Magnetic disk apparatus

The hole that penetrates the axial direction in the hub, the force of the axial direction by fluid force that operates on the spindle motor is reduced during the rotation. Fluctuation of fluid power is reduced by this hole. The rotary precision of the axial direction improves. Against the oil leakage from the bearing equipment, magnetic fluid is used as a lubrication fluid of the bearing. Magnetic fluid is magnetized with the permanent magnet arranged in the bearing equipment, and oil leakage is prevented. Against scattering of the oil particle, the groove for dynamic pressure generation is in the opening of bearing equipment. The oil particle is kept inside the bearing equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As follows, the embodiment of the present invention is explained. In FIG. 1 , case 24 of magnetic disk equipment is comprised of casing 15 and casing cover 20 . Part of case 24 is omitted in this figure. The transducer is arranged in the surface of the magnetic disk for recording information in the magnetic disk and for reproducing information recorded in the magnetic disk. The transducer is positioned to a truck where the information is recorded or reproduced in. In FIG. 1, a positioning device to position the transducer is omitted. In this case 24 , motor (spindle motor) 25 for the drive of magnetic disk 13 is arranged. Motor 25 is composed of multipolar permanent magnet 10 provided in the inside circuit of hub 11 of the cup shape, armature winding 9 for magnetic field generation provided on the casing 15 side and armature iron core 8 . That is, armature iron core 8 is adjusted to the projection part of casing 15 . Seal ring 7 , dynamic pressure radial bearing 2 , permanent magnet 3 provided between dynamic pressure bearings, stopper ring 16 and thrust bearing 5 are arranged in the bearing equipment along rotary axis 1 from the side (the upper side of the figure) of the opening of bearing case 6 . Magnetic fluid 4 for lubrication is filled between rotary axis 1 and radial bearing 2 , between rotary axis 1 and thrust bearing 5 . Spiral groove 17 of the shape that is shown in FIG. 4 or FIG. 5 is prepared in the opening end part of this bearing case 6 . In case magnetic fluid 4 leaks in the space between the end of bearing case 6 and the face of hub 11 , this spiral groove 17 returns the leaked magnetic fluid inside seal ring 7 by using the negative pressure or pumping that occurs by the turn of rotary axis 1 . As a result the scattering to the side of motor 25 of magnetic fluid 4 can be prevented. In the inside face of seal ring 7 , spiral groove 21 is prepared. Groove 21 prepared in the seal ring 7 returns magnetic fluid 4 to the bearing side. Rotary axis 1 press fitted to the hub 11 is supported to be able to rotate by dynamic pressure radial bearing 2 provided at both ends of permanent magnet 3 . To hold magnetic fluid 4 in bearing case 6 , permanent magnet 3 is arranged. The load of the axial direction is supported by receiving the sphere part of the tip of rotary axis 1 on thrust bearing 5 . A magnetic disk Clamp 18 is fixed to the rotary axis 1 and hub 11 by bolt 19 . Stopper ring 16 held between thrust bearing 5 and radial bearing 2 is fitted in groove 26 prepared in rotary axis 1 . As a result rotary axis 1 does not come out to the axial direction. Passage 12 (hole) that connects the motor 25 side and casing cover 20 side for the air circulation penetrates the hub 11 . Several magnetic disks 13 install to the outer periphery of the hub 11 to keep the specified space by spacer 14 . The top of magnetic disk 13 is fixed with magnetic disk clamp 18 . The sectional view of the magnetic disk equipment is shown in FIG. 7 . As shown in FIG. 7 , the space between casing cover 20 and hub 11 is small, and the space is about 1 mm. The air that is shown to arrow A flows in a conventional structure that does not prepare hole 12 in the hub 11 when magnetic disk 13 spins. Therefore, the pressure difference arises between the side of the outer periphery of the magnetic disk 13 and the center of the hub 11 . Then, the power that attracts the hub 11 to the casing cover 20 side occurs. Inside the hub 11 in which motor 25 is positioned, the air flows from arrow C to the direction of arrow B. At this time, the pressure difference arises between bearing case 6 and permanent magnet 10 . But the force that attracts the hub 11 to the motor 25 side is small than the casing cover 20 side by difference between the differences of the diameter. Therefore, the hub 11 is attracted to the casing cover 20 side. Disorder of the air on the casing cover 20 side arises by magnetic disk 13 and magnetic disk clamp 18 . It acts as a fluctuation load of the axial direction. This fluctuation load is shown to arrow D. On the other hand, magnet thrust power is given to the hub 11 by force (about 100 GRF) that operates between permanent magnet 10 and armature iron core 8 . But the bearing load that acts on the thrust bearing 5 becomes smaller than the thrust load at the time of standing still because the force that works by the pressure difference on the casing cover 20 side becomes the reverse direction. The magnetic attraction force is at most 100 GRF. Therefore, when the load of the axial direction that occurs by the spin of this magnetic disk 13 approaches the magnetic attraction force, the vibration displacement of the axial direction by disorder of the air on the casing cover 20 side enlarges. The vibration displacement by this disorder of the air is the asynchronous vibration that does not relate to the number of revolutions. This asynchronous vibration cannot be controlled by the control system of magnetic disk equipment. Therefore, when the asynchronous vibration is large, the recording density of magnetic disk 13 cannot be raised. In this embodiment, the hole 12 is prepared in the hub 11 to maintain the magnetic attraction force that operates between permanent magnet 10 and armature iron core 8 , and to reduce the fluctuation load by disorder of the air. As a result the axial load that acts on the hub 11 is made to balance by making the pressure on the motor 25 side balance with the pressure on the casing cover 20 side. When the holes 12 are prepared in the hub 11 , because the flow of the air becomes the arrow direction of FIG. 1 , there is also an Advantage in cooling of the motor 25 side. By raising cooling of the motor side, the bearing equipment can be cooled. Therefore, evaporation of magnetic fluid enclosed in the bearing equipment can be suppressed. As a result the life of magnetic disk equipment becomes long, and reliability of magnetic disk equipment improves. In this embodiment, passage 12 (hole) for the air circulation is built, and the flow of the air that is shown in the arrow of FIG. 1 is made. Even if passage 12 (hole) for the air circulation is applied to magnetic disk equipment on which the spindle motor using a conventional roller bearings is mounted, the fluctuation load by disorder of the air can be reduced. Therefore, the Function Advantage that is similar to the case of the slide bearing of FIG. 1 is obtained. With the magnetic disk equipment of this embodiment. Using dynamic pressure radial bearing 2 that has three circular arcs or herringbone type dynamic pressure bearing 2 , the hub 11 can maintain the high precision rotation. But as it is mentioned above, the flow of the air arises in the arrow direction shown in FIG. 1 on the motor 25 side. When the oil particle occurs by evaporation of magnetic fluid 4 enclosed in bearing equipment, the oil particle comes out to the magnetic disk 13 side along the flow of the air, and magnetic disk 13 is polluted. As shown in FIG. 2 , this pollution can be prevented by using the filter 27 , made of fluorine resin or coated fluorine resin on fiber, to cover hole 12 . While these filters 27 pass the air, liquid is not passed. Therefore, these filters 27 have the advantage that fits the purpose of the present invention. Filter 27 ′ can be made ring shaped against hole 12 ′ shown in FIG. 3 . In this embodiment, by building passage 12 ′ for the air circulation that penetrates the axial direction in the hub 11 ′, the flow of the air arises in the arrow direction shown in FIG. 1 . Because filter 27 shields the dust of bearing equipment and the motor part, the damage of magnetic disk 13 by the dust can be prevented. In the slide bearing equipment, the occurrence of the oil particle by evaporation of the lubricant enclosed in the bearing equipment is not avoided. Therefore, long-term use decreases magnetic fluid 4 for lubrication enclosed in bearing equipment. When magnetic fluid 4 decreases, the dynamic pressure function of the bearing is harmed. When the dynamic pressure Function of the bearing is harmed, the vibration occurs by the oil shortage, and rotary precision deteriorates. As shown in FIG. 4 , FIG. 5 and FIG. 6 , to prevent magnetic fluid 4 from decreasing by scattering, in this embodiment, spiral grooves 17 and 21 for dynamic pressure generation are prepared in the end of the bearing case 6 and in the inside circuit of the seal ring 7 . In case there is not spiral groove 17 for dynamic pressure generation in the end of bearing case 6 , the rotation of the hub 11 generates the turning flow of the air inside the hub 11 in which motor 25 was arranged. And, as shown in FIG. 7 , the air flows from arrow C to the direction of arrow B, and the pressure difference arises between axis 1 and permanent magnet 10 . Therefore, the air of the end part of bearing case 6 becomes the turning flow. The oil particle that evaporated in bearing case 6 mixes in this turning flow and scatters on the motor 25 side. In this embodiment, spiral groove 17 for dynamic pressure generation is prepared in the end of bearing case 6 to converge on the direction that is the same as the rotary direction of axis 1 . The oil particle is returned to the seal ring 7 side by making the turning flow along spiral groove 17 (arrow direction of FIG. 4 and FIG. 5 ). As a result the oil particle that occurs because of evaporation, etc. in bearing case 6 does not scatter on the motor 25 side. The space between the end of bearing case 6 and the hub 11 is made small so that an occurrence of the dynamic pressure becomes easy. For example, this space is 0.1 MM-0.3 MM. The space between the inside circuit of seal ring 7 and axis 1 is made 10 &mgr;M-30 &mgr;M, and the turning flow of the air of the arrow direction of the figure is generated in parts of the spiral groove 21 . As a result the oil particle and magnetic fluid 4 that adhered to seal ring 7 is returned to radial bearing 2 . Groove 17 for dynamic pressure generation can be prepared in the face of the hub 11 that is opposed to the end of bearing case 6 instead of preparing in the end of bearing case 6 . While the hub 11 rotated, the flow of the air was conducted to the radial bearing 2 side in the opening of the bearing equipment, and in the part of motor 25 the air flows in the arrow direction shown in FIG. 1 . As a result the oil particle that comes out from the bearing equipment is prevented from scattering. In this embodiment, when the impact operates on the axial direction, axis 1 is prevented from getting out by stopper ring 16 . But magnetic fluid 4 enclosed in bearing equipment overcomes holding power by magnetic attraction force of permanent magnet 3 and sometimes comes out to the end part of bearing case 6 . The space between seal ring 7 and axis 1 and the space between bearing case 6 and the hub 11 is made small like above. In case magnetic fluid 4 comes out, it also can be stopped to the neighborhood of the end part of seal ring 7 . In the embodiment shown in FIG. 8 , hollow 23 of the ring-form in which magnetic fluid 4 is held is provided in the press fitting part of the hub 11 and axis 1 . In case the hollow 23 is not provided, when the hub 11 rotates, the centrifugal force scatters magnetic fluid 4 . In this embodiment, magnetic fluid 4 that comes out by impact force of the axial direction is held in hollow 23 . When the hub 11 rotates, the oil particle is prevented from scattering, and magnetic fluid 4 is recovered into the bearing equipment by the function of the spiral groove prepared in bearing case 6 and seal ring 7 . As a result pollution of magnetic disk 13 by the oil particle can be prevented.