Bearing structures, spindle motor, and hard disk drive

Details Bearing structures, spindle motor, and hard disk drive Bearing structures, spindle motor, and hard disk drive

2001-03-15

2004-02-03

Le, Dang (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S06700R

Reexamination Certificate

active

06686673

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to bearing structures, spindle motors, and hard disk drives. More particularly, the present invention relates to bearing structures, spindle motors, and hard disk drives with measures against electrostatic problems.
BACKGROUND OF THE INVENTION
One conventional hard disk drive (hereinafter referred to as a “HDD”) is schematically indicated in FIG.
10
. In the drawing, an HDD
100
is made of two major components; a disk section
110
and a head section
120
both being housed in a housing
130
. The disk section
110
is made of a spindle motor
111
which rotates at high speed, and a plurality of storage media
90
having information storage surfaces and being mounted on a periphery of the spindle motor
111
. The head section
120
is made of a plurality of head assemblies
121
which access the information storage surface of the storage media
90
rotating at a high-speed so as to record or replay necessary information, a carriage
125
which supports the head assemblies
121
, and a head mount
128
which performs a pivot operation of the carriage
125
allowing the head assemblies
121
to access information on each storage media
90
.
In response to recent needs for storage devices with smaller size, higher speed, and larger capacity, a hydrodynamic bearing tends to be used for a spindle motor
111
in place of a conventional ball bearing to implement a rotation with high speed of 10,000 rpm. or more with high accuracy. Especially, an attention has been directed to the use of a spindle motor with a hydrodynamic gas bearing which is free from heating during high-speed rotation and easy to be handled.
FIG. 11
shows an example of the spindle motor
111
having a hydrodynamic gas bearing. In this drawing, a column like shaft
113
is fixed to a base
112
, and a hollow cylinder-shaped sleeve
114
is fitted to the outer peripheral surface of the shaft
113
leaving a certain clearance therebetween. The outer peripheral surface of the shaft
113
and the inner peripheral surface of the sleeve
114
constitute a radial bearing section. Opposed to one end face of the sleeve
114
in an axial direction, a disk-shaped thrust plate
115
is attached to the base
112
perpendicular to the axis of the shaft
113
. On the surface of the thrust plate
115
opposed to one end face of the sleeve
114
, there is provided a groove
116
as shown in a dotted line for generating a thrust hydrodynamic pressure. The end surface of the sleeve
114
and the thrust plate
115
constitute a thrust bearing section The radial bearing section and the thrust bearing section constitute the hydrodynamic gas bearing, and a gas (normally the air) present between the components of each bearing section generates a hydrodynamic pressure by relative rotating movements of the components. A rotor hub
117
is fixed to the sleeve
114
, and a plurality of storage media
90
are mounted on the outer peripheral surface of the rotor hub
117
. Attached also to the base
112
is a radially-disposed stator
118
, which is wound with a coil. On the inner peripheral surface of the rotor hub
117
, there is mounted a rotor magnet
119
, which is faced with the stator
118
.
In operation of spindle motor
111
so constructed, an electric current supplied to the coil wound around the stator
118
induces repellent/attraction forces between the stator
118
and the rotor magnet
119
. This produces a rotational driving force of the rotor hub
117
, which drives the sleeve
114
fixed to the rotor hub
117
to rotate about the shaft
113
. This rotation generates hydrodynamic pressure in a radial direction at the radial bearing section, and this keeps the shaft
113
and the sleeve
114
out of contact with each other. On the other hand, in the thrust bearing section, the relative rotation between the end face of the sleeve
114
and the thrust plate
115
generates a hydrodynamic pressure in a thrust direction by the effect of the groove
116
. As a result, the sleeve
114
is lifted up from the thrust plate
115
, which makes the sleeve
114
, the rotor hub
117
, the storage media
90
, and other rotatable components out of contact with the shaft
113
, the thrust plate
115
, and other fixed components, thereby enabling a high-speed rotation.
As described above, the use of a hydrodynamic gas bearing provides the spindle motor
111
with stable and high-speed rotation. The high-speed rotation in a non-contact state, however, has problems, For example, the high-speed rotation causes an air friction, which generates an electrostatic charge in the rotatable components. The electrostatic charge is accumulated in the rotatable components since they are isolated from the fixed components. The bearing section with the ball bearing allows the electrostatic charge to flow into the fixed components being in contact with the ball bearing, which causes no problems. On the other hand, since the rotatable components of the hydrodynamic bearing are out of contact with the fixed components, the electrostatic charge generated in the rotatable components is prevented from leaking to the fixed components.
The electrostatic charge, if it is accumulated to a certain extent, can cause an electrostatic discharge between, for example, the disc section
110
and the head section
120
of the HDD (see FIG.
10
). This may in turn damage the head assemblies
121
, the storage media
90
, and other HDD components. The same problem can occur in other bearings such as magnetic and hydrostatic gas bearings in which the rotatable components are rotated without any contact with the fixed components.
In the hydrodynamic gas bearing, no hydrodynamic pressure is generated as long as the spindle motor is de-energized and then the rotatable components are maintained in contact with the fixed components. Therefore, the bearing member made of conductive material such as stainless steel allows the accumulated electrostatic charge to be discharged by the contacts with the components during the halts of the spindle motor. This means that a relatively short on/off driving of the spindle motor can prevent the accumulation of the electrostatic charge in the rotatable components. A relatively long time rotation without any contacts between the rotatable and fixed components accumulates a great amount of electrostatic charge, which may damage the HDD components.
The bearing components may be made of ceramics having an enhanced abrasion resistance to prevent abrasion and seizing thereof. Typically, the ceramic bearing member is insulative. Therefore, the bearing member made of ceramics disables the electrostatic charge from being discharged even by the contact of the bearing members during the halt of the spindle motor.
Japanese Patent Laid-Open Publication (A) No. 55916/1999 discloses a spindle motor having means for overcoming such problem.
FIG. 12
schematically illustrates the spindle motor
140
. In the drawing, a base
141
supports a shaft
142
onto which a rotor hub
143
is fitted. On an outer peripheral surface of the rotor hub
143
, a hard disk, not illustrated, is to be mounted. A radial bearing component
144
is attached to the shaft
142
, and a radial bearing component
145
is attached to the rotor hub
143
. The radial bearing component
144
and the radial bearing component
145
are faced with each other leaving a specified clearance therebetween in such a manner as to enable relative rotation thereof. Attached to both axial ends of the rotatable radial bearing component
145
are a pair of thrust bearing components
146
and
147
so that the components face with the bottom face and the top face of the fixed radial bearing component
144
, respectively, leaving a specified clearance. The shaft
142
, which is equipped with a stator
148
wound with a coil, is faced with a rotor magnet
149
attached to the rotor hub
143
for driving the spindle motor.
In operation of the spindle motor
140
so constructed, an electric current supplied to the coil of the stator
148
produces a rotational d

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