JP4211046B2 - Spindle device - Google Patents

Description

【００１２】
ここで、Ｅｆは影響係数と呼ばれ振動とアンバランスの関係を結ぶ行列である。又、Ｅｆ^−１は、Ｅｆの逆行列を表す。Ｕｙ＿、Ｖｘｙ＿、ΔＵｙ＿（ｘ、ｙは上式における添字１〜３、＿は高速時Ｈ、低速時Ｌのいずれか）は、大きさと位相を持つ以下の複素数である。以下は、各符号の説明である。
Ｕ１，Ｕ２、Ｕ３、Ｕ４： 各バランス修正面の修正アンバランス量
ΔＵｙＬ（ｙ＝１、２、３、４、）： 低速時にバランス修正面ｙに付加した試しおもりの量
ΔＵｙＨ（ｙ＝１、２、３、４、）： 高速時にバランス修正面ｙに付加した試しおもりの量
Ｖ１０Ｌ、Ｖ２０Ｌ： 測定点１、２における低速時の初期の振動値
Ｖ１０Ｈ、Ｖ２０Ｈ： 測定点１、２における高速時の初期の振動値
ＶｌｙＬ、Ｖ２ｙＬ（ｙ＝１、２、３、４）：低速時、バランス修正面ｙのみに試しおもりΔＵｙＬのおもりを付加したときの測定点１、２における振動値
Ｖ１ｙＨ、Ｖ２ｙＨ（ｙ＝１、２、３、４）：高速時、バランス修正面ｙのみに試しおもりΔＵｙＨのおもりを付加したときの測定点１、２における振動値
【００１３】
（１）式より求まるＵ１、Ｕ２、Ｕ３、Ｕ４の量のバランス修正を行うことによって理論的には測定した低速および高速の２つの回転速度で、振動を０にできるが、この２つの回転速度以外の回転数において振動が低下するか否かは、かかる理論では保証されない。そこで発明者は、工作機械主軸に用いられるビルトインスピンドルの特性に着目し、使用回転数全域にわたって、振動を低下させる技術を発明した。
【００１４】
使用する回転速度全域にわたって、振動レべルが低いということは、軸がアンバランスによって曲げ変形をおこさないということを意味する。すなわち、アンバランスのある部品の近くでバランス修正することが必要となる。
【００１５】
図１のように、バランス修正面Ｐ２とＰ３を、転がり軸受３、４とモータロータ６の間（ローターの両端）にそれぞれとることで、モータロータ６のアンバランスなど、主軸５の中央部に存在する初期アンバランスによって生ずる主軸５の曲げ変形を小さくすることが可能となり、高速回転での振動を低減させることが可能となる。しかし、バランス修正面Ｐ２、Ｐ３においてスピンドル組立後に外部からバランスを調整する必要が生じる。工作機械では精度維持のため外筒冷却を行うが、この外筒冷却経路と干渉しないように、バランス調整ネジの取付けスぺースを確保する必要がある。後述する実施の形態では、軸受用の冷却溝とモータの冷却溝を分離し、その中間に調整ネジ組込用のねじ孔のスぺースを確保することでこれを可能にした。
【００１６】
工作機械ビルトインスピンドルでは、以下のような理由でリヤ側（図１で右側）の剛性が低くなる傾向があるため、バランス修正面Ｐ４の設定に関しては注意が必要である。
（１）工作機械では、工具をクランプするためのばね部品を挿入するため、主軸５を中空軸にする必要があり、一般的にリヤ側の主軸の肉厚は薄くなる。
（２）モータロータ６に強度の弱いアルミダイキャスト及び積層のケイ素鋼板などを使用するため、高速回転時に遠心力によるモータロータ６の破壊を防ぐためにその直径（φ２）を小さくし、その応力を小さくする必要がある。これに伴い、モータロータ６よりリヤ側の主軸の直径（φ３）は細くなる。
（３）ビルトインスピンドルでは、回転数と位相の制御のため、歯車状のリングの凹凸を磁気的に感知するビルトインセンサ（ここでは回転検出部）Ｔを設けることが必要である。高速回転では、ビルトインセンサＴの感度を上げるため、歯車状のリング直径を小さくし、周速度を下げなければならない場合があり、これに伴ってセンサＴの取り付け部よりリヤ側の軸径（φ４）はさらに細くなる場合がある。
【００１７】
このように工作機械用ビルトインスピンドルでは、リヤ側の軸径が細く薄肉になり、主軸５の剛性が低下する。このため、バランス修正面Ｐ４が主軸５の後端にあると、高速回転において曲げ変形を生じ、振動を発生する原因となる。すなわち、バランスの修正面Ｐ４を、ビルトインセンサＴよりフロント側に設けることにより曲げ変形を少なくし、振動低減を可能にできる。尚、フロント側（図１で左側）は主軸剛性が高く曲げ変形は少ないが、出来るだけ軸受の近くにバランス修正面Ｐ１を配置することが望ましい。
【００１８】
即ち、前記第二の軸受手段（転がり軸受４）と、前記主軸（５）の軸端との間に回転検出部（ビルトインセンサＴ）を設け、前記第二の軸受手段より軸端側のバランス修正面を、前記第二の軸受手段と回転検出部の間に配置すると好ましい。
【００１９】
又、前記主軸（５）は中空軸を含み、前記中空軸は、前記第一の軸受手段（転がり軸受２、３）嵌合部、前記モータロータ（６）嵌合部、前記第二の軸受手段（転がり軸受４）嵌合部、前記回転検出部（ビルトインセンサＴ）嵌合部の順序で外径が小さくなる（φ１＞φ２＞φ３＞φ４）。一方向から各部品の組み付けが行える利点も生じる。尚、図１では、図を簡略化するために、主軸１を中実で外径が一様なものとして表している。
【００２０】
更に、前記バランス修正を行うために用いるねじ孔を、前記主軸に形成すると、おもりの取り付けが容易になるので好ましいが、例えば前記主軸にバランスリング等を取り付けて、その表面（これもバランス修正面）に、バランス修正用のねじ孔加工などを行っても良い。
【００２１】
【発明の実施の形態】
以下、本発明にかかる実施の形態である主軸装置を、図面を参照して詳細に説明する。図２は、本実施の形態にかかる主軸装置（主軸径φ７０，最高回転速度４５０００ｍｉｎ^−１のモータビルトインスピンドル）の断面図である。尚、図２において、工具取り付け部がある左方を主軸装置のフロント側と呼び、右方をリヤ側と呼ぶこととする。
【００２２】
図２において、主軸装置１４は、ハウジング２８と、主軸５（上下で軸線方向にずらせて図示）と、この主軸５を、ハウジング２８に対して回転自在に支承する複数個（図示例では合計４個のアンギュラ玉軸受）の軸受１０ａ，１０ｂ，１０ｃ，１０ｄとを備えている。
【００２３】
軸受１０ａ，１０ｂ（第一の軸受手段）と、軸受１０ｃ，１０ｄ（第二の軸受手段）は，２個づつ組となって主軸５のフロント側とリヤ側とを、それぞれ荷重を分担して支承するように、軸方向に所定間隔をおいて配置されている。フロント側の軸受１０ａ、１０ｂの外輪は、ハウジング２８に固定された内ハウジング２０に外輪抑え３０を介して固定されている。リア側軸受１０ｃ、１０ｄの外輪は、軸受スリーブ２２に外輪抑え３４を介して固定されている。軸受スリーブ２２は、ハウジング内径面２８ｓに軸方向にスライド可能に支持され、バネ３６によって軸方向後方に弾性付勢されており、これによりフロント側軸受とリヤ側軸受に予圧を付与している。軸受１０ａ、１０ｂの外輪は、冷却溝２８ａを流れる冷却油によって冷却される。
【００２４】
一方、各軸受１０ａ〜１０ｄの内輪は、主軸５の外周面に嵌合され、フロント側・リヤ側のそれぞれで，各軸受１０ａ〜１０ｄの間に，軸受１０ａ〜１０ｄを軸方向に固定するための円筒状の内輪間座４０が設けられている。
【００２５】
主軸５は、中空の軸５ａと、その両端近傍に固定された軸受ナット５ｂ及びバランスリング５ｃとから構成されており、軸５ａの内部において、左方の取付部５１に工具を取り付けるための機構５０（ばね部品５０ａを含む）が配置されている。かかる機構５０については公知のため、以下に詳細は記載しない。
【００２６】
軸５ａの中央にはモータ部６０が配置されている。モータ部６０は、モータロータ６１と、ハウジング２８に固定されたステータ６４からなる。ステータ６４は、固定子鉄心６４ａと、固定子鉄心６４ａ内部を巻回するコイル６３からなり、冷却ジャケット６２を介して冷却溝２８ｂを流れる冷却油によって冷却される。
【００２７】
ロータ６１は、積層の珪素鋼板の周囲にアルミダイキャストを施した、かご型回転子の構成であり、軸５ａに対し１００から１５０μｍの締まりばめによって強固に嵌合されている。ロータ６１は、積層構造であるという特性からバランスが悪く、主軸中央部にアンバランスが発生する大きな要因となる。この対策として、あらかじめロータ単体でバランス修正する方法が取られてきたが、軸と締結される際、大きな嵌めあいで生じた変形によって新たにアンバランスが生じるため、本ロータ部分にはアンバランスが残留してしまう。又、高速回転のロータでは、遠心力破壊の恐れがあるため、ロータを削るなどしてバランスをとることができない場合も多い。
【００２８】
更に、軸５ａの回転速度と位相とを検出するためのセンサ（ビルトインセンサ）６５が、軸５ａのリヤ側端部近傍の外周に配置され且つ歯車状の凹凸が形成された検出リング６６に対向して、ハウジング２８に対して取り付けられている。
【００２９】
軸５ａは、軸受１０ａ、１０ｂに嵌合する部分の外径がφ１で、モータロータ６１が嵌合する部分の外径がφ２で、軸受１０ｃ、１０ｄが嵌合する部分の外径がφ３で、検出リング６６が嵌合する部分の外径がφ４であり、φ１＞φ２＞φ３＞φ４の関係が成立している。
【００３０】
潤滑油供給装置２２Ａに接続された配管１８は，それぞれ主軸装置１４の内ハウジング２０において、各軸受１０ａ，１０ｂ，１０ｃ，１０ｄ近傍に配置されたノズル１２ａ，１２ｂ，１２ｃ，１２ｄに接続されている。
【００３１】
次に、本実施の形態の動作について説明する。取付部５１に工具（不図示）を取り付けた状態で、不図示の駆動回路からの動力供給により、モータ部６０がモータロータ６１を回転駆動し、それにより主軸５と共に工具が回転するようになっている。主軸５の回転速度及び位相の制御は、センサ６５からの信号に基づいて行われる。主軸５の回転速度に応じて、不図示の潤滑油供給装置から配管１８を介して潤滑油が供給され、ノズル１２ａ〜１２ｄを介して軸受１０ａ〜１０ｄが潤滑されるようになっている。
【００３２】
本実施の形態においては、主軸５において、第一の軸受手段である転がり軸受１０ａ、１０ｂより軸端側に配置された軸受ナット５ｂ上、転がり軸受１０ａ、１０ｂとモータロータ６１との間、モータロータ６１と転がり軸受１０ｃとの間のバランスリング５ｄ上、第二の軸受手段である転がり軸受１０ｃ、１０ｄより軸端側であって且つ回転検出部である検出リング６６より内側に配置されたバランスリング５ｃ上を、それぞれバランス修正面Ｐ１，Ｐ２，Ｐ３、Ｐ４としており、ここに修正バランスを施すことで、４面修正を行っている。本実施の形態では、センサ６５のフロント側にバランスリング５ｃを設けて、軸の曲がりを抑制している。尚、比較例（図６を参照して後述）として、主軸５のリヤ側でリング５ｆと共に取り付けられた軸受ナット５ｂに、比較修正面Ｐ４’を図示した。
【００３３】
なお、バランス修正面Ｐ１〜Ｐ４’は、円周複数箇所（４等配〜１６等配程度）にねじ孔を設ける構造となっており、そこに挿入するネジ長さ（重さ）によってアンバランスの修正をおこなう。この方法がもっとも作業性がよいが、直接バランス修正面を削る方法や、またアンバランスを持つ２つ（複数）のリングの位相を組み合せて修正することも可能である。
【００３４】
尚、軸受ナット５ｂ、バランスリング５ｃのバランス修正面Ｐ１，Ｐ４は、カバー３７ａ、３７ｂをはずせば、フロント側もしくはリヤ側からバランス調整用のネジを取り付け、取り外しすることでバランス調整が行える。一方、軸５ａの表面に形成されるバランス修正面Ｐ２，及びバランスリング５ｃに形成されるバランス修正面Ｐ３については、ねじ孔加工は軸５ａ単体で行えるものの、ねじ孔にバランス用おもりをどのようにして取り付けるかが問題である。そこで、本実施の形態では、軸受用冷却溝２８ａと、モータ冷却溝２８ｂを分け、修正窓２８ｃ、２８ｄを形成し、ここからバランス修正面Ｐ２，Ｐ３の加工を行えるようにしている。修正窓２８ｃ、２８ｄは、バランス調整作業中にネジ等が落下しても、それを介して磁石付き棒を用いて回収できるよう、十分大きな形状とするのが好ましい。加工後は、蓋２８Ａ、２８Ｂにより修正窓２８ｃ、２８ｄが閉止され、外部からの異物の侵入を阻止する。
【００３５】
又、修正加工を容易にすべく、軸受冷却用の溝２８ａを含む内ハウジング２０と、モータ冷却用溝２８ｂを含むハウジング２８のモータ冷却部とを分離するようにし、更にハウジング２８と、内ハウジング２０とに、それぞれ軸線に直交する方向に延在する孔２１、２１を穿孔している。万一、作業中にネジやおもりが落下しても、この穴を下方向に設ければ、穴を介してネジ等が下側へ落下し、取り出すことが容易となる。バランス調整後は、孔２１、２１の外方端に止め栓２１ａ、２１ａを嵌め込むことによって、外部からの切削水の侵入などを防ぐことが出来る。
【００３６】
バランス修正時における振動の測定点は、任意の２点を選ぶことが出来るが、バランス修正面Ｐ１及びＰ４近傍のハウジング外径部とするのが修正精度向上の面で望ましい。
【００３７】
図３〜５は図２における軸系の動的解析結果である。図３は、モータロータの中央に初期の残留アンバランス３ｇ・ｃｍ（ＪＩＳ Ｇ２．５程度のアンバランス）があった場合において、従来の２面修正および本発明による４面修正を行った際の、４万回転における軸の曲げ変形曲線である。２面修正の場合は剛性ロータとして、低速アンバランスを０とするように修正おもりを負荷して解析している。４面修正の場合は、１２０００ｍｉｎ^−１および３６０００ｍｉｎ^−１において軸受反力が０となるよう、各バランス修正面に修正おもりを付加して解析した。２面修正の場合は、中央部のアンバランスを軸端付近のみで修正するため、大きな曲げ変形を生じている。高速回転では曲がり変形自体がアンバランスとなるので、このように大きな変形を生じる。それに対し、本発明の４面修正によれば、曲げ変形は、２面修正の場合に比べ１／５〜１／１０程度に減少している。
【００３８】
図４は、従来の２面修正と本発明の４面修正において、軸のアンバランスによって生じる軸受の反力（軸受４つの合力）を解析した結果で、回転数を横軸にとって比較した結果である。図４の軸受反力は回転力であり、軸受反力が大きくなれば主軸の振動が大きくなることを意味する。２面修正と４面修正を比較するに、２〜３万ｍｉｎ^−１程度までは同等の軸受反力であるが、４面修正の場合では、それ以上の高速回転で軸受反力が低くなっている。４面修正により、軸の曲がり変形が小さくなった効果が顕著に現れている。
【００３９】
図５は、リア側のバランス修正面位置を軸端ナットとした場合と、センサよりフロント側にバランスリングを設けた場合とにおける、軸の変形曲線の比較結果である。各バランス修正面に約１．５ｇ・ｃｍの修正おもりを付加した時の４００００ｍｉｎ^−１における変形を解析した。本発明のようにバランス修正面を、ビルトインセンサ６５（すなわち検出リング６６）よりフロント側に設けた場合には、軸端にバランス修正面があるのに比べて変形が約１／２に減少する。これにより振動を低減することが可能である。
【００４０】
図６は、バランス修正の違いによる振動を実際に計測した結果を示す図であり、主軸フロント側のハウジングのラジアル方向の振動値の回転周波数成分を記録した。２面修正の場合は、それぞれ低速１２０００ｍｉｎ^−１、高速３６０００ｍｉｎ^−１の回転数において２種類、４面修正の場合は、それぞれ低速１２０００ｍｉｎ^−１、高速３６０００ｍｉｎ^−１の回転数にて、Ｇ０．４相当のバランス修正を行った。
【００４１】
１２０００ｍｉｎ^−１で２面修正を行った場合は、低速では振動は小さいが、高速になると振動が大きくなる。３６０００ｍｉｎ^−１で２面修正を行った場合は、３６０００ｍｉｎ^−１での振動は小さいが、その他の回転数での振動が大きい。これは、軸に曲げ変形が生じた状態でバランスを修正しているためで、曲げ変形の生じていない低速や、曲げ変形の大きさが変わるさらに高速域では釣り合いが取れないことを意味している。一方、４面修正の場合では、１２０００、３６０００ｍｉｎ^−１の両回転数で振動が低下するように修正されており、さらに適切にバランス修正面を選んでいることで使用回転数全域にわたって振動が小さくなっていることがわかる。
【００４２】
次に、主軸のリア側の曲げ変形の効果を確認するために、リア軸端ナット５ｆでの修正（比較修正面Ｐ４’での修正）と、ビルトインセンサ６５のフロント側でのバランスリング５ｃの修正（バランス修正面Ｐ４での修正）とを比較した。リア軸端ナットで修正した場合には、曲げ変形によるアンバランスで、４００００ｍｉｎ^−１付近で振動が上昇している。ビルトインセンサ６５のフロント側での修正の場合では、４００００ｍｉｎ^−１という超高速においても振動の上昇が少なくなっている。
【００４３】
図７は、騒音の測定結果を示す図であり、スピンドル前側１ｍでの測定結果である。４面修正の場合は、振動が低下するため、これに伴う騒音も低下することがわかる。
【００４４】
図８は、工具取り付け部５１先端に円形のダミー工具５２を取り付け、回転中の面５２Ａの振れ精度を非接触変位計にて測定した結果を示す図である。従来の２面修正では、高速回転で振動が増加し軸の曲げ変形も大きくなるため回転精度が悪化するが、本実施の形態では、軸に曲げ変形が殆ど発生しないため、回転精度の劣化が少ないことがわかる。本発明の適用により、高回転精度も達成でき、加工精度の高い工作機械主軸を提供することが可能となった。
【００４５】
本発明にかかるバランス修正法は、転がり軸受以外に、磁気軸受、空気軸受などを用いた高速回転する主軸装置においても有効である。
【００４６】
【発明の効果】
本発明によれば、高速回転する工作機械主軸のアンバランスを的確に修正することが出来、高速回転での振動および騒音を低減する主軸装置が提供される。磁気軸受の場合、本発明のごとく４面修正を行わなくても制御により振動を少なくすることはできるが、この場合は、軸が曲がった状態でバランスされているため、軸の回転速度が低下してしまう。本発明を用いたバランス修正により、軸の曲げ変形を抑制できるため、磁気軸受では回転精度を向上できる。
【図面の簡単な説明】
【図１】本発明の概念を説明するための模式図である。
【図２】本実施の形態にかかる主軸装置の断面図である。
【図３】本発明の実施例に関する軸系の動的解析結果を示す図である。
【図４】本発明の実施例に関する軸系の動的解析結果を示す図である。
【図５】本発明の実施例に関する軸系の動的解析結果を示す図である。
【図６】バランス修正の違いによる振動を実際に計測した結果を示す図である。
【図７】本発明の実施例における騒音の測定結果を示す図である。
【図８】工具取り付け部５１先端に円形のダミー工具５２を取り付け、回転中の振れ精度を非接触変位計５２Ａにて測定した結果を示す図である。
【符号の説明】
５ 主軸
５ａ 軸
５ｂ 軸端ナット
５ｃ バランスリング
１０ａ〜１０ｄ 軸受
１４ 主軸装置
２８ ハウジング[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spindle device of a machine tool, and more particularly to a spindle device that can effectively achieve vibration reduction in a high-speed rotation speed region.
[0002]
[Prior art]
On the spindle of a machine tool that rotates at high speed, the balance is usually corrected to reduce vibration. Conventionally, after the assembly of the spindle is completed, the balance of the main shaft is corrected in a two-plane balancer to reduce vibration. On the main spindle of the machine tool, balance correction is performed with a good balance of about G2.5 to G0.4 in JIS B 0905, thereby achieving a certain vibration reduction effect.
[0003]
As an example of conventional balance correction, since the main shaft is handled as a rigid rotor (a rotor that can be assumed that the shaft does not deform due to the balance), the balance correction surface can be any two surfaces. The surface is provided at a position where the work can be easily performed (both the bearing nut and the balance adjusting ring portion near the shaft end on both the front side and the rear side), and the balance correction surface is drilled to perform correction. This is referred to as two-surface correction (see Patent Document 1 below).
[Patent Document 1]
JP-A-6-126588 [0004]
[Problems to be solved by the invention]
By the way, in recent years, there is a tendency to rotate the machine tool spindle at a high speed in order to improve the machining efficiency. Here, when the rotational speed of the main shaft is 60 to 70% or more of the critical speed, even if the two-surface correction is performed, the shaft is deformed and the deformation itself becomes unbalanced, and the vibration rapidly increases. all right. In particular, in motor built-in spindles for machine tools, there is an initial residual unbalance mainly in the central part of the main shaft. It was found that bending deformation occurred and vibration increased.
[0005]
On the other hand, when the shaft cannot be handled as a rigid rotor (elastic rotor), it is theoretically known that vibration can be reduced by multi-face balancing. However, theoretically or mathematically, there was a method of balance correction ("Balance of rotating machines", p. 217-, published by Miwa, Shimomura, Corona), but it was like a machine tool spindle. There is still no specific technology to apply to the motor built-in spindle. That is, in a spindle device such as a machine tool spindle, it is generally difficult to rotate at a rotation speed of 60 to 70% or more of the critical speed.
[0006]
In view of the problems of the prior art, the present invention reduces the vibration in the high-speed rotation speed region by performing balance correction for preventing shaft deformation (bending) while considering the characteristics of the motor built-in spindle for the machine tool spindle, for example. An object is to provide a spindle device.
[0007]
[Means for Solving the Problems]
The spindle device of the present invention is
A housing, a main shaft, and the main shaft are mounted between a first bearing means and a second bearing means for rotatably supporting the housing, and between the first bearing means and the second bearing means. In the spindle device that has a motor rotor and the spindle is driven to rotate by the motor rotor,
The main shaft has a shaft end side from the first bearing means, between the first bearing means and the motor rotor, between the motor rotor and the second bearing means, and from the second bearing means. Balance correction surfaces are arranged in at least four locations on the end side,
At least one of the balance correction surfaces between the first bearing means and the second bearing means is subjected to balance adjustment from the outside through a correction window provided in the housing in a state where the main shaft is assembled. It is possible to do it.
[0008]
[Action]
The spindle device of the present invention includes a housing, a spindle, the first bearing means and the second bearing means for rotatably supporting the spindle relative to the housing, the first bearing means, and the second bearing means. In a spindle device having a motor rotor mounted between bearing means, and wherein the spindle is rotationally driven by the motor rotor,
The main shaft has a shaft end side from the first bearing means, between the first bearing means and the motor rotor, between the motor rotor and the second bearing means, and from the second bearing means. Balance correction surfaces are arranged in at least four positions on the end side, and at least one of the balance correction surfaces between the first bearing means and the second bearing means has the main shaft assembled thereto. Since the balance can be adjusted from the outside through the correction window provided in the housing in the state, compared to the case of correcting at the shaft end as in the prior art, the deformation of the main shaft in the high-speed rotation speed region is suppressed, Vibration can be effectively reduced. The main shaft may be, for example, a single shaft, or may have a configuration in which a bearing nut or a balance ring is fixed to the shaft. The first and second bearing means may be a single row or a plurality of rows of rolling bearings.
[0009]
The present invention will be described in more detail. In the present invention, so-called four-surface correction is performed in which four balance correction surfaces are provided and balance correction is performed on each surface so that bending deformation does not occur as much as possible during high-speed rotation. Here, the theory of four-surface correction will be described. FIG. 1 is a schematic diagram for explaining the concept of the present invention.
[0010]
In FIG. 1, a main shaft 5 is rotatably supported with respect to a housing 1 by rolling bearings 2, 3, and 4. A motor rotor 6 is installed on the outer periphery of the center of the main shaft 5. In the present invention, in the main shaft 5, the shaft end side of the rolling bearings 2 and 3 as the first bearing means, between the rolling bearings 2 and 3 and the motor rotor 6, between the motor rotor 6 and the rolling bearing 4 as the second bearing means. And at least four locations on the shaft end side from the rolling bearing 4 as the balance correction surfaces P1 to P4, respectively, and the four surfaces are corrected by applying correction balance.
[0011]
Four-surface correction is usually applied to elastic rotors that rotate below the primary critical speed. Four balance correction surfaces are provided on the shaft, and vibrations at two rotation speeds (low speed and high speed) are measured and influenced. A method called a coefficient method is used to calculate a balance correction amount with zero vibration. More specifically, using the fact that the relationship between the unbalance amount on the balance correction surfaces P1 to P4 and the vibrations V1 and V2 at the measurement points 1 and 2 can be approximated by a linear relationship, the balance correction surfaces P1 to P4 are respectively The amount of correction of the balance on each balance correction surface is calculated from the change in vibration when the test weight is added at low speed and high speed. Mathematically, the correction amount is calculated by the following matrix calculation of complex numbers.
[Expression 1]

[0012]
Here, Ef is called an influence coefficient and is a matrix that connects the relationship between vibration and unbalance. Ef ⁻¹ represents an inverse matrix of Ef. Uy_, Vxy_, and ΔUy_ (x and y are subscripts 1 to 3, and _ is either H at high speed or L at low speed) are the following complex numbers having magnitude and phase. The following is a description of each symbol.
U1, U2, U3, U4: Correction unbalance amount ΔUyL (y = 1, 2, 3, 4,) of each balance correction surface: The amount of trial weight ΔUyH (y = 1, added to the balance correction surface y at low speed) 2, 3, 4,): Amount of trial weight added to balance correction surface y at high speed V10L, V20L: Initial vibration value V10H at low speed at measurement points 1, 2 V20H: High speed at measurement points 1, 2 Initial vibration values VlyL and V2yL (y = 1, 2, 3, 4): vibration values V1yH and V2yH at measurement points 1 and 2 when the weight of the trial weight ΔUyL is added only to the balance correction surface y at low speed. (Y = 1, 2, 3, 4): Vibration value at measurement points 1 and 2 when a weight of a test weight ΔUyH is added only to the balance correction surface y at high speed.
By correcting the balance of the amounts U1, U2, U3, and U4 obtained from the equation (1), the vibration can be reduced to zero at two low and high rotational speeds theoretically measured. It is not guaranteed by this theory whether or not the vibration is reduced at other rotational speeds. Accordingly, the inventor has focused on the characteristics of the built-in spindle used for the machine tool spindle, and invented a technique for reducing vibration over the entire rotation speed range.
[0014]
A low vibration level over the entire rotational speed used means that the shaft does not undergo bending deformation due to unbalance. That is, it is necessary to correct the balance near the unbalanced part.
[0015]
As shown in FIG. 1, the balance correction surfaces P <b> 2 and P <b> 3 are respectively provided between the rolling bearings 3 and 4 and the motor rotor 6 (both ends of the rotor), thereby existing in the central portion of the main shaft 5 such as unbalance of the motor rotor 6. It is possible to reduce the bending deformation of the main shaft 5 caused by the initial imbalance, and it is possible to reduce vibration at high speed rotation. However, it is necessary to adjust the balance from the outside after the spindle assembly on the balance correction surfaces P2 and P3. The machine tool cools the outer cylinder to maintain accuracy, but it is necessary to secure a space for mounting the balance adjusting screw so as not to interfere with the outer cylinder cooling path. In the embodiment described later, this is made possible by separating the cooling groove for the bearing and the cooling groove for the motor, and securing a space for the screw hole for incorporating the adjusting screw in the middle.
[0016]
In the machine tool built-in spindle, the rigidity on the rear side (right side in FIG. 1) tends to be low for the following reasons, so care must be taken in setting the balance correction surface P4.
(1) In a machine tool, since a spring part for clamping a tool is inserted, the main shaft 5 needs to be a hollow shaft, and the thickness of the main shaft on the rear side is generally reduced.
(2) Since the motor rotor 6 is made of weak aluminum die-cast and laminated silicon steel plate, the diameter (φ2) is reduced to reduce the stress in order to prevent the motor rotor 6 from being broken by centrifugal force during high-speed rotation. There is a need. Accordingly, the diameter (φ3) of the main shaft on the rear side from the motor rotor 6 becomes thinner.
(3) In the built-in spindle, it is necessary to provide a built-in sensor (here, a rotation detection unit) T that magnetically senses the unevenness of the gear-shaped ring in order to control the rotation speed and phase. In high-speed rotation, in order to increase the sensitivity of the built-in sensor T, it may be necessary to reduce the gear-shaped ring diameter and lower the peripheral speed. Along with this, the shaft diameter (φ4 on the rear side from the mounting portion of the sensor T may be required. ) May be even thinner.
[0017]
Thus, in the built-in spindle for machine tools, the shaft diameter on the rear side is thin and thin, and the rigidity of the main shaft 5 is reduced. For this reason, when the balance correction surface P4 is at the rear end of the main shaft 5, bending deformation occurs at high speed rotation, which causes vibration. That is, by providing the balance correction surface P4 on the front side of the built-in sensor T, bending deformation can be reduced and vibration can be reduced. The front side (left side in FIG. 1) has a high spindle rigidity and little bending deformation, but it is desirable to arrange the balance correction surface P1 as close to the bearing as possible.
[0018]
That is, a rotation detector (built-in sensor T) is provided between the second bearing means (rolling bearing 4) and the shaft end of the main shaft (5), and the balance on the shaft end side from the second bearing means. Preferably, the correction surface is disposed between the second bearing means and the rotation detection unit.
[0019]
The main shaft (5) includes a hollow shaft, and the hollow shaft includes the first bearing means (rolling bearings 2, 3) fitting portion, the motor rotor (6) fitting portion, and the second bearing means. (Rolling bearing 4) The outer diameter decreases in the order of the fitting portion and the rotation detecting portion (built-in sensor T) fitting portion (φ1>φ2>φ3> φ4). There is also an advantage that each part can be assembled from one direction. In FIG. 1, in order to simplify the drawing, the main shaft 1 is shown as being solid and having a uniform outer diameter.
[0020]
Furthermore, it is preferable to form a screw hole used for correcting the balance in the main shaft because it makes it easier to attach a weight, but for example, a surface of a balance ring or the like attached to the main shaft (this is also a balance correction surface). ) May be processed with a screw hole for balance correction.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, a spindle device according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a cross-sectional view of the spindle device (motor built-in spindle having a spindle diameter of φ70 and a maximum rotational speed of 45000 min ⁻¹ ) according to the present embodiment. In FIG. 2, the left side with the tool mounting portion is called the front side of the spindle device, and the right side is called the rear side.
[0022]
In FIG. 2, the spindle device 14 includes a housing 28, a spindle 5 (shown shifted in the axial direction above and below), and a plurality of (in the illustrated example, a total of 4) that rotatably supports the spindle 5. Individual angular ball bearings) 10a, 10b, 10c, and 10d.
[0023]
The bearings 10a and 10b (first bearing means) and the bearings 10c and 10d (second bearing means) are divided into two sets to share the load between the front side and the rear side of the main shaft 5, respectively. It arrange | positions at predetermined intervals in the axial direction so that it may support. The outer rings of the front bearings 10 a and 10 b are fixed to the inner housing 20 fixed to the housing 28 via the outer ring retainer 30. The outer rings of the rear bearings 10c and 10d are fixed to the bearing sleeve 22 via an outer ring retainer 34. The bearing sleeve 22 is supported on the housing inner surface 28s so as to be slidable in the axial direction, and is elastically biased rearward in the axial direction by a spring 36, thereby preloading the front side bearing and the rear side bearing. The outer rings of the bearings 10a and 10b are cooled by the cooling oil flowing through the cooling grooves 28a.
[0024]
On the other hand, the inner rings of the bearings 10a to 10d are fitted to the outer peripheral surface of the main shaft 5 to fix the bearings 10a to 10d in the axial direction between the bearings 10a to 10d on the front side and the rear side, respectively. A cylindrical inner ring spacer 40 is provided.
[0025]
The main shaft 5 is composed of a hollow shaft 5a, a bearing nut 5b and a balance ring 5c fixed in the vicinity of both ends thereof, and a mechanism for mounting a tool to the left mounting portion 51 inside the shaft 5a. 50 (including the spring part 50a) is arranged. Since the mechanism 50 is publicly known, details are not described below.
[0026]
A motor unit 60 is disposed at the center of the shaft 5a. The motor unit 60 includes a motor rotor 61 and a stator 64 fixed to the housing 28. The stator 64 includes a stator core 64a and a coil 63 wound around the stator core 64a, and is cooled by cooling oil flowing through the cooling groove 28b via the cooling jacket 62.
[0027]
The rotor 61 has a squirrel-cage rotor configuration in which an aluminum die cast is provided around a laminated silicon steel plate, and is firmly fitted to the shaft 5a by an interference fit of 100 to 150 μm. The rotor 61 has a poor balance due to the characteristic of being a laminated structure, and becomes a major factor in causing an unbalance in the central portion of the spindle. As a countermeasure to this, a method of correcting the balance of the rotor alone has been taken in advance.However, when the shaft is fastened, a new unbalance occurs due to the deformation caused by the large fit. It will remain. In addition, since there is a risk of centrifugal force destruction in a high-speed rotor, there are many cases where balance cannot be achieved by cutting the rotor.
[0028]
Further, a sensor (built-in sensor) 65 for detecting the rotational speed and phase of the shaft 5a is disposed on the outer periphery in the vicinity of the rear side end portion of the shaft 5a and faces the detection ring 66 formed with gear-like irregularities. Thus, it is attached to the housing 28.
[0029]
In the shaft 5a, the outer diameter of the portion that fits the bearings 10a and 10b is φ1, the outer diameter of the portion that fits the motor rotor 61 is φ2, the outer diameter of the portion that fits the bearings 10c and 10d is φ3, The outer diameter of the portion into which the detection ring 66 is fitted is φ4, and the relationship φ1>φ2>φ3> φ4 is established.
[0030]
The pipes 18 connected to the lubricating oil supply device 22A are connected to nozzles 12a, 12b, 12c, and 12d disposed in the vicinity of the bearings 10a, 10b, 10c, and 10d in the inner housing 20 of the main spindle device 14, respectively. .
[0031]
Next, the operation of the present embodiment will be described. With the tool (not shown) attached to the attachment portion 51, the motor 60 rotates the motor rotor 61 by the power supply from the drive circuit (not shown), so that the tool rotates together with the spindle 5. Yes. The rotation speed and phase of the main shaft 5 are controlled based on a signal from the sensor 65. Lubricating oil is supplied from a lubricating oil supply device (not shown) via a pipe 18 in accordance with the rotational speed of the main shaft 5, and the bearings 10a to 10d are lubricated via nozzles 12a to 12d.
[0032]
In the present embodiment, in the main shaft 5, on the bearing nut 5b disposed on the shaft end side from the rolling bearings 10a and 10b as the first bearing means, between the rolling bearings 10a and 10b and the motor rotor 61, the motor rotor 61 is provided. On the balance ring 5d between the rolling bearing 10c and the rolling bearing 10c, the balance bearing 5c disposed on the shaft end side of the rolling bearings 10c and 10d, which is the second bearing means, and on the inner side of the detection ring 66, which is the rotation detector. The top is the balance correction surfaces P1, P2, P3, and P4, respectively, and four-surface correction is performed by applying correction balance thereto. In the present embodiment, the balance ring 5c is provided on the front side of the sensor 65 to suppress the bending of the shaft. As a comparative example (described later with reference to FIG. 6), a comparative correction surface P4 ′ is shown on a bearing nut 5b attached to the rear side of the main shaft 5 together with the ring 5f.
[0033]
The balance correction surfaces P1 to P4 ′ have a structure in which screw holes are provided at a plurality of circumferential positions (about 4 to 16), and are unbalanced depending on the length (weight) of the screw inserted therein. Make corrections. This method has the best workability, but it is also possible to directly correct the balance correction surface or to correct by combining the phases of two (a plurality of) unbalanced rings.
[0034]
The balance adjusting surfaces P1 and P4 of the bearing nut 5b and the balance ring 5c can be adjusted by attaching and removing a balance adjusting screw from the front side or the rear side if the covers 37a and 37b are removed. On the other hand, with respect to the balance correction surface P2 formed on the surface of the shaft 5a and the balance correction surface P3 formed on the balance ring 5c, the screw hole can be processed by the shaft 5a alone, but how is the weight for balancing applied to the screw hole? The problem is whether to install it. Therefore, in the present embodiment, the bearing cooling groove 28a and the motor cooling groove 28b are separated to form the correction windows 28c and 28d, from which the balance correction surfaces P2 and P3 can be processed. It is preferable that the correction windows 28c and 28d have a sufficiently large shape so that even if a screw or the like falls during the balance adjustment work, the correction windows 28c and 28d can be recovered using a magnet-attached rod through the correction windows 28c and 28d. After the processing, the correction windows 28c and 28d are closed by the lids 28A and 28B to prevent foreign matter from entering from the outside.
[0035]
Further, in order to facilitate correction processing, the inner housing 20 including the bearing cooling groove 28a and the motor cooling portion of the housing 28 including the motor cooling groove 28b are separated, and the housing 28 and the inner housing are separated. 20, holes 21, 21 extending in a direction perpendicular to the axis are drilled. Even if a screw or weight falls during the work, if this hole is provided in the downward direction, the screw or the like will fall down through the hole and can be easily taken out. After the balance adjustment, by inserting the stoppers 21a and 21a into the outer ends of the holes 21 and 21, it is possible to prevent the cutting water from entering from the outside.
[0036]
Two arbitrary measurement points can be selected as the vibration measurement point at the time of balance correction. However, it is desirable that the outer diameter portion of the housing is in the vicinity of the balance correction surfaces P1 and P4 in terms of improving correction accuracy.
[0037]
3 to 5 show dynamic analysis results of the shaft system in FIG. FIG. 3 shows a case where the conventional two-surface correction and the four-surface correction according to the present invention are performed when there is an initial residual imbalance of 3 g · cm (an unbalance of about JIS G2.5) in the center of the motor rotor. It is a bending deformation curve of the shaft at 40,000 revolutions. In the case of two-surface correction, the analysis is performed by applying a correction weight so that the low-speed unbalance is zero as a rigid rotor. In the case of four-surface correction, analysis was performed by adding a correction weight to each balance correction surface so that the bearing reaction force becomes 0 at 12000 min ⁻¹ and 36000 min ⁻¹ . In the case of the two-surface correction, the unbalance at the center is corrected only in the vicinity of the shaft end, resulting in a large bending deformation. Since the bending deformation itself becomes unbalanced at high speed rotation, such a large deformation occurs. On the other hand, according to the four-surface correction of the present invention, the bending deformation is reduced to about 1/5 to 1/10 compared to the case of the two-surface correction.
[0038]
FIG. 4 is a result of analyzing the reaction force of the bearing (the resultant force of the four bearings) caused by the unbalance of the shaft in the conventional two-surface modification and the four-surface modification of the present invention. is there. The bearing reaction force in FIG. 4 is a rotational force, which means that if the bearing reaction force increases, the vibration of the main shaft increases. Comparing the two-surface modification and the four-surface modification, the bearing reaction force is the same up to about 30,000 min ^-1 , but in the case of the four-surface modification, the bearing reaction force becomes lower at higher speeds. ing. The effect that the bending deformation of the shaft is reduced by the four-surface correction is remarkable.
[0039]
FIG. 5 is a comparison result of shaft deformation curves when the rear side balance correction surface position is the shaft end nut and when the balance ring is provided on the front side of the sensor. The deformation at 40000 min ⁻¹ when a correction weight of about 1.5 g · cm was added to each balance correction surface was analyzed. When the balance correction surface is provided on the front side of the built-in sensor 65 (that is, the detection ring 66) as in the present invention, the deformation is reduced to about ½ compared to the balance correction surface at the shaft end. . Thereby, vibration can be reduced.
[0040]
FIG. 6 is a diagram showing a result of actually measuring vibration due to a difference in balance correction, and recording a rotational frequency component of a vibration value in a radial direction of the housing on the front side of the spindle. If two faces modification, respectively slow 12000Min ^-1, 2 types in the rotational speed of the high-speed 36000Min ^-1, in the case of four-sided modification at each slow 12000Min ^-1, the rotational speed of the high-speed 36000min ^-1, G0.4 Appropriate balance corrections were made.
[0041]
When the two-surface correction is performed at 12000 min ⁻¹ , the vibration is small at a low speed, but the vibration is large at a high speed. If the dihedral fixes in 36000min ^-1, the vibration is small in 36000min ^-1, it is greater vibration in the other rotational speed. This is because the balance is corrected in a state where bending deformation has occurred on the shaft, meaning that it cannot be balanced at low speeds where bending deformation does not occur or at higher speeds where the magnitude of bending deformation changes. Yes. On the other hand, in the case of four-surface correction, the vibration is corrected so as to decrease at both the rotational speeds of 12000 and 36000 min ⁻¹ , and the vibration is reduced over the entire operating rotational speed by appropriately selecting the balance correction surface. You can see that
[0042]
Next, in order to confirm the effect of the bending deformation on the rear side of the main shaft, the rear shaft end nut 5f (correction on the comparative correction surface P4 ′) and the balance ring 5c on the front side of the built-in sensor 65 are corrected. The correction (correction on the balance correction surface P4) was compared. When corrected with the rear shaft end nut, the vibration increases in the vicinity of 40000 min ⁻¹ due to unbalance due to bending deformation. In the case of correction on the front side of the built-in sensor 65, the increase in vibration is small even at an ultra high speed of 40000 min ⁻¹ .
[0043]
FIG. 7 is a diagram showing a measurement result of noise, and is a measurement result at 1 m on the front side of the spindle. In the case of the four-surface correction, since the vibration is reduced, it can be seen that the noise accompanying this is also reduced.
[0044]
FIG. 8 is a diagram illustrating a result of measuring the deflection accuracy of the rotating surface 52A with a non-contact displacement meter by attaching a circular dummy tool 52 to the tip of the tool attachment portion 51. FIG. In the conventional two-surface correction, the vibration accuracy increases because the vibration increases at a high speed rotation and the bending deformation of the shaft increases. However, in this embodiment, the bending accuracy hardly deteriorates in the shaft. I understand that there are few. By applying the present invention, it is possible to achieve a high rotational accuracy and to provide a machine tool spindle with high machining accuracy.
[0045]
The balance correction method according to the present invention is also effective in a spindle device that rotates at high speed using a magnetic bearing, an air bearing, or the like in addition to a rolling bearing.
[0046]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the spindle apparatus which can correct the imbalance of the machine tool spindle which rotates at high speed exactly, and reduces the vibration and noise in high speed rotation is provided. In the case of a magnetic bearing, the vibration can be reduced by the control without performing the four-surface correction as in the present invention, but in this case, since the shaft is balanced in a bent state, the rotational speed of the shaft is reduced. Resulting in. Since the bending deformation of the shaft can be suppressed by the balance correction using the present invention, the rotational accuracy of the magnetic bearing can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining the concept of the present invention.
FIG. 2 is a cross-sectional view of a spindle device according to the present embodiment.
FIG. 3 is a diagram showing a dynamic analysis result of a shaft system according to an example of the present invention.
FIG. 4 is a diagram showing a dynamic analysis result of a shaft system according to an example of the present invention.
FIG. 5 is a diagram showing a dynamic analysis result of a shaft system according to an example of the present invention.
FIG. 6 is a diagram illustrating a result of actual measurement of vibration due to a difference in balance correction.
FIG. 7 is a diagram showing a measurement result of noise in the example of the present invention.
FIG. 8 is a diagram showing a result of measuring a deflection accuracy during rotation with a non-contact displacement meter 52A by attaching a circular dummy tool 52 to the tip of the tool attachment portion 51.
[Explanation of symbols]
5 Spindle 5a Shaft 5b Shaft end nut 5c Balance ring 10a to 10d Bearing 14 Spindle device 28 Housing

Claims (2)

A housing, a main shaft, and the main shaft are mounted between a first bearing means and a second bearing means for rotatably supporting the housing, and between the first bearing means and the second bearing means. In the spindle device that has a motor rotor and the spindle is driven to rotate by the motor rotor,
The main shaft has a shaft end side from the first bearing means, between the first bearing means and the motor rotor, between the motor rotor and the second bearing means, and from the second bearing means. Balance correction surfaces are arranged in at least four locations on the end side,
At least one of the balance correction surfaces between the first bearing means and the second bearing means is subjected to balance adjustment from the outside through a correction window provided in the housing in a state where the main shaft is assembled. A spindle device characterized by being able to perform . The spindle device according to claim 1, further comprising a lid that closes the correction window .

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