JP4829039B2 - Fluid dynamic bearing device and motor equipped with the same - Google Patents

Description

  The present invention relates to a fluid dynamic bearing device and a motor including the same.

In recent years, motors using a fluid dynamic pressure shaft device as a bearing device have increased in number with the increase in speed.
Motors equipped with this fluid dynamic bearing device are used in, for example, HDDs (hard disk drives) and LBPs (laser beam printers) to drive hard disks and polygon mirrors, respectively.

The radial dynamic pressure bearing in this fluid dynamic pressure bearing device includes an inner peripheral surface of the sleeve, an outer peripheral surface of the shaft, and a lubricating fluid filled in a slight gap between the two, and a pair is separated in the axial direction. It is set as the provided structure.
The thrust dynamic pressure bearing generally includes a sleeve, a shaft having a flange at the tip and inserted through the sleeve, and a thrust plate facing the flange and sealing one end of the sleeve. Provided on the side.

  More specifically, there are dynamic pressure grooves on both end faces of the flange, while a slight gap is provided between the sleeve, the flange, the thrust plate, and the like, and the lubricating fluid is filled. A dynamic pressure is generated by the groove, and the shaft having the flange floats with respect to the sleeve and the thrust plate and rotates in a non-contact manner.

Examples of such a fluid dynamic bearing device and a motor including the fluid dynamic bearing device are described in Patent Document 1 and Patent Document 2.
JP 2004-183864 A JP 2005-114165 A

  Incidentally, as described above, the thrust plate is fixed to the sleeve so as to seal one end side of the sleeve. This will be described as a conventional fluid dynamic bearing device J50 with reference to FIG.

First, the sleeve J3 has a through hole J3b, and a step portion J3a is formed on one end side thereof.
On the other hand, the shaft J4 has a flange J13 on the tip end side and is inserted through the through hole J3b of the sleeve J3.

A thrust plate J14 is fixed to the step portion J13a of the sleeve J3 by an adhesive J5 to seal one end portion side of the sleeve J3.
Since the curing of the normal adhesive is promoted as the temperature is higher, in the fixing of the thrust plate J14 in the assembly of the fluid dynamic bearing device J50, a temperature higher than room temperature, for example, 60 ° C. or higher for improving productivity. The adhesive J5 is cured by the above.

When the adhesive J5 is cured at a relatively high temperature of 60 ° C. or higher, if the materials of the sleeve J3 and the thrust plate J14 are different, the normal temperature after the adhesive J5 is cured due to the difference in thermal expansion coefficient between them. When the temperature drops to, residual strain that cannot be ignored occurs in the vicinity of the adhesion site.
Since this residual distortion distorts the inner peripheral surface of the sleeve J3, the bearing performance of the radial bearing may be adversely affected.

Generally, in a fluid dynamic pressure bearing device, as a material for a sleeve, a copper-based alloy C6782 (linear expansion coefficient: about 1.7 × 10 ⁻⁵ / ° C.) that has good machinability and is easily subjected to surface treatment such as plating is used. As the material of the thrust plate, SUS420J2 (linear expansion coefficient: about 1.1 × 10 ⁻⁵ / ° C.), which is an iron-based alloy that hardly wears and is hard, is used.
Accordingly, when such a material is used, the gap between the sleeve J3 and the thrust plate J14 is fixed wider than in the normal temperature under a high temperature environment in which the adhesive is cured, and the normal temperature is obtained after the adhesive is cured. In other words, since the stress in the direction of reducing the diameter of the inner peripheral surface remains in the sleeve J3, the cylindricity of the sleeve inner diameter portion (inner peripheral surface) which is a radial dynamic pressure generating portion is lowered.

  For example, if the sleeve J3 is deformed so that the inner diameter of the sleeve J3 becomes larger on the thrust plate side (downward trumpet shape in FIG. 7), the effect of the dynamic pressure on the radial bearing on the side opposite to the flange J13 is caused. There is a concern that the pressure of the lubricating fluid on the flange J13 side will increase and the flying height of the shaft J4 (including the flange J13) will vary greatly, leading to a decrease in long-term reliability.

  On the other hand, if the inner diameter of the sleeve J3 is deformed so as to be smaller on the thrust plate J13 side (upward trumpet shape in FIG. 7), the influence of the dynamic pressure on the radial bearing on the non-flange side becomes weak and the overall dynamic pressure is reduced. The shaft J4 (including the flange J13) does not rise, and the amount of floating of the shaft J4 (not including the flange J13) is insufficient.

  In Patent Document 1, a sleeve or the like where the outer peripheral surface of the sleeve is reduced in diameter toward the end thereof is provided for deformation of the sleeve or the like due to thermal expansion, and the deformation of the sleeve affects the press-fitting into the motor base. Although a technique devised so as not to occur is disclosed, it does not prevent deformation of the inner peripheral surface of the sleeve caused by residual stress, and there is a concern that the long-term reliability may be impaired due to a decrease in cylindricity as well. .

  Therefore, the problem to be solved by the present invention is to provide a fluid motion that can provide high long-term reliability without decreasing the cylindricality of the sleeve inner diameter even when the thrust plate is fixed to the sleeve with an adhesive at a high temperature. A pressure bearing device and a motor including the same are provided.

  In order to solve the above problems, the present invention has the following configurations 1) to 3) as means.

1) A sleeve (1) and a shaft (2) inserted through the sleeve (1), the shaft (2) being connected to the sleeve (1) via a hydrodynamic bearing (RB, SB). In a fluid dynamic pressure bearing device configured to be rotatably supported,
The sleeve (1) has a through hole (1a) and a first diameter (D2) smaller than the outer diameter (D4) of the sleeve (1) formed on one end side of the sleeve (1). A first step portion (1b2) having an inner peripheral surface and a second step portion (1b1) having an inner peripheral surface of a second diameter (D3) smaller than the first diameter (D2). While having
A flange (5) fixed to the tip of the shaft (2) and housed in the second step (1b1);
A thrust plate (3) housed in the first step (1b2) and sealed at the one end of the through hole (1a) and fixed to the sleeve (1) with an adhesive (4); ,
Dynamic pressure grooves (DM1, DM2) formed on the inner peripheral surface of the through hole (1a) or the outer peripheral surface of the shaft (2);
A circumferential groove (1d, 1dd) provided on the one end side of the outer peripheral surface of the sleeve (1),
The end (1d1) on the other end side of the sleeve (1) in the circumferential groove (1d, 1dd) is more than the end (DM2t) on the one end side of the dynamic pressure groove (DM1, DM2). The fluid dynamic pressure bearing device (50, 50A) is located on the one end side.
2) The fluid dynamic bearing device (50, 50A) according to 1), wherein a minimum diameter (D1) in the circumferential groove (1d, 1dd) is equal to or smaller than the first diameter (D2). is there.
3) A motor (51) provided with the fluid dynamic bearing device (50, 50A) described in 1) or 2).

  According to the present invention, even if the thrust plate is fixed to the sleeve with an adhesive at a high temperature, there is an effect that high long-term reliability can be obtained without reducing the cylindricity of the sleeve inner diameter.

The preferred embodiments of the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional view showing an embodiment of the fluid dynamic bearing device of the present invention.
FIG. 2 is a cross-sectional view showing an embodiment of the motor of the present invention.
FIG. 3 is a graph showing the relationship between the difference ΔD between the circumferential groove minimum diameter D1 and the second step portion inner diameter D2, and the cylindricity change amount ΔET.
FIG. 4 is a graph showing the relationship between the difference ΔD between the circumferential groove minimum diameter D1 and the second step portion inner diameter D2 and the adhesive strength of the thrust plate 3.
FIG. 5 is a graph for explaining the difference in cylindricity change amount ΔET between the comparative example and the embodiment according to the invention.
FIG. 6 is a cross-sectional view showing a modification of the fluid dynamic bearing device of the present invention.

  FIG. 1 shows an embodiment of a fluid dynamic bearing device according to the present invention, and FIG. 2 shows an embodiment of a motor equipped with the fluid bearing device.

  In FIG. 1, the hydrodynamic bearing device 50 includes a cylindrical sleeve 1 having a through hole 1a, a shaft 2 having a ring-shaped flange 5 fixed at the tip and inserted into the through hole 1a, and one end side of the sleeve 1. And a thrust plate 3 fixed so as to seal the through-hole 1a (lower side in FIG. 1).

Here, the sleeve 1 and the shaft 2 are made of copper-based alloy C6782, and the linear expansion coefficient thereof is about 1.7 × 10 ⁻⁵ / ° C.
The thrust plate 3 is made of an iron-based alloy SUS420J2, and its linear expansion coefficient is about 1.1 × 10 ⁻⁵ / ° C.

  A pair of radial dynamic pressure grooves DM <b> 1 and DM <b> 2 are formed on the inner peripheral surface of the through hole 1 a of the sleeve 1 so as to be separated from each other in the axis CL direction. In FIG. 1 and other figures to be described later, for the sake of easy understanding, it is shown on the shaft 2 for convenience.

  The radial dynamic pressure grooves DM1 and DM2, the outer peripheral surface of the shaft 2 opposed to each other with a slight gap therebetween, and a lubricating fluid (for example, lubricating oil) 6 filled in the gap, each includes a pair of radials. The dynamic pressure bearing portions RB1 and RB2 are configured (hereinafter, the pair is also simply referred to as a radial dynamic pressure bearing portion RB).

Further, on one end portion side of the through hole 1a, a step portion 1b formed in a step shape with a different inner diameter is provided.
In this embodiment, the step portion 1b has two steps of a first step portion 1b1 and a second step portion 1b2 in order from the small diameter side.

The thrust plate 3 is accommodated in the second step portion 1b2, and the edge portion of the outer surface 3a and the inner wall portion of the second step portion 1b2 are fixed by the adhesive 4, and the thrust plate 3 is a through hole of the sleeve 1. The one end side of 1a is sealed.
Curing of the adhesive 4 in this fixing is performed not at room temperature but in a high temperature environment in order to increase the curing speed and improve production efficiency.
The improvement in the curing rate at high temperature is effective for various adhesives because it is manifested regardless of the adhesive curing system.
As the adhesive, an epoxy-based thermosetting type can be used, but not limited to this, an epoxy-based UV curable type or an acrylic type adhesive may be used.
Moreover, high temperature is 60 degreeC, for example, and is normally set in the range of 60 to 80 degreeC.

  The flange 5 has thrust dynamic pressure grooves (not shown) formed on both surfaces (upper and lower surfaces) thereof in the axis CL direction, and is accommodated in the first step portion 1 b 1 of the sleeve 1.

  Here, a slight gap is provided between the flange 5 and the front end surface of the shaft 2, and the sleeve 1 and the thrust plate 3, and the gap 6 is filled with the lubricating fluid 6 to constitute the thrust dynamic pressure bearing portion SB. ing.

  In the configuration of these dynamic pressure bearing portions RB and SB, a dynamic pressure is generated as the shaft 2 rotates, and the shaft 2 is rotatably supported without contact with the sleeve 1.

On the other end side (upper side in FIG. 1) of the through hole 1a of the sleeve 1, a taper seal whose diameter is expanded so that the radial distance from the outer peripheral surface of the shaft 2 increases as the inner peripheral surface thereof approaches the end surface 1e. Part TS is formed.
The lubricating fluid 6 filled in the radial dynamic pressure bearing portion RB and the thrust dynamic pressure bearing portion SB is shared and sealed at the taper seal portion TS to prevent leakage to the outside.

In addition, a circumferential groove 1d having a substantially triangular cross section and recessed inward is formed on one end side of the outer peripheral surface 1c of the sleeve 1.
If this is explained in detail, first, in the axis CL direction, the distance L1 from the end surface 1e of the other end of the sleeve 1 to the end 1d1 of the circumferential groove 1d (indentation start site) is the one end side of the sleeve 1 The radial dynamic pressure groove DM2 is set so as not to overlap.
More specifically, the distance L1 is set to be larger than the distance L2 from the end surface 1e of the sleeve 1 to the end portion DM2t on the thrust plate 3 side of the radial dynamic pressure groove DM2.

  On the other hand, in the direction (radial direction) orthogonal to the axis CL, the diameter of the deepest portion of the circumferential groove 1d, that is, the minimum diameter D1 is formed to be equal to or smaller than the inner diameter D2 of the second step portion of the sleeve 1. Yes.

As described above, the thrust plate 3 is fixed to the sleeve 1 by curing the adhesive 4 at a high temperature, and the material of the thrust plate 3 has a larger linear expansion coefficient than the material of the sleeve 1.
Accordingly, the inner diameter of the second step portion 1b2 of the sleeve 1 is thermally expanded to be larger than the outer diameter of the thrust plate 3, and the second step portion 1b2 is fixed in a state where the difference in diameter between the two is larger than that at room temperature.
For this reason, the peripheral wall of the second step portion 1b2 of the sleeve 1 tends to be reduced in diameter as the temperature of the adhesive 4 decreases to room temperature after curing, but this is prevented because it is bonded and fixed to the thrust plate 3. Resulting in residual stress

In this state, since the circumferential groove 1d as described above is formed in the embodiment, it is possible to prevent the radial dynamic pressure bearing portion RB from being deformed by this residual stress.
In other words, the deformation due to the residual stress is blocked from propagating at the portion thinned by the circumferential groove 1d having a portion having a smaller diameter than the inner peripheral diameter D2 of the second step portion 1b2.

Therefore, deformation on the radial dynamic pressure bearing RB side with respect to the end 1d1 in the sleeve 1 is extremely difficult to occur.
Further, the position of the circumferential groove 1d that blocks the propagation of the deformation in the axial CL direction, that is, the position closest to the radial dynamic pressure bearing RB, that is, the end 1d1 is the position of the end DM2t of the radial dynamic pressure groove DM2 on the thrust plate 3 side. Since it is on the thrust plate 3 side, deformation of the sleeve 1 on the radial dynamic pressure bearing RB side is further less likely to occur.

Further, a taper portion TP that is reduced in diameter toward the end portion is formed on one end portion side of the outer peripheral surface of the sleeve 1 further than the peripheral groove 1d.
This is provided so that the motor 51 (described later) can be fixed well without interfering with the motor base 31 when fitted.

  In the fluid dynamic bearing device 50 of the above-described embodiment, the circumferential groove 1d is not limited to the above-described one having a substantially triangular cross section, and may be a circumferential groove 1dd having a substantially rectangular cross section. A fluid dynamic bearing device 50A having the circumferential groove 1dd is shown in FIG.

Also in this example, the minimum diameter D1 of the circumferential groove 1dd is set to be equal to or smaller than the inner circumferential diameter D2 of the second step portion 1b2, and the end portion of the circumferential groove 1dd from the end surface 1e of the other end portion of the sleeve 1 in the axis CL direction ( The distance L1 to the dent starting portion) 1dd1 is set so as not to overlap the radial dynamic pressure groove DM2 on one end side of the sleeve 1.
More specifically, the distance L1 is set to be larger than the distance L2 from the end surface 1e of the sleeve 1 to the end portion DM2t on the thrust plate 3 side of the radial dynamic pressure groove DM2.

  Specifically, the distance L1 is set to be larger than the distance L2 from the end surface 1e of the sleeve 1 to the end portion DM2t of the radial dynamic pressure groove DM2 on the thrust plate 3 side.

  The fluid dynamic bearing devices 50 and 50A of the embodiment described above can be mounted on various motors, and a motor 51 mounted with the fluid dynamic bearing device 50 will be described with reference to FIG.

  The motor 51 is a motor that is mounted on an HDD (Hard Disk Drive) and drives the hard disk, and, for example, constantly rotates at 5400 times / minute.

  As the stator S, a motor base 31 in which a through hole 31b and an annular wall 31a raised in the periphery thereof are formed, and a fluid dynamic pressure in which an outer peripheral surface is press-fitted and fixed to an inner peripheral surface of the annular wall 31a. The sleeve 1 of the bearing device 50, the thrust plate 3 fixed to the sleeve 1, the core 33 fixed to the outer peripheral surface of the annular wall 31a and wound with the drive coil 32 around the salient pole, and the inner bottom surface of the motor base 31 And a ring-shaped suction plate 34 fixed to 31f.

  Further, the rotor R that is rotatably supported by the stator S via the fluid dynamic pressure bearing device 50 is fixed to the shaft 2 and is raised from a disc-shaped base portion 35a and a peripheral edge of the base portion 35a. A hub 35 having a peripheral wall portion 35b, and a ring magnet 36 that is fixed to the inner surface of the peripheral wall portion 35b and that is in close proximity to the outer peripheral surface of the core 33.

  The suction plate 34 is disposed so as to face and oppose the ring magnet 36, exhibits a suction force that attracts the rotor R toward the stator S, and is well balanced with the floating force of the flange 5 of the fluid dynamic bearing device 50. It is comprised so that a favorable rotation characteristic may be acquired.

When the motor 51 is mounted on the HDD, two hard disks HD are disposed on the outer peripheral surface of the peripheral wall portion 35 b of the hub 35 with the spacer 37 interposed therebetween.
The periphery of the through hole 31b in the outer bottom surface 31h of the motor base 31 is a circular recess 31g. The recess 31g is used to prevent the adhesive from protruding from the outer bottom surface 31h when a conductive adhesive is applied between the motor base 31 and the sleeve 1 to ensure conduction between the motor base 31 and the sleeve 1. Is provided.

  Here, in the fluid dynamic bearing device 50, the difference between the minimum diameter D1 of the circumferential groove 1d and the inner diameter D2 of the second step portion 1b2 is ΔD = D1−D2, and ΔD and the change amount ΔET of the cylindricity ET The relationship is shown in FIG. 3, and the relationship between ΔD and the adhesive strength F of the thrust plate 3 to the sleeve 1 is also shown in FIG. 4 and will be described in detail.

In either case, the circumferential groove 1d is formed with L1 = L2, but similar results are obtained even when L1> L2.
The change amount ΔET of the cylindricity ET indicates a difference between the cylindricity ΔET and the reference set value when the adhesive 4 is cured in an environment of 60 ° C. and then returned to normal temperature (23 ° C.). Each figure is a comparison with the same process and work.

<Relationship between ΔD and ΔET (FIG. 3)>
As ΔD is larger (as the circumferential groove 1d becomes shallower), the amount of change ΔET increases, and particularly when it exceeds 0 (zero), it rapidly increases (deteriorates).
In the region where ΔD is negative, ΔET stably maintains a small value.
Therefore, it can be seen that when ΔD ≦ 0, that is, the minimum diameter D1 of the circumferential groove 1d is set to be equal to or smaller than the inner diameter D2 of the second step portion 1b2, a very good cylindricity ET can be obtained.

<Relationship between ΔD and F (FIG. 4)>
It can be seen that the strength F increases as ΔD increases.
Accordingly, ΔD may be set to such an extent that the necessary intensity F can be obtained.
In this case, it is clear from FIG. 3 that if the minimum diameter D1 of the circumferential groove 1d is excessively increased, the change amount ΔET of the cylindricity is deteriorated. Therefore, it is preferable to set an optimum dimension in a region where ΔD ≦ 0.
Further, in this region of ΔD ≦ 0, the outer diameter of the flange 5 may be reduced, that is, the inner diameter D3 (see FIG. 1) of the first step portion 1b1 may be reduced to ensure the radial thickness.

In general, it is known that the acceleration resistance required for a motor mounted on a hard disk drive mounted on an HDD is 1000 G, and the adhesive strength F of a thrust plate that satisfies this acceleration resistance is 600 N or more.
Therefore, in FIG. 4, ΔD is set to −0.14 ≦ ΔD at which an intensity F of 600 N or more is obtained, and in accordance with the conditions of FIG.
By satisfying −0.14 ≦ ΔD ≦ 0, both good cylindricity and strength can be obtained at the same time.

Assuming that the inner diameter of the first step portion 1b1 is D3 and the outer diameter of the sleeve 1 is D4, in order to satisfy the above-described conditions, as an example,
D1 = φ6.90mm
D2 = φ6.92mm
D3 = φ5.80mm
D4 = φ7.80mm
Can be set.

FIG. 5 shows a graph comparing the cylindricity change amount ΔET between this example and a comparative example which is different only in that it does not have the circumferential groove 1d and is otherwise the same.
From this figure, the cylindricity change amount ΔET of the embodiment provided with the circumferential groove 1d is reduced to about 1/3, 0.03 μm, compared to the conventional 0.13 μm, and the variation is also greatly reduced. You can see that

As described above in detail, the fluid dynamic pressure bearing devices 50 and 50A of the embodiment and the motor 51 including the same can be used even if the thrust plate 3 is fixed to the sleeve 1 with the adhesive 4 at a high temperature. The cylindricity of the inner diameter of 1 is maintained with high accuracy, and high long-term reliability is obtained.
In addition, in the manufacturing process, the adhesive can be cured at a high temperature without reducing the cylindricity, so that the effect of promoting the curing and extremely high productivity can be obtained.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

The circumferential grooves 1d and 1dd are not limited to the example described above, and may have a circular cross section.
Further, the number of grooves is not limited to one, and may be a plurality of grooves formed side by side in the axis CL direction.
In that case, the start portion of the recess closest to the other end 1e of the sleeve 1 can be regarded as the portion corresponding to the end 1d1 (1dd1) of the circumferential groove, and the diameter of the deepest portion can be regarded as the minimum diameter D1. .

In the embodiment, the dynamic pressure grooves DM1 and DM2 of the radial dynamic pressure bearing RB are formed on the inner peripheral surface of the sleeve 1. However, the dynamic pressure grooves DM1 and DM2 may be provided on the outer peripheral surface of the shaft 2.
Even in this case, it goes without saying that a high cylindricity of the inner peripheral surface of the sleeve 1 facing each of the dynamic pressure grooves DM1 and DM2 is maintained and the same effect is obtained.

The circumferential grooves 1d and 1dd are most preferably grooves that circulate around the outer peripheral surface 1c, but may be grooves that are formed so as to circulate generally even when divided into a plurality of parts.
If the ratio of the range in which the circumferential grooves 1d and 1dd are formed to the circumferential length of the outer peripheral surface 1c of the sleeve 1 is 50% or more, a remarkable effect can be exhibited.

  The motor on which the fluid dynamic pressure bearings 50 and 50A of the embodiment can be mounted is not limited to the HDD motor, and various motors such as a polygon mirror driving motor and an optical disk driving motor can be applied. Needless to say.

It is sectional drawing which shows the Example of the fluid dynamic pressure bearing apparatus of this invention. It is sectional drawing which shows the Example of the motor of this invention. It is a graph which shows the relationship of difference (DELTA) D of the circumferential groove minimum diameter D1 and 2nd step part internal diameter D2, and cylindricity change amount (DELTA) ET. 4 is a graph showing a relationship between a difference ΔD between a circumferential groove minimum diameter D1 and a second step portion inner diameter D2, and an adhesive strength of the thrust plate 3. It is a graph explaining the difference of cylindricity change amount (DELTA) ET between the comparative example and the Example which concerns on this invention. It is sectional drawing which shows the modification of the fluid dynamic pressure bearing apparatus of this invention. It is sectional drawing explaining an example of the conventional fluid dynamic pressure bearing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sleeve 1a Through-hole 1b Step part 1b1, 1b2 1st, 2nd step part 1c Peripheral surface 1d, 1dd Circumferential groove 1d1, 1dd1 End part 1e (of other end part) End face 1f Outer bottom face 2 Shaft 3 Thrust plate 3a Outer face 4 Adhesive 5 Flange 6 Lubricating fluid 31 Motor base 31a Annular wall 31b Through hole 31f Inner bottom 31g Recess 31h Outer bottom 32 Coil 33 Core 34 Suction plate 35 Hub 35a Base 35b Peripheral wall 36 Ring magnet 37 Spacer 50 Fluid dynamic bearing device 51 Motor CL Shaft DM1, DM2 Radial dynamic pressure groove HD Hard disk SB Thrust dynamic pressure bearing portion RB Radial dynamic pressure bearing portion

Claims (7)

A fluid dynamic bearing device comprising a sleeve and a shaft inserted through the sleeve, wherein the shaft is rotatably supported with respect to the sleeve via a dynamic pressure bearing portion;
The sleeve has a first step portion having a through hole and an inner peripheral surface having a first diameter smaller than the outer diameter of the sleeve formed on one end side of the sleeve,
A thrust plate which is adhesively secured to the sealed said sleeves said one end of the through hole while being pre SL contained in the first stage portion,
A dynamic pressure groove formed on the inner peripheral surface of the through hole or the outer peripheral surface of the shaft;
A circumferential groove provided on the one end side of the outer peripheral surface of the sleeve,
The sleeve has a linear expansion coefficient greater than that of the thrust plate,
An end portion of the circumferential groove that is the other end portion side of the sleeve is located closer to the one end portion than an end portion of the one end portion side of the dynamic pressure groove ,
The minimum diameter in the circumferential groove is not more than the first diameter,
The fluid dynamic bearing device according to claim 1, wherein the adhesive is cured in a heated state . The circumferential groove is a groove that circulates around the outer peripheral surface of the sleeve, or a groove having a ratio of a range in which the groove is formed with respect to the peripheral length of the outer peripheral surface of the sleeve is 50% or more. Item 2. The fluid dynamic bearing device according to Item 1.   3. The fluid dynamic bearing device according to claim 1, wherein propagation of stress is blocked at a portion of the sleeve thinned by the circumferential groove. 4. The fluid dynamic pressure bearing device according to any one of claims 1 to 3, wherein a cross section of the circumferential groove has a substantially triangular shape, a substantially rectangular shape, or an arc shape . The fluid according to any one of claims 1 to 4, wherein -0.14 mm≤D1-D2≤0 mm is satisfied, where D1 is a minimum diameter of the circumferential groove and D2 is an inner diameter of the first diameter. Hydrodynamic bearing device.   The fluid dynamic bearing device according to claim 1, wherein the adhesive is cured by being heated at a temperature of 60 ° C. or higher. A motor comprising the fluid dynamic bearing device according to any one of claims 1 to 6 .

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