JP4005826B2 - Permanent magnet motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to a permanent magnet motor and can be suitably used for, for example, a spindle motor having a hydrodynamic bearing mechanism.
[0002]
[Prior art]
In a recording apparatus such as a hard disk, a spindle motor (hereinafter referred to as a motor) used to drive a disk includes a rotor that rotates with the disk mounted thereon, a bracket that rotatably supports the rotor via a bearing mechanism, and a permanent motor. A driving magnet (hereinafter referred to as a magnet) that is made of a magnet and is provided on the rotor, and a stator that is disposed on the bracket so as to face the magnet in the radial direction are basically provided.
[0003]
In recent years, a hydrodynamic bearing mechanism has been adopted as the above-described bearing mechanism for a motor in order to meet the demands for downsizing, noise reduction, and speeding up of the recording apparatus. The hydrodynamic bearing mechanism is formed with a hydrodynamic fluid generating groove such as a herringbone groove on either the shaft or the bearing surface, and the lubricating fluid is held in the gap between the shaft and the bearing surface, and the rotor The rotor is supported in a non-contact manner with respect to the bracket by the dynamic pressure generated in the fluid as the rotor rotates. Since the hydrodynamic bearing mechanism supports the rotor via the fluid, it is superior to other bearing mechanisms in that the rotational noise is relatively small.
[0004]
By the way, in a recording apparatus such as a hard disk, a magnetic head follows a track while flying over a disk rotating at high speed with a small gap. For this reason, the rotor that rotates with the disk mounted thereon must not swing or move in the axial direction during rotation with respect to a bracket that supports the disk via a bearing.
Therefore, in order to stabilize the position of the rotor with respect to the bracket, a thrust force composed of an axial magnetic attractive force is generated by shifting the relative position of the magnet and the stator core in the axial direction from the neutral point of the mutual magnetic attractive force. Is employed (Japanese Patent Laid-Open No. 6-223494). In this case, the larger the deviation amount, the greater the axial magnetic attraction force, but the mechanical noise increases accordingly. Therefore, the relative position of the magnet and the stator core is shifted in the axial direction so that mechanical noise does not increase, and a thrust yoke made of a magnetic material is disposed on the bracket so as to face the magnet in the axial direction. Insufficient thrust force is compensated by magnetic attractive force.
[0005]
Since the rotation of the rotor has been stabilized and the mechanical noise has been reduced in this way, the issue to be addressed in the future is to reduce the electromagnetic noise, especially the transistor switching noise during phase switching in the drive circuit. This is a reduction of electromagnetic noise generated by being superimposed on the coil voltage.
As means for reducing such electromagnetic noise, for example, conventionally, (1) weakening the magnetization of a motor driving magnet, (2) a stator serving as an excitation source in the motor and its peripheral members are adhesives. There are known measures such as (3) switching with a soft switching method in the drive circuit.
[0006]
[Problems to be solved by the invention]
However, in the case of the above countermeasure (1), the torque constant Kt of the motor is lowered and the rotational torque is weakened. In the case of the measure (2), a significant effect cannot be obtained although it takes a lot of man-hours. The measure (3) is not an improvement of the motor itself but has a disadvantage that the drive circuit becomes complicated.
Therefore, an object of the present invention is to provide a permanent magnet motor in which electromagnetic noise caused by switching noise is reduced without increasing man-hours and lowering the torque constant Kt by improving the structure of the motor itself. There is.
[0007]
[Means for Solving the Problems]
In order to solve the problem, a permanent magnet motor of the present invention includes a rotor having a shaft or a bearing surface, and a bracket having a bearing surface or a shaft facing the shaft or bearing surface of the rotor and rotatably supporting the rotor. And a magnet held by the rotor concentrically with the shaft, a stator fixed to the bracket in a radial direction facing the magnet, and a magnetic material. In a permanent magnet motor including a thrust yoke fixed to a bracket so as to face the magnet in the axial direction, the magnet and the thrust yoke are opposed to each other on a substantially parallel surface substantially orthogonal to the shaft, magnet gap of more than 0.4mm is provided between the thrust yoke axis of the magnet and the stator core The relative positional relationship in direction is characterized in that the 0.1mm or more magnet from a neutral point of magnetic attraction to each other are shifted in the direction away from the thrust yoke.
[0008]
Experiments have confirmed that the electromagnetic noise caused by switching noise is significantly reduced by the gap. In the present invention, the upper limit of the gap is not particularly limited. One of the sacrifices made by widening the gap is a reduction in the thrust force. In this regard, the relative positional relationship between the magnet and the stator core in the axial direction is determined by the neutral force of each other. By shifting the magnet away from the thrust yoke by t = 0.1 mm or more from the point, the shortage of the thrust force is compensated using the axial magnetic attractive force between the magnet and the stator.
[0009]
In the case of a motor in which the neutral point of the magnetic attraction force between the magnet and the stator coincides with the thrust direction, the magnetic force in the thrust direction does not act between the two during motor rotation, so that vibration and noise can be reduced. Of course, the motor efficiency is also improved.
On the other hand, in order to apply a magnetic attractive force in the thrust direction, when the thrust yoke is disposed on the bracket side so as to face the magnet as in the present invention, the smaller the gap between the magnet and the thrust yoke, the larger the gap. Although magnetic attraction force can be obtained, more magnetic flux that should act on the stator of the magnet escapes to the thrust yoke, and the amount of deviation between the magnet's mechanical center and the magnetic neutral point of the magnetic flux acting on the magnet's stator As a result, the magnetic force in the thrust direction acts when the motor rotates, resulting in vibration and noise.
[0010]
In view of such an event, the present invention finds out that there is d and t in which vibration and noise (vibration and noise due to switching noise) become smaller when a desired magnetic attractive force is obtained. A permanent magnet motor configured is obtained.
It is assumed that the neutral point of the magnetic attraction force when determining t is determined with the thrust yoke removed. This neutral point coincides with the upper and lower bisectors when the stator and the magnet are symmetrical in the axial direction.
[0011]
From such a point of view, a preferable ratio t / d between the amount t of relative positional relationship in the axial direction between the magnet and the stator core and the gap d in the axial direction is 0.25 or more and 0.9 or less. In another preferred configuration of the present invention, the total magnetic attractive force acting between the magnet and both the stator and the thrust yoke is 50 gf or more and 90 gf or less. As described above, since the axial magnetic attractive force between the magnet and the stator and the magnetic attractive force between the magnet and the thrust yoke are complementary to each other to generate a predetermined thrust force, the magnetic attractive force is more than the individual magnetic attractive force. Because the total is important. If the total magnetic attractive force is less than 50 gf, it is difficult to stabilize the rotation of the rotor. On the other hand, if it exceeds 90 gf, both t and d must be significantly increased in order to reduce electromagnetic noise. It goes against miniaturization.
[0012]
In the motor bearing mechanism according to the present invention, a dynamic fluid generating groove is formed in at least one shaft or bearing surface of the rotor and bracket, and the lubricating fluid is held between the shaft and the bearing surface facing each other. A hydrodynamic bearing mechanism is preferred. This is because the mechanical noise reduction effect becomes prominent because the mechanical noise is originally relatively small.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a motor of the present invention will be described with reference to the drawings. FIG. 1 is an axial sectional view of a three-phase motor for driving a hard disk.
The motor 1 includes a rotor 2 that rotates with the recording disk D mounted thereon, and a bracket 3 that rotatably supports the rotor. The rotor 2 includes a rotating shaft 4 and a disk-shaped hub 5 fixed to one end thereof. A wall extending in the same direction as the rotating shaft 4, that is, downward in the drawing, is formed on the periphery of the hub 5. A magnet 6 that is concentric with the rotating shaft 4 and divided into a plurality of magnetic poles is attached to the inside.
[0014]
The bracket 3 includes a bracket body 31 in which a through hole concentric with the rotation shaft 4 is formed, a cylindrical support member 32 fitted between the bracket body 31 and the rotation shaft 4, and a support member 32. A disc-shaped cover 33 is fixed to the opening end face and faces the end face of the rotating shaft 4 opposite to the hub 5 side. The bracket body 31 is formed with a cylindrical wall extending toward the hub 5 at the periphery of the through hole, and a plurality of stators 7 are formed on the outer peripheral surface of the wall so as to face the magnet 6 in the radial direction. Each stator 7 is formed by winding a stator coil 72 around a stator core 71 projecting from the outer peripheral surface of the wall, and the coil is connected to a lead (not shown) so as to be energized from the outside. Further, a thrust yoke 37 made of a magnetic material is fixed to the bracket body 31 so as to face the lower end surface of the magnet 6 in the axial direction with a predetermined gap d. The thrust yoke 37 has a concentric ring shape with the rotary shaft 4.
[0015]
An annular notch is formed at the free end of the rotating shaft 4, and a ring 41 protruding outward in the radial direction from the outer peripheral surface of the rotating shaft 4 is fixed to the notch, and a support facing the ring 41 is supported. An annular recess 42 is formed on the inner peripheral surface of the member 32, and the ring 41 and the recess 42 are fitted together to prevent the rotary shaft 4 from coming off.
[0016]
The inner peripheral surface of the support member 32 is a radial bearing surface 34, and the lubricating fluid 8 is held between the radial bearing surface 34 and the outer peripheral surface of the rotary shaft 4 facing the radial bearing surface 34. The end surface of the support member 32 on the hub 5 side is a thrust bearing surface 35, and the lubricating fluid 8 is held between the thrust bearing surface 35 and the upper surface of the support member 32 facing the thrust bearing surface 35. The lubricating fluid on the radial bearing surface 34 side and the lubricating fluid on the thrust bearing surface 35 side are continuous. The bearing surfaces 34 and 35 or the rotor-side surface facing these are formed with axially asymmetric herringbone-shaped dynamic pressure generating grooves 9 and spiral-shaped dynamic pressure generating grooves 10, respectively. In FIG. 1, these dynamic pressure generating grooves 9 and 10 are symbolically shown by broken lines for convenience. By these dynamic pressure generating grooves, the lubricating fluid held between the radial bearing surface 34 and the outer peripheral surface of the rotating shaft 4 is pumped during rotation, and a radial load supporting pressure is generated in the lubricating fluid. Further, a thrust load supporting pressure is generated in the lubricating fluid held between the thrust bearing surface 35 and the lower surface of the hub 5. As a result, the rotor 2 is not in contact with the bracket 3.
[0017]
When electric power is supplied to the stator coil, the stator 7 forms a magnetic field by the current flowing through the coil, and a magnetic attraction force or a repulsive force is generated between the stator 6 and the rotor 2 is rotated. The magnet 6 also generates a magnetic attraction force even between the thrust yoke 37, which becomes a thrust force that balances with the thrust load support pressure, and the rotor 2 rotates stably without moving in the axial direction. The axial gap d between the magnet 6 and the thrust yoke is set to 0.4 mm or more, thereby reducing electromagnetic noise caused by switching noise. When the gap d is set to 0.4 mm or more, when the thrust force is reduced and the rotation of the rotor 2 becomes unstable, the relative positional relationship between the magnet 6 and the stator core 71 in the axial direction is changed to the mutual magnetic relationship. By shifting the magnet away from the thrust yoke by t = 0.1 mm or more from the neutral point of the attractive force, the shortage of the thrust force is compensated using the axial magnetic attractive force between the magnet and the stator.
[0018]
In the above embodiment, the configuration of the present invention is applied to a hydrodynamic bearing motor for driving a hard disk. However, the present invention is not limited to this. For example, a motor for CD-R / RW / ROM / RAM, a fan motor, etc. Thus, the present invention can be applied to all permanent magnet motors using oil-impregnated sleeve bearings.
[0019]
【Example】
The configuration of the motor of the above embodiment is applied to a motor of a disk device having a disk diameter of 2.5 inches, in which the number of poles of the magnet 6 is 12 and the total height of the motor 1 is 9.5 mm, and the gap d In addition, various trials were made with various amounts of misalignment t. And the electromagnetic noise was measured by supplying power to the stator coil. The measurement results are shown in FIG. FIG. 2 is a graph in which the vertical axis indicates a positional deviation amount t and the horizontal axis indicates a gap d, and t is a positive direction in which the magnet 6 is separated from the thrust yoke 37. The size of each circle in the graph represents the magnitude of electromagnetic sound caused by the switching noise primary. The curve is an isobaric line of the total magnetic attractive force between the magnet, the stator and the thrust yoke, and represents curves of 50 gf, 60 gf, 70 gf, 80 gf and 90 gf from the bottom.
[0020]
As shown in FIG. 2, the electromagnetic noise is remarkably reduced by setting d = 0.4 mm or more and t = 0.1 mm or more regardless of the magnitude of the magnetic attractive force, and the value is d <0. Assuming that the average value of electromagnetic sound in the case of .4 mm is 1, the average is 0.54. Incidentally, this ratio was 1: 0.16 for the second switching noise and 1: 0.34 for the third switching noise.
[0021]
【The invention's effect】
As described above, since the permanent magnet motor of the present invention has low mechanical noise as well as mechanical noise, a user such as a recording apparatus can read and write electronic data and programs in a comfortable environment. In addition, the permanent magnet motor of the present invention does not require a complicated manufacturing process or combination of parts for noise reduction, and is excellent in mass productivity.
[Brief description of the drawings]
FIG. 1 is an axial sectional view showing a motor according to an embodiment.
FIG. 2 is a graph obtained by measuring the relationship between a gap d, a positional deviation amount t, and the magnitude of electromagnetic sound.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Motor 2 Rotor 3 Bracket 4 Rotating shaft 5 Hub 6 Magnet 7 Stator 8 Lubricating fluid 9, 10 Dynamic pressure generating groove 37 Thrust yoke

Claims (3)

A rotor having a shaft or bearing surface, a bracket surface having a bearing surface or shaft facing the shaft or bearing surface of the rotor and rotatably supporting the rotor, a magnet held concentrically with the shaft, and a magnet The stator is fixed to the bracket facing the magnet in the radial direction, and is made of a magnetic material, and is fixed to the bracket facing the magnet in the axial direction so as to generate a thrust force consisting of a magnetic attractive force between the magnet and the magnet. In a permanent magnet motor equipped with a thrust yoke,
The magnet and the thrust yoke are opposed to each other in a substantially parallel plane substantially orthogonal to the axis, and an axial gap of 0.4 mm or more is provided between the magnet and the thrust yoke.
The relative positional relationship between the magnet and the stator core in the axial direction is shifted by 0.1 mm or more from the neutral point of the magnetic attraction force in a direction in which the magnet is separated from the thrust yoke ,
A permanent magnet motor, wherein a total of magnetic attractive forces acting between the magnet and both the stator and the thrust yoke is 50 gf or more and 90 gf or less .   2. The permanent magnet motor according to claim 1, wherein a ratio t / d between a relative positional shift amount t in the axial direction between the magnet and the stator core and the axial gap d is 0.25 or more and 0.9 or less. . 3. The permanent fluid according to claim 1, wherein a dynamic pressure fluid generating groove is formed in at least one of the shaft and the bearing surface of the rotor and the bracket, and the lubricating fluid is held between the shaft and the bearing surface facing each other. Magnet motor.

Images