JP2004211796A - Method of manufacturing thrust plate and shaft for dynamic pressure bearing, dynamic pressure bearing, spindle motor and recording disc driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively manufacture a thrust plate having a groove on its inner peripheral face, in a constitution of a dynamic pressure bearing formed by using a shaft obtained by fitting the thrust plate to a shaft main body. <P>SOLUTION: This thrust plate 46 is a member configurating the shaft 15 for the dynamic pressure bearing, with the shaft main body 45 composing a part of a radial bearing part at its outer peripheral face, has the circular shape having a center hole to fit the shaft main body 45 therein, and is provided with thrust faces 47, 48 configurating a part of the thrust bearing part on its both end faces. This method of manufacturing the thrust plate 46 comprises an extended pipe forming process for forming a cylindrical extended pipe 61 having the center hole, a drawing process for obtaining a drawn material 62 by drawing the extended pipe 61, and forming the groove on the inner peripheral face 61b, and a cutting process for cutting the drawn material 62 in the radial direction to form a plurality of disc members. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a thrust plate for forming a dynamic pressure bearing shaft together with a shaft main body whose outer peripheral surface forms a part of a radial bearing portion. In particular, the present invention relates to a method of manufacturing a thrust plate having an annular shape in which a center hole into which a shaft main body fits is formed, and having a thrust surface forming a part of a thrust bearing on both end surfaces.
[0002]
[Prior art]
2. Description of the Related Art A recording disk drive such as a hard disk has a spindle motor for rotational drive arranged concentrically with a recording disk in the device. The spindle motor mainly includes a stationary member to which a stator having an armature coil is fixed, a rotating member to which a rotor magnet facing the stator is fixed, and a bearing mechanism which rotatably supports the rotating member to the stationary member. It is composed of
[0003]
As a bearing mechanism, a fluid dynamic bearing is adopted for the purpose of high speed and low vibration (noise). The fluid dynamic pressure bearing is composed of a lubricating fluid such as oil disposed in a minute gap between the shaft and the sleeve, and a radial / thrust bearing portion including a dynamic pressure generating groove formed on the facing surface. .
As a specific configuration, a spindle motor for a hard disk drive using a dynamic pressure bearing will be described (for example, see Patent Document 1). The spindle motor described in Patent Document 1 includes a stationary member, a rotating member, and a bearing mechanism provided therebetween.
[0004]
The stationary member includes a motor frame 10 fixed to the base of the hard disk drive, a cylindrical boss portion provided concentrically and integrally therewith, and a sleeve 14 fitted and fixed to the inner peripheral surface thereof. . The stator 20 is externally fitted and fixed to the outer peripheral surface of the boss.
The rotating member includes the rotor hub 16 and a shaft 22 provided integrally therewith. A recording disk is mounted on the rotor hub 16. Further, an annular rotor magnet 18 is mounted on the inner side of the lower outer peripheral wall of the rotor hub 16 so as to face the stator 20 in the radial direction. The shaft 22 is rotatably arranged inside the sleeve 14, and has a herringbone-shaped groove for generating dynamic pressure formed on one or both of the surfaces facing the outer peripheral surface of the shaft 22 and the inner peripheral surface of the sleeve 14. A pair of upper and lower radial dynamic pressure bearing portions are formed by filling a lubricant such as oil between the opposed surfaces. A thrust plate (not numbered) provided at the lower end of the shaft is accommodated in the lower end large diameter portion of the sleeve 14, and the thrust cover 12 is closed by the thrust cover 12 so as to close the lower end large diameter portion of the sleeve 14. Is fitted and fixed. A herringbone-shaped or spiral-shaped dynamic pressure generating groove is formed on one or both of the upper surface of the thrust plate and the thrust surface of the sleeve 14 facing the thrust plate. A pressure bearing is formed. Herringbone-shaped or spiral-shaped grooves for generating dynamic pressure are formed on one or both of the lower surface of the thrust plate and the thrust cover 12 facing the thrust plate, and the opposing surface is filled with a lubricant to form a lower thrust dynamic pressure bearing. A part is formed.
[0005]
In the hydrodynamic bearing spindle motor having such a configuration, when a coil of the stay 20 is energized, a rotating torque is generated by an electromagnetic interaction between the rotating magnetic field of the stator 20 and the multipolar magnetic field of the rotor magnet 18, The rotating member including the port hub 16, the shaft 22, and the rotating load (recording disk) rotates. During this rotation, the radial load of the rotating member is supported by a pair of upper and lower radial dynamic pressure bearings formed between the shaft 22 and the sleeve 14, and the radial load is formed between the thrust plate, the sleeve 14, and the thrust cover 12. The thrust load of the rotating member is supported by the pair of thrust dynamic pressure bearing portions thus formed.
[0006]
On the other hand, air is dissolved in the lubricating oil used for the fluid dynamic pressure bearing, and these airs appear as bubbles when the internal pressure of the lubricating oil becomes negative pressure (pressure lower than atmospheric pressure). Bubbles cause vibration and deterioration of NRRO (Non-Repeatable Run-Out: non-repetitive shake component). In addition, the bubbles expand in volume as the temperature increases, causing leakage of lubricating oil. In the thrust bearing portion, due to processing errors in the grooves and bearing components, the generated dynamic pressure becomes unbalanced, and a negative pressure may be generated in the lubricating oil held on the outer peripheral portion of the thrust plate. Therefore, in order to prevent a negative pressure from being generated in the lubricating oil, a hole communicating between the upper and lower surfaces of the thrust plate is provided, and the fluid is circulated between the two thrust dynamic pressure bearing portions, so that a vertical A structure for compensating for the imbalance of dynamic pressure generated in the thrust bearing portion has begun to be adopted. The communication hole is, specifically, a plurality of grooves formed in the inner peripheral surface of the thrust plate and extending in the axial direction.
[0007]
The following method is employed as a method of processing the communication hole, that is, a method of manufacturing the shaft. The shaft and the thrust plate are separate members, and a plurality of longitudinal grooves extending in the axial direction are formed on the inner peripheral surface of the thrust plate. Subsequently, one end of the shaft is pressed into the inner peripheral surface of the thrust plate. Then, a plurality of communication holes communicating with each other in the axial direction are secured in a corner portion which is a boundary portion between the outer peripheral surface on one end side of the shaft and the inner peripheral edge of the end surface on the shaft side of the thrust plate.
[0008]
[Patent Document 1]
JP 2000-134897 A
[0009]
[Problems to be solved by the invention]
As a method of manufacturing a thrust plate, a method of obtaining an inner peripheral surface of a blank material by press punching (shearing) is generally used.
However, when manufacturing a thrust plate by press working, if a vertical groove is formed on the inner peripheral surface of the thrust plate and the inner diameter is not a uniform circle, the product cost increases due to mold cost and labor for trial production. The problem arises.
[0010]
An object of the present invention is to construct a dynamic pressure bearing using a shaft in which a thrust plate is fitted to a shaft body, and to manufacture a thrust plate having a groove formed on an inner peripheral surface at low cost.
[0011]
[Means for Solving the Problems]
A thrust plate manufactured by the method for manufacturing a thrust plate according to claim 1 is a member for forming a shaft for a dynamic pressure bearing together with a shaft body whose outer peripheral surface forms a part of a radial bearing portion, and the shaft body. Is formed in a ring shape having a center hole to be fitted therein, and a thrust surface forming a part of a thrust bearing portion is formed on both end surfaces. This method of manufacturing a thrust plate includes the following steps.
[0012]
◎ Drawing tube forming process for forming a tubular drawing tube with a central hole formed
◎ A drawing process in which a drawn material is obtained by drawing a drawn tube and a groove extending in the longitudinal direction is formed on the inner peripheral surface of the drawn material.
◎ Cut-off process to cut out the drawn material in the radial direction to create multiple disc-shaped members
In this method of manufacturing a thrust plate, unlike the press working, a thrust plate having a groove formed on the inner peripheral surface can be manufactured at low cost.
[0013]
In the method for manufacturing a thrust plate according to the second aspect, in the first aspect, the drawing step includes a diameter reducing step of reducing the inner and outer diameters of the drawn pipe, and a groove on the inner peripheral surface of the drawn pipe whose inner and outer diameters are reduced. Forming an inner peripheral surface.
In this manufacturing method, since the diameter reduction of the drawn tube and the inner peripheral surface processing are continuously performed in the drawing step, the number of steps is reduced, and as a result, the manufacturing cost is reduced.
[0014]
The method for manufacturing a thrust plate according to claim 3 further comprises a polishing step of polishing both end faces of the disc-shaped member after the cutting-off step in claim 1 or 2.
In this manufacturing method, since both end surfaces (thrust surfaces) of the thrust plate are polished after the cutting-off step, the accuracy of the both end surfaces with respect to the inner peripheral surface is improved. As a result, the perpendicularity of the plane of the thrust plate to the axis of the shaft body is improved.
[0015]
A method for manufacturing a shaft for a dynamic pressure bearing according to a fourth aspect includes the following steps.
◎ A method for manufacturing a thrust plate according to any one of claims 1 to 3.
◎ Fitting process for fitting the shaft body to the center hole of the thrust plate
In this method for manufacturing a shaft, the method for manufacturing a thrust plate according to any one of claims 1 to 3 is used, so that a shaft for a dynamic pressure bearing can be manufactured at low cost. In addition, when both end surfaces of the thrust plate are polished after the cutting process, the perpendicularity between the center axis of the shaft main body and the plane of the thrust plate can be realized with high accuracy.
[0016]
A dynamic pressure bearing according to a fifth aspect includes a dynamic pressure bearing shaft manufactured by the manufacturing method according to the fourth aspect, and a hollow cylindrical member having a through hole formed through the dynamic pressure bearing shaft. I have. The hollow cylindrical member has a radial inner peripheral surface opposed to the outer peripheral surface of the shaft main body via a minute gap, and a thrust surface opposed to both end surfaces of the thrust plate via a minute gap. A radial bearing portion is constituted by the outer peripheral surface of the shaft main body, the radial inner peripheral surface of the hollow cylindrical member, and the lubricating fluid in the minute gap. A thrust bearing is constituted by both end surfaces of the thrust plate, the thrust surface of the hollow cylindrical member, and the lubricating fluid in the minute gap.
[0017]
In this dynamic pressure bearing, the manufacturing cost is low because the shaft for the dynamic pressure bearing manufactured by the manufacturing method of claim 4 is used. In addition, when both end surfaces of the thrust plate are polished after the cutting-off process, the bearing performance of the dynamic pressure bearing is improved. That is, the improvement of the perpendicularity between the center axis of the shaft main body and the plane of the thrust plate contributes to the high-speed rotation of the dynamic pressure bearing.
[0018]
According to a sixth aspect of the present invention, there is provided a spindle motor according to the fifth aspect, a stator which is non-rotatably disposed with respect to one of the dynamic pressure bearing shaft and the hollow cylindrical member, and a dynamic pressure bearing shaft. And a rotor magnet which is arranged so as not to rotate with respect to the other of the hollow cylindrical members and cooperates with the stator to generate a rotating magnetic field.
[0019]
Since the spindle motor uses the dynamic pressure bearing according to claim 5, the manufacturing cost is low.
According to a seventh aspect of the present invention, there is provided a recording disk drive which is fixed to the inside of the housing and cannot rotate with respect to the other of the spindle motor, the dynamic pressure bearing shaft and the hollow cylindrical member. And a disc-shaped recording medium on which information can be recorded, and information access means for writing or reading information at a required position on the recording medium.
[0020]
Since the recording disk drive uses the spindle motor according to claim 6, the manufacturing cost is low.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
1. First embodiment
(1) Overall configuration of spindle motor
FIG. 1 is a longitudinal sectional view schematically showing a schematic configuration of a spindle motor 1 as one embodiment of the present invention. The spindle motor 1 is a spindle motor for driving a recording disk, and constitutes a part of a recording disk drive such as a hard disk.
[0022]
Note that OO shown in FIG. 1 is the rotation axis of the spindle motor 1. In the description of the present embodiment, the vertical direction in FIG. 1 is referred to as “axial vertical direction” for convenience, but the direction in the actual mounting state of the spindle motor 1 is not limited.
In FIG. 1, the spindle motor 1 mainly includes a stationary member 2, a rotating member 3, and a bearing mechanism 4 for rotatably supporting the rotating member 3 on the stationary member 2. The spindle motor 1 further includes a stator 6 fixed to the stationary member 2 and a coil 6 wound around the stator core, and a rotor magnet 7 fixed to the rotating member 3. A magnetic circuit unit for giving a rotational force to the magnetic circuit unit is provided.
[0023]
(2) Stationary member
The stationary member 2 includes a bracket 10 and a sleeve 11 fixed in a central opening of the bracket 10. More specifically, a cylindrical portion 10a extending upward in the axial direction is formed at the center opening edge of the bracket 10, and the outer peripheral surface of the sleeve 11 is fitted to the inner peripheral surface thereof. The stator 6 is fixed to the outer peripheral surface of the cylindrical portion 10a.
[0024]
The sleeve 11 is a cylindrical member, and a through hole 51 that penetrates in the axial direction is formed at a substantially central portion thereof. As shown in FIG. 2, the inner peripheral surface of the through hole 51 of the sleeve 11 has a radial inner peripheral surface 53 and a lower inner peripheral surface 54 from the upper side to the lower side. The lower inner peripheral surface 54 of the sleeve 11 forms a step 52 at the lower end of the through hole 51. The step portion 52 has a larger diameter than the radial inner peripheral surface 53, and has a thrust surface 56 facing the lower side in the axial direction around the through hole 51 and a lower inner peripheral surface 54.
[0025]
A thrust cover 12 is fixed to a lower end of the through hole 51 of the sleeve 11, and the thrust cover 12 closes a lower end of the through hole 51. The outer peripheral side of the upper surface in the axial direction of the thrust cover 12 is a thrust surface 12 a axially opposed to the thrust surface 56 of the sleeve 11.
(3) Rotating member
The rotating member 3 is a member rotatably supported by a sleeve 11 via a bearing mechanism 4, and is located on a rotor hub 14 on which a recording disk is mounted on an outer peripheral portion and on an inner peripheral side of the rotor hub 14. And a shaft 15 that is supported by the sleeve 11 via the bearing mechanism 4.
[0026]
The rotor hub 14 is arranged above and close to the stationary member 2 and the stator 6. The rotor magnet 7 is fixed to the inner peripheral surface of the cylindrical portion of the rotor hub 14 by means such as bonding. The rotor magnet 7 faces the stator 6 with a small gap in the radial direction. When the stator 6 is energized, a torque acts on the rotating member 3 due to electromagnetic interaction between the stator 6 and the rotor magnet 7.
[0027]
The shaft 15 includes a cylindrical shaft main body 45 and a thrust plate 46 fitted to the lower end thereof. The axially upper end of the shaft body 45 of the shaft 15 is fitted into the center hole of the rotor hub 14. Note that the fitting method described above includes press-fitting and bonding.
The thrust plate 46 is an annular and disk-shaped member protruding radially outward from the outer peripheral surface of the lower end of the shaft main body 45, and forms a flange of the shaft main body 45. The thrust plate 46 has an inner peripheral surface 49 into which one end of the shaft main body 45 is press-fitted, an outer peripheral surface 50, an upper thrust surface 47 on the shaft main body side, and a lower thrust surface 48 on the opposite side. . The upper thrust surface 47 of the thrust plate 46 is opposed to the thrust surface 56 of the sleeve 11 with a small gap, and the lower thrust surface 48 of the thrust plate 46 is opposed to the thrust surface 12a of the thrust cover 12 with a small gap. are doing.
[0028]
(4) Bearing mechanism
The bearing mechanism 4 is a fluid dynamic pressure bearing for rotatably supporting the rotating member 3 with respect to the stationary member 2, more specifically, the rotor hub 14 and the shaft 15 with respect to the sleeve 11 via the lubricating oil 8. It is. The bearing mechanism 4 has first and second radial bearing portions 21 and 22 and first and second thrust bearing portions 23 and 24. Hereinafter, the structure of each of the bearing portions 21 to 24 will be described with reference to FIG. 2 while touching the structures of the sleeve 11, the thrust cover 12, and the shaft 15.
[0029]
(1) Radial bearing
The radial inner peripheral surface 53 of the sleeve 11 is opposed to the outer peripheral surface 37 of the shaft main body 45 of the shaft 15 so as to secure a radial minute gap for retaining the lubricating oil 8. A plurality of herringbone-shaped dynamic pressure generating grooves 25 and 26 arranged in the circumferential direction for generating dynamic pressure in the lubricating oil 8 are formed on the radial inner peripheral surface 53 so as to be arranged in the axial direction. . Thus, the first and second radial bearing portions 21 and 22 are arranged in the axial direction by the radial inner peripheral surface 53 of the sleeve 11, the outer peripheral surface 37 of the shaft main body 45 of the shaft 15, and the lubricating oil 8 therebetween. It is composed of
[0030]
(2) Thrust bearing
A plurality of herringbone dynamic pressure generating grooves 27 for generating a dynamic pressure in the lubricating oil 8 with the rotation of the shaft 15 are formed on the thrust surface 56 of the sleeve 11 in a state of being arranged in the circumferential direction. ing. Thus, the first thrust bearing portion 23 is formed by the thrust surface 56 of the sleeve 11, the upper thrust surface 47 of the thrust plate 46, and the lubricating oil 8 therebetween.
[0031]
On the thrust surface 12a of the thrust cover 12, a plurality of herringbone-shaped dynamic pressure generating grooves 28 for generating a dynamic pressure in the lubricating fluid with the rotation of the shaft 15 are formed in a state of being arranged in a circumferential direction. ing. As described above, the second thrust bearing portion 24 is formed by the lower thrust surface 48 of the thrust plate 46, the thrust surface 12a of the thrust cover 12, and the lubricating oil 8 therebetween.
[0032]
Thus, the sleeve 11 and the thrust cover 12 constitute a hollow cylindrical member that rotates relative to the shaft 15. That is, the hollow cylindrical member is formed with a through hole 51 through which the shaft 15 penetrates, a radial inner peripheral surface 53 facing the outer peripheral surface 37 of the shaft main body 45 through a minute gap, and upper and lower sides of the thrust plate 46. Thrust surfaces 56 and 12a are opposed to thrust surfaces 47 and 48 via a minute gap.
[0033]
Further, as shown in FIG. 2, a plurality of (three) longitudinal grooves 49 a extending in the axial direction are formed on the inner peripheral surface 49 of the center hole of the thrust plate 46. The vertical groove 49a is open on both sides in the axial direction, and functions as an oil circulating portion that communicates the first thrust bearing portion 23 and the second thrust bearing portion 24. By the vertical groove 49a, both sides in the axial direction of the thrust plate 46, that is, the first and second thrust bearing portions 23 and 24 communicate with each other on the inner peripheral portion thereof, and between the first and second thrust bearing portions 23 and 24. The lubricating oil 8 easily circulates. Therefore, the imbalance in dynamic pressure between the first and second thrust bearing portions 23 and 24 is compensated, and a negative pressure is less likely to be generated in the lubricating oil 8 held on the outer peripheral portion of the thrust plate 46. As a result, as in the present embodiment, a bearing mechanism 4 which is a full-fill type dynamic pressure bearing is provided, and herringbone-shaped dynamic pressure generating grooves 27, 28 are provided in the first and second thrust bearing portions 23, 24, respectively. Even when it is formed, a problem due to the generation of bubbles is unlikely to occur.
[0034]
The surface tension seal portion 29 is a structure for preventing the leakage of the lubricating oil 8 from the first radial bearing portion 21, and at the axially outer end of the first radial bearing portion 21, the inner circumferential surface of the sleeve 11 is formed. And the outer peripheral surface of the shaft 15. Specifically, in a portion of the outer peripheral surface of the shaft 15 in the axial direction outside the first radial bearing portion 21 in the axial direction, the gap between the outer peripheral surface of the shaft 15 and the inner peripheral surface of the sleeve 11 is expanded outward in the axial direction. An inclined surface 30 is formed. The surface tension of the lubricating oil 8 held in the bearing portion and the air pressure of the outside air are balanced, and the meniscus of the lubricating oil 8 is located on the inclined surface 30. As a result, when the lubricating oil 8 tries to move further outward, the curvature of the liquid surface tends to increase, which acts as a resistance and suppresses the movement of the lubricating oil 8 to the outside of the bearing.
[0035]
As described above, the bearing mechanism 4 includes the first radial bearing portion 21, the second radial bearing portion 22, the first thrust bearing portion 23, and the second thrust bearing portion 24. Is continuously filled with lubricating oil. Further, the lubricating oil 8 in each bearing portion is sealed by a surface tension seal portion 29 formed in an axially upper portion of a gap between the outer peripheral surface of the shaft 15 and the inner peripheral surface of the sleeve 11.
[0036]
In FIGS. 1 and 2, each of the dynamic pressure generating grooves 25, 26, 27, and 28 is symbolically shown in the form of a letter for convenience, but actually, as described above, each of the surfaces 53, 53 is used. , 56, 12a.
(5) Shaft manufacturing method
Hereinafter, a method for manufacturing the shaft 15, particularly, a method for manufacturing the thrust plate 46 will be described. This manufacturing method mainly has (1) a drawing process for forming a pipe → (2) a drawing process → (3) a cutting process → (4) an end surface polishing process → (5) a finishing barrel process.
[0037]
(1) Tube forming process
First, in a melting furnace, a material such as stainless steel and a copper alloy is melted, and a circular billet having an outer diameter of 155 mm and a length of 200 to 500 mm is cast. A 60 mm pipe material is used, and a cylindrical drawn tube 61 is formed in a drawn tube forming step including heat treatment. As shown in FIG. 3, the extension tube 61 has a perfect circular outer peripheral surface 61a and an inner peripheral surface 61b. Note that the inner and outer diameters of the extension tube 61 are larger than the inner and outer diameters of the thrust plate 46 as a final product.
[0038]
(2) Extraction process
Next, as shown in FIG. 4, the inner and outer peripheral surfaces of the drawn tube 61 are processed using a drawing machine 70. In the following description, the left-right direction in FIG. 4 is referred to as a longitudinal direction, and the right side in FIG.
The drawing machine 70 includes a metal core 71, a die 72, and a chuck 73. The metal core 71 and the die 72 are supported by a support (not shown). The chuck 73 is connected to a drive mechanism including a chain and a sprocket (not shown).
[0039]
The metal core 71 is a tool for processing the inner peripheral surface 61b of the drawn tube 61, and includes a central rod-shaped portion 74 and a processed portion 75 formed at the leading end on the drawing side. The outer diameter of the central rod portion 74 is smaller than the inner diameter of the extension tube 61, so that the extension tube 61 can move in the longitudinal direction without contact around the central rod portion 74. The processing portion 75 is formed at the longitudinal end of the central rod portion 74, and is a portion for forming a groove in the inner peripheral surface 61 b of the extension tube 61. The processing portion 75 has an outer diameter larger than that of the center rod portion 74, and includes a processing outer peripheral surface 75a and a tapered surface 75b located on a side opposite to a side from which the processing portion 75 is pulled out. On the outer peripheral surface 75a for processing, three groove forming projections (not shown) extending in the longitudinal direction are formed. The outer diameter of the tapered surface 75b increases toward the drawing side.
[0040]
The die 72 is an annular member that is disposed slightly away from the drawing side of the processing section 75. The die 72 is a member for processing by passing the elongate tube 61 therein, and has an inner peripheral surface 72a for processing and a tapered surface 72b located on the side opposite to the drawing side. And The inner diameter of the die 72 is smaller than the outer diameter of the drawn tube 61, and is substantially equal to the outer diameter of the processed portion 75. The maximum inner diameter of the tapered surface 72b of the die 72 on the side where the extension tube 61 is fed is larger than the outer diameter of the extension tube 61. For this reason, when the extension tube 61 passes through the die 72, the extension tube 61 is deformed so that both the inner and outer diameters become shorter.
[0041]
The chuck 73 is arranged further on the drawing side of the die 72. The chuck 73 holds the distal end of the elongate tube 61, and in that state, can move to the longitudinal withdrawal side.
As shown in FIG. 4, the tip of the extension tube 61 passes through the inside of the die 72 and is held by the chuck 73. When the chuck 73 moves to the drawing side in this state, the drawn tube 61 is subjected to the drawing process in the following steps.
[0042]
First, both the outer and inner diameters of the drawn tube 61 are reduced at the tapered surface 72b of the die 72 (drawing zone A), and then the outer diameter of the drawn tube 61 is continuously reduced at the tapered surface 72b of the die 72. On the other hand, the reduced inner diameter of the drawn tube 61 is enlarged by the tapered surface 75b of the processed portion 75 of the core metal 71, and the plate thickness is reduced by the die 72 and the core metal 71 (rolling zone B). ). Thereafter, the inner and outer diameters of the drawn tube 61 are determined by the inner peripheral surface 72a for processing of the die 72 and the outer peripheral surface 75a of the processing part 75, and the plurality of longitudinal grooves ( (Not shown)), and at the same time, the inner and outer surfaces of the elongate tube 61 are mirror-finished (finishing zone C).
[0043]
Through the above-described drawing step, as shown in FIG. 5, a drawn material 62 is formed. The extraction member 62 is a tubular member, and has an outer peripheral surface 62a and an inner peripheral surface 62b. The outer peripheral surface 62a is a perfect circle. Three grooves 62c extending linearly in the longitudinal direction are formed in the inner peripheral surface 62b. Note that the drawn material 62 has a smaller inner and outer diameter than the drawn tube 61.
[0044]
(3) Cut-off process
Next, using an unillustrated NC lathe (NC automatic lathe), the inner and outer peripheral surfaces of the drawn material 62 are turned by an NC automatic lathe to finish the inner and outer diameters to the product dimensional level, and the drawn material 62 is further radially cut. Are sequentially cut off along the line to create a disk-shaped member serving as the original shape of the thrust plate 46. In this case, the cutting is performed with a thickness including a polishing allowance. As described above, by performing the inner / outer diameter finishing and the cutting simultaneously on the extracted material 62 by the NC automatic lathe, high precision and low cost can be realized.
[0045]
(4) Edge polishing process
Next, both end surfaces of the disc-shaped member are polished to increase the accuracy of the perpendicularity of the end surface to the center hole. When the right-angle accuracy is within several μm, a dynamic pressure bearing with good rotational runout accuracy can be obtained.
(5) Finish barrel process
Finally, the disk-shaped member is rounded by a barrel (rounding) process, and burrs generated by the polishing are removed. As a result, as shown in FIG. 6, a thrust plate 46 having a vertical groove 49a formed in the inner peripheral surface 49 is obtained.
[0046]
The shaft 15 is completed by fitting one end of the shaft body 45 into the center hole of the thrust plate 46, that is, the inner peripheral surface 49 by press-fitting or bonding.
(6) Effect of manufacturing method of thrust plate
{Circle around (1)} In this method of manufacturing a thrust plate, unlike the press working, the thrust plate can be manufactured at low cost. If the thrust plate is inexpensive, the shaft, dynamic pressure bearing, spindle motor, recording disk drive and the like in which it is used are also inexpensive.
[0047]
{Circle around (2)} In this manufacturing method, the inner peripheral surface processing of the drawn pipe and the diameter reduction are performed continuously in the drawing step, so that the number of steps is reduced, and as a result, the manufacturing cost is reduced.
{Circle around (3)} In this manufacturing method, the finishing and the cutting-off process of the inner peripheral surface of the thrust plate are simultaneously processed, thereby realizing high precision and low cost. As a result, the bearing performance of the dynamic pressure bearing using this shaft is improved. That is, the improvement in the accuracy of the inner peripheral surface of the thrust plate contributes to the high-speed rotation of the dynamic pressure bearing. Further, the improvement of the accuracy of the inner peripheral surface of the thrust plate contributes to the high-speed rotation of the spindle motor and the improvement of the information writing or reading speed in the recording disk drive.
[0048]
(7) Hard disk drive configuration
The embodiment of the recording disk drive spindle motor 1 according to the present invention has been described above, but a hard disk device as a recording disk drive device including the spindle motor 1 according to the present invention will be described as an example.
FIG. 7 is a schematic diagram showing the internal configuration of a general hard disk drive 80. The interior of the housing 81 forms a clean space with extremely little dust and dirt, and the spindle motor 1 on which a disk-shaped recording disk 83 for storing information is mounted. In addition, inside the housing 81, a magnetic head moving mechanism 87 for reading and writing information from and to the recording disk 83 is arranged. The magnetic head moving mechanism 87 is a head 86 for reading and writing information on the recording disk, and a head 86 for reading and writing information on the recording disk. It is composed of a supporting arm 85 and an actuator section 84 for moving the head and the arm to a required position on the disk.
[0049]
In the hard disk device 80, an increase in the speed of writing or reading information is realized by increasing the speed of the spindle motor 1 described above.
2. Other embodiments
The present invention is not limited to the above embodiment, and various changes or modifications can be made without departing from the scope of the present invention.
[0050]
Specifically, the present invention is not limited to the dynamic pressure bearing, the motor or the recording disk drive shown in the embodiment. Furthermore, in each bearing portion of the dynamic pressure bearing, the presence or absence of the dynamic pressure generating groove, the formed member, or the shape is not limited to the above-described embodiment.
Further, in the illustrated embodiment, the shaft 15 is fixed to the rotor hub 14 and the rotating member 3 is formed, that is, a so-called rotary shaft type spindle motor is described as an example. However, the shaft forms a part of the stationary member. The present invention is also applicable to a so-called fixed shaft type spindle motor.
[0051]
【The invention's effect】
In the method for manufacturing a thrust plate according to the first aspect, unlike the pressing, the thrust plate can be manufactured at low cost.
In the method of manufacturing a thrust plate according to the second aspect, in the drawing step, the reduction of the diameter of the drawn tube and the processing of the inner peripheral surface are continuously performed, so that the number of steps is reduced, and as a result, the manufacturing cost is reduced. .
[0052]
In the method for manufacturing a thrust plate according to the third aspect, since both end surfaces of the thrust plate are polished after the cutting step, the accuracy of the both end surfaces with respect to the center hole is improved. As a result, the perpendicularity of the plane of the thrust plate to the axis of the shaft body is improved.
In the method of manufacturing a dynamic pressure bearing shaft according to the fourth aspect, since the method of manufacturing a thrust plate according to any one of the first to third aspects is used, the dynamic pressure bearing shaft can be manufactured at low cost. In addition, when both end surfaces of the thrust plate are polished after the cutting process, the perpendicularity between the center axis of the shaft main body and the plane of the thrust plate can be realized with high accuracy.
[0053]
In the dynamic pressure bearing according to the fifth aspect, the manufacturing cost is low because the shaft for the dynamic pressure bearing manufactured by the manufacturing method of the fourth aspect is used. In addition, when both end surfaces of the thrust plate are polished after the cutting-off process, the bearing performance of the dynamic pressure bearing is improved. That is, the improvement of the perpendicularity between the central axis of the shaft main body and the plane of the thrust plate contributes to the high-speed rotation of the dynamic pressure bearing.
[0054]
In the spindle motor according to the sixth aspect, the manufacturing cost is low because the dynamic pressure bearing according to the fifth aspect is used.
In the recording disk drive according to the seventh aspect, since the spindle motor according to the sixth aspect is used, the manufacturing cost is low.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view of a spindle motor as a first embodiment of the present invention.
FIG. 2 is a diagram for explaining a communication hole of each bearing portion and a shaft of the bearing mechanism, and is a partially enlarged view of FIG. 1;
FIG. 3 is a partial perspective view of a cannula.
FIG. 4 is a schematic cross-sectional view for explaining a drawing step.
FIG. 5 is a partial perspective view of a drawing member.
FIG. 6 is a perspective view of a thrust plate.
FIG. 7 is a schematic configuration diagram of a general hard disk device.
[Explanation of symbols]
1 spindle motor
2 Stationary member (hollow cylindrical member)
3 rotating members
11 sleeve
14 Rotor hub
15 Shaft
21 1st radial bearing part
22 Second radial bearing
23 First thrust bearing
24 Second thrust bearing
45 Shaft body
46 Thrust plate
47 Upper thrust surface
48 Lower thrust surface
49 Inner circumference
49a groove
50 Outer surface
61 Extension
62 Extracted material

Claims (7)

An outer peripheral surface is a member for forming a dynamic pressure bearing shaft together with a shaft main body forming a part of a radial bearing portion, and is a ring having a center hole into which the shaft main body fits, and has an end surface on both ends. A method for manufacturing a thrust plate on which a thrust surface forming a part of a thrust bearing portion is formed,
An elongation tube forming step of forming a cylindrical elongation tube having a center hole formed therein,
A drawing step of forming a groove extending in the longitudinal direction on the inner peripheral surface of the drawn material while obtaining a drawn material by drawing the drawn tube,
A cutting step of cutting the drawn material in the radial direction to create a plurality of disc-shaped members,
A method for manufacturing a thrust plate provided with: The drawing step includes a diameter reducing step of reducing the inner and outer diameters of the drawn tube, and an inner peripheral surface processing step of forming the groove on the inner peripheral surface of the drawn tube whose inner and outer diameters have been processed to be smaller. A method for manufacturing a thrust plate according to claim 1. The method for manufacturing a thrust plate according to claim 1 or 2, further comprising a polishing step of polishing both end faces of the disc-shaped member after the cutting-off step. A method for manufacturing a thrust plate according to any one of claims 1 to 3,
A fitting step of fitting the shaft body to a center hole of the thrust plate,
A method for manufacturing a shaft for a dynamic pressure bearing, comprising: A shaft for a hydrodynamic bearing manufactured by the manufacturing method according to claim 4,
A through hole through which the dynamic pressure bearing shaft penetrates is formed, a radial inner peripheral surface facing the outer peripheral surface of the shaft main body via a minute gap, and a thrust opposed to both end surfaces of the thrust plate via a minute gap. And a hollow cylindrical member having a surface,
An outer peripheral surface of the shaft main body, a radial inner peripheral surface of the hollow cylindrical member, and a lubricating fluid in the minute gap constitute a radial bearing portion,
Both end surfaces of the thrust plate, the thrust surface of the hollow cylindrical member, and the lubricating fluid in the minute gap form a thrust bearing portion.
Dynamic pressure bearing. A dynamic pressure bearing according to claim 5,
A stator arranged non-rotatably with respect to one of the dynamic pressure bearing shaft and the hollow cylindrical member,
A rotor magnet arranged to be non-rotatable with respect to the other of the dynamic pressure bearing shaft and the hollow cylindrical member, and to generate a rotating magnetic field in cooperation with the stator;
With spindle motor. A housing,
7. A disc capable of recording information, wherein the disc is fixed to the inside of the housing, and is arranged so as not to rotate with respect to the other of the shaft for dynamic pressure bearing and the hollow cylindrical member. State recording medium;
Information access means for writing or reading information at a required position on the recording medium;
Recording disk drive device comprising:

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