JP2010004625A - Piezoelectric vibrator and method of driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple piezoelectric vibrator that eliminates the need for complicated electrode arrangement and geometric accuracy in the formation of electrodes, and to provide a method of driving the piezoelectric vibrator. <P>SOLUTION: A rectangular plate includes the following areas substantially on a diagonal line of the rectangular plate: an area parallel with the direction of the thickness of the rectangular plate and polarized by a pair of an upper surface electrode 12 and a lower surface electrode 13; and two areas 14 not polarized in the direction of the thickness. Longitudinal vibration and bending vibration are thereby excited. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric vibrator configured using a piezoelectric ceramic, particularly suitable for an ultrasonic motor, and a driving method thereof.

  A conventional piezoelectric vibrator and a driving method thereof will be described with reference to drawings and the like, including an explanation of an ultrasonic motor which is a main field of application of the present invention.

  FIG. 7 is a schematic diagram showing the principle of a general ultrasonic motor. FIG. 7A is a diagram for explaining the operation, and FIG. 7B shows the locus of the vibrator. The ultrasonic motor includes a vibrator 31 and a moving body (slider) 32, and at least a part of the vibrator 31 has an elliptical motion due to a combination of expansion and contraction. For example, the point p (center point of the left end face of the vibrator) in FIG. 7A draws the trajectory shown in FIG. (Longitudinal direction, y is an axis perpendicular to the upper and lower surfaces of the vibrator). A wear resistant material to be a fixed sliding member (stator) 33 is usually bonded to the portion of the vibrator 31 that is in an elliptical motion. The elliptical motion of the vibrator is transmitted to the slider 32 via the stator 33 and becomes a driving force for moving the slider 32. In FIG. 7A, the slider 32 is sent downward along the guide 34 in FIG. In this example, the moving body is driven linearly. However, if the moving body is formed into an annular shape, it is possible to cause a rotational motion.

  FIG. 8 is a perspective view of a conventional piezoelectric vibrator using conventional longitudinal longitudinal vibration and bending secondary vibration. FIG. 10 is a stress diagram (stress contour) of the longitudinal longitudinal vibration driven in the conventional example and the present invention. FIG. 11 is a stress diagram (stress contour) of the bending secondary vibration driven in the conventional example and the present invention. The shape of the piezoelectric vibrator 41 of the conventional example is a rectangular plate shape of a hard (high Qm) ceramic having a length of 20 mm, a width of 5 mm, and a thickness of 5 mm, and four excitation electrodes A42 polarized in the thickness direction. An excitation electrode B43, an excitation electrode C44, and an excitation electrode D45 are provided. A method of operating the piezoelectric vibrator 41 is as follows. In the case of longitudinal primary vibration, when AC drive signals having the same phase are applied to the upper and lower electrode portions of the excitation electrodes A to D, the four electrodes are integrated to act as a pair of substantially rectangular plates. In the vicinity of 83 kHz, a longitudinal longitudinal vibration having a length as shown in FIG. 10 is excited. On the other hand, with respect to the secondary bending vibration, the upper and lower electrode portions of the diagonal two-point excitation electrode A42, the excitation electrode D45, the excitation electrode B43, and the excitation electrode C44 are respectively provided for the four electrode portions. By applying alternating drive signals having the same amplitude and different phases, the bending secondary vibration shown in FIG. 11 is similarly excited in the vicinity of 81 kHz.

  In FIG. 8, longitudinal longitudinal vibration is excited by applying the same phase voltage between the excitation electrode A42, the excitation electrode D45, the excitation electrode B43, and the excitation electrode C44. In the stress diagram at that time, as shown in FIG. 10, a region where the stress becomes maximum appears symmetrically in the longitudinal direction of the rectangular plate piezoelectric vibrator. Further, in FIG. 8, bending secondary vibration is excited by applying an antiphase voltage between the excitation electrode A 42, the excitation electrode D 45 and the excitation electrode B 43, and the excitation electrode C 44. In the stress diagram at that time, as shown in FIG. 11, a region where the stress becomes maximum appears symmetrically on the diagonal in the longitudinal direction of the rectangular plate piezoelectric vibrator. In addition, by switching voltages applied with different amplitudes and phases between the excitation electrode A42, the excitation electrode D45 and the excitation electrode B43, and the excitation electrode C44 with different directions, the longitudinal longitudinal vibration and the bending 2 It is possible to excite vibration with superposed next vibration. As described with reference to FIGS. 7A and 7B, the traveling wave type is obtained by fixing the piezoelectric vibrator 41 on which the electrode is formed and bringing the slider 32 that is arbitrarily movable into contact with the piezoelectric vibrator 41. It can be operated as an ultrasonic motor. In the case of the piezoelectric vibrator 41 of the conventional example, in order to apply an alternating electric field to four electrodes, eight signal input electrodes, two in each of forward and reverse directions, are required, and complicated electrode arrangement and electrodes are required in actual product design. It is necessary to ensure the shape accuracy of the formation.

  FIG. 9 shows impedance characteristics of a conventional piezoelectric vibrator. FIG. 9A shows the case of longitudinal longitudinal vibration, and FIG. 9B shows the case of bending secondary vibration. In the case of longitudinal longitudinal vibration, resonance vibration is excited in the vicinity of 83 kHz, and in the case of bending secondary vibration, resonance vibration is excited in the vicinity of 81 kHz. In the conventional example, by switching the input voltage between the electrodes, the longitudinal longitudinal vibration and the bending secondary vibration are generated, so the impedance characteristics of both the longitudinal longitudinal vibration and the bending secondary vibration at the same time are as follows: Never appear.

  As shown in FIG. 8, four polarized regions are formed on a piezoelectric ceramic rectangular plate using a hard piezoelectric ceramic with little loss, and a drive signal is appropriately applied to these polarized regions, so that the longitudinal length can be increased. It is possible to excite vibrations in which the primary vibration and the bending secondary vibration are individually or superimposed. In FIGS. 10 and 11, the forms of the longitudinal longitudinal vibration and the bending secondary vibration of the rectangular plate are represented by stress contour lines. In the case of the bending secondary vibration, approximately 1 / In a total of four locations in region 4, there are regions where the strain and stress are maximized.

  As a method for solving the above problem, for example, Patent Document 1 provides electrodes for stretching vibration and bending secondary vibration, respectively, to alleviate nonlinearity of input / output characteristics of the piezoelectric vibrator, and controllability in a fine movement region. The provision of an ultrasonic motor vibrator with high (positioning accuracy) and the provision of an ultrasonic motor vibrator with high vibration efficiency are disclosed. However, there is a problem that the structure of the piezoelectric vibrator is complicated, the control circuit is complicated, and the cost is high.

JP 2008-54407 A

  A technical problem of the present invention is to provide a simple piezoelectric vibrator that does not require complicated arrangement of electrodes, ensuring of dimensional accuracy in forming electrodes, and a driving method thereof.

  In order to solve the above problems, in the present invention, a region polarized by a pair of two electrodes parallel to the rectangular plate in the thickness direction and two regions that are not polarized in the thickness direction are substantially diagonal lines of the rectangular plate. The piezoelectric vibrator is characterized by exciting longitudinal vibration and bending vibration by being provided above. In the two unpolarized regions provided on this diagonal line, the material rigidity and Young's modulus of the polarized region are different while being originally the same material, so not only the longitudinal vibration by selecting the operating frequency, Bending vibration occurs. As a result, although only a pair of electrode terminals, it is possible to excite vibrations that are individually or superposed on both vibration forms by selecting the drive frequency, and the number of signal input electrodes can be reduced. The degree of freedom in product design increases. Moreover, not only a single rectangular plate but also a plurality of rectangular plates are laminated so that the polarization region overlaps in the thickness direction, thereby reducing the impedance and enabling low voltage driving.

  According to the present invention, a piezoelectric vibrator using a piezoelectric ceramic rectangular plate and polarized by a pair of two electrodes parallel to the thickness direction of the piezoelectric ceramic rectangular plate, In the region where the strain is maximum, a piezoelectric vibrator having two regions that are not polarized in the thickness direction of the piezoelectric ceramic on the diagonal line of the rectangular plate can be obtained.

  Further, according to the present invention, a piezoelectric vibrator that is a stacked piezoelectric vibrator in which a plurality of the piezoelectric vibrators are laminated in the electrode thickness direction can be obtained.

  Further, according to the present invention, the piezoelectric vibrator that arbitrarily drives the longitudinal vibration, the bending vibration, or the state in which both are superimposed by driving between the resonance frequencies of the longitudinal vibration and the bending vibration in the piezoelectric vibrator. A child driving method is obtained.

  According to the present invention, it is possible to construct a simple resonance type piezoelectric vibrator having a small number of terminals and a piezoelectric vibrator that excites longitudinal vibration and bending vibration using resonance of a rectangular plate. By selecting, it is possible to provide a piezoelectric vibrator and a driving method thereof that can excite each vibration and any form in which each vibration is superimposed.

  The piezoelectric vibrator of the present invention and the driving method thereof can use a resonance of a rectangular plate to easily excite a longitudinal vibration mode and a bending vibration mode and to form a simple resonance type piezoelectric vibrator. It becomes.

(Embodiment 1)
FIG. 1 shows a perspective view of a piezoelectric vibrator of the present invention. FIG. 1A shows a case where the non-polarized region has a semi-cylindrical shape, and FIG. 1B shows a case where the non-polarized region has a rectangular parallelepiped shape. As in FIG. 8, the outer shape of the piezoelectric vibrator 11 is, for example, 20 mm long × 5 mm wide × 5 mm thick, and is substantially the same as the rectangular plate shape of a hard (high Qm) ceramic, but is similar to the conventional example. The upper surface electrode 12 and the lower surface electrode 13 are provided slightly inside the outline of the rectangular plate, and this region is polarized in the thickness direction. Further, two regions 14 that are not polarized in the thickness direction are provided along the diagonal line in the same rectangular plate.

  FIG. 2 shows the impedance characteristics of the piezoelectric vibrator of the present invention. As a result of observing the frequency characteristics (impedance waveform) of the impedance between the upper surface electrode 12 and the lower surface electrode 13 at 70 kHz to 100 kHz, this piezoelectric vibrator has a large resonance (impedance minimum) point in the vicinity of 83 kHz. The region is driven in the longitudinal primary vibration mode. On the other hand, a small resonance is shown in the vicinity of 81 kHz, but it operates with a bending secondary vibration in the vicinity of this frequency.

  FIG. 3 shows an operation mode at the driving frequency of the piezoelectric vibrator of the present invention. It is shown that as the drive frequency is changed, the form gradually changes from a bending secondary vibration of 81 kHz to a longitudinal longitudinal vibration of 83 kHz in length. In the vicinity of 82 kHz, a vibration form in which a longitudinal primary vibration is superimposed on a bending secondary vibration is taken. In the piezoelectric vibrator 11 according to the present invention, a single vibration mode, two types can be obtained by changing the operating frequency of the pair of electrodes in the vibrator without changing the applied voltage phase, forward / reverse, or the like. It is possible to freely excite the state in which the vibration forms are superimposed.

  10 and FIG. 11 show the length longitudinal primary vibration and the bending secondary vibration of the rectangular plate driven in the conventional example and the present invention by the stress contour lines. With the electrode configuration of the present invention, as in the case of the conventional example, in the case of longitudinal longitudinal vibration, two points in the region approximately 1/4 from the end in the longitudinal direction of the rectangular plate, and bending secondary vibration In this case, a region where the strain and stress are maximized can be generated at a total of four points in a region substantially ¼ from the end in the longitudinal direction of the rectangular plate. Therefore, according to the structure of the present invention, the number of electrodes required to excite the vibration of the same form as the conventional one can be reduced to about 1/4 of the conventional piezoelectric vibrator.

(Embodiment 2)
Next, FIG. 4 shows a perspective view of the laminated piezoelectric vibrator of the present invention (the figure shows an example in which 10 layers are laminated). FIG. 5 shows an internal electrode structure diagram of the multilayer piezoelectric vibrator of the present invention. 5A is a perspective view, and FIG. 5B is a cross-sectional view. In FIG. 5A, the piezoelectric ceramic is omitted. The shape, material used, and the like of the laminated piezoelectric vibrator 21 are the same as those in the first embodiment, but the region polarized in the thickness direction is composed of the internal electrode A22 and the internal electrode B23, and each layer is a cross section in FIG. As shown in the figure, the electrodes are polarized in opposite directions with respect to the thickness direction, and are connected to receive external driving signals at the external electrodes A24 and B25 on the side surfaces. Further, two regions 26 (shown in FIG. 4) that are not polarized in the thickness direction are provided along the diagonal line in the same rectangular plate. The arrow in the figure indicates the polarization direction.

  FIG. 6 shows the impedance characteristics of the laminated piezoelectric vibrator of the present invention. As a result of observing the frequency characteristics (impedance waveform) of the impedance of this piezoelectric vibrator from 70 kHz to 100 kHz with the external electrode A24 and the external electrode B25, there is a large resonance (minimum impedance) point in the vicinity of 83 kHz. The region is driven in the primary vibration mode. On the other hand, a small resonance is shown in the vicinity of 81 kHz, but it operates with a bending secondary vibration in the vicinity of this frequency. Compared to the first embodiment, the impedance is reduced.

  As is clear from the first and second embodiments, a pair of electrodes is required for one electrode part. In the conventional example of FIG. An external electrode is required. The same is true when lowering the impedance by stacking multiple pairs for low-voltage driving. With the structure of the present invention, the number of electrodes required to excite the vibration of the same form is about ¼. It will be a thing.

  As mentioned above, although embodiment of this invention was described, this invention is not restricted to these embodiment, Even if there is a design change of the range which does not deviate from the summary of this invention, it is included in this invention. That is, various changes and modifications that can be naturally made by those skilled in the art are also included in the present invention.

  By using the piezoelectric vibrator and the driving method thereof of the present invention, an ultrasonic motor capable of exciting a longitudinal vibration mode, a bending vibration mode, and any form in which each is superposed can be easily configured. it can.

The perspective view of the piezoelectric vibrator of this invention is shown. FIG. 1A shows a case where a non-polarized region has a semi-cylindrical shape, and FIG. 1B shows a case where a non-polarized region has a rectangular parallelepiped shape. The figure which shows the impedance characteristic of the piezoelectric vibrator of this invention. The figure which shows the operation | movement form in the drive frequency of the piezoelectric vibrator of this invention. The perspective view of the lamination type piezoelectric vibrator of the present invention. The internal electrode structure figure of the lamination type piezoelectric vibrator of the present invention. FIG. 5A is a perspective view, and FIG. 5B is a cross-sectional view. The figure which shows the impedance characteristic of the laminated piezoelectric vibrator of this invention. The schematic diagram showing the principle of a general ultrasonic motor. FIG. 7A is a diagram for explaining the operation, and FIG. 7B is a diagram showing the locus of the vibrator. The perspective view of the piezoelectric vibrator of a prior art example. The figure which shows the impedance characteristic of the piezoelectric vibrator of a prior art example. FIG. 9A is a diagram showing a case of longitudinal longitudinal vibration, and FIG. 9B is a diagram showing a case of bending secondary vibration. FIG. 6 is a stress diagram (stress contour line) of a lengthwise primary vibration driven in the conventional example and the present invention. The stress figure (stress contour) of the bending secondary vibration driven in the conventional example and this invention.

Explanation of symbols

11 Piezoelectric vibrator 12 Upper surface electrode 13 Lower surface electrode 14 Unpolarized region 21 Multilayer piezoelectric vibrator 22 Internal electrode A
23 Internal electrode B
24 External electrode A
25 External electrode B
26 Unpolarized region 31 Vibrator 32 Moving object (slider)
33 Fixed sliding member (stator)
34 Guide p Center A to D of left end face of vibrator Trajectory 41 Piezoelectric vibrator 42 Excitation electrode A
43 Excitation electrode B
44 Excitation electrode C
45 Excitation electrode D

Claims (3)

  A piezoelectric vibrator using a piezoelectric ceramic rectangular plate and polarized by a pair of two electrodes parallel to the thickness direction of the piezoelectric ceramic rectangular plate, and in a region where the strain of the bending vibration form of the piezoelectric ceramic rectangular plate is maximum. A piezoelectric vibrator comprising two regions that are not polarized in the thickness direction of the piezoelectric ceramic on a diagonal line of a rectangular plate.   The piezoelectric vibrator according to claim 1, wherein the piezoelectric vibrator is a laminated piezoelectric vibrator in which a plurality of the piezoelectric vibrators are laminated in an electrode thickness direction.   3. The piezoelectric vibrator according to claim 1, wherein the piezoelectric vibrator is driven between a longitudinal longitudinal vibration and a resonance frequency of a bending vibration to arbitrarily excite a longitudinal longitudinal vibration, a bending vibration, or a state in which both are superimposed. A driving method of the piezoelectric vibrator.

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