Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2001-08-20
2002-03-12
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S517000
Reexamination Certificate
active
06354743
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rolling bearing suitable for use as a bearing for, for example, a swing arm which is provided in a magnetic disk apparatus and swings minutely at a high speed.
A swing arm for a magnetic disk apparatus is required to swing minutely at a high speed in order that a magnetic head disposed at the leading end of the swing arm is able to seek a target track on a magnetic disk at a high speed and with high accuracy. To realize such high-speed and minute swing motion, there is used a rolling bearing in the base end swing portion of the swing arm.
FIG. 9
is a section view of a swing arm base end which is supported by a conventional rolling bearing. On the inside portion of a casing
1
for an actuator (for example, a voice coil motor) which carries out a high-speed and minute swinging motion, there is threadedly mounted a base plate
3
; and, the lower end of a support shaft
5
is fitted with and fixed to one end of the base plate
3
. Also, the upper end of the support shaft
5
is threadedly mounted on the casing
1
by a screw
6
which extends through the casing
1
.
On the outer periphery of the support shaft
5
, there are disposed a pair of ball bearings (rolling bearings)
7
in such a manner that they are spaced apart from each other in the axial direction of the support shaft
5
. Each of the ball bearing
7
is disposed in such a manner that its inner race is fixed to the support shaft
5
and its outer race is fixed to a housing
9
. To the outer periphery of the housing
9
, there is fixed the base end of a swing arm
11
, while the swing arm
11
is swingably supported on the support shaft
5
through the ball bearings
7
. At the leading end of the swing arm
11
, there is disposed a magnetic head (not shown). Also, on the outer periphery of the housing
9
, there is disposed a voice coil portion
13
, while the voice coil portion
13
is situated in a magnetic field which is formed by two permanent magnets
15
disposed within the housing
9
. Accordingly, in case where a given current is caused to flow in the voice coil portion
13
by a magnetic circuit, there is applied a rotational force to thereby swing the swing arm
11
by a given amount.
By the way, into the ball bearing
7
of this type, there is enclosed lubricant such as lubricating oil or grease for the purpose of lubrication. Conventionally, the amount of enclosure of the lubricant into the ball bearing is generally set in the range of 10 to 20% of the capacity of a space formed in the inside portion of the ball bearing.
Also, conventionally, the two ball bearings
7
,
7
, into which grease is enclosed as lubricant, are respectively given a pre-load (that is, an axial load applied to a bearing to thereby adjust a clearance between a rolling element and inner and outer races in order to prevent the shaft of the bearing from swinging as well as prevent the rolling element from slipping, swinging and generating noises) before they are put into practical use. And, as shown in
FIG. 10
, adhesives are applied to the peripheries of inner race inside diameter surfaces
7
a
,
7
a
and outer race outside diameter surface
7
b
,
7
b
, so that the two ball bearings
7
,
7
can be bonded and fixed to the support shaft
5
and housing
9
. Also, the both side surfaces of each of the ball bearings
7
,
7
can be normally sealed through seal members
73
. By the way, conventionally, the pre-load is generally set in the range of 300 gf to 800 gf.
In recent years, as the magnetic disk apparatus becomes highly dense, the magnetic disk apparatus is required that a spacing between the magnetic head and magnetic disk is as narrow as possible. Due to this, for the reliability of the magnetic disk apparatus, control of contamination becomes more and more important. Especially, since the swing arm is disposed adjacent to the magnetic disk surface, the swing arm is required that it is as free as possible from the contamination. For this reason, for the ball bearing, there are needed lubricant and lubricating method which can reduce the evaporation and scattering of the lubricant further than the conventional lubricant and lubricating method.
On the other hand, the track width of the magnetic disk has been made narrower and narrower, which requires the swing arm to speed up its access to the target track and enhance the accuracy of its positioning operation. This in turn requires the ball bearing, which supports the swing arm, that it can prevent an increase in torque as well as a sudden variation in the torque (torque spike).
However, the conventional ball bearing for a swing arm generally aims at extending its life and enclosing thereinto a large amount of grease in the range of 10 to 20% of the capacity of the space formed in the inside portion of the ball bearing. Therefore, in the conventional ball bearing, there are necessary various devices to eliminate a fear that outgases can be generated due to the evaporated or scattered grease, and a fear that such outgases can stick to the surface of the magnetic disk. Also, in case where the grease enclosure amount is increased for enhancement of the durability of the bearing, the viscosity and mixing resistance of the grease increase to thereby cause the torque to vary and increase.
SUMMARY OF THE INVENTION
The present invention aims at eliminating the drawbacks found in the conventional rolling bearings. Accordingly, it is an object of the invention to provide a rolling bearing which, while preventing fretting wear occurring when lubricant is small in amount, can keep torque from increasing or varying and can prevent contaminations from being produced due to the evaporation and scattering of the lubricant.
In attaining the above object, according a first aspect of the invention, there is provided a rolling bearing structured such that, in the inner peripheral surface of an outer race and the outer peripheral surface of an inner race, there are formed raceway surfaces respectively and, between these raceway surfaces, there are interposed a plurality of rolling elements, whereby the inner and outer races are assembled to each other through the rolling elements, wherein, in a space formed between the raceways of the outer and inner races, there is enclosed lubricant in an amount of 0.3% to 3% of the capacity of the space.
In the present rolling bearing, in the space formed between the raceways of the outer and inner races, there is enclosed the lubricant and the lubricant enclosure amount is set in the range of 0.3-3% of the capacity of the space. Due to this, there can be secured a proper amount of lubricant. The proper amount of w lubricant can prevent not only the early fretting wear of the bearing surfaces as well as the damage of raceway surfaces and rolling elements which are easy to occur in case of the lubricant enclosure amount of less than 0.3%, but also the evaporation and scattering of the lubricant as well as the increase and variation in the torque which are easy to occur in case of the lubricant enclosure amount of more than 3%. Therefore, in case where a rolling bearing according to the invention is used as a bearing for a swing arm provided in a magnetic disk apparatus, the high-speed and high-accuracy operation of the swing arm can be realized with reduced contaminations.
Also, according to a second aspect of the invention, there is provided a rolling bearing, wherein a seal member for closing an annular clearance of the above-mentioned space opened on the two end faces of the above-mentioned outer and inner races may be fixed to either of the outer race or inner race.
In the present rolling bearing, the annular clearance of the above-mentioned space opened on the two end faces of the outer and inner races is sealed by the seal member, thereby being able not only to prevent foreign objects from invading the inside portion of the bearing from outside but also to prevent the lubricant enclosed in the space from evaporating and scattering to the outside. This not only can extend the life of the rollin
Muraki Hiromitsu
Seshimo Takashi
Takamizawa Toru
Tani Hiroshi
Hannon Thomas R.
NSK Ltd.
Sughrue & Mion, PLLC
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