Abstract:
The present invention discloses an automatic balancing apparatus including moveable balancing members located in hollow tubular portions of a rotating member which may include a rotation shaft and a turntable. The automatic balancing apparatus suppresses vibration of the rotation shaft and turntable by adjusting a center of gravity with balancing members so that even high speed rotation of the shaft is possible without excessive vibration. The present invention uses magnets and may use low friction surfaces to further improve the free and fine movement of the balancing members which ensures a finely tuned balancing apparatus in operation.

Description:
[0001]    This application claims foreign priority to Japanese patent application 2001-164392 filed May 31, 2001.  
         FIELD OF INVENTION  
         [0002]    The present invention relates to a motor that is used to drive driving rotation of data storage media disks such as flexible disks, CDs, and DVDs. More specifically, it relates to a mechanism for automatic suppression of vibration including vibration in the horizontal (tracking) direction of a data storage disk rotated by a motor and the like.  
         BACKGROUND OF INVENTION  
         [0003]    Usually, the rotation speed requirement for a recording and reproducing apparatus, which rotates a data storage disk, is 6,000-10,000 rpm. However, a disk loses its balance during rotation due to its uneven thickness or a printing media labeled on the disk providing an uneven mass during rotation. When rotating such a disk at a high speed, a centrifugal force acts on a biased rotation center of the disk. Particularly, at a certain speed called a “dangerous speed,” at which the speed of the rotation shaft reaches a specific horizontal frequency of the rotation system, the rotation shaft vibrates very hard in the horizontal direction (in the direction orthogonal to the shaft direction). For this reason, high-speed rotation of a disk causes inconveniences such as generation of noise, reduction of a disk&#39;s usable life time due to vibration-induced damages, or failing of recording or reproduction on a disk due to a tracking error and the like. In addition, such vibrations may propagate to adversely affect peripheral terminals.  
         SUMMARY OF THE INVENTION  
         [0004]    For this reason, unfavorable vibrations due to unbalanced rotation of a disk must be suppressed. In FIG. 4, spindle motor  51  comprises: stator  53  fixed onto hub  52 ; rotor  54  having magnet  54   a  arranged opposite to stator  53 ; and spindle shaft  55  rotatably supported by bearing  52   a . When current flows through stator  53 , a magnetic field for rotating rotor  54  is generated between stator  53  and rotor  54  and rotor  54  rotates around spindle shaft  55  integrally.  
           [0005]    Automatic balancing apparatus  56  is constructed with case  57  that is fixed onto spindle shaft  55  and a turntable (not illustrated) such that all of these components rotate together. In case  57 , a tubular space is formed circumferentially around spindle shaft  55  and a ring-like magnet  58  is arranged along the inner circumference of the tubular space. Ring-like magnet  58  is magnetized such that a magnetic flux is generated in a direction other than the circumference of spindle shaft  55 . In addition, a selected number of multiple (magnetic) balls  59  made of a magnetic material having the same diameter are inserted along circumference of magnet  58  in the space provided in case  57  to suppress horizontal vibration. Therefore, when spindle shaft  55  does not rotate, balls  59  are held to the circumferential surface of magnet  58  by magnetic force.  
           [0006]    Automatic balancing apparatus  56  as configured in the above mentioned manner rotates together with spindle shaft  55  while balls  59  are attached to the circumferential surface of magnet  58  as spindle motor  51  is actuated. As the rotation of spindle shaft  55  accelerates and rotation speed exceeds a specific horizontal frequency, the magnitude of centrifugal force exceeds the attracting force of magnet  58 . As a result, balls  59  are removed from magnet  58  and moved (pushed) toward the case&#39;s outer circumferential wall  57   a . Such movement of balls  59  approximates a new center of gravity at the center of rotation shaft, thereby suppressing vibration due to the spindle shaft rotating at a high speed.  
           [0007]    Nevertheless, balls  59  move contacting two points, the case&#39;s outer circumference wall  57   a  and the case&#39;s bottom surface  57   b  under the influence of centrifugal force and gravity. For this reason, the movement of balls  59  is diminished due to friction generated between the circumference wall  57   a  and the bottom surface  57   b  of the case (tubular space), preventing balls  59  from reaching the perfect balancing point (equilibrium) and from canceling the amount of vibration generated during high-speed spinning.  
           [0008]    The object of the present invention is to provide an automatic balancing apparatus with a rotation member with improved balancing capability that generates little vibration during rotation by decreasing the contact pressure to reduce friction generated between the case&#39;s circumference wall and the case&#39;s bottom surface.  
           [0009]    To accomplish the task, the automatic balancing apparatus of the present invention is constituted as follows: an automatic balancing apparatus having a hollow tubular portion containing balancing members is fixed onto a rotation shaft wherein, when a frequency of rotation members that are integrally rotated by a driving source exceeds a resonance frequency of a system comprising the rotation shaft and the rotation member, the automatic balancing apparatus suppresses vibration derived from the rotation member being unbalanced, and at least one of the inner walls in the hollow tubular portion includes a single polarity magnet. The hollow tubular portion may be molded using a synthetic resin mold and the magnet may be integrally formed or press fitted using the insert-mold. Also, the magnet or tubular space may have a surface (exposed in the tubular space) coated with a synthetic resin film.  
           [0010]    The balancing member contains a plurality of balls having the same diameter (to suppress horizontal vibrations). Also, the hollow tubular portion partitions a tubular space by assembling an upper tubular portion and a lower tubular portion, wherein the upper tubular portion provides a space opening downward between an inner wall near the rotation member&#39;s rotation center and an outer wall surrounding the inner wall; the lower tubular portion provides a tubular space opening upward by connecting an inner support plate to be engaged with a tubular mating wall provided inside the inner wall, and outer support plate to be engaged with the outer wall on a tubular bottom plate; and a plurality of the balls are inserted into the tubular portion such that multiple balls can move freely therein.  
           [0011]    In the hollow tubular portion, a cylindrical magnet is attached along the inner wall and a crossectionally L-shaped magnet is integrally formed with a turntable using an insert mold, wherein the crossectionally L-shaped flat ring-like magnet has a magnetized plane of a polarity which is different form the cylindrical magnet and extends radially from top of the cylindrical magnet toward the outside. A flat ring-like magnet may only extend radially from top of the cylindrical magnet toward the outside. Also, the hollow tubular portion comprises: a flat ring-like magnet extending radially from the upper end of the inner wall near its rotation center toward the outside; a back yoke made of a magnetic plate may be provided such that the back yoke is sealingly attached to the flat ring-like magnet between the hollow tubular portion&#39;s base; a cylindrical yoke may extend vertically from the inner end of the back yoke downward so as to surround the hollow tubular portion&#39;s inner wall.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic side view showing a cross section of the automatic balancing apparatus of Embodiment  1  of the present invention.  
         [0013]    [0013]FIG. 2 is a schematic side view showing a magnified cross section of a part of the automatic balancing apparatus of Embodiment  2  of the present invention.  
         [0014]    [0014]FIG. 3 is a schematic side view showing a magnified cross section of a part of the automatic balancing apparatus of Embodiment  3  of the present invention.  
         [0015]    [0015]FIG. 4 is a schematic side view showing a cross section of an automatic balancing apparatus of conventional technology together with a spindle motor. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Embodiments of the automatic balancing apparatus of the present invention are described herein with reference to the drawings. FIG. 1 is a schematic configuration showing a cross section of Example I of the automatic balancing apparatus of the present invention. In FIG. I, Reference Number  10  is the automatic balancing apparatus. Spindle motor  11  of the present invention is a driving source that rotates disk-type data storage media (not illustrated) such as CDs, DVDs, and magneto-optical disks. In spindle  11 , rotor  13  constituting rotation member R rotates when current flows to stator  12 .  
         [0017]    Stator  12  comprises stator hub  14  fixed onto a mechanical chassis (not illustrated) and stator member  15  fixed onto stator hub  14 . Stator hub  14  comprises bearing case  17  supporting rotation shaft  16 , which is the rotation center of rotor  13 . Bearing  18  is attached to bearing case  17  to rotatably support rotation shaft  16  formed integral with rotor  13 , is attached to bearing case  17 . In rotor  13 , cylindrical yoke  20  is provided in such a way that rotor magnet  19  is secured inside cylindrical yoke  20  and rotor  19  and stator member  15  are arranged opposite to each other.  
         [0018]    Turntable  21  is press fitted to rotation shaft  16  through center hole  21   a  to be concentric with rotor  13 . Boss  21   b  to be mated with the clamp hole of a data storage medium such as CD and magneto-optical disk (not illustrated) is formed integral with turntable  21  such that a disk is centered as its clamp hole and boss  21   b  are mated with each other. Facing yoke  22  is embedded on top of boss  21   b  and a disk is securely wedged between turntable surface  21   c  and a magnet embedded to a clamper (not illustrated). The damper has a projection in its center which press fits into the same center hole  21   a  as turntable  21 , to which rotation shaft  16  is press fitted. As a result, the clamper is automatically aligned with rotation shaft  16  in a concentric manner. Thin plate  23  made of a rubber band is attached along the circumference of turntable surface  21   c  so as to efficiently retain the disk by means of friction and to protect the disk surface from scratches.  
         [0019]    Turntable  21  is molded utilizing a synthetic resin mold. Automatic balancing apparatus  10  is molded integrally with the circumference of turntable  21 . In other words, automatic balancing apparatus  10  is fixed onto rotation shaft  16  with a damper and a disk via turntable  21  in an integral manner, thereby constituting part of rotation member R. Automatic balancing apparatus  10  is constructed with a hollow tubular portion  25  containing multiple magnetic balls  24  configured to be concentric to turntable  21 . That is, upper tubular portion  25 - 1  comprises partitions created by: (1) inner wall  25   a  along the circumference of turntable  21 , which is part of rotation member R near the center of rotation; (2) outer wall  25   b  of the same height as inner wall  25   a  extending downward; and (3) upper surface  25   d , which is the tubular portion constituting a part of the circumference of turntable  21  with opening  25   c  therebelow.  
         [0020]    On turntable  21 , tubular mating wall  25   e  to be engaged with lower tubular portion  25 - 2  described later is given nearly the same height as the inner wall  25   a  and extends from inner wall  25   a  toward the rotation center of turntable  21  so as to be engaged with cylindrical inner support plate  25 - 2   c , which extends upward from inner edge  25 - 2   b  of tubular bottom plate  25 - 2   a  in lower tubular portion  25 - 2 . In addition, cylindrical outer support plate  25 - 2   e  extends upward from outer circumference  25 - 2   d  of tubular bottom plate  25 - 2   a  in lower tubular portion  25 - 2  to be engaged with outer wall  25   b  extending downward from turntable  21 . Upper end  25 - 2   f  is of outer support plate  25 - 2   e  is given enhanced resistance to centrifugal force induced deformation such that the outer neck (corner) from which outer wall  25   b  hangs downward from turntable  21  is fitted into a narrow groove  21   e  formed in the thickness (vertical) direction of turntable  21  on outer support plate  25 - 2   e.    
         [0021]    Lower tubular portion  25 - 2 , into which an appropriate number of independent magnetic balls  24  having the same diameter are inserted such that the balls  24  can move freely, is press fitted to upper tubular portion  25 - 1 . Tubular bottom plate  25 - 2   a  of lower tubular portion  25 - 2  closes opening  25   c  below upper tubular portion  25 - 1  to partition tubular space  25   d  in hollow tubular portion  25 . Lower tubular portion  25 - 2  is formed by molding a synthetic resin such that magnetic balls  24  generate little noise when they contact each other and move.  
         [0022]    Cylindrical magnet  26 , having a free surface magnetized in a single polarity, is sealingly attached along the outer circumference of inner wall  25   a  in upper tubular portion  25 - 1  to be fixed thereon and a flat ring-like magnet  27  is sealingly attached onto upper surface  21   d  in upper tubular portion  25 - 1  to be fixed thereon. Flat ring-like magnet  27  is magnetized with a polarity different from that of the free surface of cylindrical magnet  26  and molded integral with cylindrical magnet  26  so as to form a cross-sectional L-shape. For this reason, when turntable  21  does not rotate, magnetic balls  24  housed in tubular space  25   d  are attracted (to two points) in the direction of corner  28 , cylindrical magnet  26  on inner wall  25   a  and flat ring-like magnet  27  on upper surface  21   d , thereby staying still in equilibrium (See the left hand side of FIG. 1).  
         [0023]    Turntable  21  is molded utilizing a synthetic resin. Cylindrical magnet  26  and flat ring-like magnet  27  are formed integrally using an insert-mold, providing a composite magnet shaped in an inverse L in cross-section. Each cylindrical magnet  26  and flat ring-like magnet  27  is magnetized in a single polarity wherein the polarity may be either the same or different. A back yoke (not illustrated) may be insert-molded between inner wall  25   a  and cylindrical magnet  26 , and between upper surface  21   d  and flat ring-like magnet  27 . Moreover, if a synthetic resin coating is provided on the surfaces of cylindrical magnet  26  and flat ring-like magnet  27  exposed to tubular space  25   d  in hollow tubular portion  25 , noise from bombardment of magnetic balls  24  can be suppressed.  
         [0024]    Operation of the automatic balancing apparatus  10  of the present invention is described herein. As turntable  21  having an unbalanced data storage disk begins rotating, a centrifugal force exercises its automatic center adjusting effect such that magnetic balls  24  themselves move to a balancing point and the resulting center of gravity stays on the rotation shaft  16 . An unbalanced data storage disk, therefore, can be spun at a high speed while maintaining its balancing point on the rotation shaft  16 . Such an automatic center adjusting effect is desirable when the frequency of the combined rotation member R exceeds the number of specific horizontal frequency (resonance frequency) of combined rotation member R itself. In the left side of FIG. 1, turntable  21  is in a static state. FIG. 1 also depicts the position of magnetic balls  24  when they are spun at a slow speed. The right side of FIG. 1 depicts the position of magnetic balls  24  when they are spun at a high speed.  
         [0025]    The automatic balancing point adjustment effect works in the above mentioned rotation system as follows: when the centrifugal force of the rotational system exceeds the attracting force from cylindrical magnet  26  on inner wall  25   a , magnetic balls  24  are removed from cylindrical magnet  26  and are moved (pushed) to the inner surface of outer wall  25   b . However, being repelled, or attracted depending upon the embodiment, by cylindrical magnet  26  to inner wall  25   a , magnetic balls  24  contact the inner surface of outer wall  25   b  only with a small pressure, limiting the friction generated thereon to prevent magnetic balls  24  from moving toward the balancing point along the inner surface of outer wall  25   b.    
         [0026]    Magnetic balls  24  also slide along bottom surface  25 - 2   g  of tubular bottom plate  25 - 2   a  in lower tubular portion  25 - 2  due to gravity. The magnetic force from flat ring-like magnet  27  attached to the upper surface  21   d  of upper tubular portion pushes magnetic balls  24  against bottom surface  25 - 2   g , or pulls away from the bottom surface  25 - 2   g  depending upon the polarity of the magnet selected to be used, mitigating the contacting pressure thereon. The unfavorable friction that works against magnetic balls  24  from moving toward the balanced point is thus eliminated. Moreover, by molding lower tubular portion  25 - 2  utilizing a synthetic resin having a low friction coefficient, magnetic balls  24  can move more smoothly. As described, automatic balancing apparatus  10  of the present invention allows magnetic balls  24  to reach the balancing point quickly and smoothly, thereby improving balancing effectively.  
         [0027]    [0027]FIG. 2 shows the automatic balancing apparatus of Embodiment  2  of the present invention depicting a magnified side view of a part of hollow tubular portion  25  in cross section. Members that are common to Embodiment  1  are given the same reference symbols and their descriptions are not repeated. Embodiment  2  differs from Embodiment  1  in that the flat ring-like magnet  27  is attached to upper surface  21   d  of hollow tubular portion  25  and the cylindrical magnet on the inner wall  25   a  is eliminated. By eliminating cylindrical magnet on inner wall  25   a , the cost of the component is saved. When a small centrifugal force is applied to the rotation system, the magnetic force from flat ring-like magnet  27  alone can reduce the contact pressure on both the inner surface of outer wall  25   b  and bottom surface  25 - 2   g.    
         [0028]    [0028]FIG. 3 shows the automatic balancing apparatus of Embodiment  3  of the present invention depicting a magnified side view of a cross section of hollow tubular portion  25 . Members that are common to the embodiments previously discussed are given the same reference symbols and their descriptions are not repeated. In Embodiment  3 , a ring-like back yoke  29  made of a magnetic plate is pinched between upper surface  21   d  of upper tubular portion  25 - 1  and flat ring-like magnet  27  utilizing the insert mold technique. Cylindrical yoke  30  hangs vertically against the points between inner edge  29   a  of ring-like back yoke  29  and inner wall  25   a . Embodiment  3  is applicable to a relatively well-balanced rotation system not affected by centrifugal force and the differential magnetic force required for flat ring-like magnet  27  (to maintain equilibrium) is supplemented. It is particularly desirable to stop magnetic balls  24  in a stable manner when turntable  21  does not rotate.  
         [0029]    Embodiments of the automatic balancing apparatus of the present invention as applied to a turntable that holds a data storage disk have been described above. However, these embodiments do not limit the present invention. The spirit of the present invention is to provide a smooth movement for balls by taking advantage of the automatic center adjustment effect. The automatic balancing apparatus of the present invention may be applied to a rotor or a clamper, or even another independent member may be provided as long as the rotation system rotates integral with a turntable. The present invention may be applied to any applications with many different modifications as long as the operation of a rotation member that rotates at a high speed exceeds the resonance frequency and is within the scope of claims. A good result should be expected in any case.  
         [0030]    As is apparent from what is described above, the automatic balancing apparatus of the present invention limits the magnitude of influence from centrifugal force exercised on magnetic balls contained in a hollow tubular portion utilizing the magnet&#39;s attracting force, thereby reducing the friction from contact between magnetic balls and the inner surface of the outer wall in the hollow tubular portion. It also limits the influence of gravity exercised on the magnetic balls contained in the hollow tubular portion utilizing the attracting force from a magnet attached to the upper surface side in the hollow tubular portion, thereby reducing the friction between magnetic balls and the bottom surface of the hollow tubular portion. Magnetic balls thus have an easy-to-move feature. They move to the balancing point smoothly and quickly to establish equilibrium, thereby ensuring reduction of vibration.  
         [0031]    If an exposed surface of a magnet is coated with a synthetic resin film, noise generated by the magnetic balls&#39; contacting the walls can be reduced. Moreover, two surfaces of the hollow tubular portion are given a single polarity, therefore, multiple magnetic balls can be magnetized to the same level. Magnetic balls are unlikely to push against each other, reducing noise and vibration generated by the balls contacting each other.  
         [0032]    As described above, by limiting the rate of vibration acceleration, little side pressure generated by loss of equilibrium is applied to the spindle motor bearing. As a result, problems such as an increase in torque due to damages to the shaft, damages to bearings (magnetic balls) and a reduction in useable life of bearings (magnetic balls) are resolved. CDs, DVDs, magneto-optical disks can thus record and reproduce data in a stable fashion.