JP4714405B2

JP4714405B2 - Ultrasonic motor and electronic device with ultrasonic motor

Info

Publication number: JP4714405B2
Application number: JP2003041500A
Authority: JP
Inventors: 朗弘飯野; 聖士渡辺; 政雄春日; 貴之小坂
Original assignee: Seiko Instruments Inc
Current assignee: Seiko Instruments Inc
Priority date: 2003-02-19
Filing date: 2003-02-19
Publication date: 2011-06-29
Anticipated expiration: 2023-02-19
Also published as: JP2004254406A

Description

【０００１】
【発明の属する技術分野】
本発明は圧電素子を有する振動体の振動で移動体を摩擦駆動させる超音波モータ及び超音波モータを用いた電子機器にかかわり、特に駆動信号を印加する圧電素子の電極を選択することで移動方向を切り換える定在波型の超音波モータに関する。
【０００２】
【従来の技術】
超音波モータは小型で高トルク等の優れた特徴を有することから様々な研究開発、並びに応用開発が進められている。そして最近では超音波モータの欠点であった複雑な駆動回路を改善する方法として超音波モータ自体を振動子として利用し、自励発振回路を構成する方法が採られている。この場合、電気的に単相信号で駆動が可能で正逆転方向の切り換えが可能な超音波モータが望まれ、この様な方式として同相駆動型超音波モータが提案されている。
【０００３】
同相駆動型超音波モータの原理は振動体に励振する定在波の1/４波長間隔の電極を圧電素子に設け、一つおきの電極を短絡して二つの電極群を構成し、一方の電極群に信号を印加することで弾性体に設けた突起が定在波の腹に位置する振動モードと突起が節に位置する振動モードの二つが同時に励振され、二つの振動変位の合成により突起と接する移動体を駆動する。また他方の電極群に信号を印加すると二つの振動の位相関係が逆転し、移動体は逆方向に駆動される（例えば、非特許文献１参照。）。
【０００４】
【非特許文献１】
T.Takano, Y.Tomikawa, and C.Kusakabe,: Same phase Drive-type Ultrasonic Motors Using Two Degenerate Bending Vibration Modes of a Disk, IEEE Trans. On UFFC, Vol.39,no.2, March 1992.
【０００５】
【発明が解決しようとする課題】
しかしながら、本原理に基づいて駆動した場合、二つの振動の共振点が異なると共に、電気的にも共振のピークが二つ存在する。その為、自励発振回路を構成しようとした場合、発振ポイントが不安定となり、温度や負荷等の環境で変動する恐れがある。また、駆動回路の構成に関係なく若干の駆動周波数の変動でモータ特性が大きく変化するとともに、製造上のばらつきにより二つの共振点の位置もモータ個々で変動する為、得られるモータ特性もばらつきの大きなものになる恐れがあった。
【０００６】
そこで本発明では、一つの振動モードだけで駆動出来るモータ、即ち電気的にもほぼ一つの共振ピークだけが存在する振動体構造を得ることにある。
【０００７】
【課題を解決するための手段】
本発明は振動体の設計パラメータを最適化することにより突起が振動の腹と節の間に位置する振動モードを励振するようにする。これにより一つの振動モードで移動体を駆動できると共に、信号入力時に一つの固有モードだけが極めて強く励振され、電気的にもほぼ一つの共振ピークを有する振動体を実現する。以下具体的にその方法を説明する。
【０００８】
本発明の第１の態様は、圧電素子を有する振動体と、前記圧電素子の第一の面に設けられた複数の電極と、前記圧電素子の第二の面の前記複数の電極と対向する位置に前記第一の面に設けられた複数の電極と同一の形状で設けられ複数の電極と、前記振動体に設けられた突起と、前記突起と接する移動体からなり、前記圧電素子の第一の面に設けられた複数の電極の中の一つおきの電極と、これと対向する第二の面に設けられた電極の間に信号を印加することで移動体を駆動することを特徴とする超音波モータにある。これによれば突起が振動の腹と節の間に位置する振動モードが励振され、一つの振動モードで移動体を駆動できると共に、信号入力時に一つの固有モードだけが励振され、電気的にもほぼ一つの共振ピークを有する振動体となる。そして不用振動の影響を受けずに安定な自励振駆動が実現できるとともにモータ個々のばらつきが小さく出来る。
【０００９】
本発明の第２の態様は、第一の面にほぼ全体に渡って電極を有し、第二の面の周方向に四分の一波長間隔で設けられた電極を有する圧電素子と、前記圧電素子と接合された弾性体と、前記弾性体の前記圧電素子の第二の面の電極と電極の境界に位置する部分に設けられた突起からなる振動体の振動により、前記突起と接する移動体を駆動する超音波モータにおいて、前記圧電素子と前記弾性体の厚みは前記振動体に励振される縮退モードである二つの振動の内、共振点が高い方の共振のアドミッタンスのピーク値を共振点が低いモードの共振のアドミッタンスのピーク値で割った値が０．１よりも低くなるように決められていることを特徴とする超音波モータにある。これによれば不用振動の影響を受けずに安定な自励振駆動が実現できるとともにモータ個々のばらつきが小さく出来る。
【００１０】
本発明の第３の態様は、第一の面にほぼ全体に渡って電極を有し、第二の面の周方向に四分の一波長間隔で設けられた電極を有する圧電素子と、前記圧電素子と接合された弾性体と、前記弾性体の前記第二の面の電極と電極の境界に位置する部分に設けられた突起からなる振動体の振動により、前記突起と接する移動体を駆動する超音波モータにおいて、前記圧電素子の厚みは、前記振動体の電気−機械結合係数のとる値が最大となる厚み近傍である様にすることを特徴とする超音波モータにある。これによれば不要モードの影響を殆ど受けず安定な自励振駆動が実現できると共に高出力な超音波モータが実現できる。
【００１１】
本発明の第４の態様は、第一の面にほぼ全体に渡って電極を有し、第二の面の周方向に四分の一波長間隔で設けられた電極を有する圧電素子と、前記圧電素子と接合された弾性体と、前記弾性体の前記第二の面の電極と電極の境界に位置する部分に設けられた突起からなる振動体の振動により、前記突起と接する移動体を駆動する超音波モータにおいて、前記圧電素子の厚みは、前記振動体の電気−機械結合係数のとる値が最大となる厚みよりも薄くなる様にすることを特徴とする超音波モータにある。これによれば不要モードの影響を全く受けず安定な自励振駆動が実現できると共に、高出力な超音波モータが実現できる。
【００１２】
本発明の第５の態様は、第一の面にほぼ全体に渡って電極を有し、第二の面の周方向に四分の一波長間隔で設けられた電極を有する圧電素子と、前記圧電素子と接合された弾性体と、前記弾性体の前記第二の面の電極と電極の境界に位置する部分に設けられた突起からなる振動体の振動により、前記突起と接する移動体を駆動する超音波モータにおいて、前記突起の高さは前記振動体に励振される縮退モードである二つの振動の内、共振点が高い方の共振のアドミッタンスのピーク値を共振点が低いモードの共振のアドミッタンスのピーク値で割った値が０．０５よりも低くなるように決めることを特徴とする超音波モータにある。これによれば不用振動の影響を受けずに安定な自励振駆動が実現できると共に、高出力な超音波モータが実現できる。
【００１３】
本発明の第６の態様は、圧電素子を有する振動体と、前記振動体に設けられた突起と、前記突起と接する移動体からなり、前記振動体の屈曲振動により前記突起と接する移動体を駆動する超音波モータにおいて、前記屈曲振動の波数と同じ波数を有する前記振動体の面内振動の固有振動数が前記屈曲振動の固有振動数近傍に来ないように前記振動体の厚みを決めることを特徴とする超音波モータにある。これによれば不用振動の影響を受けずに安定な自励振駆動が実現できる。
【００１４】
本発明の第７の態様は、第１から第６のいずれかの態様における超音波モータと増幅回路とで自励発振回路を構成し、前記移動体を駆動することを特徴とする超音波モータにある。これによれば小型で簡易な駆動回路でしかも安定な駆動が出来る。
【００１５】
本発明の第８の態様は、第１から第７の何れかの態様における超音波モータを備えた電子機器とすることを特徴とする超音波モータ付き電子機器にある。これによれば小型、低消費電力でかつ性能のばらつきの少ない電子機器が実現できる。
【００１６】
【発明の実施の形態】
以下図１から図１９を参照して本発明を適用した実施の形態を詳細に説明する。
【００１７】
まず始めに本発明の超音波モータの構成、原理について説明する。図１に示す様に円板状の弾性体１の下面には圧電素子２が接着され振動体を構成している。圧電素子２の弾性体１との接着面にはほぼ前面に渡って図示しない共通電極が設けられている。圧電素子２の他方の面には励振する屈曲振動の１/４波長間隔で分極領域が決められ図中＋、−の方向に分極処理されている。そして、各分極領域の上には電極３が設けられており一つおきの電極を短絡して二つの電極群を構成する。圧電素子２の各電極３a、３ｂ、３ｃ、３ｄの境界に相当するの弾性体１の部分には突起１aが設けられている。
【００１８】
従来例で示した同相駆動型超音波モータの駆動原理に基づくと、一つの電極群と共通電極との間に駆動信号を印加する（ｃｈ１駆動）と突起１aが腹に位置するモード１と、突起１aが節に位置するモード２が同時に励振され、二つの振動モードの合成変位で図示しない移動体は駆動される。ここで、二つの振動モードの共振点は異なるため共振のピークは二つ現れる。図２に二つの共振点付近の振動体の周波数−アドミッタンスの関係を示す。この様な特性を有する振動体では安定な自励振駆動が難しい。
【００１９】
しかしながら同じ構成の振動体であっても設計パラメータを最適化することにより一つの振動モードのみで駆動できるようになる。即ち突起１aが腹と節の間に位置するモードを固有モードに持つ様になる。図３に示す様に（a）（ｃｈ１駆動）と（ｂ）（ｃｈ２駆動）とでは上昇した突起１aの傾く方向が反対となるため移動体４の移動方向も反対になる。また、本振動体の周波数−アドミッタンスの関係を図４に示すが、本振動体は一つの振動モードのみが極めて強く励振され、本モードの縮退モード（不要モード）の励振は極めて小さい。その為、駆動モードの共振で安定に自励振駆動が実現できる。この様に一つの振動モードだけで駆動でき、電気的にも駆動モードの共振点のアドミッタンスは極めて大きく、縮退モード（不要モード）の共振点のアドミッタンスは極めて小さい振動体の設計条件を以下の実施の形態に示す。
【００２０】
｛実施の形態１｝
振動体設計パラメータの影響を確認するため、有限要素法により解析した。図５に解析モデルを示す。突起５aを有する弾性体５の下面には圧電素子６が設けられている。圧電素子６は周方向に励振する振動の１/４波長毎の分極領域に分けられ、図中＋、−で示す方向（圧電素子の厚み方向）に分極処理されている。圧電素子６の弾性体５との接合面にはほぼ前面に黒塗り部で示す電極７aが設けられている。他方の面には二つの電極群を構成する斜線部と点部で示す電極が設けられている。本解析では電極と電極の隙間は突起５aの幅とした。弾性体５と圧電素子６からなる振動体７の固定は中心穴の内周全体を完全固定した。
【００２１】
突起５aの高さを０．２５ｍｍに固定し、圧電素子６の厚みｔ１、弾性体５の厚みｔ２を変えた際の周波数−アドミッタンスの関係の一例を図６及び図７に示す。この様に弾性体５及び圧電素子６の厚みによって駆動モードの共振のアドミッタンス値と不要モードのアドミッタンス値の値は大きく変化する。不要モードが大きく励振されるほど、固有モードは同相駆動型超音波モータの原理に基づき、突起が腹に位置するモードと突起が節に位置するモードに近づいていくことが確認されている。ここでは周方向に三つの節を、径方向に一つの節円を有するいわゆる（３，１）モードを利用した場合であるが屈曲振動であれば例えば（３，０）モードや（４，１）モードを利用してもよく、モードの次数を問わない。解析した各寸法に対し、不要モードの共振のアドミッタンスのピーク値を駆動モードの共振のアドミッタンスのピーク値で割った値を不要モードの大きさを示す指数として、グラフにして図８に、表にして図９に示す。圧電素子６の厚みを厚くしていくとある点から急激に不要モードの励振力が大きくなり始め、この変化の勾配は大きい。従って、この様な変化を示す寸法に設計すると実際の製品個々の若干の寸法のばらつきでも不要モードの影響度は大きく変化し、強いては製品個々の特性に大きなばらつきを生じる恐れが有る。また不要モードが大きく励振されると、その分だけ駆動モードの励振力が弱まってしまう。その目安は不要モードの大きさを示す指数が０．１であり、それを超えないように圧電素子６及び弾性体５の厚みを設定すればよい。本結果からその傾向は弾性体５の厚みにあまり影響されず、圧電素子６の厚みに大きく影響されることが確認されている為、不要モードの大きさを示す指数が０．１以下になるような圧電素子６の厚みとすればよい。
【００２２】
また、図１０及び図１１に示す弾性体５及び圧電素子６の厚みと電気−機械結合係数ｋの関係と、弾性体５及び圧電素子６の厚みと不要モードの大きさの関係を比較すると以下のようなことが分かった。電気−機械結合係数が最大付近もしくはこの点の圧電素子６の厚みよりも薄い範囲では不要モードの励振力は小さく、この範囲に圧電素子６の厚みを設定すれば良い。特に、不要モードが全く励振されない（図６（a））のは電気−機械結合係数が最大となる圧電素子６の厚みよりも薄い範囲である。但し、モータの出力を優先するのであれば電気−機械結合係数が最も大きくなる厚みに設定すればよい。ちなみに電気−機械結合係数の値は圧電素子６全体、即ち電極７aと７ｂ、７ｃの間に駆動信号を印加した条件で解析した周波数−アドミッタンスの関係から求めた。この条件では、不要モードは励振されないから電気−機械結合係数の評価は容易となる。
【００２３】
ところが上記の条件であっても、圧電素子６の厚みが３０μｍ、弾性体の厚みが０．３５ｍｍの時には不要モードが大きく励振されてしまった。（図７（e））これは屈曲振動と波数が同じ面内振動の影響である。図１２及び図１３に夫々縮退モードを有する屈曲振動の固有周波数と面内振動の固有周波数の関係を示す。図６、図７並びに図１２、図１３の結果から分かる様に屈曲振動の固有周波数が面内振動の固有振動数近傍に位置しない様に振動体、即ち圧電素子６及び弾性体５の厚みを設定すれば良い。
【００２４】
｛実施の形態２｝
弾性体５に設けられた突起５aの高さによっても不要モードの大きさが変化することが分かっている。図５のモデルに対して弾性体５の厚みを０．２５ｍｍ、圧電素子６の厚みを８０μｍに固定し、突起５aの高さを変化させた場合について解析した。一例として突起５aの高さを０．４ｍｍとした場合の、周波数−アドミッタンスの関係を図１４に示す。この様に突起５aの高さによって駆動モードの共振のアドミッタンス値と不要モードのアドミッタンス値の値は大きく変化する。不要モードが大きく励振されるほど、固有モードは同相駆動型超音波モータの原理に基づき、突起５aが腹に位置するモードと突起５aが節に位置するモードに近づいていくことが確認されている。解析した各寸法に対し、不要モードの共振のアドミッタンス値を駆動モードの共振のアドミッタンス値で割った値を不要モードの大きさを示す指数としてグラフにして図１５に示す。突起５aを高くしていくと突起高さが０．３ｍｍ近傍（不要モードの大きさを示す指数が０．０４３）から急激に不要モードの励振力が大きくなり始め、この変化の勾配は大きい。従って、この様な変化を示す寸法に設計すると実際の製品個々の寸法の若干のばらつきでも不要モードの影響度は大きく変化し、強いては製品個々の特性に大きなばらつきを生じる恐れが有る。また不要モードが大きく励振されると、その分駆動モードの励振力が弱まってしまう。不要モードの励振力は小さいほど良いが、自励発振で駆動するにはその限界はおよそ不要モードの大きさを示す指数が０．１でありそれを超えないように突起の高さを設定すればよい。以上の事柄から総合的に判断すると不要モードの大きさを示す指数が０．０５となる突起の高さよりも突起を低く設定すればよい。
【００２５】
｛実施の形態３｝
実施の形態１において不要モードの大きさが圧電素子６の厚みに影響されることを示した。この理由として以下のことが考えられる。二つの電極群７ｂ、７ｃと共通電極７aをGNDとして共用している為、図１６に示す様に二つの電極７ｂ、７ｃの境界部分では圧電縦効果（ｄ_３３）も働いている為であり、圧電素子６の厚みを厚くすると不要モードが大きく励振されるのは圧電素子６の厚みの増加に従い、この影響が大きくなりモードパターンがシフトする為であると考えられる。
【００２６】
そこで、図１７に示す様に共通電極を分割し表裏の電極を同形状とする。即ち電極７ｂと７ｄの間に駆動信号を印加するか電極７ｃと7eの間に駆動信号を印加することで駆動する。
【００２７】
実際に解析した例を図１８に示すが圧電素子の厚みを増やしていっても図５に示す従来の電極を用いた場合に比べ不要モードの励振力の大きさは小さいことが分かる。本解析では解析モデルの都合状、電極と電極の隙間を突起５aの幅としたが、実際にはこれよりも小さく出来る為不要モードの励振力は更に小さくなる。
【００２８】
本発明の電極の使用方法としては、例えば弾性体５と圧電素子６の接合面に絶縁層を設けるか、弾性体５自体を絶縁体で構成する。圧電素子６の弾性体５との接合面にある電極は圧電素子６の内径部側面もしくは外径部側面を通じて引き回され、駆動信号が印加される。
【００２９】
また、モータの駆動に用いる振動モードに面内振動を用いることも可能であり、この場合、弾性体５は不用となるからこの様に表裏同じ電極形状とした圧電素子６の外周部側面に例えば突起５aを設けて移動体４と接触させればよい。
【００３０】
｛実施の形態４｝
図１９は本発明の駆動回路により駆動される超音波モータ２０を電子機器の駆動源に適用したブロック図を示したものであり、圧電素子１０と圧電素子と接合される弾性体１１と、弾性体１１により摩擦駆動される移動体１２と移動体１２と一体に動作する伝達機構１３と、伝達機構１３の動作に基づいて動作する出力機構１４からなる。例えば面内振動で駆動する場合には弾性体１１は圧電素子１０のみで構成されていても構わない。
【００３１】
ここで、伝達機構１３は例えば歯車列、摩擦車等の伝達車を用いる。出力機構１４としては、プリンタにおいては紙送り機構、カメラにおいてはシャッタ駆動機構、レンズ駆動機構、フィルム巻き上げ機構等を、また電子機器や計測器においては指針等を、ロボットにおいてはアーム機構、工作機械においては歯具送り機構や加工部材送り機構等を用いる。
【００３２】
尚、本実施の形態における電子機器としては電子時計、計測器、カメラ、プリンタ、印刷機、ロボット、工作機、ゲーム機、光情報機器、医療機器、移動装置等を実現できる。さらに移動体１２に出力軸を設け、出力軸からのトルクを伝達するための動力伝達機構を有する構成とすれば、超音波モータ付き電子機器を実現できる。
【００３３】
本発明の超音波モータを電子機器に適用することにより、電子機器の低電圧化、低消費電力化、小型化、低コスト化が実現できる。超音波モータを利用することから当然、磁気の影響を受けずまた、有害な磁気ノイズも発生しない。
【００３４】
【発明の効果】
以上のように、本発明は振動体の設計パラメータを最適化することにより、突起が振動の腹と節の間に位置する振動モードを励振するようにできる為、一つの振動で駆動でき、モータ個々のばらつきが小さくしかも温度や負荷等に対しても性能の変動が小さい超音波モータが得られる。また、信号入力時に一つの固有モードだけが励振され、電気的にもほぼ一つの共振ピークを有する振動体の為、安定な自励振駆動が実現できる。
【図面の簡単な説明】
【図１】同相駆動型超音波モータの構造及び原理を示す図である。
【図２】同相駆動型超音波モータの振動体の共振特性を示す図である。
【図３】本発明の超音波モータの駆動原理を示す図である。
【図４】本発明の超音波モータの振動体の共振特性を示す図である。
【図５】本発明の超音波モータの振動体の解析モデルを示す図である。
【図６】本発明の超音波モータの固有値解析の結果を示す図である。
【図７】本発明の超音波モータの固有値解析の結果を示す図である。
【図８】振動体の厚みと不要モードの励振力の大きさの関係をグラフにして示す図である。
【図９】振動体の厚みと不要モードの励振力の大きさの関係を表にして示す図である。
【図１０】振動体の厚みと電気−機械結合係数の関係を示す図である。
【図１１】振動体の厚みと電気−機械結合係数の関係を示す図である。
【図１２】振動体の厚みを変えた場合の屈曲振動と面内振動の固有振動の関係を示す図である。
【図１３】振動体の厚みを変えた場合の屈曲振動と面内振動の固有振動の関係を示す図である。
【図１４】突起高さ０．４ｍｍの振動体の共振特性を示す図である。
【図１５】突起高さと不要モードの励振力の関係を示す図である。
【図１６】共通電極の影響を示す図である。
【図１７】本発明の電極パターンを示す図である。
【図１８】本発明の電極パターンを用いた場合の共振特性の解析結果を示す図である。
【図１９】本発明の超音波モータを電子機器に応用した例のブロック図を示す図である。
【符号の説明】
１、５、１０弾性体
２，６，１１圧電素子
４，１２移動体
７電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor that frictionally drives a moving body by vibration of a vibrating body having a piezoelectric element, and an electronic device using the ultrasonic motor, and in particular, a moving direction by selecting an electrode of a piezoelectric element to which a driving signal is applied. The present invention relates to a standing wave type ultrasonic motor that switches between the two.
[0002]
[Prior art]
Since the ultrasonic motor is small and has excellent characteristics such as high torque, various research and development and application development are being promoted. Recently, as a method of improving the complicated drive circuit, which has been a drawback of the ultrasonic motor, a method of forming a self-excited oscillation circuit using the ultrasonic motor itself as a vibrator has been adopted. In this case, an ultrasonic motor that can be electrically driven by a single-phase signal and can be switched between forward and reverse directions is desired, and an in-phase drive type ultrasonic motor has been proposed as such a system.
[0003]
The principle of the in-phase drive type ultrasonic motor is that the electrode of the standing wave 1/4 wavelength interval excited on the vibrating body is provided in the piezoelectric element, and every other electrode is short-circuited to form two electrode groups. By applying a signal to the electrode group, the vibration mode in which the protrusion provided on the elastic body is positioned at the antinode of the standing wave and the vibration mode in which the protrusion is positioned at the node are excited simultaneously, and the protrusion is obtained by combining the two vibration displacements. The moving body in contact with is driven. When a signal is applied to the other electrode group, the phase relationship between the two vibrations is reversed, and the moving body is driven in the opposite direction (see, for example, Non-Patent Document 1).
[0004]
[Non-Patent Document 1]
T. Takano, Y. Tomikawa, and C. Kusakabe ,: Same phase Drive-type Ultrasonic Motors Using Two Degenerate Bending Vibration Modes of a Disk, IEEE Trans. On UFFC, Vol.39, no.2, March 1992.
[0005]
[Problems to be solved by the invention]
However, when driven based on this principle, the resonance points of the two vibrations are different, and there are also two resonance peaks electrically. For this reason, when an attempt is made to configure a self-excited oscillation circuit, the oscillation point becomes unstable and may fluctuate in an environment such as temperature or load. In addition, the motor characteristics change greatly due to slight fluctuations in the drive frequency regardless of the configuration of the drive circuit, and the position of the two resonance points also varies from one motor to another due to manufacturing variations. There was a fear of becoming big.
[0006]
Therefore, the present invention is to obtain a motor that can be driven by only one vibration mode, that is, a vibrating body structure that has only one resonance peak electrically.
[0007]
[Means for Solving the Problems]
The present invention optimizes the design parameters of the vibrating body so as to excite the vibration mode in which the protrusion is located between the vibration antinode and the node. As a result, the moving body can be driven in one vibration mode, and only one eigenmode is excited very strongly when a signal is input, so that a vibration body having substantially one resonance peak is realized. The method will be specifically described below.
[0008]
According to a first aspect of the present invention, a vibrating body having a piezoelectric element, a plurality of electrodes provided on a first surface of the piezoelectric element, and the plurality of electrodes on a second surface of the piezoelectric element are opposed. A plurality of electrodes provided in the same shape as the plurality of electrodes provided on the first surface, a protrusion provided on the vibrating body, and a moving body in contact with the protrusion; The movable body is driven by applying a signal between every other electrode of the plurality of electrodes provided on one surface and the electrode provided on the second surface opposite to the electrode. It is in the ultrasonic motor. According to this, the vibration mode in which the protrusion is located between the vibration antinode and the node is excited, and the moving body can be driven in one vibration mode, and only one eigenmode is excited when a signal is input, The vibrating body has almost one resonance peak. In addition, stable self-excited drive can be realized without being affected by unnecessary vibrations, and variations among individual motors can be reduced.
[0009]
According to a second aspect of the present invention, there is provided a piezoelectric element having electrodes over the entire first surface and electrodes provided at a quarter wavelength interval in the circumferential direction of the second surface; Movement in contact with the protrusion by the vibration of the elastic body joined to the piezoelectric element and the vibration body formed of a protrusion provided on the boundary between the electrode on the second surface of the piezoelectric element of the elastic body In the ultrasonic motor for driving the body, the thickness of the piezoelectric element and the elastic body resonates with the peak value of the resonance admittance of the higher resonance point of the two vibrations in the degenerate mode excited by the vibrating body. The ultrasonic motor is characterized in that the value divided by the peak value of the resonance admittance of the mode with a low point is determined to be lower than 0.1. According to this, it is possible to realize a stable self-excited drive without being affected by unnecessary vibrations, and to reduce variations in individual motors.
[0010]
According to a third aspect of the present invention, there is provided a piezoelectric element having electrodes over the entire first surface and electrodes provided at a quarter wavelength interval in the circumferential direction of the second surface; The movable body in contact with the protrusion is driven by the vibration of the elastic body joined to the piezoelectric element and the vibration body including a protrusion provided on the boundary between the electrode on the second surface of the elastic body. In the ultrasonic motor, the thickness of the piezoelectric element is in the vicinity of the thickness where the value taken by the electro-mechanical coupling coefficient of the vibrator is maximized. According to this, it is possible to realize a stable self-excited drive that is hardly affected by the unnecessary mode and a high-power ultrasonic motor.
[0011]
According to a fourth aspect of the present invention, there is provided a piezoelectric element having an electrode over the entire first surface and having electrodes provided at a quarter wavelength interval in the circumferential direction of the second surface; The movable body in contact with the protrusion is driven by the vibration of the elastic body joined to the piezoelectric element and the vibration body including a protrusion provided on the boundary between the electrode on the second surface of the elastic body. In the ultrasonic motor, the thickness of the piezoelectric element is set to be thinner than the thickness at which the value taken by the electromechanical coupling coefficient of the vibrator is maximized. According to this, it is possible to realize a stable self-excited drive without being influenced by the unnecessary mode at all, and to realize a high output ultrasonic motor.
[0012]
According to a fifth aspect of the present invention, there is provided a piezoelectric element having electrodes over the entire first surface and electrodes provided at a quarter wavelength interval in the circumferential direction of the second surface; The movable body in contact with the protrusion is driven by the vibration of the elastic body joined to the piezoelectric element and the vibration body including a protrusion provided on the boundary between the electrode on the second surface of the elastic body. In the ultrasonic motor, the height of the protrusion is the peak value of the resonance admittance of the resonance with the higher resonance point of the two vibrations in the degenerate mode excited by the vibrating body. The ultrasonic motor is characterized in that the value divided by the peak value of admittance is lower than 0.05. According to this, stable self-excited drive can be realized without being affected by unnecessary vibration, and a high-output ultrasonic motor can be realized.
[0013]
According to a sixth aspect of the present invention, there is provided a vibrating body having a piezoelectric element, a protrusion provided on the vibrating body, and a moving body in contact with the protrusion, and the moving body in contact with the protrusion by bending vibration of the vibrating body. In the ultrasonic motor to be driven, the thickness of the vibrating body is determined so that the natural frequency of the in-plane vibration of the vibrating body having the same wave number as that of the bending vibration does not come close to the natural frequency of the bending vibration. The ultrasonic motor is characterized by the following. According to this, stable self-excited drive can be realized without being affected by unnecessary vibration.
[0014]
According to a seventh aspect of the present invention, the ultrasonic motor according to any one of the first to sixth aspects includes a self-excited oscillation circuit configured to drive the movable body. It is in. According to this, stable driving can be performed with a small and simple driving circuit.
[0015]
An eighth aspect of the present invention is an electronic apparatus with an ultrasonic motor, characterized in that the electronic apparatus includes the ultrasonic motor according to any one of the first to seventh aspects. According to this, it is possible to realize an electronic device that is small in size, has low power consumption, and has little performance variation.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment to which the present invention is applied will be described in detail with reference to FIGS.
[0017]
First, the configuration and principle of the ultrasonic motor of the present invention will be described. As shown in FIG. 1, a piezoelectric element 2 is bonded to the lower surface of a disk-like elastic body 1 to form a vibrating body. A common electrode (not shown) is provided on the adhesive surface of the piezoelectric element 2 with the elastic body 1 almost over the entire surface. A polarization region is determined on the other surface of the piezoelectric element 2 at 1/4 wavelength intervals of bending vibration to be excited, and is polarized in the + and-directions in the figure. An electrode 3 is provided on each polarization region, and every other electrode is short-circuited to form two electrode groups. A protrusion 1a is provided on a portion of the elastic body 1 corresponding to the boundary between the electrodes 3a, 3b, 3c, and 3d of the piezoelectric element 2.
[0018]
Based on the driving principle of the in-phase driving type ultrasonic motor shown in the conventional example, when a driving signal is applied between one electrode group and the common electrode (ch1 driving), the mode 1 in which the protrusion 1a is positioned on the belly, The mode 2 in which the protrusion 1a is located at the node is excited simultaneously, and the moving body (not shown) is driven by the combined displacement of the two vibration modes. Here, since the resonance points of the two vibration modes are different, two resonance peaks appear. FIG. 2 shows the frequency-admittance relationship of the vibrating body near the two resonance points. A stable self-excited drive is difficult with a vibrator having such characteristics.
[0019]
However, even vibration bodies having the same configuration can be driven in only one vibration mode by optimizing the design parameters. That is, the eigenmode has a mode in which the protrusion 1a is located between the belly and the node. As shown in FIG. 3, in (a) (ch1 drive) and (b) (ch2 drive), the direction in which the raised protrusion 1a tilts is opposite, so the moving direction of the moving body 4 is also opposite. Further, FIG. 4 shows the frequency-admittance relationship of the present vibrating body. The vibrating body is excited very strongly in only one vibration mode, and the excitation in the degenerate mode (unnecessary mode) of this mode is extremely small. Therefore, the self-excited drive can be stably realized by the resonance of the drive mode. In this way, the drive mode can be driven by only one vibration mode, and the admittance at the resonance point in the drive mode is also extremely large electrically, and the admittance at the resonance point in the degenerate mode (unnecessary mode) is extremely small. It is shown in the form.
[0020]
{Embodiment 1}
In order to confirm the influence of the vibration body design parameters, it was analyzed by the finite element method. FIG. 5 shows an analysis model. A piezoelectric element 6 is provided on the lower surface of the elastic body 5 having the protrusions 5a. The piezoelectric element 6 is divided into polarization regions for each quarter wavelength of vibration excited in the circumferential direction, and is polarized in directions indicated by + and-in the figure (thickness direction of the piezoelectric element). An electrode 7a indicated by a black portion is provided almost on the front surface of the joining surface of the piezoelectric element 6 with the elastic body 5. On the other surface, electrodes indicated by hatched portions and dot portions constituting two electrode groups are provided. In this analysis, the gap between the electrodes is the width of the protrusion 5a. The vibration body 7 composed of the elastic body 5 and the piezoelectric element 6 was completely fixed on the entire inner periphery of the center hole.
[0021]
An example of the relationship between frequency and admittance when the height of the protrusion 5a is fixed to 0.25 mm and the thickness t1 of the piezoelectric element 6 and the thickness t2 of the elastic body 5 are changed is shown in FIGS. As described above, the admittance value of the resonance in the driving mode and the value of the admittance value in the unnecessary mode vary greatly depending on the thickness of the elastic body 5 and the piezoelectric element 6. It has been confirmed that the more the unnecessary mode is excited, the closer the eigenmode is to the mode in which the protrusion is located on the antinode and the mode in which the protrusion is located on the node based on the principle of the in-phase drive type ultrasonic motor. Here, a case where a so-called (3, 1) mode having three nodes in the circumferential direction and one nodal circle in the radial direction is used. ) Mode may be used, regardless of the order of the mode. For each analyzed dimension, a value obtained by dividing the peak value of the resonance mode admittance in the unwanted mode by the peak value of the resonance mode admittance in the drive mode is used as an index indicating the size of the unwanted mode as a graph. FIG. As the thickness of the piezoelectric element 6 is increased, the excitation force in the unnecessary mode suddenly increases from a certain point, and the gradient of this change is large. Therefore, when the dimensions are designed so as to exhibit such changes, the influence of the unnecessary mode is greatly changed even if there is a slight variation in the actual size of each product, and there is a risk that the characteristics of the product will vary greatly. In addition, if the unnecessary mode is greatly excited, the excitation force in the drive mode is weakened accordingly. As a guide, the index indicating the size of the unnecessary mode is 0.1, and the thickness of the piezoelectric element 6 and the elastic body 5 may be set so as not to exceed it. From this result, it has been confirmed that the tendency is not greatly influenced by the thickness of the elastic body 5 and is greatly influenced by the thickness of the piezoelectric element 6, so the index indicating the size of the unnecessary mode is 0.1 or less. Such a thickness of the piezoelectric element 6 may be used.
[0022]
Further, the relationship between the thickness of the elastic body 5 and the piezoelectric element 6 and the electromechanical coupling coefficient k shown in FIGS. 10 and 11 and the relationship between the thickness of the elastic body 5 and the piezoelectric element 6 and the size of the unnecessary mode are compared as follows. I found out. In the range where the electro-mechanical coupling coefficient is near the maximum or thinner than the thickness of the piezoelectric element 6 at this point, the excitation force in the unnecessary mode is small, and the thickness of the piezoelectric element 6 may be set in this range. In particular, the unnecessary mode is not excited at all (FIG. 6A) is in a range thinner than the thickness of the piezoelectric element 6 having the maximum electro-mechanical coupling coefficient. However, if priority is given to the output of the motor, the thickness may be set so that the electro-mechanical coupling coefficient is maximized. Incidentally, the value of the electro-mechanical coupling coefficient was obtained from the relationship between frequency and admittance analyzed under the condition that the drive signal was applied between the entire piezoelectric element 6, that is, the electrodes 7a, 7b and 7c. Under this condition, since the unnecessary mode is not excited, the electromechanical coupling coefficient can be easily evaluated.
[0023]
However, even under the above conditions, the unnecessary mode is greatly excited when the thickness of the piezoelectric element 6 is 30 μm and the thickness of the elastic body is 0.35 mm. (FIG. 7 (e)) This is the influence of in-plane vibration having the same wave number as bending vibration. FIG. 12 and FIG. 13 show the relationship between the natural frequency of bending vibration and the natural frequency of in-plane vibration each having a degenerate mode. As can be seen from the results of FIGS. 6, 7, 12, and 13, the thickness of the vibrating body, that is, the piezoelectric element 6 and the elastic body 5 is set so that the natural frequency of the bending vibration is not located near the natural frequency of the in-plane vibration. Set it.
[0024]
{Embodiment 2}
It has been found that the size of the unnecessary mode changes depending on the height of the protrusion 5a provided on the elastic body 5. The case where the thickness of the elastic body 5 was fixed to 0.25 mm, the thickness of the piezoelectric element 6 was fixed to 80 μm, and the height of the protrusion 5 a was changed with respect to the model of FIG. As an example, FIG. 14 shows the frequency-admittance relationship when the height of the protrusion 5a is 0.4 mm. Thus, the resonance admittance value in the driving mode and the admittance value in the unnecessary mode vary greatly depending on the height of the protrusion 5a. It is confirmed that the eigenmode is closer to the mode in which the protrusion 5a is located on the belly and the mode in which the protrusion 5a is located on the node, based on the principle of the common-phase drive type ultrasonic motor, as the unnecessary mode is greatly excited. . FIG. 15 is a graph showing a value obtained by dividing the admittance value of the unnecessary mode resonance by the admittance value of the resonance in the drive mode as an index indicating the size of the unnecessary mode for each analyzed dimension. As the protrusion 5a is made higher, the unnecessary mode excitation force suddenly increases from the vicinity of the protrusion height of 0.3 mm (the index indicating the size of the unnecessary mode is 0.043), and the gradient of this change is large. Therefore, if the dimensions are designed so as to exhibit such changes, the influence of the unnecessary mode is greatly changed even if there is a slight variation in the actual size of each product, and there is a risk that the characteristics of the product will vary greatly. If the unnecessary mode is greatly excited, the driving force in the driving mode is reduced accordingly. The smaller the excitation force in the unnecessary mode, the better, but the limit for driving by self-excited oscillation is that the index indicating the size of the unnecessary mode is about 0.1, and the height of the protrusion should be set so that it does not exceed it. That's fine. When judging comprehensively from the above matters, the protrusion may be set lower than the height of the protrusion at which the index indicating the size of the unnecessary mode is 0.05.
[0025]
{Third embodiment}
In the first embodiment, it has been shown that the size of the unnecessary mode is affected by the thickness of the piezoelectric element 6. The following can be considered as this reason. Because the two electrode groups 7b and 7c and the common electrode 7a are shared as GND, the piezoelectric longitudinal effect (d ₃₃ ) also works at the boundary between the two electrodes 7b and 7c as shown in FIG. The reason why the unnecessary mode is greatly excited when the thickness of the piezoelectric element 6 is increased is considered to be that the influence increases as the thickness of the piezoelectric element 6 increases and the mode pattern shifts.
[0026]
Therefore, as shown in FIG. 17, the common electrode is divided so that the front and back electrodes have the same shape. That is, driving is performed by applying a drive signal between the electrodes 7b and 7d or by applying a drive signal between the electrodes 7c and 7e.
[0027]
An example of actual analysis is shown in FIG. 18, but it can be seen that even when the thickness of the piezoelectric element is increased, the magnitude of the excitation force in the unnecessary mode is smaller than when the conventional electrode shown in FIG. 5 is used. In this analysis, the convenience of the analysis model and the gap between the electrodes are set as the width of the protrusion 5a. However, since it can actually be made smaller than this, the excitation force in the unnecessary mode is further reduced.
[0028]
As a method of using the electrode of the present invention, for example, an insulating layer is provided on the joint surface between the elastic body 5 and the piezoelectric element 6 or the elastic body 5 itself is made of an insulating material. The electrode on the joint surface of the piezoelectric element 6 with the elastic body 5 is drawn through the inner diameter side surface or the outer diameter side surface of the piezoelectric element 6 and a drive signal is applied.
[0029]
It is also possible to use in-plane vibration as the vibration mode used for driving the motor. In this case, the elastic body 5 is unnecessary, and thus, for example, on the outer peripheral side surface of the piezoelectric element 6 having the same electrode shape on the front and back sides. What is necessary is just to provide the protrusion 5a and to make it contact with the mobile body 4. FIG.
[0030]
{Embodiment 4}
FIG. 19 is a block diagram in which an ultrasonic motor 20 driven by a drive circuit of the present invention is applied to a drive source of an electronic device. The piezoelectric element 10 and an elastic body 11 bonded to the piezoelectric element, A moving body 12 that is frictionally driven by the body 11, a transmission mechanism 13 that operates integrally with the moving body 12, and an output mechanism 14 that operates based on the operation of the transmission mechanism 13. For example, when driven by in-plane vibration, the elastic body 11 may be composed of only the piezoelectric element 10.
[0031]
Here, the transmission mechanism 13 uses a transmission wheel such as a gear train or a friction wheel, for example. The output mechanism 14 includes a paper feed mechanism in a printer, a shutter drive mechanism, a lens drive mechanism, a film winding mechanism in a camera, a pointer in an electronic device and a measuring instrument, an arm mechanism in a robot, and a machine tool. In this case, a tooth tool feeding mechanism, a processing member feeding mechanism, or the like is used.
[0032]
Note that an electronic timepiece, a measuring instrument, a camera, a printer, a printing machine, a robot, a machine tool, a game machine, an optical information device, a medical device, a moving device, and the like can be realized as the electronic device in this embodiment. Furthermore, if the moving body 12 is provided with an output shaft and has a power transmission mechanism for transmitting torque from the output shaft, an electronic apparatus with an ultrasonic motor can be realized.
[0033]
By applying the ultrasonic motor of the present invention to an electronic device, the electronic device can be reduced in voltage, reduced in power consumption, reduced in size, and reduced in cost. Naturally, since an ultrasonic motor is used, it is not affected by magnetism and no harmful magnetic noise is generated.
[0034]
【The invention's effect】
As described above, the present invention optimizes the design parameters of the vibrating body, so that the protrusion can excite the vibration mode located between the antinode and the node of the vibration. An ultrasonic motor can be obtained in which individual variations are small and performance fluctuations are small even with respect to temperature and load. In addition, since only one eigenmode is excited at the time of signal input and the vibrator has almost one resonance peak electrically, stable self-excited drive can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing the structure and principle of an in-phase drive type ultrasonic motor.
FIG. 2 is a diagram illustrating resonance characteristics of a vibrating body of an in-phase drive type ultrasonic motor.
FIG. 3 is a diagram illustrating a driving principle of an ultrasonic motor according to the present invention.
FIG. 4 is a diagram showing resonance characteristics of a vibrating body of an ultrasonic motor according to the present invention.
FIG. 5 is a diagram showing an analysis model of a vibrating body of the ultrasonic motor of the present invention.
FIG. 6 is a diagram showing a result of eigenvalue analysis of the ultrasonic motor of the present invention.
FIG. 7 is a diagram showing a result of eigenvalue analysis of the ultrasonic motor of the present invention.
FIG. 8 is a graph showing the relationship between the thickness of a vibrating body and the magnitude of excitation force in an unnecessary mode.
FIG. 9 is a table showing the relationship between the thickness of the vibrator and the magnitude of the excitation force in the unnecessary mode.
FIG. 10 is a diagram illustrating a relationship between the thickness of a vibrating body and an electro-mechanical coupling coefficient.
FIG. 11 is a diagram showing the relationship between the thickness of a vibrating body and an electro-mechanical coupling coefficient.
FIG. 12 is a diagram showing the relationship between the bending vibration and the natural vibration of the in-plane vibration when the thickness of the vibrating body is changed.
FIG. 13 is a diagram showing the relationship between flexural vibration and in-plane natural vibration when the thickness of the vibrating body is changed.
FIG. 14 is a diagram illustrating resonance characteristics of a vibrating body having a protrusion height of 0.4 mm.
FIG. 15 is a diagram illustrating a relationship between a protrusion height and an excitation force in an unnecessary mode.
FIG. 16 is a diagram showing the influence of a common electrode.
FIG. 17 is a diagram showing an electrode pattern of the present invention.
FIG. 18 is a diagram showing an analysis result of resonance characteristics when the electrode pattern of the present invention is used.
FIG. 19 is a diagram showing a block diagram of an example in which the ultrasonic motor of the present invention is applied to an electronic device.
[Explanation of symbols]
1, 5, 10 Elastic body 2, 6, 11 Piezoelectric element 4, 12 Moving body 7 Electrode

Claims

Electrodes are provided on the first surface at intervals of a quarter wavelength of the vibration excited in the circumferential direction, and electrodes are provided on the second surface at positions opposite to the electrodes on the first surface. A piezoelectric element having two electrode groups by short-circuiting, an elastic body bonded to the first surface of the piezoelectric element, and an electrode on the second surface of the piezoelectric element of the elastic body and located at the boundary between the electrodes Between the electrode on the first surface facing the one of the two electrode groups on the second surface, in contact with the protrusion, and the vibrating body comprising the protrusion provided on the portion to be An ultrasonic motor comprising: a moving body driven by bending vibration of the vibrating body obtained by applying a driving signal to the motor.

Two electrode groups having electrodes on the first surface almost entirely and shorting every other electrode provided in the circumferential direction of the second surface at quarter-wave intervals of the vibration to be excited A piezoelectric element comprising: an elastic body joined to the piezoelectric element; and a vibrating body comprising a protrusion provided at a portion of the elastic body located on the boundary between the electrode of the second surface of the piezoelectric element; By bending vibration of the vibrating body obtained by applying a drive signal between one of the two electrode groups of the first surface and the second surface, in contact with the protrusion. The piezoelectric element has a thickness of the piezoelectric element, and, among the two vibrations that are a degenerate mode excited by the vibrating body, the resonance admittance peak value of the driving mode is set to the peak value of the admittance of the unnecessary mode So that the value divided by the peak value is lower than 0.1 Ultrasonic motor, which is a set thickness.

Two electrode groups having electrodes on the first surface almost entirely and shorting every other electrode provided in the circumferential direction of the second surface at quarter-wave intervals of the vibration to be excited A piezoelectric element comprising: an elastic body joined to the piezoelectric element; an oscillating body comprising a protrusion provided at a portion of the elastic body at the boundary between the electrode and the second surface; and the protrusion. In contact with each other and driven by bending vibration of the vibrating body obtained by applying a drive signal between one of the two electrode groups of the first surface and the second electrode group of the second surface A moving body,
As for the thickness of the piezoelectric element, the value taken by the electro-mechanical coupling coefficient of the vibrating body when a drive signal is applied between the electrode group on the first surface and the two electrode groups on the second surface is the maximum. An ultrasonic motor characterized by being set near the thickness.

Two electrode groups having electrodes on the first surface almost entirely and shorting every other electrode provided in the circumferential direction of the second surface at quarter-wave intervals of the vibration to be excited A piezoelectric element comprising: an elastic body joined to the piezoelectric element; an oscillating body comprising a protrusion provided at a portion of the elastic body at the boundary between the electrode and the second surface; and the protrusion. In contact with each other and driven by bending vibration of the vibrating body obtained by applying a drive signal between one of the two electrode groups of the first surface and the second electrode group of the second surface Have a moving body,
Regarding the thickness of the piezoelectric element, the value of the electro-mechanical coupling coefficient of the vibrating body is maximized when a drive signal is applied between the electrode group on the first surface and the two electrode groups on the second surface. An ultrasonic motor characterized by being set to be thinner than the thickness.

5. The ultrasonic motor according to claim 2, wherein a thickness of the vibrating body is equal to a natural frequency of in-plane vibration of the vibrating body having the same wave number as the bending vibration. An ultrasonic motor characterized in that it is set to deviate from the vicinity of the natural frequency of .

An ultrasonic motor comprising a self-excited oscillation circuit comprising the ultrasonic motor according to any one of claims 1 to 5 and an amplifier circuit, and driving the movable body.

An electronic apparatus with an ultrasonic motor, comprising the ultrasonic motor according to claim 1.