JP2024067713A

JP2024067713A - Bearing device with strain sensor and spindle device for machine tool

Info

Publication number: JP2024067713A
Application number: JP2022177989A
Authority: JP
Inventors: 勇介澁谷; Yusuke Shibuya; 耀示大口; Yoji Oguchi
Original assignee: NTN Corp; NTN Toyo Bearing Co Ltd
Current assignee: NTN Corp
Priority date: 2022-11-07
Filing date: 2022-11-07
Publication date: 2024-05-17

Abstract

To provide a bearing device with a strain sensor which can detect a bearing preload with high accuracy.SOLUTION: A plurality of first protrusion parts 50 are provided at intervals in a circumferential direction on a first outer ring 30 side end surface of both axial end surfaces of an outer ring spacer 26. On a second outer ring 35 side end surface, the same number of second protrusion parts 51 as the number of the first protrusion parts 50 are provided at the same circumferential positions as the first protrusion parts 50. Strain sensors 28 are disposed at the same circumferential positions as the circumferential positions of the first protrusion parts 50 and the second protrusion parts 51.SELECTED DRAWING: Figure 2

Description

この発明は、ひずみセンサ付き軸受装置、およびそのひずみセンサ付き軸受装置を使用した工作機械用スピンドル装置に関する。 This invention relates to a bearing device with a strain sensor and a spindle device for a machine tool that uses the bearing device with a strain sensor.

マシニングセンタや旋盤等の工作機械や、その他の産業機械では、工具や加工物等の対象物が取り付けられる回転軸を回転可能に支持するスピンドル装置が用いられる。このようなスピンドル装置の使用分野において、近年、省人化や無人化のための状態監視機能の強化が求められるようになっている。 In machine tools such as machining centers and lathes, and other industrial machines, spindle devices are used that rotatably support a rotating shaft on which objects such as tools and workpieces are attached. In recent years, there has been a demand in fields where such spindle devices are used to strengthen the status monitoring function in order to reduce manpower and achieve automation.

そこで、本願の出願人は、状態監視機能の強化のニーズに応えるため、ひずみセンサ付き軸受装置を既に提案している（特許文献１）。 Therefore, the applicant of this application has already proposed a bearing device equipped with a strain sensor to meet the need for enhanced condition monitoring functions (Patent Document 1).

特許文献１のひずみセンサ付き軸受装置は、軸方向に間隔をおいて配置された第１軸受および第２軸受と、第１軸受と第２軸受の間に設けられた筒状の外輪間座と、外輪間座に取り付けられたひずみセンサとを有する。 The bearing device with strain sensor in Patent Document 1 has a first bearing and a second bearing spaced apart in the axial direction, a cylindrical outer ring spacer provided between the first bearing and the second bearing, and a strain sensor attached to the outer ring spacer.

第１軸受は、第１外輪と、第１外輪の径方向内側に設けられた第１内輪と、第１外輪と第１内輪の間に組み込まれた複数の第１転動体とを有する。同様に、第２軸受は、第２外輪と、第２外輪の径方向内側に設けられた第２内輪と、第２外輪と第２内輪の間に組み込まれた複数の第２転動体とを有する。外輪間座は、第１外輪と第２外輪の間に軸方向に挟み込まれて配置されている。 The first bearing has a first outer ring, a first inner ring provided radially inward of the first outer ring, and a plurality of first rolling elements assembled between the first outer ring and the first inner ring. Similarly, the second bearing has a second outer ring, a second inner ring provided radially inward of the second outer ring, and a plurality of second rolling elements assembled between the second outer ring and the second inner ring. The outer ring spacer is arranged by being sandwiched between the first outer ring and the second outer ring in the axial direction.

第１軸受と第２軸受の間には、第１内輪、第１転動体、第１外輪、外輪間座、第２外輪、第２転動体、第２内輪を通って予圧が伝達するように軸方向の予圧が付与されている。第１軸受は、軸方向の予圧で、第１転動体が第１外輪を押圧する径方向分力を生じるように構成されたアンギュラ玉軸受であり、第２軸受も、軸方向の予圧で、第２転動体が第２外輪を押圧する径方向分力を生じるように構成されたアンギュラ玉軸受である。 An axial preload is applied between the first bearing and the second bearing so that the preload is transmitted through the first inner ring, the first rolling element, the first outer ring, the outer ring spacer, the second outer ring, the second rolling element, and the second inner ring. The first bearing is an angular ball bearing configured so that the axial preload generates a radial component force that causes the first rolling element to press the first outer ring, and the second bearing is also an angular ball bearing configured so that the axial preload generates a radial component force that causes the second rolling element to press the second outer ring.

ひずみセンサは、外輪間座の外周（または内周）に取り付けられ、このひずみセンサの出力に基づいて、第１軸受および第２軸受の予圧荷重（以下「軸受予圧」という）を検出することが可能となっている。 The strain sensor is attached to the outer periphery (or inner periphery) of the outer ring spacer, and the preload of the first bearing and the second bearing (hereinafter referred to as "bearing preload") can be detected based on the output of this strain sensor.

特開２０２１－０１４８８６号公報JP 2021-014886 A

ところで、特許文献１のひずみセンサ付き軸受装置において、外輪間座のひずみセンサの出力に基づいて検出される軸受予圧の大きさに誤差が生じることがあった。この誤差を無くし、高い精度で軸受予圧を検出することができれば、省人化や無人化のための状態監視の信頼性を高めることが可能となる。 However, in the strain sensor-equipped bearing device of Patent Document 1, an error could occur in the magnitude of the bearing preload detected based on the output of the strain sensor in the outer ring spacer. If this error could be eliminated and the bearing preload could be detected with high accuracy, it would be possible to improve the reliability of condition monitoring for labor-saving or unmanned operation.

この発明が解決しようとする課題は、高い精度で軸受予圧を検出することが可能なひずみセンサ付き軸受装置を提供することである。 The problem that this invention aims to solve is to provide a bearing device with a strain sensor that can detect bearing preload with high accuracy.

本願の発明者らは、上記の特許文献１のひずみセンサ付き軸受装置を試作評価したところ、外輪間座やその周辺の各部品の微小な加工誤差（例えば、数ミクロンといった僅かな平面度の誤差）等の影響で、外輪間座の軸方向端面の接触の強さが、周方向位置によって変化し、外輪間座の軸方向端面に、強く接触する箇所と、弱く接触する箇所とが発生していることが分かった。 The inventors of the present application prototyped and evaluated the strain sensor-equipped bearing device of Patent Document 1 above, and found that due to minute machining errors (for example, slight flatness errors of a few microns) in the outer ring spacer and its surrounding parts, the strength of contact on the axial end face of the outer ring spacer varies depending on the circumferential position, resulting in some areas of strong contact and other areas of weak contact on the axial end face of the outer ring spacer.

そして、強く接触する箇所がひずみセンサと同じ周方向位置にくる場合と、弱く接触する箇所がひずみセンサと同じ周方向位置にくる場合とで、ひずみセンサの出力に差が生じ、そのことが、ひずみセンサの出力に基づいて検出される軸受予圧の誤差の原因となっていることを見出した。 They then discovered that a difference in the output of the strain sensor occurs when the strong contact point is in the same circumferential position as the strain sensor and when the weak contact point is in the same circumferential position as the strain sensor, and that this difference causes an error in the bearing preload detected based on the strain sensor output.

そこで、本願の発明者らは、外輪間座の軸方向端面を特定の周方向位置で強く接触する形状とし、その周方向位置にひずみセンサを配置すれば、ひずみセンサの出力に基づいて検出される軸受予圧の誤差を小さく抑えることができるという着想を得た。 The inventors of the present application came up with the idea that by shaping the axial end face of the outer ring spacer so that it comes into strong contact at a specific circumferential position and locating a strain sensor at that circumferential position, it would be possible to minimize the error in the bearing preload detected based on the output of the strain sensor.

この着想に基づいて、この発明では、上記の課題を解決するため、以下の構成のひずみセンサ付き軸受装置を提供する。
［構成１］
軸方向に間隔をおいて配置された第１軸受および第２軸受と、前記第１軸受と前記第２軸受の間に設けられた筒状の外輪間座と、前記外輪間座に取り付けられたひずみセンサとを有し、
前記第１軸受は、第１外輪と、第１外輪の径方向内側に設けられた第１内輪と、第１外輪と第１内輪の間に組み込まれた複数の第１転動体とを有し、
前記第２軸受は、第２外輪と、第２外輪の径方向内側に設けられた第２内輪と、第２外輪と第２内輪の間に組み込まれた複数の第２転動体とを有し、
前記第１軸受と前記第２軸受の間には、前記第１内輪、前記第１転動体、前記第１外輪、前記外輪間座、前記第２外輪、前記第２転動体、前記第２内輪を通って予圧が伝達するように軸方向の予圧が付与されているセンサ付き軸受装置において、
前記外輪間座の軸方向両側の端面のうち、前記第１外輪の側の端面には、前記軸方向の予圧で前記第１外輪の軸方向端面に押し付けられる複数の第１凸部が周方向に間隔をおいて設けられ、
前記外輪間座の軸方向両側の端面のうち、前記第２外輪の側の端面には、前記軸方向の予圧で前記第２外輪の軸方向端面に押し付けられる前記複数の第１凸部の個数と同数の第２凸部が、周方向に間隔をおいて前記複数の第１凸部と同じ周方向位置に設けられ、
前記ひずみセンサは、前記第１凸部および前記第２凸部の周方向位置と同じ周方向位置に配置されていることを特徴とするひずみセンサ付き軸受装置。 Based on this idea, in order to solve the above problems, the present invention provides a bearing device with a strain sensor having the following configuration.
[Configuration 1]
The bearing has a first bearing and a second bearing spaced apart in the axial direction, a cylindrical outer ring spacer provided between the first bearing and the second bearing, and a strain sensor attached to the outer ring spacer,
the first bearing includes a first outer ring, a first inner ring provided radially inside the first outer ring, and a plurality of first rolling elements assembled between the first outer ring and the first inner ring,
the second bearing includes a second outer ring, a second inner ring provided radially inside the second outer ring, and a plurality of second rolling elements assembled between the second outer ring and the second inner ring,
In a sensor-equipped bearing device, an axial preload is applied between the first bearing and the second bearing such that the preload is transmitted through the first inner ring, the first rolling element, the first outer ring, the outer ring spacer, the second outer ring, the second rolling element, and the second inner ring,
a plurality of first convex portions are provided at intervals in the circumferential direction on the end face on the first outer ring side out of end faces on both axial sides of the outer ring spacer, the first convex portions being pressed against the axial end face of the first outer ring by the axial preload,
of end faces on both axial sides of the outer ring spacer, the end face on the side of the second outer ring has second convex portions, the number of which is the same as the number of the plurality of first convex portions pressed against the axial end face of the second outer ring by the axial preload, the second convex portions being provided at the same circumferential positions as the plurality of first convex portions at intervals in the circumferential direction,
A bearing device with a strain sensor, characterized in that the strain sensor is arranged at the same circumferential position as the first convex portion and the second convex portion.

この構成を採用すると、第１外輪から外輪間座に加わる軸方向荷重が、周方向に間隔をおいて配置された各第１凸部の位置に集約され、同様に、第２外輪から外輪間座に加わる軸方向荷重も、周方向に間隔をおいて配置された各第２凸部の位置に集約される。そして、第１凸部および第２凸部の周方向位置と同じ周方向位置にひずみセンサが配置されているので、第１外輪および第２外輪から外輪間座に加わる軸方向荷重が、ひずみセンサの位置に安定して伝わる。そのため、ひずみセンサの出力が、外輪間座やその周辺の各部品の微小な加工誤差等の影響を受けにくく、高い精度で軸受予圧を検出することが可能となる。 When this configuration is adopted, the axial load applied from the first outer ring to the outer ring spacer is concentrated at the position of each of the first convex parts arranged at intervals in the circumferential direction, and similarly, the axial load applied from the second outer ring to the outer ring spacer is concentrated at the position of each of the second convex parts arranged at intervals in the circumferential direction. And because the strain sensor is arranged at the same circumferential position as the first convex part and the second convex part, the axial load applied from the first outer ring and the second outer ring to the outer ring spacer is stably transmitted to the position of the strain sensor. Therefore, the output of the strain sensor is less susceptible to minute machining errors of the outer ring spacer and its surrounding parts, making it possible to detect the bearing preload with high accuracy.

［構成２］
前記複数の第１凸部の個数が３つであり、前記複数の第２凸部の個数が３つである、構成１に記載のひずみセンサ付き軸受装置。 [Configuration 2]
2. The bearing device with a strain sensor according to claim 1, wherein the number of the first convex portions is three, and the number of the second convex portions is three.

この構成を採用すると、外輪間座の第１外輪の側の端面の第１凸部の個数が３つなので、外輪間座による第１外輪の支持が３点支持となる。そのため、第１外輪から外輪間座に加わる軸方向荷重に偏り等がある場合にも、各第１凸部の第１外輪との接触が安定する。同様に、外輪間座の第２外輪の側の端面の第２凸部の個数が３つなので、外輪間座による第２外輪の支持も３点支持となる。そのため、第２外輪から外輪間座に加わる軸方向荷重に偏り等がある場合にも、各第２凸部の第２外輪との接触が安定する。 When this configuration is adopted, the number of first convex portions on the end face of the outer ring spacer on the side of the first outer ring is three, so the first outer ring is supported by the outer ring spacer at three points. Therefore, even if there is an imbalance in the axial load applied from the first outer ring to the outer ring spacer, the contact of each first convex portion with the first outer ring is stable. Similarly, the number of second convex portions on the end face of the outer ring spacer on the side of the second outer ring is three, so the second outer ring is also supported by the outer ring spacer at three points. Therefore, even if there is an imbalance in the axial load applied from the second outer ring to the outer ring spacer, the contact of each second convex portion with the second outer ring is stable.

［構成３］
前記ひずみセンサは、前記複数の第１凸部および前記複数の第２凸部の個数と同じ個数設けられ、
前記各ひずみセンサは、前記各第１凸部および前記各第２凸部の周方向位置と同じ周方向位置に配置されている、構成１または２に記載のひずみセンサ付き軸受装置。 [Configuration 3]
the strain sensors are provided in the same number as the number of the first convex portions and the number of the second convex portions;
3. The bearing device with strain sensor according to claim 1, wherein each of the strain sensors is disposed at the same circumferential position as each of the first convex portions and each of the second convex portions.

この構成を採用すると、複数のひずみセンサのそれぞれの出力に基づいて、モーメント荷重を検知することが可能となる。また、各ひずみセンサが、各第１凸部および各第２凸部の周方向位置と同じ周方向位置に配置されているので、第１外輪および第２外輪から外輪間座に加わる軸方向荷重が、各ひずみセンサの位置に安定して伝わる。そのため、複数のひずみセンサの出力がいずれも安定し、高い精度で軸受予圧を検出することが可能となる。 By adopting this configuration, it becomes possible to detect moment loads based on the output of each of the multiple strain sensors. In addition, since each strain sensor is positioned at the same circumferential position as each of the first convex portions and each of the second convex portions, the axial load applied to the outer ring spacer from the first outer ring and the second outer ring is stably transmitted to the position of each strain sensor. As a result, the output of each of the multiple strain sensors is stable, making it possible to detect bearing preload with high accuracy.

［構成４］
前記各第１凸部は、前記第１外輪の軸方向端面と周方向に長さをもって接触するように一定の軸方向高さで周方向に延びる形状を有し、
前記ひずみセンサは、前記第１凸部の周方向中心に対応する周方向位置に配置され、
前記第１凸部の先端から前記ひずみセンサまでの軸方向距離をｂ１とし、前記第１凸部の周方向長さをｃ１としたときに、ｃ１≦２×ｂ１を満たすように前記第１凸部の周方向長さｃ１が設定されている、構成１から３にいずれかに記載のひずみセンサ付き軸受装置。 [Configuration 4]
each of the first convex portions has a shape extending in a circumferential direction at a constant axial height so as to be in contact with an axial end face of the first outer ring over a certain length in the circumferential direction;
the strain sensor is disposed at a circumferential position corresponding to a circumferential center of the first protrusion,
A bearing device with a strain sensor as described in any one of configurations 1 to 3, wherein when the axial distance from the tip of the first convex portion to the strain sensor is b1 and the circumferential length of the first convex portion is c1, the circumferential length c1 of the first convex portion is set so as to satisfy c1≦2×b1.

この構成を採用すると、第１外輪から第１凸部に加わる軸方向荷重が、軸方向に対して４５°の角度をなす範囲で外輪間座の内部に広がりながら伝わるとしたときに、第１凸部の周方向一端から周方向他端までのいずれの位置に加わった軸方向荷重も、ひずみセンサの位置に伝わることとなる。そのため、第１外輪から外輪間座に加わる軸方向荷重を、ひずみセンサの位置に効果的に集約させ、ひずみセンサの分解能を高めることが可能となる。 When this configuration is adopted, if the axial load applied from the first outer ring to the first convex portion is transmitted while spreading inside the outer ring spacer within a range forming an angle of 45° with respect to the axial direction, the axial load applied anywhere from one circumferential end to the other circumferential end of the first convex portion will be transmitted to the position of the strain sensor. Therefore, the axial load applied from the first outer ring to the outer ring spacer can be effectively concentrated at the position of the strain sensor, making it possible to increase the resolution of the strain sensor.

［構成５］
前記各第２凸部は、前記第２外輪の軸方向端面と周方向に長さをもって接触するように一定の軸方向高さで周方向に延びる形状を有し、
前記ひずみセンサは、前記第２凸部の周方向中心に対応する周方向位置に配置され、
前記第２凸部の先端から前記ひずみセンサまでの軸方向距離をｂ２とし、前記第２凸部の周方向長さをｃ２としたときに、ｃ２≦２×ｂ２を満たすように前記第２凸部の周方向長さｃ２が設定されている、構成１から４のいずれかに記載のひずみセンサ付き軸受装置。 [Configuration 5]
each second protrusion has a shape extending in the circumferential direction at a constant axial height so as to be in contact with an axial end face of the second outer ring over a certain length in the circumferential direction,
the strain sensor is disposed at a circumferential position corresponding to a circumferential center of the second protrusion,
A bearing device with a strain sensor as described in any one of configurations 1 to 4, wherein the axial distance from the tip of the second convex portion to the strain sensor is b2, and the circumferential length of the second convex portion is c2, and the circumferential length c2 of the second convex portion is set so as to satisfy c2≦2×b2.

この構成を採用すると、第２外輪から第２凸部に加わる軸方向荷重が、軸方向に対して４５°の角度をなす範囲で外輪間座の内部に広がりながら伝わるとしたときに、第２凸部の周方向一端から周方向他端までのいずれの位置に加わった軸方向荷重も、ひずみセンサの位置に伝わることとなる。そのため、第２外輪から外輪間座に加わる軸方向荷重を、ひずみセンサの位置に効果的に集約させ、ひずみセンサの分解能を高めることが可能となる。 When this configuration is adopted, if the axial load applied from the second outer ring to the second convex portion is transmitted while spreading inside the outer ring spacer within a range forming an angle of 45° with respect to the axial direction, the axial load applied anywhere from one circumferential end to the other circumferential end of the second convex portion will be transmitted to the position of the strain sensor. Therefore, the axial load applied from the second outer ring to the outer ring spacer can be effectively concentrated at the position of the strain sensor, making it possible to increase the resolution of the strain sensor.

［構成６］
前記外輪間座の軸方向両側の端面のうち、前記第１外輪の側の端面には、前記各第１凸部の周方向両側から軸方向に切り込む第１スリットが形成され、前記第２外輪の側の端面にも、前記各第２凸部の周方向両側から軸方向に切り込む第２スリットが形成されている構成１から５のいずれかに記載のひずみセンサ付き軸受装置。 [Configuration 6]
A bearing device with a strain sensor as described in any one of configurations 1 to 5, wherein, of the end faces on both axial sides of the outer ring spacer, the end face on the side of the first outer ring has a first slit cutting in the axial direction from both circumferential sides of each of the first convex portions, and the end face on the side of the second outer ring has a second slit cutting in the axial direction from both circumferential sides of each of the second convex portions.

この構成を採用すると、第１外輪から外輪間座に加わる軸方向荷重と、第２外輪から外輪間座に加わる軸方向荷重とを、特に効果的にひずみセンサの位置に集約させることが可能となる。 By adopting this configuration, it becomes possible to concentrate the axial load applied from the first outer ring to the outer ring spacer and the axial load applied from the second outer ring to the outer ring spacer particularly effectively at the position of the strain sensor.

［構成７］
前記ひずみセンサは、前記外輪間座の内周に配置されている、構成１から６のいずれかに記載のひずみセンサ付き軸受装置。 [Configuration 7]
7. The bearing device with a strain sensor according to any one of configurations 1 to 6, wherein the strain sensor is disposed on an inner circumference of the outer ring spacer.

［構成８］
前記ひずみセンサは、前記外輪間座の外周に配置されている、構成１から６のいずれかに記載のひずみセンサ付き軸受装置。 [Configuration 8]
7. The bearing device with a strain sensor according to any one of configurations 1 to 6, wherein the strain sensor is disposed on an outer periphery of the outer ring spacer.

また、この発明では、上記のひずみセンサ付き軸受装置を使用した工作機械用スピンドル装置として、以下の構成のものを併せて提供する。
［構成９］
構成１から８のいずれかに記載のひずみセンサ付き軸受装置と、
前記ひずみセンサ付き軸受装置で回転可能に支持される工作機械の主軸と、
前記主軸を回転駆動するモータと、を有する工作機械用スピンドル装置。 The present invention also provides a machine tool spindle device using the above-mentioned strain sensor-equipped bearing device, the spindle device having the following configuration.
[Configuration 9]
A bearing device with a strain sensor according to any one of configurations 1 to 8,
a main spindle of a machine tool rotatably supported by the bearing device with a strain sensor;
a motor that drives and rotates the main shaft.

この構成を採用すると、工作機械の省人化や無人化のための状態監視を安定して行なうことが可能となる。また、切削加工中の工作機械の主軸に作用する加工荷重を検出することも可能となる。 By adopting this configuration, it becomes possible to stably monitor the status of machine tools to reduce the number of workers required or to operate them unmanned. It also becomes possible to detect the processing load acting on the spindle of the machine tool during cutting.

この発明のひずみセンサ付き軸受装置は、第１外輪から外輪間座に加わる軸方向荷重が、周方向に間隔をおいて配置された各第１凸部の位置に集約され、同様に、第２外輪から外輪間座に加わる軸方向荷重も、周方向に間隔をおいて配置された各第２凸部の位置に集約される。そして、第１凸部および第２凸部の周方向位置と同じ周方向位置にひずみセンサが配置されているので、第１外輪および第２外輪から外輪間座に加わる軸方向荷重が、ひずみセンサの位置に安定して伝わる。そのため、ひずみセンサの出力が、外輪間座やその周辺の各部品の微小な加工誤差等の影響を受けにくく、高い精度で軸受予圧を検出することが可能である。 In the bearing device with strain sensor of this invention, the axial load applied from the first outer ring to the outer ring spacer is concentrated at the position of each of the first convex parts arranged at intervals in the circumferential direction, and similarly, the axial load applied from the second outer ring to the outer ring spacer is concentrated at the position of each of the second convex parts arranged at intervals in the circumferential direction. And since the strain sensor is arranged at the same circumferential position as the first convex part and the second convex part, the axial load applied from the first outer ring and the second outer ring to the outer ring spacer is stably transmitted to the position of the strain sensor. Therefore, the output of the strain sensor is not easily affected by minute processing errors of the outer ring spacer and its surrounding parts, and it is possible to detect the bearing preload with high accuracy.

この発明の実施形態にかかるひずみセンサ付き軸受装置を使用した工作機械用スピンドル装置を示す断面図FIG. 1 is a cross-sectional view showing a spindle device for a machine tool that uses a bearing device with a strain sensor according to an embodiment of the present invention. 図１のひずみセンサ付き軸受装置の近傍の拡大図An enlarged view of the vicinity of the strain sensor-equipped bearing device of FIG. 図２のIII－III線に沿った断面図3 is a cross-sectional view taken along line III-III in FIG. 2 . 図３のIV－IV線に沿った断面図4 is a cross-sectional view taken along line IV-IV of FIG. 図３に示す外輪間座の斜視図FIG. 4 is a perspective view of the outer ring spacer shown in FIG. 図５に示すひずみセンサの配置を外輪間座の内周から外周に変更した変形例を示す斜視図FIG. 6 is a perspective view showing a modified example in which the arrangement of the strain sensor shown in FIG. 5 is changed from the inner periphery to the outer periphery of the outer ring spacer. 図５に示す外輪間座に、第１凸部の周方向両側から軸方向に切り込む第１スリットと、第２凸部の周方向両側から軸方向に切り込む第２スリットとを設けた変形例を示す斜視図FIG. 7 is a perspective view showing a modified example in which the outer ring spacer shown in FIG. 5 is provided with first slits cut in the axial direction from both circumferential sides of the first convex portion and second slits cut in the axial direction from both circumferential sides of the second convex portion; 図７に示す外輪間座を内径側から見た図FIG. 8 is a view of the outer ring spacer shown in FIG. 7 from the inner diameter side. 図５に示す第１凸部および第２凸部の周方向長さの説明図FIG. 6 is an explanatory diagram of the circumferential lengths of the first convex portion and the second convex portion shown in FIG. 5 .

図１に、この発明の実施形態にかかるひずみセンサ付き軸受装置１（以下、単に「軸受装置１」という）を使用した工作機械用スピンドル装置を示す。このスピンドル装置は、工作機械の主軸２と、主軸２を収容する主軸ハウジング３と、主軸２を回転駆動するモータ４と、モータ４よりも軸方向前側で主軸２を回転可能に支持する実施形態の軸受装置１と、モータ４よりも軸方向後側で主軸２を回転可能に支持する後側軸受装置５とを有する。 Figure 1 shows a spindle device for a machine tool that uses a bearing device with a strain sensor 1 (hereinafter simply referred to as "bearing device 1") according to an embodiment of the present invention. This spindle device has a main spindle 2 of the machine tool, a main spindle housing 3 that accommodates the main spindle 2, a motor 4 that drives and rotates the main spindle 2, the bearing device 1 of the embodiment that rotatably supports the main spindle 2 axially forward of the motor 4, and a rear bearing device 5 that rotatably supports the main spindle 2 axially rearward of the motor 4.

主軸ハウジング３は、両端が開放した中空筒状に形成されている。主軸ハウジング３は、軸方向の前側から後側に向かって順に軸受装置１とモータ４とを収容している。図では、主軸ハウジング３の軸受装置１を収容する部分と、主軸ハウジング３のモータ４を収容する部分とを継ぎ目の無い一体に形成しているが、主軸ハウジング３の軸受装置１を収容する部分と、主軸ハウジング３のモータ４を収容する部分とを別体に形成し、その両部分を連結して一体化してもよい。 The spindle housing 3 is formed in a hollow cylinder with both ends open. The spindle housing 3 accommodates the bearing device 1 and the motor 4 in that order from the front to the rear in the axial direction. In the figure, the part of the spindle housing 3 that accommodates the bearing device 1 and the part of the spindle housing 3 that accommodates the motor 4 are formed seamlessly as one piece, but the part of the spindle housing 3 that accommodates the bearing device 1 and the part of the spindle housing 3 that accommodates the motor 4 may be formed separately and then connected to form an integrated unit.

主軸２は、主軸２の前端が主軸ハウジング３の前端開口から突出した状態で主軸ハウジング３に挿入されている。主軸２の前端には、工具または加工物を把持するチャック（図示せず）が着脱可能に取り付けられるようになっている。主軸２には、工作機械のドローバー（図示せず）を軸方向に摺動可能に収容する貫通孔６が軸方向に貫通して形成されている。 The spindle 2 is inserted into the spindle housing 3 with the front end of the spindle 2 protruding from the front end opening of the spindle housing 3. A chuck (not shown) for gripping a tool or workpiece is removably attached to the front end of the spindle 2. A through hole 6 is formed axially through the spindle 2 to accommodate a drawbar (not shown) of the machine tool so that it can slide axially.

モータ４は、主軸２の外周に取り付けられたロータ７と、ロータ７に回転力を付与する環状のステータ８とを有する。ロータ７は、主軸２の外周に嵌合するロータスリーブ９と、ロータスリーブ９の外周に固定されたロータコア１０とを有する。ロータコア１０は、例えば、電磁鋼板の積層体である。ロータスリーブ９は、主軸２と一体回転するように主軸２に回り止めされている。ロータスリーブ９の軸方向前端は、主軸２の外周に形成された段差部１１に接触し、その段差部１１との接触によって軸方向に位置決めされている。 The motor 4 has a rotor 7 attached to the outer periphery of the main shaft 2 and an annular stator 8 that applies a rotational force to the rotor 7. The rotor 7 has a rotor sleeve 9 that fits onto the outer periphery of the main shaft 2 and a rotor core 10 fixed to the outer periphery of the rotor sleeve 9. The rotor core 10 is, for example, a laminate of electromagnetic steel sheets. The rotor sleeve 9 is prevented from rotating on the main shaft 2 so as to rotate integrally with the main shaft 2. The axial front end of the rotor sleeve 9 contacts a step 11 formed on the outer periphery of the main shaft 2, and is positioned in the axial direction by the contact with the step 11.

ステータ８は、主軸ハウジング３の内周に固定されたステータコア１２と、ステータコア１２に周方向に間隔をおいて形成された複数のティース部分にそれぞれ巻回された電磁コイル１３とを有する。電磁コイル１３に通電すると、ステータコア１２とロータコア１０の間に働く電磁力によってロータコア１０に回転力が発生し、ロータ７と主軸２が一体に回転する。ここでは、モータ４として、電力で回転力を発生する電動モータを採用したが、電動モータに代えて、圧縮空気など他の動力源で回転力を発生する方式のモータを採用することも可能である。 The stator 8 has a stator core 12 fixed to the inner circumference of the spindle housing 3, and an electromagnetic coil 13 wound around each of a number of teeth formed at intervals in the circumferential direction on the stator core 12. When electricity is applied to the electromagnetic coil 13, a rotational force is generated in the rotor core 10 by the electromagnetic force acting between the stator core 12 and the rotor core 10, and the rotor 7 and the spindle 2 rotate together. Here, an electric motor that generates rotational force using electricity is used as the motor 4, but instead of an electric motor, it is also possible to use a motor that generates rotational force using another power source such as compressed air.

後側軸受装置５は、主軸ハウジング３の後端に同軸に固定された環状の軸受支持部材１４と、軸受支持部材１４に組み込まれた転がり軸受１５とを有する。転がり軸受１５は、軸受支持部材１４の内周に嵌合する外輪１６と、主軸２の外周に嵌合する内輪１７と、外輪１６と内輪１７の間に組み込まれた複数の円筒ころ１８とを有する円筒ころ軸受である。 The rear bearing device 5 has an annular bearing support member 14 that is coaxially fixed to the rear end of the spindle housing 3, and a rolling bearing 15 that is assembled into the bearing support member 14. The rolling bearing 15 is a cylindrical roller bearing that has an outer ring 16 that fits into the inner periphery of the bearing support member 14, an inner ring 17 that fits into the outer periphery of the spindle 2, and a number of cylindrical rollers 18 that are assembled between the outer ring 16 and the inner ring 17.

軸受支持部材１４には、外輪押さえ部材１９が取り付けられている。外輪押さえ部材１９は、外輪１６の軸方向後端面に接触することで外輪１６の軸方向位置を固定している。主軸２の外周には、内輪１７を軸方向前方に押圧するナット部材２０と、内輪１７とナット部材２０の間に組み込まれた環状のスペーサ２１とが装着されている。ナット部材２０は、主軸２の後端部外周に形成された雄ねじ２２にねじ係合している。スペーサ２１の軸方向前端面は、内輪１７の軸方向後端面に接触し、スペーサ２１の軸方向後端面は、ナット部材２０の軸方向前端面に接触している。内輪１７の軸方向前端面は、ロータスリーブ９の軸方向後端に接触している。 An outer ring pressing member 19 is attached to the bearing support member 14. The outer ring pressing member 19 fixes the axial position of the outer ring 16 by contacting the axial rear end face of the outer ring 16. A nut member 20 that presses the inner ring 17 axially forward and an annular spacer 21 assembled between the inner ring 17 and the nut member 20 are attached to the outer periphery of the main shaft 2. The nut member 20 is threadedly engaged with a male thread 22 formed on the outer periphery of the rear end of the main shaft 2. The axial front end face of the spacer 21 contacts the axial rear end face of the inner ring 17, and the axial rear end face of the spacer 21 contacts the axial front end face of the nut member 20. The axial front end face of the inner ring 17 contacts the axial rear end of the rotor sleeve 9.

軸受装置１は、主軸ハウジング３に固定された軸受支持筒２３と、軸受支持筒２３に軸方向に間隔をおいて組み込まれた第１軸受２４および第２軸受２５と、第１軸受２４と第２軸受２５の間に設けられた外輪間座２６および内輪間座２７と、外輪間座２６に取り付けられたひずみセンサ２８とを有する。 The bearing device 1 has a bearing support tube 23 fixed to the spindle housing 3, a first bearing 24 and a second bearing 25 assembled in the bearing support tube 23 at an axial distance from each other, an outer ring spacer 26 and an inner ring spacer 27 provided between the first bearing 24 and the second bearing 25, and a strain sensor 28 attached to the outer ring spacer 26.

図２に示すように、第１軸受２４は、軸受支持筒２３の内周に嵌合する第１外輪３０と、第１外輪３０の径方向内側に回転可能に設けられた第１内輪３１と、第１外輪３０と第１内輪３１の間に組み込まれた複数の第１転動体３２とを有する。第１転動体３２は、ここでは玉である。第１外輪３０の内周には、第１転動体３２が転がり接触する断面円弧状の第１外輪軌道面３３が設けられている。第１外輪３０は、第１外輪軌道面３３に対して軸方向前側の外輪肩部と軸方向後側の外輪肩部のうち、軸方向前側の外輪肩部を除去した形状の肩落とし外輪である。第１内輪３１の外周には、第１転動体３２が転がり接触する断面円弧状の第１内輪軌道面３４が設けられている。第１内輪３１は、第１転動体３２が転がり接触する第１内輪軌道面３４に対して軸方向前側の内輪肩部と軸方向後側の内輪肩部のうち、軸方向後側の内輪肩部を除去した形状の肩落とし内輪である。第１内輪３１は、主軸２の外周に締め代をもって嵌合している。 As shown in FIG. 2, the first bearing 24 has a first outer ring 30 that fits into the inner circumference of the bearing support tube 23, a first inner ring 31 that is rotatably provided on the radially inner side of the first outer ring 30, and a plurality of first rolling elements 32 that are assembled between the first outer ring 30 and the first inner ring 31. The first rolling elements 32 are balls here. The inner circumference of the first outer ring 30 is provided with a first outer ring raceway surface 33 that has an arc-shaped cross section with which the first rolling elements 32 roll and contact. The first outer ring 30 is a shoulder-drop outer ring that has a shape in which the axially front outer ring shoulder is removed from the outer ring shoulder on the axially front side and the outer ring shoulder on the axially rear side with respect to the first outer ring raceway surface 33. The outer circumference of the first inner ring 31 is provided with a first inner ring raceway surface 34 that has an arc-shaped cross section with which the first rolling elements 32 roll and contact. The first inner ring 31 is a shoulder-reduced inner ring with a shape in which the axially rear inner ring shoulder is removed from the axially front inner ring shoulder and the axially rear inner ring shoulder with respect to the first inner ring raceway surface 34 with which the first rolling element 32 rolls. The first inner ring 31 is fitted to the outer periphery of the main shaft 2 with a tightening margin.

第２軸受２５は、軸受支持筒２３の内周に嵌合する第２外輪３５と、第２外輪３５の径方向内側に回転可能に設けられた第２内輪３６と、第２外輪３５と第２内輪３６の間に組み込まれた複数の第２転動体３７とを有する。第２転動体３７は、ここでは玉である。第２外輪３５の内周には、第２転動体３７が転がり接触する断面円弧状の第２外輪軌道面３８が設けられている。第２外輪３５は、第１外輪３０から軸方向後方に間隔をおいて配置され、第２内輪３６も、第１内輪３１から軸方向後方に間隔をおいて配置されている。第２外輪３５は、第２外輪軌道面３８に対して軸方向前側の外輪肩部と軸方向後側の外輪肩部のうち、軸方向後側の外輪肩部を除去した形状の肩落とし外輪である。第２内輪３６の外周には、第２転動体３７が転がり接触する断面円弧状の第２内輪軌道面３９が設けられている。第２内輪３６は、第２転動体３７が転がり接触する第２内輪軌道面３９に対して軸方向前側の内輪肩部と軸方向後側の内輪肩部のうち、軸方向前側の内輪肩部を除去した形状の肩落とし内輪である。第２内輪３６は、主軸２の外周に締め代をもって嵌合している。 The second bearing 25 has a second outer ring 35 that fits into the inner circumference of the bearing support tube 23, a second inner ring 36 that is rotatably provided radially inside the second outer ring 35, and a plurality of second rolling elements 37 that are incorporated between the second outer ring 35 and the second inner ring 36. The second rolling elements 37 are balls here. The inner circumference of the second outer ring 35 is provided with a second outer ring raceway surface 38 that has an arc-shaped cross section with which the second rolling elements 37 roll and contact. The second outer ring 35 is spaced axially rearward from the first outer ring 30, and the second inner ring 36 is also spaced axially rearward from the first inner ring 31. The second outer ring 35 is a shoulder-drop outer ring that has a shape in which the axially rear outer ring shoulder is removed from the axially front outer ring shoulder and the axially rear outer ring shoulder relative to the second outer ring raceway surface 38. The outer periphery of the second inner ring 36 is provided with a second inner ring raceway 39 with an arc-shaped cross section with which the second rolling element 37 rolls. The second inner ring 36 is a shoulder-reduced inner ring with an axially front inner ring shoulder removed from the axially rear inner ring shoulder with respect to the second inner ring raceway 39 with which the second rolling element 37 rolls. The second inner ring 36 is fitted to the outer periphery of the main shaft 2 with a tightening margin.

ここで、第１軸受２４は、軸方向の予圧で、第１転動体３２が第１外輪３０を押圧する径方向分力を生じるように構成され、同様に、第２軸受２５も、軸方向の予圧で、第２転動体３７が第２外輪３５を押圧する径方向分力を生じるように構成されている。この実施形態では、第１軸受２４は、第１内輪３１と第１転動体３２の接触点と、第１外輪３０と第１転動体３２の接触点とを結ぶ直線が、半径方向内側から半径方向外側に向かって軸方向後方に傾斜するアンギュラ玉軸受である。また、第２軸受２５は、第２内輪３６と第２転動体３７の接触点と、第２外輪３５と第２転動体３７の接触点とを結ぶ直線が、半径方向内側から半径方向外側に向かって軸方向前方に傾斜するアンギュラ玉軸受である。つまり、第１軸受２４と第２軸受２５は、背面合わせの関係で軸方向に間隔をおいて配置された一対のアンギュラ玉軸受である。 Here, the first bearing 24 is configured so that the first rolling body 32 generates a radial component force pressing the first outer ring 30 under axial preload, and similarly, the second bearing 25 is configured so that the second rolling body 37 generates a radial component force pressing the second outer ring 35 under axial preload. In this embodiment, the first bearing 24 is an angular ball bearing in which the straight line connecting the contact point of the first inner ring 31 and the first rolling body 32 and the contact point of the first outer ring 30 and the first rolling body 32 is inclined axially backward from the radial inner side toward the radial outer side. Also, the second bearing 25 is an angular ball bearing in which the straight line connecting the contact point of the second inner ring 36 and the second rolling body 37 and the contact point of the second outer ring 35 and the second rolling body 37 is inclined axially forward from the radial inner side toward the radial outer side. In other words, the first bearing 24 and the second bearing 25 are a pair of angular contact ball bearings arranged back-to-back with a gap in the axial direction.

外輪間座２６は、両端が開放した中空の筒状部材である。外輪間座２６は、軸受支持筒２３の内周に隙間をもって嵌合している。外輪間座２６は、第１外輪３０の軸方向後端面と第２外輪３５の軸方向前端面との間で軸方向に挟み込まれている。 The outer ring spacer 26 is a hollow cylindrical member with both ends open. The outer ring spacer 26 fits into the inner circumference of the bearing support tube 23 with a gap. The outer ring spacer 26 is sandwiched in the axial direction between the axial rear end face of the first outer ring 30 and the axial front end face of the second outer ring 35.

内輪間座２７も、外輪間座２６と同様、両端が開放した中空の筒状部材である。内輪間座２７は、主軸２の外周に隙間をもって嵌合している。内輪間座２７は、第１内輪３１と第２内輪３６の間で軸方向に挟み込まれている。 Like the outer ring spacer 26, the inner ring spacer 27 is a hollow cylindrical member with both ends open. The inner ring spacer 27 fits onto the outer periphery of the main shaft 2 with a gap. The inner ring spacer 27 is sandwiched axially between the first inner ring 31 and the second inner ring 36.

主軸ハウジング３の軸方向前端には、外輪押さえ部材４０が固定されている。外輪押さえ部材４０は、第１外輪３０の軸方向前端面に接触することで第１外輪３０の軸方向位置を固定している。外輪押さえ部材４０は、軸受支持筒２３の内周に嵌合する筒部４１と、筒部４１の軸方向前端から径方向外方に延びるフランジ部４２とを有する。フランジ部４２は、軸受支持筒２３の軸方向前端面に固定されている。主軸２の軸方向前端部の外周には、第１内輪３１の軸方向前方への移動を規制する段差部４３が設けられている。段差部４３は、第１内輪３１の軸方向前端面に接触し、第１内輪３１を軸方向に位置決めしている。 An outer ring pressing member 40 is fixed to the axial front end of the spindle housing 3. The outer ring pressing member 40 fixes the axial position of the first outer ring 30 by contacting the axial front end face of the first outer ring 30. The outer ring pressing member 40 has a cylindrical portion 41 that fits into the inner circumference of the bearing support tube 23 and a flange portion 42 that extends radially outward from the axial front end of the cylindrical portion 41. The flange portion 42 is fixed to the axial front end face of the bearing support tube 23. A step portion 43 that restricts the axial forward movement of the first inner ring 31 is provided on the outer circumference of the axial front end of the spindle 2. The step portion 43 contacts the axial front end face of the first inner ring 31 to position the first inner ring 31 in the axial direction.

主軸２の外周には、第２内輪３６を軸方向前方に押圧する予圧ナット４４と、第２内輪３６と予圧ナット４４の間に組み込まれた環状のスペーサ４５とが装着されている。予圧ナット４４は、主軸２の外周の段差部１１（図１参照）から軸方向前側に延びる部分に形成された雄ねじ４６にねじ係合している。スペーサ４５の軸方向前端面は、第２内輪３６の軸方向後端面に接触し、スペーサ４５の軸方向後端面は、予圧ナット４４の軸方向前端面に接触している。軸受支持筒２３の内周には、第２外輪３５の軸方向後方への移動を規制する段差部４７が設けられている。段差部４７は、第２外輪３５の軸方向後端面に接触し、第２外輪３５を軸方向に位置決めしている。 A preload nut 44 that presses the second inner ring 36 axially forward and an annular spacer 45 that is assembled between the second inner ring 36 and the preload nut 44 are attached to the outer periphery of the main shaft 2. The preload nut 44 is threadedly engaged with a male thread 46 formed on a portion extending axially forward from a stepped portion 11 (see FIG. 1) on the outer periphery of the main shaft 2. The axial front end face of the spacer 45 contacts the axial rear end face of the second inner ring 36, and the axial rear end face of the spacer 45 contacts the axial front end face of the preload nut 44. A stepped portion 47 that restricts the axial rearward movement of the second outer ring 35 is provided on the inner periphery of the bearing support tube 23. The stepped portion 47 contacts the axial rear end face of the second outer ring 35 to position the second outer ring 35 in the axial direction.

図１に示すように、軸受支持筒２３は、主軸ハウジング３の内周に嵌合している。軸受支持筒２３の外周には、軸受装置１の冷却用の冷媒が流れる冷却溝４８が形成されている。冷却溝４８は、軸受支持筒２３の外周に軸方向に間隔をおいて形成された複数の環状溝または軸受支持筒２３の外周を螺旋状に延びる螺旋溝である。 As shown in FIG. 1, the bearing support cylinder 23 is fitted to the inner circumference of the spindle housing 3. A cooling groove 48 is formed on the outer circumference of the bearing support cylinder 23, through which a refrigerant for cooling the bearing device 1 flows. The cooling groove 48 is a plurality of annular grooves formed at intervals in the axial direction on the outer circumference of the bearing support cylinder 23, or a spiral groove extending in a spiral shape around the outer circumference of the bearing support cylinder 23.

図２に示すように、予圧ナット４４は所定の力で締め付けられ、その予圧ナット４４の軸力が、スペーサ４５、第２内輪３６、第２転動体３７、第２外輪３５、外輪間座２６、第１外輪３０、第１転動体３２、第１内輪３１を伝達し、段差部４３で受け止められた状態となっている。すなわち、予圧ナット４４の軸力により、第１軸受２４と第２軸受２５の間には、第１内輪３１、第１転動体３２、第１外輪３０、外輪間座２６、第２外輪３５、第２転動体３７、第２内輪３６を順に通って予圧が伝達するように軸方向の予圧が付与された状態となっている。 2, the preload nut 44 is tightened with a predetermined force, and the axial force of the preload nut 44 is transmitted through the spacer 45, the second inner ring 36, the second rolling element 37, the second outer ring 35, the outer ring spacer 26, the first outer ring 30, the first rolling element 32, and the first inner ring 31, and is received by the step portion 43. In other words, the axial force of the preload nut 44 applies an axial preload between the first bearing 24 and the second bearing 25 so that the preload is transmitted through the first inner ring 31, the first rolling element 32, the first outer ring 30, the outer ring spacer 26, the second outer ring 35, the second rolling element 37, and the second inner ring 36 in this order.

ひずみセンサ２８は、外輪間座２６の軸方向中央部に取り付けられている。具体的には、ひずみセンサ２８は、外輪間座２６の軸方向の中心位置から、外輪間座２６の軸方向全長の１／４の軸方向距離の範囲内の領域にひずみセンサ２８が収まるように外輪間座２６に取り付けられている。 The strain sensor 28 is attached to the axial center of the outer ring spacer 26. Specifically, the strain sensor 28 is attached to the outer ring spacer 26 so that the strain sensor 28 fits within an axial distance range of 1/4 of the total axial length of the outer ring spacer 26 from the axial center position of the outer ring spacer 26.

外輪間座２６の軸方向両側の端面のうち、軸方向前端面（第１外輪３０の側の端面）には、軸方向の予圧で第１外輪３０の軸方向後端面に押し付けられる複数の第１凸部５０が周方向に間隔をおいて設けられている。同様に、外輪間座２６の軸方向後端面（第２外輪３５の側の端面）にも、軸方向の予圧で第２外輪３５の軸方向端面に押し付けられる複数の第２凸部５１が、周方向に間隔をおいて設けられている。 Of the end faces on both axial sides of the outer ring spacer 26, the axial front end face (the end face on the side of the first outer ring 30) has a plurality of first protrusions 50 spaced apart in the circumferential direction, which are pressed against the axial rear end face of the first outer ring 30 by axial preload. Similarly, the axial rear end face (the end face on the side of the second outer ring 35) of the outer ring spacer 26 has a plurality of second protrusions 51 spaced apart in the circumferential direction, which are pressed against the axial end face of the second outer ring 35 by axial preload.

図３に示すように、第１凸部５０の個数は、３つである。各第１凸部５０は、周方向に等間隔の位置（図では、各第１凸部５０の周方向中心が、外輪間座２６の上端から時計回りに０°、１２０°、２４０°の方向にくる位置）に配置されている。各第１凸部５０は、第１外輪３０（図２参照）の軸方向端面と周方向に長さをもって接触するように一定の軸方向高さで周方向に延びる形状を有する。各第１凸部５０の先端は、周方向に延びる軸直角平面である。第１凸部５０の軸方向の高さは、０．１ｍｍ以上に設定されている。 As shown in FIG. 3, there are three first protrusions 50. The first protrusions 50 are arranged at equal intervals in the circumferential direction (in the figure, the circumferential center of each first protrusion 50 is at a position at 0°, 120°, or 240° clockwise from the upper end of the outer ring spacer 26). Each first protrusion 50 has a shape that extends in the circumferential direction at a constant axial height so as to contact the axial end face of the first outer ring 30 (see FIG. 2) with a certain length in the circumferential direction. The tip of each first protrusion 50 is a plane perpendicular to the axis that extends in the circumferential direction. The axial height of the first protrusions 50 is set to 0.1 mm or more.

また、図５に示すように、第２凸部５１は、第１凸部５０の個数と同数（３つ）設けられている。各第２凸部５１は、各第１凸部５０の周方向位置と同じ周方向位置（各第２凸部５１の周方向中心が、図３の０°、１２０°、２４０°の方向にくる位置）に配置されている。第２凸部５１も、第１凸部５０と同様に、第２外輪３５（図２参照）の軸方向端面と周方向に長さをもって接触するように一定の軸方向高さで周方向に延びる形状を有する。各第２凸部５１の先端は、周方向に延びる軸直角平面である。第２凸部５１の軸方向の高さは、０．１ｍｍ以上に設定されている。外輪間座２６の形状は、軸方向の前後に対称である。 As shown in FIG. 5, the second convex portions 51 are provided in the same number (three) as the number of the first convex portions 50. Each second convex portion 51 is arranged at the same circumferential position as each first convex portion 50 (the circumferential center of each second convex portion 51 is in the 0°, 120°, or 240° direction in FIG. 3). Like the first convex portions 50, the second convex portions 51 also have a shape that extends in the circumferential direction at a certain axial height so as to contact the axial end face of the second outer ring 35 (see FIG. 2) with a circumferential length. The tip of each second convex portion 51 is a plane perpendicular to the axis that extends in the circumferential direction. The axial height of the second convex portions 51 is set to 0.1 mm or more. The shape of the outer ring spacer 26 is symmetrical in the axial direction.

図３に示すように、ひずみセンサ２８は、外輪間座２６の内周に周方向に間隔をおいて複数設けられている。ひずみセンサ２８の個数は、第１凸部５０および第２凸部５１の個数と同じ個数（３つ）である。各ひずみセンサ２８は、各第１凸部５０と同じ周方向位置（各第１凸部５０の周方向中心に対応する周方向位置）に配置されている。外輪間座２６の内周には、ひずみセンサ２８の個数と同数の軸方向溝５２が周方向に等間隔に形成されている。軸方向溝５２は、それぞれ軸線に平行な平面状の溝底面を有し、その各溝底面にひずみセンサ２８が取り付けられている。 As shown in FIG. 3, a plurality of strain sensors 28 are provided at intervals in the circumferential direction on the inner circumference of the outer ring spacer 26. The number of strain sensors 28 is the same as the number of first convex portions 50 and second convex portions 51 (three). Each strain sensor 28 is disposed at the same circumferential position as each first convex portion 50 (the circumferential position corresponding to the circumferential center of each first convex portion 50). Axial grooves 52, the same number as the number of strain sensors 28, are formed at equal intervals in the circumferential direction on the inner circumference of the outer ring spacer 26. Each axial groove 52 has a planar groove bottom surface parallel to the axis, and a strain sensor 28 is attached to each groove bottom surface.

図４に示すように、各ひずみセンサ２８は、ひずみ検出部５３と、ひずみ検出部５３に接続された処理部５４とを有する。ひずみ検出部５３は、ひずみに応じて電気抵抗が変化するひずみゲージである。処理部５４は、ひずみゲージの電気抵抗の変化に基づいてひずみを検出するひずみ検出回路と、その検出回路で検出されたひずみをアナログ信号からデジタル信号に変換して出力するＡＤ変換回路とを有する。 As shown in FIG. 4, each strain sensor 28 has a strain detection unit 53 and a processing unit 54 connected to the strain detection unit 53. The strain detection unit 53 is a strain gauge whose electrical resistance changes according to strain. The processing unit 54 has a strain detection circuit that detects strain based on the change in the electrical resistance of the strain gauge, and an AD conversion circuit that converts the strain detected by the detection circuit from an analog signal to a digital signal and outputs it.

ここで、ひずみ検出部５３は、ひずみセンサ２８の取り付け位置における外輪間座２６の軸方向ひずみを検出する軸方向ひずみ検出部５３（軸方向をひずみ検出方向として配置したひずみゲージ）と、ひずみセンサ２８の取り付け位置における外輪間座２６の周方向ひずみを検出する周方向ひずみ検出部（周方向をひずみ検出方向として配置したひずみゲージ）とを有するものを採用している。そして、処理部５４は、軸方向ひずみ検出部で検出される軸方向ひずみと、周方向ひずみ検出部で検出される周方向ひずみとの差分（つまり、軸方向ひずみの絶対値と周方向ひずみの絶対値の和）をとり、その差分をひずみセンサ２８の出力とするように構成されている。 The strain detection unit 53 includes an axial strain detection unit 53 (strain gauges arranged with the axial direction as the strain detection direction) that detects the axial strain of the outer ring spacer 26 at the installation position of the strain sensor 28, and a circumferential strain detection unit (strain gauges arranged with the circumferential direction as the strain detection direction) that detects the circumferential strain of the outer ring spacer 26 at the installation position of the strain sensor 28. The processing unit 54 is configured to take the difference between the axial strain detected by the axial strain detection unit and the circumferential strain detected by the circumferential strain detection unit (i.e., the sum of the absolute value of the axial strain and the absolute value of the circumferential strain), and to use this difference as the output of the strain sensor 28.

図９に示すように、第１凸部５０の先端からひずみセンサ２８のひずみ検出位置（図４のひずみ検出部５３の中心に対応する位置）までの軸方向距離をｂ１とし、第１凸部５０の周方向長さをｃ１としたときに、ｃ１≦２×ｂ１を満たすように各第１凸部５０の周方向長さｃ１が設定されている。同様に、第２凸部５１の先端からひずみセンサ２８のひずみ検出位置までの軸方向距離をｂ２とし、第２凸部５１の周方向長さをｃ２としたときに、ｃ２≦２×ｂ２を満たすように各第２凸部５１の周方向長さｃ２が設定されている。図では、第１凸部５０の周方向長さｃ１と第２凸部５１の周方向長さｃ２は同一である。 9, when the axial distance from the tip of the first convex portion 50 to the strain detection position of the strain sensor 28 (the position corresponding to the center of the strain detection portion 53 in FIG. 4) is b1 and the circumferential length of the first convex portion 50 is c1, the circumferential length c1 of each first convex portion 50 is set so as to satisfy c1≦2×b1. Similarly, when the axial distance from the tip of the second convex portion 51 to the strain detection position of the strain sensor 28 is b2 and the circumferential length of the second convex portion 51 is c2, the circumferential length c2 of each second convex portion 51 is set so as to satisfy c2≦2×b2. In the figure, the circumferential length c1 of the first convex portion 50 and the circumferential length c2 of the second convex portion 51 are the same.

図２に示す軸受装置１において、第１軸受２４および第２軸受２５の予圧荷重（以下「軸受予圧」という）は、スピンドル装置の運転時における主軸２の回転速度によって変化する。そして、ひずみセンサ２８で検出される外輪間座２６のひずみに基づいて、その軸受予圧を検出することが可能となっている。 In the bearing device 1 shown in FIG. 2, the preload of the first bearing 24 and the second bearing 25 (hereinafter referred to as "bearing preload") changes depending on the rotational speed of the main shaft 2 when the spindle device is in operation. The bearing preload can be detected based on the strain of the outer ring spacer 26 detected by the strain sensor 28.

すなわち、スピンドル装置の運転時において、主軸２の回転速度が変化すると、第１転動体３２および第２転動体３７の遠心力が変化し、その遠心力の変化に応じて、第１転動体３２が第１外輪軌道面３３を押圧する荷重（第１軸受２４の予圧荷重）および第２転動体３７が第２外輪軌道面３８を押圧する荷重（第２軸受２５の予圧荷重）も変化する。ここで、第１外輪軌道面３３および第２外輪軌道面３８は、軸方向に対して傾斜した角度をもって第１転動体３２および第２転動体３７と接触しているので、第１転動体３２が第１外輪軌道面３３を押圧する荷重および第２転動体３７が第２外輪軌道面３８を押圧する荷重が変化すると、第１外輪３０および第２外輪３５から外輪間座２６に負荷される軸方向の予圧荷重が変化し、外輪間座２６のひずみが変化する。そのため、ひずみセンサ２８で検知される外輪間座２６のひずみに基づいて、第１軸受２４および第２軸受２５の予圧荷重（軸受予圧）を検出することが可能となっている。 In other words, when the rotational speed of the main shaft 2 changes during operation of the spindle device, the centrifugal force of the first rolling body 32 and the second rolling body 37 changes, and in response to the change in centrifugal force, the load with which the first rolling body 32 presses against the first outer ring raceway surface 33 (preload load of the first bearing 24) and the load with which the second rolling body 37 presses against the second outer ring raceway surface 38 (preload load of the second bearing 25) also change. Here, the first outer ring raceway surface 33 and the second outer ring raceway surface 38 are in contact with the first rolling body 32 and the second rolling body 37 at an angle inclined with respect to the axial direction, so when the load with which the first rolling body 32 presses the first outer ring raceway surface 33 and the load with which the second rolling body 37 presses the second outer ring raceway surface 38 change, the axial preload load applied from the first outer ring 30 and the second outer ring 35 to the outer ring spacer 26 changes, and the strain of the outer ring spacer 26 changes. Therefore, it is possible to detect the preload (bearing preload) of the first bearing 24 and the second bearing 25 based on the strain of the outer ring spacer 26 detected by the strain sensor 28.

また、主軸２にモーメント荷重が作用すると、周方向に等間隔に配置された各ひずみセンサ２８の位置には異なる大きさの荷重が加わる。そのため、複数のひずみセンサ２８のそれぞれの出力に基づいて、切削加工中の工作機械の主軸２に作用するモーメント荷重を検知することも可能である。 In addition, when a moment load acts on the spindle 2, loads of different magnitudes are applied to the positions of the strain sensors 28 arranged at equal intervals in the circumferential direction. Therefore, it is possible to detect the moment load acting on the spindle 2 of the machine tool during cutting processing based on the output of each of the multiple strain sensors 28.

ところで、図２に示す軸受装置１において、外輪間座２６の軸方向両側の端面に第１凸部５０および第２凸部５１を設けずに、外輪間座２６の両側の軸方向端面を、全周にわたって連続する軸直角平面とし、その軸直角平面に第１外輪３０および第２外輪３５を接触させた比較例を想定する。この比較例においては、外輪間座２６やその周辺の各部品の微小な加工誤差（例えば、数ミクロンといった僅かな平面度の誤差）等の影響で、外輪間座２６の軸方向端面の接触の強さが、周方向位置によって変化し、外輪間座２６の軸方向端面に、強く接触する箇所と、弱く接触する箇所とが発生する可能性がある。そして、強く接触する箇所がひずみセンサ２８と同じ周方向位置にくる場合と、弱く接触する箇所がひずみセンサ２８と同じ周方向位置にくる場合とで、ひずみセンサ２８の出力に差が生じ、そのことが原因で、ひずみセンサ２８の出力に基づいて検出される軸受予圧に誤差が生じるという問題がある。 2, a comparative example is assumed in which the first and second protrusions 50 and 51 are not provided on both axial end faces of the outer ring spacer 26, and the axial end faces on both sides of the outer ring spacer 26 are made into a continuous axis-perpendicular plane over the entire circumference, and the first outer ring 30 and the second outer ring 35 are in contact with the axis-perpendicular plane. In this comparative example, due to minute machining errors (e.g., slight flatness errors of a few microns) of the outer ring spacer 26 and its surrounding parts, the strength of contact of the axial end face of the outer ring spacer 26 varies depending on the circumferential position, and there is a possibility that some parts of the axial end face of the outer ring spacer 26 make strong contact and other parts make weak contact. Furthermore, there is a problem in that a difference occurs in the output of the strain sensor 28 between when the point of strong contact is at the same circumferential position as the strain sensor 28 and when the point of weak contact is at the same circumferential position as the strain sensor 28, which causes an error in the bearing preload detected based on the output of the strain sensor 28.

この問題に対し、この実施形態の軸受装置１では、図５に示すように、外輪間座２６の軸方向両側の端面に第１凸部５０および第２凸部５１が周方向に間隔をおいて設けられているので、第１外輪３０および第２外輪３５（図２参照）から外輪間座２６に加わる軸方向荷重が、各第１凸部５０および各第２凸部５１の位置にそれぞれ集約される。そして、第１凸部５０および第２凸部５１の周方向位置と同じ周方向位置にひずみセンサ２８が配置されているので、第１外輪３０および第２外輪３５（図２参照）から外輪間座２６に加わる軸方向荷重が、ひずみセンサ２８の位置に安定して伝わる。そのため、ひずみセンサ２８の出力が、外輪間座２６やその周辺の各部品の微小な加工誤差等の影響を受けにくく、高い精度で軸受予圧を検出することが可能である。 In response to this problem, in the bearing device 1 of this embodiment, as shown in FIG. 5, the first convex portion 50 and the second convex portion 51 are provided at intervals in the circumferential direction on both axial end faces of the outer ring spacer 26, so that the axial load applied to the outer ring spacer 26 from the first outer ring 30 and the second outer ring 35 (see FIG. 2) is concentrated at the positions of the first convex portions 50 and the second convex portions 51, respectively. And, since the strain sensor 28 is disposed at the same circumferential position as the first convex portion 50 and the second convex portion 51, the axial load applied to the outer ring spacer 26 from the first outer ring 30 and the second outer ring 35 (see FIG. 2) is stably transmitted to the position of the strain sensor 28. Therefore, the output of the strain sensor 28 is not easily affected by minute processing errors of the outer ring spacer 26 and its surrounding parts, and it is possible to detect the bearing preload with high accuracy.

また、この軸受装置１は、図５に示すように、第１凸部５０の個数が３つなので、外輪間座２６による第１外輪３０（図２参照）の支持が３点支持となる。そのため、第１外輪３０（図２参照）から外輪間座２６に加わる軸方向荷重に偏り等がある場合にも、各第１凸部５０の第１外輪３０との接触が安定する。同様に、第２凸部５１の個数が３つなので、外輪間座２６による第２外輪３５（図２参照）の支持も３点支持となる。そのため、第２外輪３５（図２参照）から外輪間座２６に加わる軸方向荷重に偏り等がある場合にも、各第２凸部５１の第２外輪３５との接触が安定する。 In addition, as shown in FIG. 5, the bearing device 1 has three first protrusions 50, so the first outer ring 30 (see FIG. 2) is supported by the outer ring spacer 26 at three points. Therefore, even if there is a bias in the axial load applied from the first outer ring 30 (see FIG. 2) to the outer ring spacer 26, the contact of each first protrusion 50 with the first outer ring 30 is stable. Similarly, since there are three second protrusions 51, the second outer ring 35 (see FIG. 2) is also supported by the outer ring spacer 26 at three points. Therefore, even if there is a bias in the axial load applied from the second outer ring 35 (see FIG. 2) to the outer ring spacer 26, the contact of each second protrusion 51 with the second outer ring 35 is stable.

また、この軸受装置１は、図９に示すように、ｃ１≦２×ｂ１を満たすように第１凸部５０の周方向長さｃ１が設定されているので、第１外輪３０（図２参照）から第１凸部５０に加わる軸方向荷重が、軸方向に対して４５°の角度をなす範囲で外輪間座２６の内部に広がりながら伝わるとしたときに、第１凸部５０の周方向一端から周方向他端までのいずれの位置に加わった軸方向荷重も、ひずみセンサ２８の位置に伝わることとなる。そのため、第１外輪３０（図２参照）から外輪間座２６に加わる軸方向荷重を、ひずみセンサ２８の位置に効果的に集約させ、ひずみセンサ２８の分解能を高めることが可能となっている。 In addition, as shown in FIG. 9, the circumferential length c1 of the first convex portion 50 of this bearing device 1 is set to satisfy c1≦2×b1. Therefore, when the axial load applied from the first outer ring 30 (see FIG. 2) to the first convex portion 50 spreads inside the outer ring spacer 26 within a range that forms an angle of 45° with respect to the axial direction and is transmitted, the axial load applied to any position from one circumferential end to the other circumferential end of the first convex portion 50 is transmitted to the position of the strain sensor 28. Therefore, the axial load applied from the first outer ring 30 (see FIG. 2) to the outer ring spacer 26 is effectively concentrated at the position of the strain sensor 28, and the resolution of the strain sensor 28 can be improved.

同様に、図９に示すように、ｃ２≦２×ｂ２を満たすように第２凸部５１の周方向長さｃ２が設定されているので、第２外輪３５（図２参照）から第２凸部５１に加わる軸方向荷重が、軸方向に対して４５°の角度をなす範囲で外輪間座２６の内部に広がりながら伝わるとしたときに、第２凸部５１の周方向一端から周方向他端までのいずれの位置に加わった軸方向荷重も、ひずみセンサ２８の位置に伝わることとなる。そのため、第２外輪３５（図２参照）から外輪間座２６に加わる軸方向荷重を、ひずみセンサ２８の位置に効果的に集約させ、ひずみセンサ２８の分解能を高めることが可能となっている。 Similarly, as shown in FIG. 9, the circumferential length c2 of the second convex portion 51 is set to satisfy c2≦2×b2. Therefore, when the axial load applied from the second outer ring 35 (see FIG. 2) to the second convex portion 51 spreads inside the outer ring spacer 26 within a range that forms an angle of 45° with respect to the axial direction and is transmitted, the axial load applied to any position from one circumferential end to the other circumferential end of the second convex portion 51 is transmitted to the position of the strain sensor 28. Therefore, the axial load applied from the second outer ring 35 (see FIG. 2) to the outer ring spacer 26 is effectively concentrated at the position of the strain sensor 28, and the resolution of the strain sensor 28 can be improved.

上記実施形態では、図３、図５に示すように、ひずみセンサ２８を外輪間座２６の内周に配置したものを例に挙げたが、図６に示すように、ひずみセンサ２８を外輪間座２６の外周に配置してもよい。図６において、外輪間座２６の外周には、ひずみセンサ２８の個数と同数の外周平面部５５が周方向に等間隔に形成され、その外周平面部５５にひずみセンサ２８が取り付けられている。外周平面部５５は、外輪間座２６の中心線と平行な平面に沿って外輪間座２６の外周を除去した形状の部分である。 In the above embodiment, as shown in Figures 3 and 5, the strain sensors 28 are arranged on the inner circumference of the outer ring spacer 26, but as shown in Figure 6, the strain sensors 28 may be arranged on the outer circumference of the outer ring spacer 26. In Figure 6, outer peripheral flat portions 55, the same number as the strain sensors 28, are formed at equal intervals in the circumferential direction on the outer circumference of the outer ring spacer 26, and the strain sensors 28 are attached to the outer peripheral flat portions 55. The outer peripheral flat portions 55 are portions shaped by removing the outer circumference of the outer ring spacer 26 along a plane parallel to the center line of the outer ring spacer 26.

また、図７、図８に示すように、外輪間座２６の軸方向両側の端面のうち、第１外輪３０の側（図では上側）の端面に、各第１凸部５０の周方向両側から軸方向に切り込む第１スリット５６を形成し、第２外輪３５の側（図では下側）の端面にも、各第２凸部５１の周方向両側から軸方向に切り込む第２スリット５７を形成してもよい。このようにすると、第１外輪３０（図２参照）から外輪間座２６に加わる軸方向荷重と、第２外輪３５（図２参照）から外輪間座２６に加わる軸方向荷重とを、特に効果的にひずみセンサ２８の位置に集約させることが可能となる。図７、図８において、第１スリット５６は、第１凸部５０の先端から外輪間座２６の軸方向全長の２０％以上の軸方向長さを有し、第２スリット５７も、第２凸部５１の先端から外輪間座２６の軸方向全長の２０％以上の軸方向長さを有する。 7 and 8, the end face on the first outer ring 30 side (upper side in the figure) of the axially opposite end faces of the outer ring spacer 26 may have a first slit 56 that cuts in the axial direction from both circumferential sides of each first protrusion 50, and the end face on the second outer ring 35 side (lower side in the figure) may have a second slit 57 that cuts in the axial direction from both circumferential sides of each second protrusion 51. In this way, the axial load applied to the outer ring spacer 26 from the first outer ring 30 (see FIG. 2) and the axial load applied to the outer ring spacer 26 from the second outer ring 35 (see FIG. 2) can be concentrated particularly effectively at the position of the strain sensor 28. In Figures 7 and 8, the first slit 56 has an axial length of 20% or more of the total axial length of the outer ring spacer 26 from the tip of the first convex portion 50, and the second slit 57 also has an axial length of 20% or more of the total axial length of the outer ring spacer 26 from the tip of the second convex portion 51.

上記実施形態では、第１軸受２４および第２軸受２５として、アンギュラ玉軸受を例に挙げて説明したが、第１軸受２４および第２軸受２５として、例えば、円すいころ軸受や深溝玉軸受など、軸方向の予圧で径方向分力を生じる他の形式の転がり軸受を採用することも可能である。 In the above embodiment, angular contact ball bearings have been used as the first bearing 24 and the second bearing 25, but it is also possible to use other types of rolling bearings, such as tapered roller bearings and deep groove ball bearings, that generate a radial component force due to an axial preload, as the first bearing 24 and the second bearing 25.

また、上記実施形態では、ひずみセンサ２８として、ひずみ検出部５３と処理部５４とを有するものを例に挙げたが、ひずみセンサ２８は、ひずみ検出部５３のみ（ひずみゲージのみ）で構成することも可能である。 In addition, in the above embodiment, the strain sensor 28 is exemplified as having a strain detection unit 53 and a processing unit 54, but the strain sensor 28 can also be configured with only the strain detection unit 53 (only a strain gauge).

また、上記実施形態では、工作機械(マシニングセンタや旋盤など)の主軸２を回転可能に支持する軸受装置１を例に挙げて説明したが、この発明は、例えば、風力発電装置の主軸など、他の装置の回転軸を回転可能に支持する軸受装置に適用することも可能である。 In addition, in the above embodiment, the bearing device 1 that rotatably supports the main shaft 2 of a machine tool (such as a machining center or a lathe) has been described as an example, but the present invention can also be applied to a bearing device that rotatably supports the rotating shaft of other devices, such as the main shaft of a wind power generation device.

今回開示された実施の形態はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。 The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

１ひずみセンサ付き軸受装置
２主軸
４モータ
２４第１軸受
２５第２軸受
２６外輪間座
２８ひずみセンサ
３０第１外輪
３１第１内輪
３２第１転動体
３５第２外輪
３６第２内輪
３７第２転動体
５０第１凸部
５１第２凸部
５６第１スリット
５７第２スリット
ｂ１第１凸部の先端からひずみセンサまでの軸方向距離
ｂ２第２凸部の先端からひずみセンサまでの軸方向距離
ｃ１第１凸部の周方向長さ
ｃ２第２凸部の周方向長さ 1 Bearing device with strain sensor 2 Main shaft 4 Motor 24 First bearing 25 Second bearing 26 Outer ring spacer 28 Strain sensor 30 First outer ring 31 First inner ring 32 First rolling element 35 Second outer ring 36 Second inner ring 37 Second rolling element 50 First convex portion 51 Second convex portion 56 First slit 57 Second slit b1 Axial distance b2 from tip of first convex portion to strain sensor Axial distance c1 from tip of second convex portion to strain sensor Circumferential length c2 of first convex portion Circumferential length of second convex portion

Claims

The bearing has a first bearing (24) and a second bearing (25) that are spaced apart in the axial direction, a cylindrical outer ring spacer (26) provided between the first bearing (24) and the second bearing (25), and a strain sensor (28) attached to the outer ring spacer (26),
The first bearing (24) has a first outer ring (30), a first inner ring (31) provided radially inside the first outer ring (30), and a plurality of first rolling elements (32) assembled between the first outer ring (30) and the first inner ring (31),
The second bearing (25) has a second outer ring (35), a second inner ring (36) provided radially inside the second outer ring (35), and a plurality of second rolling elements (37) assembled between the second outer ring (35) and the second inner ring (36),
In the bearing device with a strain sensor, an axial preload is applied between the first bearing (24) and the second bearing (25) such that the preload is transmitted through the first inner ring (31), the first rolling element (32), the first outer ring (30), the outer ring spacer (26), the second outer ring (35), the second rolling element (37), and the second inner ring (36),
a plurality of first protrusions (50) are provided at intervals in the circumferential direction on the end face on the first outer ring (30) side among end faces on both axial sides of the outer ring spacer (26), the first protrusions (50) being pressed against the axial end face of the first outer ring (30) by the axial preload;
Among end faces on both axial sides of the outer ring spacer (26), the end face on the side of the second outer ring (35) is provided with second convex portions (51) in the same number as the number of the plurality of first convex portions (50) pressed against the axial end face of the second outer ring (35) by the axial preload, the second convex portions (51) being spaced apart in the circumferential direction and at the same circumferential positions as the plurality of first convex portions (50);
The strain sensor-equipped bearing device is characterized in that the strain sensor (28) is arranged at the same circumferential position as the first convex portion (50) and the second convex portion (51).

The bearing device with strain sensor according to claim 1, wherein the number of the first protrusions (50) is three, and the number of the second protrusions (51) is three.

The strain sensors (28) are provided in the same number as the number of the first convex portions (50) and the number of the second convex portions (51),
3. A bearing device with a strain sensor as described in claim 1 or 2, wherein each of the strain sensors (28) is arranged at the same circumferential position as each of the first convex portions (50) and each of the second convex portions (51).

Each of the first protrusions (50) has a shape extending in the circumferential direction at a constant axial height so as to contact an axial end face of the first outer ring (30) with a certain length in the circumferential direction,
The strain sensor (28) is disposed at a circumferential position corresponding to the circumferential center of the first protrusion (50),
3. The bearing device with a strain sensor as described in claim 1 or 2, wherein when the axial distance from the tip of the first convex portion (50) to the strain sensor (28) is b1 and the circumferential length of the first convex portion (50) is c1, the circumferential length c1 of the first convex portion (50) is set so as to satisfy c1≦2×b1.

Each of the second protrusions (51) has a shape extending in the circumferential direction at a constant axial height so as to be in contact with an axial end face of the second outer ring (35) with a certain length in the circumferential direction,
The strain sensor (28) is disposed at a circumferential position corresponding to the circumferential center of the second protrusion (51),
3. A bearing device with a strain sensor as described in claim 1 or 2, wherein when the axial distance from the tip of the second convex portion (51) to the strain sensor (28) is b2 and the circumferential length of the second convex portion (51) is c2, the circumferential length c2 of the second convex portion (51) is set so as to satisfy c2≦2×b2.

The bearing device with a strain sensor according to claim 1 or 2, wherein the end face on the first outer ring (30) side of the outer ring spacer (26) has a first slit (56) that cuts in the axial direction from both circumferential sides of each of the first convex portions (50), and the end face on the second outer ring (35) side has a second slit (57) that cuts in the axial direction from both circumferential sides of each of the second convex portions (51).

The strain sensor-equipped bearing device according to claim 1 or 2, wherein the strain sensor (28) is disposed on the inner circumference of the outer ring spacer (26).

The strain sensor-equipped bearing device according to claim 1 or 2, wherein the strain sensor (28) is disposed on the outer periphery of the outer ring spacer (26).

A bearing device with a strain sensor (1) according to claim 1 or 2,
A main spindle (2) of a machine tool rotatably supported by the bearing device (1) with a strain sensor;
and a motor (4) for rotating the main shaft (2).