Abstract:
An appartatus for balancing a rotating member capable of preventing lubricity between balls from being reduced, and of enhancing balancing efficiency thereof. The rotational center of a turntable is the same as the center of the rotating member. A groove having a predetermined depth and a predetermined width is formed along the circumference of the turntable. A plurality of balls including first balls and second balls formed of different materials are alternately disposed in the groove. The first balls and the second balls may have different diameters.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for balancing a rotating member and, more particularly, to an apparatus for balancing a rotating member by preventing eccentricity generated due to inequality in the material, and unbalance in the shape, of the rotating member when the rotating member is rotated at a velocity that is lower than a critical rotational velocity thereof. 
     2. Description of the Related Art 
     As widely known, a balancing apparatus is provided to remove eccentricity generated due to inequality in the material, and unbalance in the shape, of a rotary shaft when the rotary shaft is rotated. The balancing apparatus includes a groove and a plurality of balls inserted in the groove. The groove is formed in the thickness, along the circumference of a turntable. The balls are inserted in the groove together with an operational fluid. When the rotary shaft is rotated at a velocity higher than a critical rotational velocity thereof, the balls and the operational fluid are automatically located at a position such that eccentricity due to inequality in the material, and unbalance in the shape, of the rotating member can be compensated. 
     FIG. 1 is a top view of a conventional balancing apparatus. As shown in FIG. 1, a groove  50  having a predetermined width and a predetermined depth is formed in the thickness along the circumference of a turntable  30 . A plurality of balls  5  formed of a same material in a same shape and a same size are disposed in the groove  50 . The balls  5  have a predetermined rigidity and can be used semi-permanently. 
     When the turntable  30  is rotated, the balls  5  are accordingly rotated at the same time. When the rotational velocity of the turntable  30  becomes higher than a predetermined velocity, the balls  5  are continuously rotated rubbing each other. 
     However, since the balls  5  are formed of the same material, frictional heat may occur between the balls  5  due to the affinity between the balls  5  when they are rotated. The frictional heat makes the balls  5  adhere to each other resulting in a reduced lubricity. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an apparatus for balancing a rotating member, which is operative to prevent reduction of lubricity between balls disposed in a groove and enhance the balancing efficiency by forming the balls with different materials or by forming them in different sizes. 
     According to an aspect of the present invention, a groove having a predetermined depth and a predetermined width is formed in the thickness along the circumference of a turntable having a center that is the same as a rotational center of a rotating member, and first balls formed of a first material and second balls formed of a second material that is different from the first material are alternately disposed in the groove. 
     Preferably, the first balls may be formed of a nonmagnetic material and the second balls may be formed of a magnetic material or vice versa. Alternatively, all the first and the second balls may be formed of a nonmagnetic material. 
     The nonmagnetic material may be a beryllium copper alloy or bronze, and the magnetic material may be formed steel or stainless steel. 
     In addition, selectively, the first balls may be surface-treated by MoS 2 , and the second balls may be surface-treated by diamond-like carbon, or vice versa. 
     Preferably, the sum of the number of first and second balls is an even number. 
     According to another aspect of the present invention, a groove having a predetermined depth and a predetermined width is formed in the thickness along the circumference of a turntable having a center that is the same as a rotational center of a rotating member, and first balls each having a first diameter and second balls each having a second diameter that is different from the first diameter are disposed. alternately in the groove. 
     Preferably, the shorter diameter of the first and the second diameters is in the range of from ⅓ to ½ of the longer diameter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which: 
     FIG. 1 is a top view of a conventional balancing apparatus; 
     FIG. 2 is a cross sectional view of a CD-ROM drive to which a balancing apparatus according to the present invention is applied; 
     FIG. 3 is a top view of an embodiment of a balancing apparatus according to the present invention; and 
     FIG. 4 is a top view of another embodiment of a balancing apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The balancing apparatus according to the present invention will be hereinafter described in detail, referring to the accompanying drawings. 
     FIG. 2 is a cross sectional view of a CD-ROM drive to which a balancing apparatus according to the present invention is applied. The CD-ROM drive mainly includes: a motor  10  fixed to a housing; a turntable  30  fixed to a rotating member  20  of the motor  10  and rotated; and a disk  40  settled on the turntable  30  and rotated. 
     A balancing apparatus is included in the turntable  30 . The balancing apparatus functions to balance the rotating member  20  when the rotating member is rotated with the disk  40  settled on the turntable  30 . In other words, a groove  50  having a predetermined width and a predetermined depth is formed in the thickness along a circumference of the turntable  30 . A plurality of balls  60  are disposed adjacent one another in the groove  50 . 
     FIG. 3 is a top view of an embodiment of a balancing apparatus according to the present invention. As shown in FIG. 3, a plurality of first balls  60  and second balls  100  are disposed adjacent one another in the groove  50  formed in the thickness along the circumference of the turntable  30 . The first and the second balls  60  and  100  are formed of different materials and are alternately disposed in the groove  50 . 
     More particularly, the first balls  60  formed of a first material and the second balls  100  formed of a second material that is different from the first material are alternately disposed in the groove  50 . At this time, it is important that none of the first and the second balls  60  and  100  are adjacent to a ball formed of the same material. That is none of the first balls  60  are adjacent one another, and none of the second balls  100  are adjacent one another. 
     Typically, the width of the groove  50  is not more than twice as long as the diameter of the balls  60  and  100 , i.e., not more than two ball diameters. Accordingly, once the first and the second balls  60  and  100  are initially alternately inserted into the groove  50 , the balls  60  and  100  cannot be out of turn. 
     There are two methods for forming the first and the second balls  60  and  100  of different materials. 
     First, a plurality of balls may be differently surface-treated so that the balls are divided into two groups: first balls  60 ; and second balls  100 . For example, the first balls  60  may be surface-treated by MoS 2  (molybdenite) and the second balls  100  may be surface-treated by diamond-like carbon (DLC), or vise versa. 
     Second, a plurality of balls may be formed of two different materials so that the balls are divided into two groups: first balls  60 ; and second balls  100 . For example, the first balls  60  may be formed of a nonmagnetic material such as beryllium copper alloy or bronze, and the second balls  100  may be formed of a magnetic material such as a chrome steel or a stainless steel. Generally, since nonmagnetic balls are costly, it is economical to use only magnetic balls formed of different materials. However, when the performance of the balancing apparatus is considered more important, nonmagnetic balls formed of different materials may be used. 
     As aforementioned, the first and the second balls  60  and  100  formed of different materials are alternately arranged in the groove  50 . After the balls are first placed in groove  50 , the sum of the number of first and second balls is an even number so that the balls at a first position and a last position are different from each other. 
     When power is supplied while the first and the second balls  60  and  100  are accommodated in the groove  50 , the rotating member  20  is rotated and the turntable  30  is accordingly rotated. At the same time, the first and the second balls  60  and  100  are rotated to balance the turntable  30 . Since the first and the second balls  60  and  100  are formed of different materials, the affinity between the balls is reduced as compared with the affinity between balls of a same material. Accordingly, heat from friction does not occur between the balls  60  and  100  and the lubricity is increased. As a result, the balancing efficiency of the balls is enhanced. 
     FIG. 4 is a top view of another embodiment of a balancing apparatus according to the present invention. As shown in FIG. 4, a plurality of first and second balls  60 ′ and  100 ′ are disposed in the groove  50  formed in the thickness along the circumference of the turntable  30 . The first and the second balls  60 ′ and  100 ′ have different diameters to prevent a rotating member from being unbalanced when rotated. 
     More particularly, first balls  60 ′ each have a first diameter and second balls  100 ′ each have a second diameter such that the second diameter is shorter than the first diameter. The first balls  60 ′ and the second balls  100 ′ are alternately disposed in the groove  50 . After the balls  60 ′ and  100 ′ are placed in groove  50 , none of the first and the second balls  60 ′ and  100 ′ are adjacent to a ball formed of the same material. That is, none of the first balls  60 ′ are adjacent one another, and none of the second balls  100 ′ are adjacent one another in the series of balls. 
     The diameter of the turntable  30  is generally fixed. Accordingly, the number of the balls that can be disposed in the groove  50  is also fixed. On the other hand, the balancing efficiency depends on the number of the balls disposed in the groove  50 . By the present invention, the number of the balls disposed in the groove  50  can be increased by inserting smaller balls into spaces between the originally disposed balls. 
     For example, if four first balls  60 ′ having a predetermined diameter are disposed in a circumference spanning an angle of 60 degrees, three second balls  100 ′ each having a diameter that is shorter than the first balls  60 ′ can be respectively disposed in spaces between the first balls  60 ′. Thereby, the whole number of the balls disposed in the groove  50  is increased. As a result, the balancing efficiency of the balancing apparatus is enhanced. For practical use, each of the second balls  100 ′ may have a diameter in the range ⅓ to ½ of the diameter of the first balls  60 ′. 
     When power is supplied with the first and the second balls  60 ′ and  100 ′ accommodated in the groove  50 , the rotating member  20  is rotated and the turntable  30  is accordingly rotated. At the same time, the first and the second balls  60 ′ and  100 ′ are rotated to balance the turntable  30 . At this time, the second balls  100 ′ having a smaller diameter fill the spaces between the first balls  60 ′. Accordingly, the number of balls disposed in a unit angle of circumference is increased. As a result, the balancing efficiency of the balancing apparatus is enhanced. 
     The balancing apparatus according to the present invention, has been described above with reference to the aforementioned embodiments. It is evident, however, that many alternative modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention embraces all such two alternative modifications and variations as fall within the spirit and scope of the appended claims.