JP2004289894A - Ultrasonic motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic motor which can make a driven body generate arbitrary movement. <P>SOLUTION: The ultrasonic motor 100 has a base 11, a horn 12, a head 13, and piezoelectric actuators 14a, 14b, 15a, and 15b provided at opposed faces of the base 11. For example, the ultrasonic motor makes a metal ball 16 rotate clockwise or counterclockwise about its vertical axis by keeping the ultrasonic motor 100 in a vertical attitude, and putting the metal ball 16 as a driven body on a head 13 by driving the piezoelectric actuators 14a, 14b, 15a, and 15b at specified frequencies. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３９】
周波数が約１０９ｋＨｚでは、１次の擬似曲げモードを主とし、少しの１次のＺ方向伸縮モード（１２０ｋＨｚの共振の低周波数側の裾）と、僅かの１次のねじりモード（１４５ｋＨｚの共振の低周波数側の裾）によって、金属球１６を動かす。このような３種類の振動モードが合わさる、つまり、ヘッド１３がＺ軸の近傍で揺れ、かつ、Ｚ方向に伸縮しながら、しかもＺ軸回りの回転の力が金属球１６に作用することによって、金属球１６を時計回り（ＣＷ）に回転させることができる。なお、擬似曲げモードの正確な運動軌跡が不明であるために、ここではヘッド１３を金属球１６との間の力の経時変化についての詳細な説明は行わず、実際に金属球１６を動かすことができるという事実のみの記載に止める。
【００４０】
周波数が約１４５ｋＨｚでは、１次のねじりモードと、１次のＺ方向伸縮モード（１２０ｋＨｚの共振の高周波数側の裾）とによって、金属球１６を動かす。この場合には、ヘッド１３は、（ａ）＋Ｚの向き（ベース部１１からヘッド１３に向かう向き）に伸張しながらＺ軸回りに反時計回り（ＣＣＷ）に回転する運動と、（ｂ）−Ｚの向き（ヘッド１３からベース部１１に向かう向き）に縮退しながら時計回り（ＣＷ）に回転する運動とを交互に繰り返す。（ａ）の運動では、金属球１６に掛かる重力の向きとヘッド１３が伸張する向きとが逆であるために金属球１６とヘッド１３との間の摩擦力が大きくなり、金属球１６はヘッド１３の（ａ）の運動による力を受けて反時計回り（ＣＣＷ）に回転しようとする。これに対し、ヘッド１３が（ｂ）の運動を行う際には、金属球１６に掛かる重力の向きとヘッド１３が後退する向きが同じであるために金属球１６とヘッド１３との間の摩擦力が小さくなり、しかも１４５ｋＨｚという周波数では金属球１６がこのヘッド１３の運動に追従することができずに、金属球１６とヘッド１３との間が滑る。この結果として、金属球１６にはヘッド１３の（ａ）の運動による力が支配的に作用することとなり、これによって金属球１６には反時計回り（ＣＣＷ）の回転が生ずる。
【００４１】
周波数が約１９０ｋＨｚでは、２次のねじりモードと、１次のヘッド１３の径方向モードとによって、金属球１６を動かす。図１２はこの１９０ｋＨｚにおいてヘッド１３に生ずる振動を模式的に示す説明図である。２次のねじりモードによる回反振動Ｓ_１と、ヘッド１３の１次の径方向振動Ｓ_２とが合成されることによって、ヘッド１３の表面には、渦巻状の振動Ｓが生ずる。
【００４２】
先に示した図４に示されているように、金属球１６とヘッド１３との間には圧力Ｎ（＝接触圧／単位径）が作用しているから、ヘッド１３の静止時の直径をｒとすると、直径ｒが長くなる（ヘッド１３が拡がる）ときには圧力Ｎは小さくなり、逆に直径ｒが短くなるときには圧力Ｎが大きくなる。このため、ヘッド１３が反時計回り（ＣＣＷ）に回転する際にヘッド１３の直径が短くなると金属球１６は反時計回り（ＣＣＷ）に回転し、ヘッド１３が時計回り（ＣＷ）に回転する際にヘッド１３の直径が短くなると金属球１６は時計回り（ＣＷ）に回転する。駆動電圧がＶ＝Ｖ_０ｓｉｎ（２πｆｔ）の場合には、金属球１６が反時計回り（ＣＣＷ）に回転するように渦巻状の振動が発生する。なお、圧電駆動部１４ａ等の駆動電圧がＶ＝−Ｖ_０ｓｉｎ（２πｆｔ）の場合には、金属球１６が時計回り（ＣＷ）に回転するように渦巻状の振動が発生する。
【００４３】
周波数が約２２１〜２２６ｋＨｚでは、３次のねじりモードとＺ方向伸縮モードとによって金属球１６を反時計回り（ＣＣＷ）に回転させ、周波数が約２２７〜２３５ｋＨｚでは、３次のねじりモードとＺ方向伸縮モードとによって金属球１６を時計回り（ＣＷ）に回転させる。これは、約２２６．５ｋＨｚにおいて、ねじりモードとＺ方向伸縮モードの位相が１８０度ずれる現象が起こることによる。
【００４４】
図１３はこのような位相の変化を示す説明図であり、図１３（ａ）は金属球１６を時計回り（ＣＷ）に回転させる場合を、図１３（ｂ）は金属球１６を反時計回り（ＣＣＷ）に回転させる場合をそれぞれ示しており、Ｎはヘッド１３と金属球１６との間の圧力を、Ｕｔｒはヘッド１３のねじれ変位を、ＵａｘはＺ方向変位を示している。ねじれ変位Ｕｔｒは横軸よりも上にあるときには時計回り（ＣＷ）であり、横軸よりも下にあるときには反時計回り（ＣＣＷ）である。また、圧力Ｎはヘッド１３のＺ方向における振動と同期しており、ヘッド１３が上昇（＋Ｚの向きに変位）する際に大きくなり、下降（−Ｚの向きに変位）する際に小さくなる。
【００４５】
図１３（ａ）では、Ｚ方向変位Ｕａｘが大きくなるときにねじれ変位Ｕｔｒが大きくなっているので、金属球１６は時計回り（ＣＷ）に回転する。なお、この場合には、圧力Ｎとねじれ変位Ｕｔｒとの間では理論的には位相差は生じないが、実測によれば図１３（ａ）に示されるように、ねじれ変位Ｕｔｒの位相が９０度進んでいた。この金属球１６が時計回り（ＣＷ）に回転するときのねじれ変位ＵｔｒとＺ方向変位Ｕａｘの理論的に位相差のない状態を基準とすると、図１３（ｂ）に示されるように、約２２１〜２２６ｋＨｚではねじれ変位ＵｔｒとＺ方向変位Ｕａｘの位相が１８０度ずれて、Ｚ方向変位Ｕａｘが大きくなるときにねじれ変位Ｕｔｒが小さくなるので、金属球１６は反時計回り（ＣＣＷ）に回転する。なお、２２１〜２３５ｋＨｚの範囲において金属球１６が回転しているときには、Ｚ方向伸縮モードは正確には、共振状態ではないこととなる。
【００４６】
上述した周波数よりも高い周波数においても、上述した各種の振動モードの組合せによって、金属球１６を所定の方向に回転させることができる。例えば、約４００ｋＨｚにおいては６次のねじれモードとＺ方向伸縮モードによって金属球１６を反時計回り（ＣＣＷ）に回転させることができ、約４７２ｋＨｚ〜４８０ｋＨｚにおいては高次のねじれモードとＺ方向伸縮モードによって、３次のねじれモードとＺ方向伸縮モードが発生する場合と同様に、金属球１６を反時計回り（ＣＣＷ）または時計回り（ＣＷ）に回転させることができ、約１．０２ＭＨｚにおいてはさらに高次のねじれモードとＺ方向伸縮モードによって金属球１６を反時計回り（ＣＣＷ）または時計回り（ＣＷ）に回転させることができる。
【００４７】
超音波モータ１００における圧電駆動部１４ａ等の駆動方法は、上述した方法に限られず、例えば、駆動電極２２ａ・２２ｂ・２４ａ・２４ｂに同位相の電圧Ｖ＝−Ｖ_０ｓｉｎ（２πｆｔ）を印加してもよい。この場合には上述した各共振周波数において金属球１６の回転方向が逆転する。
【００４８】
また、駆動電極２２ａ・２２ｂに電圧Ｖ＝Ｖ_０ｓｉｎ（２πｆｔ）を印加して圧電駆動部１４ａ・１４ｂを駆動し、圧電駆動部１５ａ・１５ｂを駆動させないという方法で金属球１６を動かすこともできる。この場合には駆動周波数が１０９ｋＨｚのときにＺ−Ｘ面内における１次の曲げモード（先に図１０に示した曲げモードと同様）の振動が生ずるために、これとＺ方向伸縮モードの振動が重なり合うことによって、金属球１６をＹ軸回りに回転させることができる。また、駆動周波数が１８１ｋＨｚの場合にはＺ−Ｘ面内における２次の曲げモードの振動が生じるために、これとＺ方向伸縮モードの振動とが重なり合うことによって金属球１６をＹ軸回りに回転させることができる。なお、駆動周波数が１０９ｋＨｚの場合と１８１ｋＨｚの場合では金属球１６の回転の向きは逆である。
【００４９】
さらに、駆動電極２２ａ・２２ｂに電圧Ｖ＝Ｖ_０ｓｉｎ（２πｆｔ）を印加して圧電駆動部１４ａ・１４ｂを駆動し、圧電駆動部１５ａ・１５ｂを駆動させない場合には、駆動周波数１１０ｋＨｚにおいてＹ−Ｚ面内における１次の曲げモードの振動が生ずるために、これとＺ方向伸縮モードの振動とが重なり合うことによって、金属球１６をＸ軸回りに回転させることができる。また、駆動周波数１８４ｋＨｚにおいてＹ−Ｚ面内における２次の曲げモードの振動が生じるために、これとＺ方向伸縮モードの振動との重なりによって金属球１６をＸ軸回りに回転させることができる。なお、駆動周波数が１１０ｋＨｚの場合と１８４ｋＨｚの場合では金属球１６の回転の向きは逆である。
【００５０】
さらにまた、駆動電極２２ａ・２２ｂには電圧Ｖ＝Ｖ_０ｓｉｎ（２πｆｔ）を印加し、同時に駆動電極２４ａ・２４ｂには電圧Ｖ＝−Ｖ_０ｓｉｎ（２πｆｔ）を印加することによって、圧電駆動部１４ａ等を駆動することもできる。この場合には、所定の共振周波数およびその近傍において、金属球１６にＹ軸回りの回転またはＸ軸回りの回転を生じさせることができる。
【００５１】
以上、本発明の実施の形態について説明したが、本発明はこのような形態に限定されるものではない。例えば、１枚の圧電セラミック板２１に分極の向きの異なる２つの圧電駆動部１４ａ・１４ｂを形成した形態を示したが、図１４の平面図に示すように、表裏面に電極（図示せず）が形成された２枚の圧電セラミック板３１ａ・３１ｂを所定の間隔を空けてベース部１１に貼り付けることによって、圧電駆動部３２ａ・３２ｂを形成してもよい。同様にして、表裏面に電極（図示せず）が形成された２枚の圧電セラミック板３３ａ・３３ｂを所定の間隔を空けてベース部１１に貼り付けることによって、圧電駆動部３４ａ・３４ｂを形成することができる。
【００５２】
また、圧電駆動部１４ａ等における分極の向きは、図１に示した状態に限定されない。例えば、図１５は図４と同様に示す平面図であり、圧電駆動部１４ａの分極の向きは矢印＋Ｐの向きのまま、圧電駆動部１４ｂの分極の向きを矢印−Ｐから矢印＋Ｐの向きに変える（以下「圧電駆動部１４ｂ´」いう）。また、圧電駆動部１５ｂの分極の向きは矢印＋Ｑの向きのまま、圧電駆動部１５ａの分極の向きを矢印−Ｑから矢印＋Ｑの向きに変える（以下「圧電駆動部１５ａ´」いう）。この場合において、圧電駆動部１４ａ・１５ｂには電圧Ｖ＝Ｖ_０ｓｉｎ（２πｆｔ）を印加し、圧電駆動部１４ｂ´・１５ａ´には電圧Ｖ＝−Ｖ_０ｓｉｎ（２πｆｔ）を印加すれば、結果的に、圧電駆動部１４ａ・１５ｂの伸縮と圧電駆動部１４ｂ´・１５ａ´の伸縮の位相を１８０度ずらすことができるために、圧電駆動部１４ａ等を電圧Ｖ＝Ｖ_０ｓｉｎ（２πｆｔ）で駆動する場合と同様に、金属球１６をＺ軸回りに回転させることができる。また、圧電駆動部１４ａ・１４ｂ´を電圧Ｖ＝Ｖ_０ｓｉｎ（２πｆｔ）で駆動し、かつ、圧電駆動部１５ａ´・１５ｂを電圧Ｖ＝−Ｖ_０ｓｉｎ（２πｆｔ）で駆動することによって、金属球１６にＹ軸回りまたはＸ軸回りの回転を生じさせることができる。
【００５３】
上記説明においては被駆動体として金属球１６を例示したが、被駆動体はこれに限定されるものではない。例えば、Ｚ方向を長手方向とするスピンドルのＺ方向端面にヘッド１３の表面を押し当てれば、このスピンドルを回転させることができる。また、ヘッド１３のステージの裏面に押し当て、金属球１６をＸ軸回りまたはＹ軸回りに回転させる駆動条件において超音波モータ１００を駆動すると、このステージをＸ−Ｙ方向に移動させることができる。超音波モータ１００のＺ方向が水平方向となるように超音波モータ１００を保持する場合等には、超音波モータ１００のヘッド１３と被駆動体との間に適切な摩擦力が作用するように、超音波モータ１００を被駆動体に押圧すればよい。
【００５４】
【発明の効果】
上述の通り、本発明によれば、４つの圧電駆動部の変位の位相をずらすことによって、接頭部に種々の方向の振動を生じさせることができる。このため、被駆動体を接頭部の動きに合わせて適切に配置しておくことによって、被駆動体に所定の動きを生じさせることができる。例えば、本発明の超音波モータは、Ｘ−Ｙステージをスライドさせるための駆動装置や、各種回転装置の回転モータ、として用いることができる。本発明の超音波モータによれば、各種機械の駆動源を省スペース化し、各種機械を小型化することができる。
【図面の簡単な説明】
【図１】本発明の超音波モータに用いられる圧電アクチュエータの概略構造を示す説明図。
【図２】図１に示す圧電アクチュエータの基本的な変位形態を示す説明図。
【図３】圧電アクチュエータの共振周波数を示すグラフ。
【図４】本発明に係る超音波モータの構造を示す概略側面図。
【図５】図４に示す超音波モータの概略平面図。
【図６】図４に示す超音波モータの概略底面図。
【図７】超音波モータのベース部のねじりモードによる変形を模式的に示す説明図。
【図８】超音波モータ１００に生ずる伸縮モードの発生形態を示す説明図。
【図９】ヘッドに生ずる径方向の伸縮振動を示す断面図。
【図１０】Ｘ方向の曲げモードを示す説明図。
【図１１】超音波モータの主要部分の寸法を示す説明図。
【図１２】周波数１９０ｋＨｚにおいてヘッドに生ずる振動を模式的に示す説明図。
【図１３】周波数２２１〜２３５ｋＨｚにおける振動モードの位相差を示す説明図。
【図１４】圧電駆動部の別の配設形態を示す平面図。
【図１５】圧電駆動部のさらに別の配設形態を示す平面図。
【符号の説明】
１０；圧電アクチュエータ
１１；ベース部
１２；ホーン部
１３；ヘッド
１４ａ・１４ｂ・１４ｂ´；圧電駆動部
１５ａ・１５ａ´・１５ｂ；圧電駆動部
１６；金属球
２１；圧電セラミック板
２２ａ・２２ｂ；駆動電極
２２ｃ；共通電極
２３；圧電セラミック板
２４ａ・２４ｂ；駆動電極
２４ｃ；共通電極
２６；ネジ穴
２７；孔部
２８；ボルト
２８ａ・２８ｂ；ネジ切り部
２８ｃ；円柱部
２９；固定部材
３１ａ・３１ｂ；圧電セラミック板
３２ａ・３２ｂ；圧電駆動部
３３ａ・３３ｂ；圧電セラミック板
３４ａ・３４ｂ；圧電駆動部
１００；超音波モータ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic motor that can be used as a driving device for various machines.
[0002]
[Prior art]
As an ultrasonic motor having a rod shape, Japanese Patent Application Laid-Open No. 7-107756 discloses an ultrasonic motor including a stator ring, a Langevin type vibrator, and a rotor. Here, the vibrator is made of a piezoelectric ceramic and a metal terminal, and the shapes and sizes of the piezoelectric ceramic and the metal terminal are set so that the resonance frequency of the length vibration of the vibrator and the resonance frequency of the bending vibration are substantially equal. I have. Further, the piezoelectric ceramic has a substantially equally divided drive unit in which the directions of polarization are reversed. In such an ultrasonic motor, an elliptical motion is generated at the tip of the vibrator by applying a predetermined AC voltage to the piezoelectric ceramic, whereby the rotor can be rotated in a predetermined direction. Further, by shifting the phase of the AC voltage applied to the piezoelectric ceramics by 180 degrees, the direction of rotation of the elliptical motion can be reversed, whereby the rotation direction of the rotor can be reversed.
[0003]
[Patent Document 1]
JP-A-7-107756 (FIG. 2, paragraphs 7 to 10)
[0004]
[Problems to be solved by the invention]
However, in the ultrasonic motor having such a rod-like shape, the elliptical motion of the portion in contact with the driven body can be generated only in the same plane. Therefore, when this ultrasonic motor is used, for example, as a linear motor, the driven body can be moved only in one direction.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic motor capable of causing a driven body to make an arbitrary movement.
[0005]
[Means for Solving the Problems]
According to the present invention, a substantially rectangular parallelepiped base portion having surfaces in the Y direction, the X direction, and the Z direction orthogonal to each other,
A substantially conical horn portion disposed on one surface of the Z-direction surface of the base portion;
A prefix provided near the apex of the horn portion and in contact with the driven body;
Four substantially rectangular piezoelectric driving units provided on both surfaces of the base unit in the Y direction and separated in the X direction and polarized in the Y direction;
Holding means for holding the base portion;
With
An ultrasonic motor is provided, wherein a predetermined vibration is applied to the prefix by applying a voltage of a predetermined frequency to the piezoelectric driving unit to move the driven body.
[0006]
In such an ultrasonic motor, vibrations in various directions can be generated in the prefix by displacing the four piezoelectric driving units with their phases shifted. Therefore, by arranging the driven body appropriately in accordance with the movement of the prefix, it is possible to cause the driven body to make a predetermined movement. For example, in order to slide the XY stage, it has conventionally been necessary to use a combination of two ultrasonic motors that can be driven only in one direction. However, if the ultrasonic motor of the present invention is used, the XY stage can be slid by one unit, and the space for disposing the driving source can be saved. Note that the piezoelectric drive unit is specifically a substantially rectangular piezoelectric ceramic element having a longitudinal direction in the Z direction, a width direction in the X direction, a thickness direction in the Y direction, and electrodes provided on the front and back surfaces.
[0007]
There is no limitation on the direction of polarization of the four piezoelectric driving units. For example, the directions of polarization of the four piezoelectric driving units are opposite to each other in the Y direction for the two piezoelectric driving units provided on the same surface, and The two piezoelectric driving units symmetrically positioned with respect to the Z-axis passing through the center of the Z-direction plane have opposite directions in the Y-direction. In this case, by driving the four piezoelectric driving units with the same phase driving voltage using the base unit as a common electrode, it is possible to cause the driven body to move in a predetermined manner. In this case, there is an advantage that the drive power supply can be configured at low cost.
[0008]
In the ultrasonic motor according to the present invention, a hole is formed in the base from the center of the Z-direction surface where the horn is not provided to the horn, and the holding means includes a piezoelectric drive in the hole. It is preferable that the base portion is held at a position corresponding to the center of the portion in the Z direction. One of the reasons for holding the base portion in this way is that the nodes of various vibrations generated in the base portion are located at positions corresponding to the center of the piezoelectric drive portion in the Z direction. Further, it is preferable to form another four holes provided in the base portion in a diagonal of the Z-direction surface of the base portion and provided in parallel with the holes so as to communicate with the holes. By forming these other four holes in the base portion, the base portion is easily deformed, and the vibration of the piezoelectric driving portion efficiently excites the vibration of the base portion. It is preferable that the prefix has a substantially disk shape whose radial direction is a direction perpendicular to the Z direction. The driven body is appropriately arranged so as to be in contact with the surface or side surface of the prefix depending on the vibration direction of the prefix.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing a schematic structure of a piezoelectric actuator 10 used in an ultrasonic motor according to the present invention. FIG. 1 (a) is a schematic perspective view of the piezoelectric actuator 10, and FIG. FIG. 2 is an explanatory view showing the parts of the piezoelectric actuator 10 disassembled to show the structure of FIG.
[0010]
The piezoelectric actuator 10 includes a rectangular parallelepiped base portion 11, a substantially conical horn portion 12 disposed on a Z-direction surface (a surface perpendicular to the Z axis) of the base portion 11, and a Y-direction surface ( And piezoelectric actuators 14a, 14b, 15a, and 15b (hereinafter, referred to as “piezoelectric actuators 14a and the like”) provided on a surface perpendicular to the Y axis.
[0011]
The base portion 11 elastically deforms by following the displacement generated in the piezoelectric driving portion 14a or the like when the piezoelectric driving portion 14a or the like is driven at a predetermined frequency, and a material whose vibration is hardly attenuated, such as phosphor bronze or titanium, It is made of a metal material such as stainless steel. Horn 12 is preferably integral with base 11.
[0012]
A piezoelectric ceramic plate 21 is attached to one of the Y-direction surfaces of the base portion 11, a common electrode 22c is formed on the entire back surface of the piezoelectric ceramic plate 21, and the surface thereof has substantially the same shape divided in the X direction. Are formed, a portion sandwiched between the drive electrode 22a and the common electrode 22c becomes a piezoelectric drive portion 14a, and a portion sandwiched between the drive electrode 22b and the common electrode 22c is a piezoelectric drive portion. 14b. In the piezoelectric drive unit 14a and the piezoelectric drive unit 14b, the polarization direction of the piezoelectric ceramic plate 21 is reversed as shown by arrows + P and -P in FIG.
[0013]
Similarly, a piezoelectric ceramic plate 23 is attached to another surface of the base portion 11 in the Y direction, and a common electrode 24c is formed on the entire back surface of the piezoelectric ceramic plate 23, and the surface thereof is substantially divided in the X direction. Drive electrodes 24a and 24b having the same shape are formed, the portion sandwiched between the drive electrode 24a and the common electrode 24c becomes the piezoelectric drive portion 15a, and the portion sandwiched between the drive electrode 24b and the common electrode 24c. Are the piezoelectric driving units 15b. In the piezoelectric drive unit 15a and the piezoelectric drive unit 15b, the polarization direction of the piezoelectric ceramic plate 23 is opposite as shown by arrows -Q and + Q in FIG.
[0014]
Thus, the directions of polarization in the piezoelectric driving units 14a, 14b, 15a, and 15b are symmetric with respect to the Z axis. That is, in the piezoelectric driving units 14a and 15b that are symmetrical with respect to the Z axis, the polarization direction is outward from the base unit 11. In other words, the polarization directions of the piezoelectric driving units 14a and 15b are opposite in the Y direction. In addition, in the piezoelectric driving unit 14b and the piezoelectric driving unit 15a that are symmetrical with respect to the Z axis, the polarization direction is from the outside to the base unit 11, and the polarization direction of the piezoelectric driving unit 14b and the piezoelectric driving unit 15a is also Y. The direction is opposite.
[0015]
Here, the basic driving principle of the piezoelectric driving unit 14a and the like will be described. FIG. 2 is an explanatory diagram showing a basic displacement mode of the piezoelectric actuator 10. FIG. FIG. 2A shows an example of a displacement mode of the piezoelectric drive unit 14a and the like included in the piezoelectric actuator 10, and FIG. 2B shows the displacement of the piezoelectric drive unit 14a and the like shown in FIG. 10 schematically shows the displacement (torsional displacement) generated in the base portion 11 (and the horn portion 12) of the ten.
[0016]
When a DC voltage is applied such that the common electrode 22c becomes a negative electrode (earth electrode) and the driving electrodes 22a and 22b become positive electrodes (high-potential electrodes), the piezoelectric driving unit 14a having the same direction of the electric field and the direction of polarization is applied to the piezoelectric driving unit 14a. Displacement that expands in the Z direction occurs, while displacement that contracts in the Z direction occurs in the piezoelectric driving unit 14b in which the direction of the electric field and the direction of polarization are opposite. As a result, the piezoelectric ceramic plate 21 is displaced so as to deform into a fan shape. Similarly, when a DC voltage is applied such that the common electrode 24c becomes a negative electrode and the drive electrodes 24a and 24b become positive electrodes, the piezoelectric drive unit 15a, whose electric field direction and polarization direction are opposite, is displaced in the Z direction. On the other hand, a displacement that extends in the Z direction occurs in the piezoelectric driving unit 15b in which the direction of the electric field and the direction of the polarization are the same. As a result, the piezoelectric ceramic plate 23 is also deformed into a fan shape.
[0017]
As described above, in the piezoelectric ceramic plate 21, the expansion and contraction of the piezoelectric driving unit 14a and the piezoelectric driving unit 14b are opposite, and in the piezoelectric ceramic plate 23, the expansion and contraction of the piezoelectric driving unit 15a and the piezoelectric driving unit 15b are opposite. The displacement of the portion 14a and the like is symmetric about the Z axis. As a result, when viewed from the horn part 12 side to the base part 11 side, a clockwise (CW) displacement around the Z-axis occurs near the Z-direction surface of the base part 11, and a displacement in the Z-direction central part of the base part 11 occurs. A counterclockwise (CCW) displacement about the Z axis occurs. Such a displacement causes a torsional displacement in the base portion 11.
[0018]
At the tip of the horn portion 12, the same clockwise (CW) displacement as in the vicinity of the Z-direction surface of the base portion 11 occurs. In order to efficiently transmit the displacement of the piezoelectric drive section 14a and the like to the base section 11, a hard adhesive such as epoxy resin is preferably used for attaching the piezoelectric ceramic plates 21 and 23 to the base section 11. . In order to increase the amount of expansion and contraction displacement in DC driving, the piezoelectric constant d ₃₁ However, as described later, the piezoelectric actuator 10 is suitably used as an ultrasonic motor. In this case, the piezoelectric actuator 14a and the like are driven to resonate. For this reason, as the piezoelectric ceramic plates 21 and 23, a material having a large mechanical quality factor Qm and a small dielectric loss δ is preferably used.
[0019]
The displacement mode of the piezoelectric actuator 10 shown in FIG. 2 is a case of DC drive, and when the piezoelectric actuator 10 is driven in resonance, in addition to the above-described torsional mode vibration, vibrations of other vibration modes, for example, Z A stretching vibration in the direction occurs. FIG. 3 is a graph showing an example of the resonance characteristics of the piezoelectric actuator 10. FIG. 3 (a) shows the relationship between the speed and the frequency of the Z-axis stretching vibration, and FIG. 3 (b) shows the relationship between the speed and the frequency of the torsional vibration. Are shown respectively. The frequency indicating the maximum in each graph is a resonance frequency of some mode. When the piezoelectric actuator 10 is driven to resonate at a predetermined frequency, a complex vibration in which a plurality of such different types of vibration modes are combined is generated. Therefore, a configuration of an ultrasonic motor using the piezoelectric actuator 10 and a driving method thereof will be described next.
[0020]
FIG. 4 is a schematic side view showing the structure of the ultrasonic motor 100, FIG. 5 is a schematic plan view of the ultrasonic motor 100, and FIG. 6 is a schematic bottom view of the ultrasonic motor 100. Here, a form in which the ultrasonic motor 100 is held in a substantially vertical posture is shown. The ultrasonic motor 100 has a structure in which a head 13 is provided at a tip of a horn portion 12 of a piezoelectric actuator 10, and the head 13 is in contact with a metal ball 16. The metal sphere 16 is an example of a driven body. A frictional force is generated between the head 13 and the metal ball 16 by using the force of the head 13 supporting the metal ball 16 as a preload, in other words, by utilizing the gravity applied to the metal ball 16.
[0021]
A screw hole 26 for holding the base portion 11 is formed in the base portion 11, and four screw holes 26 (diagonal positions on the Z-direction surface) around the screw hole 26 are formed in parallel with the screw hole 26. And four holes 27 communicating with the holes. These screw holes 26 and holes 27 have a depth from the bottom surface of the base portion 11 to the vicinity of the bottom surface of the horn portion 12. In the screw hole 26, the screw is cut only to the position corresponding to the center in the Z direction such as the piezoelectric drive unit 14a.
[0022]
The bolt 28 fitted into the screw hole 26 has threaded portions 28a and 28b threaded at both ends, and has a structure in which a cylindrical portion 28c is formed between the threaded portions 28a and 28b. I have. The threaded portion 28 a of the bolt 28 is inserted up to the tip of the threaded portion at the back of the screw hole 26, whereby the base 11 is held by the bolt 28. The outer diameter of the cylindrical portion 28c is shorter than the inner diameter of the screw hole 26, so that the cylindrical portion 28c does not contact the base portion 11. Further, the threaded portion 28b of the bolt 28 is fitted with a fixing member 29 for fixing the bolt 28, thereby fixing the ultrasonic motor 100.
[0023]
The horn section 12 is used to efficiently transmit the ultrasonic vibration generated in the base section 11 to the head 13 when the piezoelectric driving section 14a or the like is driven to resonate, as will be described later. In order to reduce the ultrasonic vibration loss, it is preferable that the horn portion 12 is made of a metal material such as phosphor bronze, titanium, and stainless steel. The horn part 12 plays a role of expanding the vibration generated in the base part 11. For the same reason, it is preferable that the head 13 is also integrated with the horn portion 12. A recess is provided on the upper surface of the head 13 so that the metal ball 16 can be supported.
[0024]
Next, the driving mode of the ultrasonic motor 100 will be described. As described above, since the base portion 11 is made of a metal material, the common electrodes 22c and 24c provided on the piezoelectric ceramic plates 21 and 23 are electrically connected to the base portion 11. Therefore, a ground electrode for driving the piezoelectric drive unit 14a and the like is attached to the base unit 11. The drive electrodes 22a, 22b, 24a, and 24b have, for example, one-phase AC voltage V = V at a frequency at which the ultrasonic motor 100 substantially drives in resonance. ₀ sin (2πft) (V ₀ A zero-peak voltage value, f; frequency, t; time).
[0025]
There are four basic vibration modes generated in the portion from the base portion 11 to the head 13 when the piezoelectric driving portion 14a and the like are driven, and at least two of these four vibration modes overlap each other to cause a metal ball. 16 can be moved. Hereinafter, each vibration mode will be outlined.
[0026]
The first vibration mode is the torsional mode previously shown in FIG. FIG. 7 is an explanatory view schematically showing a state of deformation of the base portion 11 in the torsion mode. As described above, the polarization directions of the piezoelectric driving units 14a and 14b are opposite, the polarization directions of the piezoelectric driving units 15a and 15b are opposite, and the polarization directions of the piezoelectric driving units 14a, 14b, 15a, and 15b. Are symmetric about the Z axis. FIG. 7 does not show the direction of polarization of the piezoelectric drive unit 14a and the like.
[0027]
Therefore, for example, the drive electrodes 22a, 22b, 24a, 24b ₀ 7A, a clockwise torsional displacement (CW) about the Z-axis as a rotation center occurs in the base portion 11 as shown in FIG. 7A. Subsequently, the voltage V becomes V ₀ ~ -V ₀ 7B, a counterclockwise torsional displacement (CCW) occurs in which the direction of the clockwise torsional displacement (CW) is reversed, as shown in FIG. 7B. Further, the voltage is -V ₀ ~ V ₀ 7A, the same clockwise torsional displacement (CW) as in FIG. 7A occurs. When an in-phase AC voltage is applied to the drive electrodes 22a, 22b, 24a, and 24b in this manner, torsional vibration around the Z-axis occurs in the base portion 11, and this torsional vibration is transmitted through the horn portion 12 to the head. The torsion vibration is generated in the head 13.
[0028]
Note that the vibration in the torsion mode has a central portion in the Z direction such as the piezoelectric drive unit 14a as a node of the vibration. Since the bolt 28 holds the base 11 at the center of the base 11 in the Z direction, the ultrasonic motor 100 has a structure in which the bolt 28 does not easily hinder torsional vibration of the base 11. Further, since the hole portion 27 is formed inside the base portion 11, the base portion 11 is easily deformed, and torsional vibration can be effectively generated in the base portion 11.
[0029]
The second vibration mode is an expansion / contraction mode in the Z direction (hereinafter, referred to as “Z-axis expansion / contraction mode”). There are three types of causes for the Z-axis expansion / contraction mode described below. 8A and 8B are explanatory diagrams showing a mode of occurrence of a Z-axis expansion / contraction mode generated in the ultrasonic motor 100. FIG. 8A is a plan view showing a state of deformation of the piezoelectric ceramic plate 21, and FIG. FIG. 8C is an explanatory diagram showing displacement in the Z direction in the Z-axis expansion / contraction mode, and FIG. 8C is an explanatory diagram showing a change in the length of the base portion 11 in the Z direction due to torsional vibration. FIG. 7E is an explanatory diagram of displacement in the Z direction caused by imperfect force transmitted from the piezoelectric drive unit 14a or the like to the base unit 11.
[0030]
As shown in FIG. 8 (a), the Z-direction length of the piezoelectric ceramic plate 21 when it is not deformed is L, and the longer Z-direction length when the piezoelectric ceramic plate 21 is deformed into a fan shape is L. ₁ , The shorter L ₂ Then, the average length of the piezoelectric ceramic plate 21 in the Z direction after deformation is L (= (L ₁ + L ₂ ) / 2). Similarly, the net Z-direction length (average value) when the piezoelectric ceramic plate 23 is deformed into a fan shape is the same as before and after deformation. However, as shown in FIG. 8 (b), the Z-direction center position of the piezoelectric drive unit 14a and the like, and a node in the Z-direction expansion and contraction in the portion from the base portion 11 to the head 13 due to deformation of the piezoelectric ceramic plates 21 and 23. Does not coincide with each other, stretching vibration occurs in the Z direction in the portion from the base portion 11 to the head 13. Further, as shown in FIG. 8C, when the above-described torsion mode occurs, the length of the base portion 11 in the Z direction slightly changes accompanying this. However, this effect is small.
[0031]
Further, the piezoelectric ceramic plates 21 and 23 are generally attached to the base 11 using an adhesive. As shown in FIG. 8D, if the shearing force based on the tensile stress Ut and the compressive stress Uc when the piezoelectric driving unit 14a or the like is deformed is completely transmitted to the base unit 11, in principle, the Z direction is applied to the base unit 11 in the Z direction. Does not occur. However, in actuality, it is difficult for the shearing force due to the deformation of the piezoelectric driving portion 14a or the like to be completely transmitted to the base portion 11 due to factors such as the adhesive layer becoming a buffer layer, and as shown in FIG. As a result, a difference is generated between the tensile stress of the piezoelectric driving units 14a and 15b and the compressive stress of the piezoelectric driving units 14b and 15a (conversely, the compressive stress of the piezoelectric driving units 14a and 15b and the tensile stress of the piezoelectric driving units 14b and 15a). In addition, expansion and contraction vibration in the Z direction occurs in a portion from the base portion 11 to the head 13.
[0032]
The third vibration mode is a mode of radial vibration generated in the head 13. As shown in the cross-sectional view of FIG. 9, at a specific resonance frequency, vibrations that expand and contract in the radial direction occur in the head 13.
[0033]
The fourth vibration mode is a pseudo bending mode. To describe the pseudo bending mode, the bending mode will be described first. FIG. 10 is an explanatory diagram showing a bending mode in the X direction. The voltage V = V is applied to the drive electrodes 22a and 22b. ₀ sin (2πft), and a voltage V = −V is applied to the drive electrodes 24 a and 24 b (not shown). ₀ When sin (2πft) is applied, the piezoelectric ceramic plates 21 and 23 are respectively displaced in a fan shape so as to be symmetric with respect to the ZX plane, so that the head 13 draws an arc in the X direction from the base portion 11. A bending mode vibration is generated in a portion reaching the head 13.
[0034]
However, the voltage V = V is applied to the drive electrodes 22a, 22b, 24a, 24b. ₀ When sin (2πft) is applied, as shown in FIG. 2, a symmetrical displacement occurs around the Z axis in the piezoelectric driving unit 14 a and the like, so that the piezoelectric driving unit 14 a and the like are in an ideal state, that is, in the piezoelectric driving unit 14 a and the like. In a state where the structure of the ultrasonic motor 100 is symmetric with respect to the Z axis, for example, when the driving characteristics are the same and the force applied to the base 11 by the piezoelectric driving unit 14a and the like is the same, bending is in principle possible. It is considered that no mode oscillation occurs.
[0035]
However, as described later, in the ultrasonic motor 100, a resonance point appears near the resonance frequency where the bending mode described above appears, and the ultrasonic motor 100 can actually rotate the metal ball 16 clockwise (CW). it can. Therefore, the voltage V = V is applied to the drive electrodes 22a, 22b, 24a, 24b. ₀ When sin (2πft) is applied, it is not strictly speaking a bending mode, but it is considered that another vibration mode close to this bending mode occurs. Here, this “another vibration mode close to the bending mode” is referred to as a “pseudo bending mode”.
[0036]
Next, the movement of the metal ball 16 when the ultrasonic motor 100 is driven will be described. Here, the base portion 11 electrically connected to the common electrodes 22c and 24c is used as a ground electrode, and the AC voltage V = V is applied to the drive electrodes 22a, 22b, 24a and 24b. ₀ A case in which the piezoelectric drive unit 14a and the like are driven by applying sin (2πft) will be described.
[0037]
FIG. 11 is an explanatory diagram showing the dimensions of the main part of the ultrasonic motor 100. Since FIGS. 11A and 11B are equivalent to FIGS. 4 and 6, respectively, reference numerals indicating the components of the ultrasonic motor 100 are not shown in FIGS. 11A and 11B. The unit of the numerical value shown in FIG. 11 is “mm”. Table 1 is a list showing vibration modes appearing in the ultrasonic motor 100 and resonance frequencies of the respective vibration modes. Note that the ultrasonic motor of the present invention is not limited to the shape shown in FIG. 11, and the resonance frequency of the ultrasonic motor 100 varies depending on its size and shape, the metal material used, the environmental temperature, and the like.
[0038]
[Table 1]

[0039]
When the frequency is about 109 kHz, the first-order pseudo bending mode is mainly used, and the first-order Z-direction expansion and contraction mode (lower-frequency side of the resonance at 120 kHz) and the slightly first-order torsion mode (the resonance at 145 kHz) are used. The metal ball 16 is moved by the lower frequency side skirt). The three types of vibration modes are combined, that is, the head 13 swings in the vicinity of the Z axis, and expands and contracts in the Z direction, and the rotation force about the Z axis acts on the metal ball 16. The metal ball 16 can be rotated clockwise (CW). Since the exact trajectory of the simulated bending mode is unknown, a detailed description of the change with time in the force between the head 13 and the metal sphere 16 is not given here. Stop by mentioning only the fact that
[0040]
When the frequency is about 145 kHz, the metal sphere 16 is moved in the first-order torsion mode and the first-order Z-direction expansion and contraction mode (the lower frequency side of resonance at 120 kHz). In this case, the head 13 extends counterclockwise (CCW) about the Z axis while extending in the direction of (a) + Z (the direction from the base 11 to the head 13), and (b) − The rotation in the clockwise direction (CW) while shrinking in the direction of Z (the direction from the head 13 toward the base portion 11) is alternately repeated. In the movement shown in FIG. 4A, the direction of gravity applied to the metal ball 16 and the direction in which the head 13 extends are opposite, so that the frictional force between the metal ball 16 and the head 13 increases, and the metal ball 16 Attempt to rotate counterclockwise (CCW) under the force of the motion of FIG. On the other hand, when the head 13 performs the motion (b), since the direction of gravity applied to the metal ball 16 and the direction in which the head 13 retreats are the same, the friction between the metal ball 16 and the head 13 is increased. The force is small, and at a frequency of 145 kHz, the metal ball 16 cannot follow the movement of the head 13 and the space between the metal ball 16 and the head 13 slips. As a result, the force due to the movement of the head 13 (a) predominantly acts on the metal sphere 16, whereby the metal sphere 16 rotates counterclockwise (CCW).
[0041]
At a frequency of about 190 kHz, the metal sphere 16 is moved by the secondary torsion mode and the primary head 13 radial mode. FIG. 12 is an explanatory diagram schematically showing the vibration generated in the head 13 at 190 kHz. Reciprocal vibration S by second-order torsion mode ₁ And the primary radial vibration S of the head 13 ₂ Are combined to generate a spiral vibration S on the surface of the head 13.
[0042]
As shown in FIG. 4 described above, since the pressure N (= contact pressure / unit diameter) is acting between the metal ball 16 and the head 13, the diameter of the head 13 at rest is determined. Assuming that r, the pressure N decreases when the diameter r increases (the head 13 expands), and conversely, when the diameter r decreases, the pressure N increases. Therefore, when the diameter of the head 13 decreases when the head 13 rotates counterclockwise (CCW), the metal ball 16 rotates counterclockwise (CCW), and when the head 13 rotates clockwise (CW). When the diameter of the head 13 decreases, the metal ball 16 rotates clockwise (CW). Drive voltage is V = V ₀ In the case of sin (2πft), a spiral vibration is generated so that the metal sphere 16 rotates counterclockwise (CCW). The driving voltage of the piezoelectric driving unit 14a and the like is V = −V ₀ In the case of sin (2πft), a spiral vibration is generated so that the metal sphere 16 rotates clockwise (CW).
[0043]
When the frequency is about 221 to 226 kHz, the metal sphere 16 is rotated counterclockwise (CCW) by the third-order torsion mode and the Z-direction expansion / contraction mode, and when the frequency is about 227 to 235 kHz, the third-order torsion mode and the Z-direction The metal ball 16 is rotated clockwise (CW) by the expansion / contraction mode. This is because at about 226.5 kHz, a phenomenon occurs in which the phases of the torsion mode and the Z-direction expansion / contraction mode are shifted by 180 degrees.
[0044]
FIG. 13 is an explanatory view showing such a phase change. FIG. 13A shows the case where the metal sphere 16 is rotated clockwise (CW), and FIG. 13B shows the case where the metal sphere 16 is rotated counterclockwise. (CCW), N indicates the pressure between the head 13 and the metal ball 16, Utr indicates the torsional displacement of the head 13, and Uax indicates the Z-direction displacement. The torsional displacement Utr is clockwise (CW) when it is above the horizontal axis, and counterclockwise (CCW) when it is below the horizontal axis. The pressure N is synchronized with the vibration of the head 13 in the Z direction. The pressure N increases when the head 13 moves upward (displaces in the direction of + Z) and decreases when the head 13 moves downward (displaces in the direction of -Z).
[0045]
In FIG. 13A, since the torsional displacement Utr increases when the Z-direction displacement Uax increases, the metal ball 16 rotates clockwise (CW). In this case, there is theoretically no phase difference between the pressure N and the torsional displacement Utr, but according to actual measurement, as shown in FIG. Advanced. Assuming that there is no theoretical phase difference between the torsional displacement Utr and the Z-direction displacement Uax when the metal ball 16 rotates clockwise (CW), as shown in FIG. At ２226 kHz, the phases of the torsional displacement Utr and the Z-direction displacement Uax are shifted by 180 degrees, and the torsional displacement Utr decreases when the Z-direction displacement Uax increases, so that the metal ball 16 rotates counterclockwise (CCW). When the metal ball 16 is rotating in the range of 221 to 235 kHz, the Z-direction expansion / contraction mode is not exactly in a resonance state.
[0046]
Even at a frequency higher than the above-described frequency, the metal ball 16 can be rotated in a predetermined direction by a combination of the various vibration modes described above. For example, at about 400 kHz, the metal ball 16 can be rotated counterclockwise (CCW) by the sixth-order torsion mode and the Z-direction expansion / contraction mode, and at about 472 kHz to 480 kHz, the higher-order torsion mode and the Z-direction expansion / contraction mode. As a result, the metal ball 16 can be rotated counterclockwise (CCW) or clockwise (CW) as in the case where the third-order torsion mode and the Z-direction expansion / contraction mode occur, and further at about 1.02 MHz. The metal sphere 16 can be rotated counterclockwise (CCW) or clockwise (CW) by the high-order twist mode and the Z-direction expansion / contraction mode.
[0047]
The method of driving the piezoelectric drive unit 14a and the like in the ultrasonic motor 100 is not limited to the above-described method. For example, the voltage V = −V having the same phase applied to the drive electrodes 22a, 22b, 24a, and 24b. ₀ sin (2πft) may be applied. In this case, the rotation direction of the metal sphere 16 is reversed at each resonance frequency described above.
[0048]
The voltage V = V is applied to the drive electrodes 22a and 22b. ₀ It is also possible to move the metal sphere 16 by applying sin (2πft) to drive the piezoelectric driving units 14a and 14b and not to drive the piezoelectric driving units 15a and 15b. In this case, when the driving frequency is 109 kHz, a vibration in the primary bending mode (similar to the bending mode shown in FIG. 10 previously) occurs in the ZX plane. By overlapping, the metal sphere 16 can be rotated around the Y axis. In addition, when the driving frequency is 181 kHz, since the vibration of the secondary bending mode in the ZX plane occurs, the metal sphere 16 is rotated about the Y axis by overlapping the vibration of the bending mode in the Z direction. Can be done. The direction of rotation of the metal sphere 16 is opposite between the case where the driving frequency is 109 kHz and the case where the driving frequency is 181 kHz.
[0049]
Further, the voltage V = V is applied to the drive electrodes 22a and 22b. ₀ When sin (2πft) is applied to drive the piezoelectric driving units 14a and 14b and not to drive the piezoelectric driving units 15a and 15b, vibration in the first bending mode in the YZ plane occurs at a driving frequency of 110 kHz. Therefore, the metal sphere 16 can be rotated around the X axis by overlapping the vibration in the Z-direction expansion / contraction mode. In addition, since the vibration of the secondary bending mode occurs in the YZ plane at the driving frequency of 184 kHz, the metal sphere 16 can be rotated around the X axis by the overlap of the vibration with the vibration of the Z-direction expansion / contraction mode. The rotation direction of the metal ball 16 is opposite between the case where the driving frequency is 110 kHz and the case where the driving frequency is 184 kHz.
[0050]
Furthermore, the voltage V = V is applied to the drive electrodes 22a and 22b. ₀ sin (2πft), and at the same time, a voltage V = −V ₀ By applying sin (2πft), the piezoelectric drive unit 14a and the like can be driven. In this case, it is possible to cause the metal ball 16 to rotate around the Y axis or around the X axis at a predetermined resonance frequency or in the vicinity thereof.
[0051]
Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments. For example, the form in which two piezoelectric driving portions 14a and 14b having different polarization directions are formed on one piezoelectric ceramic plate 21 is shown. However, as shown in the plan view of FIG. The piezoelectric driving sections 32a and 32b may be formed by attaching the two piezoelectric ceramic plates 31a and 31b on which are formed) to the base section 11 at a predetermined interval. Similarly, two piezoelectric ceramic plates 33a and 33b having electrodes (not shown) formed on the front and back surfaces are attached to the base portion 11 at a predetermined interval to form the piezoelectric driving portions 34a and 34b. can do.
[0052]
Further, the direction of the polarization in the piezoelectric drive unit 14a and the like is not limited to the state shown in FIG. For example, FIG. 15 is a plan view similar to FIG. 4, and the polarization direction of the piezoelectric driving unit 14a is changed from the arrow −P to the arrow + P while the polarization direction of the piezoelectric driving unit 14a is maintained in the direction of the arrow + P. (Hereinafter referred to as “piezoelectric drive unit 14b ′”). Further, the direction of polarization of the piezoelectric drive unit 15a is changed from the direction of arrow -Q to the direction of arrow + Q while the direction of polarization of the piezoelectric drive unit 15b is maintained in the direction of arrow + Q (hereinafter, referred to as "piezoelectric drive unit 15a '"). In this case, the voltage V = V is applied to the piezoelectric driving units 14a and 15b. ₀ sin (2πft) is applied, and a voltage V = −V is applied to the piezoelectric driving units 14b ′ and 15a ′. ₀ When sin (2πft) is applied, as a result, the phases of expansion and contraction of the piezoelectric driving units 14a and 15b and expansion and contraction of the piezoelectric driving units 14b 'and 15a' can be shifted by 180 degrees. Voltage V = V ₀ The metal sphere 16 can be rotated around the Z-axis as in the case of driving with sin (2πft). Further, the piezoelectric driving units 14a and 14b 'are set to a voltage V = V ₀ sin (2πft), and drives the piezoelectric driving units 15a ′ and 15b at a voltage V = −V ₀ By driving at sin (2πft), the metal sphere 16 can be rotated around the Y axis or the X axis.
[0053]
In the above description, the metal ball 16 is exemplified as the driven body, but the driven body is not limited to this. For example, if the surface of the head 13 is pressed against the end surface in the Z direction of the spindle whose longitudinal direction is the Z direction, the spindle can be rotated. In addition, when the ultrasonic motor 100 is driven under the driving condition of pressing the metal ball 16 around the X axis or the Y axis by pressing against the back surface of the stage of the head 13, the stage can be moved in the XY directions. . When the ultrasonic motor 100 is held such that the Z direction of the ultrasonic motor 100 is horizontal, an appropriate frictional force acts between the head 13 of the ultrasonic motor 100 and the driven body. The ultrasonic motor 100 may be pressed against the driven body.
[0054]
【The invention's effect】
As described above, according to the present invention, vibrations in various directions can be generated in the prefix by shifting the phases of displacement of the four piezoelectric driving units. Therefore, by arranging the driven body appropriately in accordance with the movement of the prefix, it is possible to cause the driven body to make a predetermined movement. For example, the ultrasonic motor of the present invention can be used as a driving device for sliding an XY stage or a rotating motor of various rotating devices. ADVANTAGE OF THE INVENTION According to the ultrasonic motor of this invention, the drive source of various machines can save space, and various machines can be reduced in size.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a schematic structure of a piezoelectric actuator used in an ultrasonic motor according to the present invention.
FIG. 2 is an explanatory view showing a basic displacement mode of the piezoelectric actuator shown in FIG.
FIG. 3 is a graph showing a resonance frequency of a piezoelectric actuator.
FIG. 4 is a schematic side view showing the structure of an ultrasonic motor according to the present invention.
FIG. 5 is a schematic plan view of the ultrasonic motor shown in FIG.
FIG. 6 is a schematic bottom view of the ultrasonic motor shown in FIG.
FIG. 7 is an explanatory view schematically showing deformation of a base portion of the ultrasonic motor in a torsion mode.
FIG. 8 is an explanatory diagram showing a mode of occurrence of an expansion / contraction mode generated in the ultrasonic motor 100.
FIG. 9 is a cross-sectional view illustrating radial expansion and contraction vibration generated in the head.
FIG. 10 is an explanatory diagram showing a bending mode in the X direction.
FIG. 11 is an explanatory view showing dimensions of main parts of the ultrasonic motor.
FIG. 12 is an explanatory view schematically showing vibration generated in a head at a frequency of 190 kHz.
FIG. 13 is an explanatory diagram showing a phase difference of a vibration mode at frequencies 221 to 235 kHz.
FIG. 14 is a plan view showing another arrangement of the piezoelectric driving unit.
FIG. 15 is a plan view showing still another arrangement of the piezoelectric driving unit.
[Explanation of symbols]
10; piezoelectric actuator
11; base part
12; Horn part
13; head
14a, 14b, 14b '; piezoelectric drive unit
15a, 15a ', 15b; piezoelectric drive unit
16; metal ball
21; piezoelectric ceramic plate
22a ・ 22b; drive electrode
22c; common electrode
23; piezoelectric ceramic plate
24a and 24b; drive electrodes
24c; common electrode
26; Screw hole
27; hole
28; bolt
28a, 28b; threaded part
28c; cylindrical part
29; fixing member
31a and 31b; piezoelectric ceramic plates
32a, 32b; piezoelectric drive unit
33a, 33b; piezoelectric ceramic plate
34a, 34b; piezoelectric drive unit
100; ultrasonic motor

Claims (5)

A substantially rectangular parallelepiped base portion having surfaces in X direction, Y direction, and Z direction orthogonal to each other;
A substantially conical horn portion disposed on one surface of the Z-direction surface of the base portion;
A prefix provided near the apex of the horn portion and in contact with the driven body;
Four substantially rectangular piezoelectric driving units provided on both surfaces of the base unit in the Y direction and separated in the X direction and polarized in the Y direction;
Holding means for holding the base portion;
With
An ultrasonic motor, wherein a predetermined vibration is applied to the prefix by applying a voltage of a predetermined frequency to the piezoelectric driving unit to move the driven body. The directions of polarization of the four piezoelectric driving units are opposite to each other in the Y direction in the two piezoelectric driving units provided on the same surface, and at positions symmetric with respect to the Z axis passing through the center of the Z direction surface. 2. The ultrasonic motor according to claim 1, wherein the two piezoelectric driving units have opposite directions in the Y direction. 3. The base portion has a hole formed from the center of the Z-direction surface where the horn portion is not provided toward the horn portion,
3. The ultra-high-pressure supercharger according to claim 1, wherein the holding unit holds the base at a position corresponding to a center of the piezoelectric driving unit in the Z direction in the hole. 4. Sound wave motor. The base unit is characterized in that it has another four holes provided in parallel with the hole so as to be located at a diagonal of the Z-direction surface of the base and communicating with the hole. The ultrasonic motor according to claim 3, wherein The ultrasonic motor according to any one of claims 1 to 4, wherein the prefix has a substantially disk shape with a direction perpendicular to the Z direction as a radial direction.

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