JP5457651B2 - Ultrasonic motor - Google Patents

Description

  The present invention relates to an ultrasonic motor, and more particularly, an ultrasonic motor that generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode in which a primary longitudinal vibration mode and a secondary bending vibration mode are combined. The present invention relates to a sonic motor.

  Conventionally, an ultrasonic motor that drives a rotor, a rotating shaft, and the like by vibrating a piezoelectric vibrator is known. This ultrasonic motor is configured to generate a driving force by combining a plurality of types of vibration (resonance) modes when vibrating a piezoelectric vibrator.

  FIG. 6 is a diagram showing a frequency spectrum when a rectangular piezoelectric vibrator is vibrated in a plurality of types of vibration modes. Here, F1, F2 and F3 indicate bending vibration, and L1 and L2 indicate longitudinal vibration. The length of the expansion / contraction direction when the rectangular piezoelectric vibrator vibrates in the primary longitudinal vibration mode (L1) is L, and the piezoelectric vibrator vibrates in the secondary bending vibration mode (F2). Let d be the length in the shearing direction. Then, as shown in FIG. 6, with d / L as a variable, d / L is associated with the resonance frequency of the primary longitudinal vibration mode of the piezoelectric vibrator, and d / L and the secondary longitudinal vibration mode are correlated. Corresponds to the resonance frequency. In FIG. 6, L = 20 mm is fixed, and only d (Width) is changed. In this case, when the ratio of two sides in the vertical and horizontal directions (hereinafter referred to as “side ratio”) d / L is around 0.272, the resonance frequencies of the two coincide, and the two vibrations are degenerated. Therefore, conventionally, the piezoelectric vibrator has been formed so that the side ratio d / L is around 0.272.

On the other hand, Japanese Patent Laid-Open No. 5-003688 discloses an ultrasonic motor that is driven as a piezoelectric vibrator in a multiple vibration mode in which a longitudinal vibration mode and a bending vibration mode having slightly different resonance frequencies are combined. In this ultrasonic motor, the resonance frequency ft of the longitudinal longitudinal vibration of the piezoelectric vibrator and the resonance frequency fp of the even-order in-plane bending vibration have slightly different values. Specifically, the ratio of the short-side length to the long-side length of the piezoelectric vibrator is removed from 0.26: 1, for example, a ratio such as 0.28: 1 or 0.24: 1. Next, a piezoelectric vibrator is formed. Thereby, the ultrasonic motor is driven stably.
JP-A-5-003688

  As described above, conventionally, attention has been focused only on the case where the side ratio d / L of the piezoelectric vibrator is 0.272. However, the side ratio d / L in the case where the resonance frequency of the primary longitudinal vibration mode and the resonance frequency of the secondary bending vibration mode are not the same. As shown in FIG. 6, in addition to the case where the side ratio d / L is near 0.272, the case where the side ratio d / L is around 0.6 also includes the resonance frequency and the secondary in the primary longitudinal vibration mode. The resonance frequency of the bending vibration mode matches. However, conventionally, an ultrasonic motor has not been configured with a side ratio d / L of the piezoelectric vibrator of around 0.6.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic motor in which a piezoelectric vibrator is configured with a side ratio different from the conventional one.

  (1) In order to achieve the above object, the present invention has taken the following measures. That is, the ultrasonic motor of the present invention is an ultrasonic wave that generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a primary longitudinal vibration mode and a secondary bending vibration mode. The length of the extension direction when the piezoelectric vibrator vibrates in the primary longitudinal vibration mode is L, and the length in the shear direction when the piezoelectric vibrator vibrates in the secondary bending vibration mode. D / L is a variable, and d / L and the resonance frequency of the primary longitudinal vibration mode of the piezoelectric vibrator are made to correspond to each other, and d / L and the resonance frequency of the secondary longitudinal vibration mode are When the piezoelectric vibrator has a corresponding value, the piezoelectric vibrator has a subtraction value obtained by subtracting the value of the resonance frequency of the secondary bending vibration mode from the value of the resonance frequency of the primary longitudinal vibration mode for the same d / L value. Based on the value of d / L when changing from a negative number to a positive number It is characterized in that it is had to form.

  In this way, with d / L as a variable, d / L and the resonance frequency of the primary longitudinal vibration mode of the piezoelectric vibrator are made to correspond to each other, and d / L and the resonance frequency of the secondary longitudinal vibration mode are made to correspond to each other. When d / L is small, the resonance frequency of the primary longitudinal vibration mode is larger than the resonance frequency of the secondary bending vibration mode, and when d / L exceeds about 0.272, The size is reversed. When d / L is further increased, the resonance frequency of the primary longitudinal vibration mode becomes higher than the resonance frequency of the secondary bending vibration mode. That is, the subtraction value obtained by subtracting the resonance frequency value of the secondary bending vibration mode from the resonance frequency value of the primary longitudinal vibration mode for the same d / L value changes from a negative number to a positive number. . In the present invention, the piezoelectric vibrator is configured by the value of d / L at that time. As a result, the piezoelectric vibrator has a so-called wall thickness and a length in the longitudinal direction that is smaller than that in the conventional case where the side ratio d / L is around 0.272. As a result, downsizing can be achieved. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved.

  (2) Also, the ultrasonic motor of the present invention generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a primary longitudinal vibration mode and a secondary bending vibration mode. An ultrasonic motor that performs shearing when the piezoelectric vibrator vibrates in the secondary bending vibration mode, where L is the length in the expansion / contraction direction when the piezoelectric vibrator vibrates in the primary longitudinal vibration mode. When the length in the direction is d, the piezoelectric vibrator is formed so that the value of d / L falls within the range of 0.55 to 0.65.

  Thus, since the value of d / L falls within the range of 0.55 to 0.65, the thickness ratio is longer than the case where the side ratio d / L is near 0.272 and the length in the longitudinal direction is longer. Becomes smaller. As a result, downsizing can be achieved. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved.

  (3) Also, the ultrasonic motor of the present invention generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a primary longitudinal vibration mode and a secondary bending vibration mode. An ultrasonic motor that performs shearing when the piezoelectric vibrator vibrates in the secondary bending vibration mode, where L is the length in the expansion / contraction direction when the piezoelectric vibrator vibrates in the primary longitudinal vibration mode. When the length in the direction is d, the piezoelectric vibrator is formed so that the value of d / L is substantially 0.63.

  As described above, since the value of d / L is substantially 0.63, the thickness ratio is longer than the case where the side ratio d / L is near 0.272, and the length in the longitudinal direction is larger. Get smaller. As a result, downsizing can be achieved. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved. In addition, the value of d / L being substantially 0.63 means a range in which the piezoelectric vibrator functions practically as an ultrasonic motor. Even if the value of d / L is deviated around 0.63, if the piezoelectric vibrator practically functions as an ultrasonic motor, it can be said that the value of d / L is substantially 0.63. . Conversely, the value of d / L does not have to be just 0.63 if the piezoelectric vibrator functions practically as an ultrasonic motor.

  According to the present invention, the piezoelectric vibrator has a so-called thickness and a length in the longitudinal direction that are smaller than those in the case where the side ratio d / L is around 0.272 as in the prior art. As a result, downsizing can be achieved. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved.

[First Embodiment]
Next, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a piezoelectric vibrator according to this embodiment. The piezoelectric vibrator 1 is made of piezoelectric ceramics, and the polarization direction coincides with the z-axis direction of the coordinate axis shown in FIG. The expansion / contraction direction when the piezoelectric vibrator 1 vibrates in the primary longitudinal vibration mode is parallel to the x axis, and the length of the piezoelectric vibrator 1 in the x axis direction is L. Further, the shearing direction when the piezoelectric vibrator 1 vibrates in the second bending vibration mode is parallel to the y-axis, and the length (thickness) of the piezoelectric vibrator 1 in the y-axis direction is d.

  FIG. 2 is a diagram illustrating a state of the primary longitudinal vibration of the piezoelectric vibrator 1. The primary longitudinal vibration is generated by repeatedly expanding and contracting in the longitudinal direction of the piezoelectric vibrator 1 as indicated by arrows A and B in FIG. FIG. 3 is a diagram showing a state of the secondary bending vibration of the piezoelectric vibrator 1. As shown by an arrow C in FIG. 3, the secondary bending vibration is generated by repeatedly bending in the thickness direction of the piezoelectric vibrator 1 by shearing forces having different directions. By synthesizing (degenerate) these primary longitudinal vibrations and secondary bending vibrations, the chip provided in the piezoelectric vibrator 1 performs an elliptical motion to generate a driving force.

  FIG. 4 is a diagram showing stepwise how the piezoelectric vibrator 1 drives the driven body 2 in the right direction in the drawing. In FIG. 4, the piezoelectric vibrator 1 includes a chip 1a. By synthesizing the primary longitudinal vibration and the secondary bending vibration of the piezoelectric vibrator 1, the piezoelectric vibrator 1 repeats expansion and contraction and bending, and the driven body is moved by the distance l in one cycle.

  The piezoelectric vibrator 1 generates a driving force based on such a principle. However, conventionally, the side ratio d / L of the piezoelectric vibrator 1 has attracted attention only in the vicinity of 0.272. That is, with d / L as a variable, d / L is associated with the resonance frequency of the primary longitudinal vibration mode of the piezoelectric vibrator, and d / L is associated with the resonance frequency of the secondary longitudinal vibration mode. In this case, as shown in FIG. 6, when d / L is small, the resonance frequency of the primary longitudinal vibration mode is higher than the resonance frequency of the secondary bending vibration mode. When d / L becomes 0.272, the resonance frequency of the primary longitudinal vibration mode and the resonance frequency of the secondary bending vibration mode coincide with each other, so that the piezoelectric vibrator having d / L of 0.272 is obtained. Only was used. When d / L exceeds 0.272, the resonance frequency of the secondary bending vibration mode becomes higher than the resonance frequency of the primary longitudinal vibration mode.

  However, when d / L is further increased, the resonance frequency of the primary longitudinal vibration mode becomes higher than the resonance frequency of the secondary bending vibration mode. That is, the subtraction value obtained by subtracting the resonance frequency value of the secondary bending vibration mode from the resonance frequency value of the primary longitudinal vibration mode for the same d / L value changes from a negative number to a positive number. . That is, also in this respect, the resonance frequency of the primary longitudinal vibration mode matches the resonance frequency of the secondary bending vibration mode. In the present embodiment, the piezoelectric vibrator is configured by the value of d / L at that time. Specifically, in the present embodiment, the value of d / L is substantially 0.63.

  As a result, the piezoelectric vibrator 1 has a so-called thickness and a length in the longitudinal direction that are smaller than those in the case where the side ratio d / L is around 0.272 as in the prior art. As a result, downsizing can be achieved. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved.

FIG. 5 is a diagram showing a schematic configuration of the ultrasonic motor according to the present embodiment. The piezoelectric vibrator 1 is provided with a pair of electrodes 4a and a pair of electrodes 4b that face each other diagonally so as to divide one main surface of a rectangular piezoelectric substrate 1b into four. The other main surface is grounded. The electrodes 4a and 4b are individually provided in a state of being insulated from each other, and then the electrodes 4a and 4b positioned diagonally to each other are electrically connected to each other. The drive circuit of the ultrasonic motor 10 is composed of two AC voltage sources 5a and 5b. The AC voltage source 5a applies a voltage of V ₀ sin ωt to the electrode 4b, and the AC voltage source 5b applies a voltage of V ₀ cos ωt to the electrode 4a. As described above, when the voltages V ₀ sin ωt and V ₀ cos ωt having a phase shift of π / 2 with respect to the electrodes 4a and 4b of the piezoelectric vibrator 1 are applied, the piezoelectric vibrator 1 is applied to the piezoelectric vibrator 1 shown in FIGS. As shown, the vibration in the primary longitudinal vibration mode that expands and contracts in the longitudinal direction and the vibration in the secondary bending vibration mode that flexes in the shear direction are generated. When the resonance frequency of the primary longitudinal vibration mode is equal to the resonance frequency of the secondary bending vibration mode, both vibration modes are combined (degenerated), and the chip of the piezoelectric vibrator 1 (not shown in FIG. 5). No.) generates elliptical vibration.

  Although FIG. 5 shows the configuration of the two-phase signal input, the present invention is not limited to this. For example, it is possible to adopt a configuration of a one-phase signal input. In this case, it is possible to operate by applying an AC signal to a pair of electrodes opposed to each other and opening the other pair of electrodes.

[Second Embodiment]
In this embodiment, a single plate ceramic is used for the piezoelectric vibrator. After processing this single plate ceramic to 20.0 mm x 12.8 mm x 3.0 mm, 2 rows and 2 columns are divided into 4 rows on 20.0 mm x 12.8 mm, and a silver electrode is printed on the entire back surface. It was applied and baked at 850 ° C. Thereafter, the piezoelectric vibrator was manufactured by performing a uniform polarization treatment with an electric field strength of 2 kV / mm in 120 ° C. silicon oil. The sliding tip used was a hemispherical spherical alumina ceramic.

  Thrust-speed characteristics were measured using the piezoelectric vibrator manufactured as described above. In this measurement, a driving mechanism was used in which an ultrasonic motor (piezoelectric vibrator) was pre-contacted with a mirror finished alumina plate on the side surface of a precision linear table. A weight was suspended using a fixed pulley, and position information was read on a glass scale.

  Next, FEM analysis was performed on the ultrasonic motor using the piezoelectric vibrator manufactured as described above. FIG. 7 is a diagram showing frequency-driving speed characteristics. When the driving frequency was 82 kHz, the maximum speed at the time of two-phase input was 340 mm / s. FIG. 8 is a diagram showing thrust-speed characteristics. A maximum thrust of 6N was obtained at 120Vrms input. FIG. 9 is a diagram showing thrust-efficiency characteristics. As shown in FIG. 9, the maximum efficiency was 10%. As described above, it has been found that an ultrasonic motor using a rectangular piezoelectric vibrator having a side ratio d / L not only of 0.272 but also around 0.63 is promising.

  As described above, according to this embodiment, since the side ratio d / L of the piezoelectric vibrator 1 is substantially 0.63, the side ratio d / L is around 0.272 as in the related art. As compared with the case where it is, it becomes so-called thickness and the length in the longitudinal direction becomes smaller. As a result, downsizing can be achieved. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved.

It is a perspective view of the piezoelectric vibrator concerning this embodiment. It is a figure which shows the mode of the primary longitudinal vibration of a piezoelectric vibrator. It is a figure which shows the mode of the secondary bending vibration of a piezoelectric vibrator. It is a figure which shows a mode that a piezoelectric vibrator drives a to-be-driven body rightward in a figure. It is a figure which shows schematic structure of the ultrasonic motor which concerns on this embodiment. It is a figure which shows a frequency spectrum when a rectangular-shaped piezoelectric vibrator is vibrated in a plurality of types of vibration modes. It is a figure which shows a frequency-drive speed characteristic. It is a figure which shows a thrust-speed characteristic. It is a figure which shows a thrust-efficiency characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 1a Chip 1b Piezoelectric substrate 2 Driven body 4a Electrode 4b Electrode 5a AC voltage source 5b AC voltage source 10 Ultrasonic motor

Claims (3)

A rectangular piezoelectric vibrator is an ultrasonic motor that generates a driving force by vibrating in a multiple vibration mode that combines a primary longitudinal vibration mode and a secondary bending vibration mode,
The length in the expansion / contraction direction when the piezoelectric vibrator vibrates in the primary longitudinal vibration mode is L, and the length in the shear direction when the piezoelectric vibrator vibrates in the secondary bending vibration mode is d . If
The piezoelectric vibrator is formed so that the value of d / L falls within the range of 0.55 to 0.65,
Four electrodes formed in two rows and two columns on one main surface of the piezoelectric vibrator;
Of the four electrodes, two electrodes located diagonally are electrically connected to each other to form two sets of electrode portions; and
A first AC voltage source for driving the piezoelectric vibrator by applying an AC voltage to one of the two sets of electrode portions;
A second alternating current that drives the piezoelectric vibrator by applying an alternating voltage shifted by π / 2 from the phase of the alternating voltage by the first alternating voltage source to the other of the two sets of electrode portions. An ultrasonic motor comprising: a voltage source. A rectangular piezoelectric vibrator is an ultrasonic motor that generates a driving force by vibrating in a multiple vibration mode that combines a primary longitudinal vibration mode and a secondary bending vibration mode,
The length in the expansion / contraction direction when the piezoelectric vibrator vibrates in the primary longitudinal vibration mode is L, and the length in the shear direction when the piezoelectric vibrator vibrates in the secondary bending vibration mode is d. If
The piezoelectric vibrator is formed so that the value of d / L falls within the range of 0.55 to 0.65 ,
Four electrodes formed in two rows and two columns on one main surface of the piezoelectric vibrator;
Of the four electrodes, two electrodes located diagonally are electrically connected to each other to form two sets of electrode portions; and
An AC voltage source for driving the piezoelectric vibrator by applying an AC voltage to one of the two sets of electrode portions,
An ultrasonic motor, wherein the other of the two sets of electrode portions is opened . The ultrasonic motor according to claim 1 , wherein the piezoelectric vibrator is formed so that a value of d / L is substantially 0.63.

Images