JP2012107645A - Fluid dynamic bearing device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid dynamic bearing device which is high in rigidity and has a hub-integrated shaft in which a flange is accurately fixed to a shaft part.SOLUTION: The hub-integrated shaft 9 is formed of metal, the lower end face 2c of the shaft part 2 is ground, and the shaft part 2 and the flange 11a are fixed to each other in a state that the ground lower end face 2c of the shaft part 2 is made to abut on the upper-side end face 11a1 of the flange 11a.

Description

  The present invention relates to a fluid dynamic bearing device and a manufacturing method thereof.

  The fluid dynamic pressure bearing device supports a shaft portion so as to be relatively rotatable by a dynamic pressure action of lubricating oil generated in a radial bearing gap between an inner peripheral surface of a bearing member and an outer peripheral surface of the shaft portion. Since the fluid dynamic bearing device has excellent rotational accuracy and quietness, for example, for spindle motors of various disk drive devices (such as HDD magnetic disk drive devices and CD-ROM optical disk drive devices), laser beams, etc. It is suitably used for a polygon scanner motor of a printer (LBP) or a color wheel motor of a projector.

  For example, a fluid dynamic pressure bearing device disclosed in Patent Document 1 includes a resin-integrated hub integrated shaft integrally including a shaft portion and a hub portion projecting from one end of the shaft portion to an outer diameter, and other shaft portions. A flange portion fixed to the end, and a bearing member (bearing sleeve and housing) having a shaft portion inserted in the inner periphery thereof are provided. A disk mounting surface is formed in the hub portion. When the hub integrated shaft rotates, a radial bearing gap is formed between the outer peripheral surface of the shaft portion and the inner peripheral surface of the bearing member, and between the upper end surface of the housing and the lower end surface of the hub portion, and the flange Thrust bearing gaps are formed between the upper end surface of the bearing and the lower end surface of the bearing sleeve, and the hub integrated shaft is rotatably supported by the dynamic pressure action generated in the oil film in the radial bearing gap and the thrust bearing gap. .

JP 2007-263168 A

  However, in the above fluid dynamic bearing device, since the hub integrated shaft is formed of resin, there is a possibility that sufficient strength cannot be obtained. In particular, in a fluid dynamic pressure bearing device incorporated in a disk drive device of an HDD, a plurality of disks may be mounted on the hub portion to meet the demand for higher capacity of the HDD. There is a risk that it will not be able to withstand the load of the disk.

  In addition, when the hub portion and the shaft portion are integrally formed as described above, in order to place the bearing member between the hub portion and the flange portion in the axial direction, a separately formed flange portion is provided at the end portion of the shaft portion. Need to be fixed. At this time, if the relative positioning accuracy (for example, squareness) of the flange portion relative to the shaft portion is poor, the flange portion rotates while swinging in the axial direction, which may increase the rotational torque. In particular, when the flange portion faces the thrust bearing gap, if the runout occurs in the flange portion, the supporting force in the thrust direction may be reduced. For this reason, it is necessary to fix the flange portion to the shaft portion with high accuracy.

  The problem to be solved by the present invention is to provide a fluid dynamic bearing device having a high-strength hub integrated shaft and a flange portion fixed to the shaft portion of the hub integrated shaft with high accuracy. .

  The present invention made in order to solve the above-mentioned problems is a metal part integrally including a shaft part and a hub part that protrudes from one end of the shaft part to the outer diameter and is formed with a rotating body mounting surface orthogonal to the axial direction. Hub integrated shaft, a flange portion fixed to the other end of the shaft portion, a bearing member having the shaft portion inserted into the inner periphery, and a radial bearing between the outer peripheral surface of the shaft portion and the inner peripheral surface of the bearing member In a fluid dynamic pressure bearing device including a radial bearing portion that supports a shaft portion in a radial direction by a dynamic pressure action of a lubricating fluid generated in a gap, the other end surface of the shaft portion is a ground surface, and the other end surface and the flange Provided is a fluid dynamic bearing device in which one end surface of the part is brought into contact.

  In this way, by forming the hub integrated shaft from metal, the strength of the hub integrated shaft, particularly the hub portion, can be increased. Also, the other end surface of the shaft portion of the hub-integrated shaft is ground to a high accuracy, and the flange portion is attached to the shaft portion by bringing the one end surface of the flange portion into contact with this highly accurate other end surface. Since the positioning can be performed with high accuracy, the swing of the flange portion can be prevented. In particular, when one end surface of the flange portion faces the thrust bearing gap, it is possible to increase the supporting force in the thrust direction by preventing the flange portion from swinging.

  Further, the fluid dynamic pressure bearing device according to the first aspect supports the hub integrated shaft in one thrust direction by the dynamic pressure action of the lubricating fluid generated in the thrust bearing gap between the one end surface of the bearing member and the one end surface of the hub portion. And a second thrust bearing portion that supports the hub integrated shaft in one thrust direction by a dynamic pressure action of a lubricating fluid generated in a thrust bearing gap between the other end surface of the bearing member and one end surface of the flange portion. In this case, since the one end surface of the hub portion faces the thrust bearing gap, it is desirable to finish with high precision by grinding. In this case, since both end faces of the bearing member face the thrust bearing gap, the axial dimension L1 between both end faces of the bearing member, one end face of the hub portion, and one end face of the flange portion (that is, the other end face of the shaft portion). ) To the axial dimension L2 (L2−L1), the size of the thrust bearing gap is set (see FIG. 2). Therefore, by simultaneously grinding one end surface of the hub portion and the other end surface of the shaft portion with the same grindstone, the axial dimension L2 between these surfaces can be set with high accuracy, and the accuracy of the thrust bearing gap can be improved. Figured.

  In addition, since the outer peripheral surface of the shaft portion faces the radial bearing gap, it is desirable to finish with high precision by grinding. In this case, if the outer peripheral surface of the shaft portion and the other end surface are simultaneously ground with the same grindstone, the surface accuracy of the other end surface with respect to the outer peripheral surface of the shaft portion can be set with high accuracy, so one end surface of the flange portion with respect to the outer peripheral surface of the shaft portion The surface accuracy (for example, runout accuracy) can be increased.

  Moreover, if the surface accuracy of the rotating body mounting surface of the hub portion is poor, the rotating accuracy of the rotating body is lowered. Therefore, it is desirable to perform grinding to finish with high accuracy. In this case, if the outer peripheral surface of the shaft portion is ground on the basis of the rotating body mounting surface (or the surface ground simultaneously with the rotating body mounting surface) finished with high precision by grinding, the surface accuracy of the outer peripheral surface of the shaft portion can be improved. It can be further increased. Moreover, since the relative positional accuracy (for example, deflection accuracy) of the rotating body mounting surface with respect to the outer peripheral surface of the shaft portion can be increased, the rotating accuracy of the rotating body can be increased.

  The hub-integrated shaft can be formed, for example, by subjecting a shaped material in which the shaft portion and the hub portion are integrally formed by plastic working of a metal plate to a grinding finish. Thus, formation is facilitated by forming the hub integrated shaft by plastic working. In particular, by forming a shaped material by plastic working of a metal plate, the amount of deformation due to plastic working can be suppressed compared to, for example, forming a shaped material from a block-shaped blank material. The dimensional accuracy can be increased and the amount of grinding finishing can be reduced.

  As described above, the hub integrated shaft of the present invention can increase the strength by forming the hub integrated shaft from metal. Further, by grinding the other end surface of the shaft portion and bringing the flange portion into contact with this surface, the flange portion can be fixed to the shaft portion with high accuracy, so that the swinging of the flange portion can be prevented.

It is sectional drawing which shows the spindle motor of HDD. It is sectional drawing of the fluid dynamic pressure bearing apparatus which concerns on embodiment of this invention integrated in the said spindle motor. It is sectional drawing of the bearing sleeve of the said fluid dynamic pressure bearing apparatus. It is a top view of the said bearing sleeve. It is a bottom view of the said bearing sleeve. (A)-(e) is sectional drawing which shows the process of plastically processing a metal plate and shape | molding the raw material which has a shaft part and a hub part integrally. It is sectional drawing which shows a mode that grinding finishing is performed on a base material. It is sectional drawing which shows a mode that grinding finishing is performed on a base material.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a spindle motor used in, for example, a 2.5-inch HDD disk drive device. This spindle motor includes a fluid dynamic pressure bearing device 1 that rotatably supports a hub integrated shaft 9 according to an embodiment of the present invention, a bracket 6 to which the fluid dynamic pressure bearing device 1 is attached, and a radial gap. And a stator magnet 4 and a rotor magnet 5 which are opposed to each other. The stator coil 4 is attached to the bracket 6, and the rotor magnet 5 is attached to the hub integrated shaft 9 via the yoke 10. The hub integrated shaft 9 holds a predetermined number of disks D (one in the illustrated example) as a rotating body. When the stator coil 4 is energized, the rotor magnet 5 is rotated by electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the hub integrated shaft 9 and the disk D are rotated together.

  As shown in FIG. 2, the fluid dynamic bearing device 1 includes a hub integrated shaft 9 having a shaft portion 2 and a hub portion 3, and a bearing member that rotatably supports the hub integrated shaft 9. In the present embodiment, the bearing member includes a bearing sleeve 8 in which the shaft portion 2 of the hub integrated shaft 9 is inserted on the inner periphery, and a bottomed cylindrical housing 7 that holds the bearing sleeve 8 on the inner periphery. A retaining member 11 is provided at the lower end of the shaft portion 2 of the hub integrated shaft 9. In the following, for convenience of explanation, the opening side of the housing 7 in the axial direction is the upper side and the closing side is the lower side.

  The hub integrated shaft 9 is made of metal, for example, iron-based metal, particularly stainless steel. The hub integrated shaft 9 of the present embodiment is formed by grinding a shaped material formed by plastic working (press work) of a metal plate. Since stainless steel generally has poor ductility, it is preferable to use a ferritic material (for example, SUS430) that is relatively rich in ductility among stainless steels. Moreover, in order to improve ductility, it is preferable to make content of C of stainless steel 0.2% or less, and it is preferable to mix | blend Ti 0.05% or more by weight ratio with stainless steel for the same purpose. In addition, the hub integrated shaft 9 can be formed of, for example, general structural steel, aluminum alloy, titanium alloy, or the like. The hub integrated shaft 9 is not limited to plastic working, and can be formed by machining such as turning.

  The shaft portion 2 is provided at the axis of the hub integrated shaft 9 and has an outer diameter of about 2 to 4 mm. The shaft portion 2 has a straight cylindrical outer peripheral surface 2a having no irregularities and an axial hole 2b provided in the shaft center. The axial hole 2b is provided so as to penetrate the shaft portion 2 in the axial direction, and a screw groove is formed on the inner peripheral surface thereof.

  The outer peripheral surface 2a of the shaft portion 2 may be subjected to surface hardening treatment or coating treatment, or both. Examples of the surface hardening treatment include surface hardening treatment such as vacuum quenching, vacuum carburizing treatment, vacuum nitriding treatment, gas soft nitriding treatment, or ion nitriding treatment. Examples of the coating process include a coating process using electroless Ni plating, DLC, TiN, TiAlN, or TiC. When the hub integrated shaft 9 is formed of stainless steel, if the C content is 0.2% or less as described above, the hardening process by quenching becomes difficult, so surface effect treatment other than vacuum quenching, or A coating treatment is preferably performed. The surface treatment and the coating treatment may be performed not only on the outer peripheral surface 2a of the shaft portion 2, but also on other regions, for example, the lower end surface 3a1 of the disk portion 3a of the hub portion 3 facing the thrust bearing gap. Alternatively, if the wear resistance of the outer peripheral surface 2a of the shaft portion 2 is sufficient, the surface effect treatment or the coating treatment may be omitted.

  The hub portion 3 includes a rotating body mounting surface extending from the upper end portion of the shaft portion 2 to the outer diameter and orthogonal to the axial direction. The hub portion 3 of the present embodiment includes a disc portion 3a that covers the opening of the housing 7, a cylindrical portion 3b that extends downward in the axial direction from the outer peripheral portion of the disc portion 3a, and a further outer diameter from the lower end portion of the cylindrical portion 3b. A disk mounting surface 3d as a rotating body mounting surface is formed on the upper end surface of the flange 3c. A disk fitting surface 3e is formed on the outer peripheral surface of the cylindrical portion 3b. The disk D is fitted onto the disk fitting surface 3e and placed on the disk mounting surface 3d. In this state, the upper surface of the disk D is pressed by a clamper (not shown) and pressed onto the disk mounting surface 3d. Is held by the hub portion 3. In addition, the upper part of the axial direction hole 2b of the axial part 2 functions as a screw hole for fixing a clamper.

  The hub integrated shaft 9 has a surface ground at a predetermined location. In the present embodiment, the locations indicated by dotted lines in FIG. 2, that is, the disc mounting surface 3d, the disc fitting surface 3e, the outer peripheral portion of the upper end surface 3a2 of the disc portion 3a, the inner peripheral portion of the lower end surface 3a1 of the disc portion 3a, The outer peripheral surface 2a of the shaft portion 2 and the lower end surface 2c of the shaft portion 2 are grinding surfaces. Among the above, the outer peripheral portion of the disk mounting surface 3d, the disk fitting surface 3e, and the upper end surface 3a2 of the disk portion 3a is simultaneously ground with one grindstone. Using these grinding surfaces as a reference, the inner peripheral portion of the lower end surface 3a1 of the disk portion 3a, the outer peripheral surface 2a of the shaft portion 2, and the lower end surface 2c of the shaft portion 2 are simultaneously ground by one grindstone.

  The retaining member 11 is made of metal or resin, and has a disk-shaped flange portion 11a and a fixing portion 11b extending upward from the axis of the flange portion 11a. A screw groove is formed on the outer periphery of the fixing portion 11b, and is fixed to the lower end of the screw hole formed on the inner peripheral surface of the axial hole 2b of the shaft portion 2. The flange portion 11 a protrudes to the outer diameter from the outer peripheral surface 2 a of the shaft portion 2, and the upper end surface 11 a 1 is in contact with the lower end surface 2 c of the shaft portion 2. The flange portion 11 a is disposed between the lower end surface 8 c of the bearing sleeve 8 and the upper end surface 7 b 1 of the bottom portion 7 b of the housing 7 in the axial direction. The flange portion 11 a fixed to the lower end of the shaft portion 2 and the bearing sleeve 8 are engaged in the axial direction, whereby the shaft portion 2 is prevented from coming off from the bearing sleeve 8.

  The upper end surface 11a1 of the flange portion 11a functions as a thrust bearing surface that faces a thrust bearing gap of a second thrust bearing portion T2 described later. Since the lower end surface 2c of the shaft portion 2 is finished to be a high-precision flat surface by grinding, the upper end surface 11a1 of the flange portion 11a is in good contact with the entire lower end surface 2c of the shaft portion 2, whereby the shaft portion 2, the flange portion 11a can be positioned with high accuracy. In addition, since the upper end surface 11a1 of the flange portion 11a and the lower end surface 2c of the shaft portion 2 are in close contact with each other around the entire circumference, the intrusion of lubricating oil into the axial hole 2b of the shaft portion 2 can be suppressed. The risk of the lubricating oil filling the inside leaking out through the axial hole 2b can be reduced.

  The bearing sleeve 8 is formed in a cylindrical shape from metal or resin, and in this embodiment, is formed from a sintered metal containing copper as a main component, for example. As shown in FIG. 3, herringbone-shaped dynamic pressure grooves 8a1 and 8a2 are formed on the inner peripheral surface 8a of the bearing sleeve 8 as radial dynamic pressure generating portions, for example, in two regions separated in the axial direction. (Cross hatching is hill). In the illustrated example, the upper dynamic pressure groove 8a1 is formed asymmetrically in the axial direction. Specifically, the axial dimension X1 of the region above the axial center part m is the axial dimension X2 of the lower region. (X1> X2). The lower dynamic pressure groove 8a2 is formed symmetrically in the axial direction. An axial groove 8d1 is formed over the entire length in the axial direction on the outer peripheral surface 8d of the bearing sleeve 8. For example, three axial grooves 8d1 are equally arranged in the circumferential direction.

  As shown in FIGS. 4 and 5, for example, pump-in type spiral-shaped dynamic pressure grooves 8b1 and 8c1 are formed on the upper end surface 8b and the lower end surface 8c of the bearing sleeve 8 as thrust dynamic pressure generating portions, respectively. (Cross hatching is a hill). An axial groove 8 d 1 is formed on the outer peripheral surface 8 d of the bearing sleeve 8. The number of the axial grooves 8d1 is arbitrary. For example, three axial grooves 8d1 are arranged at equal intervals in the circumferential direction.

  The housing 7 is formed of metal or resin, and in this embodiment, is formed by, for example, resin injection molding. As shown in FIG. 2, the housing 7 is formed in a bottomed cylindrical shape integrally having a side portion 7a and a bottom portion 7b. The inner peripheral surface 7a1 of the side portion 7a is formed in a straight cylindrical surface shape, and the outer peripheral surface 8d of the bearing sleeve 8 is fixed by gap bonding, press-fitting, press-fitting with an adhesive interposed therebetween, or the like. At the upper end of the outer peripheral surface of the side portion 7a, as shown in FIG. 2, a tapered seal surface 7a3 that gradually increases in diameter upward is formed. The seal surface 7a3 forms an annular seal space S whose radial dimension is gradually reduced upward, between the seal surface 7a3 and the inner peripheral surface 3b1 of the cylindrical portion 3b of the hub portion 3. When the hub integrated shaft 9 is rotated, the seal space S is provided through a gap between the lower end surface 3a1 of the disk portion 3a of the hub portion 3 and the upper end surface 7a2 of the housing 7, so that the thrust of the first thrust bearing portion T1. It communicates with the outer diameter side of the bearing gap and the upper end of the axial groove 8d1. The capillary force of the seal space S prevents the lubricating oil filled in the housing 7 from leaking out.

  The fluid dynamic pressure bearing 1 composed of the above-described members can be assembled as follows. First, the shaft portion 2 of the hub integrated shaft 9 is inserted into the inner periphery of the bearing sleeve 8, and in this state, the fixing portion 11 b of the retaining member 11 is screwed to the lower end of the axial hole 2 b of the shaft portion 2 and temporarily assembled. Composing goods. At this time, positioning of the flange portion 11a with respect to the shaft portion 2 is performed by bringing the upper end surface 11a1 of the flange portion 11a into contact with the lower end surface 2c of the shaft portion 2. Since the axial dimension L2 between the lower end surface 3a1 of the disk portion 3a of the hub portion 3 and the upper end surface 11a1 of the flange portion 11a is determined in the state of the temporary assembly product, the axial dimension L2 and the bearing The total amount of thrust bearing gaps of the first and second thrust bearing portions T1 and T2 is set based on the difference from the axial dimension L1 between both end faces 8b and 8c of the sleeve 8.

  At this time, since the lower end surface 2c of the shaft portion 2 of the hub integrated shaft 9 and the lower end surface 3a1 of the disc portion 3a of the hub portion 3 are surfaces that are simultaneously ground with the same grindstone, the axial dimension therebetween is as follows. High accuracy is set. Accordingly, by bringing the upper end surface 11a1 of the flange portion 11a into contact with the lower end surface 2c of the shaft portion 2, the axial dimension L2 between the upper end surface 11a1 of the flange portion 11a and the lower end surface 3a1 of the disk portion 3a of the hub portion 3 is determined. Is set with high accuracy. On the other hand, since the bearing sleeve 8 is formed of a sintered metal having excellent formability, the axial dimension L1 between the both end faces 8b and 8c is set with high accuracy. Therefore, the total amount of the thrust bearing gaps of the first and second thrust bearing portions T1 and T2 set by the difference between these axial dimensions (L2−L1) is set with high accuracy.

  Thus, the temporary assembly bearing sleeve 8 having a thrust bearing gap is inserted into the inner periphery of the housing 7, and the outer peripheral surface 8 d of the bearing sleeve 8 is fixed to the inner peripheral surface 7 a 1 of the housing 7. Then, the fluid dynamic bearing device 1 shown in FIG. 2 is completed by filling the space inside the housing 7 including the internal pores of the bearing sleeve 8 with the lubricating oil. At this time, the oil level is held inside the seal space S.

  When the hub integrated shaft 9 rotates, a radial bearing gap is formed between the inner peripheral surface 8 a of the bearing sleeve 8 and the outer peripheral surface 2 a of the shaft portion 2. The radial dynamic pressure generating portion (dynamic pressure grooves 8a1, 8a2) increases the pressure of the lubricating oil filled in the radial bearing gap, and the hub integrated shaft 9 can be rotated in the radial direction by this pressure (dynamic pressure action). The radial bearing portions R1 and R2 that are supported in a non-contact manner are configured.

  At the same time, between the lower end surface 3a1 of the disk portion 3a of the hub portion 3 and the upper end surface 8b of the bearing sleeve 8, and between the upper end surface 11a1 of the flange portion 11a and the lower end surface 8c of the bearing sleeve 8. A thrust bearing gap is formed in each case. The thrust dynamic pressure generating portions (dynamic pressure grooves 8b1 and 8c1) increase the pressure of the lubricating oil filled in the thrust bearing gaps, and this pressure (dynamic pressure action) raises the hub integrated shaft 9 in one direction in the thrust direction (lifts up). Direction) and a second thrust bearing portion T2 for supporting the hub integrated shaft 9 rotatably in the thrust direction in the other direction (pressing down direction). The

  At this time, the axial groove 8d1 formed in the outer peripheral surface 8d of the bearing sleeve 8 forms a communication path through which lubricating oil can flow. This communication path can prevent a local negative pressure from being generated in the lubricating oil filled in the housing 7. In particular, in the present embodiment, as shown in FIG. 3, the upper dynamic pressure groove 8a1 formed in the inner peripheral surface 8a of the bearing sleeve 8 is formed in an axially asymmetric shape, so that the rotation of the hub integrated shaft 9 is performed. Along with this, the lubricating oil in the radial bearing gap is pushed downward, and the lubricating oil circulates through the communication path, thereby reliably preventing the generation of local negative pressure.

  Hereinafter, a method for manufacturing the hub integrated shaft 9 will be described.

  The hub-integrated shaft 9 is formed by molding a metal plate to form a shaped material having the shaft portion 2 and the hub portion 3 integrally, and grinding for finishing a predetermined portion of the shaped material. It is formed through a finishing process.

(1) Shaped material forming step In the shaped material forming step, first, as shown in FIG. 6 (a), from an iron-based material, for example, stainless steel, particularly ferritic stainless steel containing 0.5% or more of Ti. A metal plate 20 is prepared. For example, in the case of the hub integrated shaft 9 for the spindle motor of the 2.5 inch HDD as in this embodiment, the thickness of the metal plate is about 1 mm.

  Then, as shown in FIG. 6B, the shaft center 21 is formed by projecting the shaft center of the metal plate 20 downward by cold plastic working (deep drawing). At this time, an axial hole 21 a is formed in the shaft center of the shaft portion 21 in order to push the shaft portion 21 to protrude by a mold (not shown).

  Next, as shown in FIG.6 (c), the hub part 22 is shape | molded around the axial part 21 by cold plastic working (press work). Specifically, a disk part 22a extending from the shaft part 21 to the outer diameter, a cylindrical part 22b extending downward from the outer diameter end of the disk part 22a, and a flange part 22c extending from the lower end of the cylindrical part 22b to the outer diameter are formed. Is done. At this time, an annular recess (relief portion) 22c10 is simultaneously formed at the inner diameter end of the upper end surface 22c1 of the flange portion 22c.

  Thereafter, as shown in FIG. 6D, the tip end portion (lower end portion) of the shaft portion 21 is cut and removed, and the axial hole 21 a is opened at the lower end of the shaft portion 21. At the same time, a thread groove is formed on the inner peripheral surface of the axial hole 21 a of the shaft portion 21.

  Finally, as shown in FIG. 6 (e), the flange portion 22 c of the hub portion 22 and the metal plate 20 are separated, and the material 30 having the shaft portion 21 and the hub portion 22 is separated from the metal plate 20.

  By forming the base material 30 from the metal plate 20 in this way, the thickness of the base material 30 is approximately uniform. Specifically, the radial thickness of the shaft portion 21, the axial thickness of the disk portion 22a of the hub portion 22, the radial thickness of the cylindrical portion 22b, and the axial thickness of the flange portion 22c. However, it is almost uniform. Specifically, the thickness of the portion (the shaft portion 21 and the cylindrical portion 22b) that is squeezed by the plastic processing and extends in the axial direction is the thickness of the surface (the disk portion 22a and the flange portion 22c) in the direction orthogonal to the axial direction. Is slightly thinner. For example, when forming the shaped member 30 using the metal plate 20 of about 1 mm, the thickness of the disk portion 22a and the flange portion 22c is about 0.8 mm, whereas the thickness of the shaft portion 21 and the cylindrical portion 22b. The thickness is about 0.5 mm. That is, in this embodiment, the amount of change in thickness when obtaining the shaped member 30 from the metal plate 20 is 50% or less. Thus, since the deformation amount from the metal plate 20 is relatively small, the base material 30 can be plastically processed with high accuracy.

(2) Grinding finishing process Grinding finishing is performed on a predetermined portion of the shaped material 30 formed as described above. In the grinding finishing process shown in FIG. 7 and FIG. 8, the axial direction of the shaped material 30 is horizontal, and processing is performed, but each part of the shaped material 30 is given the same name as above. Yes.

  First, a grinding finish is applied to a predetermined portion of the hub portion 22 of the raw material 30. Specifically, as shown in FIG. 7, rotation centers 41 and 42 are attached to the axial holes 21 a of the shaft portion 21 of the shaped material 30 to rotatably support the shaped material 30, and the hub portion 22. The lower end surface 22c2 of the collar portion 22c is supported by the backing plate 43. Then, the backing plate 43 is rotationally driven to rotate the base material 30 around the shaft portion 21, and the angular grindstone 44 is brought into contact with the base material 30 in this state. Specifically, the grinding surfaces 44a, 44b, and 44c of the angular grindstone 44 are divided into an upper end surface 22c1 (corresponding to a disc mounting surface) of the flange portion 22c, an outer peripheral surface 22b1 (corresponding to a disc fitting surface) of the cylindrical portion 22b, and Abutting on the outer peripheral portion of the upper end surface 22a1 of the disk portion 22a, these surfaces are ground simultaneously. At this time, since the escape portion 22c10 is provided at the inner diameter end of the upper end surface 22c1 of the flange portion 22c, the abrasive surfaces 44a and 44b of the angular grindstone 44 are replaced by the upper end surface 22c1 of the flange portion 22c and the outer peripheral surface 22b1 of the cylindrical portion 22b. Can be adhered to.

  Next, as shown in FIG. 8, the outer peripheral surface 21 b and the lower end surface 21 c of the shaft portion 21 and the disk portion 22 a of the hub portion 22 are defined with reference to the ground finish surface of the hub portion 22 (indicated by a dotted line in the drawing). The lower end surface 22a2 (region facing the thrust bearing gap) is ground. For example, the outer peripheral portion of the upper end surface 22 a 1 of the disk portion 22 a of the hub portion 22 is attracted and supported by the magnet chuck 51, and the outer peripheral surface 22 b 1 of the cylindrical portion 22 b is slidably supported by the shoe 52. In this state, the magnet chuck 51 is rotationally driven to rotate the base material 30 around the shaft portion 21, and the angular grindstone 53 is brought into contact with the base material 30. Specifically, the abrasive surfaces 53a, 53b, and 53c of the angular grindstone 53 are in contact with the outer peripheral surface 21b of the shaft portion 21, the lower end surface 21c of the shaft portion 21, and the inner peripheral portion of the lower end surface 22a2 of the disk portion 22a. And these surfaces are ground simultaneously. Thus, the hub integrated shaft 9 (see FIG. 2) having the shaft portion 2 and the hub portion 3 is completed.

  As described above, the outer peripheral surface 2a (radial bearing surface) of the shaft portion 2 of the hub integrated shaft 9, the inner peripheral portion (thrust bearing surface of the first thrust bearing portion T1) of the lower end surface 3a1 of the disk portion 3a, and By applying a grinding finish to the lower end surface 2c of the shaft portion 2, these surfaces are finished with high accuracy, and the supporting force by the radial bearing portion and the first thrust bearing portion T2 is enhanced. Further, the upper end surface 11a1 of the flange portion 11a (the thrust bearing surface of the second thrust bearing portion T2) is brought into contact with the lower end surface 2c of the shaft portion 2 finished with high accuracy, so that the positioning accuracy of the flange portion 11a is increased. This improves the swinging of the flange portion 11a.

  Further, by simultaneously grinding the outer peripheral surface 2a of the shaft portion 2 of the hub integrated shaft 9, the inner peripheral portion of the lower end surface 3a1 of the disk portion 3a, and the lower end surface 2c of the shaft portion 2, the relative relationship between these surfaces can be reduced. Position accuracy is set to high accuracy. As a result, the inner peripheral portion (thrust bearing surface of the first thrust bearing portion T1) of the lower end surface 3a1 of the disc portion 3a with respect to the outer peripheral surface 2a (radial bearing surface) of the shaft portion 2 and the lower portion of the shaft portion 2 The relative positional accuracy of the upper end surface 11a1 (the thrust bearing surface of the first thrust bearing portion T1) of the flange portion 11a in contact with the end surface 2c is set with high accuracy. Thereby, the swinging of the hub portion 3 and the flange portion 11a during the rotation of the hub integrated shaft 9 can be more reliably suppressed, and the rotation accuracy of the hub integrated shaft 9 can be increased. For example, when the shaft diameter is about 2 to 4 mm as in this embodiment, if the hub integrated shaft 9 is formed by the above method, the deflection accuracy of each thrust bearing surface with respect to the radial bearing surface of the hub integrated shaft 9 is increased. For example, the deflection accuracy of the thrust bearing surface of the first thrust bearing portion T1 with respect to the radial bearing surface is set to 4 μm or less, and the deflection accuracy of the thrust bearing surface of the second thrust bearing portion T2 with respect to the radial bearing surface is set to 5 μm or less. can do. In other words, if these conditions are satisfied, the outer peripheral surface 2a of the shaft portion 2 of the hub integrated shaft 9, the inner peripheral portion of the lower end surface 3a1 of the disk portion 3a, and the lower end surface 2c of the shaft portion 2 are the same. It can be estimated that grinding is performed simultaneously with a grindstone.

  Further, as described above, the outer peripheral surface of the shaft portion 2 of the hub integrated shaft 9 is obtained by grinding the outer peripheral surface 21b of the shaft portion 21 with reference to the ground finish surface of the hub portion 22 processed with high accuracy. 2a (radial bearing surface) can be processed with high accuracy. In particular, the hub 21 is ground by grinding the outer peripheral surface 21b of the shaft portion 21 with reference to the upper end surface 22a1 of the disk portion 22a of the hub portion 22 simultaneously ground with the upper end surface 22c1 of the flange portion 22c corresponding to the disk mounting surface 3d. The surface accuracy of the disk mounting surface 3d with respect to the outer peripheral surface 2a of the shaft portion 2 of the integral shaft 9 is set with high accuracy. As a result, for example, the deflection accuracy of the disk mounting surface 3d with respect to the outer peripheral surface 2a of the shaft portion 2 is set to 5 μm or less, and the rotation accuracy of the disk D is increased. Moreover, in this embodiment, the disk fitting surface with respect to the outer peripheral surface 2a of the shaft part 2 is ground by grinding the outer peripheral surface 21b of the shaft part 21 on the basis of the outer peripheral surface 22b1 of the cylindrical part 22b corresponding to the disk fitting surface 3e. The coaxiality of 3e is set to 5 μm or less. In other words, if the dimensional accuracy of the disc mounting surface 3d and the disc fitting surface 3e with respect to the outer peripheral surface 2a of the shaft portion 2 is within the above range, the outer peripheral surface 2a of the shaft portion 2 is connected to the disc mounting surface 3d and the disc fitting surface. It can be estimated that the ground surface 3e (or a surface ground simultaneously with these surfaces) is ground. The definition of runout accuracy and coaxiality is based on JIS B 0021: 1998.

  In this embodiment, when the outer peripheral surface 21b of the shaft portion 21 is ground, the upper end surface 22c1 of the flange portion 22c is not directly supported, but the outer peripheral portion of the upper end surface 22a1 of the disk portion 22a is covered by the magnet chuck 51. I support it. Since the outer peripheral portion of the upper end surface 22a1 of the disk portion 22a and the upper end surface 22c1 of the flange portion 22c are ground simultaneously, the parallelism of these surfaces is set with extremely high accuracy. Therefore, by supporting the outer peripheral portion of the upper end surface 22a1 of the disk portion 22a with the magnet chuck 51, the upper end surface 22c1 of the flange portion 22c can be indirectly used as a reference. Of course, if possible, the upper end surface 22c1 of the flange 22c may be attracted and supported by the magnet chuck 51, and this surface may be directly used as a reference.

  Moreover, you may perform a surface hardening process or a coating process to the outer peripheral surface 2a of the axial part 2 of the hub integrated shaft 9 which gave grinding finishing as needed. If surface hardening treatment or coating treatment is performed prior to the above-mentioned grinding finishing step, wrinkles due to grinding can be suppressed. Moreover, if a coating process is performed after said grinding finishing process, the grinding | polishing wrinkles can be covered with a coating. Further, both surface hardening treatment and coating treatment may be performed. For example, after the surface hardening treatment is performed on the outer peripheral surface 2a of the shaft portion 2, the above-described grinding finishing process is performed, and further this surface is coated. Also good.

  The present invention is not limited to the above embodiment. Hereinafter, although other embodiment of this invention is described, the same code | symbol is attached | subjected to the location which has the same function as said embodiment, and duplication description is abbreviate | omitted.

  In the above-described embodiment, the flange portion 11a is screwed to the lower end surface 2c of the shaft portion 2. However, the present invention is not limited to this, and for example, it can be fixed by welding, adhesion, or welding. In this case, if the gap between the lower end surface 2c of the shaft portion 2 and the upper end surface 11a1 of the flange portion 11a is completely sealed with an adhesive or the like, oil leakage through the axial hole 2b of the shaft portion 2 is ensured. Can be prevented.

  In the above embodiment, the thrust bearing gap of the first thrust bearing portion T1 is formed between the upper end surface 8b of the bearing sleeve 8 and the lower end surface 3a1 of the disk portion 3a of the hub portion 3. Not limited to. For example, a thrust bearing gap of the first thrust bearing portion T1 may be formed between the upper end surface 7a2 of the housing 7 and the lower end surface 3a1 of the disk portion 3a of the hub portion 3. In this case, the outer peripheral portion of the lower end surface 3a1 of the disk portion 3a is ground.

  In the above embodiment, as shown in FIGS. 7 and 8, the disk mounting surface (upper end surface 22c1 of the flange 22c) and the disk fitting surface (the outer periphery of the cylindrical portion 22b) of the hub portion 22 of the shaped member 30 are used. The surface 22b1) is ground and the outer peripheral surface 21b of the shaft portion 21 is ground with reference to these surfaces (or the surfaces ground at the same time), but is not limited thereto. For example, the outer peripheral surface 21b of the shaft portion 21 may be ground with reference to only the disk mounting surface that has been ground.

  In the above embodiment, the lubricating fluid is a lubricating oil. However, the present invention is not limited to this. For example, a fluid such as a magnetic fluid or air can be used.

  In the above embodiment, an example in which the hub integrated shaft 9 according to the present invention is incorporated in a fluid dynamic bearing device for an HDD spindle motor is shown, but the present invention is not limited to this. For example, the hub integrated shaft of the present invention can be applied to a fluid dynamic pressure bearing device for a polygon scanner motor or a fluid dynamic pressure bearing device for a color wheel motor.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft part 3 Hub part 3d Disk mounting surface 3e Disk fitting surface 4 Stator coil 5 Rotor magnet 6 Bracket 7 Housing 8 Bearing sleeve 9 Hub integrated shaft 10 Yoke 11 Retaining member 11a Flange part 11b Fixing part 20 Metal plate 21 Shaft portion 22 Hub portion 30 Shaped material 41 Rotating center 43 Backing plate 44 Angular whetstone 51 Magnet chuck 52 Shoe 53 Angular whetstone D Disc R1, R2 Radial bearing portion T1 First thrust bearing portion T2 Second thrust Bearing part S Seal space

Claims (8)

A metal hub integrated shaft that integrally has a shaft portion and a hub portion that projects from one end of the shaft portion to the outer diameter and is formed with a rotating body mounting surface orthogonal to the axial direction, and is fixed to the other end of the shaft portion The shaft portion by the hydrodynamic action of the lubricating fluid generated in the radial bearing gap between the flange portion, the bearing member having the shaft portion inserted into the inner periphery, and the outer peripheral surface of the shaft portion and the inner peripheral surface of the bearing member. In a fluid dynamic pressure bearing device including a radial bearing portion supported in a radial direction,
A fluid dynamic bearing device in which the other end surface of the shaft portion is a ground surface and one end surface of the flange portion is brought into contact with the other end surface.   2. The fluid dynamic bearing device according to claim 1, wherein one end surface of the flange portion faces the thrust bearing gap.   A first thrust bearing portion that supports the hub integrated shaft in one thrust direction by the dynamic pressure action of a lubricating fluid generated in a thrust bearing gap between one end surface of the bearing member and one end surface of the hub portion, and the other end surface of the bearing member The fluid dynamic pressure according to claim 2, further comprising a second thrust bearing portion that supports the hub integrated shaft in the other thrust direction by the dynamic pressure action of the lubricating fluid generated in the thrust bearing gap between the flange portion and one end surface of the flange portion. Bearing device.   4. The fluid dynamic bearing device according to claim 3, wherein the one end surface of the hub portion and the other end surface of the shaft portion are simultaneously ground surfaces.   The fluid dynamic pressure bearing device according to any one of claims 1 to 4, wherein the outer peripheral surface and the other end surface of the shaft portion are simultaneously ground surfaces.   The fluid dynamic pressure bearing device according to any one of claims 1 to 5, wherein the outer peripheral surface of the shaft portion is ground based on the ground rotating body mounting surface or a surface ground simultaneously with the rotating body mounting surface.   The fluid dynamic pressure bearing device according to any one of claims 1 to 6, wherein the hub integrated shaft is formed by grinding a base material integrally formed with the shaft portion and the hub portion by plastic working of a metal plate. A hub integrated shaft integrally including a shaft portion, a hub portion projecting from one end of the shaft portion to an outer diameter, and formed with a rotating body mounting surface orthogonal to the axial direction, and a flange fixed to the other end of the shaft portion And the bearing member in which the shaft portion is inserted into the inner periphery, and the shaft portion in the radial direction by the dynamic pressure action of the lubricating fluid generated in the radial bearing gap between the outer peripheral surface of the shaft portion and the inner peripheral surface of the bearing member. A method for manufacturing a fluid dynamic bearing device comprising a supporting radial bearing portion,
A method of manufacturing a fluid dynamic bearing device, wherein the other end surface of the shaft portion is ground and the flange portion is fixed to the shaft portion in a state where the other end surface is in contact with one end surface of the flange portion.

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