Abstract:
In a magnetic disk apparatus, the spindle motor is provided with a hole that penetrates the hub in the axial direction thereof. The hole permits fluid pressure on the outside and inside of the hub to become balanced, reducing the axial fluid force caused by the rotation of the spindle motor. The apparatus further includes a bearing provided with a groove for dynamic pressure generation and a magnetic lubrication fluid which, in combination with a permanent magnet, prevents oil leakage and scattering.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a magnetic disk equipment using a dynamic pressure slide bearing. 
     Following remarkable spread of a personal computer, the magnetic disk equipment needs high recording density, large capacity, small size and high speed. The magnetic disk equipment, that is used for a personal computer, needs high speed and high precision of the rotation more and more. Ball bearings were used for the motor for a magnetic disk drive conventionally. Improvement of the manufacture precision and the lubrication, etc. in the ball bearings has raised rotary precision. 
     But the ball bearings have a limit to the improvement of manufacture precision. Rotary precision is deteriorated by wear of bearing surfaces. A transformation is easy to arise in the inside and outside ring in assembly of a motor, when the ball bearings of a small diameter are used for miniaturization of equipment. The limit of high recording density arises by the above reason. There is a motor that adopts a dynamic pressure slide bearing instead of ball bearings. This motor is disclosed in the Japanese patent Laid-open print No. 5-336697 official gazette. The motor that adopts a dynamic pressure slide bearing has the problem of the oil leakage from the bearing part and scattering of oil particles. The seal structure of a dynamic pressure slide bearing is disclosed to the Japanese patent Laid-open print No. 7-310830 official gazette. 
     SUMMERY OF THE INVENTION 
     The magnetic disk equipment for the personal computer of a desk top type and a notebook type is easy to handle it, and it is necessary to endure an impact when it falls from the top of a desk and during a portage. When magnetic disk equipment receives 500-1000 G impact, the intensity of the structure parts is deteriorated, and measured precision changes. In case of the magnetic disk equipment using dynamic pressure slide bearing equipment, the oil scattering from the bearing equipment occurs, and the function is sometimes harmed. 
     The structure that refers to the seal of bearing equipment is disclosed to the Japanese patent Laid-open print No. 8-310830 official gazette. This seal is used for the oil leakage measures of bearing equipment. But it is not considered against oil pollution of magnetic disk equipment. To increase rotary precision, a motor using a dynamic pressure bearing is disclosed to the Japanese patent Laid-open print No. 5-336697 official gazette. But when a spindle motor is installed in magnetic disk equipment and it is rotated, fluid power operates on a spindle motor in the axial direction. This fluid power is generated by the flow of the air between rotary parts such as the magnetic disk and the stillness part. At this time, because the flow of the air is not uniform, the fluid power fluctuates and sometimes harms the rotary precision of the axial direction. 
     Therefore, the fluid power of the axial direction that acts on the spindle motor for high recording density of the magnetic disk equipment must be reduced. A conventional spindle motor for the magnetic disk drive is positioned to the axial direction by force that attracts magnetically. But a conventional spindle motor does not consider the fluid power and the fluctuation of the fluid power that occur by the rotation of the magnetic desk. 
     It is an object of the invention to prevent pollution of the magnetic disk by the oil leakage and scattering of the oil particles from the bearing equipment. 
     Another object of the invention to provide the magnetic disk equipment with high reliability that does not generate the fluid power and the fluctuation of the fluid power that occurs by the rotation of the magnetic desk. 
     The present invention has a motor drive part and magnetic fluid bearing structure using the dynamic pressure slide bearing inside a hub on which the magnetic disk is mounted. A passage of the axial direction for air circulation is built in the hub. As a result, the fluid power and the fluctuation of the fluid power of the axial direction that acts on the spindle motor during the rotation is reduced, and the rotary precision of the axial direction is improved. To prevent the oil leakage from the bearing equipment, magnetic fluid is used as a lubrication fluid of the bearing. And magnetic fluid is magnetized with the permanent magnet arranged in the bearing equipment. 
     By preparing the spiral groove to generate the dynamic pressure in the opening of bearing equipment or in the face of hub that is opposed to this opening, the oil particle is prevented from rushing outside the bearing equipment. In case magnetic fluid leaks outside the bearing equipment by impact force that operates on magnetic disk equipment, the magnetic fluid leaked is recovered in the bearing equipment along the spiral groove by using the rotation of hub. 
     A hollow of a ring-form is provided in the hub in the neighborhood of the connection of the hub and the rotary axis. In case magnetic fluid leaks outside the bearing equipment by impact force that operates on magnetic disk equipment, the magnetic fluid leaked is held in this hollow. As a result magnetic fluid is prevented from scattering. 
     The passage for the air circulation that penetrates the axial direction was built in the hub on which the magnetic disk is mounted. As a result the fluid power of the axial direction that acts on the hub and the fluctuation of this fluid power can be suppressed. Because the rotary precision of the axial direction can be raised, the recording density of magnetic disk equipment improves. The groove for dynamic pressure generation was prepared in the opening of bearing equipment. The hollow of a ring-form was provided in the press fitting part of the hub and the axis. As a result, leakage of magnetic fluid that was enclosed in the bearing equipment and scattering of the oil particles can be prevented during the rotation. Leakage of magnetic fluid that was enclosed in the bearing equipment and scattering of the oil particle can be prevented even if impact power operates on magnetic disk equipment. Pollution of the magnetic disk is prevented, the precise spin of the magnetic disk can be maintained, and the life of the magnetic disk becomes long. By the above, magnetic disk equipment with a high recording density and with high reliability can be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is the part vertical sectional view of the magnetic disk equipment of the present invention. 
     FIG. 2 is the part vertical sectional view of the filter structure of the passage formed to the hub for the air circulation of the present invention. 
     FIG. 3 is the part vertical sectional view of the filter structure of the passage formed to the hub for the air circulation of the present invention. 
     FIG. 4 shows the groove shape of the upper end face of the bearing case for the dynamic pressure occurrence of the bearing equipment opening of the present invention. 
     FIG. 5 shows the groove shape of the upper end face of the bearing case for the dynamic pressure occurrence of the bearing equipment opening of the present invention. 
     FIG. 6 is the vertical sectional view of the seal ring and shows the spiral groove of the inside circuit (on the face that is opposed to the rotary axis of the seal ring) of the present invention. 
     FIG. 7 is the part vertical sectional view of a magnetic disk equipment not having a hole in the hub with respect to FIG.  1 . 
     FIG. 8 is the part vertical sectional view of the magnetic disk equipment of other embodiment of the present invention. 
    
    
     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 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  22  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 μM-30 μM, 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.