JP5329912B2 - Ultrasonic motor - Google Patents

Description

  The present invention relates to an ultrasonic motor, and in particular, a laminated rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a primary longitudinal vibration mode and a secondary bending vibration mode, thereby generating a driving force. The present invention relates to a generated ultrasonic 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. 8 is a diagram illustrating 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. As shown in FIG. 8, 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. 8, L is fixed at 20 mm, 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. 8, 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. In addition, a rectangular single-plate piezoelectric vibrator is configured with the above-described side ratio, and an ultrasonic motor in which this is laminated has not been performed.

  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 single-plate piezoelectric vibrator is configured with a side ratio different from the conventional one and laminated. .

  (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 comprises a laminated piezoelectric vibrator formed by laminating rectangular and single-plate piezoelectric vibrators, and the laminated piezoelectric vibrator has a primary longitudinal vibration mode and a secondary bending. An ultrasonic motor that generates a driving force by oscillating in a multiple vibration mode combined with a vibration mode, the length in the expansion / contraction direction when the single-plate piezoelectric vibrator vibrates in a primary longitudinal vibration mode Where L is L, d is the length in the shear direction when the single-plate piezoelectric vibrator vibrates in the second bending vibration mode, and d / L is a variable, and d / L and the single-plate piezoelectric vibrator When the resonance frequency of the primary longitudinal vibration mode is made to correspond to the resonance frequency of d / L and the resonance frequency of the secondary longitudinal vibration mode, the single-plate piezoelectric vibrators have the same d / L From the value of the resonance frequency of the primary longitudinal vibration mode for the value of The subtracted value obtained by subtracting the resonance frequency value of the switch is formed based on the value of d / L when the negative number changes to a positive number, and the single-plate piezoelectric vibrator has the shear direction It is characterized in that a plurality of layers are laminated.

  In this way, with d / L as a variable, d / L corresponds to the resonance frequency of the primary longitudinal vibration mode of the single-plate piezoelectric vibrator, and d / L and the resonance frequency of the secondary longitudinal vibration mode. 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 d / L exceeds about 0.272. And 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, a single-plate piezoelectric vibrator is formed according to the value of d / L at that time. As a result, the single-plate piezoelectric vibrator has a so-called thickness and a length in the longitudinal direction that are smaller than 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. Furthermore, by laminating a plurality of single-plate piezoelectric vibrators formed in this way in the shear direction, a large electric field strength can be applied to the piezoelectric vibrator with the same input voltage as the single plate. The voltage can be reduced. As a result, it is possible to eliminate the step-up component required in the conventional ultrasonic motor, and to reduce the size of the driver board. As a result, a small driver system capable of multi-channel operation can be realized.

  (2) Further, the ultrasonic motor of the present invention is configured by stacking rectangular and single-plate piezoelectric vibrators to form a laminated piezoelectric vibrator, and the laminated piezoelectric vibrator has a first longitudinal vibration mode and a first piezoelectric vibrator. An ultrasonic motor that generates a driving force by oscillating in a multiple vibration mode combined with a secondary bending vibration mode, and in which the single-plate piezoelectric vibrator vibrates in a primary longitudinal vibration mode Where L is the length of the single plate and the length in the shear direction when the piezoelectric vibrator of the single plate vibrates in the secondary bending vibration mode is d, the piezoelectric vibrator of the single plate is d / L The value is in the range of 0.55 to 0.65, and a plurality of the single-plate piezoelectric vibrators are stacked in the shear direction.

  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, the piezoelectric vibrator can be reduced in size. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved. Furthermore, by laminating a plurality of single-plate piezoelectric vibrators formed in this way in the shear direction, a large electric field strength can be applied to the piezoelectric vibrator with the same input voltage as the single plate. The voltage can be reduced. As a result, it is possible to eliminate the step-up component required in the conventional ultrasonic motor, and to reduce the size of the driver board. As a result, a small driver system capable of multi-channel operation can be realized.

  (3) Further, the ultrasonic motor of the present invention is configured by stacking rectangular and single-plate piezoelectric vibrators to form a laminated piezoelectric vibrator, and the laminated piezoelectric vibrator has a first longitudinal vibration mode and a first piezoelectric vibrator. An ultrasonic motor that generates a driving force by oscillating in a multiple vibration mode combined with a secondary bending vibration mode, and in which the single-plate piezoelectric vibrator vibrates in a primary longitudinal vibration mode Where L is the length of the single plate and the length in the shear direction when the piezoelectric vibrator of the single plate vibrates in the secondary bending vibration mode is d, the piezoelectric vibrator of the single plate is d / L The value is substantially 0.63, and a plurality of the single-plate piezoelectric vibrators are laminated in the shear direction.

  Thus, since the value of d / L is substantially 0.63, it becomes what is called a wall thickness rather than the case where side ratio d / L is near 0.272. As a result, since the length in the L direction can be shortened with the same volume as compared with the case where the side ratio d / L is around 0.272, the size can be reduced. Moreover, since it becomes thicker than before, damage due to fatigue or over-input is less likely to occur, and durability can be improved. Furthermore, by laminating a plurality of single-plate piezoelectric vibrators formed in this way in the shear direction, a large electric field strength can be applied to the piezoelectric vibrator with the same input voltage as the single plate. The voltage can be reduced. As a result, it is possible to eliminate the step-up component required in the conventional ultrasonic motor, and to reduce the size of the driver board. As a result, a small driver system capable of multi-channel operation can be realized. 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 single-plate piezoelectric vibrator has a so-called thickness and a smaller length in the longitudinal direction than 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. Furthermore, by laminating a plurality of single-plate piezoelectric vibrators formed in this way in the shear direction, a large electric field strength can be applied to the piezoelectric vibrator with the same input voltage as the single plate. The voltage can be reduced. As a result, it is possible to eliminate the step-up component required in the conventional ultrasonic motor, and to reduce the size of the driver board. As a result, a small driver system capable of multi-channel operation can be realized.

  Next, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a rectangular, single-plate piezoelectric vibrator according to this embodiment. The piezoelectric vibrator 1 is formed 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, but conventionally, only a side ratio d / L of the piezoelectric vibrator 1 of a single plate has been noticed around 0.272. That is, with d / L as a variable, d / L and the resonance frequency of the primary longitudinal vibration mode of the single-plate piezoelectric vibrator are made to correspond to each other, and d / L and the resonance frequency of the secondary longitudinal vibration mode are In the case of correspondence, as shown in FIG. 8, 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, a single-plate piezoelectric vibrator is constituted by the value of d / L at that time. Specifically, in the present embodiment, the value of d / L is substantially 0.63.

  Thereby, the piezoelectric vibrator 1 has a so-called thickness as compared with the case where the side ratio d / L is around 0.272 as in the related art. As a result, since the length in the L direction can be shortened with the same volume as compared with the case where the side ratio d / L is around 0.272, the size can be reduced. 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 conceptually showing a laminated piezoelectric vibrator configured by laminating a plurality of single-plate piezoelectric vibrators 1 formed as described above in the shear direction. In FIG. 5, a part is expressed by cutting. The laminated piezoelectric vibrator 50 includes a piezoelectric layer 51 in which a single-plate piezoelectric vibrator 1 is laminated and an inner layer electrode 52 provided between the piezoelectric layers. The laminated piezoelectric vibrator 50 includes an input electrode 53, two external extraction electrodes 54, and a ground electrode 55.

  For example, when the single-plate piezoelectric vibrator 1 is laminated in eight layers to form the multi-layer piezoelectric vibrator 50, the single-plate piezoelectric vibrator 1 having an input voltage of 200 Vpp is the multi-layer piezoelectric vibrator. In the vibrator 50, the voltage could be lowered to 25Vpp. In this case, since the stacking direction and the displacement direction are perpendicular to each other, the “lateral effect” is used as the piezoelectric effect. Further, in order to further increase the efficiency, it is possible to adopt a configuration using the “vertical effect”. For example, the vertical effect can be used by stacking in the displacement direction. For example, when a single-plate piezoelectric vibrator is polarized in the vertical direction, the drive voltage needs to be 500 Vpp or more. On the other hand, by laminating single-plate piezoelectric vibrators at intervals of 0.5 mm to form a laminated piezoelectric vibrator, it becomes possible to drive with a drive voltage of 10 Vpp or less.

  FIG. 6 is a diagram showing a piezoelectric vibrator to which a cross finger electrode is attached. The piezoelectric vibrator 60 has a cross finger electrode 61 and a ground electrode 62. A similar effect can also be obtained by configuring a laminated piezoelectric vibrator using such a crossed finger electrode 61 and forming an ultrasonic motor by polarization in the direction of the interval between the crossed fingers. Further, the number of stacked layers is small, which is industrially advantageous.

Specifically, when the horizontal effect is used, d31 = 130 × 10 ⁻¹² m / V, and when the vertical effect is used, d33 = 290 × 10 ⁻¹² m / V. When the effect is used, the efficiency can be improved by about 2.2 times the lateral effect.

  FIG. 7 is a diagram illustrating a schematic configuration of the ultrasonic motor device according to the present embodiment. In the ultrasonic motor device 50, the multilayer piezoelectric vibrator 50a slides the drive target 15 in the direction of arrow A or B in FIG. The laminated piezoelectric vibrator 50 has electrodes as shown in FIG. 5, is supplied with voltage from two locations, and the center electrode is grounded.

  In FIG. 7, a driving device 70 includes a position sensor 31 that detects the position of the driven object 15, a resonance driving device 32 that resonates and drives an ultrasonic motor (laminated piezoelectric vibrator) 50 a, and directs the ultrasonic motor 50 a to direct current. A DC drive device 33 for driving and a drive control device (CPU) 34 for sending a drive command signal to the resonance drive device 32 or the DC drive device 33 in accordance with a detection signal of the position sensor 31 are provided. The resonance driving device 32 and the DC driving device 33 share the amplifiers 35a and 35b. Further, the resonance driving device 32 includes a first feedback control device 36 and a phase control device 37. The DC drive device 33 includes a second feedback control device 38 and a signal inverter 39.

  Since the ultrasonic motor 50a is composed of a laminated piezoelectric vibrator, as described above, it is possible to exhibit the same driving force even when the driving voltage is smaller than that of a single-plate piezoelectric vibrator. For this reason, in the amplifiers 35a and 35b, it is not necessary to use a boosting component as in the prior art, and the amplifiers 35a and 35b can be downsized. More specifically, the amplifiers 35a and 35b according to the present embodiment are about 1/3 smaller in size than the conventional amplifier.

  As the position sensor 31, a non-contact optical sensor system using a laser is preferably used. For example, marking (not shown) for indicating the position of the driving object 15 is provided on the driving object 15, and the position sensor 31 detects the position of the driving object 15 from the reflected light pattern.

  When the first feedback control device 36 receives a command signal for resonantly driving the ultrasonic motor 50a from the drive control device (CPU) 34, the first feedback control device 36 generates a resonant drive signal for resonantly driving the ultrasonic motor 50a and amplifies it. Send to 35a, 35b. Further, the first feedback control device 36 receives the detection signal of the position sensor 31 and adjusts the moving speed of the driven object 15. Therefore, the first feedback control device 36 can appropriately change the waveform of the resonance drive signal (for example, change the zero-peak voltage value).

A resonance drive signal having the same waveform is output from the first feedback control device 36 to the amplifiers 35a and 35b. Therefore, the phase of the resonance drive signal sent to one amplifier, that is, the amplifier 35a, is shifted by 90 degrees by the phase controller 37 before being input to the amplifier 35a. For example, when the resonance drive signal output from the first feedback control device 36 is V = V ₀ sin (2πft), this resonance drive signal of V = V ₀ sin (2πft) is input to the amplifier 35b. However, a resonance drive signal of V = V ₀ cos (2πft) or V = −V ₀ cos (2πft) phase-controlled by the phase controller 37 is input to the amplifier 35a.

The resonance drive signal output from the first feedback control device 36 may be V = V ₀ cos (2πft). In this case, the phase controller 37 outputs a resonance drive signal of V = V ₀ sin (2πft) or V = −V ₀ sin (2πft).

  When the second feedback control device 38 receives a command signal for direct drive of the ultrasonic motor 50a from the drive control device (CPU) 34, the second feedback control device 38 generates a direct current voltage signal for direct drive of the ultrasonic motor 50a and amplifies it. Send to 35a, 35b. The second feedback control device 38 can receive a signal from the position sensor 31 and appropriately adjust the voltage value of the DC voltage signal and send it to the amplifiers 35a and 35b.

  The same DC voltage signal is output from the second feedback control device 38 to the amplifiers 35a and 35b. For this reason, the DC voltage signal sent to the amplifier 35a is inverted by the signal inverter 39 before being input to the amplifier 35a.

  As described above, according to the present embodiment, the single-plate piezoelectric vibrator has a so-called thickness and a longer length than the conventional case where the side ratio d / L is around 0.272. The length of the 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. Furthermore, by laminating a plurality of single-plate piezoelectric vibrators formed in this way in the shear direction, a large electric field strength can be applied to the piezoelectric vibrator with the same input voltage as the single plate. The voltage can be reduced. As a result, it is possible to eliminate the step-up component required in the conventional ultrasonic motor, and to reduce the size of the driver board. As a result, a small driver system capable of multi-channel operation can be realized.

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 the piezoelectric vibrator which attached the cross finger electrode. It is a figure which shows schematic structure of the ultrasonic motor apparatus 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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 1a Chip 2 Driven object 2a Sliding chip 15 Drive target 31 Position sensor 32 Resonance drive device 33 DC drive device 34 Drive control device 35a Amplifier 35b Amplifier 36 Feedback control device 37 Phase control device 38 Feedback control device 39 Signal inverter 50 Ultrasonic motor device 50a Multilayer piezoelectric vibrator 51 Piezoelectric layer 52 Inner layer electrode 53 Input electrode 54 Electrode 55 Ground electrode 70 Drive device

Claims (2)

A rectangular single plate piezoelectric vibrator is laminated to form a laminated piezoelectric vibrator, and the laminated piezoelectric vibrator is in a multiple vibration mode combining a primary longitudinal vibration mode and a secondary bending vibration mode. An ultrasonic motor that generates a driving force by vibrating,
The length of the expansion / contraction direction when the single-plate piezoelectric vibrator vibrates in the primary longitudinal vibration mode is L, and the shear direction when the single-plate piezoelectric vibrator vibrates in the secondary bending vibration mode is L. If the length is d,
The single-plate piezoelectric vibrator is formed so that the value of d / L falls within the range of 0.55 to 0.65,
The ultrasonic motor according to claim 1, wherein a plurality of the single-plate piezoelectric vibrators are stacked in the shear direction. A rectangular single plate piezoelectric vibrator is laminated to form a laminated piezoelectric vibrator, and the laminated piezoelectric vibrator is in a multiple vibration mode combining a primary longitudinal vibration mode and a secondary bending vibration mode. An ultrasonic motor that generates a driving force by vibrating,
The length of the expansion / contraction direction when the single-plate piezoelectric vibrator vibrates in the primary longitudinal vibration mode is L, and the shear direction when the single-plate piezoelectric vibrator vibrates in the secondary bending vibration mode is L. If the length is d,
The single-plate piezoelectric vibrator is formed so that the value of d / L is substantially 0.63,
The ultrasonic motor according to claim 1, wherein a plurality of the single-plate piezoelectric vibrators are stacked in the shear direction.

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