JP2007183000A - Hydrodynamic fluid bearing device and spindle motor therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrodynamic fluid bearing device having an improved pumping action and a spindle motor therewith. <P>SOLUTION: The hydrodynamic fluid bearing device has a static member 3 having a radial bearing surface and a thrust bearing surface, a rotation member 2 supported by the bearing surfaces and rotatable around its axis relative to the static member 3, and a lubricating fluid 8 retained between the bearing surfaces and the rotation member 2. On the radial bearing surface, a plurality of grooves 9 which have folded points and are repeated asymmetrically in the direction of a rotation axis and regularly in the rotating direction are formed for producing dynamic pressure. On a surface of the rotation member 2 opposed to the thrust bearing surface, a plurality of grooves 10 which have folded points and are repeated asymmetrically in the radial direction and regularly in the rotating direction are formed for producing dynamic pressure. The hydrodynamic fluid bearing device is characterized in that grooves 9 are formed more densely on lubricating fluid paths 9c from a movement origin side than on lubricating fluid paths 9a to a movement destination side at boundaries of folded points. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention belongs to a hydrodynamic bearing device and a spindle motor using the same, and can be suitably used for a mechanism that requires high-speed rotation, such as a recording disk drive motor.

  In a mechanism that requires high-speed rotation, such as a recording disk drive motor, grooves such as a V-shape, U-shape, and herringbone shape are formed on the bearing surface and / or the surface of the rotating member facing the bearing surface. A dynamic fluid that retains the lubricating fluid between the rotating member and the bearing surface, maintains the rotating member and the bearing surface in a non-contact state by the pressure generated by the pumping action of the groove during rotation, that is, dynamic pressure, and enables high-speed rotation. A hydrodynamic bearing device is used.

  Among such hydrodynamic bearing devices, a radial bearing surface that receives a load in the radial direction and a thrust bearing surface that receives a load in the thrust direction are each provided on a stationary member to support a rotating member. Bubbles may stay near the boundary between the bearing surface and the thrust bearing surface. The staying bubbles are not preferable because they are thermally expanded at a high temperature of the motor to push out the lubricating fluid to the outside of the bearing device, which impedes writing / reproducing on the recording disk.

  Therefore, in order to prevent air bubbles from staying, the dynamic pressure generating groove on the radial bearing surface has a herringbone shape that is asymmetric in the axial direction, that is, the path far from the thrust bearing surface is long at the turning point of the herringbone. The unbalanced herringbone shape that shortens the path on the near side, the dynamic pressure generating groove on the thrust bearing surface is spiral shaped, and these radial bearings and thrust bearings are directly connected to each other, and the levitation force of the rotating member is radial bearings. The structure given by the dynamic pressure of the part has been proposed (Patent Document 1). With this configuration, both the lubricating fluid retained on the radial bearing surface and the lubricating fluid retained on the thrust bearing surface generate dynamic pressure that moves toward the boundary, thereby preventing air bubbles from staying. The

JP 2000-215589 A

  The dynamic pressure generating groove of the conventional bearing device has a moving side of the lubricating fluid (thrust bearing) on the radial bearing surface, except for the curved shape such as V shape, U shape, herringbone shape, spiral shape, etc. One groove having a constant gradient and depth from the side far from the surface) to the destination side (side closer to the thrust bearing surface), and one groove having a continuous gradient and constant depth on the thrust bearing surface These grooves were merely formed repeatedly in the rotation direction. However, since the size of the motor has been large in the prior art, by increasing the dynamic pressure generating groove with the configuration described in Patent Document 1, a sufficient pumping force can be obtained and no trouble occurs.

  However, with the demand for miniaturization of the motor size, it is necessary to design a dynamic pressure generating groove that generates a large pumping force with a limited bearing area.

  Therefore, an object of the present invention is to provide a hydrodynamic bearing device with improved pump action as compared with the configuration described in Patent Document 1.

  In order to solve the above problems, a hydrodynamic bearing device according to the present invention includes a stationary member having a radial bearing surface, and a rotating member that is supported by the radial bearing surface and is rotatable about an axis relative to the stationary member. And a lubricating fluid held between the rotating member and the radial bearing surface, and a radial load supporting pressure is generated in the lubricating fluid on the radial bearing surface and / or the surface of the rotating member facing the radial bearing surface. A radial dynamic pressure bearing portion having a plurality of radial dynamic pressure generating grooves that repeat regularly in the rotational direction is formed, and the thrust bearing surface and / or the surface of the rotating member opposed to the radial dynamic pressure bearing portion is regularly aligned in the rotational direction. In the hydrodynamic bearing device in which a thrust hydrodynamic bearing portion having a plurality of thrust dynamic pressure generating grooves is formed, the radial hydrodynamic bearing portion causes the lubricating fluid to flow through the radial hydrodynamic shaft. The movement source side path and the movement destination side path are configured to move toward the center of the section, and each radial dynamic pressure generating groove is a groove portion located in the movement source side path and a groove located in the movement destination side path. The second groove is formed only between the adjacent radial dynamic pressure generating grooves and on the movement source side path of the lubricating fluid on the radial bearing surface, and at the time of relative rotation, A groove portion in which the lubricating fluid is moved toward the thrust dynamic pressure bearing portion by the second groove, and the groove constituted by the radial dynamic pressure generating groove and the second groove is located in the destination path of the lubricating fluid The groove portion positioned in the movement source side path is more densely formed, and the gas-liquid interface of the lubricating fluid is positioned on the movement source side.

  The hydrodynamic bearing device of the present invention includes a stationary member having a radial bearing surface and a thrust bearing surface, a rotating member supported by these bearing surfaces and rotatable about an axis relative to the stationary member, And a lubricating fluid held between the rotating member and the bearing surface, and a dynamic pressure is generated on the radial bearing surface and / or the surface of the rotating member facing the radial bearing surface to move the lubricating fluid toward the thrust bearing surface. As described above, a plurality of dynamic pressure generating grooves that are regularly repeated in the rotation direction are formed, and the lubricating fluid is moved toward the axis of rotation on the thrust bearing surface and / or the surface of the rotating member opposed thereto. In the hydrodynamic bearing device in which a plurality of dynamic pressure generating grooves that are regularly repeated in the rotational direction are formed so as to generate dynamic pressure, the grooves move more than in the destination path of the lubricating fluid. Former side Characterized in that towards the road are densely formed.

  In the bearing device of the present invention, the second groove is formed in the extended region where the gas-liquid interface is located in the dynamic pressure generating groove, and the number of grooves in this portion is increased, so the amplitude of the wave at the gas-liquid interface It becomes a structure that is less likely to cause entrainment of bubbles.

  Further, in the bearing device of the present invention, the conventional fixed concept is broken, the groove density is made different between the movement destination side path and the movement source side path of the lubricating fluid, and the grooves are formed densely on the movement source side. As a result, the dynamic pressure generating groove is asymmetrical in the direction in which the lubricating fluid is moved, and a pumping action is generated to move the lubricating fluid in a predetermined direction. In addition, since it is only necessary to change the density at the turning point as a boundary, a desired pumping force can be obtained even with a limited bearing area.

  The first means for making the movement source side path relatively dense is that the groove of the radial bearing surface has a herringbone shape in which the movement source side path extends a predetermined length longer than the movement destination side path, and the extension A second groove is formed between adjacent grooves of the portion. By forming one second groove between the grooves in the extended portion, the density of the grooves in the extended portion is doubled, and if two are formed, the density is tripled and the pumping force is improved.

  The second means for making the movement source side path relatively dense is to form the groove of the radial bearing surface in a herringbone shape and form a second groove between adjacent grooves of the movement source side path. . In this case, the herringbone shape before forming the second groove may be symmetrical in the axial direction, or may be asymmetric with the movement source side path extended longer by a predetermined length. In any case, by forming one second groove, the density of the groove in the entire movement source side path is doubled, and if two are formed, the density is tripled and the pumping force is improved.

  The third means for making the movement source side path relatively dense is that the groove of the radial bearing surface has a herringbone shape in which the movement source side path extends a predetermined length longer than the movement destination side path, and the extension The angle of the part with respect to the circumferential line is made smaller than that of the non-extended part. Thereby, compared with the case where the movement origin side path | route is extended with the same gradient, even if the axial direction length of an extension part is the same, the space | interval of a groove | channel and a groove | channel becomes narrow and the density of a groove | channel can be raised.

  The fourth means for making the movement source side path relatively dense is that the groove of the radial bearing surface has a herringbone shape in which the movement source side path extends a predetermined length longer than the movement destination side path, and the extension The depth of the part is to be deeper than the non-extended part. Although the flat area of the groove does not change, an improvement in pumping power approximate to the case where one second groove having the same depth is formed by doubling the depth can be expected.

  On the other hand, one means for making the movement source side path relatively dense on the thrust bearing surface is to form a spiral groove on the thrust bearing surface and to form a second groove between adjacent grooves on the movement source side path. It is to be. Although it depends on the curvature of the spiral and the length of the second groove, it is certain that the density of the groove increases according to the number of the second grooves.

  Similarly, another means is to form a groove on the thrust bearing surface in a herringbone shape and form a second groove between adjacent grooves on the movement source side path. Like the spiral, it depends on the curvature of the herringbone, the length of the second groove, and the like, but it is certain that the density of the groove increases according to the number of the second grooves.

  A spindle motor including the above-described hydrodynamic bearing device, a magnet fixed to the rotating member, and a stator provided on the stationary member so as to be able to energize in order to generate a rotational force in cooperation with the magnet is a lubricating fluid. It becomes a drive source of high-speed rotation without leaking.

  According to the bearing device of the present invention, the dynamic pressure generating groove having the turning point for generating the load supporting pressure at the time of rotation in the lubricating fluid is formed densely on one side with the turning point as a boundary. The pump action for moving the lubricating fluid in a predetermined direction is improved. Therefore, the lubricating fluid can be stably held on the bearing surface without leaking, and the bearing area can be small.

  <Embodiment 1> An embodiment of the present invention will be described with reference to FIGS. 1 is an axial sectional view showing a spindle motor for driving a recording disk to which the hydrodynamic bearing device of the present invention is applied, FIG. 2 is a front view showing a main part of a radial bearing surface of the motor of FIG. 1, and FIG. It is a front view which shows the groove | channel of the radial bearing surface of embodiment. In FIG. 3, the filled area is a groove, and the white area is a hill between the grooves.

  The motor 1 includes a rotor 2 as a rotating member that rotates the recording disk D and a bracket 3 as a stationary member. The rotor 2 includes a rotating shaft 4 and a disc-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 is attached inside.

  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 the stator 7 is fixed to the outer peripheral surface of the wall. The stator 7 is connected to a lead (not shown) and can be energized from the outside.

  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.

  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. Further, the end surface on the hub 5 side of the support member 32 becomes 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. Predetermined dynamic pressure generating grooves 9 and 10 to be described later are formed on the bearing surfaces 34 and 35 or on the surface of the rotating member facing the bearing surfaces 34 and 35, respectively. When these dynamic pressure generating grooves rotate, a radial load supporting pressure is generated in the lubricating fluid held between the radial bearing surface 34 and the outer peripheral surface of the rotary shaft 4, thereby constituting a radial dynamic pressure bearing portion. 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, thereby forming a thrust dynamic pressure bearing portion, and the rotating member is in a non-contact state with respect to the stationary member Keep.

  The dynamic pressure generating groove 9 formed in the radial bearing surface 34 has a herringbone shape that is asymmetric in the axial direction as shown in FIG. 2, and is repeatedly formed in the circumferential direction (this embodiment) In FIG. 2, only the herringbone groove is shown for easy understanding of the pumping action, but in reality, a second groove is formed as will be described later with reference to FIG. The lubricating fluid facing the radial bearing surface 34 tends to go from the upper and lower end portions toward the center turning point by the pumping action of the groove 9, but in this embodiment, the lower side of the upper path 9b at the turning point 9a. Since the path 9c has an asymmetrical shape extended longer by a predetermined length, the lower pumping action is won and the lubricating fluid tends to move upward in the drawing, that is, toward the thrust bearing surface 35. Therefore, in this embodiment, the lower path 9c is the movement source side, and the upper path 9b is the movement destination side. On the other hand, on the lower surface of the hub 5 (the surface facing the thrust bearing surface 35), a spiral dynamic pressure generating groove (indicated by a broken line in FIG. 1) that generates a moving pressure of the lubricating fluid from the radially outer side toward the shaft core. ) 10 is formed. As a result, when the rotor 2 rotates, a dynamic pressure is generated that directs the lubricating fluid 8 radially inward, that is, toward the radial bearing portion. The lubricating fluid in the radial dynamic pressure bearing portion and the lubricating fluid in the thrust dynamic pressure bearing portion are continuous, and both the bearing portions are directly connected, so that the pump action and the dynamic pressure generating groove by the dynamic pressure generating groove 9 are achieved. The pressure of the lubricating fluid filled across both bearings is increased by the pumping action of 10, and a radial load support pressure and a thrust load support pressure are generated. Here, the pump pressure to the thrust dynamic pressure bearing portion generated by the unbalanced herringbone dynamic pressure generating groove 9 is applied to the radial dynamic pressure bearing portion generated by the spiral dynamic pressure generating groove 10 at the initial stage of rotation. It is set larger than the pump pressure. For this reason, when the rotor rotates twice, the force for feeding the lubricating fluid in the radial dynamic pressure bearing portion to the thrust side is superior to the force for feeding the lubricating fluid in the thrust dynamic pressure bearing portion to the radial side, and both bearing portions are continuously filled. A moving pressure toward the thrust side is generated in the lubricating fluid. As the lubricating fluid moves, as the gas-liquid interface 8a (FIG. 1) on the moving source side of the radial dynamic pressure bearing portion moves in the dynamic pressure generating groove 9, the dynamic pressure generating groove 9 moves toward the thrust side. Since the moving pressure decreases, the pump pressure from the thrust side and the pump pressure from the radial side gradually balance, eventually the movement of the lubricating fluid stops and this state is maintained. The balance position of the gas-liquid interface 8a is automatically adjusted according to temperature, load, motor attitude, and the like.

  Furthermore, in this embodiment, when the center is a circumferential line P that connects the turn-back points 9a as shown in FIG. 3, the extension region E of the lower path 9c excluding the symmetric area C is parallel to the lower path 9c. Two second grooves 9d are formed at equal intervals with respect to one lower path 9c. As a result, the pumping action as the entire movement source side path is further improved. In this regard, the known dynamic pressure generating groove is formed only in the symmetric region C, or even if the extended region E is formed, the second groove is not formed. Is different.

  As described above, the gas-liquid interface on the source side of the lubricating fluid in the radial dynamic pressure bearing portion settles at the position of the lower path 9 c of the dynamic pressure generating groove 9 when the rotor 2 rotates. When the rotor 2 rotates, the hills and grooves of the dynamic pressure generating groove 9 are continuously repeated at this gas-liquid interface, and the gap between the radial bearing surface 34 and the outer peripheral surface of the rotating shaft 4 is repeated. It will be. Therefore, the gas-liquid interface undulates so as to pulsate. When the number of dynamic pressure generating grooves at the gas-liquid interface is small, the number of waves is small and the amplitude is large, and the waves at the gas-liquid interface are likely to entrain bubbles. In the present embodiment, as described with reference to FIG. 3, the second groove 9d is formed in the extended region where the gas-liquid interface is located in the dynamic pressure generating groove 9, and the number of grooves in this portion is increased. The structure has a structure in which the amplitude of the wave at the gas-liquid interface is reduced and bubbles are hardly generated.

  Note that the depth of the second groove 9d is not necessarily the same as the depth of the lower path 9c, and may be formed deeper than the lower path 9c to further improve the pumping action. Further, the dynamic pressure generating groove may be formed on the outer peripheral surface of the rotating shaft 4 facing the radial bearing surface 34. The dynamic pressure generating groove on the thrust bearing surface 35 side will be described in detail in the fourth and fifth embodiments.

  <Embodiment 2> A second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a front view showing grooves on the radial bearing surface. Even in this embodiment, the groove 19 has a herringbone shape, but unlike the first embodiment, there is no extension region E. Instead, a second groove 19d is formed between the lower path 19c in parallel with the lower path 19c. Also in this case, the depth of the groove 19 d may be the same as that of the groove 19 or deeper than the groove 19. Other configurations are the same as those of the first embodiment.

  As a result, the lower pumping action is won by the amount of the groove 19d, and the lubricating fluid tends to move upward in the drawing, that is, toward the thrust bearing surface. Without securing the extension region E, the pump pressure to the thrust side can be secured in the lubricating fluid in the radial bearing portion, which is useful for an ultra-thin motor with a short shaft length. In the case of this embodiment as well, entrainment of bubbles at the gas-liquid interface can be reduced.

  <Embodiment 3> A third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a front view showing grooves on the radial bearing surface. Also in this embodiment, the groove 29 has a herringbone shape, and an extension region E exists as in the first embodiment. However, the second groove is not formed between the lower paths 29c, and instead, the angle with the circumferential line of the lower path 29c is smaller in the extended region E than in the symmetric region C. Therefore, even if the area of the extension region E is ½ of the area of the symmetric region C, the length L1 in the extension region E of the lower path 29c is longer than L2. This is different from the conventional asymmetric herringbone shape in which the gradient of the lower path is uniform and L1 and L2 are equal. Other configurations are the same as those of the first embodiment.

  As a result, the lower pumping action prevails and the lubricating fluid tries to move upward in the drawing, that is, toward the thrust bearing surface, and the pumping action is greater than that of the conventional configuration with L1 = L2.

  <Fourth Embodiment> A fourth embodiment of the present invention will be described with reference to FIGS. The above embodiments all relate to the improvement of the groove for generating the radial load supporting pressure. On the other hand, this embodiment is an example of a groove for generating a thrust load supporting pressure. FIG. 6 is a bottom view of the hub 5 of FIG.

  On the bottom surface of the hub 5 (surface facing the thrust bearing surface 35), a spiral dynamic pressure generating groove 10 (broken line in FIG. 1) is formed which concentrates from the radially outer side toward the shaft core. As a result, when the rotor rotates, a dynamic pressure is generated that directs the lubricating fluid 8 inward in the radial direction. Therefore, in this embodiment, the half on the axial center side of the entire length of the groove 10 is the movement destination side path, and the outer half is the movement source side path. A second groove 10d is formed in the middle of the adjacent movement source side paths. For this reason, the pump action for directing the lubricating fluid 8 inward in the radial direction is improved as compared with the configuration in which the groove 10d is not formed. This embodiment may be used in combination with the first to third embodiments, or may be applied to a motor alone.

  <Fifth Embodiment> A fifth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a bottom view of another hub 15 applied to the motor of FIG. A herringbone-shaped dynamic pressure generating groove 20 is repeatedly formed in the circumferential direction on the bottom surface of the hub 15. Both sides of the folding point of the herringbone may be symmetric or asymmetric. However, a second groove 20d is formed between the adjacent grooves 20 outside the turning point. This increases the pumping action that directs the lubricating fluid toward the shaft core. Moreover, even if the bottom area of the hub 15 is not increased, the pump action can be further increased by increasing the number of the second grooves 20d.

It is an axial sectional view showing a spindle motor to which the hydrodynamic bearing device of the present invention is applied. It is a front view which shows the principal part of the radial bearing surface of FIG. FIG. 3 is a front view showing a groove on the radial bearing surface of the first embodiment. FIG. 6 is a front view showing a groove on a radial bearing surface of a second embodiment. FIG. 6 is a front view showing a groove on a radial bearing surface of a third embodiment. It is a bottom view of the hub which opposes the thrust bearing surface of Embodiment 4. FIG. 10 is a bottom view of a hub facing a thrust bearing surface according to a fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor 2 Rotor 3 Brackets 4, 14 Rotating shafts 5, 15 Hub 6 Magnet 7 Stator 8 Lubricating fluid 32 Support member 34 Radial bearing surface 35 Thrust bearing surface 9, 19, 29, 10, 20 Groove (for generating dynamic pressure)
9a, 19a, 29a Return points 9b, 19b, 29b Route (destination side)
9c, 19c, 29c route (source side)
9d, 19d, 10d, 20d Second groove

Claims (7)

A stationary member having a radial bearing surface;
A rotating member supported on the radial bearing surface and rotatable about an axis relative to a stationary member;
A lubricating fluid held between the rotating member and the radial bearing surface;
The radial bearing surface and / or the surface of the rotating member facing the radial bearing surface has a plurality of grooves for generating radial dynamic pressure that repeat regularly in the rotational direction so that a radial load supporting pressure is generated in the lubricating fluid. A radial dynamic pressure bearing portion is formed, and a thrust dynamic pressure bearing portion having a plurality of grooves for generating thrust dynamic pressure regularly repeating in the rotation direction is formed on the thrust bearing surface and / or the surface of the rotating member opposed thereto. In the formed hydrodynamic bearing device, the radial hydrodynamic bearing portion constitutes a source side path and a destination side path for moving the lubricating fluid toward the center of the radial hydrodynamic bearing part,
Each of the radial dynamic pressure generating grooves has a herringbone shape having a groove part located in the movement source side path and a groove part located in the movement destination side path,
On the radial bearing surface, a second groove is formed only between the adjacent radial dynamic pressure generating grooves and on the movement source side path of the lubricating fluid, and the second groove is at the time of the relative rotation. The lubricating fluid is moved toward the thrust hydrodynamic bearing by
The groove portion formed by the radial dynamic pressure generation groove and the second groove is located in the movement source side path of the groove, rather than the groove part located in the movement destination side path of the lubricating fluid. Densely formed,
The hydrodynamic bearing device according to claim 1, wherein a gas-liquid interface of the lubricating fluid is located on the movement source side.   Each of the grooves for generating radial dynamic pressure has a herringbone shape in which a groove portion located in the movement source side path and a groove portion located in the movement destination side path are symmetrical in the axial direction. Item 2. The hydrodynamic bearing device according to Item 1.   Each of the radial dynamic pressure generating grooves has an axially asymmetric herringbone shape in which the groove portion located in the movement source side path extends longer than the groove portion located in the movement destination side path. The hydrodynamic bearing device according to claim 1.   4. The hydrodynamic bearing device according to claim 1, wherein the radial dynamic pressure generating groove and the second groove are formed at equal intervals in the rotation direction.   5. The hydrodynamic bearing device according to claim 1, wherein the gas-liquid interface is located on a groove portion located on the movement source side path and on the second groove during the relative rotation. . The groove for generating the thrust dynamic pressure is configured to move the lubricating fluid toward the radial dynamic pressure bearing portion during the relative rotation, and the thrust dynamic pressure bearing portion includes the thrust dynamic pressure bearing. The fluid dynamic pressure bearing device according to any one of claims 1 to 5, characterized in that a radially inner pressure in the portion is higher than a radially outward pressure.   A hydrodynamic bearing device according to any one of claims 1 to 4, a magnet fixed to the rotating member, and a stator provided on the stationary member so as to be energized in order to generate a rotational force in cooperation with the magnet. A spindle motor comprising: