Abstract:
A high precision spindle suitable for hard disk drives, optical disk drives, such as DVDs, CD drives, and other applications includes a hub, a hybrid hydrodynamic an aerodynamic bearing system, a brushless motor, a starting/stopping assistant device and a base. The hybrid fluid film bearing system ensures that the spindle works at high precision, low acoustic noise and low power consumption. The starting/stopping assistant device lifts the rotating portion of the spindle and its load by means of magnetic force, hence, reduces the friction between the contacted surfaces of thrust air bearing. It reduces the starting/stopping time and lessens the wear of bearing, therefore, effectively suppresses the contamination caused by wear particles. Magnetic seals are also provide to prevent journal bearing fluid from leaking.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a high precision spindle with hybrid fluid bearing system and starting/stopping assistant device. It has the advantages of high speed, high precision, low acoustic noise, low power consumption, shorten starting/stopping time and reduced risk of contamination. The spindle is suitable for applications such as hard disk drive, DVD drive, printer and other suitable cases. 
     BACKGROUND OF THE INVENTION 
     Description of Related Art 
     With the advance of computer technology, more and more is required of a hard disk drive, optical disk drive, and other motor-driven storage drives. It is expected that data storage capability of a hard disk drive will be much higher with shorter read/write time. Besides the larger storage capacity, the hard disk drive is also expected to have characteristics of lower acoustic noise and better reliability under external shock and vibration. The higher requirements result in each component in hard disk drive to do more and perform better. 
     There is no exception for a spindle motor. The key task of a spindle motor is to provide a disk drive with turning power that is rotatably stable and reliable for many years. The ideal spindle motor should possess the characteristics of lower repeatable runout (RRO) and non-repeatable runout (NRRO), lower acoustic noise, lower power consumption, fast starting and stopping, and higher resistance to external shock and vibration. 
     It is difficult for conventional ball bearing spindle motors to meet all of these requirements. Therefore, a conventional ball bearing spindle motor is not likely suitable to be used in next generation of hard disk drive due to its drawbacks of higher non-repeatable runout as well as higher acoustic noise. The drawbacks of ball bearing are caused by the imperfect geometry on the inner race, outer race and balls or rolling elements of ball bearings. 
     In contrast, fluid film bearings have no surface contact during operation. Hence, it may be a better alternative for ball bearings used in hard disk drives. The fluid film bearing shows significantly lower non-repeatable runout and acoustic noise, and its relative higher damping provides better resistance to external shock and vibration as described in U.S. Pat. No. 5,358,339 to Konno et al., U.S. Pat. No. 5,697,708 to Leuthold et al. and U.S. Pat. No. 5,770,906 to Hazelton et al. 
     One of the major difficulties with a fluid film bearing in a hard disk drive is leakage of liquid lubricant. The leakage of lubricant degrades the performance of the fluid bearing. Besides, the oil droplets that leaks from the bearing may contaminate the surfaces of disks and cause the failure of the hard disk drive. 
     In this aspect, the aerodynamic bearing is attractive because there is no risk of lubricant leakage. The spindle motors using aerodynamic bearings are described in U.S. Pat. No. 5,283,491 to Jabbar et al. and U.S. Pat. No. 5,760,509 to Chung et al. However, the air bearings have relatively lower load capacity and stiffness compared with oil bearings at similar geometric conditions. Furthermore, with a pure aerodynamic bearing system, the hub and the base of spindles are electrically insulated during the operation of spindles. The electrical insulation blocks the discharging of static charges from the base of spindles, which would otherwise result in possible damage of magnetoresistence (MR) head and cause failure of hard disk drives. 
     The air bearings also have relatively higher wear ratio, especially during the starting and stopping times of the spindle motor. Besides, the prior inventions cannot prevent the contamination caused by the tiny particles out of the bearings, which are generated by the wearing of bearing surfaces, especially at the moment of starting and stopping of spindles. 
     The present invention attempts to overcome the above-mentioned drawbacks in prior inventions and provides a hybrid fluid-bearing system spindle with the advantages of power saving, fast starting, contamination free and cost-effective. 
     SUMMARY OF THE INVENTION 
     A general objective of the present invention is to provide a power saving, fast starting, contamination free, cost-effective, spindle motor with hybrid fluid bearing system for hard disk drive and other storage devices. The present invention will overcome the limitations and drawbacks of the prior art. 
     Another objective of the present invention is to provide a spindle motor with magnetic assisting starting/stopping device, which reduces the friction and wearing during the moment of starting/stopping, therefore, results in a fast starting spindle motor with reduced risk of contamination caused by worn particles. 
     A further objective of the present invention is to provide a hybrid bearing design for disk drive spindles, which comprises hydrodynamic journal bearings and aerodynamic thrust bearings. With the hybrid design of the bearing system, the total power consumption is reduced. By means of ferrofluid seals, the bearing system obtains substantially a contamination free condition. 
     The basic construction of the hybrid bearing system comprises two hydrodynamic journal bearings and two aerodynamic thrust bearings. The journal bearings are sealed by means of magnetic fluid seals. 
     An additional objective of the present invention is to provide an electrical path for discharging the static charges in order to protect electric charge sensitive devices, especially for Magnetoresistance (MR) head disk drives. 
     In one embodiment of the present invention, the aforementioned hybrid bearing unit is assembled to a disk drive spindle. The spindle comprises a rotational hub assembly and a stationary base assembly. The hub assembly consists of a hub onto which the magnetic recording disks can be mounted, a shaft sleeve housing that is securely fixed to the hub, two magnetic ring and two sealing rings that are fixed to the upper and bottom ends of the shaft sleeve housing, a shaft sleeve, two thrust bearing covers, rotor of an electric motor, e.g. magnetic poles and their back iron. The base assembly consists of a base, an electric motor stator, a shaft that is fixed to the base, a thrust plate that is also fixed to the base, a magnetic starting/stopping device that is located beneath the lower cover of thrust bearing, respectively. 
     The invention will be described in details with reference to the drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The features of present invention will be more apparent by reference to the following detailed descriptions together with the following drawings: 
     FIG. 1 illustrates an enlarged cross-sectional view of an exemplary hard disk drive spindle in accordance with the principles of the present invention. 
     FIG. 2 illustrates an enlarged cross-sectional view an exemplary hybrid fluid bearing system that is used in the spindles as described in FIG.  1 . 
     FIGS. 3.1 and  3 . 2  illustrate enlarged cross-sectional views of exemplary magnetic seals in accordance with the principles of the invention. 
     FIGS. 4.1 through  4 . 8  illustrate enlarged cross-sectional views of exemplary hard disk drive spindles with variations in the starting/stopping assistant device in accordance with the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an exemplary spindle assembly for a high performance hard disk drive. The spindle assembly comprises a stationary sub-assembly and a rotating sub-assembly. The stationary sub-assembly includes a base  11 , a shaft  10 , a thrust plate  29 , a stator  24  and two components  51  and  52  of a starting/stopping assistant device. The rotating sub-assembly comprises a hub  23 , a magnet ring  25  and its yoke  26 , a shaft sleeve  13  and its housing  14 , two magnetic sealing rings  15  and  16  having respective two sealing pole rings  17  and  18 , and two thrust plate covers  27  and  28 . 
     The shaft  10  is fixed to the base  11  by being press-fit and/or bonded into a suitable sized opening  12  defined in the base  11 . A shaft sleeve  13  is co-cylindrically situated and rotatable around the shaft  10 , and is securely attached to a housing  14 . The shaft  10  and the shaft sleeve  13  form a fixed shaft journal bearing configuration, which has better vibration resistance than that of a rotating shaft configuration. Therefore, the fixed shaft configuration is preferred in hard disk drive application. 
     Two magnetic rings  15  and  16  together with corresponding sealing poles  17  and  18  are fixed to the upper and bottom ends of the sleeve housing  14 , respectively. The cylindrical inner surface of the sleeve  13  together with the cylindrical outer surface of the shaft  10  cooperatively define two hydrodynamic journal bearings  21  and  22 . The oil lubricant is filled into the gaps of journal bearings  21  and  22 . Compared to aerodynamic journal bearings, the oil journal bearings provide higher radial load capacity and stiffness as well as higher radial damping. 
     A spindle hub  23  is attached to the sleeve housing  14  and supports one or more data storage disks. An electrical motor is provided to rotate the hub  23  and disks relative to the base  11  and the shaft  10  at a predetermined angular velocity. The motor includes a stator assembly  24 , a rotating magnet  25 , and a ferromagnetic flux return yoke  26 . The magnet  25  is fixed to the inner wall of the yoke  26 , while the yoke  26  is fixed to the hub  23  as shown in FIG.  1 . 
     An upper annular thrust bearing cover  27  and a lower annular thrust bearing cover  28  fit securely to the hub  23 . A thrust plate  29  is fixed to the upper end of a thrust plate supporter  30 , and a lower end of the thrust plate supporter  30  is tightly fixed to the base  11 . Together, the upper plane surface  31  and the lower plane surface  32  of the thrust plate  29  with corresponding thrust bearing covers  27  and  28  provide two aerodynamic thrust bearings  33  and  34 . 
     The radial bearings  21  and  22  comprise the shaft  10  and the sleeve  13 , and the axial bearings  33  and  34  comprise the thrust plate  29  and the thrust bearings  27  and  28 . It is preferred that the materials of these parts have complementary coefficients of thermal expansion since the motor as well as the frictional loss of bearings will generate heat during operation and cause the expansion of the shaft  10 , sleeve  13 , thrust plate  29  and thrust bearings  27  and  28 . It is preferred that the shaft  10  and the thrust plate  29  are made of stainless steel or carbon steel, and in these cases a bronze alloy is chosen for the sleeve  13 . Alternatively, the shaft  10  and the sleeve  13  may be both formed of stainless steel. Or, the shaft  10  could be made of stainless steel AISI 440C that can be hardened and the sleeve  13  could be made of AISI 303 that is relatively softer than AISI 440C. 
     The bearing surfaces are preferably finished to an ANSI surface finish of approximately 0.2 μm root-mean-square, or better. To increase the load capacity and stiffness of the bearing system, the outer cylindrical surface of the shaft  10  and/or the inner cylindrical surface of the shaft sleeve  13  is engraved with herringbone grooves. The upper plane surface  31  and the bottom plane surface  32  of the thrust plate  29  or their matting surface of thrust bearing covers  27  and  28  may also be grooved with herringbone or spiral grooves. 
     Two magnetic seals  41  and  42  are applied at the upper end and bottom end of the journal bearings. The upper seal comprises magnet ring  15 , sealing ring  17 , the cylindrical surface of the shaft  10  and the ferrofluid  47  in the gap between the sealing ring  17  and the cylindrical surface of the shaft  10 . The lower seal comprises a magnet ring  16 , sealing ring  18 , the cylindrical surface of the shaft  10  and the ferrofluid  47  in the gap between the sealing ring  18  and the cylindrical surface of the shaft  10 . The magnetic force captures the ferrofluid tightly within the gaps formed by the shaft  10  and magnetic seal rings  17  and  18 . 
     FIGS. 3.1 and  3 . 2  illustrate two different exemplary designs of magnetic seals. Except the design considerations for magnetic path, the recessions in FIG. 3.1 and wedge in FIG. 3.2 also function as the reservoir of the oil when it is pushed out due to the temperature rising of the bearing system. Therefore, the magnetic seals effectively prevent the lubricant leaking from journal bearings. Two oil absorbers  48  and  49  are attached to the bottom end and upper end of the sleeve housing  14  to absorb oil and prevent it from contaminating the disks surfaces due to the evaporation at the condition of extreme low environment pressure. 
     The magnetic starting/stopping device comprises a stator lamination  52 , a coil  51  and a magnetic platter  53 . By a control circuit, at the starting moment, current is supplied to coil  52 , which together with magnetic platter  53  generates an axial force to separate the whole rotary sub-assembly of the spindle from the base sub-assembly rapidly before the spindle rotates. While in stopping process, the magnetic force generated by the starting/stopping assistant device holds the rotating portion of the spindle motor quickly and helps the spindle motor to reach steady state in shorter time. Therefore, the device effectively reduces the friction and wear of thrust bearings, resulting in fast starting/stopping, and results in a worn particle free condition. Together with the oil sealing devices  41  and  42 , the contamination free condition is safely guaranteed. 
     FIGS.  4 . 1 - 4 . 8  show various alternative configurations of the starting/stopping assistant device. The electric spindle motors described are the same as the spindle shown in FIG. 1, except for variations in the starting/stopping device. 
     FIG. 4.1 illustrates an exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  61  with a coil  62  and a magnetic platter  63 . The stator lamination  61  and coil  62  are securely fixed to the thrust supporter  30 . The magnetic platter  63  is securely fixed to the inner wall of the hub  23 . In this exemplary configuration, the stator lamination  61  and coil  62  are oriented in a manner that the opening of the lamination  61  faces downward towards the horizontally-oriented magnetic platter. In operation, when current is supplied to the coil  62 , a magnetic field is created which attracts the magnetic platter  63  towards the lamination  61 /coil  62 . Because the magnetic platter  63  is securely fixed to the hub  23 , this action moves the rotating assembly away from the base assembly to allow freer rotation of the rotating assembly. 
     FIG. 4.2 illustrates another exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  71  with a coil  72  and a magnetic platter  73 . The configuration of the starting/stopping device is the same as the one illustrated in FIG. 4.1, except with the addition of a magnetic washer  74  which is securely coupled to the hub  23  and the magnetic platter  73 , and together with magnet  25  creates a magnet preloading. 
     FIG. 4.3 illustrates another exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  81  with a coil  82  a magnetic platter  83 , and a magnetic washer  84 . The configuration of the starting/stopping device is the same as the one illustrated in FIG. 4.2, except that the magnetic platter  83  has embedded (or disposed thereon) a permanent magnet ring  85  which creates a magnetic preloading to prevent free movement of rotating assembly during shipping, and generates additional thrust and journal bearing force to stabilize the bearing system. 
     FIG. 4.4 illustrates another exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  91  with a coil  92  and a magnetic platter  93 . The configuration of the starting/stopping device is the same as the one illustrated in FIG. 4.1, except that the magnetic platter  93  has embedded (or disposed thereon) a permanent magnet ring  95  which creates a magnetic preloading to prevent free movement of rotating assembly during shipping, and generates additional thrust and journal bearing force to stabilize the bearing system. 
     FIG. 4.5 illustrates another exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  101  with a coil  102  and a magnetic platter  103 . The stator lamination  101  and coil  102  are securely fixed to the thrust supporter  30 . The magnetic platter  103  including a permanent magnet ring  105  is securely fixed to the inner wall of the hub  23  and/or the lower annular thrust bearing  28 . In this exemplary configuration, the stator lamination  101  and coil  102  are oriented in a manner that the opening of the lamination  101  faces upward towards the horizontally-oriented magnetic platter  103 . 
     FIG. 4.6 illustrates an exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  111  with a coil  112  and a magnetic platter  113 . The stator lamination  111  and coil  112  are securely fixed to the thrust supporter  30 . The magnetic platter  113  is securely fixed to the inner wall of the hub  23 . In this exemplary configuration, the stator lamination  61  and coil  62  are oriented in a manner that the opening of the lamination  111  faces radially outward and is vertically offset above the magnetic platter  113 . In operation, when current is supplied to the coil  112 , a magnetic field is created which attracts the magnetic platter  113  towards the lamination  111 /coil  112 . This magnetic attraction causes the magnetic platter  113  to move vertically upward so that it is more aligned with the lamination  111 /coil  112 . Because the magnetic platter  113  is securely fixed to the hub  23 , this action moves the rotating assembly away from the base assembly to allow freer rotation of the rotating assembly. 
     FIG. 4.7 illustrates another exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  121  with a coil  122  and a magnetic platter  123 . The configuration of the stating/stopping device is the same as the one illustrated in FIG. 4.6, except with the addition of a magnetic washer  124  which is securely coupled to the hub  23  and the magnetic platter  123 . 
     FIG. 4.8 illustrates another exemplary electric spindle motor having an exemplary starting/stopping device comprising a stator lamination  131  with a coil  132  a magnetic platter  133 , and a magnetic washer  134 . The configuration of the stating/stopping device is the same as the one illustrated in FIG. 4.7, except that the magnetic platter  133  has embedded (or disposed thereon) a permanent magnet ring  135 . 
     While the invention has been described in connection with various embodiments, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within known and customary practice within the art to which the invention pertains.