GB2298464A

GB2298464A - Spindle unit having dynamic pressure bearings

Info

Publication number: GB2298464A
Application number: GB9603092A
Authority: GB
Inventors: Takeshi Takahashi; Takashi Honda
Original assignee: Koyo Seiko Co Ltd; TDK Corp
Current assignee: Koyo Seiko Co Ltd; TDK Corp
Priority date: 1995-02-15
Filing date: 1996-02-14
Publication date: 1996-09-04
Anticipated expiration: 2016-02-14
Also published as: GB2298464A8; GB2298464B; GB9603092D0; JPH08221896A

Abstract

A compact spindle unit for a hard disk drive comprises a vertical shaft 1 fixed to a motor base 10 which also carries a stator coil 20. A cap-shaped hub 3 carrying a magnet 30 rotates about the shaft and is supported by a radial bearing R1 and a thrust bearing S1. The thrust bearing is constituted by a part 3b integral with the hub and either a flange 2 mounted on the shaft or an end surface of the shaft itself. At least one bearing surface 1d-1, 1d-2, 2a of each bearing is provided with dynamic pressure generating grooves.

Description

A SPINDLE UNIT RAVING DYNAMIC PRESSURE BEARINGS The present invention relates to spindle units and, more particularly, to a spindle unit to be used for hard disk drive (HDD) units.

Generally, conventional spindle units of the aforementioned type use dynamic pressure bearings as a radial bearing and a thrust bearing for the purpose of size reduction. Fig. 8 shows such a conventional spindle unit.

The spindle unit uses a radial bearing R and a thrust bearing S which each consists of a dynamic pressure bearing. In Fig. 8, "SC" denotes a stator coil, "RM" denotes a rotor magnet, and reference numeral 7 denotes a hub on which a magnetic disk or other information according medium (not shown) is mounted.

As known well, dynamic pressure bearings are required to have a bearing surface with a hith flatness.

In the prior art shown in Fig. 8, in order to accomplish such a high flatness of a bearing surface in the thrust bearing S, a thrust support 8 with its bearing surface 8a previously finished to a necessary flatness is fit in a central hole provided in a top portion 7B of the hub 7.

Such technique is common and publications such as, for example, Japanese Patent Laid-Open Publication No. 6-178497 (issued in 1994) and U.S.P. 4,445,793 to Shinohara disclose similar technique.

As a result of using a separate thrust support 8, the hub 7 becomes axially thick as a whole, so that the spindle unit and hence the HDD unit could hardly be formed into thinner type. Also, use of the thrust support 8 which is a separate element, increases the number of parts involved and also ' complexes the hub configuration, resulting in an disadvantageous increase of the manufacturing cost.

An . object of the present invention is therefore to provide a spindle unit which allows the formation into thinner type, reduction in the constituent part count, and cutdown of manufacturing cost.

A spindle unit according to an aspect of the present invention comprises: a stationary element to which a stator coil is fixed; a shaft having a free end and a fixed,,end.which is fixed to the stationary element; a flange fixed to the shaft on the fixed end side; a hub placed opposite to the stationary element so as to be rotatable around the shaft, the hub having a top portion and a cylindrical portion axially extending from the top portion, a rotor magnet being fixed to the cylindrical portion so as to oppose the stator coil; a sleeve which is fixed at a central part of the top portion of the hub and which is fitted around the shaft such that the sleeve can rotate around the shaft together with the hub;; a radial dynamic pressure bearing consisting of an inner periphery of the sleeve and an outer periphery of the shaft, at least one of the inner periphery and the outer periphery having dynamic pressure generating grooves; and a thrust dynamic pressure bearing consisting of an end surface of the flange and a surface of the top portion of the hub confronting the end surface of the flange, at least one of the end surface of the flange and the surface of the top portion having dynamic pressure generating grooves.

In an embodiment, the flange is fixed to the free end of the shaft, and the top portion of the hub has a recessed portion formed on an inner side of the top portion to receive the sleeve and the flange. Also, the surface confronting the end surface of the flange is constituted of a surface which defines a bottom of the recessed portion and which is positioned radially inside the sleeve.

In another embodiment, the flange is fixed around the shaft near the free end such that a shaft end portion on the free end side protrudes from the flange. The top portion of the hub has an aperture to receive the shaft end portion, and also has a recessed portion formed on an inner side of the top portion to receive the flange and the sleeve, the recessed portion surrounding the aperture.

Also, the surface confronting the end surface of the flange is constituted of an annular surface which defines a bottom of the recessed portion and which is positioned radially inside the sleeve.

In an embodiment, the sleeve has an annular step which is positioned in the recessed portion so as to confront the other end surface of the flange, and at least one of the annular step and the other end surface of the flange has dynamic pressure generating grooves such that the annular step and the other end surface of the flange constitute a further thrust dynamic pressure bearing.

The present invention also provides a spindle unit comprising: a stationary element to which a stator coil is fixed; a shaft having a free end and a fixed end which is fixed to the stationary element; a hub placed opposite to the stationary element so as to be rotatable around the shaft, the hub having a top portion and a cylindrical portion axially extending from the top portion, a rotor magnet being fixed to the cylindrical portion so as to oppose the stator coil; a sleeve which is fixed at a central part of the top portion of the hub and which is fitted around the shaft such that the sleeve can rotate around the shaft together with the hub; a radial dynamic pressure bearing consisting of an inner periphery of the sleeve and an outer periphery of the shaft, at least one of the inner periphery and the outer periphery having dynamic pressure generating grooves; and a thrust dynamic pressure bearing consisting of an end face of the free end of the shaft and a surface confronting the end face of the top portion of the hub, at least one of the end face of the shaft and the surface of the top portion having dynamic pressure generating grooves.

In the spindle unit according to any embodiment of the present invention, since a bearing surface of the thrust dynamic pressure bearing is formed by part of the hub, the need of providing a separate thrust support, which is required in the prior art,can be eliminated, so that the hub may be formed into a thinner one, compared with the prior art. This in turn allows the spindle unit, and hence, the magnetic disk drive unit to be thinned and downsized.

Since the need of a separate thrust support member can be eliminated, the number of parts and the number of assembling steps can be reduced, so that the manufacturing cost is also reduced. Also, according to the present invention, it is not necessary to handle such an extremely small part as the thrust support any more, so that the spindle unit is manufactured easily. There is a further advantage that the hub configuration is simplified.

The present invention will become more fully understood from the detailed description of preferred embodiments given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: Fig. 1 is a sectional view of a spindle unit according to a first embodiment of the present invention; Fig. 2 illustrates dynamic pressure grooves formed on an end surface of a flange in the first embodiment; Fig. 3 is a sectional view of a spindle unit according to a second embodiment of the present invention; Figs. 4 and 5 illustrate dynamic pressure grooves formed on each of opposite end surfaces of a flange in the second embodiment, respectively; Fig. 6 is a sectional view of a spindle unit according to a third embodiment of the present invention;; Fig. 7 illustrates dynamic pressure grooves formed on an end face of a stationary shaft in the third embodiment; and Fig. 8 is a sectional view of the conventional spindle unit.

Embodiments of the present invention will be described below in detail with reference to the attached drawings, wherein similar or same parts are designated by same reference numerals.

(First embodiment) Fig. 1 shows a spindle unit according to a first embodiment of the present invention. The spindle unit has a motor base 10 which is a stationary element, and a generally cap-shaped hub 3 placed opposite to the base 10.

A stationary shaft 1 is provided between the base 10 and the hub 3. One end la of the stationary shaft 1 is fitted in a hole lOa formed in a central part of the base 10, whereby the stationary shaft 1 is secured to the base 10.

Further, herringbone-shaped dynamic pressure generating grooves ld-l, ld-2 are formed on an outer periphery lc of the stationary shaft 1. Also, a flange 2 is secured to the other, free end lb of the stationary shaft 1. The flange 2 is formed with a plurality of spiral-shaped dynamic pressure generating grooves 2a-1 as shown in Fig. 2 on an end surface 2a thereof on the side opposite from the stationary shaft 1.

A stator coil 20 is fixed to a surrounding portion 10b extending axially around the hole 10a of the base 10.

Meanwhile, the generally cap-shaped hub 3 has a top portion 3B and a cylindrical portion 3C axially extending from the top portion 3B. On the inner side of the hub 3, a recessed portion 3a is formed substantially in the center of the top portion 3B, and a sleeve 4 is fitted in and secured to the recessed portion 3a. An inner periphery 4a of the sleeve 4 is opposed to the outer periphery lc of the stationary shaft 1. The inner periphery 4a of the sleeve 4 and the outer periphery lc of the stationary shaft 1 having the dynamic pressure generating grooves id-i, ld-2 constitute a radial dynamic pressure bearing R1.

Also, in the top portion 3B of the hub 3, a surface 3b-1 of a central part 3b defining a bottom of the recessed portion 3a and located radially inside of the sleeve 4 is opposed to the end surface 2a of the flange 2 fixed at the free end lb of the stationary shaft 1. The flange end surface 2a having the dynamic pressure generating grooves 2a-1, and the surface 3b of the hub top portion 3B constitute a thrust bearing S1. The surface 3b1 confronting the end surface 2a of the flange 2 has been so machined that its flatness is a few pm or less.

Also, a rotor magnet 30 is fixed to an inner periphery 3c-1 of the cylindrical portion 3C of the hub 3 via an element 50. This rotor magnet 30 and the stator coil 20 constitute a motor. In addition, wiring 40 is provided for feeding electrical current to the stator coil 20. A magnetic disk or other information recording medium (not shown) is to be mounted on the outer periphery of the hub 3.

The hub 3 is formed by cutting process. The surface 3b-1 serving as a thrust bearing surface is given a flatness of a few ssm or less by slowing down the cutting feed speed. It is noted that the surface 3b-1 can be subjected to a lapping process, cutting process or barrel process.

Lubricating oil is provided between the opposing surfaces in the radial and thrust bearings R1 and S1.

In the spindle unit with the above arrangement, the stator coil 20 fixed to the base 10 generates a rotational magnetic field that causes the hub 3 having the rotor magnet 30 fixed thereto to rotate. Then, by this rotation, the dynamic pressure generating grooves ld-1, ld- 2 formed on the stationary shaft 1 generate a dynamic pressure to radially hold the sleeve 4, and hence, the hub 3 relative to the stationary shaft 1. At the same time, the dynamic pressure generating grooves 2a-1 formed on the flange 2 fixed to the stationary shaft 1 generate a dynamic pressure to hold the hub 3 axially.

According to the first embodiment, the central part 3b of the hub 3, whose surface 3b-1 constitutes part of the thrust dynamic pressure bearing S1, is not a component other than the hub 3, but part of the hub 3, integral with the hub 3. Therefore, according to the first embodiment, the hub 3 can be formed into thinner type, as compared with the conventional counterpart in which a component separate from the hub constitutes part of the thrust dynamic pressure bearing. Consequently, according to the first embodiment, the spindle unit can be designed for thinner and smaller form so that the magnetic disk drive unit, an end product, can be designed for thinner and smaller type.

Also, according to the first embodiment, there is no need of handling minute parts such as the conventional thrust support 8 (see Fig. 8), so that the spindle unit is manufactured easily. Moreover, the count of parts involved is reduced. Thus, the manufacturing cost can be reduced.

Further, according to the first embodiment, the top portion 3B of the hub 3 is fully closed, thus eliminating the possibility of any leak of the dynamic pressure fluid (lubricating oil). Thus, a mounted magnetic disk will never be dirtied with the lubricating oil.

In the first embodiment, the dynamic pressure generating grooves id-l, ld-2 are formed on the outer periphery ic of the stationary shaft 1. Alternatively, the dynamic. pressure generating grooves can be formed on the inner periphery 4a of the sleeve 4. Further, the spiralshaped dynamic pressure generating grooves can be formed not only on the end surface 2a of the flange 2 but also either on the other flange end surface 2b (on the shaft's stationary end side) or on an annular step 4b facing the end surface 2b of the sleeve 4.

(Second embodiment) Next, a spindle unit according to a second embodiment of the present invention is described with reference to Figs. 3, 4, and 5. Parts same as those in the first embodiment are designated by the same reference numeral and the description on those parts is omitted here.

The spindle unit has a base 10 and a generally cap-shaped hub 13 placed opposite to the base 10, as shown in Fig. 3. The base 10 has the same configuration as that of the base in the first embodiment. The hub 13 is composed of a top portion 13B, and a cylindrical portion 13C axially extending from the top portion 13B. Unlike the top portion 3B in the first embodiment, the top portion 13B in the second embodiment has an aperture 13b-1 in its central part to receive a free end lib of a stationary shaft 11, as described later.

As in the first embodiment, the other end ila of the stationary shaft 11 is fitted into a hole 10a formed in a central part of the base 10, whereby the stationary shaft 11 is secured to the base 10. Further, herringbone-shaped dynamic pressure generating grooves lid-i, lld-2 are formed on an outer periphery lic of the stationary shaft 11.

Also, a flange 12 is secured around the stationary shaft 11 and near its free end llb in such a way that the free end lib of the shaft 11 protrudes from the flange 12. The free end lib of the stationary shaft 11 is disposed so as to be fitted in the aperture 13b-1 formed within a central part 13b of the top portion 13B of the hub 13. The flange 12 is formed with a plurality of spiral-shaped dynamic pressure generating grooves 12a-1, as shown in Fig. 4, on an end surface 12a thereof closer to the free end lib of the shaft 11.

Meanwhile, the hub 13 has a recessed portion 13a in the central part 13b of the top portion 13B, and a sleeve 14 having an annular step 14b on its inner side is fitted in and secured to the recessed portion 13a, as shown in Fig. 3. The recessed portion 13a surrounds the aperture 13b-1.

An inner periphery 14a of the sleeve 14 is opposed to the outer periphery lic of the stationary shaft 11. The inner periphery 14a of the sleeve 14 and the outer periphery lic of the stationary shaft 11 having the dynamic pressure generating grooves lid-i, lld-2 constitute a radial dynamic pressure bearing R2.

Also, an annular surface 13b-2 defining part of a bottom of the recessed portion 13a of the hub 13 is located radially inside the sleeve 14. The annular surface 13b-2 is opposed to the end surface 12a of the flange 12 fixed around the stationary shaft 11. These opposing end surface 12a and annular surface 13b-2 constitute a first thrust dynamic pressure bearing S2-1. The flange 12 is also formed with a plurality of herringbone-shaped dynamic pressure generating grooves 12b-1, as shown in Fig. 5, on its other end surface 12b (i.e., an end surface on the shaft's stationary end side). The end surface 12b of the flange 12 and the step 14b, of the sleeve 14, facing the end surface 12b constitute a second thrust dynamic pressure bearing S2-2.

The annular surface 13b-2 facing the end surface 12a of the flange 12 has been so machined that its flatness is a few ;m or less.

The hub 13 is formed by cutting process. The surface 13b-2 serving as a thrust bearing surface is given the flatness of a few pm or less by slowing down the cutting feed speed. The surface 13b-2 can be subjected to a lapping process, cutting process or barrel process.

A magnetic disk or other information recording medium (not shown) is to be fixed to the outer periphery of the cylindrical portion 13C of the hub 13.

Lubricating oil is provided between the opposing surfaces in the radial and thrust bearings R2, S2-1 and S22.

In the spindle unit with the above arrangement, the stator coil 20 fixed to the base 10 generates a rotational magnetic field that causes the hub 13 having the rotor magnet 30 fixed thereto to rotate. Then, by this rotation, the dynamic pressure generating grooves lid-i, lld-2 formed on the stationary shaft 11 generate a dynamic pressure to hold the sleeve 14 and hence the hub 13 relative to the stationary shaft 11 in the radial direction. At the same time, dynamic pressure generating grooves 12a-1 and 12b-1 formed on both end surfaces of the flange 12 fixed to the stationary shaft 11 generate a dynamic pressure to hold the hub 13 and the sleeve 14 in the axial direction.

According to the second embodiment, the central part 13b of the hub 13, whose annuluar surface 13b-2 constitutes part of the first thrust dynamic pressure bearing S2-1, is not a component other than the hub 13, but part of the hub 13, integral with the hub 13. Therefore, according to the second embodiment, the constituent parts of the spindle unit are reduced in number, the spindle unit can be formed into thinner type, and thus the manufacturing cost can be reduced, as compared with the conventional counterpart in which a component separate from the hub constitutes part of the thrust dynamic pressure bearing.

In the second embodiment, spiral-shaped dynamic pressure generating grooves 12a-1 are formed on the end surface 12a of the flange 12, and the herringbone-shaped dynamic pressure generating grooves 12b-1 are formed on the other end surface 12b. However, the dynamic pressure generating grooves to be formed on the end surfaces 12a and 12b can be either spiral- or herringbone-shaped. Also, in the second embodiment, the dynamic pressure generating grooves lld-l, lld-2 are formed on the outer periphery lic of the stationary shaft 11. Instead of this arrangement, the dynamic pressure generating grooves can be formed on the inner periphery 14b of the sleeve 14. Further, instead of forming dynamic pressure generating grooves on both end surfaces 12a and 12b of the flange 12, dynamic pressure generating grooves can be formed on the annular surface 13b-2 of the hub 13 and on the step 14b of the sleeve 14.

(Third embodiment) Next, a spindle unit according to a third embodiment of the present invention is described with reference to Figs. 6 and 7. Parts same as those in the first and second embodiments are designated by -the same reference numerals and the description on those parts is omitted here.

The spindle unit comprises a motor base 10 as a stationary element, and a generally cap-shaped hub 23 placed opposite to the base 10, as shown in Fig. 6. The base 10 has the same configuration as that of the base in the first embodiment. Also, the configuration of the hub 23 is similar to that of the hub 3 in the first embodiment.

A stationary shaft 21 is provided between the base 10 and the hub 23. One end 21a of the stationary shaft 21 is fitted and secured in a hole 10a formed in a central part of the base 10. Further, herringbone-shaped dynamic pressure generating grooves 21d-i, 21d-2 are formed on an outer periphery 21c of the stationary shaft 21.

Also, as shown in Fig. 7, a plurality of spiral-shaped dynamic pressure generating grooves 21a-1 are formed on an end face 21b of the stationary shaft 21 on its free end side.

Meanwhile, the hub 23 generally consists of a top portion 23B, and a cylindrical portion 23C extending axially from the top portion 23B. A recessed portion 23a is formed on an inner side of a central part 23b of the top portion 23B, and a sleeve 24 is fitted in and secured to the recessed portion 23a. An inner periphery 24a of the sleeve 24 is opposed to an outer periphery 21c of the stationary shaft 21. The inner periphery 24a of the sleeve 24 and the outer periphery 21c of the stationary shaft 21 having the dynamic pressure generating grooves 21d-1, 21d-2 constitute a radial dynamic pressure bearing R3.

Also, a surface 23b-1 of the central part 23b defining a bottom of the recessed portion 23a and located radially inside the sleeve 24 is opposed to the end face 21a of the stationary shaft 21. This end face 21a having the dynamic pressure generating grooves 21an1 and the surface 23b-1 of the central part 23b of the hub 23 constitute a thrust dynamic pressure bearing S3. The surface 23b-1 facing the end face 21a of the stationary shaft 21 has been so machined that its flatness is a few Sm or less.

Lubricating oil is provided between the opposing surfaces in the radial and thrust bearings R3 and S3.

The hub 23 is made in the same manner as that for the hub 3 of the first embodiment.

In the spindle unit with the above arrangement, the stator coil 20 fixed to the base 10 generates a rotational magnetic field that causes the hub 23 having the rotor magnet 30 fixed thereto to rotate. Then, by this rotation, the dynamic pressure generating grooves 2ld-l, 21d-2 formed on the stationary shaft 21 generate a dynamic pressure to hold the sleeve 24 and hence the hub 23 relative to the stationary shaft 21 in the radial direction. At the same time, dynamic pressure generating grooves 21a-1 formed on the end face 21a of the stationary shaft 21 generate a dynamic pressure to hold the hub 23 in the axial direction.

The third embodiment has effects and advantages similar to those of the first embodiment. Also, since the third embodiment does not use a flange which the first and second embodiment use, the constituent parts of the spindle unit are reduced in number more than in the first and second embodiments.

In the third embodiment, the dynamic pressure generating grooves 21d are formed on the outer periphery 21c of the stationary shaft 21. Alternatively, the dynamic pressure generating grooves can be formed on the inner periphery 24a of the sleeve 24. Further, in place of the dynamic pressure generating grooves 21a-1 formed on the end face 21a of the stationary shaft 21, dynamic pressure generating grooves can be formed on the surface 23b-1 of the central part 23b of the hub 23.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

CLBMS

1. A spindle unit comprising: a stationary element to which a stator coil is fixed; a shaft having a free end and a fixed end which is fixed to the stationary element; a flange fixed to the shaft; a hub placed opposite to the stationary element so as to be rotatable around the shaft, said hub having a top portion and a cylindrical portion axially extending from the top portion, a rotor magnet being fixed to the cylindrical portion so as to oppose the stator coil; a sleeve which is fixed at a central part of the top portion of the hub and which is fitted around the shaft such that the sleeve can rotate around the shaft together with the hub; a radial dynamic pressure bearing consisting of an inner periphery of the sleeve and an outer periphery of the shaft, at least one of said inner periphery and said outer periphery having dynamic pressure generating grooves; and a thrust dynamic pressure bearing consisting of an end surface of the flange and a surface of the top portion of the hub confronting said end surface of the flange, at least one of said end surface of the flange and said surface of the top portion having dynamic pressure generating grooves.

2. A spindle unit as claimed in Claim 1, wherein said flange is fixed to the free end of the shaft; said top portion of the hub has a recessed portion formed on an inner side of the top portion to receive the sleeve and the flange; and said surface confronting the end surface of the flange is constituted of a surface which defines a bottom of the recessed portion and which is positioned radially inside the sleeve.

3. A spindle unit as claimed in Claim 1, wherein said flange is fixed around the shaft near the free end such that a shaft end portion on the free end side protrudes from the flange; said top portion of the hub has an aperture to receive the shaft end portion, and also has a recessed portion formed on an inner side of the top portion to receive the flange and the sleeve, said recessed portion surrounding said aperture; and said surface confronting the end surface of the flange is constituted of an annular surface which defines a bottom of the recessed portion and which is positioned radially inside the sleeve.

4. A spindle unit as claimed in any preceding claim, wherein said sleeve has an annular step which is positioned in the recessed portion so as to confront the other end surface of the flange; and at least one of the annular step and the other end surface of the flange has dynamic pressure generating grooves such that the annular step and the other end surface of the flange constitute a further thrust dynamic pressure bearing.

5. A spindle unit comprising: a stationary part to which a stator coil is fixed; a shaft having a free end and a fixed end which is fixed to the stationary element; a hub placed opposite to the stationary element so as to be rotatable around the shaft, said hub having a top portion and a cylindrical portion axially extending from the top portion, a rotor magnet being fixed to the cylindrical portion so as to oppose the stator coil; a sleeve which is fixed at a central part of the top portion of the hub and which is fitted around the shaft such that the sleeve can rotate around the shaft together with the hub; a radial dynamic pressure bearing consisting of an inner periphery of the sleeve and an outer periphery of the shaft, at least one of said inner periphery and said outer periphery having dynamic pressure generating grooves; and a thrust dynamic pressure bearing consisting of an end face of the free end of the shaft and a surface confronting the end face of the top portion of the hub, at least one of said end face of the shaft and said surface of the top portion having dynamic pressure generating grooves.

6. A spindle unit substantially as herein described with reference to Figures 1 to 5 and Figures 6 and 7 of the accompanying drawings.

7. A spindle unit comprising: a stationary part on which a stator coil is mounted; a shaft projecting from the stationary element; a hub opposed to the stationary element and rotatable on the shaft, a rotor magnet being mounted on the hub so as to oppose the stator coil; and a sleeve which depends from a central part of the hub and which surrounds the shaft; a radially inner surface of the sleeve and a radially outer surface of the shaft constituting a radial dynamic pressure bearing, said inner and/or outer surface having dynamic pressure generating grooves formed thereon; an integral bearing face on the hub being opposed to an end face of the shaft and constituting a thrust dynamic pressure bearing, said face of the shaft and/or of the hub having dynamic pressure generating grooves formed thereon.

8. A spindle unit according to claim 7, wherein said end face of the shaft is provided by an end face of an axially extending flange on the shaft.