 201, 211) of the comparative example 100 and the first example 101 previously shown in FIGS. 6A and 6B. ing.

  As shown in FIG. 11A, the phase characteristic curves (202 to 204) of the second to fourth embodiments (102 to 104) have almost the same shape. Further, as shown in (B), the shapes of the amplitude characteristic curves (212 to 214) are almost the same. 11A and 11B, the second to fourth examples (102 to 104) are inferior to the first example 101, but the phase characteristics are improved by about 10 ° with respect to the comparative example 100. The amplitude characteristic is improved by about 25%. Therefore, the piezoelectric body based on the technical idea of the present invention has almost the same characteristics except for the “ideal” arrangement as in the first embodiment 101, and moreover than the comparative example 100 corresponding to the conventional ultrasonic motor. It was also proved that the characteristics were improved. Further, except for an ultrasonic motor including a piezoelectric body having an ideal arrangement like the piezoelectric body 101 according to the first embodiment, an ultrasonic motor employing a piezoelectric body based on the technical idea of the present invention is It was also found to have almost the same characteristics.

<Fifth embodiment>
The piezoelectric bodies (101 to 104) according to the first to fifth examples had an angle corresponding to 1 / 2λ of 45 °. Therefore, the rotationally symmetric polarization region is disposed at a substantially point-symmetrical position. Accordingly, as a fifth embodiment, a piezoelectric body having an angle corresponding to 1 / 2λ of 60 ° is cited, and it is confirmed that the present invention extends to rotational symmetry including point symmetry.

  FIG. 12 shows the concept of the polarization polarity and the arrangement of the drive electrodes in an annular piezoelectric body whose angle corresponding to 1 / 2λ is 60 °. This FIG. 12 is the same except that the angle of 1 / 2λ in FIG. 2 is changed from 45 ° to 60 °, and FIG. 2A shows the A-phase polarization pattern 110a. The A + regions 11a and the A− regions 12a corresponding to the A phase are alternately arranged in an annular shape every 60 °. (B) shows a B-phase polarization pattern 110b. Similarly, B + regions 11b and A− regions 12b corresponding to the B phase are alternately arranged in an annular shape every 60 °. The A phase pattern 110a and the B phase pattern 110b are shifted by an angle of 30 ° corresponding to 1 / 4λ.

  FIG. 13 shows a piezoelectric body 110 (hereinafter also referred to as a second comparative example 110) in a conventional ultrasonic motor based on the A-phase and B-phase polarization patterns (201a, 201b) shown in FIGS. ) Is a diagram for explaining the arrangement of polarization regions (11a, 12a, 11b, 12b). In the second comparative example 110, similarly to the piezoelectric body 100 in the conventional ultrasonic motor shown in FIG. 3, the A-phase region 10a and the B-phase region are respectively formed in the half regions (30a, 30b) obtained by dividing the ring into two. 10b is arranged, and in each phase region (10a, 10b), the polarization region (11a, 12a) of the A phase pattern 110a and the polarization region (11b, 12b) of the B phase pattern 110b shown in FIG. Has been placed. Further, the polarization region 114 in which the polarization patterns (110a, 110b) of the A phase and the B phase shown in FIG. 12 are separated by a bisector 21 of a circle dividing the A phase region 10a and the B phase region 10a. The polarization region 114 is divided into two regions (115a and 115b) corresponding to 3 / 8λ. A portion where only the polarization region of the B-phase polarization pattern 110b is divided is a gap 113.

  FIG. 14 shows the arrangement state of the polarization regions (11a, 12a, 11b, 12b) of the piezoelectric body 105 (hereinafter also referred to as the fifth embodiment 105) according to the fifth embodiment. Similar to the second comparative example 110, although based on the A-phase and B-phase patterns (110a, 110b) shown in FIG. 12, each polarization region (11a, 12a, 11b, 12b) are arranged at intervals of 30 ° corresponding to 1 / 4λ. When focusing on a specific type of polarization region (any one of 11a, 12a, 11b, and 12b), the polarization region (any one of 11a, 12a, 11b, and 12b) is arranged at a point-symmetrical position. They are arranged at positions that are rotationally symmetric.

  In FIG. 15, the characteristics of the fifth example 105 and the second comparative example 110 are compared and shown. FIG. 15A shows the phase with respect to the frequency of the drive signal, and FIG. 15B shows the relationship between the frequency of the drive signal and the amplitude in the thickness direction of the piezoelectric body (105, 110). In the phase characteristic curve 230 of the second comparative example 110 and the phase characteristic curve 231 of the fifth example 105 shown in FIG. 15A, from the phase in the vicinity of the resonance frequency (about 65.9 KHz), the fifth example 105 It can be seen that the phase is improved by about 47 ° with respect to the second comparative example 110. Further, from the amplitude characteristic curve 240 of the second comparative example 110 and the phase characteristic curve 241 of the fifth example 105 shown in (B), in the fifth example 105, the amplitude is about 0.02 μm, and the ratio is about 40%. It was confirmed to improve.

=== Other Embodiments ===
In the second to fifth embodiments (102 to 104), among the four types of polarization regions (11a, 12a, 11b, and 12b), the virtual A phase polarization pattern 1a and the B phase polarization pattern 1b The predetermined polarization region arranged so as to be rotationally symmetric by rule was selected and arranged on the actual piezoelectric body. Naturally, if it is arranged according to the predetermined rule, the polarization to be selected The type of region is not limited to these examples, and other types of polarization regions may be used. For example, in the second embodiment 102, the A-regions 12a corresponding to 1 / 2λ are arranged at two positions which are rotationally symmetric with respect to the center O of the ring, Any of the polarization regions (12a, 11b, 12b) may be disposed at two positions at positions that are rotationally symmetric with respect to the center O of the ring.

  In the first to fourth embodiments, the angle of 22.5 ° in the ring corresponds to ¼λ, and polarization regions (11a, 12a, 11b, 12b) for 4λ are arranged on the ring. In the fifth embodiment, an angle of 30 ° corresponds to 1 / λ. Of course, the present invention is not limited to these examples, and if n is a natural number of 2 or more and nλ polarization regions (11a, 12a, 11b, 12b) are arranged on the ring, it is easy to obtain the same performance. To be expected.

1, 100, 101 to 105, 110 Piezoelectric material, 10a A phase region, 10b B phase region,
11a, 11b, 12a, 12b Polarization region

Claims (5)

An ultrasonic motor including a piezoelectric body in which a + polarization region and a -polarization region having opposite polarities are arranged so as to form a ring,
Either the A phase electrode or the B phase electrode to which the high frequency signals of the A phase and the B phase are shifted from each other by 90 ° is formed on the surfaces of the + polarization region and the − polarization region, and the + and − The polarization region is divided into any of four types of polarization regions of A phase + region, A phase-region, B phase + region, and B phase-region,
The A phase + region and the A phase-region have a polarization region in which the center angle of the ring corresponds to an angle corresponding to ½ wavelength, and n in a ring shape so that the polarization polarity is alternately reversed. (Where n is a natural number equal to or greater than 2), from the A-phase polarization pattern arranged for the wavelength, a 1/2 wavelength polarization region constituting the pattern , and a 1/4 wavelength that divides the polarization region into two equal parts A region for a total of n / 2 wavelengths is selected and arranged from the region of minutes,
The B phase + region and the B phase − region are obtained by rotating the A phase polarization pattern at an angle corresponding to a quarter wavelength from the B phase polarization pattern, and the A phase + region and the A phase − region. Is selected and arranged from the polarization region in a position that does not overlap with both,
Of the four types of polarization regions, at least one type of polarization region is disposed at a point-symmetrical position with respect to the center of the ring at an angle corresponding to a half wavelength .
Ultrasonic motor characterized by that. In claim 1,
One specific polarization region belonging to one of the A phase and the B phase, ie, a + polarization region and a -polarization region, is divided into ½ wavelength at four locations at equal angular intervals of 90 ° on the ring. Is arranged at an angle of
The + polarization region and the -polarization region belonging to the other phase of the A phase or the B phase are at an angle of ¼ wavelength and 90 ° on the ring in a region where the specific polarization region is not arranged. Are arranged at equiangular intervals,
Ultrasonic motor characterized by that. In claim 1,
The + polarization region and the -polarization region belonging to one phase of the A phase or the B phase are located at two points symmetrical with respect to the center of the ring at an angle corresponding to ½ wavelength. Arranged,
One polarization region of the + polarization region and the-polarization region belonging to the other phase of the A phase or the B phase is disposed at two rotationally symmetric positions at an angle corresponding to ½ wavelength.
Ultrasonic motor characterized by that. 4. The ultrasonic motor according to claim 3, wherein a + polarization region and a -polarization region belonging to one of the A phase and the B phase are adjacent to each other. 5. The ultrasonic motor according to claim 1, wherein an angle corresponding to the ¼ wavelength is 22.5 °.

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