JP4786157B2 - Shaft member for hydrodynamic bearing device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a shaft member for a hydrodynamic bearing device and a manufacturing method thereof. This bearing device is a spindle motor such as an information device, for example, a magnetic disk device such as an HDD, an optical disk device such as a CD-ROM, CD-R / RW, DVD-ROM / RAM, or a magneto-optical disk device such as MD or MO, It is suitable for polygon scanner motors of laser beam printers (LBP) and other small motors.

  In addition to high rotational accuracy, the various motors are required to have high speed, low cost, low noise, and the like. One of the components that determine the required performance is a bearing that supports the spindle of the motor. In recent years, the use of a hydrodynamic bearing having characteristics excellent in the required performance has been studied or actually used. Yes.

A dynamic pressure bearing is a member that rotatably supports a shaft member in a non-contact manner by the dynamic pressure action of lubricating oil generated in a bearing gap, and is used by being incorporated in a spindle motor of a disk-shaped recording medium driving device such as an HDD. The This type of hydrodynamic bearing device is provided with a radial bearing portion that supports the shaft member in a non-contact manner so as to be rotatable in the radial direction, and a thrust bearing portion that supports the shaft member in a non-contact manner so as to be rotatable in the thrust direction. A dynamic pressure generating groove (dynamic pressure groove) is formed on the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member constituting the bearing portion. Further, both end surfaces of the flange portion of the shaft member constituting the thrust bearing portion, or surfaces facing the flange surface (the end surface of the bearing sleeve, the end surface of the thrust member fixed to the housing, the inner bottom surface of the bottom of the housing, etc.) In addition, a dynamic pressure groove is formed (see, for example, Patent Document 1).

The dynamic pressure grooves are formed, for example, in a state of being arranged in a herringbone shape or a spiral shape on the outer peripheral surface of the shaft member. As a method for forming this type of dynamic pressure groove, for example, cutting (see, for example, Patent Document 2), etching (see, for example, Patent Document 3), and the like are known.
JP 2002-61641 A Japanese Patent Laid-Open No. 08-196056 Japanese Patent Laid-Open No. 06-158357

Recently, in order to cope with an increase in information recording density and high-speed rotation in information equipment, the spindle motor for the information equipment has been required to have higher rotational accuracy. Higher rotational accuracy is also required for the hydrodynamic bearing device incorporated in the motor.

  By the way, in order to increase the rotational accuracy of the hydrodynamic bearing device, it is important to manage the radial bearing gap and the thrust bearing gap in which the dynamic pressure is generated with high accuracy. In order to properly manage this gap, high dimensional accuracy is required for the shaft member of the hydrodynamic bearing device involved in the formation of the bearing gaps. In particular, when dynamic pressure grooves are formed on the shaft member side (for example, the outer peripheral surface of the shaft portion or both end surfaces of the flange portion), the processing accuracy of the dynamic pressure grooves affects the accuracy of each bearing gap. High precision machining of the groove is required. However, when an existing processing method (for example, etching or cutting) is used to increase the precision of the dynamic pressure groove processing, the processing cost is remarkably increased.

  An object of the present invention is to precisely process a dynamic pressure groove formed in a shaft member while avoiding such a rise in processing cost, and to manage a bearing gap in this type of dynamic pressure bearing device with high accuracy. .

In order to solve the above-mentioned problem, the present invention provides a metal dynamic pressure bearing device shaft member integrally including a shaft portion and a flange portion, and a plurality of dynamic pressure grooves and dynamic pressure grooves on an outer periphery of the shaft portion. the consists partition part for partitioning the herringbone pattern, chromatic and radial dynamic pressure groove regions spaced apart formed at two positions in the axial direction, and a grinding undercut portion formed between the two radial dynamic groove region by plastic working The ends of the dynamic pressure grooves are opened at both ends in the axial direction of both radial dynamic pressure groove regions without partitioning them in the partition portions, and both sides in the axial direction of the Numi portion are opened in the dynamic pressure grooves of both radial dynamic pressure groove regions. The region other than the partition portion on the outer peripheral surface of the shaft portion is smaller in diameter than the partition portion, and the outer peripheral surface of the partition portion in the radial dynamic pressure groove region is finished by grinding. A partition part here refers to the part which divides each dynamic pressure groove, and includes the back part between what is called dynamic pressure grooves. In addition, when the dynamic pressure grooves are formed to be inclined with respect to the axial direction, a so-called smooth portion that divides the inclined dynamic pressure grooves in the axial direction is also included in the partition portion.

  As described above, in the present invention, the radial dynamic pressure groove region including the dynamic pressure grooves and the partition portions that partition the dynamic pressure grooves is formed on the outer periphery of the shaft portion of the shaft member by plastic working. In addition, material can be saved without generating chips during cutting. Further, compared with the processing method by etching, the labor of masking in advance due to corrosion can be saved, so that the processing cost can be greatly reduced as a whole. In the present invention, the outer peripheral surface of the partition portion in the radial dynamic pressure groove region is a ground surface. This grinding surface is obtained by grinding the outer diameter part of the partitioning part (the part that becomes a mountain adjacent to the dynamic pressure groove) that partitions the dynamic pressure groove in the radial dynamic pressure groove region formed by plastic working. Therefore, according to this, it is possible to perform precision machining of the dynamic pressure groove region, which cannot be achieved only by plastic machining, and to obtain the outer diameter dimensional accuracy and the surface roughness with high accuracy. For this reason, according to the present invention, both improvement in machining accuracy and reduction in machining cost can be achieved, and the radial bearing gap in such a dynamic pressure bearing device can be managed with high accuracy.

  Such a dynamic pressure groove region can also be formed on both end faces of the flange portion formed integrally with the shaft portion by plastic working, for example. In this case, the flange portion forms a thrust dynamic pressure groove region composed of a dynamic pressure groove and a partition portion partitioning each dynamic pressure groove on both end faces thereof, and the axial direction of the partition portion in the thrust dynamic pressure groove region The end surface is a ground surface.

  The radial dynamic pressure groove region can be formed by rolling, for example, or can be formed by forging. Further, both the radial dynamic pressure groove region and the thrust dynamic pressure groove region can be formed by forging. Alternatively, the shaft portion and the flange portion in which the dynamic pressure groove regions are respectively formed can be integrally formed by forging, for example.

Further, the present invention includes a radial dynamic pressure groove region that includes a shaft portion and a flange portion integrally, and includes a plurality of dynamic pressure grooves and a partition portion that divides each dynamic pressure groove into a herringbone shape on the outer periphery of the shaft portion. And a Nusumi portion formed between the two radial dynamic pressure groove regions, and without dividing the end portions of the dynamic pressure grooves at the respective axial ends of both radial dynamic pressure groove regions by the partition portions. In the manufacturing method of a shaft member for a hydrodynamic bearing device in which the axially opposite sides of the Nusumi part are connected to the dynamic pressure grooves of both radial dynamic pressure groove areas, the radial dynamic pressure groove area is plasticized on the outer periphery of the shaft part of the shaft material. Formed by machining, forming the Nusumi part between two radial dynamic pressure groove areas, and making the area other than the partition part of the outer peripheral surface of the shaft part smaller than the partition part, and then the radial dynamic pressure groove area the finish of the outer circumferential surface of the partition portion in the only grinding the outer peripheral surface of the compartment unit It shall be made by.

  According to such a manufacturing method, it is possible to achieve both improvement in processing accuracy of the radial dynamic pressure groove region and reduction in processing cost. Further, if the shaft material having the shaft portion and the flange portion is integrally formed by forging, the processing cost can be further reduced or the cycle time per processed product can be shortened.

  As the plastic working of the radial dynamic pressure groove region, forging can be employed, for example. In this case, both the shaft material and the radial dynamic pressure groove region are formed by forging, and the forging of both is performed simultaneously. It is also possible. According to this, such a processing step can be simplified and the cycle time required for processing can be further shortened.

  The shaft portion of the shaft material can be subjected to a rolling process for correcting the cylindricity of the portion including the radial dynamic pressure groove region of the shaft portion. In this case, for example, the formation of the radial dynamic pressure groove region and the correction of the cylindricity of the portion including the radial dynamic pressure groove region of the shaft portion are both performed by rolling, and both the rolling processes are performed simultaneously. This simplifies the machining process and shortens the cycle time. As a result, the mass productivity of processed products can be dramatically improved.

  Alternatively, the shaft material is formed and the thrust dynamic pressure groove region formed by the dynamic pressure grooves and the partition portions defining the respective dynamic pressure grooves are formed on both end surfaces of the flange portion by forging, and both are forged. Processing can also be performed simultaneously. According to this, the machining process related to the formation of the shaft material and the thrust dynamic pressure groove region can be simplified, and the machining time can be shortened.

  The shaft member for a hydrodynamic bearing device includes, for example, a shaft member for a hydrodynamic bearing device, and a sleeve member in which the shaft member is inserted into the inner periphery and forms a radial bearing gap with the shaft member. It can be provided as a hydrodynamic bearing device that holds the shaft member and the sleeve member in a non-contact manner by the dynamic pressure action of the fluid generated in the gap. The bearing sleeve can be made of, for example, oil-impregnated sintered metal, and a thrust dynamic pressure groove region can be formed on the axial end face instead of the end face of the flange portion.

  Moreover, the said dynamic pressure bearing apparatus can also be provided as a motor provided with this dynamic pressure bearing apparatus, a rotor magnet, and a stator coil.

  According to the present invention, the dynamic pressure groove formed in the shaft member can be processed with high accuracy while avoiding such increase in processing cost. In addition, the bearing performance of the hydrodynamic bearing device can be stably exhibited over a long period of time by managing the bearing gap in the hydrodynamic bearing device incorporating the shaft member with high accuracy.

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

  FIG. 3 conceptually shows a configuration example of a spindle motor for information equipment incorporating the fluid dynamic bearing device 1 according to one embodiment of the present invention. This spindle motor for information equipment is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a disk hub 3 attached to the shaft member 2, For example, a stator coil 4 and a rotor magnet 5 which are opposed to each other via a gap in the radial direction, and a bracket 6 are provided. The stator coil 4 is attached to the outer periphery of the bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The bracket 6 has the hydrodynamic bearing device 1 mounted on the inner periphery thereof. The disk hub 3 holds one or more disk-shaped information recording media (hereinafter simply referred to as disks) D such as a magnetic disk on the outer periphery thereof. In the spindle motor for information equipment, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the magnetic force between the stator coil 4 and the rotor magnet 5, and accordingly, the disk hub 3 and the disk hub 3 hold the rotor magnet 5. The disk D rotates together with the shaft member 2.

  FIG. 4 shows an example of the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 mainly includes a housing 7 having a bottom 7b at one end, a bearing sleeve 8 fixed to the housing 7, a shaft member 2 inserted into the inner periphery of the bearing sleeve 8, and a seal member 9. Configured as a simple component. For convenience of explanation, the following description will be made with the bottom 7b side of the housing 7 as the lower side and the side opposite the bottom 7b as the upper side.

  As shown in FIG. 4, the housing 7 is positioned on one end side of the side portion 7 a and the side portion 7 a formed in a cylindrical shape with a resin material such as LCP, PPS, or PEEK, and is formed of, for example, a metal material. And a bottom portion 7b. In this embodiment, the bottom portion 7b is formed as a separate body from the side portion 7a and is retrofitted to the lower inner periphery of the side portion 7a. In this embodiment, the bottom portion 7b is formed separately from the side portion 7a and is fixed to the lower inner periphery of the side portion 7a. However, the bottom portion 7b can be integrally molded with the side portion 7a, for example, with a resin material. .

  The bearing sleeve 8 is formed in a cylindrical shape with a porous body made of sintered metal, in particular, a sintered metal porous body mainly composed of copper, and is fixed at a predetermined position on the inner peripheral surface 7 c of the housing 7. The

  A cylindrical surface 8 a having a perfect circular cross section is formed on the inner periphery of the bearing sleeve 8 in the axial direction.

  One or a plurality of axial grooves 8b1 are formed on the outer peripheral surface 8b of the bearing sleeve 8 over the entire axial length. In this embodiment, three axial grooves 8b1 are formed at equal intervals in the circumferential direction.

  As shown in FIG. 4, the sealing member 9 as a sealing means is formed in a ring shape separate from the housing 7 with a soft metal material such as brass, other metal materials, or a resin material. It is fixed to the inner periphery of the upper part of 7a by means such as press fitting or adhesion. In this embodiment, the inner peripheral surface 9 a of the seal member 9 is formed in a cylindrical shape, and the lower end surface 9 b of the seal member 9 is in contact with the upper end surface 8 d of the bearing sleeve 8.

  For example, as shown in FIG. 1, the shaft member 2 is formed of a metal material such as stainless steel and has a T-shaped cross section integrally including a shaft portion 21 and a flange portion 22 provided at the lower end of the shaft portion 21. . As shown in FIG. 4, radial dynamic pressure groove regions 23 a and 23 b facing the cylindrical surface 8 a formed on the inner periphery of the bearing sleeve 8 are separated in the axial direction in a partial cylindrical region on the outer periphery of the shaft portion 21. Two places are formed. The upper and lower two dynamic pressure groove regions 23a and 23b are each composed of a plurality of dynamic pressure grooves 23a1 and 23b1 and partition portions 23a2 and 23b2 that partition the dynamic pressure grooves 23a1 and 23b1, respectively. As shown in FIG. 1, both form a herringbone shape. Of these, the upper radial dynamic pressure groove region 23a is formed to be axially asymmetric with respect to the axial center m (the axial center of the upper and lower inclined groove regions). The direction dimension X1 is larger than the axial direction dimension X2 of the lower region.

  For example, as shown in FIG. 2A, a thrust dynamic pressure groove region 22a is formed on the entire upper surface of the flange portion 22 or a partial annular region. Further, a thrust dynamic pressure groove region 22b is formed in a partial annular region on the lower end surface of the flange portion 22 as shown in FIG. 2B, for example. These thrust dynamic pressure groove regions 22a and 22b are each composed of a plurality of dynamic pressure grooves 22a1 and 22b1 and partitioning portions 22a2 and 22b2 that partition the dynamic pressure grooves 22a1 and 22b1, respectively. In this embodiment, FIG. ) And (b), each has a spiral shape. In addition, each thrust dynamic pressure groove area | region 22a, 22b can take not only the shape shown in particular but shapes, such as a herringbone shape, for example. Also, different dynamic pressure groove shapes can be formed on the upper and lower surfaces.

  Above one of the radial dynamic pressure groove regions 23a, a tapered surface 24 that gradually decreases in diameter toward the shaft tip is formed adjacently, and a cylindrical surface 25 that serves as a mounting portion of the disk hub 3 is formed above the tapered surface 24. ing. Between the two radial dynamic pressure groove regions 23a and 23b, between the other radial dynamic pressure groove region 23b and the flange portion 22 and between the taper surface 24 and the cylindrical surface 25, an annular nose portion 26, 27 and 28 are formed.

  Between the taper surface 24 of the shaft portion 21 and the inner peripheral surface 9a of the seal member 9 facing the taper surface 24, an annular seal whose radial dimension gradually increases from the bottom 7b side of the housing 7 upward. A space S is formed. In the hydrodynamic bearing device 1 (see FIG. 4) after the assembly is completed, the oil level is maintained within the range of the seal space S.

  In the dynamic pressure bearing device 1 configured as described above, when the shaft member 2 is rotated, the cylindrical surface 8a formed on the inner periphery of the bearing sleeve 8 and the radial dynamic pressure groove of the shaft portion 21 facing the cylindrical surface 8a. The dynamic pressure of the lubricating oil is generated in the radial bearing gap between the regions 23a and 23b, and the shaft portion 21 of the shaft member 2 is supported in a non-contact manner so as to be rotatable in the radial direction. As a result, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in a non-contact manner so as to be rotatable in the radial direction are formed. Further, the first thrust bearing gap between the lower end surface 8c of the bearing sleeve 8 and the thrust dynamic pressure groove region 22a on the upper side (shaft side) of the flange portion 22 facing the lower end surface 8c, and the upper side of the bottom portion 7b. The dynamic pressure of the lubricating oil is generated in the second thrust bearing gap between the end surface 7b1 and the thrust dynamic pressure groove region 22b on the lower side (on the opposite shaft side) of the flange portion 22 facing the upper end surface 7b1, respectively. The two flange portions 22 are supported in a non-contact manner so as to be rotatable in both thrust directions. Thereby, the 1st thrust bearing part T1 and the 2nd thrust bearing part T2 which support the shaft member 2 in a non-contact manner so as to be rotatable in the thrust direction are formed.

  Hereinafter, the manufacturing method of the shaft member 2 which comprises the said dynamic-pressure bearing apparatus 1 is demonstrated.

  The shaft member 2 is manufactured mainly through two steps of (A) forming step and (B) grinding step. Of these, the molding process (A) includes a shaft material molding process (A-1), a thrust dynamic pressure groove area molding process (A-2), and a radial dynamic pressure groove area molding process (A-3). And shaft part straightening (A-4). The grinding process (B) includes a width grinding process (B-1), a whole surface grinding process (B-2), and a finish grinding process (B-3).

(A) Molding step (A-1) Shaft material molding process, and (A-2) Thrust dynamic pressure groove region molding process First, a metal material such as stainless steel, which is a material of the shaft member 2 to be molded, is molded into a mold. For example, as shown in FIG. 5, for example, as shown in FIG. 5, a shaft-corresponding region (hereinafter simply referred to as a shaft portion) 11 and a flange-corresponding region (hereinafter simply referred to as a flange portion) are used. That is, the shaft material 10 having the integral body 12 is formed (shaft material forming process (A-1)). Moreover, the metal mold | die used for the forge molding of this shaft raw material 10 serves as the metal mold | die for shape | molding the thrust dynamic pressure groove area | region 12a, 12b in the flange part 12 in this embodiment. Therefore, at the same time as forging of the shaft material 10, plastic working is performed at locations corresponding to both end faces of the flange portion 12. For example, as shown in FIGS. 6 (a) and 6 (b), a plurality of dynamic pressure grooves 12 a 1, Thrust dynamic pressure groove regions 12a (shaft side) and 12b (counter shaft side) are formed (thrust dynamic pressure groove region), which includes 12b1 and partition portions 12a2 and 12b2 that partition these dynamic pressure grooves 12a1 and 12b1. Forming process (A-2)).

  As a method of cold forging in the forming step, any of extrusion processing, upsetting processing, heading processing, or the like, or a combination thereof can be adopted. In the illustrated example, the outer peripheral surface 11a of the shaft portion 11 after forging has a different diameter shape with the tapered surface 14 and the tapered surface 14 being continuous upward and a cylindrical surface 15 having a smaller diameter than that of the other portion. The tapered surface 14 may be omitted and the uniform diameter may be formed over the entire length. In this embodiment, the case where the forming of the shaft material 10 and the forming of the thrust dynamic pressure groove regions 12a and 12b are performed simultaneously by forging is described. However, both steps are not necessarily performed at the same time. Then, the thrust dynamic pressure groove regions 12a and 12b may be formed by plastic working, for example, forging or pressing.

(A-3) Radial dynamic pressure groove region forming process, and (A-4) Shaft part straightening process The shaft part 11 of the shaft material 10 forged and formed in the previous step is omitted, for example, although a pair of rolling parts is omitted. By pressing and clamping with a forming die (for example, a flat die or a round die) and reciprocating the pair of rolling dies in opposite directions, either one of the pair of rolling dies is held on one clamping surface. The previously formed dynamic pressure groove transfer surface is transferred to the outer peripheral surface 11a of the shaft portion 11 (radial dynamic pressure groove region forming process (A-3)). In addition, in this embodiment, the pair of rolling dies also serves as a correction tool for correcting the shaft portion 11 of the shaft material 10, so that the dynamic pressure groove is formed on the outer peripheral surface 11 a of the shaft portion 11. Simultaneously with the transfer, a rolling process for correcting the cylindricity is performed (shaft part correcting process (A-4)). As a result, on the outer peripheral surface 11a of the shaft portion 11, for example, radial dynamic pressure groove regions 13a and 13b having a shape as shown in FIG. Among them, the surface 13 including the radial dynamic pressure groove regions 13a and 13b (for example, the bottom surfaces of the dynamic pressure grooves 13a1 and 13b1 and the outer peripheral surfaces of the partition portions 13a2 and 13b2 that partition the dynamic pressure grooves 13a1 and 13b1) is corrected and corrected. The cylindricity of the processed surface 13 is improved within a desired range (for example, 10 μm or less). At the same time, the cylindrical surface 15 at the upper end of the shaft portion 11 is also corrected, and the cylindricity of the cylindrical surface 15 is similarly improved.

  As described above, the formation of the radial dynamic pressure groove regions 13a and 13b and the correction of the shaft outer peripheral surface 11a can be both performed by rolling and at the same time. It is also possible to take a procedure of rolling the radial dynamic pressure groove regions 13a and 13b on the surface subjected to the straightening process after the straightening process is performed on 11a. In this case, various processing methods such as rolling, squeezing and ironing, or sizing by split-type press (pinching), etc. can be employed for the correction of cylindricity. Further, the correction process can be performed over the entire length of the outer peripheral surface 11a of the shaft portion 11 and can be performed only on a part of the outer peripheral surface 11a as long as the radial dynamic pressure groove regions 13a and 13b are included.

  In this manner, the shaft material 10 integrally including the shaft portion 11 and the flange portion 12 and the thrust dynamic pressure groove regions 12a and 12b on both end surfaces of the flange portion 12 are both forged and simultaneously performed. In addition, since the radial dynamic pressure groove regions 13a and 13b and the straightening of the shaft outer peripheral surface 11a are both rolled and performed at the same time, the machining process is simplified and the machining time is greatly increased. Can be shortened. In addition, by adopting forging and rolling processes that have a shorter cycle time per workpiece compared to cutting and etching processes, the processing time can be further shortened, further reducing costs. Mass productivity can be improved.

  At the stage where the molding step (A) is completed, as shown in FIG. 7A, for example, in the thrust dynamic pressure groove region 12b, the height from the bottom surface 12b3 of the dynamic pressure groove 12b1 to the axial end surface 12b4 of the partition portion 12b2 is increased. The length h1 is set to an appropriate value in consideration of the forming accuracy during the forging process and the grinding allowance for the width grinding process (B-1) of the shaft material 10 described later. Further, in the radial dynamic pressure groove regions 13a and 13b, the height (not shown) from the bottom surface of each of the dynamic pressure grooves 13a1 and 13b1 to the outer peripheral surface of each of the partition portions 13a2 and 13b2, and the thrust dynamic pressure groove on the shaft portion 11 side In the region 12a, the height (not shown) from the bottom surface of the dynamic pressure groove 12a1 to the end surface in the axial direction of the partition portion 12a2 is the molding accuracy at the time of the forging process and the overall grinding process (B- In consideration of the grinding allowance in the case of 2) and finish grinding (B-3), it is set to an appropriate value.

(B) Grinding Step (B-1) Width Grinding Work The opposite shaft portion on the side where the shaft end surface 11b and the thrust dynamic pressure groove region 12b of the flange portion 12 are formed, which are both end surfaces of the shaft material 10 that has undergone the forming step. A side end surface (see FIG. 6B) is ground using the surface 13 subjected to the correction processing as a reference. For example, as shown in FIGS. 8A and 8B, a grinding device 40 used in this grinding process includes a carrier 41 that holds a plurality of shaft materials 10 as workpieces, and a shaft material 10 that is held by the carriers 41. A pair of grindstones 42 and 42 that grind the end surface on the side opposite to the shaft including the shaft end surface 11b and the thrust dynamic pressure groove region 12b of the flange portion 12 are provided.

  As shown in the drawing, a plurality of notches 43 are provided at equal pitches in the circumferential direction in a partial region in the circumferential direction of the outer peripheral edge of the carrier 41. The shaft material 10 is accommodated in the notch 43 in a state in which the straightened surface 13 is in angular contact with the inner surface 43 a of the notch 43. The straightened surface 13 of the shaft material 10 protrudes slightly from the outer peripheral surface of the carrier 41, and a belt 44 is stretched on the outer diameter side of the carrier so as to constrain the protruding portion of the shaft material 10 from the outer diameter side. Has been. For example, as shown in FIG. 9, a pair of grindstones 42, 42 face each other (grinding surfaces) at predetermined intervals on both ends in the axial direction of the carrier 41 in which the shaft material 10 is accommodated in the notch 43. Coaxially arranged.

  As the carrier 41 rotates, the shaft material 10 is sequentially put into the notch 43 from a fixed position. The thrown shaft material 10 traverses from the outer diameter end to the inner diameter end on the end faces of the rotating grindstones 42 and 42 in a state where the dropping from the notch 43 is restrained by the belt 44. Along with this, both end surfaces of the shaft material 10, in other words, the shaft end surface 11b and the non-shaft side end surface including the thrust dynamic pressure groove region 12b of the flange portion 12 are ground by the end surfaces of the grindstones 42, 42 (see FIG. 9). At this time, since the straightened surface 13 of the shaft material 10 is supported by the carrier 41 and the straightened surface 13 has a high degree of cylindricity, the perpendicularity between the rotation axis of the grindstone 42 and the ground surface of the grindstone 42 in advance, If the parallelism between the rotation axis of the grindstone 42 and the rotation axis of the carrier 41 is managed with high accuracy, both end surfaces of the shaft material 10 (the shaft end surface 11b, The end surface on the side opposite to the shaft portion including the thrust dynamic pressure groove region 12b of the flange portion 12) can be finished with high accuracy, and the value of the squareness with respect to the straightened surface 13 can be kept small. Moreover, the axial direction width | variety (full length including the flange part 12) of the shaft raw material 10 is finished to a predetermined dimension.

In this grinding process, as described above, the thrust dynamic pressure groove region 12b of the flange portion 12 is ground, for example, as shown in FIG. 7 (b), partition section 12b2 is given from the height h ₁ at the time of forging Is ground by a grinding allowance (h ₁ -h _{2 in} the figure). Thereby, the height of the partition portion 12b2 (depth of the dynamic pressure groove 12b1) is aligned to a predetermined value h ₂ (for example, 3 μm to 15 μm), and the opposing member (in this embodiment, the bottom portion 7b of the housing 7). Can be managed with high accuracy at intervals of several μm to several tens of μm.

(B-2) Whole surface grinding process Next, the outer periphery of the shaft material 10 with reference to both end surfaces of the ground shaft material 10 (the end surface 11b of the flange portion, the opposite end surface including the thrust dynamic pressure groove region 12b of the flange portion 12). Grinding of the end face on the shaft part side including the surface 10a and the thrust dynamic pressure groove region 12a of the flange part 12 is performed. A grinding device 50 used in this grinding process performs plunge grinding with a grindstone 53 while pressing a backing plate 54 and a pressure plate 55 against both end surfaces of the shaft material 10 as shown in FIG. The straightened surface 13 of the shaft material 10 is rotatably supported by a shoe 52.

  The grindstone 53 is a general-purpose grindstone provided with a grinding surface 56 corresponding to the outer peripheral surface shape of the shaft member 2 as a finished product. The grinding surface 56 includes a cylindrical grinding portion 56a that grinds the outer circumferential surface 11a over the entire axial length of the shaft portion 11 and the outer circumferential surface 12c of the flange portion 12, and a shaft portion side end surface including the thrust dynamic pressure groove region 12a of the flange portion 12. The surface grinding part 56b which grinds. In the illustrated example, the grindstone 53 includes, as the cylindrical grinding portion 56a, portions 56a1 and 56a2 for grinding the regions corresponding to the radial dynamic pressure groove regions 23a and 23b of the shaft member 2, portions 56a3 for grinding the regions corresponding to the tapered surface 24, A portion 56a4 for grinding a region corresponding to the cylindrical surface 25, portions 56a5 to 56a7 for grinding each of the portions 26 to 28, and a portion 56a8 for grinding a region corresponding to the outer peripheral surface 22c of the flange portion 22 are provided.

  The grinding process in the grinding apparatus 50 having the above-described configuration is performed according to the following procedure. First, with the shaft material 10 and the grindstone 53 rotated, the grindstone 53 is fed in an oblique direction (in the direction of arrow 1 in the figure), and the flange portion 12 shaft side end surface (the thrust dynamic pressure groove region 12a side) of the shaft material 10 is sent. ) Is pressed against the surface grinding portion 56b of the grindstone 53, and the shaft portion side end surface including the thrust dynamic pressure groove region 12a of the flange portion 12 is ground. Thereby, the flange 22 of the shaft member 2 and the shaft-side end surface are formed, and the grinding of the thrust dynamic pressure groove region 12a is completed, so that the thrust dynamic pressure groove region 22a of the shaft member 2 is formed. Next, the grindstone 53 is fed in a direction orthogonal to the rotational axis of the shaft blank 10 (in the direction of arrow 2 in the figure), and the grindstone 53 is placed on the outer circumferential surface 11 a of the shaft portion 11 and the outer circumferential surface 12 c of the flange portion 12. The cylindrical grinding portion 56a is pressed to grind the surfaces 11a and 12c. Thereby, among the outer peripheral surface of the shaft portion 21 of the shaft member 2, the regions corresponding to the radial dynamic pressure groove regions 23a, 23b and the cylindrical surface 25 are ground, respectively, and the tapered surface 24, the outer peripheral surface 22c of the flange portion 22, Further, each of the nosumi portions 26 to 28 is formed. In the above grinding, for example, as shown in FIG. 10, it is preferable to perform grinding while measuring the remaining grinding allowance with a measurement gauge 57.

  In this grinding step (entire grinding), the partition portion 12a2 of the thrust dynamic pressure groove region 12a formed on the end surface on the shaft portion side of the flange portion 12 is, for example, omitted, but in the case of the thrust dynamic pressure groove region 12b In the same manner as described above, grinding is performed for a predetermined grinding allowance from the height during forging. As a result, the height of the partition portion 12a2 (depth of the dynamic pressure groove 12a1) is set to a predetermined value, and a thrust bearing between the opposing member (the lower end surface 8c of the bearing sleeve 8 in this embodiment) is opposed. The gap is managed with high accuracy. In this embodiment, since the accuracy of the perpendicularity of both end faces (shaft end face 11b, flange part 12 opposite end part end face) of the shaft blank 10 is determined in advance by width grinding, the thrust dynamic pressure groove region The grinding of 12a can be performed more precisely.

(B-3) Finishing grinding process (B-2) Of the surfaces ground by the whole surface grinding process, the final grinding is performed in the regions corresponding to the radial dynamic pressure groove regions 23 a and 23 b and the cylindrical surface 25 of the shaft member 2. Apply finish grinding. The grinding apparatus used for this grinding process is a cylindrical grinder shown in FIG. 11 that performs plunge grinding with the grindstone 63 while rotating the shaft material 10 sandwiched between the backing plate 64 and the pressure plate 65. The shaft material 10 is rotatably supported by the shoe 62. The grinding surface 63a of the grindstone 63 includes a first cylindrical grinding portion 63a1 for grinding a region corresponding to the radial dynamic pressure groove regions 23a and 23b of the shaft member 2 (regions indicated by 13a and 13b in the figure), and a cylindrical surface 25. And a second cylindrical grinding portion 63a2 for grinding a region corresponding to (a region indicated by 15 in the figure).

  In the grinding device 60 having the above-described configuration, the radial dynamic pressure groove regions 23a, 23b and the regions 13a, 13b, and 15 corresponding to the cylindrical surface 25 are ground by applying a radial feed to the rotating grindstone 63. Is finished to the final surface accuracy. In this grinding step, the partitioning portions 13a2 and 13b2 of the radial dynamic pressure groove regions 13a and 13b are not illustrated, for example, but the height at the time of rolling forming is the same as in the case of the thrust dynamic pressure groove regions 12a and 12b. Grinding is performed for a predetermined grinding allowance. As a result, the heights of the partition portions 13a2 and 13b2 (the depths of the dynamic pressure grooves 13a1 and 13b1) are adjusted to a predetermined value, and between the opposing members (in this embodiment, the cylindrical surface 8a of the bearing sleeve 8). The radial bearing clearance is managed with high accuracy.

  After passing through the forming step (A) and the grinding step (B), the shaft member 2 shown in FIG. 1 is completed by performing heat treatment and cleaning treatment as necessary.

  The shaft member 2 manufactured by the above-described manufacturing method has radial dynamic pressure groove regions 23a and 23b formed on the outer periphery of the shaft portion 21 at two locations in the upper and lower portions by rolling, and the radial dynamic pressure groove region 23a, The outer peripheral surfaces of the partition portions 23a2 and 23b2 of 23b form a ground surface. Further, thrust dynamic pressure groove regions 22a and 22b formed by forging are formed on both end surfaces of the flange portion 22, and the axial end surfaces of the thrust dynamic pressure groove regions 22a and 22b are ground surfaces. The grinding surfaces of the partition portions 23a2 and 23b2 in the radial dynamic pressure groove regions 23a and 23b are formed during (B-2) full surface grinding and (B-3) finish grinding. Further, the grinding surface of the partition portion 22a2 in the thrust dynamic pressure groove region 22a is (B-2), and the grinding surface of the partition portion 22b2 in the thrust dynamic pressure groove region 22b is (B-1) width grinding. Each is formed at the time.

  As described above, the radial dynamic pressure groove regions 13a and 13b of the shaft material 10 are formed by rolling, and the outer diameter portions of the partition portions 13a2 and 13b2 are ground in the radial dynamic pressure groove regions 13a and 13b. The outer diameter dimensional accuracy and the surface roughness can be finished with high accuracy while the dynamic pressure groove regions 23a and 23b are formed at low cost. For the same reason, the thrust dynamic pressure groove regions 22a and 22b can achieve both low-cost molding and high-precision finishing. Thereby, the radial bearing gap and the thrust bearing gap in the fluid dynamic bearing device 1 can be managed with high accuracy, and the bearing performance can be stably exhibited.

Moreover, according to the said manufacturing method, the cylindrical degree of the radial dynamic pressure groove area | regions 23a and 23b formed in the axial part 21 outer periphery can also be finished with high precision. Thereby, for example, the variation in the circumferential direction or the axial direction of the radial bearing gap formed between the inner circumference of the bearing sleeve 8 and the cylindrical surface 8a in the hydrodynamic bearing device 1 is suppressed within a predetermined range. The adverse effect on the bearing performance due to the variation in the radial bearing gap can be avoided. Further, the grinding allowance (h ₁ -h _{2 in} FIG. 7B) at the time of grinding varies depending on the forming accuracy at the time of forging or roll forming, as shown in this embodiment. By correcting the cylindricity of the shaft portion 21, it is possible to improve the forming accuracy of the partition portions 23a2 and 23b2 particularly in the radial dynamic pressure groove regions 23a and 23b, and to reduce the grinding allowance during grinding. As a result, the processing time can be further shortened and the processing cost can be reduced. Or the grinding allowance at the time of grinding can also be reduced by raising the shaping | molding precision of the dynamic pressure groove area | region at the time of forge or roll forming.

  Further, in this embodiment, since the finish grinding process (see FIG. 11) is performed on the region corresponding to the cylindrical surface 25 of the shaft portion 21, the cylindricity of the cylindrical surface 25 is also finished with high accuracy, and the disk hub 3 and the like. Assembling accuracy when attaching the member to the shaft member 2 is improved. As a result, it is possible to improve the accuracy when fixing a clamper or the like for holding the disk D to the disk hub 3 to the shaft member 2, and the shaft member of the disk D clamped and fixed between the clamper and the disk hub 3. Assembling accuracy with respect to 2 is further increased, and further improvement in motor performance is achieved.

  Further, as described above, if the radial dynamic pressure groove regions 23 a and 23 b are formed on the outer periphery of the shaft member 2, the dynamic pressure groove processing on the inner periphery of the bearing sleeve 8 becomes unnecessary. It can be set as the cylindrical surface 8a, and such processing cost can be reduced. Further, if it is not necessary to process a dynamic pressure groove on the inner periphery of the bearing sleeve 8, the bearing sleeve 8 and the housing 7 need not be formed as separate members. be able to. Thereby, the number of parts can be reduced and the manufacturing cost can be reduced.

  In the above embodiment, the case where the radial dynamic pressure groove regions 23a and 23b are formed by rolling is described. However, for example, the radial dynamic pressure simultaneously with the forging of the shaft material or the thrust dynamic pressure groove region. It is also possible to forge the groove regions 23a and 23b. In this case, the dynamic pressure groove shape is not particularly limited by forging, and various dynamic pressure groove shapes such as a herringbone shape and a spiral shape can be employed.

  Moreover, although the above embodiment demonstrated the case where the thrust dynamic pressure groove area | regions 22a and 22b were formed in the both end surfaces of the flange part 22, it does not restrict in particular to this form, for example, respectively opposes the both end surfaces of the flange part 22. A thrust dynamic pressure groove region can be provided on the lower end surface 8c of the bearing sleeve 8 and the upper end surface 7b1 of the bottom 7b.

  Moreover, in the above embodiment, the inside of the hydrodynamic bearing device 1 is filled, and the radial bearing gap between the bearing sleeve 8 and the shaft member 2 and the thrust between the bearing sleeve 8 and the housing 7 and the shaft member 2 are filled. Although the lubricating oil is exemplified as the fluid that causes the dynamic pressure action in the bearing gap, it is not particularly limited to this fluid. A fluid capable of generating a dynamic pressure in each bearing gap having the dynamic pressure groove region, for example, a gas such as air, or a fluid lubricant such as a magnetic fluid may be used.

It is a side view of the shaft member for fluid dynamic bearing devices concerning one embodiment of the present invention. (A) is the top view which looked at the flange part of the shaft member from arrow a, (b) is the bottom view which looked at the flange part from arrow b. It is sectional drawing of the spindle motor for information devices incorporating the dynamic pressure bearing apparatus provided with the shaft member. It is a longitudinal cross-sectional view of a fluid dynamic bearing device. It is a side view of the shaft raw material shape | molded by the forging process. (A) is the top view which looked at the flange part of the shaft raw material from arrow a, (b) is the bottom view which looked at the flange part from arrow b. (A) is an enlarged sectional view of the thrust dynamic pressure groove region formed on the end surface on the opposite shaft side of the flange portion before grinding, and (b) is an enlarged sectional view of the thrust dynamic pressure groove region after grinding. is there. (A) is the schematic which shows an example of the grinding apparatus which concerns on the width grinding process of a shaft raw material, (b) is an enlarged view of the notch periphery of the carrier holding a shaft raw material. It is a partial cross section figure showing an example of a grinding device concerning the above-mentioned width grinding process. It is the schematic which shows an example of the grinding device which concerns on the shaft material whole surface grinding process. It is the schematic which shows an example of the grinding apparatus which concerns on the grinding finishing process of a shaft raw material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 3 Disc hub 4 Stator coil 5 Rotor magnet 7 Housing 8 Bearing sleeve 9 Seal member 10 Shaft material 11 Shaft part 11b End surface 12 Flange part 12a, 12b Thrust dynamic pressure groove area | region 12a1, 12b1 Dynamic pressure groove 12a2, 12b2 Partition portion 12b3 Bottom surface 12b4 Axial end surface 13 Straightening processed surface 13a, 13b Radial dynamic pressure groove region 13a1, 13b1 Dynamic pressure groove 13a2, 13b2 Partition portion 14 Tapered surface 15 Cylindrical surface 21 Shaft portion 21b End surface 22 Flange portion 22a, 22b Thrust dynamic pressure groove region 22a1, 22b1 Dynamic pressure groove 22a2, 22b2 Partition portion 23a, 23b Radial dynamic pressure groove region 23a1, 23b1 Dynamic pressure groove 23a2, 23b2 Partition portion 24 Tapered surface 25 Cylindrical surface 26, 27, 28 Nusumi portion 40 Grinding device 41 Carrier 42 Grinding wheel 43 Notch 43a Inner surface 50, 60 Grinding device 52, 62 Shoe 53, 63 Grinding wheel 54, 64 Backing plate 55, 65 Pressure plate 56 Grinding surface 56a Cylindrical grinding unit 56b Surface grinding unit 57, 67 Measuring gauge 63 Grinding wheel 63a Grinding surface h1 Height of the partition part before grinding h2 Height of the partition part after grinding D Disk S Seal space R1, R2 Radial bearing part T1, T2 Thrust bearing part

Claims (13)

In a shaft member for a hydrodynamic bearing device that is integrally provided with a shaft portion and a flange portion,
On the outer periphery of the shaft portion, a plurality of dynamic pressure grooves and a partition portion that divides the dynamic pressure grooves into a herringbone shape, a radial dynamic pressure groove region that is formed at two locations in the axial direction by plastic working, and two A radial portion formed between the radial dynamic pressure groove regions, and the end portions of the dynamic pressure grooves are opened at both ends in the axial direction of both radial dynamic pressure groove regions without being divided by the partition portions. The axially opposite sides of the portion are connected to the dynamic pressure grooves of both radial dynamic pressure groove regions, and the region other than the partition portion on the outer peripheral surface of the shaft portion has a smaller diameter than the partition portion, and the outer periphery of the partition portion in the radial dynamic pressure groove region A shaft member for a hydrodynamic bearing device, wherein the surface is finished by grinding.   A thrust dynamic pressure groove region including a plurality of dynamic pressure grooves and a partition portion partitioning each dynamic pressure groove is formed by plastic working on both end faces of the flange portion, and the axial direction of the partition portion in the thrust dynamic pressure groove region The shaft member for a hydrodynamic bearing device according to claim 1, wherein the end surface is a ground surface.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein the radial dynamic pressure groove region is formed by rolling or forging.   3. The shaft member for a hydrodynamic bearing device according to claim 2, wherein the thrust hydrodynamic groove region is formed by forging.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein the shaft portion and the flange portion are integrally formed by forging.   A shaft member for a hydrodynamic bearing device according to any one of claims 1 to 5, and a sleeve member in which the shaft member is inserted into an inner periphery and forms a radial bearing gap with the shaft member, A hydrodynamic bearing device that holds the shaft member and the sleeve member in a non-contact manner by a hydrodynamic action of a fluid generated in a radial bearing gap.   The hydrodynamic bearing device according to claim 6, wherein the sleeve member is made of oil-impregnated sintered metal.   The hydrodynamic bearing device according to claim 6, wherein a hydrodynamic groove for generating a hydrodynamic action of fluid is formed asymmetrically in the axial direction on the outer peripheral surface of the shaft portion facing the radial bearing gap.   A motor comprising the hydrodynamic bearing device according to any one of claims 6 to 8, a rotor magnet, and a stator coil. A shaft portion and a flange portion are integrally provided, and on the outer periphery of the shaft portion, a plurality of dynamic pressure grooves and a radial dynamic pressure groove region including a partition portion that divides each dynamic pressure groove into a herringbone shape, and two radial motions and a grinding undercut portion formed between the groove regions, in each of the axial ends of the two radial dynamic pressure groove region, the end of the dynamic pressure grooves is opened without partitioned by partition portion, grinding undercut portion In the method of manufacturing a shaft member for a hydrodynamic bearing device in which both axial sides are connected to the hydrodynamic grooves in both radial hydrodynamic groove regions ,
The radial dynamic pressure groove region is formed on the outer periphery of the shaft portion of the shaft material by plastic working, and the Nusumi portion is formed between the two radial dynamic pressure groove regions, so that a region other than the partition portion on the outer peripheral surface of the shaft portion is formed. a smaller diameter than the partition part, then, the finish of the outer circumferential surface of the partition portion in the radial dynamic pressure groove region, the dynamic pressure bearing device and performs subjected to grinding only the outer peripheral surface of the compartment unit Manufacturing method of shaft member.   11. The method for manufacturing a shaft member for a hydrodynamic bearing device according to claim 10, wherein both the shaft material and the radial dynamic pressure groove region are formed by forging, and the forging process of both is simultaneously performed.   The formation of the radial dynamic pressure groove region and the correction of cylindricity of the portion including the radial dynamic pressure groove region of the shaft portion are both performed by rolling, and both of the rolling processes are simultaneously performed. Item 11. A method for producing a shaft member for a hydrodynamic bearing device according to Item 10.   Forming the shaft material and forming a thrust dynamic pressure groove region composed of a dynamic pressure groove and a partition portion that divides each dynamic pressure groove on both end faces of the flange portion are both performed by forging, and both are forged. The method for manufacturing a shaft member for a hydrodynamic bearing device according to claim 10 or 11, wherein the steps are performed simultaneously.

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