JP5275734B2 - Ultrasonic motor - Google Patents

Description

  The present invention relates to an ultrasonic motor that generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a spread vibration mode and a bending vibration mode.

  Conventionally, an ultrasonic motor that generates a driving force by forming a piezoelectric element in a rectangular shape and oscillating in a multiple vibration mode in which a primary longitudinal vibration mode (L1) and a secondary bending vibration mode (F2) are combined. It has been known. For example, Japanese Unexamined Patent Application Publication No. 2006-094597 discloses an ultrasonic transducer in which a plurality of piezoelectric bodies are stacked and driven in the L1F2 resonance mode. The ultrasonic transducer includes piezoelectric elements and internal electrodes that are alternately stacked, and includes an internal electrode group that is substantially divided into four along a second direction and a third direction orthogonal to the stacking direction. ing. In addition, the first external electrode group and the second external electrode group that are electrically connected to the internal electrode group, respectively. Then, by applying a voltage to the first and second external electrode groups, the longitudinal vibration mode generated in the second direction and the bending vibration mode generated in the third direction are excited simultaneously, thereby causing an elliptical Generate vibration.

JP-T-2007-538484 discloses a piezoelectric ultrasonic motor in which a vibrator is formed of a piezoelectric plate having a length L and a height H and is driven in a lame mode. In this piezoelectric ultrasonic motor, a primary asymmetric standing wave is excited by the piezoelectric plate, and the sliding tip makes an elliptical motion to generate a driving force.
JP 2006-094597 A Special table 2007-538484 gazette

  Conventionally, ultrasonic motors have been used for various purposes, but the main characteristics required for ultrasonic motors industrially are small size, high efficiency, and simple structure. Here, the fact that the ultrasonic motor is small means that the resonance frequency of the piezoelectric vibrator is as low as possible. Moreover, high efficiency means that the mechanical-electrical coupling coefficient of the piezoelectric vibrator is large.

  However, when the ultrasonic motor is driven in a multiple vibration mode that combines the primary longitudinal vibration mode (L1) and the secondary bending vibration mode (F2), the main surface is divided into four regions, Electric power must be arranged for each of the electrodes, and the electrodes positioned diagonally must be connected, and the electrode structure must be complicated. Also, when trying to drive the ultrasonic motor in the lame mode, the resonance frequency is higher than in other modes, so when trying to drive at the same resonance frequency as other modes, use other modes. The ultrasonic motor becomes larger than the case, making it difficult to reduce the size.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic motor that is small in size, high in efficiency, and simple in structure.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the ultrasonic motor of the present invention is an ultrasonic motor that generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a spread vibration mode and a bending vibration mode. Of the two sides of the rectangular piezoelectric vibrator, the length of one side is L, the length of the other side is w, and w / L is a variable. When the resonance frequency of the vibration mode is made to correspond, and the w / L is made to correspond to the resonance frequency of the bending vibration mode, the piezoelectric vibrator substantially has a resonance frequency of the expansion vibration and a resonance frequency of the bending vibration. It is characterized by being formed based on the same w / L value.

  In this way, since the resonance frequency of the spread vibration and the resonance frequency of the bending vibration are formed based on the value of w / L, which is substantially the same, the driving is performed in another mode, for example, the L1F2 mode. Also, the shape of the main surface of the piezoelectric vibrator can be made close to a square. As a result, the overall dimension does not become flat, and the depth dimension can be reduced. Thereby, it becomes possible to take a power input larger than the conventional one. The w / L value at which the resonance frequency of the spread vibration and the resonance frequency of the bending vibration are substantially the same means a range in which the piezoelectric vibrator functions practically as an ultrasonic motor. Even if the resonance frequency of the spread vibration and the resonance frequency of the bending vibration are somewhat different, if the piezoelectric vibrator functions practically as an ultrasonic motor, it can be said that the value of w / L is substantially the same. . Conversely, if the piezoelectric vibrator functions practically as an ultrasonic motor, the value of w / L must be the same value as the resonance frequency of the spread vibration and the resonance frequency of the bending vibration. is not.

  (2) The ultrasonic motor of the present invention is an ultrasonic motor that generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a spreading vibration mode and a bending vibration mode. Of the two sets of sides of the rectangular piezoelectric vibrator, the length of one set of sides is L, the length of the other set of sides is w, and w / L is a variable. When L is associated with the resonance frequency of the spreading vibration mode and w / L is associated with the resonance frequency of the bending vibration mode, the piezoelectric vibrator has a value of w / L of 0.75 to 0. It is characterized by being formed so as to be within the range of 90.

  Thus, since the piezoelectric vibrator is formed so that the value of w / L falls within the range of 0.75 to 0.90, the piezoelectric vibrator is more piezoelectric than when driven in other modes, for example, the L1F2 mode. The shape of the main surface of the vibrator can be close to a square. As a result, the overall dimension does not become flat, and the depth dimension can be reduced. As a result, the power input can be made larger than the conventional one.

  (3) In addition, the ultrasonic motor of the present invention is an ultrasonic motor that generates a driving force when a rectangular piezoelectric vibrator vibrates in a multiple vibration mode that combines a spread vibration mode and a bending vibration mode. Of the two sets of sides of the rectangular piezoelectric vibrator, the length of one set of sides is L, the length of the other set of sides is w, and w / L is a variable. When L is associated with the resonance frequency of the spreading vibration mode and w / L is associated with the resonance frequency of the bending vibration mode, the piezoelectric vibrator has a value of w / L substantially equal to 0.85. It is characterized by being formed.

  As described above, the piezoelectric vibrator is formed so that the value of w / L is substantially 0.85. Therefore, the piezoelectric vibrator is more main than the case of driving in another mode, for example, the L1F2 mode. The shape of the surface can be close to a square. As a result, the overall dimension does not become flat, and the depth dimension can be reduced. As a result, the power input can be made larger than the conventional one. Note that the value of w / L is substantially 0.85 means a range in which the piezoelectric vibrator functions practically as an ultrasonic motor. Even if the value of w / L is deviated around 0.85, it can be said that the value of w / L is substantially 0.85 if the piezoelectric vibrator practically functions as an ultrasonic motor. . In other words, the value of w / L does not have to be exactly 0.85 if the piezoelectric vibrator functions practically as an ultrasonic motor.

  (4) In the ultrasonic motor according to the present invention, the piezoelectric vibrator includes two electrodes arranged in parallel on one of the main surfaces, and is applied to at least one of the two electrodes. It is characterized by being driven by voltage.

  Thus, since two electrodes are arranged in parallel on one of the main surfaces, the electrode structure can be simplified as compared with the case of the L1F2 mode.

  (5) In the ultrasonic motor of the present invention, the piezoelectric vibrator applies a first AC voltage to any one of the electrodes, and the first AC voltage to any one of the electrodes. A two-phase signal input method for applying a second AC voltage whose phase is shifted by π / 2, or a one-phase signal input method for applying an AC voltage to one of the electrodes and opening the other electrode It is characterized by driving by either one of the methods.

  With this configuration, the piezoelectric vibrator can be driven by either the two-phase signal input method or the one-phase signal input method.

  According to the present invention, the piezoelectric vibrator is formed based on the value of w / L in which the resonance frequency of the spreading vibration and the resonance frequency of the bending vibration are substantially the same. The shape of the main surface of the piezoelectric vibrator can be made closer to a square than when driven in the L1F2 mode. As a result, the overall dimension does not become flat, and the depth dimension can be reduced. Thereby, it becomes possible to take a power input larger than the conventional one.

  Conventionally, piezoelectric transformers have realized high-operability piezoelectric transformers by using spreading vibration (contour vibration) and avoiding bending vibration (spurious vibration). That is, the piezoelectric transformer has taken measures to avoid bending vibration. The inventor paid attention to this point and found that a driving force is generated by vibrating a rectangular piezoelectric vibrator in a multiple vibration mode in which a spread vibration mode and a bending vibration mode are combined. In addition, the present inventor has known an ultrasonic motor in which two electrodes are arranged in parallel on one main surface of a piezoelectric vibrator. However, in a rectangular piezoelectric vibrator, a resonance frequency of spreading vibration is known. Focusing on the fact that an ultrasonic motor using the case where the resonance frequency of the bending vibration and the resonance frequency of the bending vibration are substantially the same has not been realized, the ultrasonic vibrator is formed by forming the piezoelectric vibrator based on the dimensions at that time. The present inventors have found that it is possible to realize miniaturization, high efficiency and simplification of the configuration of the motor.

  That is, the present invention is an ultrasonic motor in which a rectangular piezoelectric vibrator generates a driving force by vibrating in a multiple vibration mode that combines a spreading vibration mode and a bending vibration mode, and the rectangular piezoelectric vibrator Of the two sets of sides of the vibrator, the length of one set of sides is L, the length of the other set of sides is w, and w / L is a variable. When the frequency is made to correspond and w / L is made to correspond to the resonance frequency of the bending vibration mode, the piezoelectric vibrator has the resonance frequency of the expansion vibration substantially the same as the resonance frequency of the bending vibration. It is formed based on the value of / L.

  As a result, the inventor has made it possible to reduce the size, increase the efficiency, and simplify the configuration. Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

  1 to 3 are plan views of the piezoelectric vibrator according to the present embodiment. The piezoelectric vibrator 1 is made of piezoelectric ceramics and is polarized in a direction perpendicular to the paper surface. A known material such as a lead zirconate titanate ceramic can be used for the piezoelectric vibrator 1. The piezoelectric vibrator 1 is manufactured according to a general ceramic manufacturing process, for example, a manufacturing process of forming (degreasing), firing, and processing of piezoelectric ceramic powder. By applying a silver paste to the manufactured piezoelectric vibrator 1 in a predetermined pattern by screen printing or the like and baking it, two electrodes described later can be provided on one main surface.

  In addition, a sliding chip 2 for transmitting a driving force is provided in the central portion on the upper side with respect to the paper surface of the piezoelectric vibrator 1. The sliding tip 2 is made of a material having excellent wear resistance. For example, ceramic parts such as alumina, zirconia, silicon nitride, and silicon carbide, wear-resistant metal parts such as super-rigid, parts with a ceramic thin film or diamond thin film coated on the surface of a hard metal material, and the like are preferably used.

  2 and 3, sliding chips 3a and 3b may be provided at both ends on the upper side with respect to the paper surface of the piezoelectric vibrator 1 as indicated by dotted lines. When the sliding tip 2 is provided at the center portion on the upper side with respect to the paper surface of the piezoelectric vibrator 1, it is suitable for driving a rotating body such as a disk or a sphere, and with respect to the paper surface of the piezoelectric vibrator 1. When the sliding tips 3a and 3b are provided at both upper ends, it is suitable for driving a linearly moving sliding body. Also, as shown in FIG. 1, the length of one set of the two sides of the rectangular piezoelectric vibrator 1 is L, and the length of the other set of sides is w.

  FIG. 2 is a diagram illustrating a state in which the piezoelectric vibrator 1 is expanding and vibrating. This spreading vibration is a vibration in which the rectangular piezoelectric vibrator 1 repeatedly expands and contracts in the direction of four sides from the center. The potential distribution of the piezoelectric vibrator 1 becomes higher toward the end face with equipotential lines almost in parallel. FIG. 3 is a diagram illustrating a state in which the piezoelectric vibrator 1 is causing bending vibration. The bending vibration means that the rectangular piezoelectric vibrator 1 bends two-dimensionally. However, in the potential distribution, potentials having opposite signs are generated at the output-side central portion and both sides in the width direction. When the expansion vibration mode shown in FIG. 2 and the bending vibration mode shown in FIG. 3 are combined (degenerated), the sliding tip 2 or the sliding tips 3a and 3b perform an elliptical motion, and a driving force is generated.

Next, the driving principle of the ultrasonic motor according to this embodiment will be described. FIG. 4 is a diagram illustrating a frequency spectrum when a rectangular piezoelectric vibrator is vibrated in an expansion vibration mode (Expand Mode) and a bending vibration mode (Flexural Mode). Of the two sets of sides of the rectangular piezoelectric vibrator 1, the length of one set of sides is L and the length of the other set of sides is w. As shown in FIG. Using / L as a variable, w / L and the resonance frequency of the vibration mode of the piezoelectric vibrator are made to correspond, and w / L and the resonance frequency of the bending vibration mode are made to correspond. In FIG. 4, L is fixed at 20 mm, and only w (Width) is changed. In this case, w is 1
7.0 mm, that is, the ratio of the two sides in the vertical and horizontal directions (hereinafter referred to as “side ratio”) w / L is around 0.85, the resonance frequencies of the two coincide, and the two vibrations degenerate. The resonance frequency at this time is 107 kHz to 108 kHz.

  Thus, the side ratio is 0.85, and one side is a square having a length of about 20 mm, so that the size can be reduced.

FIG. 5 is a diagram illustrating a schematic configuration of the ultrasonic motor according to the first embodiment. The ultrasonic motor 10 employs a configuration in which one sliding chip 2 is provided at the center of the left end with respect to the paper surface of the piezoelectric vibrator 1. This configuration is suitable for driving a rotating body such as a disk or a sphere, and in Embodiment 1, the disk 50 is rotated in the direction of the arrow in FIG. In the ultrasonic motor 10, the piezoelectric vibrator 1 is provided with an electrode 4a and an electrode 4b so that one main surface of the rectangular piezoelectric substrate 1b is divided into two. The other main surface is grounded. These electrodes 4a and 4b are individually provided in a state of being insulated from 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, vibration in the spread vibration mode and vibration in the bending vibration mode are generated. When the resonance frequency of the spreading vibration mode and the resonance frequency of the bending vibration mode are equal, both vibration modes are combined (degenerate), and the chip of the piezoelectric vibrator 1 (not shown in FIG. 5) has an elliptical vibration. Will occur. The voltages V ₀ sin ωt and V ₀ cos ωt correspond to the first AC voltage and the second AC voltage, respectively. There is no problem even if the two are interchanged.

  As described above, since two electrodes are arranged side by side on either one of the main surfaces, the main surface is divided into four regions as in the L1F2 mode, and electric power is arranged in each region. The configuration can be made simpler than the configuration in which the electrodes positioned at the corners must be connected.

  FIG. 6 is a diagram illustrating a schematic configuration of the ultrasonic motor according to the second embodiment. The ultrasonic motor 10 employs a configuration in which two sliding chips 3 a and 3 b are provided at both ends at the left end with respect to the paper surface of the piezoelectric vibrator 1. This configuration is suitable for driving a sliding body that operates linearly. In the second embodiment, a slider 61 that is slidably disposed on the linear guide 60 is slid in the direction of the arrow in FIG.

5 and 6 show the configuration of the two-phase signal input, the present invention is not limited to this. For example, as shown in FIG. 7, it is possible to adopt a configuration of a one-phase signal input. In this case, it is also possible to operate by applying an AC signal of V ₀ sin ωt to the one electrode 4b by the AC power source 5a and opening the other electrode 4a.

  As described above, according to this embodiment, the piezoelectric vibrator 1 is formed based on the value of w / L at which the resonance frequency of the spreading vibration and the resonance frequency of the bending vibration are substantially the same. Therefore, the shape of the main surface of the piezoelectric vibrator can be made closer to a square than when driven in another mode, for example, the L1F2 mode. As a result, the overall dimension does not become flat, and the depth dimension can be reduced. Thereby, it becomes possible to take a power input larger than the conventional one.

It is a top view of the piezoelectric vibrator concerning this embodiment. It is a figure which shows a mode that the piezoelectric vibrator 1 is expanding and vibrating. It is a figure which shows a mode that the piezoelectric vibrator 1 is raising the bending vibration. It is a figure which shows a frequency spectrum when a rectangular-shaped piezoelectric vibrator is vibrated in an expansion vibration mode (Expand Mode) and a bending vibration mode (Flexural Mode). 1 is a diagram illustrating a schematic configuration of an ultrasonic motor according to Embodiment 1. FIG. 6 is a diagram illustrating a schematic configuration of an ultrasonic motor according to Embodiment 2. FIG. It is a figure which shows schematic structure of the ultrasonic motor of a 1 phase signal input system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 1b Piezoelectric substrate 2 Sliding tip 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 oscillating in a multiple vibration mode that combines a spread vibration mode and a bending vibration mode,
Of the two sets of sides of the rectangular piezoelectric vibrator, the length of one set of sides is L, the length of the other set of sides is w, w / L is a variable, and w / L When the resonance frequency of the spreading vibration mode is made to correspond, and w / L and the resonance frequency of the bending vibration mode are made to correspond,
In the piezoelectric vibrator, the w / L value is in the range of 0.75 to 0.90 based on the w / L value at which the resonance frequency of the spreading vibration and the resonance frequency of the bending vibration are substantially the same. It is formed to fit in,
Two electrodes juxtaposed on one main surface of the piezoelectric vibrator;
A first AC power source for driving the piezoelectric vibrator by applying an AC voltage to one of the two electrodes;
A second AC power source for driving the piezoelectric vibrator by applying an AC voltage to the other of the two electrodes;
The first AC power source applies a first AC voltage to one of the two electrodes, and the second AC power source applies to the other of the two electrodes. The ultrasonic motor according to claim 1, wherein the piezoelectric vibrator is driven by a two-phase signal input method by applying a second AC voltage whose phase is shifted by π / 2 from the first AC voltage . A rectangular piezoelectric vibrator is an ultrasonic motor that generates a driving force by oscillating in a multiple vibration mode that combines a spread vibration mode and a bending vibration mode,
Of the two sets of sides of the rectangular piezoelectric vibrator, the length of one set of sides is L, the length of the other set of sides is w, w / L is a variable, and w / L When the resonance frequency of the spreading vibration mode is made to correspond, and w / L and the resonance frequency of the bending vibration mode are made to correspond,
In the piezoelectric vibrator, the w / L value is in the range of 0.75 to 0.90 based on the w / L value at which the resonance frequency of the spreading vibration and the resonance frequency of the bending vibration are substantially the same. It is formed to fit in,
Two electrodes juxtaposed on one main surface of the piezoelectric vibrator;
An AC power source for driving the piezoelectric vibrator by applying an AC voltage to one of the two electrodes;
The AC power source applies an AC voltage to one of the two electrodes, and the other electrode is opened, so that the piezoelectric vibrator is driven by a one-phase signal input method. Ultrasonic motor characterized by The ultrasonic motor according to claim 1 , wherein the piezoelectric vibrator is formed so that the value of w / L is substantially 0.85.

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