JP2005098394A - Fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device of low torque, without malfunction or failure due to static charged on a rotary part to achieve stability, and a magnetic disc rotation device using that. <P>SOLUTION: This fluid bearing device is composed by filling lubricant with lithium salt added as conductivity providing agent with less effect of increasing viscosity to a bearing gap between a bearing sleeve 5 and a shaft 2. An electricity continuity passage can thus be securely held between the rotary part and a fixed part. The rotary part can thus be prevented from being charged with static, without worsening torque loss at low temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bearing member used in a high-speed digital copying machine, a laser printer, a rotating magnetic head device of a video tape recorder, etc. in which a magnetic disk drive spindle motor or polygon mirror rotary drive device is used. The present invention relates to a hydrodynamic bearing device that uses a lubricant filling a gap with a shaft member as a pressure generating fluid, and in particular, prevents static charging of a rotating part that occurs during high-speed rotation.

  Conventionally, a hydrodynamic bearing device fills a gap between a bearing member and a shaft member with a lubricating fluid and increases dynamic pressure on at least one of the inner peripheral surface of the bearing member and the outer peripheral surface of the shaft member. A generation groove is formed, whereby a pressure increase is generated in the dynamic pressure generation groove when the bearing member or the shaft member is rotated, and both members are maintained in a non-contact state. The lubricants used in these hydrodynamic bearing devices use synthetic oils such as mineral oils, poly-α-olefin oils, ester oils, silicone oils, and fluorine oils as base oils.

In the hydrodynamic bearing device, since either the bearing member or the shaft member rotates at a high speed in a non-contact state, the rotating portion is charged by the flow of the lubricant. Further, when used in a magnetic recording apparatus using a magnetic disk, the magnetic disk is charged by friction with air, the lubricant is sandwiched between them, and the rotating member that rotates in a non-contact manner stores electric charges. When used in a magnetic recording device such as a VTR using a magnetic tape, the rotating cylinder stores electric charges due to friction with the magnetic tape. Conventionally, a conductivity-imparting agent such as carbon black or alkyl allyl sulfonate has been added to the lubricant in order to release this charge. (For example, refer to Patent Document 1.)
Japanese National Patent Publication No. 11-514778

  The problem to be solved is that the addition of the above conductivity-imparting agent has a thickening effect on the lubricant, resulting in an increase in torque loss during high-speed rotation and accompanying deterioration of the lubricant due to heat generation. It is.

  An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a hydrodynamic bearing device that has lower torque loss and higher heat resistance while preventing charging of a rotating member.

  In order to solve the above problems, a hydrodynamic bearing device according to the present invention includes a bearing member and a shaft member in which a dynamic pressure generating groove is formed on at least one facing surface of the bearing member and the shaft member, and the dynamic pressure generating groove is opened. In the hydrodynamic bearing device in which a gap is filled with a lubricant, a lithium salt is added as a conductivity imparting agent to the lubricant.

  Moreover, various well-known additives, such as antioxidant, an oil improvement agent, an extreme pressure agent, and a rust preventive agent, can also be mix | blended as needed.

According to the hydrodynamic bearing device of the present invention, the lubricant sandwiched between the shaft and the bearing sleeve contains a conductivity-imparting additive, so that static electricity does not accumulate in the rotating portion, and is stable even under use conditions such as high-speed rotation. And low torque loss can be realized.
Further, by using the hydrodynamic bearing device, it is possible to provide a magnetic disk rotating device that is stable and has a low torque loss even under use conditions such as high-speed rotation without accumulation of static electricity at the rotating portion.

  Hereinafter, embodiments of the invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows an example of a hydrodynamic bearing device used in a hard disk drive, which has the same configuration as that of a conventional hydrodynamic bearing device except for a lubricant 10, and has a dynamic pressure generating groove 4a and a dynamic pressure generating groove on the outer peripheral surface. One end of the shaft 2 on which 4b is formed is press-fitted into the base 1, and a thrust receiver 3 is fixed to the other end to form a shaft portion. A bearing sleeve 5 is press-fitted into the inner peripheral surface of the hub 6 for attaching a magnetic disk or the like, and a thrust plate 11 is attached to one end of the bearing sleeve 5 to form a bearing body. Then, the bearing sleeve 5 is mounted on the shaft 2 so that the thrust plate 11 and the thrust receiver 3 face each other, and a lubricant 10 is filled in the gap between the shaft portion and the bearing body.

  A stator coil 9 is provided on the outer wall 1a formed on the base 1, and a rotor magnet 7 is attached to the inner peripheral surface of the hub 6 facing the stator coil 9 via a rotor yoke 8, thereby constituting a motor drive unit. The

  When the bearing sleeve 5 and the hub 6 are rotationally driven by the motor drive unit, dynamic pressure is generated in the lubricant 10 by the pumping action of the dynamic pressure generating groove 4a and the dynamic pressure generating groove 4b formed in the shaft 2, and the bearing body is The shaft floats from the shaft portion, and the shaft portion and the bearing body are rotatably supported without contact.

  The dynamic pressure generating groove 4a and the dynamic pressure generating groove 4b may be formed on one or both of the outer peripheral surface of the shaft 2 and the inner peripheral surface of the bearing sleeve 5, and the thrust dynamic pressure generating groove is formed. Alternatively, it may be formed on one or both of the opposing surfaces of the thrust receiver 3 and the thrust plate 11. Further, both the radial side and thrust side dynamic pressure generating grooves may have a shape in which the pressure of the lubricant 10 increases in the gap between the opposing surfaces, and various forms such as providing a refracting portion and changing the depth are possible. . Further, a fluid bearing device in which the shaft portion rotates and the bearing sleeve 5 is fixed may be used.

  Here, since the characteristic of the hydrodynamic bearing device of the present invention resides in the lubricant 10, an example of a lithium salt will be described below.

  As described above, the hydrodynamic bearing device of the present invention has lithium-bis-trifluoromethane-sulfonimide or lithium-bis-pentafluoroethane-sulfonimide in the lubricant 10 held in a non-contact manner between the rotating portion and the fixed portion. By adding a lithium salt such as the above, constant conductivity can be imparted to the lubricant, and the electrical conduction path between the rotating part and the fixed part can be reliably maintained.

(Embodiment 2)
Next, an example of the magnetic disk rotating device of the present invention will be described. In FIG. 2, in a magnetic disk rotating apparatus incorporating a shaft-rotating type fluid bearing, three magnetic disks 33 are stacked on a hub 30 with a spacer 32 interposed therebetween, and are fixed by a clamp 31. A rotor magnet 29 is provided on the inner peripheral side of the hub 30, and a motor is formed with the stator coil 28 provided on the fixed side, and rotating parts such as the magnetic disk 33 and the hub 30 are rotated at high speed. To drive.

The stator coil 28 is provided on the outer periphery of the bearing sleeve 22, and the bearing sleeve 22 is fixed to a base 27 connected to the ground. A shaft 21 is press-fitted into the hub 30, and the shaft 21 is inserted into a bearing sleeve 22 to which a thrust receiver 23 is attached. The thrust plate 24 is fixed to the opening on the base 27 side of the bearing sleeve 22.

  A thrust gap and a radial gap between the shaft 21 and the bearing sleeve 22, between the thrust receiver 23 and the bearing sleeve 22, and between the thrust receiver 23 and the thrust plate 24 are filled with a lubricant 26 added with lithium salt as a conductivity-imparting agent. Yes. A dynamic pressure generating groove is provided on at least one of the surfaces where the shaft 21 and the bearing sleeve 22, the thrust receiver 23 and the thrust plate 24 face each other, and the shaft 21 floats due to the dynamic pressure generated by the rotation.

  In the above configuration, the magnetic disk 33 and the hub 30 can be electrically connected by using, for example, a conductive material such as metal or conductive resin for the spacer 32 and the clamp 31 that are in contact with the magnetic disk 33. The hub 30 is usually made of aluminum or an iron-based metal material, and is electrically equivalent to the press-fitted shaft 21. Accordingly, the magnetic disk 33 is electrically connected to the bearing sleeve 22 via the lubricant, and static electricity generated in the magnetic disk 33 is discharged to the base 27.

  Similarly, in the bearing sleeve rotating type, static electricity generated on the magnetic disk fixed to the rotating member is discharged to the base via a lubricant added with lithium salt as a conductivity imparting agent.

  The hydrodynamic bearing device of the present invention and the conventional hydrodynamic bearing device are incorporated into the magnetic recording disk rotating device described in the second embodiment, and the magnetic disk is detached and rotated at a current consumption of 245 milliamperes in an atmosphere of 20 ° C. The characteristics were compared using the motor unit. In addition, the compared real machine rotator was cleaned and recombined.

  Dioctyl sebacic acid (purity 99.8% by gas chromatography) is used for the base oil of the hydrodynamic bearing device, and various known additives such as commercially available antioxidants, oiliness improvers, extreme pressure agents, and rust inhibitors are used. The blended bearing oil was designated as Conventional Example A. The bearing oil of Example A of the present invention is obtained by adding 2 parts by weight of lithium-bis-trifluoromethane-sulfonimide as a lithium salt when the bearing oil of Conventional Example A is 100 parts by weight. Similarly, the bearing oil of Example B is obtained by adding 2 parts by weight of lithium-bis-pentafluoroethane-sulfonimide as a lithium salt. On the other hand, the bearing oil of Conventional Example B is obtained by adding 2 parts by weight of a linear alkylbenzene sulfonic acid Na salt having 8 to 12 carbon atoms. A sample to which Ketjen Black, known as fine particle carbon black, was added as Conventional Example C was prepared, but it was not dispersed in the bearing oil and separated, so it was not measured in this experiment.

  Here, values (current consumption, electric resistance value between the rotating part and the fixed part) measured as characteristic comparison are shown in the following table.

Thus, the hydrodynamic bearing device of the present invention can secure an electrical conduction path between the rotating part and the fixed part without generating a large torque loss as in the conventional example.

  The hydrodynamic bearing device of the present invention is useful for precision bearings and the like that do not like electrostatic charging, such as magnetic recording devices.

Sectional drawing of the hydrodynamic bearing apparatus in one embodiment of this invention Sectional drawing of the magnetic-disk rotating apparatus in one embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base 2 Shaft 3 Thrust receiving 4a, 4b Dynamic pressure generating groove 5 Bearing sleeve 6 Hub 7 Rotor magnet 8 Rotor yoke 9 Stator coil 10, 26 Lubricant 11 Thrust plate 31 Clamp 32 Spacer 33 Magnetic disk

Claims (2)

A hydrodynamic bearing device in which a lubricant is added to a lubricant in a fluid bearing device in which a lubricant is filled in a bearing gap between a shaft inserted into a bearing hole of a sleeve. A disk rotating device for magnetic recording on which the hydrodynamic bearing device according to claim 1 is mounted.

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