Patent Application
20060256469
1. Field of the Invention
The present invention relates to a hydrodynamic bearing member that is used for a motor for rotatably driving a disc recording medium and a manufacturing method thereof.
2. Description of the Related Art
A hard disc drive (HDD) has an excellent function as a storage unit that can record and reproduce a large amount of data. Not only a personal computer but also various kinds of home electric appliances including audio-visual products having HDD included therein have been wide spread. HDD requires rotating a disc at a high speed and with a high degree of accuracy and also HDD requires a decay durability (a longer operating life) that can stand long use, so that a spindle motor using a hydrodynamic bearing member has been used as a motor thereof.
In recent years, due to development of a compact digital equipment such as a compact portable music record reproduction apparatus and a recording medium for a digital camera having HDD incorporated, HDD is required to be further reduced in size and thickness. In order to reduce its size and thickness, it is necessary to reduce the spindle motor for rotatably driving a disc in size and thickness. A typical conventional example of such spindle motor is shown in a sectional view in
In
For example, the following materials are used as a material of each part. As the housing 21, an aluminum die cast material or an iron material is used, and as the sleeve 22, a material obtained by nickel-plating a brass material (a copper alloy) is used. As the shaft 23, a stainless steel material (for example, SUS420J2) is used, and as the flange 25, a stainless steel material (for example, SUS304) is used. Further, as the thrust support 24, a stainless steel material (for example, SUS420J2) is used, and as the hub 27, a stainless steel material (for example, DHS1) or an aluminum material is used.
On the upper end portion of the shaft 23, the hub 27 is fitted. At the center part of the shaft 23, a screw hole 31 disposed in parallel with the axial direction of the shaft 23 is formed. By screwing a screw (its illustration is herein omitted) into the screw hole 31 and fixing a clamp member (its illustration is herein omitted), a magnetic disc or the like to be fitted to a disc support face 27g at the outer circumferential part of the hub 27 is held. On the inside of the hub 27, a rotor magnet 37 is provided. A stator core 29 with a coil wounded threaround is fitted to the housing 21 so as to oppose the rotor magnet 37.
When the current is applied to the coil wounded around the stator core 29, a magnetic force in a radial direction works between the stator core 29 and the rotor magnet 37, and then, receiving a driving force due to this magnetic force, the hub 27, the shaft 23, and the flange 25 are rotated without contacting the thrust support 24 and the sleeve 22.
In order to reduce a noise and an oscillation, the stator core 29 and the magnet 37 are arranged with the magnetic center position in each axial direction misaligned so as to generate a magnetic attraction force in the axial direction. In place of this structure, arranging a ring-type suction plate in the housing 21 just below a magnet 37 (not illustrated in
As compared to a hard disk drive incorporated in a common personal computer, the compact hard disk drive for the above-described use has many opportunities to turn on and off a power source and on each occasion, and on each occasion, the motor of the hard disk drive repeats the activation and the stop. Upon the activation and the stop of the motor, a force is added to a connection part between the shaft 23 and the flange 25 in the hydrodynamic bearing incorporated in such a motor. In addition, the high impact may be added when the motor drops down on a floor during use. Therefore, it is especially needed to set the connection intensity of the shaft 23 and the flange 25 sufficiently high.
As a conventional method to connect the shaft and the flange, there is a “press work method” shown in the JP-A No. 2004-204916. According to the press work method, a circular flange member having a shaft mounting hole at its center and a shaft to be inserted in the shaft mounting hole have been manufactured as a component in advance. The shaft and the flange member are connected in the following respective steps.
Step (1):
A concave mold (a metal mold) having a hole for inserting a shaft at its center and having an inner diameter that is slightly larger than an outer diameter of a flange member is mounted on a pressing machine, and in the hole of this concave mold, a shaft is loaded (hereinafter, in place of “load”, “set” is used).
Step (2):
Inserting the end of the shaft in the shaft mounting hole of the flange member, the flange member is set in the concave mold. There is a minute gap between the outer circumferential face of the flange member and the inner circumferential face of the concave mold, however, the outer circumferential face of the flange member is more bound substantially by the inner circumferential face of the concave mold. The concave mold moving being opposed to the concave mold is fitted to the pressing machine so as to add a predetermined press pressure on the face of the flange member. For example, at least one of the bottom face of the concave mold and the surface of a convex mold has a whorl-like groove in order to form the thrust dynamic pressure generation groove on the opposite surfaces or one surface of the flange member.
Step (3):
Operating the pressing machine, the opposite surfaces of the flange member are sandwiched by the concave mold and the convex mold to apply pressures thereto (a pressure step). During the pressure step, the thrust dynamic pressure generation groove is formed on the opposite surfaces or one surface of the flange member.
During this pressure step, the flange member having the opposite surfaces compressed intends to stretch in the outer circumferential direction, however, the outer circumferential face is bound by the concave mold and this makes the flange member to stretch toward the shaft mounting hole. As a result, the diameter of the shaft mounting hole is decreased (hereinafter, referred to as a contraction of a diameter) to be fastened by the shaft.
Step (4):
The shaft whereby the flange member is fixed is detached from the concave mold.
The flange member fastened by the shaft has a distortion (a warpage) generated in the pressure step and the warpage is corrected in the next step (a correcting step).
Step (5):
In the correction step, a flange mounted on the shaft is set between two flat metal molds having flat faces.
Step (6):
Closing two flat metal molds, the opposite surfaces of the flange are pressurized to carry out flash molding.
Step (7):
The flange is detached from the flat metal mold.
By the steps (1) to (7), the shaft having the flange member mounted thereon is manufactured. The steps (1) to (4) are referred to as “a compression molding step”, and the steps (5) to (7) are referred to as “a flash molding step”. Further, the shaft having the flange member mounted thereon will be called as “a hydrodynamic bearing member”.
In the manufacturing step of the conventional hydrodynamic bearing member, at least steps (1) and (2) are carried out by the manual operations by a worker. Therefore, a necessary time of the steps (1) and (2) largely depends on the skill of the worker. In addition, when the flange member is set in the concave mold in the step (2), the flange member may not be set accurately. For example, the edge of the flange member may be set overlapping the edge of the concave mold. This involves a problem that expensive concave mold and convex mold are damaged and they cannot be used if the concave mold and the convex mold are closed in this state.
The compression molding steps (1) to (4) and the flash molding steps (5) to (7) have different working hours (the tact hour). In other words, normally, the working hour of the compression molding step is longer. Therefore, the both steps cannot be progressed in parallel and it is difficult to improve productivity. As a result, it is difficult to decrease a manufacturing cost thereof.
The present invention has been made taking the foregoing problems into consideration and an object of which is to provide a high-grade hydrodynamic bearing member at a low cost and a manufacturing method thereof.
A hydrodynamic bearing member according to the present invention may comprise a shaft having a step part with a surface that is approximately vertical to a center axis of a column-shaped member formed at one end of the column-shaped member, and a mounting part having a diameter larger than the minimum diameter of the step part and forming a concave part on the end face; and a flange shaped in a disc having a hole into which the mounting part of the shaft is inserted; wherein one surface of the flange abuts against the step part of the shaft, and the shaft and the flange are combined by the clamping processing.
According to this invention, since one surface of the flange abuts against the step part of the shaft, the flange is mounted on the shaft at a correct angle. Since the flange is mounted on the shaft by the clamping processing, the inner circumferential part of the hole on the flange bites into the step part of the shaft, and the shaft and the flange are solidly attached each other.
A manufacturing method of a hydrodynamic bearing member according to the present invention comprises a tentative clamping step of inserting a mounting part of the shaft into a hole of the flange, pressurizing the concave part of the shaft by a metal mold formed in a certain shape to enlarge the mounting part, and tentatively combining the flange with the shaft; a proper clamping step of pressurizing the opposite faces of the flange by the metal mold while binding the outer circumference of the flange and making the inner circumferential part of the hole of the flange to bite into the step part of the shaft to clamp the flange with the shaft in the flange and the shaft that were tentatively combined in the tentative clamping step; and a flash molding step of correcting a distortion of the flange by pressurizing the opposite faces of the flange; wherein the hydrodynamic bearing member comprises a shaft having a step part with a surface that is approximately vertical to a center axis of a column-shaped member formed at one end of the column-shaped member, and a mounting part having a diameter larger than the minimum diameter of the step part and forming a concave part on the end face; and a flange shaped in a disc having a hole into which the mounting part of the shaft is inserted.
According to this invention, by tentatively attached the shaft and the flange each other in a tentative clamping step, in the following proper clamping step, it becomes very easy to treat the shaft and the flange in a step of loading the shaft and the flange in the metal mold for the proper clamping step. The tentatively clamped shaft and flange are solidly attached in the proper clamping step. A hydrodynamic bearing device can be appropriately made by using this hydrodynamic bearing member. Moreover, a spindle motor can be made appropriately by using this hydrodynamic bearing device.
According to the present invention, in the step of connecting the shaft and the flange, which are component parts of a hydrodynamic bearing, each other, the shaft and the flange have been previously made into one unit in the tentative clamping step. The metal mold in the tentative clamping step is easily composed and the operation to set the shaft and the flange in the metal mold is simple. Since the shaft and the flange that are made into one unit by the tentative clamping can be easily treated, they can be easily set in a slightly-complex metal mold used in the proper clamping step. Therefore, it is possible to prevent the shaft and the flange from being set in the metal mold by mistake and damage to the metal mold can be prevented. Moreover, by applying the said member to a hydrodynamic bearing, the hydrodynamic bearing with excellent productivity and high reliability is obtained. In addition, by applying this hydrodynamic bearing to a spindle motor, the spindle motor with high reliability is obtained.
The preferred embodiments of a hydrodynamic bearing member and a manufacturing method thereof according to the present invention will be described below with reference to FIGS. 1 to 9. The “hydrodynamic bearing member” means a member in which a shaft serving as a radial bearing and a flange serving as a thrust bearing which are main components of hydrodynamic bearing have been combined into one unit.
The hydrodynamic bearing member according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 7.
The flange 5 is a disc member having a shaft mounting hole 6 for mounting the shaft at the center and the flange 5 is made of a metal material of a stainless steel such as SUS304. Fit of the mounting part 3 and the shaft mounting hole 6 may be loosed to the extent that the mounting part 3 can be easily inserted in the shaft mounting hole 6.
The manufacturing step of coupling the shaft 1 and the flange 5 shown in
The “proper clamping step” is a step of solidly fixing the shaft 1 and the flange 5. The “flash molding step” is a step of correcting a distortion such as a warpage of the flange.
The tentatively clamped shaft 1 and flange 5 are referred to as “a tentative clamping bearing support 10”.
In
(A) Proper Clamping Step
Step (A1): By the manual operation, the shaft 1 is inserted in a hole 8a of a fixing jig 8 with its end 1a turned up.
Step (A2): The mounting part 3 of the shaft 1 is inserted in the shaft mounting hole 6 of the flange 5.
Step (A3): Operating the pressing machine, the concave part 4 of the shaft 1 is pressed or struck at the ball of the clamping metal mold 9 or the front end 9a shaped in the ball. The diameter of the ball-shaped part of the front end 9a is preferably large to the extent that the sphere face of this ball-shaped part contacts the diameter (d2 in
Step (4a): The tentative clamping bearing support 10 is detached from the jig 8 to be kept in a predetermined container.
(B) Proper Clamping Step
The proper clamping step of the tentative clamping bearing support 10 will be described with reference to the sectional views from
In the drawing, both of a lower metal mold 11 and an upper metal mold 12 are mounted on the pressing machine that has been well known generally, and in press working, for example, the upper metal mold 12 is moved in the direction indicated by an arrow b to carry out the press working.
The lower metal mold 11 has a concave part 11a on the upper face and has a hole 11b on the center of the concave part 11a. A depth of the concave part 11a, namely, a height of a side face 11c is made to be slightly lower than the thickness of the flange 5. On a bottom face 11d of the concave part 11a, a molding tool for forming a thrust dynamic pressure generation groove is disposed on the lower face of the flange 5 in
On a lower face 12a of an upper metal mold 12, a molding tool for the thrust dynamic pressure generation groove is disposed.
In a step (B2), making the upper metal mold 12 to decline as shown in
The specification according to the specific example is as follows. For example, in the case that a diameter d3 of a small diameter part is about 1.9 mm, a diameter d4 of the concave part 4 is about 1.5 mm, and a depth d5 of the concave part is 0.6 mm in
It is assumed that a combined body made by the shaft 1 and the flange 5, of which proper clamping step has been completed, is referred to as “a proper clamping bearing 10a”.
In a step (B3), the proper clamping bearing 10a is detached from the lower metal mold 11.
(C) Flash Molding Step
In a step (C1), the proper clamping bearing 10a is set in a lower metal mold 14 and an upper metal mold 15 mounted on the other pressing machines shown in
In a step (C2), making the upper metal mold 14 to decline as shown in
In a step (C3), the proper clamping bearing 10a that was flash-molded is detached from the lower metal mold 14.
According to the above-described respective steps, the completed hydrodynamic bearing member can be obtained.
According to the manufacturing method of the first embodiment, it is possible to make the necessary time of the step (A) from the step (A1) to the step (A3), the necessary time of the step (B) from the step (B1) to the step (B3), and the necessary time of the step (C) from the step (C1) to the step (C3) can be made approximately the same. Therefore, when carrying out the steps A, B, and C in parallel, “waiting” is not generated so often in the all manufacturing steps from the step (A) to the step (C) and this leads to the improvement of a productivity. In addition, by providing the tentative clamping step, “the tentative clamping bearing support 10” that was tentatively-clamped can be easily treated. In the proper clamping step shown in FIGS. 4 to 5, the tentative clamping bearing support 10 can be normally loaded in the lower metal mold 11 without fail and there is no fear to damage the lower metal mold 11 and the upper metal mold 12 due to the error loading. In the proper clamping state shown in
The hydrodynamic bearing member according to the second embodiment of the present invention will be described with reference to
In the case of tentatively clamping this shaft 18 into the flange 5, by using clamping metal mold 16 or 19 having three projections shown in
FIGS. 9 (a) and 9 (b) are perspective views of the front ends of the clamping metal molds 16 and 19 that are used in the tentative clamping step, respectively. In the clamping metal mold shown in
According to the second embodiment, in place of the clamping metal mold 9 according to the first embodiment shown in
In the tentative clamping step according to the second embodiment, since tree comparative narrow parts of the mounting part 18c of the shaft 18 are enlarged to the outer circumferential direction, the welding force given to the clamping metal mold 16 in the tentative clamping step may be smaller than that of the first embodiment. Accordingly, as the pressing machine used for the tentative clamping step, a compact one can be used. In the shaft 18 shown in
By applying the hydrodynamic bearing member described in the first and second embodiments to a hydrodynamic bearing and a spindle motor including it as shown in
The present invention is available for the mass production of the bearing member of the hydrodynamic bearing member.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2005-120224 | Apr 2005 | JP | national |
