JP3723669B2 - Rotating balancer and related technologies - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rotary balancer by rotating an unbalanced rotating system at a relatively high rotational speed, and a rotating body, a recording medium driving device, and a recording disk driving device including the rotating balancer.
[0002]
[Prior art and problems to be solved by the invention]
In a device having a rotating part such as a motor, one of the causes of generating vibration and noise is an imbalance of the rotating part. Causes of the occurrence of unbalance include manufacturing errors of parts, eccentricity due to gaps during assembly, and the like. For such manufacturing errors and eccentricity due to gaps at the time of assembly, accuracy has been improved. However, as long as a certain error is allowed, the occurrence of unbalance to some extent cannot be eliminated. As a method for correcting such an imbalance, there is a method for comprehensively correcting the imbalance of the assembled rotating part with a balance correcting machine. However, since the productivity is not good, it is not suitable for mass-produced products.
[0003]
As another means for reducing the unbalance of the rotating system, conventionally, a rotating balancer in which a liquid b in a required ratio with respect to its capacity is enclosed in an annular tubular part a as shown in FIG. Are known. When the annular tubular portion a rotates approximately in the circumferential direction about the rotation axis in the vertical direction due to the rotation of the rotation system including the rotation balancer, the rotation system is unbalanced and the rotation is unbalanced. When rotating, the rotating system rotates in the radial direction. In this case, it rotates in a state where the distribution amount of the liquid b in the tubular portion a is increased at a position delayed with respect to the direction in which the rotating system touches (the unbalanced position [0 ° position] of the rotating system). When the rotational speed of the rotating system becomes sufficiently higher than the natural frequency of the transverse vibration (radial vibration) of the rotating system, the delay angle approaches 180 °, and the rotating system approaches a balanced state.
[0004]
However, since such a conventional rotary balancer has a space in the tubular portion a in which the distribution amount of the sealed liquid b in the circumferential direction can be biased, the circumferential bias of the sealed liquid b due to gravity greatly occurs depending on the posture. When the rotation axis is inclined to a certain extent with respect to the vertical direction, it cannot be used as a rotation balancer. Moreover, in order to prevent leakage of the liquid b in the tubular part a, it was necessary to seal the tubular part a.
[0005]
The present invention has been made in view of the above-described points existing in the prior art, and the object of the present invention can be widely used because there are few restrictions due to the posture of the rotating system. Another object of the present invention is to provide a rotating balancer that is easy to manufacture in that it is not necessary to seal the working fluid, and a recording medium driving device and a recording disk driving device including the rotating balancer.
[0006]
[Means for Solving the Problems]
(1) A rotary balancer of the present invention that achieves the above object is
A rotary balancer comprising an annular magnetic fluid holding part and a magnetic fluid,
Has 2 or more the magnetic fluid holding portion coaxially,
The magnetic fluid holding portion uses an annular permanent magnet body magnetized in the axial direction as a magnetomotive force means,
The magnetic fluid holding portion holds the magnetic fluid in a continuous shape over its entire circumference magnetically,
The distribution of the magnetic fluid held in each magnetic fluid holding portion can fluctuate,
When the magnetic fluid holding part rotates substantially in the circumferential direction, the entire magnetic fluid holding part rotates integrally on the same axis, and the magnetic fluid held thereby rotates together with each magnetic fluid holding part. Rotating balancer (Claim 1).
[0007]
As the magnetic fluid, there can be used one in which magnetic fine particles stably dispersed using a surfactant are suspended in a fluid medium at a high concentration.
[0008]
The magnetic fluid holding unit can hold the magnetic fluid in a part of a magnetic circuit including magnetomotive force means such as a permanent magnet body. In a normal case, a certain portion of the magnetic circuit is constituted by a magnetic circuit component made of a magnetic material such as a ferromagnetic material.
[0009]
That is, for example, a magnetic circuit component made of an annular ferromagnetic material is provided coaxially with the annular permanent magnet body, and magnetic fluid is magnetized continuously over the entire circumference between the annular permanent magnet body and the magnetic circuit component. (Claim 3).
[0010]
It is desirable that the distribution of the magnetic fluid held in the magnetic fluid holding unit varies over the entire circumference of the magnetic fluid holding unit.
[0011]
In addition, when the driven body that is held and rotated by a rotating portion or the like in an electric motor such as a spindle motor or the like includes the annular magnetic fluid holding portion and the magnetic fluid as described above, the driven body itself Constitutes a rotating balancer.
[0012]
When the magnetic fluid holding part rotates approximately in the circumferential direction (that is, approximately around the axial center line) by rotation of the rotating system including the rotating balancer, the rotating system is in the radial direction when the rotating system is unbalanced. Rotate while touching. Then, the distribution of the magnetic fluid that is held by the magnetic fluid holding portion and rotates together with the magnetic fluid holding portion varies from the distribution in the case where the magnetic fluid holding portion is in a stationary state, and the rotation system touches (the unbalanced position of the rotation system). In the delayed position, the magnetic fluid held in the magnetic fluid holding portion rotates with an increased distribution amount.
[0013]
When the rotational speed of the rotating system is between the start of rotation and the natural frequency of the transverse vibration (radial vibration) of the rotating system, the rotating system is held in the magnetic fluid holding part against the direction of contact with the radial direction. Thus, the delay angle in the direction in which the distribution amount of the rotating magnetic fluid increases is in the range of 0 to 90 degrees.
[0014]
When the rotational speed of the rotating system is equal to the natural frequency, the delay angle in the direction in which the distribution amount of the rotating magnetic fluid held by the magnetic fluid holding portion increases with respect to the direction in which the rotating system touches in the radial direction is 90 degrees.
[0015]
In a state where the rotational speed of the rotating system exceeds the natural frequency, the delay angle in the direction in which the distribution amount of the rotating magnetic fluid held by the magnetic fluid holding portion increases with respect to the direction in which the rotating system touches in the radial direction is When the rotational frequency is in the range of 90 to 180 degrees and the rotational speed is sufficiently higher than the natural frequency, the delay angle approaches 180 degrees, and accordingly, the rotational system approaches the balanced state.
[0016]
The magnetic fluid that acts to balance the rotation in the rotary balancer is rotated while being magnetically held continuously over the entire circumference of the magnetic fluid holding portion. Therefore, unlike the case of using a normal liquid, it is not necessary to seal the magnetic fluid, and the circumferential deviation due to gravity does not occur so much regardless of the posture. By appropriately selecting the magnetic holding force, it can be used almost regardless of the posture of the rotating system.
(1-1) In this rotating balancer, it is desirable that the magnetic fluid holding part holds the magnetic fluid with a substantially constant magnetic holding force over the entire circumference (claim 2).
[0017]
The magnetic fluid holding part holds the magnetic fluid with a substantially constant magnetic holding force over the entire circumference, thereby rotating the magnetic fluid in a stationary state substantially uniform in the circumferential direction. Avoiding unbalance in the system, it is possible to smoothly achieve the balance of rotation.
[0018]
By increasing the number of magnetic fluid holders, the total amount of magnetic fluid to be held and the amount of fluctuation in the distribution of the magnetic fluid are increased, so that an unbalanced rotating system can be used to increase the number of rotations and bring it closer to a balanced state. The range of the unbalance amount to be obtained can be widened.
(1-2-1) In the rotation balancer of (1-2), the position of each magnetic fluid holding portion in the axial center direction may be different (claim 4 ).
[0019]
When the unbalanced position of the rotating system is different in the axial direction, the distribution of the magnetic fluid held by the magnetic fluid holding portions having different axial positions in the axial direction shows different fluctuations. Can be easily approached.
(1-3) In the rotary balancer described above, the magnetic fluid held in the magnetic fluid holding part is formed by the annular concave part of the non-magnetic material annular member and the magnetic substance holding part, and has a bottom part radially outward. Located in the annular groove,
Of the annular member, the portion facing the annular groove portion repels the magnetic fluid,
The radially outward portion of the magnetic fluid held by the magnetic fluid holding portion may be close to the portion of the annular member that faces the bottom in the annular groove portion (Claim 5 ).
[0020]
Nonmagnetic materials include paramagnetic materials and diamagnetic materials.
[0021]
A portion facing the inside of the annular groove of the annular member can be repelled with a normal magnetic fluid if an oil repellency treatment is applied thereto.
[0022]
The magnetic fluid held in the magnetic fluid holding part is located in an annular groove part having a bottom portion radially outward by an annular member made of a nonmagnetic material or by the annular member and the magnetic fluid holding part. The portion facing the annular groove repels the magnetic fluid.
[0023]
When the magnetic fluid is about to be detached from the magnetic fluid holding portion by the centrifugal force acting on the magnetic fluid by rotating the magnetic fluid holding portion substantially in the circumferential direction, the radially outer portion of the magnetic fluid is annular in the annular member. The magnetic fluid which is close to the portion facing the bottom in the groove and is about to be detached is repelled by the portion facing the annular groove of the annular member made of non-magnetic material, so that the magnetic fluid is separated from the magnetic fluid holding portion. It is hard to do. Even if the magnetic fluid is once separated to a place other than the bottom, the magnetic fluid tends to gather at the bottom due to the centrifugal force due to rotation and be magnetically held again by the magnetic fluid holding portion.
(2) The rotating body of the present invention is a rotating body including the rotating balancer according to (1),
The axial center line of the magnetic fluid holding part in the rotary balancer is coaxial with the rotational axis of the rotating body (Claim 6 ).
[0024]
As an example of this rotating body, there can be mentioned a rotating part in an electric motor such as a spindle motor or other machines.
[0025]
The rotating body may include two or more rotating balancers. In this case, the total amount of the magnetic fluid to be held and the amount of fluctuation in the distribution of the magnetic fluid are increased, and the range of the unbalance amount that can be dealt with in bringing the unbalanced rotating body closer to the balanced state by increasing the rotational speed is widened. can do.
[0026]
Moreover, in the thing provided with 2 or more of the said rotation balancers, the axial center direction position of the magnetic fluid holding | maintenance part of each rotation balancer can differ. In this case, when the unbalanced position of the rotating body is different in the axial direction, the distribution of the magnetic fluid held by the magnetic fluid holding portions having different axial positions in the axial direction shows different fluctuations. As shown in FIG.
(3) A recording medium driving device for rotationally driving the recording medium held in the rotating unit,
The rotating part, (1) a rotation balancer according to its axial center line of the magnetic fluid holding portion can be made with so as to form an axis of rotation coaxial with said rotary portion (claim 7 ).
[0027]
Examples of the recording medium include a non-detachable recording medium such as a hard disk, an optical disk (CD, CDR, DVD, etc.) normally used in a removable state, a magneto-optical disk, a removable hard disk, and the like.
[0028]
As an example of the recording medium driving device, there can be mentioned a spindle motor for holding and rotating the disk-shaped recording medium coaxially in the rotating portion.
(4) A recording disk drive device in which two or more recording disks and an annular spacer interposed between the recording disks are fixedly held coaxially on the rotating part,
At least one of said annular spacer, may be formed so as to constitute a rotation balancer according to (1) (claim 8).
[0029]
Examples of the recording disk include a non-detachable recording medium such as a hard disk.
[0030]
This recording disk drive device has two or more annular spacers, and the positions of the magnetic fluid holding portions in the annular spacers in the axial center direction can be different. In this case, when the unbalanced position of the rotating system including the recording disk, the annular spacer, and the rotating portion is different in the axial direction, the distribution of the magnetic fluid held in the magnetic fluid holding portions having different axial positions is different. By showing different fluctuations, the rotating system as a whole can be made closer to a balanced state.
[0031]
Further, the annular spacer may have two or more magnetic fluid holding portions, and the axial direction positions of the magnetic fluid holding portions may be different. In this case, even if there is one annular spacer fixedly held by the rotating part, in this case, when the unbalanced position of the rotating system including the recording disk, the annular spacer, and the rotating part differs in the axial direction, When the distribution of the magnetic fluid held in the magnetic fluid holding portions having different positions in the central direction shows different fluctuations, the rotation system as a whole can be easily brought into a balanced state.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS.
[0033]
1 to 3 relate to a hard disk drive device as an example of embodiments of a rotary balancer, a rotating body, a recording medium drive device, and a recording disk drive device according to the present invention. FIG. FIG. 2 is a cross-sectional view, FIG. 2 is a fragmentary perspective view of a main part of the rotary balancer, and FIG.
[0034]
In this hard disk drive, six hard disks 60 are fixedly held on the rotor hub 22 of the spindle motor 10.
[0035]
The rotor 20 in the spindle motor 10 is mainly fitted in and fixed to a rotor yoke 24 made of a ferromagnetic material such as a substantially cylindrical magnetic stainless steel whose inner diameter is reduced at the upper end and an upper and lower intermediate position of the rotor yoke 24. A rotor magnet 26, a bush 28 fitted and fixed to the lower end of the rotor yoke 24, a rotor hub 22 fitted and fixed to the rotor yoke 24, and an annular seal member 30 fitted and fixed to the upper end of the rotor hub 22. .
[0036]
A stator core 44 around which a stator coil 42 is wound is fitted and fixed at an intermediate position in the vertical axis direction of the fixed shaft body 40 in the spindle motor 10 and is opposed to the rotor magnet 26 in the radial direction. The rotor 20 is rotatably supported coaxially with respect to the fixed shaft body 40 via upper and lower ball bearings 50 and 52 disposed above and below the stator core 44. The upper end diameter-reduced portion of the rotor yoke 24 in the rotor 20 is supported by the outer ring of the upper ball bearing 50, and the lower end portion of the rotor yoke 24 is supported by the outer ring of the lower ball bearing 52 via the bush 28.
[0037]
The rotor hub 22 is made of a non-magnetic material such as aluminum and has a substantially cylindrical shape. An annular seal member 30 is fitted and fixed to the upper end portion of the rotor hub 22 whose inner diameter is reduced. An annular projecting portion 22 a is provided outside the lower end of the rotor hub 22.
[0038]
In the rotor hub 22, six identical hard disks 60, four identical annular spacers 70, with hard disks 60 and annular spacers 70 or rotating balancers 80 stacked alternately on the annular projecting portion 22 a, An annular rotary balancer 80 having the same inner and outer diameters and thickness as the annular spacer 70 is externally fitted coaxially. The rotation balancer 80 is located in the central gap among the five gaps between the hard disks 60. The hard disk 60, the annular spacer 70, and the rotary balancer 80 are clamped and fixed between the clamp ring 100 and the annular projecting portion 22a by fixing the clamp ring 100 to the upper end portion of the rotor hub 22.
[0039]
As shown in FIG. 2, the rotary balancer 80 includes an annular member 82 made of a non-magnetic material such as aluminum, an elastic annular permanent magnet 84 magnetized in the vertical direction (axial direction), and an annular ferromagnetic member. It consists of a body-made magnetic circuit component 86 and magnetic fluids 88 and 89.
[0040]
The annular member 82 has an annular recess 82a that opens radially inward and has a bottom portion radially outward. An inward projection that contacts the outer peripheral surface of the rotor hub 22 may be above (or below) the annular recess 82a. Part 82b. The inner peripheral surface of the annular member 82 is treated with an oil repellent 90 for repelling the magnetic fluids 88 and 89.
[0041]
A flexible elastic annular permanent magnet body 84 is fixed at an intermediate position between the bottom of the annular recess 82 a and a magnetic circuit component 86 is fixed to the inner peripheral side of the elastic annular permanent magnet body 84. The inner diameter of the inner peripheral surface of the lower end of the annular member 82 is equal to the outer diameter of the magnetic circuit component member 86.
[0042]
The upper and lower end portions of the magnetic circuit component member 86 protrude vertically from the upper and lower surfaces of the elastic annular permanent magnet body 84, and are between the outer peripheral surface of the upper end portion of the magnetic circuit component member 86 and the upper surface of the elastic annular permanent magnet body 84. And, between the outer peripheral surface of the lower end portion of the magnetic circuit constituting member 86 and the lower surface of the elastic annular permanent magnet body 84, respectively, the annular magnetic fluid holding portions 92 and 93 are formed over the entire circumference. Both magnetic fluid holding portions 92 and 93 are symmetrical in the vertical direction with different positions in the vertical direction (axial direction).
[0043]
Magnetic fluids 88 and 89 are respectively injected into the magnetic fluid holding portions 92 and 93, and the magnetic fluids 88 and 89 are magnetically held continuously over the entire circumference by a substantially constant magnetic holding force. The distribution of the quiescent fluids 88 and 89 is substantially uniform in the circumferential direction. The magnetic circuit in the rotary balancer 80 includes an elastic annular permanent magnet body 84, a lower magnetic fluid 88, a magnetic circuit constituent member 86, and an upper magnetic fluid 89.
[0044]
The radially outward portions of the magnetic fluids 88 and 89 held by the magnetic fluid holding portions 92 and 93 are close to the bottom surface in the annular recess 82a. Near the upper and lower corners of the annular recess 82a, there is a space that can vary the distribution of the magnetic fluids 88 and 89 held by the magnetic fluid holding portions 92 and 93 over the entire circumference. Is rotated together with the magnetic fluid holding portions 92 and 93 when the magnetic fluid holding portions 92 and 93 are rotated in the circumferential direction along with the rotation of the rotor 20. Unlike the case of using a normal liquid, it is not necessary to seal the magnetic fluids 88 and 89.
[0045]
The magnetic fluids 88 and 89 held by the magnetic fluid holding portions 92 and 93 are formed by the annular recess 82a of the annular member 82 made of a non-magnetic material and the upper and lower magnetic fluid holding portions 92 and 93 , and the bottom portion is radially outward. The portions of the annular member 82 facing the annular grooves 94 and 95 that are located in the annular grooves 94 and 95 are treated with the oil repellent 90 and repel the magnetic fluids 88 and 89. When the magnetic fluid 88 or 89 is about to be detached from the magnetic fluid holding portions 92 or 93 by the centrifugal force acting on the magnetic fluid 88 or 89 due to the rotation of the magnetic fluid holding portions 92 or 93 in the substantially circumferential direction, The radially outer portions of the fluids 88 and 89 are close to the bottom surfaces in the annular grooves 94 and 95 of the annular member 82, and the magnetic fluids 88 and 89 that are about to be separated are the inner periphery of the annular member 82 made of a nonmagnetic material. The magnetic fluids 88 and 89 are hardly separated from the magnetic fluid holding portions 92 and 93 because they are bounced to the side surfaces. Even if the magnetic fluids 88 and 89 are once separated to a place other than the bottom, the magnetic fluids 88 and 89 are gathered at the bottom due to the centrifugal force caused by the rotation and are again magnetically held by the magnetic fluid holding portions 92 and 93. It is easy to become.
[0046]
The hard disk drive device is used in a state where the upper and lower ends of the fixed shaft body 40 are fixed.
[0047]
The rotating body (rotating system) including the outer ring of the rotor 20, the hard disk 60, the annular spacer 70, the rotating balancer 80, the clamp ring 100, and the upper and lower ball bearings 50 and 52 is axisymmetrically assembled. Each part is manufactured and assembled under a certain tolerance, and there is a possibility that a certain degree of unbalance is caused.
[0048]
When the magnetic fluid holding portion 92 rotates in the circumferential direction clockwise in FIG. 3 by the rotation of the rotating body, when the rotating body is unbalanced, the rotating body rotates in a state of touching in the radial direction. Then, the distribution of the magnetic fluid 88 held by each magnetic fluid holding portion 92 and rotating together varies from a uniform distribution [FIG. 3A] in the circumferential direction when the magnetic fluid holding portion 92 is in a stationary state. .
[0049]
In a state where the rotational speed of the rotating body is between the start of rotation and the natural frequency of the transverse vibration (radial vibration) of the rotating body (FIG. 3B), the rotating body is in the direction X in which the rotating body touches in the radial direction. On the other hand, the delay angle in the direction Y in which the distribution amount of the rotating magnetic fluid 88 held by the magnetic fluid holding portion 92 increases is in the range of 0 to 90 degrees.
[0050]
When the rotational speed of the rotating body is equal to the natural frequency [FIG. 3 (c)], the magnetic fluid 88 is rotated by being held by the magnetic fluid holding portion 92 with respect to the direction X in which the rotating body touches in the radial direction. The delay angle in the direction Y in which the distribution amount increases is 90 degrees.
[0051]
In a state where the rotational speed of the rotating body exceeds the natural frequency, the direction Y in which the distribution amount of the rotating magnetic fluid 88 held by the magnetic fluid holding section 92 increases with respect to the direction X in which the rotating body touches in the radial direction. The delay angle is in the range of 90 to 180 degrees, and if the rotation speed is a steady rotation sufficiently higher than the natural frequency [FIG. 3 (d)], the delay angle approaches 180 degrees, and accordingly, the rotating body Approaches the balanced state.
[0052]
Since the magnetic fluids 88 and 89 are continuously held magnetically and rotated over the entire circumference of the magnetic fluid holding portions 92 and 93, the circumferential deviation due to gravity does not occur so much regardless of the posture, and the hard disk drive It can be used almost regardless of the posture of the device.
[0053]
FIG. 4 is a half cross-sectional view of a hard disk drive device as another example of the embodiment of the rotating body, recording medium drive device, and recording disk drive device of the present invention.
[0054]
In this hard disk drive, the annular rotary balancer 80 is located in the upper and lower end gaps among the five gaps between the hard disks 60, and the three annular spacers 70 are located in the three gaps therebetween. . Other parts are the same as in the above example.
[0055]
In this case, since the two rotary balancers 80 are provided on the upper and lower sides, the distribution of the magnetic fluids 88 and 89 held by the magnetic fluid holding portions 92 and 93 whose axial center positions are greatly different from each other exhibits different fluctuations, so that the rotor As a whole, the rotating body including 20 and the hard disk 60 can be made close to a balanced state.
[0056]
Note that the vertical positional relationship in the description of the above embodiments is merely for convenience of explanation based on the drawings, and does not limit the actual use state or the like.
[0057]
【The invention's effect】
According to the rotary balancer of the present invention, the rotational system is automatically brought close to a balanced state at a rotational speed sufficiently higher than the natural frequency of the lateral vibration of the rotational system to reduce vibration and noise caused by the rotation, and the rotational accuracy. Since the restriction by the posture of the rotating system is small, the usable range is much wider than in the past. Further, it is possible to avoid unbalance in the rotating system and to smoothly realize the balance of rotation. However, it is easy to manufacture in that it is not necessary to seal the magnetic fluid that is the working fluid.
[0058]
According to the rotation balancer of the second aspect, it is possible to avoid the unbalance in the rotation system and to realize the rotation balance smoothly.
[0060]
According to the rotation balancer of the fourth aspect, when the unbalance position of the rotation system is different in the axial direction, the rotation system as a whole can be easily brought close to the balanced state.
[0061]
According to the rotary balancer of the fifth aspect , it is possible to prevent the magnetic fluid held in the magnetic fluid holding portion from being separated and dissipated by the centrifugal force that acts when the magnetic fluid holding portion rotates substantially in the circumferential direction.
[0062]
The rotating system of the rotating body of the present invention, and the recording medium driving apparatus and recording disk driving apparatus of the present invention exhibit the same effects as the rotating system including the rotating balancer according to claims 1 to 6, respectively. Therefore, according to the recording medium driving device and the recording disk driving device of the present invention, it is highly effective in improving the recording density by improving the rotation accuracy of the recording medium.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a hard disk drive device.
FIG. 2 is a fragmentary perspective view of a main part of a rotary balancer.
FIG. 3 is a schematic explanatory view of the distribution of the magnetic fluid held in the magnetic fluid holding unit.
FIG. 4 is a half sectional view of another hard disk drive.
FIG. 5 is a fragmented perspective view of a rotary balancer.
[Explanation of symbols]
22 Rotor hub 60 Hard disk 80 Rotating balancer 82 Annular member 82a Annular recess 84 Elastic annular permanent magnet body 86 Magnetic circuit component 88 Magnetic fluid 89 Magnetic fluid 92 Fluid holding part 93 Fluid holding part

Claims (8)

A rotary balancer comprising an annular magnetic fluid holding part and a magnetic fluid,
Has 2 or more the magnetic fluid holding portion coaxially,
The magnetic fluid holding part uses an annular permanent magnet body magnetized in the axial direction as a magnetomotive force means,
The magnetic fluid holding portion holds the magnetic fluid in a continuous shape over its entire circumference magnetically,
The distribution of the magnetic fluid held in each magnetic fluid holding portion can fluctuate,
When the magnetic fluid holding part rotates substantially in the circumferential direction, the entire magnetic fluid holding part rotates integrally on the same axis, and the magnetic fluid held thereby rotates together with each magnetic fluid holding part. Rotating balancer. The rotary balancer according to claim 1, wherein the magnetic fluid holding part holds the magnetic fluid with a substantially constant magnetic holding force over the entire circumference. The magnetic fluid holding portion, an annular ferromagnetic steel of the magnetic circuit component is provided in the annular permanent magnet coaxially, magnetic continuous shape over the entire circumference between the annular permanent magnet member and the magnetic circuit constituting member The rotary balancer according to claim 1 or 2, wherein the fluid is magnetically held. The rotary balancer according to claim 1, 2 or 3, wherein the magnetic fluid holding portions have different axial positions. The magnetic fluid held in the magnetic fluid holding part is formed by the annular recess of the non-magnetic material-like annular member and the magnetic body holding part, and is located in the annular groove part having the bottom part in the radially outward direction
Of the annular member, the portion facing the annular groove portion repels the magnetic fluid,
5. The rotary balancer according to claim 1, wherein a radially outward portion of the magnetic fluid held by the magnetic fluid holding portion is close to a portion of the annular member facing the bottom in the annular groove portion. A rotary body comprising the rotary balancer according to claim 1, 2, 3, 4 or 5,
A rotating body in which an axial center line of a magnetic fluid holding portion in the rotating balancer is coaxial with a rotating axis of the rotating body. A recording medium driving apparatus for rotationally driving a recording medium held in a rotating unit, wherein the rotating balancer according to claim 1, 2, 3, 4, or 5 is connected to the shaft of the magnetic fluid holding unit. A recording medium driving device provided with a core wire coaxial with a rotation axis of the rotating portion. A recording disk drive device comprising two or more recording disks and an annular spacer interposed between the recording disks fixed and held coaxially with the rotating part,
6. A recording disk drive device, wherein at least one of the annular spacers constitutes a rotary balancer according to claim 1, 2, 3, 4 or 5.

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