Abstract:
An automatic balancing system is provided for canceling a rotational imbalance of a rotary device that includes a body to be rotated. A rotation support member rotates with the rotary device and has a polyhedron shape to have multiple flat ball operating surfaces that define an outer circumferential surface. A hollow storage channel around the rotation support member provides an inner circumferential surface so that the balance balls positioned in the hollow storage channel can move freely between the outer circumferential surface and the inner circumferential surface. The polyhedron shape of the ball operating surfaces allows the balance balls to come in contact with the surfaces with minimized force during low speed rotation and beginning of rotation to prevent abrupt collisions of the balance balls which results in smooth and quiet operation of the rotary device.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an automatic balancing system and a magnet for the automatic balancing system configured to cancel rotational unbalance of rotary bodies.  
         BACKGROUND OF THE INVENTION  
         [0002]    Generally in rotation drive devices used for various machines such as industrial machines, home electronics products or computers, an automatic balancing system is used for canceling rotational unbalance of rotary bodies to prevent rotational vibrations. Conventionally various structures have been suggested for the automatic balancing system. For example, in the device shown in FIGS. 5 and 6, an automatic balancing system A that includes a hollow annular storage case is attached to a rotary shaft  2  which is an output shaft of a motor portion  1 , and a plurality of balance balls  4 ,  4  are stored freely movable inside the hollow annular storage case  3 .  
           [0003]    Each of the balance balls  4  starts moving freely inside the hollow storage case  3  with a centrifugal force. When the rotation of the motor portion  1  exceeds the proper operating rotation such as resonant rotation CR (resonant frequency), each ball  4  moves along an inner circumferential wall of the hollow storage case  3  in the opposite direction from the center of gravity of the rotary bodies which include the rotary shaft  2  and the automatic balancing system A, i.e., toward a position at which the rotational unbalance of the rotary bodies is cancelled. Thus, a balancing effect takes place to provide rotational balance for the rotary bodies. With the balancing effect (canceling effect) created by the balance balls, the vibrations of the rotary bodies are reduced to stabilize the condition of rotation.  
           [0004]    For such an automatic balancing system, various countermeasures for preventing noise, caused by collisions of the balance balls  4 , have been proposed. In other words, when the entire device is placed vertically, a tare in addition to the centrifugal force of the rotation is exerted on each of the balance balls that are stored freely movable inside the hollow storage case  3 . In the range of low speed rotation including the beginning of rotation, the centrifugal force exerted on each of the balance balls  4  is smaller than the tare. Accordingly the balance balls  4  cannot climb up the inner circumferential wall of the hollow storage case  3  but fall downward. At that time, the balance balls  4  collide with each other making noise.  
           [0005]    In the related art, particularly as illustrated in FIG. 7, a rotation support member  5  that rotates together with the hollow storage case  3  is placed in the center area of the hollow storage case  3  of the longitudinal type device. On an outer circumferential wall surface of a base annular portion  5   a  of the rotation support member  5 , a plurality of protrusions  5   b,    5   b , . . . are arranged in the circumferential direction at the proper pitch, and a plurality of recesses  5   c,    5   c , . . . are formed between the adjacent protrusions  5   b  (see, for example, Laid-open Patent Application H11-185369 Publication, which is incorporated herein by reference) for receiving the balance balls.  
           [0006]    With such a rotation support member  5  provided, the falling balance balls  4  are received inside the recesses  5   c  of the rotation support member  5  even in the range of low speed rotation including the beginning of rotation. Also, the balls are pushed up with a force by a transporting action of the protrusions. Thus, the noise which is normally caused by the collisions between the balance balls  4  in the range of low speed rotation including the beginning of rotation can be prevented.  
           [0007]    However, in the automatic balancing system having such a rotation support member  5 , the balance balls  4  are kicked up by the protrusions  5   b  of the rotation support member  5 . The abrupt force by the protrusions  5   b  of the rotation support member  5  generates the same collision noise as the one caused between the balance balls  4 , thus making great noise. Further, since the balance balls  4  are kicked up with a great initial velocity by the abrupt force of the protrusions  5   b  of the rotation support member  5 , the kicked-up balance balls  4  hit the inner circumferential wall surface on the upper side of the hollow storage case  5 , generating even more collision noise.  
           [0008]    Therefore, an objective of the present invention is to provide an automatic balancing system with a simple configuration in which the balance balls are smoothly and quietly moved in the range of low speed rotation including the beginning of rotation.  
         SUMMARY OF THE INVENTION  
         [0009]    To achieve the above objective, in an automatic balancing system of the present invention, a rotation support member, which controls or supports the free movement of balance balls inside a hollow storage case, is formed in a polyhedron shape to obtain multiple flat ball operating surfaces on an outer circumferential surface thereof; each of the multiple flat ball operating surfaces has a proper distance from an inner circumferential wall surface of the hollow storage case to come into smooth contact with the balance balls at the beginning of rotation.  
           [0010]    According to the automatic balancing system having such a configuration, the balance balls slide on or come into smooth contact with the flat ball operating surfaces of the rotation support member in the range of low speed rotation including the beginning of rotation. Thus, the abrupt collision that is normally caused by the protrusions kicking up the balls can be prevented. Further, the force of contact with the flat ball operating surfaces has been minimized, moving each of the balance balls smoothly and obtaining quiet rotations.  
           [0011]    Also, in the automatic balancing system of the present invention, the rotation support member is formed in a polyhedron shape. According to the automatic balancing system of the present invention having such a configuration, the above-mentioned operation is performed in a stable manner, and the rotation support member can be manufactured easily.  
           [0012]    Further, in the automatic balancing system of the present invention, the rotation support member is formed to have five or more ball operating surfaces, and the open angle created between circumferentially adjacent ball operating surfaces is set as an obtuse angle exceeding 90°.  
           [0013]    According to the automatic balancing system having such a configuration, the force generated by the ball operating surfaces with respect to the balance balls is certainly minimized, obtaining quiet rotations.  
           [0014]    Further, in the automatic balancing system of the present invention, the shortest distance, L, in the radial direction between the inner circumferential wall of the hollow storage case and the ball operating surfaces of the rotation support member is established within the following range:  
           1.03 ×D&lt;L&lt; 1.15 ×D    
           [0015]    where D is the diameter of the balance ball.  
           [0016]    According to the automatic balancing system having such a configuration, the balance balls move smoothly in the gap between the inner circumferential wall of the hollow storage case and the ball operating surfaces of the rotation support member in the range of low speed rotation including the beginning of rotation even if a means of retaining the balance ball (with magnets, for example) is not provided. Thus, this simple configuration creates a good rotational balance.  
           [0017]    In the automatic balancing system of the present invention, a disk table for mounting the member-to-be-rotated is integrated with the hollow storage case, and also the rotation support member is integrated with the disk table.  
           [0018]    According to the automatic balancing system having such a configuration, the above-mentioned excellent effect can be obtained even when the member-to-be-rotated such as a CD-ROM and a DVD is mounted on the disk table. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is an external perspective diagram showing a CD-ROM or DVD drive unit which is an example of a device to which the present invention is applied.  
         [0020]    [0020]FIG. 2 is a vertical cross-section diagram of an embodiment of a motor with an automatic balancing system which is used in the CD-ROM or DVD drive unit illustrated in FIG. 1.  
         [0021]    [0021]FIG. 3 is a bottom view of the inside of a disk table used in the motor with automatic balancing system of FIG. 2.  
         [0022]    [0022]FIG. 4 is an internal diagram showing balance balls roll inside a hollow storage case.  
         [0023]    [0023]FIG. 5 is a vertical cross-section diagram of a configuration of a rotation support member that has a general automatic balancing system.  
         [0024]    [0024]FIG. 6 is a plan view of a diagram of the inside of the hollow storage case of the general automatic balancing system of FIG. 5.  
         [0025]    [0025]FIG. 7 is the internal diagram of a conventional configuration of a rotation support member provided inside the hollow storage case. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Embodiments of the present invention are described hereinafter in detail based on the drawing. Prior to the description, the entire structure of a longitudinal type CD-ROM or DVD drive unit to which the present invention is applied is first described.  
         [0027]    As illustrated in FIG. 1, mounted onto a chassis  11  of a longitudinal type CD-ROM drive unit are a spindle motor portion  13  for driving an information recording disk  12  which is the member-to-be-rotated, and an optical pickup device  14  which writes and reads information on the information recording disk  12  by illuminating the information recording disk  12  with a laser beam light.  
         [0028]    The information recording disk  12  is mounted on the disk table (see code  139  in FIG. 2) which is attached to the rotary shaft of the spindle motor portion  13 . The optical pickup device  14  is attached to a pair of parallel guide shafts  15 ,  15  in the chassis  11  to move along the shafts  15 ,  15  and is configured to focus a light beam emitted by a laser light source (not illustrated) onto the information recording disk  12  through an objective lens  16  and then to detect the reflected light beam from the information recording disk  12 .  
         [0029]    As illustrated in FIG. 2, the spindle motor portion  13  is configured such that a hollow cylindrical bearing holder  132  is attached to a flat main frame  131  to project horizontally, and a bearing member  133  is press-fitted into the hollow inside of the bearing holder  132 . The bearing member  133  has two bearing portions in the axial direction. Various kinds of bearing members such as an oil retaining bearing, a ball bearing, a metallic bearing or a dynamic pressure bearing device can be used for the bearing member  133 .  
         [0030]    In the center portion of the bearing holder  132 , a rotary shaft  134  is rotatably supported via the bearing member  133  and a stator core  135  composed of a laminated silicon steel plate and the like is fitted onto the outer circumferential wall of the bearing holder  132 . The surface of the stator core  135  is coated with film to form an insulating layer. A coil wire  136  is wound around each of salient-poles of the stator core  135  via the insulating layer.  
         [0031]    Further, at the position on the left side of the figure at which the bearing holder  132  greatly projects from the main frame  131  in the axial direction, the center portion of a cup-like rotor case  137  formed to be hollow and cylindrical is fixed onto the rotary shaft  134  by press-fitting. Onto the inner circumferential wall of an annular circumferential wall portion  137   a  of the rotor case  137 , a ring-like rotor magnet  138  is fixed. The rotor magnet  138  is placed such that the inner circumferential wall thereof is close to each of the salient-poles of the stator core  135  from the radial direction.  
         [0032]    Fixed to the portion of the rotary shaft  134  that projects to the left in the figure is a disk table (turntable) composed of resin which is a non-magnetic material. The disk table  139  is fixed by press-fitting a mounting hole formed in the center thereof to the rotary shaft  134 . By a conical positioning protrusion  139   a  that projects from the fixing portion of the disk table to the left in the figure, an information recording disk (see code  12  in FIG. 1) placed on the disk table  139  is held in a predetermined position. To the point of the positioning protrusion  139   a,  a chucking magnet  139   b  formed as a ring plate that acts as a retaining magnet is attached via a ring-like magnetic yoke plate  139   c.    
         [0033]    The chucking magnet  139   b  has two magnetic poles magnetized in the axial direction, and is arranged to be exposed to the left (in FIG. 2) or upwardly in the figure (in FIG. 5) from the center opening of the information recording disk  12  that is held by the positioning protrusion  139   a.  The information recording disk  12  is held in a predetermined position by magnetically attracting the ring-like yoke plate provided on the side of a publicly-known (well-known) clamper (not illustrated) which is used as a pressing member onto the information recording disk  12 .  
         [0034]    Also, an automatic balancing system  20  is added next to the disk table  139  in the axial direction to balance the rotations of the rotary bodies including the rotor case  137  and the rotary shaft  134 .  
         [0035]    The automatic balancing system  20  functions to cancel the rotational unbalance of the rotary bodies, which is caused when the rotation of the motor portion  13  exceeds the resonant rotation CR (resonant frequency) of the rotary bodies, with a balancing operation by a shift of mass. A secondary hollow annular member  20   b  composed of a non-magnetic press product is fitted to a cup-shaped primary hollow annular member  20   a  composed of resin, which is united with the disk table  139 , to configure a hollow storage case  20   c.  The primary and secondary hollow annular members are fitted such that the openings thereof meet each other in the axial direction from the right side in the figure.  
         [0036]    The hollow storage case  20   c  configured in the above manner rotates together with the disk table  139 . Inside the hollow storage case  20   c,  an annular space is created to store a plurality of balance balls  20   d.  Inside the annular space, the balance balls  20   d,    20   d , . . . of proper mass are stored freely movable in all the circumferential and radial directions.  
         [0037]    The balance balls  20   d,    20   d , . . . are installed to freely move in the radial and circumferential directions along the bottom wall surface of the secondary hollow annular member  20   b  or the outer circumferential wall surface of the primary hollow annular member  20   a  to balance the rotation of the rotary bodies including the rotor case  137  and the rotary shaft  134 .  
         [0038]    In other words, the mass is so adjusted that the rotation of the spindle motor portion  13  is within a predetermined proper operating rotation and the balls move in the opposite direction from the center of gravity of the rotary bodies, i.e., they move toward the outer position in the radial direction indicated by the two-dotted line in FIG. 2 to cancel the rotational unbalance of the rotary bodies.  
         [0039]    When the rotations of the rotary bodies are balanced, the vibrations of the rotary bodies are reduced, stabilizing their rotations.  
         [0040]    Inside the hollow storage case  20   c,  a rotation support member  20   e  is placed for controlling or supporting the free movement of the balance balls  20   d.  The rotation support member  20   e  is integrated with the disk table  139  in the center area of the disk table  139 , as illustrated in FIG. 3, and also is formed in a regular polyhedron shape (regular dodecahedron as shown in FIG. 3) which is coaxial with the disk table  139 .  
         [0041]    In other words, around the outer circumference of the rotation support member  20   e,  a plurality of flat ball operating surfaces  20   f,    20   f , . . . (12 surfaces) are formed. Each of the flat ball operating surfaces  20   f  is arranged to come into contact with the balance balls  20   d  by sliding or smoothly moving thereon; when the flat ball operating surfaces  20   f  of the rotation support member  20   e  come in contact with the balance balls  20   d  in the range of low speed rotation including the beginning of rotation, a minimized force is exerted on the balance balls  20   d  in the upward direction, which is the rotational direction. With this force, each of the balance balls  20   d  is smoothly raised, as illustrated by the arrow in FIG. 4.  
         [0042]    Five or more ball operating surfaces  20   f  are formed on the rotation support member  20   e  of this embodiment. The open angle created between the circumferentially adjacent ball operating surfaces  20   f  is set as an obtuse angle exceeding 90° so that a minimized force is applied to each of the balance balls  20   d.    
         [0043]    In this embodiment, the ball operating surfaces  20   f  of the rotation support member  20   e  are positioned to have a proper gap from the inner circumferential wall  20   g  of the hollow storage case  20   c.  Because of the proper gap, the ball operating surfaces  20   f  excellently come in contact with the balance balls  20   d  at the beginning of rotation.  
         [0044]    More specifically, the shortest distance, L, between the inner circumferential wall surface  20   g  of the hollow storage case  20   c  and the ball operating surface  20   f  of the rotation support member  20   e  in the radial direction is established within the following range:  
         1.03 ×D&lt;L&lt; 1.15 ×D    
         [0045]    where D is the diameter of the balance ball  20   d.  The balance balls  20   d  smoothly pass through the gap created within the above range.  
         [0046]    According to this embodiment, the balance balls  20   d  come in contact with the flat ball operating surfaces  20   f  as if sliding or smoothly moving thereon in the range of low speed rotation including the beginning of rotation. Thus, the abrupt collision which is normally caused by the protrusions (see code  5   c  in FIG. 7) kicking up the balls can be prevented. The minimized force by the flat ball operating surfaces  20   f  smoothly raises each of the balance balls  20   d,  making it possible to obtain quiet rotations.  
         [0047]    In this embodiment, the rotation support member  20   e  is formed in a regular polyhedron shape. Therefore, the above-mentioned operation can be performed in a stable manner and the rotation support member  20   e  can be manufactured easily. Particularly in this embodiment, the rotation support member  20   e  has five or more ball operating surfaces  20   f  and the open angle between the circumferentially adjacent ball operating surfaces  20   f  is set as an obtuse angle exceeding 90°. With this configuration, the operating force of the ball operating surfaces  20   f  with respect to the balance balls  20   d  is certainly minimized, obtaining quiet rotations.  
         [0048]    Also, in this embodiment, the shortest distance, L, between the inner circumferential wall  20   g  of the hollow storage case  20   c  and the ball operating surface  20   f  of the rotation support member  20   e  in the radial direction is set to be within the range of 1.03×D&lt;L&lt;1.15×D, where D is the diameter of the balance ball  20   d.  Therefore, the balance balls  20   d  move smoothly inside the gap between the inner circumferential wall  20   g  of the hollow storage case  20   c  and the ball operating surface  20   f  of the rotation support member  20   e  in the range of low speed rotation including the beginning of rotation, even without the usual retaining means such as magnets to hold the balance balls  20   d.  Thus, an excellent rotational balancing operation can be performed with a simple configuration.  
         [0049]    Furthermore, in this embodiment, the disk table  139  is integrated with the hollow storage case  20   c  to mount the member-to-be-rotated such as a CD and DVD, and also the rotation support member  20   e  is integrated with the disk table  139 . Therefore, the above-mentioned excellent rotational condition can be obtained even when the member-to-be-rotated such as a CD or DVD is mounted on the disk table  139 .  
         [0050]    Although the embodiments of the present invention devised by the present inventors have been described in detail, the present invention is not limited to the above embodiment, but can be varyingly modified within the scope of the invention.  
         [0051]    For example, although the rotation support member in the embodiment illustrated in FIGS. 3 and 4 is formed in a dodecahedron shape to have twelve flat ball operating surfaces around the outer circumference thereof, the shape of the rotation support member is not limited to this, but the same effect can be obtained with a polyhedron shape in which five to eighteen ball operating surfaces are formed.  
         [0052]    Also, although the above embodiments use a longitudinal type device, the present invention can be applied to lateral or horizontal type devices in the same manner.  
         [0053]    Further, although the above embodiments use an information recording disk as the member-to-be-rotated, the present invention can be applied in the same manner to devices which take other kinds of members-to-be-rotated.  
         [0054]    As described above, in the automatic balancing system of the present invention, the rotation support member for controlling or supporting the free movement of the balance balls inside the hollow storage case is formed in a polyhedron shape to have multiple flat ball operating surfaces, and is arranged such that the balance balls come smoothly into contact with the multiple flat ball operating surfaces at the beginning of rotation. With this configuration, each balance ball moves smoothly with a minimized force in the range of low speed rotation including the beginning of rotation, preventing abrupt collisions of the balance balls to obtain quiet rotations. Thus, a very smooth, quiet rotation can be obtained with a simple configuration, improving the usefulness and reliability of the rotation drive device.  
         [0055]    In the automatic balancing system of the present invention, the rotation support member is formed in a regular polyhedron shape with which more stable rotations can be obtained and its manufacturing is simplified. Accordingly, the above effects can certainly be obtained and productivity can be improved.  
         [0056]    In the automatic balancing system of the present invention, the rotation support member is formed to have five or more ball operating surfaces and the angle created between the circumferentially adjacent ball operating surfaces is set as an obtuse angle exceeding 90°. With this configuration, the force the ball operating surfaces give to the balance balls is certainly minimized, obtaining quiet rotations. Thus, the above-mentioned effects can be easily obtained.  
         [0057]    In the automatic balancing system of the present invention, the shortest distance, L, between the inner circumferential wall of the hollow storage case and the ball operating surface of the rotation support member in the radial direction is established within the range of 1.03×D&lt;L&lt;1.15×D, where D is the diameter of the balance ball. With this configuration, the balance balls move smoothly inside the gap between the inner circumferential wall of the hollow storage case and the ball operating surfaces of the rotation support member, even without the usual retaining means such as magnets for retaining the balance balls. Thus, a good rotational balancing effect can be obtained with a simple configuration, obtaining the above-mentioned effects with certainty.  
         [0058]    In the magnet for the automatic balancing system of the present invention, the disk table for mounting a member-to-be-rotated is integrated with the hollow storage case and the rotation support member is integrated with the disk table. Therefore, the above-mentioned effects can be obtained even when the member-to-be-rotated such as a CD-ROM or DVD is mounted on the disk table.  
         [0059]    The foregoing specific embodiments represent just some of the ways of practicing the present invention. Many other embodiments are possible within the spirit of the invention. Accordingly, the scope of the invention is not limited to the foregoing specification, but instead is given by the appended claims along with their full range of equivalents.