Bearing device, method for manufacturing bearing device, hard disk drive device, and motor

Abstract

[Problem] To provide a bearing device capable of easily imparting preload and securing mass producibility. [Solution] This bearing device is provided with: a cylindrical sleeve 110; a shaft 150 held inside the sleeve 110; a first ball bearing 120 and a second ball bearing 130 for holding the shaft 150 in a rotatable state with respect to the sleeve 110; and an inner peripheral projection part 111 formed on an inner periphery of the sleeve 110. Outer rings 122, 132 of the first and second ball bearings 120, 130 are in contact with end faces of the inner peripheral projection part 111. A predetermined gap is provided between outer peripheries of the outer rings 122, 132 of the first and second ball bearings 120, 130 and the inner periphery of the sleeve 110. A predetermined gap is provided between inner peripheries of inner rings 121, 131 of the first and second ball bearings 120, 130 and an outer periphery of the shaft 150. A delayed ultraviolet curable epoxy-based adhesive is provided in the gaps.

Description

Bearing device, manufacturing method of bearing device, hard disk drive device and motor

[0001] The present invention relates to a bearing device suitable for use in, for example, a pivot assembly bearing device for a hard disk drive, and in particular to a technique for effectively suppressing the generation of outgassing.

[0002] Anaerobic ultraviolet-curing acrylic adhesive has traditionally been used to bond the ball bearings to the shaft and sleeve in pivot assembly bearing devices. In this case, the acrylic adhesive is applied to the bonding surfaces of the ball bearings, shaft, and sleeve, and any excess acrylic adhesive is cured by irradiating it with ultraviolet light after assembling the components. Furthermore, since the excess acrylic adhesive does not cure in areas not exposed to ultraviolet light, the assembled components must be heated in a vacuum oven to cure the uncured adhesive and forcibly generate outgassing to remove it.

[0003] Outgassing from acrylic adhesive components can affect the cleanliness of hard disk drives, so there has been a strong demand for bearing devices that use epoxy adhesives instead of acrylic adhesives, which do not contain the risky outgassing components.

[0004] For example, Patent Document 1 includes a description suggesting the use of an epoxy adhesive as the adhesive (paragraph 0018, etc.), and Patent Document 2 includes a description suggesting the use of a thermosetting epoxy adhesive as the adhesive (paragraph 0041).

[0005] Japanese Patent No. 5749523 Japanese Patent Application Laid-Open No. 2017-211072

[0006] However, when a thermosetting epoxy adhesive is used as the adhesive, after assembling the ball bearing, shaft, and sleeve, it is necessary to insert the assembled assembly into an oven while applying preload with a jig, and heat it for a predetermined period of time to cure the adhesive. For this reason, the technology described in Patent Document 2 has the problem of being unsuitable for mass production.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a bearing device that not only suppresses the adverse effects of outgassing by using an epoxy adhesive as the adhesive, but also allows for easy application of preload and ensures mass productivity.

[0008] The present invention is a bearing device comprising a cylindrical outer member, a shaft member arranged inside the outer member, first and second ball bearings that hold the shaft member in a rotatable state relative to the outer member, and a spacer portion that is provided on the inner circumference of the outer member or the outer circumference of the shaft member and with which the end faces of the outer rings or inner rings of the first and second ball bearings come into contact, with a predetermined gap between the outer circumferences of the outer rings of the first and second ball bearings and the inner circumference of the outer member, and a predetermined gap between the inner circumferences of the inner rings of the first and second ball bearings and the outer circumference of the shaft member, and a delayed ultraviolet-curing epoxy adhesive provided in the gap.

[0009] The present invention also provides a hard disk drive device comprising a bearing device as described above, a swing arm that is swingably supported by the bearing device and moves a magnetic head on a magnetic disk, and a base plate to which the shaft member of the bearing device is fixed.

[0010] FIG. 1 is a front view showing a bearing device of a first embodiment of the present invention. FIG. 2 is an enlarged view of a portion indicated by arrow III in FIG. 2. FIG. 3 is a schematic side view showing an assembly process of the first embodiment. FIG. 4 is a front view showing a bearing device of a second embodiment of the present invention. FIG. 5 is a cross-sectional view taken along line VI-VI of FIG. 1. FIG. 6 is a schematic side view showing an assembly process of the second embodiment. FIG. 7 is a perspective view showing a hard disk drive device of an embodiment of the present invention. FIG. 8 is a cross-sectional view showing a motor of an embodiment of the present invention. FIG. 9 is a cross-sectional view showing a bearing device of a third embodiment of the present invention. FIG. 11 is a cross-sectional view showing a motor equipped with a bearing device of the third embodiment of the present invention. FIG. 12 is a cross-sectional view showing a modified example of the third embodiment of the present invention. FIG. 13 is a schematic side view showing an assembly process of the third embodiment. FIG. 14 is a cross-sectional view showing a bearing device of a fourth embodiment of the present invention. FIG. 15 is a schematic side view showing an assembly process of the fourth embodiment.

[0011] [1] First Embodiment 1. Configuration of Bearing Device A bearing device according to an embodiment of the present invention will be described. Figures 1 to 4 show a bearing device 100 according to an embodiment of the present invention. The bearing device 100 includes a cylindrical sleeve (outer member) 110. An inner peripheral protrusion (spacer portion) 111 that protrudes radially inward is formed in the axial center of the sleeve 110. A first ball bearing 120 and a second ball bearing 130 are fixed to either side of the inner peripheral protrusion 111 with adhesive 140. End faces of the inner peripheral protrusion 111 contact the end faces of the outer rings 122 and 132 of the first and second ball bearings 120 and 130.

[0012] The outer peripheral surfaces of the outer rings 122 and 132 are fitted to the inner peripheral surface of the sleeve 110 in a clearance fit relationship as defined by JIS B 0401-1 and -2, and the gap is filled with adhesive 140. The gap is preferably 2 to 15 μm.

[0013] The inner rings 121, 131 are fixed to a shaft (shaft member) 150 with adhesive 140. A flange portion 151 that protrudes radially outward is formed at the base end of the shaft 150. The end face of the inner ring 131 of the second ball bearing 130 contacts the flange portion 151. The fit between the inner peripheral surfaces of the inner rings 121, 131 and the outer peripheral surface of the shaft 150 is also a clearance fit as defined in JIS B 0401-1 and -2, and adhesive 140 is filled into the gap. It is desirable that the gap be 2 to 15 μm.

[0014] 2, reference numeral 125 denotes balls, and a plurality of balls 125 are arranged at regular intervals in the circumferential direction between the raceway surface 121 a of the inner ring 121 and the raceway surface 122 a of the outer ring 122 by a cage 126. The second ball bearing 130 also has balls 125 arranged in a similar configuration.

[0015] 3, annular grooves 123 are formed on both axial ends of the inner peripheral surface of the outer ring 122, and a C-ring 124 is fitted into the annular groove 123, with the C-ring 124 pressing the outer peripheral edge of a seal member 127 against the outer ring 122. The inner peripheral edge of the seal member 127 faces the outer peripheral surface of the inner ring 121 with a small gap between them. Such a seal member 127 is also provided in the second ball bearing 130.

[0016] Meanwhile, a first hub cap 128, which faces the first ball bearing 120, is fixed to the outer peripheral surface of the shaft 150. The outer peripheral edge of the first hub cap 128 faces the inner peripheral surface of the sleeve 110 with a small gap between them. A second hub cap 129, which faces the first hub cap 128, is fixed by press fitting or adhesive to the opening of the sleeve 110. The second hub cap 129 is ring-shaped, and its inner peripheral edge faces the outer peripheral surface of the shaft 150 with a gap between them.

[0017] As a result, the gap between the seal member 127 and the inner ring 121 overlaps with the first hub cap 128 in the axial direction, and the gap between the first hub cap 128 and the sleeve 110 overlaps with the second hub cap 129 in the axial direction. This effectively prevents leakage of grease filled between the inner ring 121 and the outer ring 122 and the intrusion of dust and other foreign matter from the outside.

[0018] On the other hand, the flange portion 151 formed at the base end of the shaft 150 causes the gap between the sealing member 127 and the inner ring 121 to overlap with the flange portion 151 in the axial direction, effectively preventing grease leakage and the intrusion of dust and other foreign matter from the outside.

[0019] 2. Structure of adhesive The adhesive 140 is a delayed UV-curing epoxy adhesive that begins to harden within 10 seconds to 30 minutes after UV irradiation. The hardening start time is preferably 10 seconds to 5 minutes after UV irradiation. The hardening start time is determined by applying UV light at 100 mW / cm using a UV-LED with a wavelength of 365 nm. ２The viscosity increase is monitored using a rheometer after 20 seconds of UV irradiation, and the time it takes for the viscosity to increase tenfold compared to the viscosity before UV irradiation is considered to be initiation. Curing is not considered to have begun until the viscosity reaches ten times the viscosity before UV irradiation. Furthermore, the viscosity of the adhesive at 25°C before curing is preferably 100 to 1,000 mPa·s, with 100 to 400 mPa·s being particularly desirable. If the viscosity is less than 100 mPa·s, the applied adhesive may run off. If the viscosity exceeds 1,000 mPa·s, springback may occur when preload is applied, preventing the adhesive from applying preload. Here, the viscosity of the adhesive at 25°C before curing or after UV irradiation is measured using a cone-plate rheometer with a diameter of 75 mm and a cone angle of 1.0° at a shear rate of 100 / s. This springback is more likely to occur when the applied preload is smaller. In this embodiment, the preload applied to each bearing of the bearing device in the axial direction can be 5 to 30 N, or 7 to 13 N. It is preferable that the adhesive 140 reach a viscosity 10,000 times higher than its viscosity before UV irradiation within 10 minutes, more preferably within 5 minutes, after the aforementioned curing start time has elapsed. Using such an adhesive can appropriately shorten the time required for the preload application process described below. It is preferable that the axial natural frequency of the bearing device 100 after the preload application process described below is 80% or more of the axial natural frequency of the bearing device 100 after the heating process described below. The preload application process can last, for example, 3 to 30 minutes.

[0020] The glass transition temperature of the adhesive after curing is preferably 100°C or higher, and more preferably 120°C or higher. By setting the glass transition temperature in this range, changes in the natural frequency of the bearing device due to temperature changes can be suppressed. Furthermore, it is preferable that the adhesive composition before curing does not contain particles larger than the minimum value of the adhesive gap.

[0021] The delayed UV-curing epoxy adhesive may be an adhesive made of a bisphenol F liquid epoxy resin, a bisphenol A liquid epoxy resin, a glycidyl compound, and a photopolymerization initiator. If necessary, other additives such as modified acrylate may be added.

[0022] In this case, when the entire adhesive component before curing is taken as 100 parts by weight, the adhesive may contain a total of 40 to 60 parts by weight of bisphenol A and bisphenol F, 40 to 60 parts by weight of a glycidyl compound, 0.1 to 10 parts by weight of a photopolymerization initiator, and, if necessary, 0.1 to 5 parts by weight of other additives.

[0023] Examples of the glycidyl compound include neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, phenyl glycidyl ether, 2-methylphenyl glycidyl ether, tert-butylphenyl glycidyl ether, 4-chlorophenyl glycidyl ether, 4-methoxyphenyl glycidyl ether, and 2-biphenyl glycidyl ether. , 1-naphthyl glycidyl ether, methyl glycidyl ether, isopropyl glycidyl ether, butyl glycidyl ether, tert-butyl glycidyl ether, 2-ethyl glycidyl ether, 2-ethylhexyl glycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol #200 diglycidyl ether, polyethylene glycol #400 diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol #400 diglycidyl ether, glycerin diglycidyl ether, etc. can be used alone or in combination of two or more. The glycidyl compound preferably has a viscosity at 25°C of 30 mPa·s or less, more preferably 20 mPa·s or less, and even more preferably 10 mPa·s or less.

[0024] Examples of the photopolymerization initiator include salts whose cation species is an iodonium-based cation species or a sulfonium-based cation species, and whose anion species is a phosphorus-based anion species or a boron-based anion species, and these can be used alone or in combination of two or more. Specific examples include, but are not limited to, the following:

[0025] Examples of iodonium-based cation species include diphenyliodonium, di-p-tolyliodonium, bis(4-dodecylphenyl)iodonium, bis(4-methoxyphenyl)iodonium, (4-octyloxyphenyl)phenyliodonium, bis(4-decyloxyphenyl)iodonium, 4-(2-hydroxytetradecyloxy)phenylphenyliodonium, 4-isopropylphenyl(p-tolyl)iodonium, and isobutylphenyl(p-tolyl)iodonium.

[0026] Examples of sulfonium-based cation species include triarylsulfonium such as triphenylsulfonium, tri-p-tolylsulfonium, tri-o-tolylsulfonium, 4-(phenylthio)phenyldiphenylsulfonium, bis[4-(diphenylsulfonio)phenyl]sulfide, 5-(4-methoxyphenyl)thianthrenium, 5-(4-ethoxyphenyl)thianthrenium, and 5-(4-(2-hydroxyethoxy)phenyl)thianthrenium; diarylsulfonium such as diphenylphenacylsulfonium, diphenyl(4-nitrophenacyl)sulfonium, diphenylbenzylsulfonium, and diphenylmethylsulfonium; phenylmethylbenzylsulfonium, (4-hydroxyphenyl)methylbenzylsulfonium, and phenylmethylbenzylsulfonium; and monoarylsulfoniums such as phenylsulfonium, (4-methoxyphenyl)methylbenzylsulfonium, (4-acetocarbonyloxyphenyl)methylbenzylsulfonium, (2-naphthyl)methylbenzylsulfonium, (2-naphthyl)methyl[(1-ethoxycarbonyl)ethyl]sulfonium, phenylmethylphenacylsulfonium, (4-hydroxyphenyl)methylphenacylsulfonium, (4-methoxyphenyl)methylphenacylsulfonium, (4-acetocarbonyloxyphenyl)methylphenacylsulfonium, (2-naphthyl)methylphenacylsulfonium, (2-naphthyl)octadecylphenacylsulfonium, and (9-anthracenyl)methylphenacylsulfonium.

[0027] Examples of phosphorus-based anion species include hexafluorophosphate and fluorinated alkylfluorophosphate. A specific example of a preferred fluorinated alkylfluorophosphate anion is [(CFCF)PF]. - , [(CF3CF2)3PF3] - , [((CF3)2CF)2PF4] - , [((CF3)2CF)3PF3] - , [(CF3CF2CF2)2PF4] - , [(CF3CF2CF2)3PF3] - , [((CF3)2CFCF2)2PF4] - , [((CF3)2CFCF2)3PF3]- , [(CF3CF2CF2CF2)2PF4] - and [(CF3CF2CF2CF2)3PF3] - Among these, [(CF3CF2)3PF3] - , [(CF3CF2CF2)3PF3] - , [((CF3)2CF)3PF3] - , [((CF3)2CF)2PF4] - , [((CF3)2CFCF2)3PF3] - and [((CF3)2CFCF2)2PF4] - The boron-based anion species include tetrafluoroboric acid and tetrakis(pentafluorophenyl)boric acid.

[0028] Specific examples of the photopolymerization initiator include CPI-100P, CPI-101A, CPI-110B, CPI-200K, CPI-210S, IK-1, IK-2, CPI-410S, and HS-1A manufactured by San-Apro Ltd.; WPI-113, WPI-116, WPI-169, WPI-170, WPAG-336, WPAG-367, WPAG-370, WPAG-469, and WPAG-638 manufactured by Wako Pure Chemical Industries, Ltd.; and ADEKA Chemical Industries, Ltd. Examples of such silicone rubbers include, but are not limited to, Adeka Optomer SP-103, SP-150, SP-151, SP-170, SP-171, and SP-172 manufactured by Polyset Corporation; PC-2506, PC-2508, and PC-2520 manufactured by Polyset Corporation; San-Aid SI-60, SI-80, SI-100, SI-60L, SI-80L, SI-100L, SI-L145, SI-L150, SI-L160, SI-L110, and SI-L147 manufactured by Sanshin Chemical Industry Co., Ltd.; and BLUESIL PI2074 manufactured by Bluestar Silicones HK.

[0029] Other delayed UV-curable epoxy adhesives include those made of alicyclic epoxy resins, oxetane compounds, photopolymerization initiators, and photosensitizers. Other additives, such as modified acrylates, may also be added as needed.

[0030] In this case, when the total adhesive components before curing are taken as 100 parts by weight, the adhesive may contain 75 to 97 parts by weight of an alicyclic epoxy resin, 1 to 15 parts by weight of an oxetane compound, 0.1 to 10 parts by weight of a photopolymerization initiator, 0.1 to 10 parts by weight of a photosensitizer, and, if necessary, 0.1 to 5 parts by weight of other additives.

[0031] Alicyclic epoxy resins include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate compounds, such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-1-methylcyclohexyl-methyl-3,4-epoxy-1-methylcyclohexanecarboxylate, 6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, 3,4-epoxy-3-methylcyclohexyl-methyl-3,4-epoxy-3-methylcyclohexanecarboxylate, and 3,4-epoxy-5-methylcyclohexyl-methyl-3,4-epoxy-5-methylcyclohexanecarboxylate. The alicyclic epoxy resin preferably has a viscosity of 400 mPa·s or less at 25°C.

[0032] Examples of the oxetane compound include 3-ethyl-3-hydroxymethyloxetane, 3-(meth)allyloxymethyl-3-ethyloxetane, (3-ethyl-3-oxetanylmethoxy)methylbenzene, 4-fluoro-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene, [1-(3-ethyl-3-oxetanylmethoxy)ethyl]phenyl ether, isobutoxymethyl (3-ethyl-3-oxetanylmethyl) ether, 2-ethylhexyl (3-ethyl-3-oxetanylmethyl) ether, ethyl diethylene glycol (3-ethyl-3-oxetanylmethyl) ether, tetrahydrofurfuryl (3-ethyl-3-oxetanylmethyl) ether, tetrabromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2-tetrabromophenoxyethyl (3-ethyl-3-oxetanylmethyl) ether, phenyl ... pentachlorophenyl (3-ethyl-3-oxetanylmethyl) ether, pentabromophenyl (3-ethyl-3-oxetanylmethyl) ether, ethylene glycose bis(3-ethyl-3-oxetanylmethyl) ether, triethylene glycol bis(3-ethyl-3-oxetanylmethyl) ether, tetraethylene glycol bis(3-ethyl-3-oxetanylmethyl) ether, trimethylolpropane tris(3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tris(3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tetrakis(3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol tetrakis(3-ethyl-3-oxetanylmethyl) ether, ditrimethylolpropane tetrakis(3-ethyl-3-oxetanylmethyl) ether, and the like.

[0033] As the photopolymerization initiator, for example, in addition to triarylsulfonium salts, those equivalent to those mentioned above can be used. Among them, triarylsulfonium salts are preferable. Specific examples thereof include CPI-100P manufactured by San-Apro Co., Ltd. and those equivalent to those mentioned above.

[0034] The photosensitizer may be any compound that, when combined with the photopolymerization initiator, increases the photoactivity of the composition, regardless of the type of sensitization mechanism, such as energy transfer, electron transfer, or proton transfer. From the viewpoint of compatibility with the photopolymerization initiator and excellent photocurability, radical polymerization initiators, aromatic hydrocarbons, nitro compounds, and the following dyes are preferred. For example, the photosensitizer is preferably selected from the group consisting of benzyl ketal-based radical photopolymerization initiators, α-hydroxyacetophenone-based radical photopolymerization initiators, benzoin-based radical photopolymerization initiators, aminoacetophenone-based photoinitiators, oxime ketone-based radical photopolymerization initiators, acylphosphine oxide-based radical photopolymerization initiators, naphthalene derivatives, and anthracene derivatives (e.g., 9,10-dibutoxyanthracene); nitro compounds selected from the group consisting of nitrobenzoic acid and nitroaniline; or dyes selected from the group consisting of riboflavin, rose bengal, eosin, erythrosine, methylene blue, and new methylene blue rose.

[0035] Further, examples of photosensitizers include 9-fluorenone, 2-hydroxy-9-fluorenone, 2-amino-9-fluorenone, fluorene, 2-bromofluorene, 9-bromofluorene, 9,9-dimethylfluorene, 2-fluorofluorene, 2-iodofluorene, 2-fluoreneamine, 9-fluorenol, 2,7-dibromofluorene, 9-aminofluorene hydrochloride, 2,7-diaminofluorene, 9,9'-spirobi[9H-fluorene], 2-fluorenecarboxaldehyde, 9-fluorenylmethanol, 2 -Anthracenes such as acetylfluorene, fluoranthene, anthracene, 9,10-dibutoxyanthracene, 9,10-dimethoxyanthracene, 9,10-diethoxyanthracene, 2-ethyl-9,10-dimethoxyanthracene, and 9,10-dipropoxyanthracene; pyrene; 1,2-benzanthracene; perylene; tetracene; coronene; thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 2,4-diethylthioxane phenothiazines such as phenothiazine, N-methylphenothiazine, N-ethylphenothiazine, and N-phenylphenothiazine; xanthones; naphthalenes such as 1-naphthol, 2-naphthol, 1-methoxynaphthalene, 2-methoxynaphthalene, 1,4-dihydroxynaphthalene, and 4-methoxy-1-naphthol; dimethoxyacetophenone, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 4'-isopropyl-2-hydroxy-2-methyl ... ketones such as thiophenone and 4-benzoyl-4'-methyldiphenyl sulfide; carbazoles such as N-phenylcarbazole, N-ethylcarbazole, poly-N-vinylcarbazole and N-glycidylcarbazole; chrysene such as 1,4-dimethoxychrysene and 1,4-di-α-methylbenzyloxychrysene; phenanthrenes such as 9-hydroxyphenanthrene, 9-methoxyphenanthrene, 9-hydroxy-10-methoxyphenanthrene and 9-hydroxy-10-ethoxyphenanthrene.When a triarylsulfonium salt is used as the photopolymerization initiator, it is preferable to use anthracene, perylene, or phenothiazine, which have high reducing properties, as the photosensitizer.

[0036] Additionally, examples of the photosensitizer include intramolecular cleavage-type photoradical polymerization initiators, hydrogen abstraction-type photoradical polymerization initiators, etc. The intramolecular cleavage-type photoradical polymerization initiator is a type of radical initiator in which the compound is cleaved to generate radicals upon irradiation with active energy rays, and specific examples thereof include benzyl ketal-based photoradical polymerization initiators, α-hydroxyacetophenone-based photoradical polymerization initiators, benzoin-based photoradical polymerization initiators, aminoacetophenone-based photoinitiators, oxime ketone-based photoradical polymerization initiators, acylphosphine oxide-based photoradical polymerization initiators, titanocene-based photoradical polymerization initiators, S-phenyl thiobenzoate polymerization initiators, and their polymerized derivatives. Among these intramolecular cleavage type radical initiators, benzyl ketal-based photoradical polymerization initiators, α-hydroxyacetophenone-based photoradical polymerization initiators, benzoin-based photoradical polymerization initiators, aminoacetophenone-based photoinitiators, oxime ketone-based photoradical polymerization initiators, and acylphosphine oxide-based photoradical polymerization initiators are preferred because they have good compatibility with the above-mentioned photopolymerization initiators and exhibit excellent photocurability, and more preferred are α-hydroxyacetophenone-based photoradical polymerization initiators, benzoin-based photoradical polymerization initiators, aminoacetophenone-based photoinitiators, and oxime ketone-based photoradical polymerization initiators.

[0037] Examples of the hydrogen abstraction type photoradical polymerization initiator include benzophenone-based photoradical polymerization initiators, thioxanthone-based photoradical polymerization initiators, and anthraquinone-based photoinitiators.

[0038] 3. Bearing Device Assembly Method The assembly method for the bearing device 100 configured as described above will be described with reference to Figure 4. (1) The adhesive 140 is applied to the outer periphery of the end of the shaft 150 near the flange portion 151, and the adhesive 140 is also applied to the inner periphery of one end of the sleeve 110. Next, ultraviolet light L is irradiated onto the adhesive 140.

[0039] (2) Before the adhesive 140 begins to harden, the second ball bearing 130 is fitted onto the shaft 150 and pushed into the adhesive 140 until the end face of the inner ring 131 abuts against the flange portion 151, and the first ball bearing 120 is inserted into the sleeve 110 and pushed into the adhesive 140 until the end face of the outer ring 122 abuts against the end face of the inner peripheral protrusion 111.

[0040] (3) Adhesive 140 is applied to the outer periphery of the end of shaft 150 away from flange 151, and adhesive 140 is also applied to the inner periphery of the other end of sleeve 110 (the end opposite to the end into which first ball bearing 120 is inserted). Next, ultraviolet light L is irradiated onto adhesive 140. Note that (3) shows the state in which sleeve 110 is turned upside down 180° from the state shown in (2).

[0041] (4) Before adhesive 140 begins to harden, shaft 150 with second ball bearing 130 attached is inserted into sleeve 110 with first ball bearing 120 attached, and the end face of outer ring 132 of second ball bearing 130 is brought into contact with the end face of inner peripheral protrusion 111. This brings the inner peripheral surface of inner ring 121 of first ball bearing 120 and the outer peripheral surface of outer ring 132 of second ball bearing 130 into contact with adhesive 140.

[0042] (5) The sleeve 110 is held in place with a suitable jig, and the inner ring 121 of the first ball bearing 120 is pressed with the preload jig 160. This state is maintained until the adhesive has cured to a certain extent and the preload is no longer released. (6) Because the adhesive has not completely cured, the bearing device 100 is inserted into an oven and heated to complete the curing. Once curing is complete, the first hub cap 128 is fixed to the outer periphery of the shaft 150, and then the second hub cap 129 is fixed to the inner periphery of the sleeve 110.

[0043] 4. Effects In the bearing device configured as described above, a predetermined gap is provided between the outer peripheral surfaces of the outer rings 122, 132 of the first and second ball bearings 120, 130 and the inner peripheral surface of the sleeve 110, and a predetermined gap is provided between the inner peripheral surfaces of the inner rings 121, 131 of the first and second ball bearings 120, 130 and the outer peripheral surface of the shaft 150. A delayed ultraviolet-curing epoxy adhesive 140 is applied to these gaps. Because the adhesive 140 is epoxy-based, it can suppress outgassing. Furthermore, because the adhesive 140 cures upon exposure to ultraviolet light, the entire assembly process, from the start of assembly to the application of preload, can be carried out at room temperature. Compared to the technology described in Patent Document 2, this technology simplifies the application of preload and offers superior mass productivity. Furthermore, because the adhesive 140 cures slowly after exposure to ultraviolet light, assembly is not compromised.

[0044] Furthermore, in the above embodiment, ultraviolet light L can be irradiated onto the adhesive 140 before components such as the first and second ball bearings 120, 130 are brought into contact with the adhesive 140, thereby preventing uncured portions from occurring in the adhesive 140.

[0045] [2] Second Embodiment 1. Configuration of Bearing Device A second embodiment of the present invention will be described with reference to Figures 5 to 7. A bearing device 200 of the second embodiment differs from the first embodiment in that it does not include a sleeve 110 and includes a spacer 170. Therefore, components equivalent to those of the first embodiment are designated by the same reference numerals and their description will be omitted.

[0046] 6, in bearing device 200, a spacer 170 is interposed between outer ring 122 of first ball bearing 120 and outer ring 132 of second ball bearing 130. Spacer 170 is annular, and a protrusion 171 that fits inside outer ring 132 is formed on the end face of spacer 170 facing second ball bearing 130. This protrusion 171 ensures that the center of spacer 170 coincides with the center of outer ring 132.

[0047] 2. Method of Assembling the Bearing Device The method of assembling the bearing device 200 having the above configuration will be described with reference to Figure 7. (1) The adhesive 140 is applied to the outer periphery of the end of the shaft 150 close to the flange portion 151, and ultraviolet light L is irradiated.

[0048] (2) Before the adhesive 140 begins to harden, the second ball bearing 130 is fitted onto the shaft 150 and pushed into the adhesive 140 so that the end face of the inner ring 131 of the second ball bearing 130 abuts against the flange portion 151.

[0049] (3) The spacer 170 is passed over the shaft 150, and the convex portion 171 is fitted into the outer ring 132 of the second ball bearing 130. (4) The adhesive 140 is applied to the outer periphery of the end portion of the shaft 150 away from the flange portion 151, and the adhesive 140 is irradiated with ultraviolet light L.

[0050] (5) Before the adhesive 140 begins to harden, the first ball bearing 120 is fitted onto the shaft 150 so that the end face of the outer ring 122 abuts against the end face of the spacer 170. This brings the inner circumferential surface of the inner ring 121 of the first ball bearing 120 into contact with the adhesive 140.

[0051] (6) The outer rings 122, 132 of the first and second ball bearings 120, 130 are held in place by an appropriate jig, and the inner ring 121 of the first ball bearing 120 is pressed with the preload jig 160. This state is maintained until the adhesive has hardened to a certain extent and the preload is no longer released.

[0052] (7) The first hub cap 128 is fixed to the outer periphery of the shaft 150. After that, since the adhesive is not completely hardened, the bearing device 200 is inserted into an oven and heated to complete the hardening.

[0053] 3. Modifications The present invention is not limited to the above embodiment, and various modifications are possible as follows. i) In the first embodiment, the inner peripheral protrusion 111 is formed on the sleeve 110, but the inner peripheral protrusion 111 may be integral with the sleeve 110 or may be separate. Also, instead of the inner peripheral protrusion 111, an outer peripheral protrusion may be formed on the shaft 150. In this case, the end faces of the outer peripheral protrusion are brought into contact with the end faces of the inner rings 121, 131 of the first and second ball bearings 120, 130, and preload is applied by pressing the outer ring 122 of the first ball bearing 120 with a preload jig 160.

[0054] ii) In the second embodiment, the end face of the spacer 170 is in contact with the end faces of the outer rings 122, 132 of the first and second ball bearings 120, 130, but it may also be in contact with the end faces of the inner rings 121, 131. In this case, preload is applied by pressing the outer ring 122 of the first ball bearing 120 with a preload jig 160.

[0055] 4. Hard Disk Drive Device Figure 8 is a perspective view showing the overall configuration of a hard disk drive device 300 according to an embodiment of the present invention, which uses the above-described bearing device 100. The hard disk drive device 300 includes a base portion 101 having a recess 117, in which a spindle motor 102 and a plurality of hard disks 113 that are attached to the spindle motor 102 and rotate are disposed. Also disposed in the recess 117 are a swing arm assembly 201 including a swing arm 210 that supports a plurality of magnetic heads 112 that face the respective hard disks 113, an actuator 114 that drives the swing arm 210, and a control unit 115 that controls these devices. A cover is attached to the top surface of the base portion 101 to keep the recess 117 airtight, but the cover is omitted from Figure 1.

[0056] The swing arm assembly 201 has a structure that uses the bearing device 100 to rotatably hold the swing arm 210 of the hard disk drive device 300. A through hole (not shown) is provided in the shaft portion of the swing arm 210. The bearing device 100 is fitted into this through hole. The bearing device 200 of FIG. 6 can also be used in the hard disk drive device 300.

[0057] 5. Motor Figure 9 is a cross-sectional view showing a motor 400 according to an embodiment of the present invention that uses the bearing device 100 described above. In this embodiment, a third hub cap 190 is fixed to the outer rings 122, 132 of the first and second ball bearings 120, 130. The motor 400 uses the bearing device 100 described above. However, in the motor 400, the bearing device 100 may be press-fitted to the shaft member and the inner rings 121, 131, rather than adhesively fixed with a gap between them. That is, the outer peripheral surface of the shaft 152 and the inner peripheral surfaces of the inner rings 121, 131 may be press-fitted, and a gap may be left between the inner peripheral surface of the sleeve 110 and the outer peripheral surfaces of the outer rings 122, 132, with a delayed ultraviolet-curing epoxy adhesive applied to the gap.

[0058] In Fig. 9, reference numeral 410 denotes a casing. The casing 410 is cylindrical. A stator core 420 is fixed to the inner peripheral surface of the casing 410. The stator core 420 is made by laminating a plurality of thin, annular sheets of soft magnetic material (e.g., electromagnetic steel sheets) in the axial direction, and is provided with a plurality of pole teeth that protrude radially inward. The plurality of pole teeth are provided at equal intervals along the circumferential direction, and a coil 421 is wound around each of them.

[0059] A spacer 180 is fixed to the shaft 152 adjacent to the inner ring 121 of the first ball bearing 120. A cylindrical rotor magnet 430 is also fixed to the shaft 152 adjacent to the spacer 180. The rotor magnet 430 is magnetized so that adjacent portions along the circumferential direction, SNSN..., alternately have opposite polarities. The outer periphery of the rotor magnet 430 faces the inner periphery of the pole teeth of the stator core 420 with a gap between them. Supplying a driving current to the coil 421 generates a driving force that rotates the rotor magnet 430, causing the rotor magnet 430 to rotate relative to the casing 410 around the shaft 152 as its axis. The shaft 152 protrudes from an opening 190a formed in the third hub cap 190, and an impeller 450 is attached to its end. In this way, the motor 400 is configured as a blower.

[0060] The bearing device 200 of Figure 6 can also be used in a motor 400. In this case, the bearing device 200 is inserted inside a cylindrical casing 410, which serves as a cylindrical outer member. In this structure, a gap is provided between the outer periphery of the outer ring 122 of the first ball bearing 120 and the inner periphery of the casing 410, and adhesive 140 is provided (filled) in this gap to secure the outer ring 122 of the first ball bearing 120 to the inner periphery of the casing 410. In addition, a gap is provided between the outer periphery of the outer ring 132 of the second ball bearing 130 and the inner periphery of the casing 410, and adhesive 140 is provided (filled) in this gap to secure the outer ring 132 of the second ball bearing 120 to the inner periphery of the casing 410.

[0061] [3] Third Embodiment 1. Configuration of Bearing Device A bearing device 500 according to a third embodiment of the present invention will be described with reference to Figures 10 to 13. A spacer 141 is interposed between the inner ring 121 of the first ball bearing 120 and the inner ring 131 of the second ball bearing 130. The spacer 141 is press-fitted onto a shaft 152. In the third embodiment, the inner rings 121, 131 are press-fitted onto the shaft 152 on both sides of the spacer 141. Meanwhile, the outer peripheral surfaces of the outer rings 122, 132 are bonded to the inner peripheral surface of the sleeve 110 on both sides of the inner peripheral protrusion 111 with adhesive 140.

[0062] An O-ring (elastic member) 161 is interposed between the outer ring 122 of the first ball bearing 120 and the end face of the inner peripheral protrusion 111. In the state shown in Figure 10, the O-ring 161 is compressed, and the resulting reaction force biases the outer ring 122 to the left (outward) in the axial direction. In other words, the outer ring 122 is biased to the left (outward) in the axial direction relative to the inner ring 121, and as the adhesive 140 hardens in this biased state, a fixed position preload is applied to the first ball bearing 120. In addition, the outer ring 132 is also biased to the right (outward) in the axial direction, and a fixed position preload is also applied to the second ball bearing 130.

[0063] Figure 11 shows a motor 600 incorporating the bearing device 500 configured as described above, and motor 600 has the same configuration as motor 400 shown in Figure 9, except for bearing device 500. Bearing device 500 can also be used in a structure that rotatably holds swing arm 210 in hard disk drive device 300 in Figure 8.

[0064] 12 shows a modification of the third embodiment. In this modification, the spacer 181 is thicker than that of the third embodiment, and the outer diameter of the spacer 181 is larger than the inner diameter of the seal member 127. As a result, the gap between the seal member 127 and the step portion 124a of the inner ring 121 overlaps with the spacer 181 in the axial direction, suppressing grease leakage and preventing the intrusion of water, dust, and the like from the outside. For this reason, in this modification, the inner diameter of the fourth hub cap 191 is set to be larger.

[0065] 2. Bearing Device Assembly Method The assembly method for the bearing device 500 configured as described above will be described with reference to Figure 13. (1) The inner ring 121 of the first ball bearing 120 is press-fitted onto one end of the shaft 152. (2) The spacer 141 is press-fitted onto the shaft 152 so that it abuts against the end face of the inner ring 121 of the first ball bearing 120. (3) The adhesive 140 is applied to the inner periphery of the other end of the sleeve 110, and ultraviolet light L is irradiated onto the adhesive 140.

[0066] (4) Before the adhesive 140 begins to harden, the second ball bearing 130 is fitted onto the inner periphery of the sleeve 110, and the end face of the outer ring 132 of the second ball bearing 130 is brought into contact with the end face of the inner periphery protruding portion 111. This brings the outer periphery of the outer ring 132 into contact with the adhesive 140. (5) An O-ring 161 is inserted onto the inner periphery of one end of the sleeve 110 (the opposite side of the inner periphery protruding portion 111 from the second ball bearing 130 in the axial direction), and is brought into contact with the inner periphery protruding portion 111 of the sleeve 110.

[0067] (6) Adhesive 140 is applied to the inner periphery of one end of sleeve 110, and ultraviolet light L is irradiated. (7) Before adhesive 140 begins to harden, shaft 152, onto which spacer 141 and inner ring 121 of first ball bearing 120 are press-fitted, is inserted into sleeve 110, and shaft 152 is press-fitted into inner ring 131 of second ball bearing 130. At this time, O-ring 161 is pressed by the end face of outer ring 122 of first ball bearing 120. As a result, the outer circumferential surface of outer ring 122 of first ball bearing 120 comes into contact with the adhesive.

[0068] 13(8) at room temperature, the reaction force of the compressed O-ring 161 urges the outer ring 122 toward one axial side (outward), causing the outer ring 122 to be biased toward one axial side (outward) relative to the inner ring 121, and as the adhesive 140 hardens, a fixed position preload is applied to the first ball bearing 120. In addition, the outer ring 132 of the second ball bearing 130 is also urged toward the other axial side (outward), so a fixed position preload is also applied to the second ball bearing 130.

[0069] (9) Because the adhesive 140 is not completely cured, the bearing device 500 is inserted into an oven and heated to complete the curing. Note that in step (4), instead of applying the adhesive 140 to the inner periphery of the sleeve 110, the adhesive 140 may be applied to the outer periphery of the outer ring 132 of the second ball bearing 130. Similarly, in step (6), instead of applying the adhesive 140 to the inner periphery of the sleeve 110, the adhesive 140 may be applied to the outer periphery of the outer ring 122 of the first ball bearing 120. Also, instead of press-fitting the shaft 152 into the inner rings 121, 131, the shaft 152 may be fixed with the adhesive 140.

[0070] [4] Fourth Embodiment 1. Bearing Device Configuration Figure 14 shows a bearing device 700 according to a fourth embodiment of the present invention. This bearing device 700 uses a sleeve 119 that does not have the inner peripheral protrusion 111 of the sleeve 110 in the modified example of the third embodiment shown in Figure 12, and a coil spring (elastic member) 116 is placed in the vacant space, with the O-ring 161 and fourth hub cap 191 removed. The coil spring 116 is placed between the outer ring 122 of the first ball bearing 120 and the outer ring 132 of the second ball bearing 130. The outer rings 122, 132 are axially outwardly biased by the biasing force of the coil spring 116. In this state, the outer rings 122, 132 are fixed to the inner peripheral surface of the sleeve 119 with adhesive 140, and a fixed position preload is applied to the first and second ball bearings 120, 130. After the fixed position preload is applied, the coil spring 116 may be fixed to the inner peripheral surface of the sleeve 119 with adhesive 140. In this case, it is preferable that the outer diameter of the coil spring 116 is approximately equal to the outer diameters of the outer ring 122 of the first ball bearing 120 and the outer ring 132 of the second ball bearing 130, or that the coil spring 116 and the inner peripheral surface of the sleeve 119 have a loose fit.

[0071] 2. Method of Assembly of Bearing Device The method of assembly of bearing device 700 configured as described above will be described with reference to Figure 15. (1) The inner ring 121 of the first ball bearing 120 is press-fitted onto the shaft 152 up to the other end of the shaft 152 (the lower axial end in Figure 15). (2) The spacer 141 is press-fitted onto the shaft 152 so that it abuts against the end face of the inner ring 121 of the first ball bearing 120. (3) The shaft 152 passes through the coil spring 116, and the coil spring 116 abuts against the outer ring 122 of the first ball bearing 120.

[0072] (4) The inner ring 131 of the second ball bearing is press-fitted onto one end of the shaft 152 (the upper axial end in FIG. 15 ), and the outer ring 132 presses the coil spring 116, thereby completing a bearing assembly in which the first and second ball bearings 120, 130 are mounted on the shaft 152. (5) An adhesive 140 is applied to the inner periphery of each end of the sleeve 119 in the axial direction, and ultraviolet light L is irradiated onto the adhesive 140.

[0073] (6) Before the adhesive 140 begins to harden, the bearing assembly prepared in step (4) is fitted onto the sleeve 119. This brings the outer peripheral surfaces of the outer rings 122 and 132 of the first and second ball bearings 120 and 130 into contact with the adhesive 140.

[0074] (7) By leaving the assembly at room temperature in the state shown in Figure 15 (7), the outer rings 122, 132 are urged to both sides (outside) in the axial direction by the reaction force of the compressed coil spring 116, and the outer rings 122, 132 are biased to both sides (outside) in the axial direction more than the inner rings 121, 131, and as the adhesive 140 hardens, a fixed position preload is applied to the first ball bearing 120 and the second ball bearing 130.

[0075] (8) Because the adhesive 140 has not yet completely hardened, the bearing device 700 is inserted into an oven and heated to complete the hardening. Note that in step (5), instead of applying the adhesive 140 to the inner periphery of the sleeve 110, the adhesive 140 may be applied to the outer peripheries of the outer rings 122 and 132 of the first and second ball bearings 120 and 130. Also, instead of press-fitting the inner rings 121 and 131 onto the shaft 152, they may be fixed with the adhesive 140.

[0076] 3. Others The bearing device 700 can also be used in a structure that rotatably holds the swing arm 210 in the hard disk drive device 300 in Fig. 8. The bearing device 700 can also be used in the motor 400 in Fig. 9 or the motor 600 in Fig. 11.

[0077] The present invention can be used in industrial fields such as pivot assembly bearing devices for hard disk drives, bearing devices for fans used in home appliances such as dryers and cleaners, bearing devices for motors used in automobiles, and bearing devices for machine tools.

[0078] 100, 200, 500, 700...bearing device, 101...base portion, 102...spindle motor, 110...sleeve (outer member), 111...inner peripheral protrusion portion (spacer portion), 112...magnetic head, 113...hard disk, 114...actuator, 115...control portion, 116...coil spring (elastic member), 117...recess, 119...sleeve, 120...first ball bearing, 121, 131...inner ring, 122, 132...outer ring, 121a, 122a...raceway surface, 123...annular groove, 124...C-ring, step portion...124a, 125...ball, 126...retainer, 127...sealing member, 128...first hub cap, 129...second 2 hub caps, 130...second ball bearing, 140...adhesive, 141...spacer, 150, 152...shaft (shaft member), 151...flange portion, 160...preload jig, 161...O-ring (elastic member), 170...spacer, 171...convex portion, 180, 181...spacers, 190...third hub cap, 190a...opening, 191...fourth hub cap, 201...swing arm assembly, 210...swing arm, 300...hard disk drive device, 400, 600...motor, 410...casing, 420...stator core, 421...coil, 430...rotor magnet, 450...impeller, L...ultraviolet light.

Claims

1. A bearing device comprising: a cylindrical outer member; a shaft member arranged inside the outer member; first and second ball bearings which hold the shaft member in a rotatable state relative to the outer member; and a spacer portion which is provided on the inner circumference of the outer member or the outer circumference of the shaft member with which the end faces of the outer rings or inner rings of the first and second ball bearings contact; a predetermined gap is provided between the outer circumference of the outer rings of the first and second ball bearings and the inner circumference of the outer member; a predetermined gap is provided between the inner circumference of the inner rings of the first and second ball bearings and the outer circumference of the shaft member; and a delayed ultraviolet curing epoxy adhesive is provided in the gap.

2. A bearing device comprising: a shaft member; a spacer arranged in the axial middle of the shaft member; and a first ball bearing and a second ball bearing arranged on either side of the spacer to hold the shaft member in a rotatable state relative to the spacer, wherein a predetermined gap is provided between the inner circumference of the inner rings of the first and second ball bearings and the outer circumference of the shaft member, and a delayed ultraviolet-curing epoxy-based adhesive is provided in the gap.

3. A bearing device in which the bearing device according to claim 2 is inserted inside a cylindrical outer member, wherein a predetermined gap is provided between the outer periphery of the outer rings of the first and second ball bearings and the inner periphery of the outer member, and a delayed ultraviolet curing epoxy-based adhesive is provided in the gap.

4. A method for manufacturing a bearing device, comprising the steps of applying a delayed ultraviolet-curing epoxy-based adhesive to the outer periphery of a shaft member, irradiating the adhesive with ultraviolet light, fitting a second ball bearing onto the shaft member before the adhesive starts to harden, and bringing the inner surface of the inner ring of the second ball bearing into contact with the adhesive to start hardening of the adhesive, and then reapplying a delayed ultraviolet-curing epoxy-based adhesive to the outer periphery of the shaft member, irradiating the reapplied adhesive with ultraviolet light, fitting a first ball bearing onto the shaft member before the reapplied adhesive starts to harden, and bringing the inner surface of the inner ring of the first ball bearing into contact with the reapplied adhesive to start hardening of the adhesive.

5. A method for manufacturing a bearing device, comprising the steps of applying a delayed ultraviolet-curing epoxy-based adhesive to the inner circumference of a cylindrical outer member, irradiating the adhesive with ultraviolet light, fitting a second ball bearing inside the cylindrical outer member before the adhesive starts to harden, and bringing the outer circumference of the outer ring of the second ball bearing into contact with the adhesive to start hardening of the adhesive, and then reapplying a delayed ultraviolet-curing epoxy-based adhesive to the inner circumference of the cylindrical outer member, irradiating the reapplied adhesive with ultraviolet light, fitting a first ball bearing inside the cylindrical outer member before the reapplied adhesive starts to harden, and bringing the outer circumference of the outer ring of the first ball bearing into contact with the reapplied adhesive to start hardening of the adhesive.

6. A delayed ultraviolet-curing epoxy adhesive is applied to the outer periphery of a shaft member and the inner periphery of a cylindrical outer member, the adhesive is irradiated with ultraviolet light, and before the adhesive begins to harden, a first ball bearing is fitted into the cylindrical outer member and a second ball bearing is fitted into the shaft member, respectively, and the outer periphery of the outer ring of the first ball bearing is brought into contact with the adhesive applied to the inner periphery of the cylindrical outer member, and the inner periphery of the inner ring of the second ball bearing is brought into contact with the adhesive applied to the outer periphery of the shaft member, and then: A manufacturing method for a bearing device, comprising the steps of: reapplying a delayed ultraviolet-curing epoxy-based adhesive to the outer circumference of the shaft member and the inner circumference of the cylindrical outer member; irradiating the reapplied adhesive with ultraviolet light; fitting the second ball bearing into the cylindrical outer member and the first ball bearing into the shaft member before the reapplied adhesive begins to harden; bringing the inner surface of the inner ring of the first ball bearing into contact with the reapplied adhesive on the outer circumference of the shaft member; and bringing the outer surface of the outer ring of the second ball bearing into contact with the reapplied adhesive on the inner circumference of the cylindrical outer member.

7. A method for manufacturing a bearing device as set forth in any one of claims 4 to 6, wherein the adhesive has a viscosity of 100 to 1000 mPa·s at 25°C before hardening.

8. A method for manufacturing a bearing device according to any one of claims 4 to 7, wherein the adhesive has a glass transition point of 100°C or higher after hardening.

9. A method for manufacturing a bearing device according to any one of claims 4 to 8, wherein the adhesive before hardening does not contain particles larger than the minimum value of the adhesive gap.

10. A hard disk drive comprising: a bearing device according to any one of claims 1 to 3; a swing arm that is swingably supported by said bearing device and moves a magnetic head over a magnetic disk; and a base plate to which the shaft of said bearing device is fixed.

11. A motor comprising a casing including a bearing device according to any one of claims 1 to 3 and a stator, and a rotor magnet on the shaft member, the outer circumferential surface of which faces the inner circumferential surface of the stator with a gap therebetween.

12. A bearing device comprising: a cylindrical outer member; a shaft member arranged inside the outer member; first and second ball bearings which hold the shaft member in a rotatable state relative to the outer member; a spacer arranged axially between the inner rings of the first and second ball bearings; and an elastic member arranged between an end face of the outer ring of the first ball bearing and an end face of the outer ring of the second ball bearing, wherein the spacer and the inner rings of the first and second ball bearings are pressed into the shaft member, a predetermined gap is provided between the outer circumference of the outer rings of the first and second ball bearings and the inner circumference of the outer member, and a delayed ultraviolet curing epoxy adhesive is provided in the gap.

13. A bearing device as described in claim 12, further comprising a spacer portion provided on the inner circumference of the outer member against which an end face of the outer ring of the second ball bearing abuts, the elastic member being disposed between the end face of the outer ring of the first ball bearing and the end face of the spacer portion of the outer member.

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