JP3390223B2 - motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of discharging static electricity from a rotating part to a fixed part even during rotation of a motor, for example, for driving a recording medium such as a hard disk. The present invention relates to a motor used for: 2. Description of the Related Art As a main spindle motor used for driving a recording medium such as a hard disk, a rotor hub and a rotating shaft are integrated with each other, and the rotating shaft is fixed to a stator frame. One that is rotatably supported via a ball bearing (for example, one shown in FIG. 9) and one that has a rotor hub rotatably supported on a fixed shaft via a ball bearing (for example, one shown in FIG. 10) )). When a recording medium fixed to a rotor hub is driven to rotate, static electricity is accumulated on the recording medium due to friction with air. Therefore, when a head that is weak in charging is used as a head for reading and writing on the surface of the recording medium, it is necessary to take measures for releasing static electricity. In the motor shown in FIG. 9, the upper portion of a steel ball b is inserted into a concave portion a11 provided at a lower end portion of a rotary shaft a1 of a rotor hub a, and a bearing holding cylindrical portion provided upright at the center of a motor frame c. The steel ball b is elastically supported upward by a conductive contact member e supported by a conductive elastic plate d at the lower end of c1, thereby forming the rotation axis a1 and the contact member e with the steel ball b. Contact is maintained, so that even when the motor is rotating, the static electricity of the recording medium attached to the rotor hub a can be released to the motor frame c through the steel balls b. However, in the case of this motor, the friction between the steel ball b and the contact member e or the rotating shaft a1 at the time of rotation causes them to wear, generating dust and damaging the ball bearing f.
Alternatively, the recording medium may be stained due to contamination of the external space of the motor, and the read / write head may be damaged. Also, there is a problem of noise. On the other hand, in the spindle motor shown in FIG. 10, the lubricant of the ball bearing h is scattered to the outside of the motor to contaminate the recording medium and to prevent the head from being damaged. Means is employed in which static electricity of the recording medium is released to the fixed shaft j through the magnetic fluid seal k provided. That is, a magnetic fluid m that is magnetically held over an annular pole piece k2 made of an iron-based material provided above and below the annular permanent magnet body k1 and the outer peripheral surface of the fixed shaft j, and
The conductive material is used as the adhesive n for sealing and bonding between the pole piece k2 and the rotor hub i, so that static electricity can be released even during rotation of the motor. However, since the magnetic fluid seal k seals the space between the rotor hub i and the fixed shaft j, there is a possibility that the magnetic fluid m may not be able to withstand the external pressure fluctuation depending on the degree of external pressure fluctuation. is there. In order to prevent this, the concentricity between the inner peripheral surface of the pole piece k2 and the outer peripheral surface of the fixed shaft j is set with high precision, and the magnetic fluid m is uniformly held in the circumferential direction to improve the pressure resistance. In addition, it is necessary to increase the pressure resistance by holding the magnetic fluid m in the upper and lower pole pieces k2, that is, the NS poles, respectively, to make the magnetic fluid m double. Furthermore, if there is a part where the adhesive is not applied, the sealing is incomplete, and if the applied adhesive is not cured, the adhesive is scattered and the recording medium is stained or the head is damaged. And its curing must be performed reliably. In order to satisfy these needs, considerable time and effort are required in manufacturing, and this has been a factor of cost increase. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has as its object to reduce the external space of a motor due to scattering of magnetic fluid and generation of dust. An object of the present invention is to provide a motor which can discharge static electricity from a rotating part to a fixed part even during rotation of a motor while preventing contamination and damage to a bearing, and which can be easily manufactured. In order to achieve the above-mentioned object, a motor according to the present invention is configured such that a rotating part rotates through a plurality of bearings which are arranged at an axial distance from a fixed part. A motor which is freely supported, wherein between the bearings, one of a rotating portion and a fixed portion supports an annular magnetomotive force means, and the other has a radial gap between the magnetomotive force means and a ring.
A ferromagnetic conductive portion, and a conductive magnetic fluid is magnetically held over the magnetomotive force means and the ferromagnetic conductive portion, and a portion of the magnetomotive force means in contact with the magnetic fluid and the one of the one A portion in contact with the conductive portion is provided with conductive means made of a conductive material, and a space on both sides of the rotating portion and the fixed portion, which sandwiches the magnetomotive force means in the axial direction, is provided by the conductive means. It is assumed that communication has been made in the portion of. According to the first aspect of the present invention, the annular magnetomotive force means supported by one of the rotating portion and the fixed portion of the motor, and the annular magnetomotive force at the other of the other portion separated by a gap from the magnetomotive force means . When the conductive magnetic fluid is magnetically held over the ferromagnetic conductive portion, the magnetic fluid remains magnetically held even during rotation of the motor. Since the part of the magnetomotive force means that is in contact with the magnetic fluid and the part that is in contact with the conductive part on the one side are continuous with the conductive material, even during rotation of the motor, through the conductive material and the conductive magnetic fluid. Static electricity can be released from the rotating part to the fixed part. A magnetic fluid, which is magnetically held and forms a conductive path over the magnetomotive force means supported on one of the rotating portion and the fixed portion of the motor and the ferromagnetic conductive portion on the other, scatters due to pressure fluctuation. This means that the space between the rotating part and the fixed part on both sides sandwiching the magnetomotive force means in the axial direction is
It is avoided because it communicates in the part . Also conductive hands
The step is provided between the bearings. Therefore, fixed shaft or rotation
The distance between bearings can be set longer than the length of the rolling shaft.
Therefore, the rigidity of the entire bearing is increased, and the natural frequency
To prevent vibration and effectively suppress vibration to prevent rotation.
Accuracy can be improved. An embodiment of the present invention will be described with reference to FIGS. 1 to 8. FIGS. 1 to 3 show a spindle motor for driving a recording medium (for example, a hard disk) as one embodiment of the present invention. FIG.
FIG. 2 is an enlarged view of a main part of FIG. 1, and FIG. 3 is a perspective view of a magnetomotive force assembly. At the center of the circular recess 12 at the upper opening of the bracket 10 made of aluminum, a circular projection 14 projecting upward in two steps is provided. The lower end of the inner circumference of the stator core 16 is externally fitted and fixed. A stator coil 18 is wound around the stator core 16. A cylindrical fixed shaft 20 made of ferromagnetic stainless steel is provided upright at the center of the circular recess 12 of the bracket 10. Through upper ball bearing 22 and lower ball bearing 24,
A rotor hub 26 made of aluminum (to which a recording medium is externally fixed) is rotatably supported on the outer peripheral side of the fixed shaft 20. The annular inward protrusion 260 provided on the inner periphery of the rotor hub 26 functions as a spacer for the upper and lower ball bearings 22 and 24. Flange 262 at lower part of outer periphery of rotor hub 26
, The upper end of a substantially cylindrical rotor yoke 28 is fixed,
A rotor magnet 30 is provided on the inner periphery of the rotor yoke 28.
Is fixedly held. The rotor magnet 30 faces the stator core 16 with a radial gap therebetween on the inner peripheral side. The outer peripheral surface of the rotor yoke 28 is separated from the inner peripheral surface of the circular recess 12 of the bracket 10 by a slight radial gap. An annular hanging part 26 is provided on the inner peripheral lower part of the rotor hub 26.
4 is formed, and the inner peripheral surface of the lower end portion of the annular hanging portion 264 faces the small-diameter outer peripheral portion 142 of the circular projection 14 with a slight radial gap. In addition, annular hanging part 26
4 is opposed to the inner peripheral surface of the stator core 16 with a slight radial gap therebetween. The labyrinth seal-like effect obtained thereby effectively prevents the lubricant of the lower ball bearing 24 from leaking out of the motor.
The lid 32 fixed to the upper end of the rotor hub 26 prevents the lubricant of the upper ball bearing 22 from leaking out of the motor. The magnetomotive force assembly 34 (magnetism generating means)
An annular plate-shaped upper pole piece 34 made of ferromagnetic stainless steel
An annular plate-shaped permanent magnet plate 344 (non-conductive) magnetized in the up-down direction is coaxially sandwiched between the zero pole piece 342 and the lower pole piece 342. The outer diameters of the upper pole piece 340, the permanent magnet plate 344, and the lower pole piece 342 are substantially the same, and are slightly smaller than the inner diameter of the inward projection 260 of the rotor hub 26. However, on the outer peripheral portion of the upper pole piece 340, five pointed projections 3 radially outward are provided at every fixed center angle.
40a is provided. The eccentric distance of the tip of the pointed projection 340 a is slightly larger than the inner radius of the inner projection 260. The inner diameters of the upper pole piece 340 and the lower pole piece 342 are slightly larger than the outer diameter of the fixed shaft 20 and slightly smaller than the inner diameter of the permanent magnet plate 344. The magnetomotive force assembly 34 is connected to the rotor hub 26.
Is inserted into the inner peripheral portion of the inner projection 260, and the pointed protrusion 340a cuts into the annular groove 260a provided in the inner peripheral portion of the inner projection 260, thereby being fixed substantially coaxially to the inner peripheral portion of the inner projection 260. ing. Magnetomotive force assembly 3 excluding pointed protrusion 340a
The gap 3 is provided between the outer periphery of the inner projection 4 and the inner periphery of the inner projection 260.
It is 6. A radial gap is provided between the inner peripheral portion of the magnetomotive force assembly 34 and the outer peripheral surface of the fixed shaft 20, and a conductive magnetic fluid extends between the inner peripheral portion of the upper pole piece 340 and the fixed shaft 20. 38 is magnetically held. The magnetic fluid 38 and the magnetomotive force assembly 34 constitute a conductive means. Note that the magnetic fluid 38 does not necessarily need to be held over the entire circumference. Partially empty space is acceptable. Since the magnetic fluid 38 is magnetically held over the inner periphery of the upper pole piece 340 and the fixed shaft 20 even when the rotor hub 26 rotates, the aluminum rotor hub 26 and the stainless steel fixed shaft are held. 20 and between the aluminum bracket 10 and the pointed projection 340a
Is secured to the rotor hub 26 by the stainless steel upper pole piece 340 directly connected to the rotor hub 26 by biting into the annular groove, and the conductive magnetic fluid 38. The static electricity accumulated in the medium can be released. A gap 3 is provided between the outer periphery of the magnetomotive force assembly 34 except for the pointed protrusion 340a and the inner periphery of the inner protrusion 260.
6, the air pressure (or other gas pressure) above and below the magnetomotive force assembly 34 and the magnetic fluid 38 does not greatly differ even if the external pressure fluctuates.
8 is prevented from scattering due to pressure fluctuation. Since it is not necessary to increase the pressure resistance of the magnetic fluid 38, the concentricity between the inner peripheral portion of the upper pole piece 340 and the fixed shaft 20 is set with high accuracy to equalize the force for holding the magnetic fluid 38,
The magnetic fluid 38 is provided on the NS poles of the magnetomotive force assembly 34, that is, on the inner peripheral portions of the upper and lower pole pieces 340 and 342, respectively.
It is not necessary to keep the double. The conductive means is preferably provided between the plurality of bearings as in the above embodiment. The bearing interval can be set longer than the length of the fixed shaft or rotating shaft, so the rigidity of the entire bearing is increased, the natural frequency is increased, and vibration is effectively suppressed by preventing resonance. This is because the rotation accuracy can be further improved. For example, when the conductive means is provided above the upper ball bearing 22 in the above-described embodiment, the upper ball bearing 22 must be lowered, and the interval between the upper and lower ball bearings 22 and 24 is shortened, and the rigidity of the entire bearing is reduced. Will decrease. FIG. 4 is a sectional view of a main part of a motor according to another embodiment, and FIG. 5 is a perspective view of a main part of a lower pole piece.
In this motor, a rotating shaft 52 made of stainless steel is located inside an inner peripheral wall of a fixed frame 50 made of aluminum. In the magnetomotive force assembly 54, an annular plate-shaped permanent magnet plate 544 magnetized in the vertical direction is coaxial between an upper plate piece 540 and a lower pole piece 542 made of ferromagnetic stainless steel. Be sandwiched between. An outer peripheral portion of the lower pole piece 542 is provided with a substantially rectangular projecting portion 542a outward in the radial direction at every fixed center angle.
The eccentric distance of the tip of the protrusion 542 a is slightly larger than the inner radius of the fixed frame 50. The magnetomotive force assembly 54 includes the stationary frame 5
0, and the distal end of the protrusion 542a presses the inner peripheral portion of the fixed frame 50 substantially radially outward while bending, so that the inner peripheral portion of the fixed frame 50 is substantially coaxial. Fixed. A gap 56 is formed between the outer peripheral portion of the magnetomotive force assembly 54 except for the protruding portion 542a and the inner peripheral portion of the fixed frame 50 as in the above-described embodiment. A conductive magnetic fluid 58 is magnetically held between the inner peripheral portions of the upper and lower pole pieces 540 and 542 and the outer peripheral surface of the rotating shaft 52, and the lower pole piece 542 and the lower pole piece 542 The conductivity between the fixed frame 50 and the rotating shaft 52 is secured through the magnetic fluid 58 held between the rotating shaft 52 and the rotating shaft 52. FIG. 6 is a sectional view of a main part of a motor as still another embodiment. In this motor, an aluminum rotor hub 62 is rotatably supported on the outer peripheral side of a fixed shaft 60 made of stainless steel. The magnetomotive force assembly 64 (the magnetomotive force means)
Annular plate-shaped upper pole piece 64 made of ferromagnetic stainless steel
An annular plate-shaped permanent magnet plate 644 magnetized in the up-down direction is coaxially sandwiched between the zero pole piece 642 and the lower pole piece 642. The outer diameters of the upper pole piece 640, the permanent magnet plate 644, and the lower pole piece 642 are substantially the same, and are equal to the inner diameter of the rotor hub 62. However, a radially outward projection 640a is provided at an outer peripheral portion of the upper pole piece 640 at a constant center angle. The eccentric distance of the tip of the projection 640a is slightly larger than the inner radius of the rotor hub 62. Upper pole piece 640 and lower pole piece 642
Is slightly larger than the outer diameter of the fixed shaft 60 and slightly smaller than the inner diameter of the permanent magnet plate 644. The magnetomotive force assembly 64 includes a rotor hub 62.
Annular groove 6 which is inserted into the inner peripheral portion of
When the protrusion 640a bites into the rotor hub 20, it is fixed substantially coaxially to the inner peripheral portion of the rotor hub 62. A radial gap is provided between the inner peripheral portion of the magnetomotive force assembly 64 and the outer peripheral surface of the fixed shaft 60. The inner periphery of the upper pole piece 640 and the fixed shaft 6
The spherical body 66 made of ferromagnetic stainless steel having a diameter larger than the gap with the outer peripheral surface of the upper pole piece 640 is in contact with both the upper peripheral edge of the inner peripheral portion of the upper pole piece 640 and the outer peripheral surface of the fixed shaft 60. Is held in. Since the diameter of the spherical body 66 is larger than the gap between the inner peripheral portion of the upper pole piece 640 and the outer peripheral surface of the fixed shaft 60, even when the rotor hub 62 rotates, the diameter of the spherical body 66 remains on the inner peripheral portion of the upper pole piece 640. While being in contact with both the edge and the outer peripheral surface of the fixed shaft 60, it is magnetically held while rolling with the rotation of the motor. Therefore, the rotor hub 6 made of aluminum is used.
2 and the fixed shaft 60 made of stainless steel, a projection 64
0a bites into the annular groove 620, so that the rotor hub 6
Stainless steel upper pole piece 64 directly connected to
0 and the stainless steel spherical body 66 ensure conductivity even during rotation of the motor. The spherical body 66 has an upper pole piece 640
In addition, it merely rolls while magnetically attracting and contacting the fixed shaft 60, and since each contact portion has little wear, generation of dust and noise due to wear can be prevented. In addition, since there is no direct contact with the permanent magnet plate 644, which is often made of a material that is easily broken or fine powder is peeled off by contact, various kinds of damage due to such breakage of the permanent magnet plate 644 and peeling of the fine powder occur. Inconveniences can be avoided. In this case, it is desirable that the conductive means is also provided between the plurality of bearings as in the above embodiment. This is because, in addition to the same reason as described above, detachment of the spherical body can be prevented. FIG. 7 is a sectional view of a main part of another motor. In this motor, between the upper pole piece 700 and the lower pole piece 702 made of a ferromagnetic stainless steel and having an L-shaped cross section, an annular conductive permanent magnet body 704 also having an L-shaped cross section is coaxially formed. The sandwiched magnetomotive force assembly 70 does not use an adhesive on the enlarged diameter portion 740 on the inner periphery of the aluminum rotor hub 74 supported on the outer peripheral side of the stainless steel fixed shaft 72, and accordingly, the rotor hub 74 and The inner space is fixed without sealing the space between them. Then, the conductive magnetic fluid 76 held between the upper pole piece 700 and the fixed shaft 72, the upper pole piece 700, the conductive permanent magnet body 704, and the lower pole piece 702 allow conduction between the fixed shaft 72 and the rotor hub 74. Is ensured. FIG. 8 is a sectional view of a principal part of still another motor. In this motor, an annular plate-shaped conductive permanent magnet 804 is coaxially formed between an annular upper pole piece 800 and an annular plate-shaped lower pole piece 802 made of a ferromagnetic stainless steel and having a J-shaped cross section. The sandwiched magnetomotive force assembly 80 is attached to the enlarged diameter portion 840 on the inner periphery of the aluminum rotor hub 84 supported on the outer peripheral side of the stainless steel fixed shaft 82 without using an adhesive, and thus, the rotor hub 84 and The inner space is fixed without sealing the space between them. The conductive property between the fixed shaft 82 and the rotor hub 84 is secured through the conductive magnetic fluid 86 held between the upper pole piece 800 and the fixed shaft 82 and the upper pole piece 800. In the description of the above embodiment, the vertical positional relationship, dimensions, number, material, shape,
The relative arrangement and the like are not intended to limit the scope of the present invention only to them, but are merely illustrative examples, unless otherwise specified. According to the motor of the first aspect, the space between the rotating portion and the fixed portion on both sides of the magnetomotive force means in the axial direction is formed by the conductive material.
Since the magnetic fluid communicates with the electromechanical part, the magnetic fluid can be prevented from being scattered due to pressure fluctuation, and the rotating part can be rotated during the rotation of the motor through the conductive material of the magnetomotive force and the conductive magnetic fluid. Static electricity can be released from to the fixed part. Therefore, for example, when a recording medium such as a hard disk is mounted on the rotating unit and driven, the recording medium is reliably prevented from being stained by the contamination of the external space of the motor due to the scattering of the magnetic fluid and the read / write head being damaged. The static electricity accumulated in the read / write head can be released to reliably prevent the occurrence of inconvenience due to the charging of the read / write head. Also, the conductive means is provided between the bearings and fixed.
Set the bearing interval longer than the fixed or rotating shaft length
To increase the rigidity of the bearing as a whole,
Increase natural frequency and prevent vibration effectively by preventing resonance
And the rotation accuracy can be improved. The magnetomotive force between the rotating part and the fixed part
The space on both sides sandwiching the step in the axial direction
To prevent the magnetic fluid from being scattered due to pressure fluctuations, so that the magnetomotive force means and the ferromagnetic conductive portion are concentric to improve the pressure resistance by equalizing the holding force of the magnetic fluid. It is not necessary to set the degree with high precision, nor to increase the pressure resistance by making the magnetic fluid retained in the NS poles of the magnetomotive force means and making the magnetic fluid double. Further, there is no need to seal the gap between the magnetomotive force means and the rotating part or the fixed part supporting the same by using a conductive adhesive. Can be avoided. Therefore, it is easy to manufacture. [0038]

[Brief description of the drawings] FIG. 1 is a sectional view of a motor. FIG. 2 is an enlarged view of a main part of FIG. FIG. 3 is a perspective view of a magnetomotive force assembly. FIG. 4 is a sectional view of a main part of another motor. FIG. 5 is a perspective view of a main part of a lower pole piece. FIG. 6 is a sectional view of a main part of still another motor. FIG. 7 is a sectional view of a main part of still another motor. FIG. 8 is a sectional view of a main part of still another motor. FIG. 9 is a sectional view of a main part of a conventional motor. FIG. 10 is a sectional view of another conventional motor. [Description of sign] 20 fixed shaft 26 Rotor hub 260 inward projection 260a annular groove 34 Magnetomotive force assembly 340 Upper pole piece 340a pointed protrusion 36 void 38 Magnetic fluid

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02K 5/10 H02K 5/16-5/173 F16J 15/40 H05F 3/02

Claims (1)

(1) A motor in which a rotating unit is rotatably supported by a fixed unit via a plurality of bearings disposed apart from each other in an axial direction. Between the bearings, one of the rotating part and the fixed part is supported with an annular magnetomotive force means, and the other with an annular ferromagnetic conductive portion separated from the magnetomotive force means by a radial gap,
A conductive magnetic fluid is magnetically held between the magnetomotive force means and the ferromagnetic conductive portion, and a portion of the magnetomotive force means in contact with the magnetic fluid and a portion in contact with the one of the conductive portions are formed of a conductive material. Wherein the space between the rotating part and the fixed part on both sides sandwiching the magnetomotive force means in the axial direction communicates with the conductive means part. Motor to do.