JP2002095210A - Automatic balancer for motor and media disk drive motor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain extremely smooth rotating condition of a motor of the simplified and small size structure by extremely correcting the balance of the motor itself and eliminating influence of vibration or the like from the motor side for the rotating body which is driven to rotate by the motor. SOLUTION: A rotor 137 forming a part of the motor 13 is provided with a balance member 139 in which a plurality of mass bodies 139c move freely corresponding to unbalance of rotation. As a result, unbalance of rotation of the rotor 137 can be eliminated extremely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic balancing device for a motor having a function of canceling the rotational imbalance of a rotating body, and a media disk drive motor using the same.

[0002]

2. Description of the Related Art Generally, industrial machines, household appliances,
Alternatively, an automatic balancing device is often employed in various rotary driving devices used in a computer or the like in order to cancel a rotational imbalance of a rotating body including a rotating shaft. As the automatic equilibrium device, various devices having various structures have been conventionally proposed. For example, in the device described in JP-A-10-257710, as shown in FIG.
A balancing member 3 composed of a hollow disk-shaped case body is attached to a rotating shaft 2 which is an output shaft of the motor 1, and a plurality of balancing spheres 4, 4 Are arranged to be freely movable. When the rotation speed of the motor 1 exceeds the resonance rotation speed CR, each of these balance spheres 4 starts to move in a direction opposite to the center of gravity of the rotary body including the rotation shaft 2 and the balancing member 3. As a result, the rotation of the rotating body is balanced, the vibration of the rotating body is reduced, and the rotating state is stabilized.

[0003]

However, such a conventional automatic balancing device is configured to balance the rotation of a rotating body disposed after the rotating shaft 2 of the motor 1, and the motor 1 itself, In particular, the unbalanced state of the rotor 1a cannot be directly removed. As a result, the rotational vibration from the motor 1 side is transmitted to the rotating body side, which may cause various problems.
For example, in a device for rotating and driving various media disks such as CDs and DVDs, various proposals have been made to balance the rotation of a disk support portion that holds the media disks.
High-precision rotational stability may not be obtained.

Accordingly, the present invention provides a simple and compact configuration,
It is an object of the present invention to provide an automatic balancing device for a motor capable of favorably obtaining a motor balance correcting action, and a media disk drive motor using the same.

[0005]

In order to achieve the above object, according to the present invention, a rotating body partially including a rotor constituting a motor, and the rotating speed of the motor is reduced by the rotating body. And a balancing member for canceling the rotational imbalance of the rotating body when the rotational speed exceeds the resonance rotational speed by a balance correcting action, wherein the balancing member rotates integrally with the rotor. The provided annular case, and a plurality of mass bodies housed in the annular case and held so as to be freely movable at least in the circumferential direction,
It has.

Further, in the invention according to claim 2, a rotating body including a rotor constituting a motor, and a disk holding member that rotates together with the rotor while holding the media disk and rotationally drives the media disk is provided. And a balancing member for canceling the rotational imbalance of the rotating body when the rotation speed of the motor exceeds the resonance rotation speed of the rotating body by a balance correcting action is attached to the rotating body. The equilibrium member is disposed at two locations separated in the axial direction of the motor.

According to the third aspect of the present invention, one of the two equilibrium members according to the second aspect is provided with:
An annular case provided so as to rotate integrally with the rotor, and a plurality of mass bodies accommodated in the annular case and movably accommodated at least in a circumferential direction are provided.

Further, in the invention according to claim 4,
The annular case according to claim 2 or 3, wherein a cross section substantially U extending radially outward or inward from a side surface of the rotor.
It has a U-shaped groove and a cover that covers the opening of the groove.

On the other hand, in the invention according to claim 5, the rotor according to claim 3 has an outer rotor structure, and an annular drive magnet is mounted on the inner peripheral surface side of the rotor. .

[0010] In the invention according to claim 6, one of the two equilibrium members according to claim 2 has a circular main body rotatably attached to a rotating shaft of the motor. And an unbalanced portion formed by removing a part of the circular main body.

Further, in the invention according to claim 7, the unbalanced portion according to claim 6 is configured such that a part of the circular main body is removed from a hole or a concave portion obtained by removing a part of the circular body in a plane substantially circular shape or a part thereof. At the same time, two circular body parts are attached so as to overlap in the axial direction with respect to the rotating shaft.

[0012] According to the motor automatic balancing apparatus according to the first aspect of the present invention, the rotational unbalance of the rotor constituting a part of the motor is adjusted by the balancing member attached to the rotor. Is easily and satisfactorily eliminated by the free movement of the plurality of mass bodies at.

According to a second aspect of the present invention, there is provided a media disk drive motor, in which a rotor constituting a part of the motor is constituted by two balancing members arranged in the axial direction of the motor. The rotational imbalance in both of the disk holding members that rotationally drive the media disk is satisfactorily eliminated in a mechanically stable state.

Further, according to the media disk drive motor according to the third or fourth aspect of the invention, the balancing member provided on the rotor side of the motor has a simple configuration. .

In this case, according to the media disk drive motor according to the fifth aspect of the present invention, the mass constituting the balancing member is moved by the drive magnet in the low rotation region up to the resonance rotation speed by the drive magnet. A structure that is attracted to the side is made possible, and an accurate balance forcing action can be obtained with a simple structure.

Further, according to the media disk drive motor of the present invention, the mass required for the balance correcting operation is efficiently secured by utilizing the entire circumferential area of the circular main body. From that, at least one of the outer diameter dimension or the thickness will be set significantly smaller,
The whole device can be reduced in size and flattened, and the adoption of a circular main body eliminates the extreme cantilever structure as in the past. A stable rotation state can be obtained.

At this time, as in the invention according to claim 7,
If the unbalanced portion is formed by a hole or a concave portion in which a part of the circular body is removed in a substantially circular shape in a plane, even if the size of the unbalanced portion is changed, the position of the center of gravity does not change. In addition, the mass adjustment of the balancing member is facilitated.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, a CD to which the present invention is applied
-The overall structure of the ROM or DVD drive unit will be described. That is, the mechanical chassis 11 of the CD-ROM drive unit 10 shown in FIG. 1 has a spindle motor 13 for rotating and driving the recording disk 12, and the recording disk 12 is irradiated with laser light to write or read information. Is mounted. The recording disk 12 is mounted on a disk table (see reference numeral 139 in FIG. 2) mounted on a rotating shaft of the spindle motor 13.

The optical pickup device 14 is mounted so as to be able to reciprocate with respect to a pair of parallel guide shafts 15, 15 attached to the mechanical chassis 11.
A light beam emitted from a laser light source (not shown) is applied to the recording disk 12 through the objective lens 16 and the reflected light from the recording disk 12 is detected.

On the other hand, as shown in FIG. 2, the spindle motor 13 has a hollow cylindrical bearing holder 132 attached to the main body frame 131 so as to stand substantially vertically. The bearing holder 1
The bearing member 133 is press-fitted into the hollow interior side of 32. The bearing member 133 includes two bearing portions in the axial direction.
A wide variety of bearing members such as oil-impregnated plain bearings, bearing bearings, metal bearings, or hydrodynamic bearing devices can be employed.

A rotary shaft 134 is rotatably supported at the center of the bearing holder 132 via the bearing member 133.
A stator core 135 made of a laminated body such as a silicon steel plate is fitted on the outer peripheral wall surface of the. This stator core 1
An insulating layer is formed by coating on the surface of 35, and a winding 136 is wound around a portion corresponding to each salient pole portion of the stator core 135 via the insulating layer.

At the position directly above the bearing holder 132 in FIG. 2, a central portion of a substantially cylindrical rotor case 137 formed in a hollow cylindrical shape is fixed to the rotating shaft 134. A ring-shaped rotor magnet 138 is fixed to the inner peripheral surface side of the annular wall portion 137a provided on the outer peripheral portion.
The inner peripheral surface side of the rotor magnet 138 is arranged so as to approach each salient pole portion of the stator core 135 from the radial outside.

An equilibrium member 139 is provided on the outer peripheral surface of the annular wall 137a of the rotor case 137 to balance the rotation of the rotating body including the rotor case 137 and the rotating shaft 134. The balancing member 139 has a function of canceling a rotational imbalance generated in the rotating body when the rotation speed of the motor 13 exceeds the above-described resonance rotation speed of the rotating body by a balance correction action accompanying mass transfer. The rotor case 1
An annular case 1 comprising a groove is provided on an annular wall 137a
39a are provided. This annular case 139a
The rotor case 13 is formed by bending a lower end portion of the annular wall portion 137a in a groove shape so as to protrude radially outward in a substantially U-shaped cross section.
7 so as to rotate integrally therewith.

Further, inside the annular case 139a, a balance sphere 139b composed of a plurality of mass bodies is provided.
139b are accommodated so as to be freely movable in the circumferential direction along the inner peripheral wall surface of the annular case 139a. Each of these balance spheres 139b starts moving in the direction opposite to the position of the center of gravity of the rotating body including the rotating shaft 134 and the rotor case 137 when the rotation speed of the motor 13 exceeds the resonance rotation speed CR. The mass is adjusted, and the rotation of the rotating body is balanced by the movement of the balance sphere 139b, so that the rotation of the rotating body is stabilized while the vibration is reduced.

In a low rotation region before the rotation speed of the motor 13 exceeds the resonance rotation speed CR, the balance spheres 139b, 139b,... Are generated by the magnetic attraction of the rotor magnet 138 described above. Radially inside, that is, the annular wall portion 137a of the rotor case 137
It is adapted to be held in a fixed state in which it is drawn to the side and in contact therewith.

On the other hand, a plate-like cover 139c is attached to the opening provided on the upper side of the annular case 139a in a closed state, and the above-mentioned balance spheres 139b are closed by the closing action of the cover 139c. , So as not to protrude upward from the inside of the annular case 139a.

On the other hand, a substantially disk-shaped disk table (turntable) 121 is fixed to the above-mentioned projecting portion of the rotary shaft 134 on the upper side in the figure, and the disk table 121 is automatically balanced at a position directly below the disk table 121 in the axial direction. Device 2
A pair of balancing members 21 and 21 constituting the rotating shaft 134 are rotatably mounted on the rotating shaft 134 via appropriate bearing members. The disk table 121 is fixed by press-fitting a rotary shaft press-fitting hole formed in a central portion to the rotary shaft 134, and has a substantially conical positioning projection 121a formed in an annular shape so as to include the fixed portion. Thus, a recording disk (not shown) mounted on the disk table 121 (see reference numeral 12 in FIG. 1)
Is held at a predetermined position.

Next, the structure of the automatic balancing device 20 will be described. First, as described above, a pair of balancing members 21,
21 is rotatably attached to the rotary shaft 134 directly or via a bearing member such as a bearing bearing or a metal bearing.
Due to the balance correcting action of the automatic balancing device 20 having the rotating member 21, the rotating body including the rotating shaft 134 and the disk table 121 and the like cancels the rotational imbalance that occurs when the rotating body exceeds the resonance rotation speed CR of the rotating body and performs a rated rotation. Configuration has been made. A resin sheet material made of a highly slidable resin material such as Teflon (registered trademark) is sandwiched between the respective balancing members 21 from both sides in the axial direction at the center of each balancing member 21. They are arranged in contact with each other, and the respective balancing members 21 are smoothly rotated by the interposition of the respective resin sheet materials.

More specifically, the pair of balancing members 2
1 has a planar circular main body portion 21a as shown in FIGS. 2, 3, and 4, and a part of the outer peripheral edge portion of the circular main body portion 21a has a small diameter. The structure is formed so as to be cut out by the unbalanced portion 21b formed of the through hole. The fixing hole 21c formed at the center position of the circular main body 21a is rotatably attached to the rotary shaft 134 as described above. Are arranged so as to be close to each other in the axial direction.
As the circular main body 21a of each of the pair of balancing members 21, a material having a large specific gravity, such as iron, stainless steel, or lead, is preferably used, but a variety of materials can be used. is there.

The size and position of the unbalanced portion 21b are appropriately determined according to the unbalanced amount of the entire rotating body including the recording disk 12, and the size of the unbalanced portion 21b is provided. However, the position of the center of gravity of the circular main body member 21a is different from that of the unbalanced portion 21b.
By being deviated to the opposite side from the formation position, a balance correcting action as described later can be obtained.

It is sufficient that the unbalanced portion 21b is obtained by removing a part of the circular main body portion 21a. Therefore, the unbalanced portion 21b does not have to be a through-hole as in the present embodiment. It is also possible to form from.

On the other hand, each such balancing member 21 is provided with a rotation locking member 23 as shown in FIGS. The rotation locking member 23 has a function of rotating the respective balancing members 21 integrally with the rotation shaft 134 when the rotating body is rotating at a low speed at or below the resonance rotation speed CR. , The rotating shaft 134
And a substantially disk-shaped support portion 23b to which a central boss portion 23a is fixed.
A large number of sliding contact pieces 23c,... are integrally provided on the outer peripheral edge of the b.
Each of these sliding contact pieces 23c constitutes an annular sliding contact portion by being annularly arranged along the entire outer peripheral edge of the support portion 23b. The inner peripheral wall surface of each sliding contact piece 23c is configured to press against the outer peripheral surface of each balancing member 21. The sliding force of each sliding contact piece 23c causes each balancing member 23c to slide. 21 is fixed so as to rotate integrally with the rotation shaft 134.

On the other hand, of the large number of sliding contact pieces 23c,
A slit 23d formed of a narrow gap is provided between the two sliding contact pieces 23c adjacent in the circumferential direction so as to extend in the axial direction. In addition, each of these sliding contact pieces 23
The entire rotation locking member 23 including the rotation member c is formed from an elastic material such as a deformable spring material, and when the rotating body is in a high-speed rotation state at the resonance rotation speed CR or more, the rotational centrifugal force is generated. Thereby, the free end side portion (upper portion in the drawing) of each of the sliding contact pieces 23c is configured to expand toward the outside in the radial direction.

In this embodiment having such a configuration,
The rotational unbalance of the rotor case 137 constituting a part of the motor 13 is caused by a plurality of balance spheres 1 in the balancing member 139 attached to the rotor case 137.
39b is easily and satisfactorily eliminated by the free movement.

In particular, in this embodiment, since the two balancing members 139 and 20 are arranged so as to be separated from each other in the axial direction of the motor 13, the rotor case constituting a part of the motor 13 is formed. 137 and disk table 1
Rotational imbalance in both of the rotating bodies 21 is well resolved in a mechanically stable state as described below, and the whole rotating body is extremely well balanced.

That is, as shown in FIG. 6, when the rotating body W is held by a bearing portion at a position separated by a distance l, in order to balance the rotating body W, With respect to the minute portion dm, it is necessary that Xa + Xb + ω ² ∫xdm = 0 Ya + Yb + ω ² ∫ydm = 0−Yb · l−ω ² ∫yzdm = 0−Xb · l−ω ² ∫xzdm = 0. Therefore, it is preferable that the rotating body W be rotationally balanced by the two equilibrium members 139 and 20 which are arranged apart in the axial direction as in the present embodiment.

Further, in this embodiment, the rotor case 1
Since the balancing member 139 provided on the 37 side has a simple configuration, it can be manufactured at low cost without impairing productivity.

At this time, in this embodiment, the balance sphere 139b constituting the balancing member 139 is
Since it is configured to be attracted to the inner peripheral side by the drive magnet 138 in a low rotation region up to the resonance rotation speed, accurate addition can be achieved by a simple configuration without separately adding a holding mechanism of the balance sphere 139b. The balance forcing action is obtained.

On the other hand, the balancing member 20 in the present embodiment
Then, the rotating body including the rotating shaft 134, the disk table 121, the recording disk 12, and the auto-balancing device 20, etc.
When the motor is started from the rotation stop state by the spindle motor 13 and is in a low-speed rotation region that does not exceed the resonance rotation speed CR of the rotating body, the two two balancing members 21 and
Since the rotating body integrally rotates with the rotating shaft 134 by the locking action of each sliding contact piece 23c of the rotation locking member 23, the relative speed between the two becomes "0".
The balance correcting action described later is realized early.

When the rotation speed of the spindle motor 13 increases and the centrifugal force increases, and when the rotation speed of the spindle motor 13 reaches around the resonance rotation speed CR, each sliding contact of the rotation locking member 23 is performed. The piece 23c expands due to a large centrifugal force, whereby each of the balancing members 21
Is released, and free rotation of the balancing members 21 and 21 with respect to the rotation shaft 134 is allowed. The rotational speed of the spindle motor 13 is the resonance rotational speed CR
After that, the balancing members 21 and 21 that have become freely rotatable with respect to the rotation shaft 134 move individually in a direction to cancel the eccentricity of the rotating body, which is a so-called pull-in phenomenon. And a balance correcting action is imparted to the rotating body.

As described above, each of the balancing members 21 and 21 is
When the recording disk having a rotational imbalance is rotated, the self-movement is appropriately performed by the balance correcting action, whereby the position of the composite center of gravity is located on the rotating shaft 134. As a result, the rotating body rotates without vibrating,
Even if a recording disc with rotational imbalance is mounted,
Since the composite center of gravity is rotated while being positioned on the rotation shaft 134, the rotation is continued without vibration.

On the other hand, when the rotation speed of the rotating body is reduced after the automatic balancing is performed, each sliding contact piece 23c of the rotation locking member 23 is reduced as the rotation speed decreases.
Against the reduced centrifugal force, again presses against the outer peripheral surfaces of the balancing members 21 and 21 to exert a locking force. At this time,
Since the respective balancing members 21 and 21 are in a balanced state, there is no eccentricity in the rotating body. In this state, the holding action by the rotation locking member 23 is performed. It remains canceled. Since the balance state is maintained even after the rotation of the spindle motor 13 is stopped, when the spindle motor 13 is driven again, the eccentricity of each balancing member 21 does not occur.
The rotation starts very smoothly.

At this time, in the present embodiment, in particular, the mass required for the balance correcting action is efficiently ensured by utilizing the entire peripheral area of the circular main body 21a. In the case of the same mass, at least one of the outer diameter and the thickness is significantly smaller than that provided with the fan-shaped balancing member as described in Japanese Unexamined Patent Publication No. 11-178272. Will be set,
The entire device can be reduced in size and flattened.

Further, by adopting the circular main body portion 21a, an extreme cantilever structure as in the prior art is eliminated, and an extremely stable rotation state can be obtained from a low-speed rotation state to a high-speed rotation state.

Further, in this embodiment, the circular main body 21
Since the unbalanced portion 21b composed of a hole or a concave portion in which a part of the portion a is removed in a substantially circular shape in a plane is adopted, even if the size of the unbalanced portion 21b is changed, Since the position of the center of gravity does not change, the mass adjustment of the balancing member 21 is facilitated.

Furthermore, in the present embodiment, each of the balancing members 21 is provided by the rotation locking member 23 having the sliding contact piece (annular sliding contact portion) 23c arranged annularly over substantially the entire circumference. Regardless of the rotational position, it can be fixed by the sliding contact piece 23c of the rotation locking member 23. Therefore, after each balancing member 21 is once in the balanced state, at the time of the next rotation start, each balancing member 21 is already fixed in the balanced state by the sliding contact piece 23c, and as a result, In particular, the rotation stability in the low-speed rotation region is improved, and also in the high-speed rotation region, the balance shifting operation of each balancing member 21 is performed smoothly and in a short time.

As described in the present embodiment, such a rotation locking member 23 raises a plurality of sliding contact pieces (annular sliding contact portions) 23c in the axial direction along the outer peripheral edge of the disk-shaped support portion 23b. With such a configuration, it can be easily formed.

Although the embodiments of the present invention made by the inventor have been specifically described above, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

For example, as the two balancing members in the present invention, two fan-shaped balancing members such as those disclosed in Japanese Patent Application Laid-Open No. H11-178272, other than the above-described embodiment, may be used. Various components such as members can be employed.

The present invention can be similarly applied to a device other than the CD-ROM or DVD drive as in the above-described embodiment, and the applicable motor is a servo motor, an air motor, or the like. Can be applied to a wide variety.

[0051]

As described above, the automatic balancing device for a motor according to the first aspect of the present invention has a plurality of rotors which form a part of the motor corresponding to the rotational imbalance of the rotating body. With a balancing member in which the mass body moves freely,
Since the configuration is such that the rotational imbalance of the rotor is satisfactorily eliminated, the motor itself can be satisfactorily corrected with a simple and small configuration, and the motor for the rotating body driven by the motor is rotated. An extremely smooth rotation state can be obtained by eliminating the influence of vibration or the like from the side.

In the media disk drive motor according to the second aspect of the present invention, a rotor constituting a part of the motor is provided by disposing two balancing members in the axial direction of the motor. Since the rotational imbalance in both of the disk holding members for driving the rotation of the media disk is eliminated in a mechanically stable state, in addition to the effects described above, the media disk can be rotated extremely smoothly. It can be driven.

Furthermore, in the media disk drive motor according to the third or fourth aspect of the present invention, the balancing member provided on the rotor side is provided with a plurality of masses in an annular case rotating integrally with the rotor. Since it is configured by housing the body, the balancing member on the rotor side can be configured with a simple configuration, and in addition to the above-described effects, a more inexpensive and highly productive device can be provided. .

In this case, in the media disk drive motor according to the fifth aspect of the present invention, by disposing an annular drive magnet on the inner peripheral surface side of the rotor, the mass body constituting the balancing member can be resonated. Since it is configured to be attracted to and held on the drive magnet side in the low rotation region up to the rotation speed, an accurate balance forcing action can be obtained with a simple configuration, and in addition to the effects described above, the device Can be improved in reliability.

On the other hand, the media disk drive motor according to the invention of claim 6 is configured such that one side of the balancing member is configured to remove a part of the circular main body,
In addition to enabling downsizing and flattening of the entire device and obtaining an extremely stable rotation state from a low-speed rotation state to a high-speed rotation state, in addition to the above-described effects, it is much simpler. A highly reliable device can be obtained.

At this time, the media disk drive motor according to the invention of claim 7 employs an unbalanced portion formed of a hole or a concave portion in which a part of a circular main body is removed in a substantially circular shape in a plane, and is used for balancing. Since the adjustment of the mass of the member is facilitated, the applicability of the device can be improved in addition to the above-described effects.

[Brief description of the drawings]

FIG. 1 shows a CD-R as an example of an apparatus to which the present invention is applied.
FIG. 2 is an explanatory perspective view showing the appearance of an OM or DVD drive unit.

FIG. 2 is an explanatory longitudinal sectional view showing an embodiment of a motor with an automatic balancing device employed in the CD-ROM or DVD drive unit shown in FIG.

FIG. 3 is an explanatory plan view showing an embodiment of the automatic balancing device shown in FIG. 2;

4 is an external perspective explanatory view showing the automatic balancing device shown in FIG. 3;

FIG. 5 is an external perspective explanatory view showing an embodiment of another portion of the automatic balancing device shown in FIG. 2;

FIG. 6 is an explanatory diagram schematically showing a balance state of a rotating plate.

FIG. 7 is an explanatory longitudinal sectional view showing an example of a conventional motor with an automatic balancing device.

[Explanation of symbols]

 Reference Signs List 10 Drive unit for CD-ROM or DVD 12 Recording disk (media disk) 13 Spindle motor 139 Disk table 131 Main frame 134 Rotating shaft 137 Rotor case 137a Annular wall 138 Rotor magnet 139 Balancing member 139a Annular case 139b Balance sphere (mass body) 139c cover 20 automatic balancing device 21 balancing member 21a circular main body 21b unbalanced portion

Continued on the front page F-term (reference) 5D038 BA04 BA10 CA03 5D109 DA11 5H607 AA04 BB01 BB14 BB17 BB25 CC03 DD19 EE40

Claims (7)

[Claims] 1. A rotating body partially including a rotor constituting a motor, and an action of correcting a rotational imbalance of the rotating body when a rotation speed of the motor exceeds a resonance rotation speed of the rotating body. Wherein the balancing member is provided with an annular case provided so as to rotate integrally with the rotor, and is accommodated in the annular case and is free at least in a circumferential direction. An automatic balancing device for a motor, comprising: a plurality of mass bodies movably held. 2. A rotating body comprising: a rotor constituting a motor; and a disk holding member that rotates together with the rotor while holding the media disk and drives the media disk to rotate. A balancing member for canceling the rotational imbalance of the rotating body by a balance correcting action when the rotational speed of the rotating body exceeds the resonance rotational speed is attached to the rotating body, and the balancing member is A media disk drive motor, which is disposed at two places separated in the axial direction of the motor. 3. One of the two balancing members has an annular case provided so as to rotate integrally with the rotor, and is accommodated in the annular case and freely moves at least in a circumferential direction. A plurality of mass bodies accommodated as possible;
The media disk drive motor according to claim 2, further comprising: 4. The annular case includes a groove having a substantially U-shaped cross section projecting radially outward or inward from a side surface of the rotor, and a cover covering an opening of the groove. 4. An automatic balancing device for a motor according to claim 1 or a media disk drive motor according to claim 3. 5. An automatic motor for a motor according to claim 1, wherein said rotor has an outer rotor structure, and an annular drive magnet is mounted on an inner peripheral surface side of said rotor. 4. A media disk drive motor according to claim 3 or a balancing device. 6. One of the two balancing members removes a circular main body rotatably mounted on a rotating shaft of the motor and a part of the circular main body. 3. The media disk drive motor according to claim 2, further comprising an unbalance portion formed as described above. 7. The unbalance portion is formed of a hole or a concave portion obtained by removing a part of the circular main body in a substantially circular plane or a part thereof, and the circular main body includes the rotating shaft. 7. The media disk drive motor according to claim 6, wherein two are mounted so as to overlap with each other in the axial direction.