JP2007218368A - Ball bearing for direct drive motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball bearing of a multipoint contact type such as a four-point contact type for compatibly securing insulating performance and durability and reducing its cost in a high order, when used for a direct drive motor. <P>SOLUTION: Each ball 14 to be assembled into the ball bearing is formed of metal. The surfaces of an outer ring 12, excluding the surface provided with an outer ring raceway 15, are coated with a ceramics insulating layer 22. This secures the insulating performance of the ball bearing without forming each ball 14 of ceramics, preventing separation between each ball 14 and each of the outer ring raceway 15 and an inner ring raceway 16 due to a difference in material property, and also reduces manufacturing cost as compared with a structure with each ball 14 formed of ceramics. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used as a ball bearing incorporated in various industrial machines such as robots, medical equipment, food machines, semiconductor and liquid crystal manufacturing devices, optical or optoelectronic devices, and direct drive motors used in automobiles and the like.

  In order to control movable parts such as robots and machine tools, conventionally, direct drive motors that directly drive the operating parts without using a reduction gear have been used. This direct drive motor has various sizes and shapes depending on the purpose of use. However, in order to reduce the size, a structure in which the rotating member is supported by a single rolling bearing to the fixed member of the motor is disclosed in, for example, a patent. Documents 1 and 2 are described.

  FIG. 4 shows the direct drive motor 1 described in Patent Document 1 among them. The direct drive motor 1 is used by being incorporated in an actuator or the like used in the field of factory automation (FA). In the direct drive motor 1, a rotating member 3 is rotatably supported by a single bearing 7 on a cylindrical fixed member 2 that does not rotate during use. The rotating member 3 has a U-shaped cross section and is formed in an annular shape as a whole, and has an outer diameter side cylindrical portion 5 and an inner diameter side cylindrical portion 8. And the front half part (the left half part of FIG. 4) of the said fixing member 2 is inserted between the outer diameter side cylindrical part 5 and the inner diameter side cylindrical part 8. The stator 4 is fixed to the outer peripheral surface of the front half of the fixing member 2, and the outer peripheral surface of the stator 4 and the inner peripheral surface of the rotor 6 fixed to the inner peripheral surface of the outer diameter side cylindrical portion 5 are: It is facing all around. In the direct drive motor 1 configured in this manner, the rotating member 3 to which the rotor 6 is fixed rotates by energizing a coil wound around a permanent magnet constituting the stator 4.

  On the other hand, FIG. 5 shows a direct drive motor 1a described in Patent Document 2. In the direct drive motor 1a, a rotating shaft 10 that is a rotating member is disposed on the radially inner side of a housing 9 that is a fixed member formed in a cylindrical shape. Then, one bearing 7 a is provided between the outer peripheral surface of one end portion (the right end portion in FIG. 5) of the rotary shaft 10 and the inner peripheral surface of the one end portion of the housing 9, and the rotary shaft is attached to the housing 9. 10 is rotatably supported. The rotor 6a is fixed to the outer peripheral surface of the other end portion (left end portion in FIG. 5) of the rotating shaft 10, and the stator 4a is fixed to the inner peripheral surface of the intermediate portion of the housing 9 at a position facing the rotor 6a. . Then, similarly to the direct drive motor 1 of FIG. 4 described above, the rotating shaft 10 to which the rotor 6a is fixed is rotationally driven by energizing the stator 4a.

  The above-described conventional direct drive motors 1 and 1a include a bearing 7 that rotatably supports the rotating member 3 with respect to the fixed member 2, or a bearing 7a that rotatably supports the rotating shaft 10 with respect to the housing 9. Cross roller bearings are used for each. This cross roller bearing is incorporated in a staggered manner so that the rollers adjacent in the circumferential direction are inclined by 90 °, and has a high load capacity. Therefore, the direct drive motors 1 and 1a can support the rotating member 3 or the rotating shaft 10 by installing only one bearing 7 and 7a at each end. In this way, if the number of bearings that support the rotating member 3 or the rotating shaft 10 can be reduced to one, the axial dimension of the direct drive motors 1 and 1a can be reduced correspondingly. Miniaturization can be achieved.

  Further, for the purpose of reducing the axial dimension of the direct drive motors 1 and 1a as described above, the bearings incorporated in the direct drive motors 1 and 1a are replaced with the above-described cross roller bearings and are of a four-point contact type. A ball bearing can be considered. As a four-point contact type ball bearing that can be used for such applications, for example, there is a structure described in Patent Document 3. FIG. 6 shows the structure described in Patent Document 3. The four-point contact type ball bearing 11 includes an outer ring 12 and an inner ring 13 that are arranged concentrically with each other, and a plurality of balls 14. Of these, an outer ring raceway 15 is formed on the inner peripheral surface of the outer ring 12, and an inner ring raceway 16 is formed on the outer peripheral surface of the inner ring 13 over the entire circumference. The cross-sectional shapes of both the tracks 15 and 16 are so-called gothic arch shapes in which arcs having a radius of curvature larger than ½ of the diameter of each ball 14 are intersected at an intermediate portion. Therefore, both the tracks 15 and 16 and the rolling surface of each ball 14 are in contact with each other at two points, and a total of four points for each ball 14. When the ball bearing 11 configured in this way is incorporated in the direct drive motor 1, 1 a, the internal clearance that is the clearance between the rolling surface of each ball 14 and both the tracks 15, 16 is a negative value. If the preload is applied to the ball bearing 11, the rigidity of the ball bearing 11 can be further increased.

  Such a four-point contact type ball bearing 11 has higher rigidity against moment load than a general single row deep groove type radial ball bearing. Therefore, even when used as a bearing incorporated in a direct drive motor, the rotating member 3 or the rotating shaft 10 (see FIGS. 5 and 6) can be sufficiently supported. However, in the case of a direct drive motor, if measures are not taken, a current such as a return current or a motor shaft current may flow through the ball bearing 11 itself that supports the rotating member 3 or the rotating shaft 10. In this case, a discharge phenomenon occurs between the rolling surface of the ball 14 and the outer ring raceway 15 or the inner ring raceway 16, and so-called electrolytic corrosion occurs in which the corrosion progresses in this portion, thereby extending the life of the ball bearing 11. It will shorten significantly. In order to prevent the occurrence of such electric corrosion, for example, as described in Patent Document 4, a technique of using ceramic balls as balls of a ball bearing has been conventionally known.

  In the case of the technique described in the above-mentioned Patent Document 4, since a ball made of a ceramic having excellent insulating properties is used as a ball to be incorporated in a ball bearing, it prevents electrolytic current from flowing as described above. Can be prevented. However, when ceramic balls are used in this way, the processing cost of these balls increases, and the entire ball bearing becomes very expensive. Further, when the outer ring or the inner ring is made of general bearing steel, the raceway surface is likely to be worn depending on the use conditions due to the difference in material characteristics, and peeling may occur. In particular, in the case of a structure in which a preload is applied to the ball bearing (when the internal gap is set to a negative value), peeling is more likely to occur.

JP 63-213461 A Japanese Utility Model Publication No. 62-68455 Japanese Patent Laid-Open No. 2005-188865 JP 2002-139048 A

  In view of the circumstances as described above, the present invention ensures insulation performance and durability even when a multi-point contact ball bearing such as a 4-point contact ball bearing is used for a direct drive motor. The invention was invented to realize a structure capable of coexisting with low cost at a high level.

The ball bearing for a direct drive motor according to the present invention includes a pair of race rings (an outer ring 12 and an inner ring 13) and a plurality of balls 14 as shown in FIG.
Of these, both race rings 12 and 13 are arranged concentrically with each other and are made of metal.
The balls 14 are provided between a pair of raceway surfaces (outer ring raceway 15 and inner ring raceway 16) formed on surfaces of the raceways 12 and 13 facing each other so as to freely roll. Each is made of metal.
The rolling contact surface of each ball 14 and the both raceway surfaces 15 and 16 are so-called four-point contact type ball bearings that contact each other at two points. The rolling surface of each ball 14 and one of the raceway surfaces 15 and 16 may be a so-called three-point contact type ball bearing in which two balls contact each ball.
At the same time, the internal clearance, which is the clearance between the rolling surfaces of the balls 14 and the raceways 15 and 16, is set to a negative value so that a preload is applied to the balls 14 to improve the moment stiffness of the ball bearings. ing.
Further, of the two race rings 12, 13, one of the race rings is provided with a rotor, and the other race ring is provided with a stator via different members. And the rotating member provided with this rotor is supported rotatably with respect to the fixing member provided with this stator. In the case of the present invention, as described above, since the moment rigidity of the ball bearing is improved, the rotating member can be sufficiently supported by only one ball bearing.
In particular, in the ball bearing for a direct drive motor according to the present invention, a surface other than the surface provided with the raceway surface among the surfaces of at least one of the raceways 12 and 13, that is, FIG. In the case of the structure shown in FIG. 1A, the outer peripheral surface 18 of the outer ring 12 and the axial end surfaces 19 and 19 of the outer ring 12, and in the case of the structure shown in FIG. Further, both end surfaces 21 and 21 in the axial direction of the inner ring 13 are covered with a ceramic insulating layer 22.

Preferably, as the insulating layer 22, as described in claim 2, the ceramic constituting the insulating layer 22 contains 99% by weight or more of alumina (Al ₂ O ₃ ). In this case, the insulating layer 22 is formed by polishing the surface of the ceramic sprayed layer formed on a surface other than the surface provided with the raceway surface. Furthermore, the thickness of this ceramic sprayed layer was 0.4 mm or less excluding the bent continuous portions 23, 23 (or 24, 24) between adjacent surfaces, and this ceramic sprayed layer was obtained by polishing. The insulating layer 22 has a thickness of 0.25 mm or more.

Alternatively, the insulating layer 22 contains any one of titanium oxide (TiO ₂ ), zirconia (ZrO ₂ ), and chromium oxide (Cr ₂ O ₃ ) as described in claims 3, 6, and 7. An alumina sprayed layer may be used.
Moreover, when it contains titanium oxide among these, as described in Claim 4, it is preferable to make content of this titanium oxide into 0.01 to 0.2 weight%. In this case, as described in claim 5, it is more preferable that the alumina content is 99% by weight or more.
Moreover, when it contains the said zirconia, it is preferable that content of this zirconia shall be 0.5 to 2.5 weight%, and content of alumina shall be 97 weight% or more.
In the case of the ceramic sprayed layer having such a composition, it is preferable to form the ceramic sprayed layer by polishing the surface of the ceramic sprayed layer other than the surface provided with the raceway surface. Also in this case, the thickness of the ceramic sprayed layer is set to 0.4 mm or less excluding the bent continuous portions 23 and 23 (or 24 and 24) between adjacent surfaces, and the ceramic sprayed layer is polished. The thickness of the insulating layer 22 obtained in this way is preferably 0.25 mm or more.

  Furthermore, when each of the above-described inventions is carried out, as described in claim 8, the accuracy relating to the thickness dimension of the ceramic sprayed layer which is the insulating layer 22 and the adhesion efficiency of the alumina constituting the ceramic sprayed layer are improved. For the purpose of improvement, it is preferable to use alumina having a particle size of 10 to 50 μm and an average particle size of 15 to 25 μm.

According to the ball bearing for a direct drive motor of the present invention configured as described above, it is possible to ensure insulation performance, durability, and cost reduction in parallel.
That is, since the surface other than the surface provided with the raceway surface among the surfaces of at least one of the raceways is covered with the ceramic insulating layer 22, the insulation performance can be sufficiently secured. In addition, since ceramic balls with high processing costs are not used for insulation, peeling due to differences in material characteristics does not occur, durability can be ensured, and costs can be reduced.

In the case of the invention described in claim 2, a ceramic sprayed layer containing 99% by weight or more of alumina is used. Such a ceramic sprayed layer has a relatively large electric resistance value (excellent Has insulating properties). Therefore, if the thickness of the insulating layer 22 after polishing is ensured to be 0.25 mm or more, the effect of preventing electrolytic corrosion of the rotation support portion of the direct drive motor can be sufficiently ensured.
Moreover, in order to ensure the thickness of the insulating layer 22 after polishing to be 0.25 mm or more, a sufficient polishing allowance can be ensured even if the thickness of the ceramic sprayed layer before polishing is 0.4 mm or less. If the thickness of the ceramic sprayed layer can be suppressed to 0.4 mm or less, the thickness of the ceramic sprayed layer covering the continuous bent portions 23, 23 (or 24, 24) between adjacent surfaces is set to 0. It is suppressed to less than 5 mm (further 0.48 mm or less). If it is a ceramic sprayed layer with a thickness of about 0.5 mm (or 0.48 mm), it cannot be said that the thickness dimension is excessive, even if it remains as it is (without reducing the thickness dimension by polishing). Also, it is difficult to cause damage such as cracking and chipping. Therefore, it is possible to reduce the cost by omitting the trouble of polishing the portion of the ceramic sprayed layer covering the bent continuous portions 23, 23 (or 24, 24). In addition, the cost can be reduced by reducing the thickness of the ceramic sprayed layer {the conventional thickness of 0.5 mm or more (generally about 0.6 to 0.7 mm) is reduced to 0.4 mm or less}. You can also plan by.

Moreover, according to the invention of the ball bearing for direct drive motors described in claims 3, 6 and 7, the insulating performance can be obtained by containing any one of titanium oxide, zirconia and chromium oxide in the sprayed layer of alumina. Ensuring high durability, ensuring durability, reducing costs, and ensuring good appearance can be arranged in a high dimension.
In particular, as described in claim 4, the titanium oxide contained in the sprayed layer of alumina is 0.01 to 0.2% by weight, or as described in claim 6, the insulating layer is made of zirconia. When the alumina spray layer is contained, the content of zirconia contained in the alumina sprayed layer is 0.5 to 2.5% by weight, and the alumina content is 97% by weight or more (claim 4). In the case of the structure described in (1), it is preferable that 99% by weight or more be ensured to ensure a good appearance. That is, among the ceramic sprayed layers containing alumina as a main component, in the case of white alumina not containing titanium oxide or the like, the insulation performance is excellent, but the appearance deteriorates with the sealing treatment. On the other hand, in the case of the above-described invention, since it contains 0.01% by weight or more of titanium oxide or 0.5% by weight or more of zirconia, the appearance can be achieved regardless of the sealing treatment. Color unevenness that leads to deterioration does not occur. That is, a part of the synthetic resin appears on the surface of the ceramic sprayed layer in accordance with the sealing treatment for closing the fine voids existing inside the ceramic sprayed layer with the synthetic resin. In the case of white alumina whose surface color is close to pure white, the synthetic resin appearing on the surface in this way causes uneven color on the surface and deteriorates the appearance of the product. On the other hand, in the case of gray alumina containing 0.01% by weight or more of titanium oxide or 0.5% by weight or more of zirconia, the surface color is gray. Therefore, if an appropriate (gray type) color resin is used as the synthetic resin used for the sealing treatment, the surface does not cause uneven color to the extent that the appearance of the product is deteriorated.

However, if the titanium oxide is contained in an amount of 0.2% by weight or the zirconia exceeds 2.5% by weight, the thickness of the ceramic sprayed layer required to ensure the required insulation performance. Becomes larger. Therefore, the titanium oxide content is regulated to 0.01 to 0.2% by weight or the zirconia content to 0.5 to 2.5% by weight.
In addition, by controlling the content of the titanium oxide in the ceramic sprayed layer to 0.2% by weight or less, or the content of the zirconia to 2.5% by weight or less, a material for forming the sprayed layer. The yield of (alumina grains) is somewhat deteriorated. However, as described in claim 8, if alumina having a particle size of 10 to 50 μm and an average particle size of 15 to 25 μm is used, the adhesion efficiency of alumina constituting the ceramic sprayed layer is improved. In addition, the accuracy related to the thickness dimension of the ceramic sprayed layer can be improved, and the cost increase can be suppressed. That is, the manufacturing cost of the ball bearing for the direct drive motor can be reduced by saving the material cost by improving the adhesion efficiency and facilitating the finishing process by reducing the dimensional accuracy (shortening the finishing process time).
Further, when zirconia having high strength and high toughness is contained in the alumina sprayed layer, the adhesion of the alumina sprayed layer can be improved. For this reason, sufficient durability can be secured.

  1A and 2 show an example of an embodiment of the present invention. In the case of this example, the outer ring 12 and the inner ring 13 constituting the ball bearing for the direct drive motor are each made of metal such as bearing steel. A plurality of balls 14 provided between the outer ring raceway 15 and the inner ring raceway 16 so as to roll freely and held by the cage 17 are also made of metal such as bearing steel, for example. And the outer peripheral surface 18 of the said outer ring | wheel 12 and the axial direction both end surfaces 19 and 19 of this outer ring | wheel 12 are coat | covered with the insulating layer 22 made from ceramics.

  In the case of this example, the ball bearing for the direct drive motor is a four-point contact type. That is, the cross-sectional shapes of both the tracks 15 and 16 are so-called gothic arch shapes in which arcs having a radius of curvature larger than ½ of the diameter of each ball 14 are intersected at an intermediate portion. Therefore, both the tracks 15 and 16 and the rolling surface of each ball 14 are in contact with each other at two points, and a total of four points for each ball 14. In the case of this example, a preload is applied to the ball bearing by setting the internal gap, which is a gap between the rolling surfaces of the balls 14 and the raceways 15 and 16, to a negative value. Further, the ball bearing of this example is incorporated in a direct drive motor, and a rotor (rotor) is provided on one of the race rings, and a stator (stator) is provided on the other race ring via different members. Provide. For example, when incorporated in the direct drive motor 1 shown in FIG. 4, the outer ring 12 is fitted and fixed to a part of the rotating member 3 provided with the rotor 6, and the inner ring 13 is fixed to the fixing member 2 provided with the stator 4. The outer fitting is fixed to a part of. Further, when incorporated in the direct drive motor 1a shown in FIG. 5, the inner ring 13 is fitted and fixed to a part of the rotating shaft 10 provided with the rotor 6a, and the outer ring 12 is fixed to a part of the housing 9 provided with the stator 4a. Fit inside. The rotating member 3 or the rotating shaft 10 is rotatably supported with respect to the fixed member 2 or the housing 9.

  In the case of this example, the insulating layer 22 is formed by spraying ceramic droplets containing 99% by weight or more of alumina onto the outer peripheral surface 18 and both axial end surfaces 19 and 19, for example, by plasma spraying. Is a layer. The insulating layer 22, which is such a ceramic sprayed layer, includes the outer peripheral surface 18 and both axial end surfaces 19, 19, as well as the both axial end edges of the outer peripheral surface 18 and the outer ends 19, 19 of the axial direction. It also covers the surfaces of the bent continuous portions 23 and 23 having a circular arc shape with a quarter of a cross section that is continuous with the periphery.

Of the thicknesses T ₁₈ , T ₁₉ , T ₂₃ (see FIG. 2) of the insulating layer 22 covering the surfaces, the surfaces of the outer peripheral surface 18 and the axial end surfaces 19, 19 are covered. The thickness dimensions T ₁₈ and T ₁₉ of the portions are limited to 0.4 mm or less. Then, by suppressing the thickness dimensions T ₁₈ and T ₁₉ of each part to 0.4 mm or less, the thickness dimension T ₂₃ of the part covering the surfaces of the both bent continuous parts ₂₃ and ₂₃ is set to 0.5 mm. Less than (preferably 0.48 mm or less).

Further, by polishing the portion of the insulating layer 22 that covers the surfaces of the outer peripheral surface 18 and the axial end surfaces 19 and 19, these portions are made smooth, and the surfaces 18 and 19 The rotating member 3 (see FIG. 4) or the inner surface of the housing 9 (see FIG. 5) that fits and fixes the outer ring 12 is in close contact. Along with such polishing, the surface portion of the insulating layer 22 (the oblique lattice portion in FIG. 2) covering the surfaces 18 and 19 is removed by the polishing allowance δ shown in FIG. The thickness dimension of the insulating layer 22 is thinner than the state in which the ceramic sprayed layer is formed. However, the thicknesses t ₁₈ (= T ₁₈ −δ) and t ₁₉ (= T ₁₉ −δ) after the removal of the polishing allowance δ are also secured to 0.25 mm or more. On the other hand, the portion of the insulating layer 22 covering the surfaces of the both bent continuous portions 23, 23 is sprayed as it is without being polished for the purpose of cost reduction. State).

The ball bearing for the direct drive motor as described above can ensure the insulation performance of the insulating layer 22, ensure the durability, and reduce the cost at a high level.
First, the insulation performance can be ensured by using a ceramic sprayed layer constituting the insulating layer 22 that contains 99% by weight or more of alumina. That is, the ceramic sprayed layer containing 99% by weight or more of alumina has a large electric resistance value (having excellent insulating properties), so that the thickness of the insulating layer 22 after polishing (in use) is secured to 0.25 mm or more. Then, as long as the rotation support portion has a potential difference of up to about 3000 V, the effect of preventing electrolytic corrosion can be sufficiently secured. For example, as shown in FIG. 3, when the thickness dimension of the insulating layer 22 after polishing is 0.3 mm (Example), an insulation resistance value of 5000 MΩ or more can be secured under the condition of 1000 V application. On the other hand, when the ball incorporated in the ball bearing is made of ceramics (comparative example), it has an insulation resistance value of about 20000 MΩ, but the insulation resistance value of the ball bearing incorporated in the direct drive motor is generally 10 MΩ. That's all you need. Therefore, it can be seen that the structure of this example can secure a necessary and sufficient insulation resistance value. FIG. 3 shows a structure in which the ball incorporated in the ball bearing is made of metal and has no insulating layer as a conventional product, but the insulation resistance value is almost zero.

  Moreover, in order to ensure the thickness of the insulating layer 22 after polishing to be 0.25 mm or more, it is sufficient (about 0.15 mm at maximum) even if the thickness of the ceramic sprayed layer before polishing is 0.4 mm or less. Polishing allowance can be secured. That is, the surface of the insulating layer 22 and, for example, the inner surface of the rotating member 3 or the housing 9 are brought into uniform contact with each other to stabilize the posture of the outer ring 3, and an excessive portion of the insulating layer 22 is excessive. In order to prevent the force from being applied, it is necessary to polish the portions covering the surfaces of the outer peripheral surface 18 and the axial end surfaces 19 and 19. Even in this case, since the necessary polishing allowance is 0.15 mm or less, even if the thickness of the ceramic sprayed layer before polishing is suppressed to 0.4 mm or less, the thickness of the insulating layer 22 after polishing is 0.25 mm. This can be secured.

If the thickness of the ceramic sprayed layer can be suppressed to 0.4 mm or less, as described above, the thickness dimension T ₂₃ of the portion covering the surfaces of the both bent continuous portions ₂₃ , ₂₃ is set to 0.5 mm ( Furthermore, it is suppressed to 0.48 mm) or less. That is, in these two bent continuous portions 23, 23, ceramic droplets that are ejected radially outward on the outer peripheral surface 18, and ceramic droplets that are ejected axially outward on the axial end surfaces 19, 19. Adheres. For this reason, the thickness dimension of the ceramic sprayed layer covering the two bent continuous portions 23, 23 is larger than the thickness dimension of the ceramic sprayed layer covering the outer peripheral surface 18 and the axial end surfaces 19, 19. In this case, if Osaere the thickness dimension T ₂₃ to 0.5mm or less, the ceramic spray layer covering the both bent continuous unit, it hardly occurs damage cracks or chipping.

In the case of this example, since a ball made of metal is used as the ball 14, peeling due to a difference in material characteristics between the outer ring 12 and the inner ring 13 does not occur. For this reason, the durability of the ball bearing can be secured. Further, as a ball bearing for a direct drive motor, a structure using ceramic balls as described in Patent Document 4, and a ball 14 made of metal as in this example, the outer peripheral surface 18 and the axial direction are used. When the manufacturing cost is compared with the case of the ball bearing in which the insulating layers 22 are provided on the both end faces 19, 19, the manufacturing cost can be reduced with the structure of this example. That is, when comparing the cost required to manufacture a ceramic ball with the cost required to coat a part of the outer ring 12 with a ceramic sprayed layer, the manufacturing cost is lower when coated with a ceramic sprayed layer. it can. The difference in manufacturing cost varies depending on the size of the bearing. For example, when compared with a ball bearing having a nominal number 6316 (outer diameter 170 mm, inner diameter 80 mm, width 39 mm), the cost is reduced by about 1/5 to 1/6. Is possible. In addition, as the bearing size increases, the difference in manufacturing cost further increases, and the cost reduction effect can be enhanced.
In addition, the above-mentioned effect is the same also when the insulating layer 22 is coat | covered to the inner ring | wheel 13 side, as shown in FIG.1 (B).

  In the above description, the case where a four-point contact type ball bearing is used as the ball bearing for the direct drive motor has been described. However, the present invention is not limited to the rolling surface of each ball and one of both raceway surfaces. However, the present invention can also be applied to a so-called three-point contact type ball bearing in which two balls contact each ball. Also in this case, in order to ensure the moment rigidity of the ball bearing, a preload is applied to each ball with the internal gap as a negative value.

The half part sectional view which shows two examples of embodiment of this invention. FIG. The graph which compared the insulation resistance value of the structure of a conventional product, a ball | bowl made from ceramics, and the structure of this invention. Sectional drawing which shows the 1st example of the direct drive motor incorporating the ball bearing of this invention. Sectional drawing which similarly shows the 2nd example. The half part sectional view showing the ball bearing of the 4 point contact type used as the object of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Direct drive motor 2 Fixed member 3 Rotating member 4, 4a Stator 5 Outer diameter side cylindrical part 6, 6a Rotor 7, 7a Bearing 8 Inner diameter side cylindrical part 9 Housing 10 Rotating shaft 11 Ball bearing 12 Outer ring 13 Inner ring 14 Ball 15 Outer ring raceway 16 Inner ring raceway 17 Cage 18 Outer peripheral surface 19 End surface 20 Inner peripheral surface 21 End surface 22 Insulating layer 23 Bending continuous portion 24 Bending continuous portion

Claims (8)

  Rollers are provided between a pair of raceways arranged concentrically, each made of metal, and a pair of raceways formed on opposite surfaces of these raceways. A plurality of balls each made of metal, and the rolling surface of each ball and at least one of the two raceways contact at two points, and the rolling surface of each ball and these The internal clearance, which is the clearance between both raceways, is a negative value. Of the above raceways, one raceway has a rotor, the other raceway has a stator, and a separate member. In a ball bearing for a direct drive motor that rotatably supports a rotating member provided with the rotor with respect to a fixing member provided with the stator, at least one of the two bearing rings is provided. The surface other than the surface provided with the raceway is made of ceramics. And wherein the coated by an insulating layer, ball bearings for direct drive motor.   The ceramic constituting the insulating layer contains 99% by weight or more of alumina, and this insulating layer is formed by polishing the surface of the ceramic sprayed layer formed on the surface other than the surface provided with the raceway surface. The thickness of the ceramic sprayed layer is 0.4 mm or less excluding the continuous bent portion between adjacent surfaces. The thickness of the insulating layer obtained by polishing the ceramic sprayed layer is 0. The ball bearing for a direct drive motor according to claim 1, wherein the ball bearing is 25 mm or more.   The ball bearing for a direct drive motor according to claim 1, wherein the insulating layer is a sprayed layer of alumina containing titanium oxide.   The ball bearing for a direct drive motor according to claim 3, wherein the titanium oxide contained in the sprayed layer of alumina is 0.01 to 0.2% by weight.   The ball bearing for a direct drive motor according to claim 4, wherein the alumina content is 99% by weight or more.   The ball bearing for a direct drive motor according to claim 1, wherein the insulating layer is a sprayed layer of alumina containing zirconia.   The ball bearing for a direct drive motor according to claim 1, wherein the insulating layer is a sprayed layer of alumina containing chromium oxide.   The particle size is 10 to 50 μm and the average particle size is 15 to 25 μm for the purpose of improving the accuracy with respect to the thickness dimension of the ceramic sprayed layer, which is an insulating layer, and improving the adhesion efficiency of alumina constituting the ceramic sprayed layer. The ball bearing for direct drive motors according to any one of claims 2 to 7, wherein alumina is used.

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