JP3700441B2

JP3700441B2 - Linear actuator

Info

Publication number: JP3700441B2
Application number: JP01745099A
Authority: JP
Inventors: 幹雄山口
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 1999-01-26
Filing date: 1999-01-26
Publication date: 2005-09-28
Anticipated expiration: 2019-01-26
Also published as: JP2000213618A

Description

【０００１】
【発明の属する技術分野】
この発明に係るリニアアクチュエータは、例えば介護用ベッド、昇降テーブル、ＣＴスキャナ、トラックのキャビンチルト装置、リフター等、各種機械装置に組み込んだ状態で使用する。
【０００２】
【従来の技術】
例えば介護用のベッド等にはリニアアクチュエータを組み込んで、電動モータや手動ハンドルを駆動源として被介護者を寝かせたベッドの角度調節等を自在としている。この様なリニアアクチュエータには、電動モータや手動ハンドルの回転運動を出力部材の軸方向運動（直線運動）に変換する機能が要求される。又、比較的少ない動力で大きな荷重を、比較的高速で移動可能な構造を実現する為には、リニアアクチュエータとして効率の良い構造が必要になる。
【０００３】
一方、上述の様な用途に利用可能なリニアアクチュエータとして従来から、例えば特開昭６１−１８００６４号公報、同６２−２５１５６０号公報、実公昭５１−４４８７１号公報等に記載されたものが知られている。
このうちの特開昭６１−１８００６４号公報及び同６２−２５１５６０号公報に記載されたリニアアクチュエータは、回転のみ自在に設けた送りねじの周囲に移動部材を設け、この移動部材の内径側にナット部材を、回転自在に、且つこの送りねじに対し偏心させた状態で支持している。そして、この送りねじの外周面に形成した雄ねじの円周方向の一部を、上記ナット部材の内周面に形成した雌ねじの円周方向の一部と噛合させている。この様な構造の場合、上記送りねじを回転させると、上記ナット部材が上記移動部材の内径側で回転しつつ軸方向に移動するので、この移動部材から直線運動を取り出せる。
又、実公昭５１−４４８７１号公報に記載されたリニアアクチュエータは、回転のみ自在に設けた送りねじの周囲にナット部材を、この送りねじと同心に設け、これら送りねじの外周面とナット部材の内周面との間に複数個のローラねじを回転自在に支持している。この様な構造の場合、上記送りねじを回転させると、上記各ローラねじがこの回転を上記ナット部材に伝達してこのナット部材を軸方向に移動させるので、このナット部材から直線運動を取り出せる。
【０００４】
【発明が解決しようとする課題】
上述の様な従来構造のうち、特開昭６１−１８００６４号公報及び同６２−２５１５６０号公報に記載されたリニアアクチュエータの場合には、効率は良いが、送りねじの周囲に配置したナット部材から直線運動を取り出す構造である為、取り出し部の構造が限定される。この為、前述した介護用ベッド、昇降テーブル、ＣＴスキャナ、トラックのキャビンチルト装置、リフター等の用途には不向きである。
又、実公昭５１−４４８７１号公報に記載されたリニアアクチュエータの場合には、構造が複雑で小型化が難しく、コストも嵩む。
リニアアクチュエータとして従来からこの他にも、ボールねじ式の送りねじ機構、一般的な滑りねじ式の送りねじ機構等が知られている。但し、このうちのボールねじ式の送りねじ機構は、構造が複雑で小型化が難しく、コストも嵩む。又、一般的な滑りねじ式の送りねじ機構の場合には、摩擦損失が大きく効率が悪い。
本発明はこの様な事情に鑑みて、小型でしかも効率が良く、且つ各種用途に使用可能なリニアアクチュエータを実現すべく発明したものである。
【０００５】
【課題を解決するための手段】
本発明のリニアアクチュエータは、回転のみ自在に支持された駆動側部材と、この駆動側部材の内径よりも小さな外径を有し、この駆動側部材に対し偏心した状態でこの駆動側部材の内径側に、回転及び軸方向に亙る変位自在に支持された被駆動側部材と、この被駆動側部材の外周面と上記駆動側部材の内周面とのうちの一方の周面に形成された螺旋状のねじ溝と、上記被駆動側部材の外周面と上記駆動側部材の内周面とのうちの他方の周面に円周方向に亙って形成された、上記ねじ溝と同じピッチを有する係合溝と、上記被駆動側部材の一部にスラスト荷重を支承自在な転がり軸受により結合された出力部材とを備え、上記ねじ溝の円周方向の一部と上記係合溝の円周方向の一部とを互いに噛合させている。
【０００６】
尚、上述の様な本発明のリニアアクチュエータとしては、次の(1) 〜 (4) の様な態様が考えられる。
(1) 上記駆動側部材を、その内周面に雌ねじを形成したナット部材とし、上記被駆動側部材を、その外周面に雄ねじを形成したねじ杆状のものとし、このねじ杆状の被駆動部材を上記ナット部材に対し平行に配置して、上記雌ねじの円周方向の一部と上記雄ねじの円周方向の一部とを互いに噛合させる。
(2) 上記駆動側部材の内周面に、それぞれが円周方向に設けられた互いに平行な複数本の突条を、上記被駆動側部材の外周面に雄ねじを、それぞれ形成すると共に、上記駆動側部材と上記被駆動側部材とを互いに平行に配置して、上記突条の円周方向の一部と上記雄ねじの円周方向の一部とを互いに噛合させる。
(3) 上記被駆動側部材の外周面に、それぞれが円周方向に設けられた互いに平行な複数本の突条を、上記駆動側部材の内周面に雌ねじを、それぞれ形成すると共に、上記被駆動側部材と上記駆動側部材とを互いに平行に配置して、上記突条の円周方向の一部と上記雌ねじの円周方向の一部とを互いに噛合させる。
(4) 上記(2)(3)の何れかで、上記被駆動側部材の外周面に形成した雄ねじ又は駆動側部材の内周面に形成した雌ねじのピッチ、及び、上記駆動側部材の内周面又は被駆動側部材の外周面に形成した突条のピッチを、それぞれＰとし、上記駆動側部材の内周面に形成した雌ねじ又は突条のピッチ円直径をＤ₀ とした場合に、上記被駆動側部材の中心軸を、β＝ tan^-1｛Ｐ／（π・Ｄ₀ ）｝で表される角度βだけ、上記駆動側部材の中心軸に対し傾斜させる。
【０００７】
【作用】
上述の様に構成する本発明のリニアアクチュエータは、駆動側部材を回転させる事により被駆動側部材を回転させつつ軸方向に変位させ、出力部材により、この被駆動側部材の軸方向変位を取り出す。
即ち、上記駆動側部材の回転に伴って上記被駆動側部材が、ねじ溝と係合溝との係合に基づき、回転する。この際、これらねじ溝の周速と係合溝の周速とは互いに等しくなる。又、互いに噛合するねじ溝のピッチと係合溝のピッチとは互いに等しい。これに対して、これらねじ溝のピッチ円直径と係合溝のピッチ円直径とは異なる為、上記駆動側部材が１回転する間に、上記被駆動側部材は１回転以上回転する。この結果、被駆動側部材が駆動側部材よりも余分に回転する分だけ、この被駆動側部材及びこの被駆動側部材に結合した出力部材が軸方向に変位する。
【０００８】
【発明の実施の形態】
図１〜４は、前述の(1) に対応する、本発明の実施の形態の第１例を示している。本例のリニアアクチュエータ１は、回転しないハウジング２の内側に、駆動側部材である円筒状のナット部材３を、回転のみ自在に支持している。即ち、上記ハウジング２は、１対の半片４ａ、４ｂを最中状に組み合わせると共に突き合わせ部同士を互いに結合する事により、中空に構成している。又、上記ナット部材３は、軸方向片半部（図１の左半部）に設けた大径部５と他半部（図１の右半部）に設けた、この大径部５と同心の小径部６とを、段部７により連続させる事により、全体を段付の円筒状に構成している。又、このうちの小径部６の内周面には、ピッチ円直径がＤ₀ である雌ねじ８を形成している。これに対して、上記大径部５の外周面にはウォームホイール歯１１を形成して、この大径部５がウォームホイールとして機能する様にしている。
【０００９】
この様なナット部材３は、上記小径部６の外周面と上記半片４ａの内周面との間に設けた、深溝型の玉軸受９により、上記ハウジング２の内側に、回転のみ自在に（軸方向に亙る変位不能に）支持している。又、上記ハウジング２にはウォーム１２を回転のみ自在に支持し、このウォーム１２と上記ウォームホイール歯１１とを噛合させている。更に、このウォーム１２を、図示しない電動モータ或はハンドルにより、回転駆動自在としている。
【００１０】
又、上記ハウジング２には、被駆動側部材１０を、回転及び軸方向に亙る変位自在に支持している。この被駆動側部材１０は、全体を円筒状に形成したもので、上記ナット部材３の内径よりも小さな外径を有する。又、この被駆動側部材１０の外周面には、ほぼその全長に亙り、ピッチ円直径がｄ₀ である雄ねじ１３を形成している。この様な被駆動側部材１０は、滑り軸受、ニードル軸受等の、ラジアル荷重を支承するがスラスト荷重を支承しない軸受１４、１４により上記ハウジング２に、回転及び軸方向に亙る変位自在に支持している。この状態で上記被駆動側部材１０の中心軸は上記ナット部材３の中心軸に対して、ピッチ円直径の差の１／２であるδ｛＝（Ｄ₀ −ｄ₀ ）／２｝だけ偏心させている。従って、上記被駆動側部材１０の外周面に形成された雄ねじ１３は、上記ナット部材３の内周面に形成した雌ねじ８に対して、円周方向の一部のみ噛合している。本例の場合、これら雄ねじ１３と雌ねじ８とのうちの一方が、請求項に記載したねじ溝に相当し、他方が同じく係合溝に相当する。
【００１１】
又、上記被駆動側部材１０の内径側には軸状の出力部材１５の基端部を、それぞれがスラスト荷重を支承自在な転がり軸受である、１対の玉軸受１６、１６により、この出力部材１５に対する回転及びこの出力部材１５と同期した軸方向移動自在に結合している。
更に、図示の例では、前記ハウジング２の一部内周面に設けた凹溝２７の底面と上記軸受１４の外周面との間に、板ばね１７等の予圧手段を設けている。この予圧手段は、上記出力部材１５にスラスト荷重が負荷されていない場合でも、上記雌ねじ８と雄ねじ１３との係合部の摩擦抵抗を或る程度大きくし、これら雌ねじ８と雄ねじ１３との係合に基づく上記出力部材１５の軸方向変位が確実に行なわれる様にする役目を果たす。即ち、上記予圧手段は、上記雌ねじ８と雄ねじ１３との係合部の摩擦抵抗を、上記軸受１４部分の抵抗並びに前記各玉軸受１６、１６部分の転がり抵抗よりも大きくする為に設ける。尚、この様な予圧手段は、本発明のリニアアクチュエータ１の機能上、必ずしも必要ではない。特に、リニアアクチュエータ１が、上記出力部材１５に常にスラスト荷重が負荷されている状態で使用されるのであれば、不要である。
【００１２】
上述の様に構成する本例のリニアアクチュエータ１は、前記ウォーム１２を介して前記ナット部材３を回転させる事により、前記被駆動側部材１０を回転させつつ軸方向に変位させ、上記出力部材１５により、この被駆動側部材１０の軸方向変位を取り出す。
【００１３】
即ち、上記リニアアクチュエータ１を伸縮させる際には、図示しない電動モータ或はハンドルにより、上記ウォーム１２を介して上記ナット部材３を所定方向に回転させる。このナット部材３の回転に伴って上記被駆動側部材１０が、上記雌ねじ８と雄ねじ１３との係合に基づき、回転する。この際、これら雌ねじ８の周速と雄ねじ１３の周速とは互いに等しくなる。又、図４に示す様に、互いに噛合する、上記雌ねじ８のピッチＰと雄ねじ１３のピッチＰとは互いに等しい。これに対して、これら雌ねじ８のピッチ円直径Ｄ₀ と雄ねじ１３のピッチ円直径ｄ₀ とは互いに異なる（Ｄ₀ ＞ｄ₀ ）。この為、上記ナット部材３が１回転する間に、上記被駆動側部材１０は１回転以上（Ｄ₀ ／ｄ₀ 回）回転する。この結果、この被駆動側部材１０が上記ナット部材３よりも余分に回転する分｛ナット部材３が１回転する毎に（Ｄ₀ ／ｄ₀ ）−１回分｝だけ、上記被駆動側部材１０及びこの被駆動側部材１０に結合した上記出力部材１５が軸方向に［Ｐ・｛（Ｄ₀ ／ｄ₀ ）−１｝分］変位する。この被駆動側部材１０は、回転しつつ軸方向に変位するが、出力部材１５はこの被駆動側部材１０に対して回転自在である為、この出力部材１５は、回転する事なく、軸方向に変位して、この出力部材１５の先端部を結合した部材を押し引きする。
【００１４】
上記雌ねじ８と雄ねじ１３との係合状態は転がり接触に近く、滑り接触状態は僅かである。この為、これら雌ねじ８と雄ねじ１３との係合部での動力損失は僅かで、リニアアクチュエータ１全体として高い伝達効率を得られる。又、出力部材１５をリニアアクチュエータ１の中心軸部分に設けている為、直線運動の取り出しが容易で、構成部材が少なく、小型に軽量できる事と合わせて、各種用途に利用できる。
【００１５】
次に、図５は、やはり前述の(1) に対応する、本発明の実施の形態の第２例を示している。本例の場合には、駆動側部材であるナット部材３ａを構成する、互いに同心である大径部５ａと小径部６ａとの直径差を、上述した第１例の場合よりも大きくしている。従って、上記大径部５ａと小径部６ａとを連続させる段部７ａの直径方向に亙る幅寸法は、上述した第１例の場合よりも大きい。
【００１６】
上述の様なナット部材３ａは、上記小径部６ａの両端部をハウジング２ａの内側に、それぞれが深溝型である、１対の玉軸受９ａ、９ｂにより、回転のみ自在に支持している。本例の場合には、上記小径部６ａの中間部外周面に、図示しない段付ベルト、或はギヤ等の駆動部材を係合させて上記ナット部材３ａを回転駆動する為の被駆動部１８を設けている。又、上記大径部５ａの内周面に雌ねじ８ａを形成している。
【００１７】
一方、軸状の出力部材１５ａを上記小径部６ａの内側に、滑り軸受、ニードル軸受等の、ラジアル荷重を支承するがスラスト荷重を支承しない軸受１４、１４により、回転及び軸方向に亙る変位自在に支持している。上記出力部材１５ａの基端部（図５の右端部）で上記大径部５ａの内側に位置する部分には被駆動側部材１０ａを、アンギュラ型の玉軸受１９により支持している。上記出力部材１５ａの基端部は、上記ナット部材３ａに対して、次述する雌ねじ８ａのピッチ円直径Ｄ₀ と雄ねじ１３ａのピッチ円直径ｄ₀ との差の１／２｛δ＝（Ｄ₀ −ｄ₀ ）／２｝であるδ分、偏心させている。そして、この被駆動軸部材１０ａの外周面に形成した雄ねじ１３ａの円周方向一部と、上記大径部５ａの内周面に形成した雌ねじ８ａの円周方向一部とを、互いに噛合させている。尚、本例のリニアアクチュエータ１ａは、上記出力部材１５ａに、図５で左方向のスラスト荷重が加わる状態で使用する。上記玉軸受１９の外輪及び内輪は、上記被駆動側部材１０ａの内周面及び上記出力部材１５ａの基端部外周面に、上記スラスト荷重に拘らずずれ動かない状態で嵌合させている。従って上記出力部材１５ａは、上記被駆動側部材１０ａに対して回転はするが、軸方向に亙っては、この被駆動側部材１０ａと共に変位する。
【００１８】
上述の様に構成する本例のリニアアクチュエータ１ａの場合、図示しない駆動部材により上記ナット部材３ａを回転駆動すると、上記雌ねじ８ａと雄ねじ１３ａとの係合に基づき、上記被駆動側部材１０ａが回転しつつ軸方向に変位する。そして、このうちの軸方向に亙る変位を、上記出力部材１５ａにより取り出し、この出力部材１５ａの先端部を結合した部材を変位させる。
【００１９】
上述の様な本例の構造の場合には、ストロークを大きくする事が難しい代わりに、外径を小さくして、限られた空間への設置が容易になる。
尚、本例の構造を実施する場合、図５の左端部に鎖線で示す様に、上記出力部材１５ａにスラスト荷重を付与する、予圧部材である圧縮ばね２０を設ける事もできる。
【００２０】
次に、図６は、やはり前述した(1) に対応する、本発明の実施の形態の第３例を示している。本例の場合には、ハウジング２ｂの内側に、ナット部材３ｂと被駆動側部材１０ｂとを支持している。即ち、このハウジング２ｂの軸方向中間部に上記ナット部材３ｂを、それぞれが深溝型の玉軸受９、９により、回転のみ自在に支持している。又、このナット部材３ｂの中間部外周面で上記両玉軸受９、９同士の間部分に、ギヤ２４或は図示しない段付ベルト等の駆動部材を係合させて上記ナット部材３ｂを回転駆動する為の、被駆動部１８ａを設けている。
【００２１】
一方、上記ハウジング２ｂの両端部には、それぞれが深溝型である１対の玉軸受２１、２１の外輪２２、２２を、締り嵌めで内嵌する事により、或は接着する事により、それぞれ固定している。そして、上記各玉軸受２１、２１の内輪２３、２３を、それぞれ上記被駆動側部材１０ｂの中間部に、それぞれ隙間嵌により外嵌している。従って、この被駆動側部材１０ｂは、上記ハウジング２ｂの内側に、回転及び軸方向に亙る変位自在に支持されている。そして、上記被駆動側部材１０ｂの外周面に、ほぼ全長に亙って形成した雄ねじ１３ｂの円周方向の一部と、上記ナット部材３ｂの内周面に全長に亙って形成した雌ねじ８ｂの円周方向の一部とを、互いに噛合させている。尚、上記雄ねじ１３ｂとしては、加工コストが安い、三角山ねじでも良いが、上記各内輪２３、２３の内周面との摩擦状態を考慮した場合には、台形ねじを含む角ねじとする事が好ましい。
【００２２】
更に、上記被駆動側部材１０ｂの先端部（図６の右端部）には、出力部材１５ｂを、スラスト荷重を支承する軸受である、深溝型の玉軸受２５により結合している。
上述の様に構成する本例のリニアアクチュエータ１ｂの場合、上記ナット部材３ｂを回転駆動すると、上記被駆動側部材１０ｂが回転しつつ軸方向に変位するので、このうちの軸方向に亙る変位を、上記出力部材１５ｂにより取り出し、この出力部材１５ｂの先端部を結合した部材を変位させる。
【００２３】
次に、図７は、前述した(3) に対応する、本発明の実施の形態の第４例を示している。本例の場合には、軸状の被駆動側部材１０ｃの外周面に、それぞれが円周方向に設けられた互いに平行な複数本の突条２６、２６を、互いに等間隔に（等ピッチで）形成し、これら各突条２６、２６を、請求項に記載した係合溝としている。尚、これら各突条２６、２６のピッチＰは、ナット部材３の内周面に形成した雌ねじ８のピッチＰと同じにしている。
【００２４】
上述の様な本例の構造の場合も、上記ナット部材３を回転させると、上記被駆動側部材１０ｃが、回転しつつ軸方向に変位する。特に、本例の場合には、被駆動側部材１０〜１０ｂの外周面に雄ねじ１３、１３ａ、１３ｂを形成した第１〜３例の場合に比べて、上記ナット部材３が１回転する毎の、上記被駆動側部材１０ｃの軸方向に亙る変位量が多くなる。即ち、本例の場合には、上記ナット部材３が１回転する毎に上記被駆動側部材１０ｃが、軸方向にＰ・（Ｄ₀ ／ｄ₀ ）分、変位する。その他の構成及び作用は、前述した第１〜３例の何れかと同様であるから、同等部分に関する図示並びに説明は省略する。
【００２５】
次に、図８は、前述した(4) に対応する、本発明の実施の形態の第５例を示している。本例の場合も、上述した第４例の場合と同様に、軸状の被駆動側部材１０ｃの外周面に互いに平行な複数本の突条２６、２６を互いに等間隔に形成して、この被駆動側部材１０ｃの外周面に係合溝を形成している。特に、本例の場合には、上記被駆動側部材１０ｃの中心軸を、ナット部材３の中心軸に対し、角度βだけ傾斜させている。この傾斜角度βは、このナット部材３の内周面に形成した雌ねじ８及び上記被駆動側部材１０ｃの外周面に形成した突条２６、２６のピッチをＰとし、上記雌ねじ８のピッチ円直径をＤ₀ とした場合に、β＝ tan^-1｛Ｐ／（π・Ｄ₀ ）｝とする。
この様な本例の場合も、上記ナット部材３を回転させると、上記被駆動側部材１０ｃが、回転しつつ軸方向に変位する。被駆動側部材１０ｃを傾斜させた点以外の構成及び作用は、上述した第４例の場合と同様である。
【００２６】
尚、図示は省略するが、図７〜８に示した第４〜５例の場合とは逆に、被駆動側部材の外周面に、複数の突条に代えて雄ねじを形成すると共に、ナット部材に代えて、それぞれが円周方向に設けられた互いに平行な複数本の突条を、被駆動側部材の外周面に形成した雄ねじと等ピッチでその内周面に形成して係合溝とした駆動側部材を設ける事もできる。
【００２７】
【発明の効果】
本発明は、以上に述べた通り構成され作用するので、小型で効率が良く、しかも組み付け状態の自由度が高く、各種機械装置の設計をし易いリニアアクチュエータを実現できる。
【図面の簡単な説明】
【図１】本発明の実施の形態の第１例を示す要部断面図。
【図２】一部を省略して示す、図１のＡ−Ａ断面図。
【図３】同Ｂ−Ｂ断面図。
【図４】一部を省略して示す、図２のＣ−Ｃ断面図。
【図５】本発明の実施の形態の第２例を示す要部断面図。
【図６】同第３例を示す要部断面図。
【図７】同第４例を示す、図４と同様の図。
【図８】同第５例を示す、図４と同様の図。
【符号の説明】
１、１ａ、１ｂリニアアクチュエータ
２、２ａ、２ｂハウジング
３、３ａ、３ｂナット部材
４ａ、４ｂ半片
５、５ａ大径部
６、６ａ小径部
７、７ａ段部
８、８ａ、８ｂ雌ねじ
９、９ａ、９ｂ玉軸受
１０、１０ａ、１０ｂ、１０ｃ被駆動側部材
１１ウォームホイール歯
１２ウォーム
１３、１３ａ、１３ｂ雄ねじ
１４軸受
１５、１５ａ、１５ｂ出力部材
１６玉軸受
１７板ばね
１８、１８ａ被駆動部
１９玉軸受
２０圧縮ばね
２１玉軸受
２２外輪
２３内輪
２４ギヤ
２５玉軸受
２６突条
２７凹溝[0001]
BACKGROUND OF THE INVENTION
The linear actuator according to the present invention is used in a state where it is incorporated in various mechanical devices such as a nursing bed, a lifting table, a CT scanner, a truck cabin tilt device, and a lifter.
[0002]
[Prior art]
For example, a linear actuator is incorporated in a nursing bed or the like, and the angle of the bed on which the care recipient is laid can be freely adjusted using an electric motor or a manual handle as a driving source. Such a linear actuator is required to have a function of converting the rotational motion of the electric motor or the manual handle into the axial motion (linear motion) of the output member. In order to realize a structure that can move a large load with relatively little power at a relatively high speed, an efficient structure as a linear actuator is required.
[0003]
On the other hand, as linear actuators that can be used for the above-mentioned applications, those described in, for example, Japanese Patent Application Laid-Open Nos. 61-180064, 62-251560, and 51-44871 are known. ing.
Of these, the linear actuators described in Japanese Patent Application Laid-Open Nos. 61-180064 and 62-251560 are provided with a moving member around a feed screw provided only for rotation, and a nut on the inner diameter side of the moving member. The member is supported so as to be rotatable and eccentric with respect to the feed screw. A part in the circumferential direction of the male screw formed on the outer peripheral surface of the feed screw is meshed with a part in the circumferential direction of the female screw formed on the inner peripheral surface of the nut member. In such a structure, when the feed screw is rotated, the nut member moves in the axial direction while rotating on the inner diameter side of the moving member, so that linear motion can be taken out from the moving member.
In addition, the linear actuator described in Japanese Utility Model Publication No. 51-44871 is provided with a nut member around a feed screw provided only for rotation, concentrically with the feed screw, and the outer peripheral surface of the feed screw and the nut member. A plurality of roller screws are rotatably supported between the inner peripheral surface. In such a structure, when the feed screw is rotated, the roller screws transmit the rotation to the nut member and move the nut member in the axial direction, so that linear motion can be extracted from the nut member.
[0004]
[Problems to be solved by the invention]
Among the conventional structures as described above, in the case of the linear actuator described in Japanese Patent Application Laid-Open Nos. 61-180064 and 62-251560, the efficiency is good, but from the nut member arranged around the feed screw. Since it is a structure which takes out linear motion, the structure of the taking-out part is limited. For this reason, it is not suitable for uses such as the above-mentioned nursing bed, lifting table, CT scanner, truck cabin tilt device, and lifter.
In the case of the linear actuator described in Japanese Utility Model Publication No. 51-44871, the structure is complicated, it is difficult to reduce the size, and the cost increases.
Conventionally, as a linear actuator, a ball screw type feed screw mechanism, a general sliding screw type feed screw mechanism, and the like are known. However, the ball screw type feed screw mechanism among these is complicated in structure, difficult to miniaturize, and increases in cost. In the case of a general sliding screw type feed screw mechanism, the friction loss is large and the efficiency is poor.
In view of such circumstances, the present invention has been invented to realize a linear actuator that is small and efficient and can be used for various applications.
[0005]
[Means for Solving the Problems]
The linear actuator of the present invention has a drive-side member that is supported only for rotation and an outer diameter smaller than the inner diameter of the drive-side member, and the inner diameter of the drive-side member is eccentric with respect to the drive-side member. The driven side member is supported on the side in a freely rotating and axially displaceable manner, and is formed on one peripheral surface of the outer peripheral surface of the driven side member and the inner peripheral surface of the driving side member. The same pitch as the thread groove formed in the circumferential direction on the other circumferential surface of the spiral thread groove and the outer peripheral surface of the driven side member and the inner peripheral surface of the driving side member And an output member coupled to a part of the driven side member by a rolling bearing capable of supporting a thrust load, and a part of the thread groove in the circumferential direction and the engagement groove A part in the circumferential direction is meshed with each other.
[0006]
As the linear actuator of the present invention as described above, the following modes (1) to (4) are conceivable.
(1) The driving side member is a nut member having an internal thread formed on the inner peripheral surface thereof, and the driven side member is a screw rod shape having an external thread formed on the outer peripheral surface thereof. A drive member is disposed in parallel to the nut member, and a part of the female screw in the circumferential direction and a part of the male screw in the circumferential direction are engaged with each other.
(2) On the inner peripheral surface of the driving side member, a plurality of parallel protrusions each provided in the circumferential direction are formed, and on the outer peripheral surface of the driven side member, a male screw is formed, respectively, The driving side member and the driven side member are arranged in parallel to each other, and a part of the protrusion in the circumferential direction and a part of the male screw in the circumferential direction are engaged with each other.
(3) A plurality of parallel protrusions each provided in a circumferential direction are formed on the outer peripheral surface of the driven side member, and a female screw is formed on the inner peripheral surface of the driving side member. The driven side member and the driving side member are arranged in parallel to each other, and a part of the protrusion in the circumferential direction and a part of the female screw in the circumferential direction are engaged with each other.
(4) In any one of the above (2) and (3) , the pitch of the male screw formed on the outer peripheral surface of the driven side member or the inner screw formed on the inner peripheral surface of the driving side member, and the inner side of the driving side member When the pitch of the ridge formed on the peripheral surface or the outer peripheral surface of the driven side member is P, and the pitch circle diameter of the female screw or ridge formed on the inner peripheral surface of the driving side member is D ₀ , The central axis of the driven side member is inclined with respect to the central axis of the driving side member by an angle β represented by β = tan ⁻¹ {P / (π · D ₀ )}.
[0007]
[Action]
The linear actuator of the present invention configured as described above displaces the driven side member in the axial direction by rotating the driving side member, and takes out the axial displacement of the driven side member by the output member. .
That is, with the rotation of the driving side member, the driven side member rotates based on the engagement between the thread groove and the engagement groove. At this time, the circumferential speed of these screw grooves and the circumferential speed of the engaging grooves are equal to each other. Further, the pitch of the thread grooves that mesh with each other is equal to the pitch of the engagement grooves. On the other hand, since the pitch circle diameter of these thread grooves and the pitch circle diameter of the engagement grooves are different, the driven side member rotates one or more times while the driving side member rotates once. As a result, the driven member and the output member coupled to the driven member are displaced in the axial direction by the amount that the driven member rotates more than the driven member.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
1 to 4 show a first example of an embodiment of the present invention corresponding to the above (1) . The linear actuator 1 of this example supports the cylindrical nut member 3 which is a drive side member inside the housing 2 which does not rotate so that only rotation is possible. That is, the housing 2 is formed hollow by combining the pair of halves 4a and 4b in the middle and connecting the butted portions to each other. The nut member 3 includes a large-diameter portion 5 provided in one axial half (the left half in FIG. 1) and a large-diameter portion 5 provided in the other half (the right half in FIG. 1). The concentric small-diameter portion 6 is made continuous by the step portion 7, so that the whole is formed into a stepped cylindrical shape. Further, an internal thread 8 having a pitch circle diameter of D ₀ is formed on the inner peripheral surface of the small diameter portion 6. In contrast, worm wheel teeth 11 are formed on the outer peripheral surface of the large-diameter portion 5 so that the large-diameter portion 5 functions as a worm wheel.
[0009]
Such a nut member 3 can be rotated only inside the housing 2 by a deep groove type ball bearing 9 provided between the outer peripheral surface of the small-diameter portion 6 and the inner peripheral surface of the half piece 4a ( It is supported so that it cannot be displaced in the axial direction). A worm 12 is supported on the housing 2 so as to be rotatable only, and the worm 12 and the worm wheel teeth 11 are engaged with each other. Further, the worm 12 can be driven to rotate by an electric motor or a handle (not shown).
[0010]
In addition, the driven member 10 is supported on the housing 2 so as to be rotatable and displaceable in the axial direction. The driven member 10 is formed in a cylindrical shape as a whole, and has an outer diameter smaller than the inner diameter of the nut member 3. Further, the outer peripheral surface of the driven-side member 10, approximately over the entire length thereof, the pitch circle diameter forms a male thread 13 is d _0. Such a driven-side member 10 is supported on the housing 2 by a bearing 14, 14 such as a sliding bearing or a needle bearing that supports a radial load but not a thrust load, so that the housing 2 can be rotated and displaced in the axial direction. ing. In this state, the central axis of the driven member 10 is decentered by δ {= (D ₀ −d ₀ ) / 2} which is ½ of the pitch circle diameter difference with respect to the central axis of the nut member 3. I am letting. Therefore, the male screw 13 formed on the outer peripheral surface of the driven member 10 is meshed with the female screw 8 formed on the inner peripheral surface of the nut member 3 only in a part in the circumferential direction. In the case of this example, one of the male screw 13 and the female screw 8 corresponds to the thread groove described in the claims, and the other corresponds to the engagement groove.
[0011]
Further, the output side is provided by a pair of ball bearings 16, 16 each of which is a rolling bearing capable of supporting a thrust load, on the inner diameter side of the driven side member 10. The rotation with respect to the member 15 and the axial movement in synchronism with the output member 15 are coupled.
Further, in the illustrated example, preload means such as a leaf spring 17 is provided between the bottom surface of the concave groove 27 provided on a part of the inner peripheral surface of the housing 2 and the outer peripheral surface of the bearing 14. This preload means increases the frictional resistance of the engaging portion between the female screw 8 and the male screw 13 to some extent even when a thrust load is not applied to the output member 15, and the engagement between the female screw 8 and the male screw 13. It plays the role of ensuring that the axial displacement of the output member 15 based on the fit is performed. That is, the preload means is provided in order to make the frictional resistance of the engaging portion between the female screw 8 and the male screw 13 larger than the resistance of the bearing 14 portion and the rolling resistance of the ball bearings 16 and 16 portions. Such a preload means is not always necessary for the function of the linear actuator 1 of the present invention. In particular, if the linear actuator 1 is used in a state where a thrust load is always applied to the output member 15, it is not necessary.
[0012]
The linear actuator 1 of the present example configured as described above displaces the driven member 10 in the axial direction by rotating the nut member 3 via the worm 12, and thereby the output member 15. Thus, the axial displacement of the driven member 10 is taken out.
[0013]
That is, when the linear actuator 1 is expanded and contracted, the nut member 3 is rotated in a predetermined direction via the worm 12 by an electric motor or a handle (not shown). As the nut member 3 rotates, the driven member 10 rotates based on the engagement between the female screw 8 and the male screw 13. At this time, the peripheral speed of the female screw 8 and the peripheral speed of the male screw 13 are equal to each other. As shown in FIG. 4, the pitch P of the female screw 8 and the pitch P of the male screw 13 that mesh with each other are equal to each other. In contrast, the different pitch circle diameter d ₀ of the pitch circle diameter D ₀ and the external thread 13 of the internal thread _{_{8 (D 0> d 0)}} . For this reason, while the nut member 3 rotates once, the driven side member 10 rotates one rotation or more (D ₀ / d ₀ times). As a result, the driven-side member 10 is rotated by the amount that the driven-side member 10 rotates more than the nut member 3 {every (D ₀ / d ₀ ) −1 times of rotation of the nut member 3}. The output member 15 coupled to the driven member 10 is displaced [P · {(D ₀ / d ₀ ) −1}] in the axial direction. The driven side member 10 is displaced in the axial direction while rotating. However, since the output member 15 is rotatable with respect to the driven side member 10, the output member 15 does not rotate but is axially moved. The member to which the distal end portion of the output member 15 is coupled is pushed and pulled.
[0014]
The engagement state between the female screw 8 and the male screw 13 is close to rolling contact, and the sliding contact state is slight. For this reason, the power loss at the engaging portion between the female screw 8 and the male screw 13 is small, and high transmission efficiency can be obtained as a whole of the linear actuator 1. Further, since the output member 15 is provided at the central axis portion of the linear actuator 1, it is easy to take out linear motion, and there are few constituent members, and it can be used for various applications in addition to being small and lightweight.
[0015]
Next, FIG. 5 shows a second example of the embodiment of the present invention, which also corresponds to the above (1) . In the case of this example, the diameter difference between the large-diameter portion 5a and the small-diameter portion 6a that constitute the nut member 3a that is the drive side member is made larger than that in the case of the first example described above. . Therefore, the width dimension over the diameter direction of the step part 7a which makes the said large diameter part 5a and the small diameter part 6a continue is larger than the case of the 1st example mentioned above.
[0016]
In the nut member 3a as described above, both ends of the small-diameter portion 6a are supported inside the housing 2a by a pair of ball bearings 9a and 9b, each of which is a deep groove type, so as to be rotatable only. In the case of this example, a driven portion 18 for rotationally driving the nut member 3a by engaging a driving member such as a stepped belt or gear not shown on the outer peripheral surface of the intermediate portion of the small diameter portion 6a. Is provided. An internal thread 8a is formed on the inner peripheral surface of the large diameter portion 5a.
[0017]
On the other hand, the shaft-shaped output member 15a can be rotated and displaced in the axial direction by bearings 14 and 14 that support a radial load but not a thrust load, such as a slide bearing and a needle bearing, inside the small diameter portion 6a. I support it. A driven-side member 10a is supported by an angular ball bearing 19 at a portion located inside the large-diameter portion 5a at the base end portion (right end portion in FIG. 5) of the output member 15a. The base end portion of the output member 15a is ½ of the difference between the pitch circle diameter D ₀ of the female screw 8a and the pitch circle diameter d ₀ of the male screw 13a described below with respect to the nut member 3a {δ = (D ₀₋ d ₀ ) / 2} is decentered by δ. Then, a part in the circumferential direction of the male screw 13a formed on the outer peripheral surface of the driven shaft member 10a and a part in the circumferential direction of the female screw 8a formed on the inner peripheral surface of the large-diameter portion 5a are engaged with each other. ing. The linear actuator 1a of this example is used in a state where a thrust load in the left direction in FIG. 5 is applied to the output member 15a. The outer and inner rings of the ball bearing 19 are fitted to the inner peripheral surface of the driven side member 10a and the outer peripheral surface of the base end portion of the output member 15a in a state that they do not move regardless of the thrust load. Accordingly, the output member 15a rotates with respect to the driven side member 10a, but is displaced together with the driven side member 10a in the axial direction.
[0018]
In the case of the linear actuator 1a of this example configured as described above, when the nut member 3a is rotationally driven by a driving member (not shown), the driven side member 10a rotates based on the engagement between the female screw 8a and the male screw 13a. However, it is displaced in the axial direction. Of these, the displacement in the axial direction is taken out by the output member 15a, and the member to which the tip of the output member 15a is coupled is displaced.
[0019]
In the case of the structure of this example as described above, it is difficult to increase the stroke, but the outer diameter is reduced to facilitate installation in a limited space.
When the structure of this example is implemented, a compression spring 20 that is a preload member that applies a thrust load to the output member 15a can be provided as shown by a chain line at the left end of FIG.
[0020]
Next, FIG. 6 shows a third example of the embodiment of the present invention, which also corresponds to (1) described above. In the case of this example, the nut member 3b and the driven side member 10b are supported inside the housing 2b. That is, the nut member 3b is supported by the deep groove type ball bearings 9 and 9 at the intermediate portion in the axial direction of the housing 2b so as to be rotatable only. Moreover, during part of both ball bearings 9, 9 to each other at the intermediate portion outer peripheral surface of the nut member 3b, to engage the drive member of the stepped belts or the like, not a gear 24 or illustrated rotation driving the nut member 3b For this purpose, a driven portion 18a is provided.
[0021]
On the other hand, the outer rings 22 and 22 of a pair of ball bearings 21 and 21 each having a deep groove type are fixed to both ends of the housing 2b by internal fitting or by bonding. are doing. And the inner ring | wheels 23 and 23 of each said ball bearing 21 and 21 are each fitted by the clearance gap fitting to the intermediate part of the said driven side member 10b, respectively. Therefore, the driven member 10b is supported on the inner side of the housing 2b so as to be rotatable and displaceable in the axial direction. Then, a part of the circumferential direction of the male screw 13b formed over the entire outer peripheral surface of the driven side member 10b and a female screw 8b formed over the entire length of the inner peripheral surface of the nut member 3b. Are partially meshed with each other. The male screw 13b may be a triangular thread screw, which is low in processing cost. However, in consideration of the frictional state with the inner peripheral surfaces of the inner rings 23, 23, a square screw including a trapezoidal screw may be used. Is preferred.
[0022]
Further, the output member 15b is coupled to the distal end portion (right end portion in FIG. 6) of the driven side member 10b by a deep groove type ball bearing 25 which is a bearing for supporting a thrust load.
In the case of the linear actuator 1b of the present example configured as described above, when the nut member 3b is rotationally driven, the driven side member 10b is displaced in the axial direction while rotating. Then, it is taken out by the output member 15b, and the member to which the tip end portion of the output member 15b is coupled is displaced.
[0023]
Next, FIG. 7 shows a fourth example of the embodiment of the present invention corresponding to the above (3) . In the case of this example, a plurality of parallel ridges 26, 26 provided in the circumferential direction on the outer peripheral surface of the shaft-like driven side member 10c are arranged at equal intervals (at equal pitches). The protrusions 26 and 26 are formed as engaging grooves described in the claims. Note that the pitch P of each of the protrusions 26 and 26 is the same as the pitch P of the female screw 8 formed on the inner peripheral surface of the nut member 3.
[0024]
Also in the case of the structure of this example as described above, when the nut member 3 is rotated, the driven member 10c is displaced in the axial direction while rotating. In particular, in the case of this example, each time the nut member 3 makes one rotation, as compared with the cases of the first to third examples in which the male threads 13, 13a, 13b are formed on the outer peripheral surfaces of the driven side members 10-10b. The amount of displacement of the driven side member 10c in the axial direction increases. That is, in this example, every time the nut member 3 rotates, the driven member 10c is displaced in the axial direction by P · (D ₀ / d ₀ ). Other configurations and operations are the same as those in any of the first to third examples described above, and thus illustrations and descriptions regarding the equivalent parts are omitted.
[0025]
Next, FIG. 8 shows a fifth example of the embodiment of the present invention corresponding to the above-described (4) . Also in the case of this example, as in the case of the above-described fourth example, a plurality of protrusions 26 and 26 parallel to each other are formed at equal intervals on the outer peripheral surface of the shaft-like driven member 10c. An engaging groove is formed on the outer peripheral surface of the driven side member 10c. In particular, in the case of this example, the central axis of the driven member 10 c is inclined with respect to the central axis of the nut member 3 by an angle β. The inclination angle β is defined by P being the pitch of the female screw 8 formed on the inner peripheral surface of the nut member 3 and the protrusions 26 and 26 formed on the outer peripheral surface of the driven member 10c, and the pitch circle diameter of the female screw 8 is defined as P. Is set to D ₀ , β = tan ⁻¹ {P / (π · D ₀ )}.
Also in this example, when the nut member 3 is rotated, the driven member 10c is displaced in the axial direction while rotating. The configuration and operation other than the point that the driven member 10c is inclined are the same as in the case of the fourth example described above.
[0026]
Although illustration is omitted, contrary to the cases of the fourth to fifth examples shown in FIGS. 7 to 8, male threads are formed on the outer peripheral surface of the driven member in place of the plurality of protrusions, and nuts are formed. Instead of a member, a plurality of parallel protrusions each provided in the circumferential direction are formed on the inner peripheral surface of the outer peripheral surface of the driven member at the same pitch as the male screw, and the engaging groove It is also possible to provide a drive side member.
[0027]
【The invention's effect】
Since the present invention is configured and operates as described above, it is possible to realize a linear actuator that is small and efficient, has a high degree of freedom in the assembled state, and is easy to design various mechanical devices.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an essential part showing a first example of an embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along the line AA in FIG.
FIG. 3 is a sectional view taken along the line BB in FIG.
4 is a cross-sectional view taken along the line CC of FIG.
FIG. 5 is a cross-sectional view of a main part showing a second example of an embodiment of the present invention.
FIG. 6 is a cross-sectional view of an essential part showing the third example.
FIG. 7 is a view similar to FIG. 4, showing the fourth example.
FIG. 8 is a view similar to FIG. 4, showing the fifth example.
[Explanation of symbols]
1, 1a, 1b Linear actuator 2, 2a, 2b Housing 3, 3a, 3b Nut member 4a, 4b Half piece 5, 5a Large diameter part 6, 6a Small diameter part 7, 7a Step part 8, 8a, 8b Female thread 9, 9a, 9b Ball bearing 10, 10a, 10b, 10c Driven side member 11 Worm wheel tooth 12 Worm 13, 13a, 13b Male thread 14 Bearing 15, 15a, 15b Output member 16 Ball bearing 17 Leaf spring 18, 18a Driven part 19 Ball bearing 20 Compression Spring 21 Ball Bearing 22 Outer Ring 23 Inner Ring 24 Gear 25 Ball Bearing 26 Projection 27 Concave Groove

Claims

A drive-side member that is supported only for rotation, and an outer diameter smaller than the inner diameter of the drive-side member. A driven-side member supported so as to be freely displaceable, and a spiral thread groove formed on one of the outer peripheral surface of the driven-side member and the inner peripheral surface of the driving-side member; An engaging groove having the same pitch as the thread groove, formed in the circumferential direction on the other peripheral surface of the outer peripheral surface of the driven side member and the inner peripheral surface of the driving side member; An output member coupled to a part of the driven side member by a rolling bearing capable of supporting a thrust load, and a part in the circumferential direction of the thread groove and a part in the circumferential direction of the engagement groove; Linear actuators that mesh with each other.