JP2008110426A

JP2008110426A - Spindle device

Info

Publication number: JP2008110426A
Application number: JP2006294457A
Authority: JP
Inventors: Takatsugu Furubayashi; 卓嗣古林; Masatsugu Mori; 正継森
Original assignee: NTN Corp; NTN Toyo Bearing Co Ltd
Current assignee: NTN Corp
Priority date: 2006-10-30
Filing date: 2006-10-30
Publication date: 2008-05-15

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an increase in friction torque in a duplex bearing by the influence of radial thermal expansion of a rotary shaft or inner rings in a spindle device provided with the duplex bearing supporting the rotary shaft in which a pre-load is applied. <P>SOLUTION: A radial distance from the center line of the rotary shaft 20 to the rolling body contact sections of the inner ring tracks is set as r, the contact angle of the inner ring tracks is set as θ, and a radial space between the rolling body contact sections of the paired inner ring tracks is set as L. The center line of the duplex bearing 30 combined back-to-back with tapered roller bearings 31, 32 is brought into line with the center line of the rotary shaft 20, the radial distance r and the contact angle θ are set to be the same between the paired inner rings, and the radial space L is set to be 2r/tanθ so that a pre-load reducing action accompanied by the enlargement of the radial space between the paired inner rings by the thermal expansion of the rotary shaft 20 and a pre-load increasing action accompanied by the enlargement of each inner ring track in the radial direction by the thermal expansion of the rotary shaft 20 and each inner ring are balanced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

この発明は、工作機械主軸用に好適なスピンドル装置に関する。 The present invention relates to a spindle device suitable for a machine tool spindle.

工作機械主軸用のように高速の回転軸に適用されるスピンドル装置の中には、高速回転による発熱を低く抑えるため、軸受箱に対して回転軸を支持する転がり軸受にアンギュラ玉軸受を採用したものがある。 Among spindle devices applied to high-speed rotating shafts, such as those for machine tool main shafts, angular ball bearings are adopted as rolling bearings that support the rotating shaft against the bearing box in order to keep heat generated by high-speed rotation low. There is something.

上記アンギュラ玉軸受は、摩擦トルクが小さく、高速回転には適するが、軸受剛性がころ軸受に比べ低いため、軸一端部に大きな外力が作用する回転軸を支持した場合、軸一端部の変位が大きく生じ易い特徴がある。このため、軸受剛性が特に求められるスピンドル装置、例えば、工作機械の主軸用スピンドル装置においては、アンギュラ玉軸受で主軸を支持すると、主軸フロント端部に位置する重切削等工具に大きな外力が作用した場合、重切削等工具の変位が比較的に大きく生じることになり、その結果、被削物の形状精度に悪影響を及ぼし易い。 The angular ball bearing has a small friction torque and is suitable for high-speed rotation, but its bearing rigidity is lower than that of a roller bearing. Therefore, when a rotating shaft with a large external force is applied to one end of the shaft, the displacement of the one end of the shaft is There is a characteristic that tends to occur greatly. For this reason, in a spindle device in which bearing rigidity is particularly required, for example, a spindle device for a spindle of a machine tool, when the spindle is supported by an angular ball bearing, a large external force acts on a tool such as heavy cutting located at the front end of the spindle. In this case, the displacement of the tool such as heavy cutting is relatively large, and as a result, the shape accuracy of the work is liable to be adversely affected.

そこで、主軸のフロント側（工具が装着される側）において、ラジアル荷重を支持する円筒ころ軸受と軸荷重を支持するアンギュラ玉軸受を配置し、適切な予圧を与えることにより、それぞれで剛性向上と高速回転時の発熱抑制との両立を図ることが行われている。 Therefore, on the front side of the main shaft (the side on which the tool is mounted), cylindrical roller bearings that support radial loads and angular ball bearings that support shaft loads are arranged, and appropriate preload is applied to improve rigidity. Attempts have been made to balance heat generation during high-speed rotation.

例えば、非特許文献１に開示されたものは、主軸フロント側に、１個の複列円筒ころ軸受と２個の単列アンギュラ玉軸受からなる組合せ軸受が定位置予圧で設けられており、加えて、軸方向の軸の伸縮を逃す自由側となるリア側に、円筒ころ軸受又は外輪をボールブッシュで軸方向に移動自在にしたアンギュラ玉軸受が設けられている。 For example, what is disclosed in Non-Patent Document 1 is that a combination bearing consisting of one double row cylindrical roller bearing and two single row angular ball bearings is provided with a fixed position preload on the spindle front side. Thus, an angular ball bearing in which a cylindrical roller bearing or an outer ring is freely movable in the axial direction by a ball bush is provided on the rear side, which is a free side where the expansion and contraction of the shaft in the axial direction is missed.

しかし、円筒ころ軸受とアンギュラ玉軸受とで主軸を支持すると、軸受個数が多くなり、軸受の装着や取り外し作業が不便である。 However, if the main shaft is supported by the cylindrical roller bearing and the angular ball bearing, the number of bearings increases, and the mounting and removing operations of the bearings are inconvenient.

そこで、回転軸系のラジアル方向と軸方向の剛性向上を可能にする組合せ用軸受として、両方向の荷重を同時に負荷できる円すいころ軸受が採用されることも行われている。 Therefore, a tapered roller bearing that can simultaneously apply loads in both directions is also employed as a combination bearing that can improve the rigidity in the radial direction and the axial direction of the rotating shaft system.

例えば、非特許文献１に開示されたものは、主軸のフロント側を２個の単列円すいころ軸受からなる組合せ軸受で支持し、リア側を円筒ころ軸受で支持し、リア側の歯車で駆動するようにした主軸スピンドル装置である。 For example, in Non-Patent Document 1, the front side of the main shaft is supported by a combination bearing composed of two single-row tapered roller bearings, the rear side is supported by a cylindrical roller bearing, and driven by a gear on the rear side. This is a main spindle device.

しかしながら、円すいころ軸受は剛性には非常に優れるものの、ころ大端面とつばとの間の転がり滑り接触の存在のため、高速回転には一般に不向きである。 However, although the tapered roller bearing is extremely excellent in rigidity, it is generally unsuitable for high-speed rotation due to the presence of a rolling-sliding contact between the large roller end face and the collar.

そこで、円すいころ軸受の潤滑方法を工夫することにより、スピンドル装置の高速運転化を図ることも行われている。例えば、組合せ用軸受として、ころの案内つばを外輪側に設け、つば部での潤滑油確保を容易にしたものがある（例えば、特許文献１）。 In view of this, high speed operation of the spindle device has been attempted by devising a method for lubricating the tapered roller bearing. For example, as a combination bearing, there is a bearing guide collar provided on the outer ring side to facilitate securing lubricating oil at the collar portion (for example, Patent Document 1).

また、内輪大つば部に外部より強制的に潤滑油供給を行うもので、つば部と外部給油部とを孔で連通させる潤滑技術が採用されることもある（例えば、特許文献２）。 In addition, the lubricating oil is forcibly supplied from the outside to the inner ring large collar portion, and a lubrication technique in which the collar portion and the external oil supplying portion are communicated with each other through a hole may be employed (for example, Patent Document 2).

前掲の特許文献１、２に開示された技術を採用すると、円すいころ軸受の大つば部での発熱を抑制することができる分、高速回転が可能である。 When the techniques disclosed in Patent Documents 1 and 2 described above are employed, high-speed rotation is possible because heat generation at the large collar portion of the tapered roller bearing can be suppressed.

特公昭５３−８８５６号公報Japanese Patent Publication No.53-8856 特開平８−２７０６６０号公報JP-A-8-270660 ＮＴＮカタログ、精密転がり軸受、ＣＡＴ．Ｎｏ．２２６０／Ｊ第２２頁表５．１）NTN catalog, precision rolling bearing, CAT. No. 2260 / J Page 22 Table 5.1)

しかしながら、近年では、工作機械の主軸用スピンドル装置の分野に代表されるように、産業界からより一層の高速回転化と組合せ軸受の高剛性化が求められることが多くなっている。 However, in recent years, as represented by the field of spindle devices for main spindles of machine tools, there is an increasing demand from the industry for higher speed rotation and higher rigidity of combination bearings.

上記の要求に応えると、前掲の非特許文献１のように、主軸フロント側に円筒ころとアンギュラ玉軸受を併用した組合せ軸受の採用により、軸受個数が多くなり、軸受の装着や取り外し作業が手間である。 In response to the above requirements, as shown in Non-Patent Document 1 above, the use of a combination bearing that uses a cylindrical roller and an angular ball bearing in combination on the front side of the spindle increases the number of bearings, making it difficult to mount and remove the bearings. It is.

また、円すいころ軸受を組合せ用軸受として採用し、前掲の特許文献１、２のような潤滑方法を採用すれば軸受個数を減らすことはできるが、ころと内外輪軌道面間の転がり粘性抵抗の増大による回転速度の低下を避けるには、潤滑剤をできるだけ希薄にすることが求められる。
ところが、円すいころ軸受を高速運転する場合、ころ大端面とつばとの間の潤滑油不足で摩擦トルクが増大し、温度上昇することが問題になり、さらなる高速回転化に限界がある。 In addition, if a tapered roller bearing is used as a combination bearing and the lubrication method as described in Patent Documents 1 and 2 described above is adopted, the number of bearings can be reduced, but the rolling viscous resistance between the rollers and the inner and outer ring raceway surfaces is reduced. In order to avoid a decrease in rotational speed due to the increase, it is required to make the lubricant as lean as possible.
However, when the tapered roller bearing is operated at a high speed, the frictional torque increases due to the lack of lubricating oil between the roller large end face and the collar, which raises the problem of temperature rise, and there is a limit to further high speed rotation.

特に、工作機械の主軸用スピンドル装置のように、回転軸と内輪の温度が外輪温度よりも上昇する場合、それらの半径方向熱膨張が軸受すきまを負にする側に作用し、摩擦トルクが増大して温度上昇に繋がる問題が生じる。この問題は、組合せ用軸受の種類を問わずに生じる。前記の熱膨張の影響を見越して組合せ用軸受の初期すきまを正にすることは、軸受剛性を減少させることになり、上記の要求に応えることができない。 In particular, when the temperature of the rotating shaft and the inner ring rises above the outer ring temperature as in the spindle device for the main spindle of a machine tool, their radial thermal expansion acts on the side that makes the bearing clearance negative, increasing the friction torque. As a result, there is a problem that leads to a temperature rise. This problem occurs regardless of the type of bearing for combination. Making the initial clearance of the combination bearing positive in anticipation of the influence of the thermal expansion reduces the bearing rigidity and cannot meet the above requirements.

そこで、この発明の課題は、回転軸を支持する組合せ軸受を備え、前記組合せ軸受に予圧を与えたスピンドル装置において、回転軸や内輪の半径方向熱膨張の影響で組合せ軸受の摩擦トルクが増大することを防ぐことにある。 Therefore, an object of the present invention is to provide a combined bearing that supports a rotating shaft, and in a spindle device in which a preload is applied to the combined bearing, the friction torque of the combined bearing increases due to the effect of radial thermal expansion of the rotating shaft and the inner ring. Is to prevent that.

上記の課題を達成するため、この発明は、回転軸を支持する組合せ軸受を備え、前記組合せ軸受に予圧を与えたスピンドル装置において、前記組合せ軸受を、背面組合せとし、前記組合せ軸受の対となる内輪間の軸方向間隔が前記回転軸の熱膨張で拡大することに伴う予圧減少作用と、前記回転軸及び各内輪の熱膨張で各内輪軌道が半径方向に拡大することに伴う予圧増大作用とが釣り合うように設定した構成を採用したものである。 In order to achieve the above object, the present invention comprises a combination bearing for supporting a rotating shaft, and in a spindle device in which a preload is applied to the combination bearing, the combination bearing is a back combination, and becomes a pair of the combination bearing. A preload reducing action associated with the axial spacing between the inner rings expanding due to thermal expansion of the rotating shaft; and a preload increasing action associated with each inner ring raceway expanding radially due to the thermal expansion of the rotating shaft and each inner ring; Adopts a configuration that is set to balance.

上記のように組合せ軸受を背面組合せとした構成を採用すれば、回転軸と内輪の半径方向の膨張変位は予圧増大の方向に作用するが、背面組合せであるので、上記回転軸が熱膨張すると、その軸方向の熱膨張変位は、組合せ軸受の対となる内輪間の軸方向間隔を拡大させ、予圧減少の方向に作用する。一方、回転軸と内輪の温度が外輪温度よりも上昇する場合、回転軸と内輪の半径方向熱膨張による各内輪軌道の半径方向変位は、予圧増大の方向に作用し、摩擦トルクを増大させる。 If the configuration in which the combined bearing is a rear combination as described above is adopted, the radial expansion displacement of the rotating shaft and the inner ring acts in the direction of increasing the preload, but since it is a rear combination, the rotating shaft is thermally expanded. The axial thermal expansion displacement increases the axial interval between the inner rings of the pair of combination bearings, and acts in the direction of decreasing the preload. On the other hand, when the temperature of the rotating shaft and the inner ring rises above the temperature of the outer ring, the radial displacement of each inner ring raceway due to the radial thermal expansion of the rotating shaft and the inner ring acts in the direction of increasing the preload and increases the friction torque.

したがって、前記組合せ軸受の対となる内輪間の軸方向間隔が前記回転軸の熱膨張で拡大することに伴う予圧減少作用と、前記回転軸及び各内輪の熱膨張で各内輪軌道が半径方向に拡大することに伴う予圧増大作用とが釣り合うように設定した構成を採用すれば、上記の予圧減少作用により上記の予圧増大作用が打ち消される。 Therefore, the inner ring raceway in the radial direction is reduced by the preload reduction effect that accompanies the expansion of the axial distance between the inner rings that form the pair of the combined bearings due to the thermal expansion of the rotating shaft, and the thermal expansion of the rotating shaft and each inner ring. If a configuration that is set so as to balance the preload increasing action that accompanies the enlargement is adopted, the preload increasing action is canceled by the preload reducing action.

ここで、外輪の熱膨張の影響は、回転軸や内輪のそれと比べて小さいので、実用上、考慮する必要はない。
また、外輪の半径方向の拡大は、外輪とハウジングとのはめあい（通常すきま嵌め）の状態やハウジングの熱膨張によっても決定されるので、一般に評価は難しいが、若干は熱膨張によって半径方向に拡大し、予圧減少の方向に作用する。
一方、転動体の径は熱膨張し予圧過大の方向に作用するが、実用上、外輪の拡大に伴う予圧減少作用により相殺されるものと考えることができる。
したがって、上記対となる内輪間の軸方向間隔の拡大に伴う予圧減少作用と、上記内輪軌道の半径方向の拡大に伴う予圧増大作用とが打ち消されれば、回転軸あるいは内輪の温度が外輪温度よりも相当程度上昇しても、熱膨張による予圧増大を実用上影響のない程度に抑えることができる。 Here, since the influence of the thermal expansion of the outer ring is smaller than that of the rotating shaft and the inner ring, there is no need to consider it in practice.
The expansion of the outer ring in the radial direction is also determined by the fit (usually a clearance fit) between the outer ring and the housing and the thermal expansion of the housing. It acts in the direction of decreasing the preload.
On the other hand, the diameter of the rolling element is thermally expanded and acts in the direction of excessive preload, but it can be considered that it is practically offset by the preload reducing action accompanying expansion of the outer ring.
Therefore, if the preload reducing action accompanying the expansion of the axial interval between the pair of inner rings and the preload increasing action accompanying the radial enlargement of the inner ring raceway are canceled out, the temperature of the rotating shaft or the inner ring becomes higher than the outer ring temperature. However, the increase in preload due to thermal expansion can be suppressed to a practically unaffected level.

上述のように、この発明は、回転軸を支持する組合せ軸受を備え、前記組合せ軸受に予圧を与えたスピンドル装置において、回転軸や内輪の半径方向熱膨張の影響が前記組合せ軸受の対となる内輪間の軸方向間隔が前記回転軸の熱膨張で拡大することに伴う予圧減少作用により打ち消されるので、組合せ軸受の摩擦トルクが増大することを防ぐことができる。 As described above, the present invention includes a combination bearing that supports a rotating shaft, and in the spindle device in which a preload is applied to the combined bearing, the effect of radial thermal expansion of the rotating shaft and the inner ring becomes a pair of the combined bearing. Since the axial distance between the inner rings is canceled by the preload reduction effect associated with the thermal expansion of the rotating shaft, it is possible to prevent the friction torque of the combined bearing from increasing.

以下、この発明の実施形態に係るスピンドル装置を添付図面に基づいて説明する。
図１に示すスピンドル装置は、ハウジング１０と、このハウジング１０に対して回転軸２０を支持する組合せ軸受３０とを備えたものである。 Hereinafter, a spindle device according to an embodiment of the present invention will be described with reference to the accompanying drawings.
The spindle device shown in FIG. 1 includes a housing 10 and a combination bearing 30 that supports the rotary shaft 20 with respect to the housing 10.

回転軸２０は、工作機械の主軸からなり、その中心線は、組合せ軸受３０の中心線と一致させて設けられている。回転軸２０のフロント側（図中の左側）の端部に工具が装着される（図示省略）。 The rotating shaft 20 is a main axis of a machine tool, and the center line thereof is provided so as to coincide with the center line of the combination bearing 30. A tool is attached to the end of the rotary shaft 20 on the front side (left side in the figure) (not shown).

組合せ軸受３０は、２個の単列円すいころ軸受３１、３２から構成されている。これら２個の円すいころ軸受３１、３２は、同一のものが利用されており、背面組合せで配列されている。２個の円すいころ軸受３１、３２の一方側で回転軸２０のフロント側が支持され、他方側で回転軸２０のリア側（図中の右側）が支持されている。すなわち、スピンドル装置全体で回転軸２０を支持するための転がり軸受は２個のみであり、軸受の装着や取り外し作業に手間取らない。 The combination bearing 30 includes two single row tapered roller bearings 31 and 32. These two tapered roller bearings 31 and 32 are the same, and are arranged in a rear combination. The front side of the rotating shaft 20 is supported on one side of the two tapered roller bearings 31 and 32, and the rear side (right side in the drawing) of the rotating shaft 20 is supported on the other side. That is, there are only two rolling bearings for supporting the rotating shaft 20 in the entire spindle device, and it does not take time to mount and remove the bearings.

２個の円すいころ軸受３１、３２の間を利用して、ハウジング１０と回転軸２０の間にビルトインモータ４０が組み込まれている。ビルトインモータ４０は、ハウジング１０の外筒１１の内周に沿って設けられたモータケーシング４１と、回転軸２０の外周に固定されたロータ４２と、モータケーシング４１とロータ４２の間に組み込まれたステータ４３を主な要素とし、ロータ４２に発生する回転力により回転軸２０を回転させるようになっている。なお、回転軸２０をリア側に延長し、プーリ、ギヤ等を設けて回転力を外部から伝達させることもできる。 A built-in motor 40 is incorporated between the housing 10 and the rotary shaft 20 by using the space between the two tapered roller bearings 31 and 32. The built-in motor 40 is incorporated between the motor casing 41 provided along the inner periphery of the outer cylinder 11 of the housing 10, the rotor 42 fixed to the outer periphery of the rotary shaft 20, and the motor casing 41 and the rotor 42. The stator 43 is a main element, and the rotating shaft 20 is rotated by the rotational force generated in the rotor 42. The rotating shaft 20 can be extended to the rear side, and pulleys, gears, etc. can be provided to transmit the rotational force from the outside.

ハウジング１０の外筒１１には、ビルトインモータ４０の発熱を考慮し、冷却路１１ａが形成されている。ハウジング１０は、冷却路１１ａに冷却油を流すと、外筒１１の熱分布がハウジング１０内の構造物に支障となる歪が生じないように熱が奪われるようになっている。 A cooling path 11 a is formed in the outer cylinder 11 of the housing 10 in consideration of heat generated by the built-in motor 40. When the cooling oil is allowed to flow through the cooling passage 11 a, the housing 10 is deprived of heat so that the heat distribution of the outer cylinder 11 does not cause distortion that hinders the structure inside the housing 10.

上記組合せ軸受３０は、各円すいころ軸受３１、３２に対して定位置予圧方式で所定の予圧が与えられている。この予圧は、通常−３〜−５μｍ程度の負すきまが適当である。 In the combination bearing 30, a predetermined preload is applied to each tapered roller bearing 31, 32 by a fixed position preload system. For this preload, a negative clearance of about −3 to −5 μm is appropriate.

なお、組合せ軸受３０の外輪側の位置決めは、モータケーシング４１、軸受箱部材１２、１２、蓋１３、１４、潤滑油供給用のノズル部材１５、１６で行われている。組合せ軸受３０の内輪側の位置決めは、ロータ４２、間座１７、１７、回転軸２０の肩２１、回転軸２０のねじ山２２に螺着して軸方向の予圧を生じさせるナット１８等で行われている。対となる円すいころ軸受３１、３２間の構造は、この間の軸方向２分点を含むラジアル平面に関して対称になっており、これにより、この間の剛性が両側で均衡し、熱分布が概ね一様になるようになっている。 The positioning of the combination bearing 30 on the outer ring side is performed by the motor casing 41, the bearing box members 12, 12, the lids 13, 14, and the nozzle members 15, 16 for supplying lubricating oil. Positioning of the combined bearing 30 on the inner ring side is performed by a nut 42 that is screwed to the rotor 42, the spacers 17 and 17, the shoulder 21 of the rotary shaft 20, and the thread 22 of the rotary shaft 20 to generate axial preload. It has been broken. The structure between the pair of tapered roller bearings 31 and 32 is symmetric with respect to a radial plane including the axial bisection point therebetween, whereby the rigidity therebetween is balanced on both sides and the heat distribution is substantially uniform. It is supposed to become.

上述のように、組合せ軸受３０の中心線は、回転軸２０の中心線に一致しており、対となる円すいころ軸受３１、３２は、同一のものが利用されている。したがって、これら円すいころ軸受３１、３２間では、回転軸２０の中心線と内輪軌道の転動体接触部までの半径方向距離ｒ、対となる内輪軌道の接触角θは同一に対応させられている。これにより、円すいころ軸受３１、３２の対となる内輪間の軸方向間隔が回転軸２０の熱膨張で拡大することに伴う予圧減少作用と、回転軸２０及び各内輪の熱膨張で各内輪軌道が半径方向に拡大することに伴う予圧増大作用とが円すいころ軸受３１、３２で均等に作用するようになっている。 As described above, the center line of the combination bearing 30 coincides with the center line of the rotary shaft 20, and the same tapered roller bearings 31 and 32 are used. Therefore, between these tapered roller bearings 31 and 32, the radial direction distance r from the center line of the rotating shaft 20 to the rolling element contact portion of the inner ring raceway and the contact angle θ of the paired inner ring raceway are made to correspond to each other. . As a result, the inner ring raceway is caused by the preload reduction effect that accompanies the expansion of the axial distance between the inner rings of the pair of tapered roller bearings 31 and 32 due to the thermal expansion of the rotating shaft 20 and the thermal expansion of the rotating shaft 20 and each inner ring. The preload-increasing action accompanying the enlargement in the radial direction works equally on the tapered roller bearings 31 and 32.

また、対となる内輪軌道の転動体接触部間の軸方向間隔Ｌは、式（１）の条件を満たす値である。
Ｌ＝２ｒ／ｔａｎθ・・・式（１）
軸方向間隔Ｌを式（１）の値に設定すれば、組合せ軸受３０の対となる内輪間の軸方向間隔が回転軸２０の熱膨張で拡大することに伴う予圧減少作用と、回転軸２０及び各内輪の熱膨張で各内輪軌道が半径方向に拡大することに伴う予圧増大作用とが釣り合い、組合せ軸受３０の摩擦トルクが増大することを防ぐことができる。 Further, the axial distance L between the rolling element contact portions of the inner ring raceway that is a pair is a value that satisfies the condition of Expression (1).
L = 2r / tan θ Formula (1)
If the axial distance L is set to the value of the expression (1), the preload reducing action that accompanies the expansion of the axial distance between the inner rings that form a pair of the combined bearings 30 due to the thermal expansion of the rotating shaft 20, and the rotating shaft 20. Further, it is possible to prevent the frictional torque of the combined bearing 30 from increasing due to the balance between the preload increasing action associated with the radial expansion of each inner ring raceway due to the thermal expansion of each inner ring.

具体的に述べると、回転軸２０が熱膨張すると、軸方向に伸張した結果、対となる円すいころ軸受３１、３２間の間隔が軸方向に拡大し、これに伴い、軸方向間隔Ｌも同じように拡大する。この軸方向間隔Ｌの拡大変位の影響は、組合せ両側に２等分して影響するから、各円すいころ軸受３１、３２において等しく作用する。
軸方向間隔Ｌの拡大変位量ΔＬは、各円すいころ軸受３１、３２に接触角θに応じて影響するため、ΔＬｔａｎθ／２の半径方向変位を縮径側に生じさせる。
この半径方向変位と共に、回転軸２０及び円すいころ軸受３１、３２の内輪の熱膨張による半径方向変位を、Δｒとすると、ΔＬｔａｎθ／２＝Δｒの関係がある。一方、内輪の線膨張係数をα、温度上昇をΔｔとすれば、ΔＬ＝αＬΔｔ、Δｒ＝αｒΔｔとなる。これらの関係式から、式（１）の条件を満たせば、上記予圧減少作用と上記予圧増大作用とが釣り合うように設定することになり、回転軸２０及び円すいころ軸受３１、３２の内輪の熱膨張による半径方向変位が打ち消されるため、上記の予圧減少作用により上記の予圧増大作用が打ち消される。 More specifically, when the rotary shaft 20 is thermally expanded, as a result of extending in the axial direction, the distance between the pair of tapered roller bearings 31 and 32 is increased in the axial direction, and accordingly, the axial distance L is the same. To enlarge. Since the influence of the enlarged displacement of the axial interval L is equally divided into both sides of the combination, it acts equally on the tapered roller bearings 31 and 32.
Since the enlarged displacement amount ΔL of the axial interval L affects the tapered roller bearings 31 and 32 according to the contact angle θ, a radial displacement of ΔLtanθ / 2 is generated on the reduced diameter side.
Along with this radial displacement, if the radial displacement due to thermal expansion of the inner ring of the rotary shaft 20 and the tapered roller bearings 31 and 32 is Δr, there is a relationship of ΔLtanθ / 2 = Δr. On the other hand, when the linear expansion coefficient of the inner ring is α and the temperature rise is Δt, ΔL = αLΔt and Δr = αrΔt. From these relational expressions, if the condition of the expression (1) is satisfied, the preload reducing action and the preload increasing action are set to be balanced, and the heat of the inner ring of the rotary shaft 20 and the tapered roller bearings 31 and 32 is set. Since the radial displacement due to the expansion is canceled out, the above preload increasing action is canceled out by the above preload reducing action.

なお、半径方向距離ｒ、内輪軌道の接触角θは、円すいころ軸受なので、転動体と接触する部分の軸方向幅の中央位置を代表に定めたが、アンギュラ玉軸受の場合は接触点を基準に定める。
上記半径方向距離ｒ、接触角θ、及び軸方向間隔Ｌは、装置全体が室温である状態で設定すればよい。熱膨張は、温度に対する線形性の変化だからである。 The radial distance r and the contact angle θ of the inner ring raceway are tapered roller bearings, so the center position of the axial width of the portion that contacts the rolling element is set as a representative, but in the case of an angular ball bearing, the contact point is the reference. Stipulated in
The radial distance r, the contact angle θ, and the axial interval L may be set in a state where the entire apparatus is at room temperature. This is because thermal expansion changes in linearity with respect to temperature.

また、組合せ軸受３０が複列に軌道が形成された内輪を含むものであっても、複列間で接触角θが同じである限り、フロント側、リア側それぞれの複数個の軸受の中心位置間のスパンで軸方向間隔Ｌを定めれば、各列において上記の釣り合いを得ることができる。 In addition, even if the combined bearing 30 includes an inner ring in which raceways are formed in double rows, as long as the contact angle θ is the same between the double rows, the center positions of the plurality of bearings on the front side and the rear side respectively. If the axial interval L is determined by the span between the above, the above balance can be obtained in each row.

ここで、通常、工作機械主軸の直径は５０〜１００ｍｍ程度であるので式（１）の半径方向距離ｒは２５〜５０ｍｍ程度となる。また、円すいころ軸受の内輪における接触角θは１５°程度であるので、軸方向間隔Ｌは、１９０〜３８０ｍｍ程度となる。このような寸法であれば、ビルトインモータ４０が２個の軸受３１、３２間に納まり、かつ回転軸２０の全長も一般的なオーダとなる。 Here, since the diameter of the main spindle of the machine tool is usually about 50 to 100 mm, the radial distance r in the formula (1) is about 25 to 50 mm. Further, since the contact angle θ in the inner ring of the tapered roller bearing is about 15 °, the axial interval L is about 190 to 380 mm. With such dimensions, the built-in motor 40 is accommodated between the two bearings 31 and 32, and the overall length of the rotary shaft 20 is in a general order.

また、回転軸２０の停止時の室温での予圧は、軸受すきま（初期すきま）を適当な負すきま（通常−３〜−５μｍ程度）としておく。このような値であれば、円すいころ軸受３１、３２が本来備えるラジアル、スラスト両方向の高剛性に加え、高速回転時の発熱による予圧過大を防ぐことができるので、特に高速回転に好適な主軸用スピンドル装置になる。 The preload at room temperature when the rotating shaft 20 is stopped is set such that the bearing clearance (initial clearance) is an appropriate negative clearance (usually about −3 to −5 μm). With such a value, it is possible to prevent excessive preload due to heat generation during high-speed rotation, in addition to the high rigidity in both radial and thrust directions that the tapered roller bearings 31 and 32 originally have, and for spindles particularly suitable for high-speed rotation. Become a spindle device.

このスピンドル装置は、円すいころ軸受３１、３２のつば部での発熱が増大しても、摩擦トルクの増大がなく、予圧は初期状態とほぼ同一に保たれるので、つば部での表面損傷等が発生しない限り、高速回転が可能である。なお、このスピンドル装置は、予圧が与えられるので、発熱の影響が少ない低速回転時でも剛性が犠牲にならないことは勿論である。 In this spindle device, even if the heat generation at the flange portions of the tapered roller bearings 31 and 32 increases, the friction torque does not increase and the preload is kept almost the same as the initial state. As long as this does not occur, high-speed rotation is possible. Since this spindle device is preloaded, it goes without saying that rigidity is not sacrificed even during low-speed rotation with little influence of heat generation.

以上に述べたように、このスピンドル装置は、円すいころ軸受３１、３２を、予圧調整のための特別な付帯設備を一切用いずに高速で運転できる。 As described above, this spindle apparatus can operate the tapered roller bearings 31 and 32 at a high speed without using any special incidental equipment for preload adjustment.

また、このスピンドル装置は、低速領域から高速領域まで、円すいころ軸受本来の剛性を維持できる。すなわち、このスピンドル装置は、工作機械の加工効率向上と被削面の品位向上に要求される高速性と高剛性を両立することができる。 Further, this spindle device can maintain the original rigidity of the tapered roller bearing from a low speed region to a high speed region. That is, this spindle device can achieve both high speed and high rigidity required for improving the machining efficiency of the machine tool and improving the quality of the machined surface.

また、このスピンドル装置は、上記０００５段落に記した意味でのリア側（自由側）の軸受を廃することができ、軸受の組み付け・取り外し作業が簡便であり、コスト的にも有利である。 Further, this spindle device can eliminate the rear side (free side) bearing in the meaning described in the above paragraph 0005, and it is easy to assemble and remove the bearing, which is advantageous in terms of cost.

このスピンドル装置は、組合せ用軸受が２個の例を示したが、同様に考えて、極めて高い剛性が要求される場合では、３個以上の多数個で構成することもできる。 In this spindle apparatus, an example in which there are two combination bearings has been shown. However, in the same way, when extremely high rigidity is required, the spindle apparatus may be composed of a large number of three or more.

また、このスピンドル装置は、軸受個数を減らすため、組合せ用軸受として円すいころ軸受を採用したが、接触角を有するアンギュラ玉軸受の背面組合せについても同様に適用することできる。 Further, this spindle device employs a tapered roller bearing as a combination bearing in order to reduce the number of bearings. However, the present invention can be similarly applied to a back combination of an angular ball bearing having a contact angle.

ただし、アンギュラ玉軸受の接触角は、回転速度上昇に伴って増加するため、予め接触角の変化量を静力学的な釣り合い方程式から概算しておき、初期接触角と高速回転時の接触角の間の適当な接触角度を用いて、式（1）から軸方向間隔Ｌを決めればよい。この実施形態のように円すいころ軸受を組合せ用軸受に採用すれば、そのような複雑な設定が避けられるので、上記の打ち消しを安定して得易い利点がある。 However, since the contact angle of angular contact ball bearings increases as the rotational speed increases, the amount of change in the contact angle is estimated in advance from the static balance equation, and the initial contact angle and the contact angle during high-speed rotation are calculated. What is necessary is just to determine the axial direction space | interval L from Formula (1) using the suitable contact angle between. If a tapered roller bearing is used for a combination bearing as in this embodiment, such a complicated setting can be avoided, and there is an advantage that the above cancellation can be obtained stably.

実施形態の全体構成を示す断面図Sectional drawing which shows the whole structure of embodiment

符号の説明Explanation of symbols

１０ハウジング
２０回転軸
３０組合せ軸受
３１、３２円すいころ軸受
４０ビルトインモータ DESCRIPTION OF SYMBOLS 10 Housing 20 Rotating shaft 30 Combination bearing 31, 32 Tapered roller bearing 40 Built-in motor

Claims

回転軸を支持する組合せ軸受を備え、前記組合せ軸受に予圧を与えたスピンドル装置において、
前記組合せ軸受を、背面組合せとし、
前記組合せ軸受の対となる内輪間の軸方向間隔が前記回転軸の熱膨張で拡大することに伴う予圧減少作用と、前記回転軸及び各内輪の熱膨張で各内輪軌道が半径方向に拡大することに伴う予圧増大作用とが釣り合うように設定したことを特徴とするスピンドル装置。 In a spindle apparatus comprising a combination bearing for supporting a rotating shaft, and applying a preload to the combination bearing,
The combination bearing is a back combination,
Each inner ring raceway expands in the radial direction due to the preload reduction effect that accompanies the axial spacing between the inner rings that form a pair of the combined bearings being expanded by thermal expansion of the rotating shaft, and the thermal expansion of the rotating shaft and each inner ring A spindle device characterized in that it is set so as to balance the accompanying preload increasing action.

前記回転軸の中心線と内輪軌道の転動体接触部までの半径方向距離をｒとし、内輪軌道の接触角をθとし、対となる内輪軌道の転動体接触部間の軸方向間隔をＬとしたとき、
前記組合せ軸受の中心線が前記回転軸の中心線に一致し、前記対となる内輪間で半径方向距離ｒ及び前記接触角θが同一であり、前記軸方向間隔Ｌが２ｒ／ｔａｎθであることを特徴とする請求項１に記載のスピンドル装置。 The radial distance from the center line of the rotating shaft to the rolling element contact portion of the inner ring raceway is r, the contact angle of the inner ring raceway is θ, and the axial distance between the rolling element contact portions of the paired inner ring raceway is L. When
The center line of the combined bearing coincides with the center line of the rotating shaft, the radial distance r and the contact angle θ are the same between the pair of inner rings, and the axial distance L is 2r / tan θ. The spindle device according to claim 1.

前記回転軸が工作機械の主軸であり、前記組合せ軸受がフロント側とリア側に配置された２個の円すいころ軸受からなる請求項１又は２に記載のスピンドル装置。 The spindle device according to claim 1 or 2, wherein the rotating shaft is a main shaft of a machine tool, and the combination bearing is composed of two tapered roller bearings arranged on a front side and a rear side.