JP4352511B2 - Truss type actuator - Google Patents

Description

一方、ばねの位置エネルギーEpは、
Ep＝(1/2)Kx(t)²＝(1/2)KX²cos²ωt
エネルギー法によると、ばねの運動エネルギーEkと位置エネルギーEpの最大値は等しいので、
(1/6)μLω²X²＝(1/2)KX²
これにより、質量mのばねの固有振動数は以下のように表される。
ω²＝K/(μL/3)＝K/(m/3)
【００３９】
これに対して、質量のないばね（ばね定数：K）の一端を固定し、他端に質量Mの重りを取り付けた場合の伸び振動の固有振動数は以下のように表される。
ω²＝K/M
【００４０】
従って、質量のあるばねの固有振動数は、同じばね定数を有し質量のないばねの一端に自重の１／３の重りを取り付けた系と等価である。
【００４１】
次に、チップ部材の質量をＭ、圧電素子の質量をm(m₁＝m/3)、圧電素子の先端の変位量をx、ばね定数k₁として、系全体の位置エネルギーEp及び運動エネルギーEkは以下のように表される。
Ep＝(1/2)k₁x²×2
Ek＝(1/2)M(√2dx/dt)²＋(1/2)m₁(dx/dt)²×2
X(t)＝Xcosωtとして、エネルギー法を用いると、
k₁X²＝Mω²X²＋m₁ω²X²
【００４２】
ここで、圧電素子の張力をT、応力をσ、弾性率をE、歪みをεとして、フックの法則は以下のように表される。
T＝k₁X， σ＝Eε
【００４３】
圧電素子の長さをL、断面積をSとすると、σ＝T/S、ε＝x/Lとなるので、k₁＝SE/Lとなる。従って、逆位相モードにおける伸び振動数ω₁は以下の式(1)のように表すことができる。
ω₁ ²＝k₁/(M＋m₁)＝SE/L(M＋m/3) ・・・(1)
【００４４】
拘束状態における同位相モードの伸び振動のモデル化
同位相モードの伸び振動は、図１２に示すように、質量ばねと重りによる伸び振動と、質量のある両端固定梁（の半分）による曲げ振動が合成された系とみなすことができる。このように複数個の復元要素、慣性要素によって構成される複合振動系の固有振動数は、孤立系の振動数を合成することにより推定することができる（振動数合成法）。復元要素は並列に、慣性要素は直列に、それぞれ連結されているので、複合系の固有振動数は、孤立系のばね定数、質量をそれぞれ加算することにより求められる。
【００４５】
伸び振動は上記逆位相モードの場合と異ならないので、曲げ振動のばね定数をk₂、等価質量をm₂として、複合系の固有振動数ω₂は以下のように表される。
ω₂ ²＝(k₁＋k₂)/(M＋m₁＋m₂)
【００４６】
質量のある梁の場合、密度をρ、断面積をS、曲げ剛性EI、長さをLとして、梁の両端を固定した場合、その曲げ振動の固有振動数は以下のように求めることができる。
【００４７】
梁の曲げ振動の位置エネルギーEp及び運動エネルギーEkは、
Ep＝(1/2)∫EI(d²y/dx²)²dx
Ek＝(1/2)∫ρS(dy/dt)²dx
となる。梁の静的なたわみ曲線をY(x)とし、その振動がy(x,t)＝Y(x)cosωtで表されると仮定すると、上記各式は、
Ep＝(1/2)EIcos²ωt∫(d²Y(x)/dx²)²dx
Ek＝(1/2)ρSω²cos²ωt∫Y(x)²dx
となる。さらに、等分布荷重を受ける両端固定梁では、Y(x)は以下のように表される。
Y(x)＝(ρS/24EI)x²(L−x)²
【００４８】
これを上記式に代入すると、

となる。以上より、質量mの両端固定梁の固有振動数は以下のように表される。
ω²＝4×630EI/5ρSL⁴＝504EI/mL³
【００４９】
一方、両端が固定された質量のない梁の中央に質量Mの重りを取り付けたときの変位yは、y＝MgL³/192EIで表される。この梁の固有振動数は以下のように表される。
ω²＝K/L＝192EI/ML³
【００５０】
従って、質量のある両端固定梁の固有振動数は、同じ曲げ剛性を有する質量のない梁の中央部に自重の192/504≒1/2.63の重りを取り付けた系と等価である。
【００５１】
そこで、L'=L/2、M'=M/2とすると、変位ｙは等しいので、
y＝MgL³/192EI＝(2M')g(2L')³/192EI＝M'gL'³/12EI
となる。これより、両端固定梁の半分による曲げ振動系のばね定数と等価質量は以下のように表される。
K₂＝12EI/L'³， m₂＝m/2.63
【００５２】
従って、同位相モードの伸び振動数ω₂は以下の式(2)ように表すことができる。
ω₂ ²＝(SE/L＋12EI/L³)/(M＋m/3＋m/2.63) ・・・(2)
【００５３】
チップ部材の軌跡が円となる条件
チップ部材の軌跡が円となるためには、同位相モードの伸び振動数ω₁と逆位相モードの伸び振動数ω₂が一致する必要がある。すなわち、
SE/L(M＋m/3)＝(SE/L＋12EI/L³)/(M＋m/3＋m/2.63)
となる必要がある。ここで、S＝W×H、I＝WH³/12を用いて整理すると（但し、W及びHはそれぞれ圧電素子の断面の幅及び高さとする）、ω₁とω₂が一致するための条件は、以下の式(3)で表される。
M＝(L²/H²−0.88)×m/2.63 ・・・(3)
【００５４】
このように、圧電素子の質量mが同じであっても、その断面の縦横比L/Hが大きいと、最適なチップ部材の質量Mが大きくなることがわかる。
【００５５】
非拘束状態における逆位相モードの伸び振動のモデル化
ベース部材を拘束しない状態での固有振動を記述する場合、基準となる振動の節を見つける必要がある。振動の節とは、振動が生じても変位しないところであり、共振状態では節を挟んで両側の振動数が一致する。一般的な圧電素子の片側が拘束された系を図１３（ａ）に示す。また、両側とも拘束されていない系を図１３（ｂ）に示す。（ａ）に示す場合、圧電素子の拘束された側の端部が振動の節となる。一方、（ｂ）に示す場合、圧電素子の中心線上に振動の節ができ、これを挟んで両側の振動数が一致する。従って、（ａ）の場合と比較してばね強数が２倍に、質量が１／２になるため、振動数は２倍になる。
【００５６】
次に、逆位相モードの伸び振動を図１４に示す。図１４中左側の（ａ）における略水平に配置された圧電素子に着目すると、その左端にはベース部材が、右端にはチップ部材がそれぞれ取り付けられている。ベース部材は回転する棒とみなすことができ、また略垂直に配置された圧電素子の影響を無視することができるので、対称となる振動系は、質量のあるばねに重りが取り付けられた系で表すことができる。
【００５７】
圧電素子の質量をm、伸び振動のばね定数をk₁、圧電素子の全長に対するベース部材の端から節までの長さの比率をp（0≦p≦1）とすると、節を挟んで左右の振動系の質量m_L，m_Rとばね定数k_L,k_Rは以下のように表される。
m_L＝pm k_L＝k₁/p
m_R＝(1-p)m k_R＝k₁/(1-p)
【００５８】
チップ部材の質量をM_c、ベース部材の慣性モーメント（の半分）をI_z、ベース部材の回転半径をR、節に対して左右の振動系の変位をそれぞれx_L，x_Rとすると、エネルギーは以下の式で表される。
(1/2)k_Lx_L ²＝(1/2)I_z(d(x_L/R)/dt)²＋(1/2)(m_L/3)(dx_L/dt)²
(1/2)k_Rx_R ²＝(1/2)M_c(dx_R/dt)²＋(1/2)(m_R/3)(dx_R/dt)²
【００５９】
ここで、x_L＝x_Lcosωt、x_R＝x_Rcosωtと仮定して上記式に代入すると、左右の振動系の各振動数ω_L，ω_Rは、それぞれ以下の式(4)で表される。
ω_L ²＝(k₁/p)/(I_z/R²＋pm/3)
ω_R ²＝(k₁/(1-p))/(M_c＋(1-p)m/3) ・・・(4)
【００６０】
節を挟んで両者の固有振動数が等しくなるので、
(k₁/p)/(I_z/R²＋pm/3)＝(k₁/(1-p))/(M_c＋(1-p)m/3)
上記式より、節の位置は以下の式(5)のように求まる。
p＝(M_c＋m/3)/(M_c＋I_z/R²＋2m/3) ・・・(5)
【００６１】
このようにして得られたpを式(4)に代入することにより、逆位相モードにおける固有振動数を求めることができる。
【００６２】
非拘束状態における同位相モードの伸び振動のモデル化
次に、同位相モードの伸び振動を図１５に示す。逆位相モードの場合と同様に、図１５中左上の（ａ）における略水平に配置された圧電素子に着目すると、その左端にはベース部材が、右端にはチップ部材を介して他の圧電素子が取り付けられている。ベース部材は下部が固定された片持ち梁とみなすことができ、各圧電素子は両端支持梁の半分とみなすことができる。
【００６３】
圧電素子の長さの比率をq(0≦q≦1)、ベース部材の曲げ変形のばね定数をk₂、ベース部材の等価質量をM_b'、圧電素子の曲げ変形のばね定数をk₃とすると、節を挟んで左右の各振動数ω_L，ω_Rはそれぞれ以下の式(6)で表される。
ω_L ²＝(k₁/q＋k₂)/(M_b'＋qm/3)
ω_R ²＝(k₁/(1-q)＋k₃)/(M_c＋(1-q)m/3＋m/2) ・・・(6)
【００６４】
節を挟んで左右の共振周波数は等しくなるので、
(k₁/q＋k₂)/(M_b'＋qm/3)＝(k₁/(1-q)＋k₃)/(M_c＋(1-q)m/3＋m/2) ・・・(7)
となる。(7)式はqに関する３次式であり、一般的に説くことは困難である。そこで、q(0≦q≦1)に適当な値を代入したところ、qとMｃとの関係は、以下の式(8)で近似することがわかった。但し、Nは定数とする。
M_c＋5m/6≒qN/(1-q) ・・・(8)
【００６５】
(8)式を変形してNを求めると、
N＝(M_b'+mq/3)×(k₁＋(1-q)k₃)/(k₁＋k₂q)＋m(1-q)/3
ここで、k₁≫k₂，k₃と仮定すると、
N≒(M_b'＋mq/3)+m(1-q)/3
＝M_b'＋m/3
このNの値を(8)式に代入すると、同位相モードにおける節の位置は以下の式(9)のように求めることができる。
q＝(M_c+5m/6)/(M_c＋5m/6＋M_b'＋m/3)
＝(M_c+5m/6)/(M_c＋M_b'＋7m/６)
【００６６】
このようにして得られたqを上記(6)式に代入することにより、同位相モードにおける固有振動数を求めることができる。
【００６７】
その他の実施形態
上記実施形態では、変位素子として圧電素子を用いているが、一般に圧電素子はセラミックス材料で作られており、金属材料と比較して振動の減衰が大きく、共振時の変位拡大率が小さい。また、セラミックスは圧縮力には強いが引っ張り力には弱く、特に積層型圧電素子の場合、その接着面で剥がれる可能性もある。そこで、変位素子として単層の圧電素子と金属製の弾性体を直列接続したものを用いることもできる。この変位素子を用いたトラス型アクチュエータの構成を図１６に示す。第１変位素子６０及び第２変位素子６０’は、それぞれ単層の圧電素子（セラミックス薄板）６１，６１’と及び弾性体６２，６２’で構成され、圧電素子６１，６１’の両面には電極は設けられていない。また、第１変位素子６０及び第２変位素子６０’は、それぞれ接着剤を用いずに、ボルト６３，６３’によりチップ部材２０及びベース部材３０に固定されている。弾性体６２，６２’及びベース部材３０をそれぞれ導電性材料で形成し、弾性体６２，６２’及びベース部材３０の間に駆動電源１６，１６’を接続し、第１変位素子６０及び第２変位素子６０’をそれぞれ上記共振周波数で駆動する。
【００６８】
圧電素子６１，６１’を振動源として弾性体６２，６２’を共振させることにより変位を拡大することができる。また、金属材料の減衰が小さいため変位がより拡大し、圧電素子６１，６１’に加わる引っ張り力が小さくなるため、圧電素子６１，６１’の破壊を防止することも可能である。弾性体６２，６２’の材料としては、アルミニウム、チタン、鉄、銅及びそれらの合金等を用いる。単層の圧電素子６１，６１’の変位素子全体に占める長さ方向の割合は非常に小さい。従って、上記固有振動モードを演算する際、圧電素子の影響を無視しても問題はない。
【００６９】
なお、上記実施形態の説明では、振動モードのモデル化による解析方法により共振周波数を求めたが、有限要素法による解析、インピーダンスアナライザによる実測等によっても求めることができる。また、チップ部材２０を駆動するための２つの変位素子１０，１０’又は６０，６０’をそれぞれ直交するように配置したが、これに限定されるものではなく、その他の角度、例えば４５°、１３５°等任意の角度であってもよい。さらに、変位素子の数は２つに限定されず、従来例１のように変位素子を３個、あるいはそれ以上用いて、３自由度又は４自由度の駆動を行うように構成してもよい。さらに、変位素子の駆動源として、圧電素子だけでなく、磁歪素子等他の電気的又は機械的変位素子を用いてもよい。
【００７０】
【発明の効果】
以上説明したように、本発明のトラス型アクチュエータは、所定の変位を発生させる複数の変位素子と、前記複数の変位素子にそれぞれ結合され、前記各変位素子の変位を合成するための変位合成部と、前記各変位素子の前記変位合成部が結合されていない側の端部を支持するための固定部と、前記変位合成部を被駆動部材に圧接させるための加圧部と、前記合成部が楕円運動を行うように前記各変位素子を共振駆動する駆動部とを含むので、共振現象を利用して変位部材の変位を拡大し、駆動効率を向上させることができる。
【００７１】
また、各変位素子が同じ位相で共振する固有振動モードにおける固有振動数と、前記各変位素子が逆位相で共振する固有振動モードにおける固有振動数とをほぼ一致させることにより、変位素子の共振による変形抵抗が減少し、変位がより拡大されるため、駆動効率をさらに高くすることができる。
【００７２】
さらに、変位合成部の質量をM、変位素子の長さをL、その高さをH、その質量をmとし、M＝(L²/H²−0.88)m/2.63 の条件を満足させることにより、各変位素子が独立して共振することができ、入力信号の振幅及び位相を任意に制御することにより、アクチュエータの回転方向、速度、駆動力等を制御することができる。
【００７３】
さらに、変位合成部の質量をM_c、変位素子の質量をm、その伸び変形のばね定数をk₁、その曲げ変形のばね定数をk₃、固定部の慣性モーメントをI_z、その回転半径をR、片持ち梁に置き換えたときの固定部の等価質量をM_b'として、
(k₁/(1-p))/(M_c＋(1-p)m/3)＝(k₁/(1-q)＋k₃)/(M_c＋(1-q)m/3＋m/2)
但し、
p＝(M_c＋m/3)/(M_c＋I_z/R²＋2m/3)
q＝(M_c+5m/6)/(M_c＋M_b'＋7m/6)
の関係を満足させることにより、設計変更可能な部材を選択することが可能となり、上記トラス型アクチュエータを容易に実現することが可能となる。
【００７４】
さらに、変位素子の少なくとも一部を弾性体とすることにより、変位素子の変位の拡大率及び駆動効率をさらに向上することができる。また、変位素子を積層する必要がないため、製造コストの低減及び素子の破壊防止をはかることができる。
【図面の簡単な説明】
【図１】 本発明のトラス型アクチュエータの一実施形態において変位素子として用いる積層型圧電素子の構成を示す図である。
【図２】 上記積層型圧電素子における各電極の間に発生する電界と圧電素子の変位の関係を示す図である。
【図３】 上記実施形態におけるトラス型アクチュエータの構成を示す図である。
【図４】 上記実施形態における駆動回路のブロック構成を示す図である。
【図５】 上記実施形態のアクチュエータによるロータの回転原理を示す図であり、図３に示すアクチュエータをばねによりロータ押しつけた状態を示す。
【図６】 上記実施形態における２つの圧電素子に印加する電圧又はそれらの変位を示す図である。
【図７】 上記実施形態におけるアクチュエータによりロータを回転させる原理を示す図である。
【図８】 上記実施形態において、２つの圧電素子に印加する駆動信号の振幅を等しくし、各駆動信号間の位相差を変化させた場合の軌跡を示す図である。
【図９】 上記実施形態において、ベース部材を拘束した状態で、各圧電素子をそれぞれ同位相モード及び逆位相モードで駆動した場合における、アクチュエータの状態を示す図である。
【図１０】 上記実施形態において、ベース部材を拘束しない状態で、各圧電素子をそれぞれ同位相モード及び逆位相モードで駆動した場合における、アクチュエータの状態を示す図である。
【図１１】 拘束状態における逆位相モードの伸び振動のモデル化を示す図である。
【図１２】 拘束状態における同位相モードの伸び振動のモデル化を示す図である。
【図１３】 （ａ）は一般的な圧電素子の片側が拘束された系を示す図であり、（ｂ）は両側とも拘束されていない系を示す図である。
【図１４】 非拘束状態における逆位相モードの伸び振動のモデル化を示す図である。
【図１５】 非拘束状態における同位相モードの伸び振動のモデル化を示す図である。
【図１６】 本発明のトラス型アクチュエータの他の実施形態の構成を示す図である。
【符号の説明】
１０ ：第１圧電素子（変位素子）
１０’：第２圧電素子（変位素子）
１１ ：セラミックス薄板
１６，１６’：駆動電源（駆動部）
２０ ：チップ部材（変位合成部）
３０ ：ベース部材（固定部）
４０ ：ロータ（被駆動部材）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an actuator using a displacement element such as a piezoelectric element, particularly a truss-type actuator that generates an elliptical motion by synthesizing the displacement of a plurality of displacement elements. It relates to technology to improve.
[0002]
[Prior art]
Conventionally, in the field of truss actuators, there is known a technique in which a tip member is provided at the intersection of three laminated piezoelectric elements, the tip member is driven to draw a spherical surface, and the spherical driven member is swung in any direction. (Development of a three-degree-of-freedom small actuator (1st report): see Sasae et al., Journal of Precision Engineering, Vol. 61, No. 31, 1995, hereinafter referred to as Conventional Example 1).
[0003]
In addition, the steel plate is punched out so that the two displacement parts are orthogonal to each other, piezoelectric elements are attached to both surfaces of each displacement part, and the piezoelectric element on either side is driven to resonate to cover the apex where the displacement parts intersect. A thin plate truss type actuator that strikes the drive member diagonally and moves the driven member in a predetermined direction is also known (production and evaluation of a thin ultrasonic linear motor: Nagatome et al., 1998 Precision Engineering Society Spring Meeting Refer to Proceedings of the Academic Lecture Conference (hereinafter referred to as Conventional Example 2).
[0004]
On the other hand, in the field of traveling wave actuators, a plurality of piezoelectric elements are attached in a comb shape on the upper surface of an annular elastic body, and a traveling wave is generated in the axial direction of the annular elastic body by causing the elastic body to resonate. A device that rotates a driven member around its axis is known (see, for example, Introduction to Ultrasonic Motors, General Electronic Publishing Company, hereinafter referred to as Conventional Example 3).
[0005]
In addition, in order to obtain a linear actuator, a plurality of piezoelectric elements are attached to the side surface of an elliptical elastic body, each piezoelectric element is driven in two types of natural vibration modes, and the displacement is synthesized to synthesize the surface of the elliptical elastic body. That generate traveling waves in the direction parallel to the oval cross section is also known (see Piezoelectric traveling wave linear actuator 1st report: Oku et al., Proc. Conventional example 4).
[0006]
[Problems to be solved by the invention]
The conventional example 1 has a problem that since the piezoelectric element is driven in a non-resonant state, the amount of displacement of the piezoelectric element is small and the driving efficiency is low.
[0007]
According to Conventional Example 2, since the piezoelectric element is driven to resonate, the amount of displacement can be increased. However, since the apex portion of the steel plate collides linearly with the driven member, noise and vibration are large, and the steel plate and the driven member are severely worn.
[0008]
Conventional Example 3 has a problem that both the driven member and the elastic body are substantially the same shape and annular, and the degree of freedom in design is small.
[0009]
Conventional Example 4 has a problem that the entire elliptical elastic body is resonated, so that the mass is large and the driving frequency and output are small. In addition, there is a problem that it is difficult to set the resonance condition and to fix the elliptical elastic body. Furthermore, the deformation is complicated and the conditions for obtaining the desired elliptical motion are complicated.
[0010]
The present invention has been made to solve the above-described problems of the conventional example, and an object thereof is to provide a truss-type actuator that has a simple structure, is easy to control, and has high driving efficiency.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a truss-type actuator according to the present invention includes a plurality of displacement elements that generate a predetermined displacement and a displacement composition that is coupled to each of the plurality of displacement elements and synthesizes the displacements of the displacement elements. A fixing portion for supporting an end of each displacement element on the side where the displacement combining portion is not coupled, a pressurizing portion for pressing the displacement combining portion against a driven member, and the combining And a driving unit that resonates and drives each of the displacement elements so that the unit performs an elliptical motion.
[0012]
In the above configuration, it is preferable that the natural frequency in the natural vibration mode in which the displacement elements resonate in the same phase and the natural frequency in the natural vibration mode in which the displacement elements resonate in the opposite phase are substantially the same.
[0013]
Further, the mass of the displacement combining unit is M, the length of the displacement element is L, its height is H, its mass is m, and M = (L²/ H²−0.88) m / 2.63 is preferably satisfied.
[0014]
Further, the mass of the displacement combining unit is M_c, M represents the mass of the displacement element, and k represents the spring constant of its extension deformation.₁, The spring constant of the bending deformation is k_Three, The moment of inertia of the fixed part is I_z, The radius of rotation is R, and the equivalent mass of the fixed part when replaced with a cantilever is M_bAs
(k₁/ (1-p)) / (M_c+ (1-p) m / 3) = (k₁/ (1-q) + k_Three) / (M_c+ (1-q) m / 3 + m / 2)
However,
p = (M_c+ M / 3) / (M_c+ I_z/ R²+ 2m / 3)
q = (M_c+ 5m / 6) / (M_c+ M_b'+ 7m / 6)
It is preferable to satisfy this relationship.
[0015]
Furthermore, the displacement element preferably includes an elastic body at least partially.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of the truss type actuator of the present invention will be described. First, FIG. 1 shows a configuration of a multilayer piezoelectric element used as a displacement element in the present embodiment. As shown in FIG. 1, the multilayer piezoelectric element 10 is formed by alternately laminating a plurality of ceramic thin plates 11 and electrodes 12 and 13 exhibiting piezoelectric characteristics such as PZT, and each of the ceramic thin plates 11 and the electrodes 12 and 13. Is fixed by an adhesive or the like. The electrode groups 12 and 13 arranged every other line are connected to the drive power supply 16 via signal lines 14 and 15, respectively. When a predetermined voltage is applied between the signal lines 14 and 15, an electric field is generated in the lamination direction of each ceramic thin plate 11 sandwiched between the electrodes 12 and 13, and every other electric field is in the same direction. . Accordingly, the ceramic thin plates 11 are laminated so that every other ceramic thin plate 11 has the same polarization direction (the polarization directions of two adjacent ceramic thin plates 11 are opposite). Note that protective layers 17 are provided at both ends of the multilayer piezoelectric element 10.
[0017]
When a DC drive voltage is applied between the electrodes 12 and 13 by the drive power supply 16, all the ceramic thin plates 11 expand or contract in the same direction and expand and contract as a whole of the piezoelectric element 10. In a region where the electric field is small and the displacement history can be ignored, the electric field generated between the electrodes 12 and 13 and the displacement of the piezoelectric element 10 can be regarded as a substantially linear relationship. This is shown in FIG. In the figure, the horizontal axis represents the electric field strength, and the vertical axis represents the distortion rate.
[0018]
Next, when an AC drive voltage (AC signal) is applied between the electrodes 12 and 13 by the drive power supply 16, the ceramic thin plates 11 repeatedly expand and contract in the same direction according to the electric field, and the piezoelectric element 10 as a whole expands and contracts. repeat. The piezoelectric element 10 has a specific resonance frequency determined by its structure and electrical characteristics. When the frequency of the alternating drive voltage matches the resonance frequency of the piezoelectric element 10, the impedance decreases and the displacement of the piezoelectric element 10 increases. Since the piezoelectric element 10 has a small displacement with respect to its outer dimensions, it is desirable to use this resonance phenomenon in order to drive at a low voltage.
[0019]
Next, FIG. 3 shows a configuration of a truss type actuator (hereinafter simply referred to as an actuator) of the present embodiment. As shown in FIG. 3, two displacement elements (laminated type first piezoelectric element and second piezoelectric element) 10 and 10 'are arranged so as to intersect each other at a substantially right angle, and a tip member (displacement) is disposed at the intersection side end portion thereof. The synthesis portion) 20 is joined with an adhesive. On the other hand, the other end portions of the first and second piezoelectric elements 10 and 10 ′ are joined to the base member (fixed portion) 30 with an adhesive. As the material of the tip member 20, tungsten or the like that can stably obtain a high coefficient of friction and is excellent in wear resistance is preferable. The material of the base member 30 is preferably stainless steel that is easy to manufacture and excellent in strength. Moreover, as an adhesive agent, the epoxy resin etc. which were excellent in adhesive force and intensity | strength are preferable. Note that the first piezoelectric element 10 and the second piezoelectric element 10 'are substantially the same as the piezoelectric element 10 shown in FIG. 1, and each component of the second piezoelectric element 10' is denoted by ('). To distinguish.
[0020]
By driving the first and second piezoelectric elements 10 and 10 ′ with AC signals having a phase difference, the tip member 20 can be elliptically moved. When the tip member 20 is pressed against, for example, the cylindrical surface of the rotor 40 that can rotate around a predetermined axis, the elliptical motion (including circular motion) of the tip member 20 can be converted into the rotational motion of the rotor 40. Become. Alternatively, by pressing the tip member 20 against, for example, a flat portion of a rod-shaped member (not shown), the elliptical motion of the tip member 20 can be converted into a linear motion of the rod-shaped member. The material of the rotor 40 is preferably a lightweight metal such as aluminum. In order to prevent wear due to friction with the tip member 20, the surface is preferably subjected to a treatment such as alumite.
[0021]
Next, FIG. 4 shows a block configuration of the drive circuit in the present embodiment. As will be described later, the oscillator 50 generates (oscillates) a sine wave signal at a resonance frequency that matches in the in-phase mode and the anti-phase mode. The phase control unit 51 controls the delay circuit 52 according to the rotational speed, driving torque, rotational direction, and the like of the rotor 40 that is a driven member, and generates a sine wave signal having a phase shift. The amplitude controller 53 controls the first amplifier 54 and the second amplifier 55 to amplify the amplitudes of two sine wave signals that are out of phase with each other. The sine wave signals amplified by the first amplifier 54 and the second amplifier 55 are applied to the first piezoelectric element 10 and the second piezoelectric element 10 ', respectively.
[0022]
Next, the principle of rotation of the rotor 40 by the actuator will be described. FIG. 5 shows a state where the actuator shown in FIG. 3 is pressed against the rotor 40 by a spring (pressurizing unit) 41 with a predetermined pressing force F. In FIG. 5, μ represents a friction coefficient. FIG. 6 shows the voltages applied to the first piezoelectric element 10 and the second piezoelectric element 10 'or their displacements. When sinusoidal voltages having different phases as shown in FIG. 6 are applied to the first piezoelectric element 10 and the second piezoelectric element 10 ′, respectively, the first piezoelectric element 10 and the second piezoelectric element 10 ′ respond to the sinusoidal wave. Is displaced. As a result, the chip member 20 coupled to each of the first piezoelectric element 10 and the second piezoelectric element 10 'performs an elliptical motion (including a circular motion).
[0023]
When the frequency of the sinusoidal voltage applied to the first piezoelectric element 10 and the second piezoelectric element 10 ′ (driving frequency of the piezoelectric element) is small and the rotation speed of the tip member 20 is slow, the actuator itself is tipped by the biasing force of the spring 41. Following the displacement of the member 20, the tip member 20 does not move away from the surface of the rotor 40, and is driven to reciprocate in contact with the surface of the rotor 40. Therefore, in this case, the rotor 40 cannot be rotated.
[0024]
On the other hand, when the frequency of the sine wave voltage applied to the first piezoelectric element 10 and the second piezoelectric element 10 ′ is large and the rotation speed of the tip member 20 is fast, the actuator itself may depend on the biasing force of the spring 41. 20 cannot follow the displacement of the tip 20, and the tip member 20 is temporarily separated from the surface of the rotor 40. Accordingly, the tip member 20 is moved in a predetermined direction while the tip member 20 is separated from the surface of the rotor 40, and the tip member 20 is moved in a direction opposite to the predetermined direction while the tip member 20 is in contact with the surface of the rotor 40. By doing so, the rotor 40 can be rotated. This state is shown in FIG.
[0025]
7A and 7E, the first piezoelectric element 10 and the second piezoelectric element 10 are both extended and the tip member 20 is in contact with the surface of the rotor 40, and FIG. 7B is the state where the first piezoelectric element 10 is in contact. The contracted second piezoelectric element 10 ′ is extended and the tip member 20 is separated from the surface of the rotor 40, (c) is the contraction of both the first piezoelectric element 10 and the second piezoelectric element 10, and the tip member 20 is the surface of the rotor 40. (D) is a state in which the first piezoelectric element 10 is extended and the second piezoelectric element 10 ′ is contracted, but the actuator catches up with the movement of the chip member 20 and the chip member 20 is in contact with the surface of the rotor 40. Indicates. As can be seen from FIG. 7, the rotor 40 can be rotated by separating the tip member 20 from the surface of the rotor 40. The conditions for separating the tip member 20 from the surface of the rotor 40 are not directly related to the essence of the present invention, and the description thereof is omitted.
[0026]
Next, drive signals for driving the first piezoelectric element 10 and the second piezoelectric element 10 'will be described. When two independent motions orthogonal to each other are synthesized, the intersection point draws a trajectory according to the elliptical vibration equation (Lissajous equation). Also in the actuator of the present embodiment, various trajectories can be obtained by changing the amplitude and phase difference of the drive signals for driving the first piezoelectric element 10 and the second piezoelectric element 10 '. When the amplitude of each drive signal is made equal, the trajectories when the phase differences between the drive signals are 0 °, 45 °, 90 °, 135 °, and 180 ° are shown in FIGS. Shown in
[0027]
Thus, by controlling the trajectory of the tip member 20, the rotation direction, rotation speed, rotation force (torque), and the like of the rotor 40 can be controlled. Specifically, if the diameter of the locus of the tip member 20 in the tangential direction with respect to the rotor 40 is increased, the rotational speed is increased. Further, if the diameter of the locus of the tip member 20 in the normal direction relative to the rotor 40 is increased, the rotational force is increased. Furthermore, if the phase is reversed, the direction of rotation can be reversed.
[0028]
Next, a case where the first piezoelectric element 10 and the second piezoelectric element 10 ′ are driven in a resonance state using sine wave signals whose phases are shifted by 90 ° and the chip member 20 is controlled to have a circular locus will be considered. .
[0029]
When the actuator shown in FIG. 3 is actually prototyped and the first piezoelectric element 10 and the second piezoelectric element 10 ′ are driven with a drive signal having a frequency close to their resonance frequency, the locus of the chip member 20 that should be essentially circular The phenomenon of deformed into an elliptical shape with a large inclination from the central axis occurred. In the course of the experiment, it was clarified that this phenomenon occurs when the vibrations of the piezoelectric elements 10 and 10 ′ affect each other via the chip member 20 and the base member 30. Since the vibration of one piezoelectric element is transmitted to the other piezoelectric element with a phase delay of about 90 °, the displacement of the piezoelectric element that is displaced later is enlarged by being superimposed on the drive signal, and the displacement of the piezoelectric element that is displaced earlier is increased. to shrink. As a result, the locus of the tip member becomes an ellipse extending in the displacement direction of the piezoelectric element that is displaced later.
[0030]
In order to solve this phenomenon, it is necessary to realize a system in which the transmission of the vibration of one piezoelectric element to the other piezoelectric element is suppressed as much as possible and the two piezoelectric elements can be displaced independently. By realizing such a system, the locus of the tip member 20 can be made circular in all frequency bands including the resonance frequency. Further, the shape of the locus of the tip member 20 can be arbitrarily changed by changing the amplitude and phase difference of the drive signal as necessary, and the speed control of the rotor 40 and the like as the driven member is performed. Can do.
[0031]
The present inventors believe that “the natural frequencies of the extension vibration in the in-phase mode and the extension vibration in the anti-phase mode match” is a condition for realizing a system in which two piezoelectric elements can be mutated independently. I guessed. Here, the in-phase mode is defined as a mode in which the phases of displacement of the two piezoelectric elements coincide, and the anti-phase mode is defined as a mode in which the phases of displacement of the two piezoelectric elements are reversed. The following shows the results of analysis using the finite element method.
[0032]
Of the resonance modes inherent in the actuator, the phase of the base member 30 is high, and the base member 30 is hardly deformed by the displacement of the piezoelectric elements 10 and 10 '(hereinafter referred to as a constrained state). FIG. 9 shows the deformation state of the mode deformed in the mode and the antiphase mode. In FIG. 9, (a) is a resonance mode (for example, 51 kHz) in which extension vibration is generated in the in-phase mode, (b) is a resonance mode (for example, 51 kHz) in which extension vibration is generated in the anti-phase mode, and (c) is in the in-phase mode. A resonance mode (for example, 157 kHz) in which bending vibration occurs, and (d) shows a resonance mode (for example, 74 kHz) in which bending vibration occurs in an antiphase mode. The frequency in each mode is a value determined by the characteristics (various conditions such as material and mass) of each part of the actuator.
[0033]
  Next, in a state where the rigidity of the base member 30 is low and the base member 30 is deformed by the displacement of the piezoelectric elements 10 and 10 '(hereinafter referred to as an unconstrained state), the piezoelectric elements 10 and 10' are respectively in the same phase mode. FIG. 10 shows the deformation state of the piezoelectric element when driven in the antiphase mode. In FIG. 10, (a) is the same phase mode.bendingResonance mode in which vibration occurs (eg 46 kHz), (b) is in antiphase modebendingResonance mode in which vibration occurs (eg 62 kHz), (c) is in-phase modeElongationResonance mode in which vibration occurs (eg 79 kHz), (d) is in antiphase modeElongationA resonance mode (for example, 72 kHz) in which vibration occurs is shown.
[0034]
As described above, in the actuator according to the present embodiment, the tip member 20 is moved by utilizing the extension vibration of the piezoelectric elements 10 and 10 ′, so that the state shown in FIGS. 9A and 9B and FIG. ) And (d) are noted. When the trajectory of the tip member is obtained by appropriately adjusting the characteristics of each part of the actuator and setting the frequency of the in-phase mode and the anti-phase mode to coincide with each other, a substantially circular trajectory is obtained, and the result supporting the above estimation is obtained. It was.
[0035]
Next, conditions of each part of the actuator for matching the frequencies of the in-phase mode and the anti-phase mode are obtained.
[0036]
Modeling elongational vibrations in antiphase mode in a constrained state.
As shown in FIG. 11, the extension phase vibration in the antiphase mode can be regarded as an extension vibration system including a mass spring and a weight. In general, since it is difficult to analytically determine the natural frequency of a spring with mass, the Rayleigh method that arbitrarily assumes a deformation curve of a spring or a beam is used as a method for obtaining an approximate solution.
[0037]
In the case of a spring having a mass, when the mass per unit length is μ, the spring constant is k, and one end of the length L is fixed, the natural frequency of the extension vibration can be obtained as follows.
[0038]
The free end of the spring makes a simple vibration with displacement x (t) = Xcosωt, and the displacement X at a position away from the fixed end_yAssuming that (t) is proportional to y / L, x_y(t) = (y / L) cosωt. Therefore, the kinetic energy Ek of the spring is

On the other hand, the potential energy Ep of the spring is
Ep = (1/2) Kx (t)²= (1/2) KX²cos²ωt
According to the energy method, the maximum value of spring kinetic energy Ek and potential energy Ep is equal,
(1/6) μLω²X²= (1/2) KX²
Thereby, the natural frequency of the spring of mass m is expressed as follows.
ω²= K / (μL / 3) = K / (m / 3)
[0039]
On the other hand, the natural frequency of the extension vibration when one end of a spring having no mass (spring constant: K) is fixed and a weight with a mass M is attached to the other end is expressed as follows.
ω²= K / M
[0040]
Therefore, the natural frequency of a spring with mass is equivalent to a system in which a weight of 1/3 of its own weight is attached to one end of a spring having the same spring constant and no mass.
[0041]
Next, the mass of the chip member is M, and the mass of the piezoelectric element is m (m₁= M / 3), displacement of the tip of the piezoelectric element is x, spring constant k₁The potential energy Ep and kinetic energy Ek of the entire system are expressed as follows.
Ep = (1/2) k₁x²× 2
Ek = (1/2) M (√2dx / dt)²+ (1/2) m₁(dx / dt)²× 2
When X (t) = Xcosωt and using the energy method,
k₁X²= Mω²X²+ M₁ω²X²
[0042]
Here, assuming that the tension of the piezoelectric element is T, the stress is σ, the elastic modulus is E, and the strain is ε, Hooke's law is expressed as follows.
T = k₁X, σ = Eε
[0043]
If the length of the piezoelectric element is L and the cross-sectional area is S, σ = T / S and ε = x / L.₁= SE / L. Therefore, the extension frequency ω in the antiphase mode₁Can be expressed as the following equation (1).
ω₁ ²= K₁/ (M + m₁) ＝ SE / L (M + m / 3) (1)
[0044]
Modeling in-phase mode stretching vibrations in a constrained state.
As shown in FIG. 12, the in-phase mode extension vibration can be regarded as a system in which the extension vibration caused by the mass spring and the weight and the bending vibration caused by the mass-fixed both ends fixed beam (half) are combined. Thus, the natural frequency of the composite vibration system composed of a plurality of restoring elements and inertia elements can be estimated by combining the frequencies of the isolated system (frequency combining method). Since the restoring elements are connected in parallel and the inertia elements are connected in series, the natural frequency of the composite system can be obtained by adding the spring constant and mass of the isolated system.
[0045]
Since the extension vibration is not different from the antiphase mode described above, the spring constant of the bending vibration is₂, M₂As the natural frequency ω of the composite system₂Is expressed as follows.
ω₂ ²= (K₁+ K₂) / (M + m₁+ M₂)
[0046]
In the case of a beam with mass, when the density is ρ, the cross-sectional area is S, the bending rigidity EI, the length is L, and both ends of the beam are fixed, the natural frequency of the bending vibration can be obtained as follows: .
[0047]
The positional energy Ep and kinetic energy Ek of the bending vibration of the beam are
Ep = (1/2) ∫EI (d²y / dx²)²dx
Ek = (1/2) ∫ρS (dy / dt)²dx
It becomes. Assuming that the static deflection curve of the beam is Y (x) and its vibration is expressed as y (x, t) = Y (x) cosωt, the above equations are
Ep = (1/2) EIcos²ωt∫ (d²Y (x) / dx²)²dx
Ek = (1/2) ρSω²cos²ωt∫Y (x)²dx
It becomes. Furthermore, Y (x) is expressed as follows for a both-end fixed beam that receives an evenly distributed load.
Y (x) = (ρS / 24EI) x²(L−x)²
[0048]
Substituting this into the above formula,

It becomes. From the above, the natural frequency of a both-end fixed beam of mass m is expressed as follows.
ω²= 4 × 630EI / 5ρSL^Four= 504EI / mL^Three
[0049]
On the other hand, when a weight of mass M is attached to the center of a massless beam with fixed ends, y = MgL^ThreeIt is represented by / 192EI. The natural frequency of this beam is expressed as follows.
ω²= K / L = 192EI / ML^Three
[0050]
Therefore, the natural frequency of a mass-fixed beam at both ends is equivalent to a system in which a weight of 192 / 504≈1 / 2.63 of its own weight is attached to the center of a massless beam having the same bending rigidity.
[0051]
So, if L '= L / 2 and M' = M / 2, the displacement y is equal,
y = MgL^Three/ 192EI = (2M ') g (2L')^Three/ 192EI = M'gL '^Three/ 12EI
It becomes. From this, the spring constant and equivalent mass of the bending vibration system with half of the fixed beams at both ends are expressed as follows.
K₂= 12EI / L '^Three, M₂= M / 2.63
[0052]
Therefore, the in-phase mode elongation frequency ω₂Can be expressed as the following equation (2).
ω₂ ²= (SE / L + 12EI / L^Three) / (M + m / 3 + m / 2.63) (2)
[0053]
Conditions that the locus of the tip member is a circle
In order for the locus of the tip member to be a circle, the in-phase mode extension frequency ω₁And antiphase mode elongation frequency ω₂Must match. That is,
SE / L (M + m / 3) = (SE / L + 12EI / L^Three) / (M + m / 3 + m / 2.63)
It is necessary to become. Where S = W × H, I = WH^Three/ 12 (W and H are the width and height of the cross section of the piezoelectric element, respectively)₁And ω₂The condition for matching is expressed by the following formula (3).
M = (L²/ H²−0.88) × m / 2.63 (3)
[0054]
Thus, it can be seen that even if the mass m of the piezoelectric elements is the same, if the aspect ratio L / H of the cross section is large, the optimum mass M of the chip member is increased.
[0055]
Modeling anti-phase mode stretching vibrations in an unconstrained state.
When describing the natural vibration without restraining the base member, it is necessary to find a reference vibration node. A vibration node is a place where it does not displace even if vibration occurs, and in a resonance state, the frequencies on both sides of the node coincide with each other. FIG. 13A shows a system in which one side of a general piezoelectric element is constrained. Moreover, the system which is not restrained on both sides is shown in FIG. In the case of (a), the end of the piezoelectric element on the restricted side becomes a vibration node. On the other hand, in the case shown in (b), a vibration node is formed on the center line of the piezoelectric element, and the frequencies on both sides coincide with each other. Accordingly, the spring strength is doubled and the mass is halved compared to the case of (a), and the frequency is doubled.
[0056]
Next, the extension vibration in the antiphase mode is shown in FIG. When attention is paid to the piezoelectric element arranged substantially horizontally in (a) on the left side in FIG. 14, a base member is attached to the left end, and a chip member is attached to the right end. Since the base member can be regarded as a rotating rod and the influence of piezoelectric elements arranged substantially vertically can be ignored, the symmetric vibration system is a system in which a weight is attached to a mass spring. Can be represented.
[0057]
The mass of the piezoelectric element is m, and the spring constant of extension vibration is k₁If the ratio of the length from the end of the base member to the node relative to the total length of the piezoelectric element is p (0 ≦ p ≦ 1), the mass m of the left and right vibration system with the node interposed_L, M_RAnd spring constant k_L, k_RIs expressed as follows.
m_L= Pm k_L= K₁/ p
m_R= (1-p) m k_R= K₁/ (1-p)
[0058]
Insert member mass is M_c, Base member inertia moment (half) I_z, The radius of rotation of the base member is R, and the displacement of the left and right vibration system is x_L, X_RThen, energy is expressed by the following formula.
(1/2) k_Lx_L ²= (1/2) I_z(d (x_L/ R) / dt)²+ (1/2) (m_L/ 3) (dx_L/ dt)²
(1/2) k_Rx_R ²= (1/2) M_c(dx_R/ dt)²+ (1/2) (m_R/ 3) (dx_R/ dt)²
[0059]
Where x_L= X_Lcosωt, x_R= X_RSubstituting into the above equation assuming cosωt, each frequency ω of the left and right vibration system_L, Ω_RIs represented by the following equation (4).
ω_L ²= (K₁/ p) / (I_z/ R²+ Pm / 3)
ω_R ²= (K₁/ (1-p)) / (M_c+ (1-p) m / 3) (4)
[0060]
Since the natural frequency of both is equal across the node,
(k₁/ p) / (I_z/ R²+ Pm / 3) = (k₁/ (1-p)) / (M_c+ (1-p) m / 3)
From the above equation, the position of the node is obtained as in the following equation (5).
p = (M_c+ M / 3) / (M_c+ I_z/ R²+ 2m / 3) (5)
[0061]
By substituting p obtained in this way into Equation (4), the natural frequency in the antiphase mode can be obtained.
[0062]
  Modeling in-phase mode stretching vibrations in an unconstrained state.
  next,sameFIG. 15 shows the phase mode elongation vibration. As in the case of the antiphase mode, paying attention to the substantially horizontally arranged piezoelectric element in (a) at the upper left in FIG. Is attached. The base member can be regarded as a cantilever beam having a fixed lower part, and each piezoelectric element can be regarded as a half of the both-end support beam.
[0063]
The length ratio of the piezoelectric element is q (0 ≦ q ≦ 1), and the spring constant of the base member is₂, The equivalent mass of the base member_b', The spring constant of the bending deformation of the piezoelectric element is k_ThreeThen each frequency ω on either side of the node_L, Ω_RIs represented by the following equation (6).
ω_L ²= (K₁/ q + k₂) / (M_b'+ Qm / 3)
ω_R ²= (K₁/ (1-q) + k_Three) / (M_c+ (1-q) m / 3 + m / 2) (6)
[0064]
Since the left and right resonance frequencies are equal across the node,
(k₁/ q + k₂) / (M_b'+ Qm / 3) = (k₁/ (1-q) + k_Three) / (M_c+ (1-q) m / 3 + m / 2) (7)
It becomes. Equation (7) is a cubic equation related to q and is generally difficult to explain. Therefore, when an appropriate value was substituted for q (0 ≦ q ≦ 1), it was found that the relationship between q and Mc was approximated by the following equation (8). N is a constant.
M_c+ 5m / 6 ≒ qN / (1-q) (8)
[0065]
When N is obtained by modifying equation (8),
N = (M_b'+ mq / 3) × (k₁+ (1-q) k_Three) / (k₁+ K₂q) + m (1-q) / 3
Where k₁≫k₂, K_ThreeAssuming
N ≒ (M_b'+ Mq / 3) + m (1-q) / 3
= M_b'+ M / 3
By substituting this value of N into equation (8), the position of the node in the in-phase mode can be obtained as in equation (9) below.
q = (M_c+ 5m / 6) / (M_c+ 5m / 6 + M_b'+ M / 3)
= (M_c+ 5m / 6) / (M_c+ M_b'+ 7m / 6)
[0066]
By substituting q obtained in this way into the above equation (6), the natural frequency in the in-phase mode can be obtained.
[0067]
Other embodiments
In the above-described embodiment, a piezoelectric element is used as the displacement element. However, the piezoelectric element is generally made of a ceramic material, has a greater vibration attenuation than a metal material, and has a small displacement expansion rate at resonance. Further, ceramics are strong in compressive force but weak in tensile force, and in the case of a multilayer piezoelectric element, there is a possibility of peeling off at the bonding surface. Therefore, a single-layer piezoelectric element and a metal elastic body connected in series can be used as the displacement element. FIG. 16 shows the structure of a truss type actuator using this displacement element. The first displacement element 60 and the second displacement element 60 ′ are respectively composed of single-layer piezoelectric elements (ceramic thin plates) 61 and 61 ′ and elastic bodies 62 and 62 ′, and on both surfaces of the piezoelectric elements 61 and 61 ′. No electrode is provided. Further, the first displacement element 60 and the second displacement element 60 'are fixed to the chip member 20 and the base member 30 by bolts 63 and 63', respectively, without using an adhesive. The elastic bodies 62, 62 ′ and the base member 30 are respectively formed of a conductive material, and the drive power supplies 16, 16 ′ are connected between the elastic bodies 62, 62 ′ and the base member 30, and the first displacement element 60 and the second displacement element 60 are connected. The displacement elements 60 ′ are each driven at the resonance frequency.
[0068]
Displacement can be expanded by resonating the elastic bodies 62 and 62 'using the piezoelectric elements 61 and 61' as a vibration source. Further, since the metal material is less attenuated, the displacement is further increased, and the tensile force applied to the piezoelectric elements 61, 61 'is reduced, so that the piezoelectric elements 61, 61' can be prevented from being broken. As the material of the elastic bodies 62, 62 ', aluminum, titanium, iron, copper, and alloys thereof are used. The ratio of the single-layer piezoelectric elements 61 and 61 'in the length direction to the entire displacement element is very small. Therefore, when calculating the natural vibration mode, there is no problem even if the influence of the piezoelectric element is ignored.
[0069]
In the description of the above embodiment, the resonance frequency is obtained by an analysis method using vibration mode modeling. However, the resonance frequency can also be obtained by analysis using a finite element method, actual measurement using an impedance analyzer, or the like. Further, the two displacement elements 10, 10 ′ or 60, 60 ′ for driving the chip member 20 are arranged so as to be orthogonal to each other. However, the present invention is not limited to this, and other angles, for example, 45 °, An arbitrary angle such as 135 ° may be used. Further, the number of displacement elements is not limited to two, and it may be configured to drive three or four degrees of freedom using three or more displacement elements as in Conventional Example 1. . Furthermore, not only the piezoelectric element but also other electrical or mechanical displacement elements such as a magnetostrictive element may be used as a driving source for the displacement element.
[0070]
【The invention's effect】
As described above, the truss-type actuator of the present invention includes a plurality of displacement elements that generate a predetermined displacement, and a displacement composition unit that is coupled to each of the plurality of displacement elements and synthesizes the displacements of the displacement elements. A fixing portion for supporting an end portion of each displacement element on which the displacement combining portion is not coupled, a pressurizing portion for pressing the displacement combining portion against a driven member, and the combining portion Includes a drive unit that resonance-drives each of the displacement elements so as to perform an elliptical motion, so that the displacement of the displacement member can be expanded using the resonance phenomenon to improve drive efficiency.
[0071]
Further, by causing the natural frequency in the natural vibration mode in which each displacement element resonates in the same phase and the natural frequency in the natural vibration mode in which each displacement element resonates in the opposite phase to substantially coincide, Since the deformation resistance is reduced and the displacement is further expanded, the driving efficiency can be further increased.
[0072]
Further, the mass of the displacement combining part is M, the length of the displacement element is L, its height is H, its mass is m, and M = (L²/ H²−0.88) By satisfying the condition of m / 2.63, each displacement element can resonate independently, and by arbitrarily controlling the amplitude and phase of the input signal, the rotational direction, speed, and driving force of the actuator Etc. can be controlled.
[0073]
Furthermore, the mass of the displacement synthesis part_c, M is the mass of the displacement element, and k is the spring constant of its elongation deformation₁, The spring constant of the bending deformation is k_Three, I_z, R is the radius of rotation, and M is the equivalent mass of the fixed part when replaced with a cantilever beam_bAs
(k₁/ (1-p)) / (M_c+ (1-p) m / 3) = (k₁/ (1-q) + k_Three) / (M_c+ (1-q) m / 3 + m / 2)
However,
p = (M_c+ M / 3) / (M_c+ I_z/ R²+ 2m / 3)
q = (M_c+ 5m / 6) / (M_c+ M_b'+ 7m / 6)
By satisfying this relationship, it is possible to select a member whose design can be changed, and the truss-type actuator can be easily realized.
[0074]
Furthermore, by using at least a part of the displacement element as an elastic body, it is possible to further improve the displacement enlargement rate and the drive efficiency of the displacement element. Further, since it is not necessary to stack displacement elements, it is possible to reduce manufacturing costs and prevent element destruction.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a laminated piezoelectric element used as a displacement element in an embodiment of a truss-type actuator of the present invention.
FIG. 2 is a diagram showing the relationship between the electric field generated between the electrodes in the multilayer piezoelectric element and the displacement of the piezoelectric element.
FIG. 3 is a diagram showing a configuration of a truss type actuator in the embodiment.
FIG. 4 is a diagram showing a block configuration of a drive circuit in the embodiment.
FIG. 5 is a diagram showing the principle of rotation of the rotor by the actuator of the embodiment, and shows a state where the actuator shown in FIG.
FIG. 6 is a diagram showing voltages applied to two piezoelectric elements or their displacements in the embodiment.
FIG. 7 is a diagram illustrating a principle of rotating a rotor by an actuator in the embodiment.
FIG. 8 is a diagram showing a locus when the amplitudes of drive signals applied to two piezoelectric elements are made equal and the phase difference between the drive signals is changed in the embodiment.
FIG. 9 is a diagram showing the state of the actuator when each piezoelectric element is driven in the in-phase mode and the anti-phase mode with the base member restrained in the embodiment.
FIG. 10 is a diagram showing the state of the actuator when each piezoelectric element is driven in the same phase mode and the opposite phase mode without restricting the base member in the embodiment.
FIG. 11 is a diagram illustrating modeling of the extension vibration in the antiphase mode in the restrained state.
FIG. 12 is a diagram showing modeling of in-phase mode extension vibration in a constrained state.
13A is a diagram showing a system in which one side of a general piezoelectric element is constrained, and FIG. 13B is a diagram showing a system in which both sides are not constrained.
FIG. 14 is a diagram illustrating modeling of extension phase vibration in an antiphase mode in an unconstrained state.
FIG. 15 is a diagram illustrating modeling of the extension vibration in the same phase mode in an unconstrained state.
FIG. 16 is a diagram showing the configuration of another embodiment of the truss-type actuator of the present invention.
[Explanation of symbols]
10: 1st piezoelectric element (displacement element)
10 ': second piezoelectric element (displacement element)
11: Ceramic thin plate
16, 16 ': Drive power supply (drive unit)
20: Chip member (displacement synthesis unit)
30: Base member (fixing part)
40: Rotor (driven member)

Claims (4)

A plurality of displacement elements that generate a predetermined displacement, a displacement synthesis unit that is coupled to each of the plurality of displacement elements and synthesizes the displacement of each displacement element, and the displacement synthesis unit of each displacement element are coupled. A fixed portion for supporting the end portion on the non-side, a pressurizing portion for pressing the combining portion against the driven member, and each displacement element being driven to resonate so that the displacement combining portion performs an elliptical motion a truss actuator and a drive unit for,
The natural frequency in the natural vibration mode in which the displacement elements resonate at the same phase and the natural frequency in the natural vibration mode in which the displacement elements resonate in the opposite phase are substantially matched. Truss type actuator. M is the mass of the displacement combining portion, L is the length of the displacement element, H is its height, m is its mass, and M = (L ² / H ² −0.88) m / 2.63 is satisfied. The truss type actuator according to claim 1 . The mass of the displacement composite part is M _c , the mass of the displacement element is m, the spring constant of the extension deformation is k ₁ , the spring constant of the bending deformation is k ₃ , the moment of inertia of the fixed part is I _z , and the rotation is When the radius is R and the equivalent mass of the fixed part when replaced with a cantilever is M _b ′,
_{(k 1 / (1-p} )) / (M c + (1-p) m / 3) = (k 1 / (1-q) + k 3) / (M c + (1-q) m / 3 + m / 2)
However,
p = (M _c + m / 3) / (M _c + I _z / R ² +2 m / 3)
q = (M _c + 5m / 6) / (M _c + M _b '+ 7m / 6)
The truss type actuator according to claim 1 , wherein the following relationship is satisfied.   The truss-type actuator according to claim 1, wherein the displacement element includes an elastic body at least partially.

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