JP2007244004A - Motor and recording disc drive equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spindle motor in which cogging and electromagnetic noise are reduced while enhancing torque. <P>SOLUTION: In the spindle motor, the core 33 is produced by laminating a plurality of core plates 34. The core 33 is produced by stacking first and second cores. The first core 34a and the second core 34b have surfaces of different profile opposing a rotor magnet 32. Cogging torque generated from the second core 34b is offset at least partially by cogging torque generated from the first core 34a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a motor having a plurality of magnetic pole teeth on a stator. In particular, a spindle motor used for rotating a recording disk achieves a demand for reduction in size and thickness.

(1. Recent trends)
In recent years, as the storage capacity density of hard disks has improved, further miniaturization of hard disk drives has been demanded. Furthermore, since application to portable devices is expanding, durability against external vibration and impact is required. For this reason, the bearing is required to have a certain level of rigidity, resulting in a large axial loss. On the other hand, in the case of a portable device, it is necessary to reduce power consumption in order to increase the continuous use time. In order to satisfy these requirements simultaneously, it is necessary to improve the driving efficiency of the motor.

(2. Structure of spindle motor)
A DC brushless motor is generally used as the spindle motor. The brushless motor includes a stator, a stationary assembly to which the stator is attached, a rotor magnet, a rotor to which the rotor magnet is attached, and a bearing.

  The stator includes a plurality of magnetic pole teeth, a back yoke that magnetically connects the outer peripheries or the inner peripheries of the magnetic pole teeth, and coils wound around the magnetic pole teeth. The magnetic pole teeth and the back yoke are formed by stacking a plurality of silicon steel core plates having very high magnetic permeability. The rotor magnet is an annular permanent magnet. The rotor magnet is arranged to face the stator on the opposite side to the back yoke of the magnetic pole teeth in the radial direction with respect to the stator. The rotor to which the rotor magnet is attached is rotatably supported by the bearing mechanism with respect to the stator assembly to which the stator is attached.

(3. Conventional structure)
Patent Document 1 describes a structure in which an end of the stator facing the rotor magnet is bent in the axial direction in order to achieve a reduction in thickness without reducing the torque of the motor. This increases the area of the stator magnetic pole teeth that faces the rotor magnet in the radial direction, so that the magnetic flux of the rotor magnet can be used efficiently. That is, the torque constant is improved. Therefore, even if the current flowing through the coil is reduced, the same torque can be obtained, so that power consumption can be reduced.

(4. Conventional problems)
When attempting to increase the torque, torque unevenness called cogging tends to occur at the same time. In particular, in the case of a spindle motor used for rotating a recording disk, if the cogging occurs, the reading accuracy of the recording disk is lowered. For example, it is well known that when the torque constant is increased by the above-described method, torque unevenness called cogging occurs or electromagnetic noise increases. Therefore, it has been difficult to improve the torque of the spindle motor that rotates the recording disk.

JP-A-4-251541

  According to the present invention, in a thin motor, the cogging torque can be reduced without reducing the motor torque.

  In the present invention, when configuring the magnetic pole teeth, at least two cores having different cogging waveforms are laminated. Each motor cogging waveform is a composite of the core cogging waveforms. At this time, for the first core and the second core, the shape of each core is selected so that the cogging waveform has an opposite phase. By doing so, the combined cogging waveform can be reduced. By adjusting the shape of each of the two types of cores, the cogging waveform can be adjusted more easily than when only one type of core is used.

  An arc shape can be selected as the shape of the core tip to be superimposed. Cogging waveforms can be adjusted by stacking cores with different arc curvatures. At this time, the tip of one core may be a straight line.

  Alternatively, the tip of one core may be bent to create a vertical portion so as to face the rotor magnet. With this configuration, a large torque can be obtained. The cogging waveform can be adjusted by laminating the other core with an appropriate curve at the tip. The part to be bent may be a straight line or a curved line depending on the design requirements.

  Although the processing is slightly complicated, the height of the vertical portion (the width in the vertical direction) may be changed along the circumferential direction. A more preferable cogging waveform can be obtained by stacking the other core on the core which is higher near the center and lower toward both ends.

  The method of the present invention is particularly effective when used to reduce cogging torque in a three-phase DC brushless motor. At this time, the effect is more remarkable when applied to a motor having a concentrated winding coil.

  The cogging torque waveform of the core is obtained by measuring the torque necessary for rotating the rotor magnet with respect to the rotation angle in a state in which the coil wound around the core is not energized. The waveform of the cogging torque is greatly influenced by the magnetizing waveform of the rotor magnet and the shape of the magnetic pole tooth end of the core.

  Other features, elements, and advantages of the invention are described in the following section, Best Mode for Carrying Out the Invention.

  A motor embodying the present invention is highly efficient due to improved torque. Furthermore, cogging is reduced at the same time. Therefore, there is little electromagnetic noise generated with cogging. Further, such a motor with a small cogging torque can be designed and manufactured relatively easily. Further, by using such a motor, a spindle motor with high efficiency and low cogging and electromagnetic noise can be produced.

  An embodiment of a spindle motor used in a hard disk drive as a motor embodying the present invention will be described with reference to the drawings. In the description of the embodiment, when using expressions such as up / down / left / right / back / front, this indicates the direction on the drawing and limits the direction when actually implemented. is not. In particular, the upper and lower parts represent the upper and lower parts in FIG. 2 unless otherwise noted. The axis is the rotation center axis of the rotor and is substantially equal to the center of the core or rotor magnet.

(First embodiment)
(1-1 Configuration of hard disk drive and spindle motor)
FIG. 1 shows a hard disk drive 1 of the present invention constructed using a spindle motor embodying the present invention. A hard disk drive 1 configured using the spindle motor 3 of the present invention includes a hard disk 11 capable of recording information, a head 13 for reading / writing information on the disk, and an arbitrary disk on the disk that supports the head 13. The head assembly 14 is moved inside the housing 12.

  FIG. 2 shows the spindle motor 3 of the present invention in the first embodiment. The spindle motor 3 includes a rotor hub 21 having a mounting surface on which the hard disk 11 is mounted, a base plate 23 that forms a part of the housing 12 and forms the base of the spindle motor 3, and the rotor hub 21 as a base plate 23. The bearing 22 is rotatably supported.

  The bearing 22 is composed of a shaft, a sleeve fitted into the shaft with a gap, and a lubricating oil interposed therebetween. Further, a dynamic pressure generating groove is formed in the sleeve to constitute a dynamic pressure bearing.

(1-2 Configuration of drive unit)
The drive unit of the spindle motor 3 includes a stator 31 having a coil 31a wound around a core 33 and a rotor magnet 32 made of an annular permanent magnet. In the present embodiment, an inner rotor type motor in which the rotor magnet 32 is located on the inner peripheral side of the stator 31 is used. However, it goes without saying that the present invention can also be applied to an outer rotor type spindle motor. The rotor magnet 32 is magnetized in the radial direction so that a plurality of magnetic poles are arranged in the circumferential direction. The spindle motor 3 of this embodiment having such a configuration is a direct current brushless motor. (1-3 Stator shape)
3A is a plan view from the upper side of the core 33 according to the first embodiment with reference to FIG. 2, and FIG. 3B is a perspective view thereof. 4a to 4c are enlarged views of only the tip portion of the magnetic pole teeth 33b of the core 33 facing the rotor magnet 32. FIG. 4a is a plan view from the upper side of FIG. 2, and FIG. 3d is a plan view from the lower side.

  The core 33 includes an annular core back 33a located on the outer peripheral side of the stator 31, and magnetic pole teeth 33b extending from the core back 33a toward the radially inner side. The core 33 is composed of a plurality of core plates 34. The core plate laminated on the uppermost side is a first core 34 a formed by bending one core plate 34. The second core 34b is composed of a plurality of flat core plates 34 stacked below the first core 34a.

  The first core 34 a whose end portion on the center side of the extension portion is bent has a bent portion 34 a 1 that is a bent portion and a vertical portion 34 a 2 whose thickness direction faces the rotor magnet 32. Moreover, the 2nd horizontal part 34a3 laminated | stacked on the 2nd core 34b in the axial direction is also provided.

  The vertical portion 34a2 of the first core plate 34a is narrower at the center in the circumferential direction than the outer peripheral surface of the rotor magnet 32, and is tangent to the outer peripheral surface of the rotor magnet that faces the narrowest portion. Is a plane parallel to the.

  The second core 34b constitutes magnetic pole teeth 33b, and is laminated in the axial direction on the opposing surface 34b1 that faces the outer peripheral surface of the rotor magnet 32 in the radial direction and the second horizontal portion 34a3 of the first core plate 34a. And a first horizontal portion 34b2.

  The vertical portion 34 a 2 forms a plane parallel to one of the tangents of the circle or arc that forms the outer peripheral surface of the rotor magnet 32. The vertical portion 34a2 is closest to the rotor magnet 32 at the center position in the circumferential direction of the magnetic pole teeth 33b formed by the vertical portion 34a2. The facing surface 34b1 has an arc shape having a larger radius of curvature than the outer peripheral surface of the rotor magnet 32. In the present embodiment, the radius of curvature of the facing surface 34b1 is approximately twice the radius of curvature of the outer peripheral surface of the rotor magnet 32. Note that the shape of the plane that forms the vertical portion 34a2 and the shape of the arc-shaped surface that forms the facing surface 34b1 are both shapes that are defined by design, and a range that takes into account the range of machining errors in implementation. Is not excluded.

(1-4 Actions and Effects of the Invention)
FIGS. 5A to 5C show the results of measuring the cogging torque when the coil is wound around three types of cores. In the present embodiment, the motor is a three-phase DC brushless motor. The rotor magnet 32 is magnetized in a sine waveform and the number of magnetic poles is 12. The number of magnetic pole teeth 33b of the stator 31 is nine. Then, the cogging torque is 36 cycles per rotation of the rotor magnet 32. 5A to 5C show the measurement of one period of cogging torque, that is, the rotation angle of the rotor magnet 32 for 10 degrees.

  FIG. 5A shows the measured cogging torque for the core consisting only of the second core in the present embodiment. On the other hand, FIG. 5B shows a circle or an arc that forms the outer peripheral surface of the rotor magnet 32 in the inner peripheral surface of the magnetic pole teeth facing the outer peripheral surface of the rotor magnet 32 as in the first core in the present embodiment. Cogging torque measured for a core composed of a core composed of a plane parallel to the tangent.

  In FIG. 5B, the phase of the cogging torque is shifted by approximately π and is in an opposite phase as compared with FIG.

  FIG.5 (c) is the cogging torque measured about the core 33 which implemented the present invention and has the form detailed in (1-3). The core 33 includes a second core 34b having the characteristics shown in FIG. 5A and a first core 34a having the characteristics shown in FIG. Therefore, the cogging torque of the second core 34b and the cogging torque of the first core 34a cancel each other, and the cogging torque is reduced as a whole of the core.

  The cogging torque waveform of each core is not close to a sine waveform as shown in FIGS. 5A and 5B, and may be a more distorted waveform. However, even in such a case, the cogging torque as the whole core can be reduced by overlapping the cores showing the waveforms having opposite phases.

  FIG. 12 shows a core 330 used in a conventional spindle motor having an inner peripheral surface made up of an arc concentric with the circle or arc constituting the outer peripheral surface of the rotor magnet 32. FIG. 6 is a diagram showing a cogging torque waveform of the conventional core 330. In the core embodying the present invention, the maximum value of the cogging torque and the average value of the absolute value are reduced to about 1/20 as compared with the conventional core.

(Second Embodiment)
The spindle motor according to the second embodiment differs from the spindle motor according to the first embodiment in the shape of the core 33. Therefore, only the parts different from the first embodiment will be described.

  In the description of the present embodiment, members having the same functions or effects are denoted by the same reference numerals as those used in the first embodiment even if they are not equivalent shapes.

(2-1 Core shape)
3c and 3d are a plan view and a perspective view from above of FIG. 2 of the core 33 used in the spindle motor 3 of the second embodiment.

  The core 33 includes a second core and a first core. A bent second core 34b is laminated on the uppermost side. A first core 34a composed of a plurality of flat core plates is stacked below the second core 34b.

  The second core 34 b has a bent portion 34 b 11 and a vertical portion 34 b 12 whose thickness direction faces the rotor magnet 32. Moreover, the 1st horizontal part 34b13 laminated | stacked on the 1st core 34a and an axial direction is also provided.

  The vertical portion 34b12 of the second core 34b is narrower at the center in the circumferential direction than the outer peripheral surface of the rotor magnet 32. The curvature of the surface of the vertical portion 34b12 facing the rotor magnet is an arc having a larger radius of curvature than the outer peripheral surface of the rotor magnet 32. In the present embodiment, the radius of curvature of the inner peripheral surface of the vertical portion 34b12 is approximately twice the radius of curvature of the outer peripheral surface of the rotor magnet 32.

  The first core 34a constitutes an end portion of the magnetic pole teeth 33b, and is opposed to the outer surface of the rotor magnet 32 in the radial direction and the first horizontal portion 34b13 of the first core plate 34b in the axial direction. And a second horizontal portion 34a12 to be stacked.

  The facing surface 34a11 is closest to the rotor magnet 32 at the circumferential center position of the magnetic pole teeth 33b, and forms a plane parallel to one of the tangents of the circles or arcs that form the outer circumferential surface of the rotor magnet 32. ing.

  In the present embodiment, the radius of curvature of the facing surface 34b1 is approximately twice the radius of curvature of the outer peripheral surface of the rotor magnet 32. It should be noted that the shape of the plane constituting the vertical portion 34b12 and the shape of the arcuate surface constituting the opposing surface 34b1 are both shapes defined by design, and a range that takes into account a range of machining errors in implementation. Is not excluded.

(2-2 Actions and effects of the implementation of the invention)
The operations and effects in the second embodiment are the same as those in the first embodiment. That is, the planar shape of the magnetic pole tooth tip of the second core 34b in the first embodiment is the same as the planar shape of the magnetic pole tooth tip of the second core 34b in the second embodiment. Even when the torque waveform is measured, a similar waveform appears. In addition, the planar shape of the magnetic pole tooth tip of the first core 34a in the first embodiment is the same as the planar shape of the magnetic pole tooth tip of the first core 34a in the second embodiment. Even when the torque waveform is measured, a similar waveform appears.

  Therefore, as in the first embodiment, the cogging torque waveform of the core of the present embodiment formed by laminating the second core 34b and the first core 34a in the axial direction is the cogging torque of the second core 34b. The torque and the cogging torque of the first core 34a cancel each other, and as a result, the cogging torque is reduced.

(Third embodiment)
The spindle motor of the third embodiment is different from the spindle motor 3 of the first embodiment in its core shape. Therefore, only the parts different from the first embodiment will be described.

  In the description of the present embodiment, members having the same functions or effects are denoted by the same reference numerals as those used in the first embodiment even if they are not equivalent shapes.

(3-1 Core shape)
7a and 7b are a plan view and a perspective view from above of FIG. 2 of the core 33 used in the spindle motor 3 of the third embodiment.

  The core 133 has an annular core back 33a located on the outer peripheral side, and magnetic pole teeth 33b extending radially inward from the core back 33a. The core 33 is composed of a plurality of core plates 134. Of these, the bent core plate is 34d. The inner peripheral end of the core plate 34d is bent upward. In the bent core plate 34d, the inner peripheral surface 34c in the thickness direction faces the rotor magnet 32.

  The inner peripheral surface 34 c of the core 33 is configured by a plane parallel to the tangent line of the opposing rotor magnet 32. Further, when the magnetic pole teeth are viewed from the inside in the radial direction, the height of the central portion is high just like a semi-cylindrical shape and is low at both ends in the circumferential direction.

  Further, the inner peripheral surface 34 c has a larger curvature than the outer peripheral surface of the rotor magnet 32. In particular, the curvature of the inner peripheral surface 34 c of the bent core plate 34 d is set to be larger than that of the inner peripheral surfaces of the other core plates 134.

(3-2 Results of implementation)
In this embodiment, the magnetizing waveform of the rotor magnet 32 is a sine waveform, and the energization waveform to the coil 31a is a three-phase sine wave drive. The experiment was performed with the rotor magnet 32 having a diameter of approximately 13 mm, a radial gap between the stator 31 and the rotor magnet 32 of 0.2 mm, the stator 31 having 9 magnetic pole teeth and the rotor magnet 32 having 8 magnetic poles. It was.

  By implementing the present invention, the torque constant is improved by 10% compared to the spindle motor using the conventional core 330 shown in FIG. Moreover, the effective value of the cogging torque indicating the magnitude of cogging was reduced to about 1/10. These numerical values are merely examples, and may vary depending on various conditions such as the magnetizing waveform of the rotor magnet, the method of energizing the stator, and the magnetic resistance of the entire spindle motor. However, when they are set to the same condition, a certain effect is recognized in improving the torque constant and reducing the cogging torque.

(Fourth embodiment)
The present invention can also be applied to an outer rotor type spindle motor 103 as shown in FIG. 11A, which is the fourth embodiment of the present invention. The rotor magnet 132 is located radially outward of the core 133.

  The shape of the core 133 is as shown in FIG. Magnetic pole teeth 133b extend radially outward from the annular core back 133a. The core 133 includes a first core 134a and a second core 134b, each of which has a different shape at the end of the magnetic pole teeth 133b. The first core 134a has a first outer peripheral surface 134a1 formed of an arc having a first radius of curvature r1, which is a circle concentric with the circle constituting the inner peripheral surface of the rotor magnet 133. The first outer peripheral surface 134a1 is defined in a range larger than 0.75 times (including a linear shape approximated by ∞) and should be larger than a second radius of curvature described later. On the other hand, the second core 134b has a second facing surface 134b1 formed of an arc having a second curvature radius r2 defined in a range smaller than 0.9 times the curvature radius R of the inner peripheral surface of the rotor magnet 133. Have. Thus, the first curvature radius r1 is made larger than the second curvature radius r2.

  The cogging torque waveform shown by the first core 134a has a sine wave shape. On the other hand, the cogging torque waveform shown by the second core 134b has a sine wave shape in which the cycle is substantially equal to the cogging torque waveform of the first core 134a and the sign is reversed. Therefore, the cogging torque waveform shown by the core 133 formed by stacking the first core and the second core is a superposition of these two cogging torque waveforms. That is, the cogging torque waveform of the first core 134a cancels at least a part of the cogging torque waveform of the second core 134b, and the cogging torque of the entire core 133 is reduced. The spindle motor 103 including the core 133 described in the present embodiment has reduced cogging and reduced torque loss, vibration, and noise.

(Other embodiments)
Although the method and structure for carrying out the present invention have been described as described above, the present invention is not limited to such an embodiment. Various changes and modifications can be made without departing from the scope of the claims of the present invention.

  For example, as shown in FIG. 10, the core in another embodiment of the present invention is formed by stacking a first core and a second core having two different inner peripheral surface shapes, and cogging each core has. The shape of the torque waveform cancels at least some of the other. The effect of the present invention can be achieved even with a so-called flat core in which the tip portion of the first core or the second core in the magnetic pole teeth 33b is not bent substantially vertically.

  Furthermore, the number of magnetic pole teeth of the stator and the number of magnetic poles of the rotor magnet can be appropriately determined according to required specifications. For example, it is known that the period per rotation of cogging is the least common multiple of the number of magnetic pole teeth and the number of magnetic poles of the rotor. Therefore, setting these values so that the greatest common multiple becomes large is effective in reducing cogging and the like.

As shown in FIGS. 8A to 8D, the shape of the magnetic pole teeth facing the rotor magnet may be a trapezoidal shape, a staircase shape that decreases toward both ends, an isosceles triangle shape, a ridge shape, or the like. Good. Depending on the characteristics of cogging, it is possible to appropriately select and improve the shape that most suppresses cogging.
Furthermore, as shown to Fig.9 (a), the core board located in the upper or lower end of an axial direction may be bent so that another core board may be wrapped. In this way, the bent core plate can have the largest facing surface with the rotor magnet, which is effective in improving the torque constant.

  Moreover, the core board which is not laminated | stacked on any edge part of an axial direction like FIG.9 (b) may be bent in any one of the upper and lower sides.

  Further, as shown in FIG. 9C, two or more core plates may be bent in the upper and lower directions. By doing so, even if the center position of the stator is changed, it is possible to obtain an optimum stator position only by changing the bending height of the core plate.

  Furthermore, the other components of the spindle motor can be optimized according to the application.

  As the bearing, a dynamic pressure bearing having another form or a sliding bearing may be used. Moreover, what is called a rolling bearing comprised via a rolling element between an outer ring | wheel and an inner ring | wheel may be sufficient.

It is sectional drawing which shows the hard-disk drive of this invention. It is sectional drawing which shows the spindle motor concerning the 1st Embodiment of this invention. It is a top view of the core of the spindle motor concerning the 1st Embodiment of the present invention. It is a perspective view of the core of the spindle motor concerning the 1st Embodiment of the present invention. It is a top view of the core of the spindle motor concerning the 2nd Embodiment of this invention. It is a perspective view of the core of the spindle motor concerning the 2nd Embodiment of this invention. (A)-(c) is the figure which expanded the magnetic pole tooth of the core of the spindle motor concerning the 1st Embodiment of this invention. (A) is the core of the spindle motor according to the first embodiment of the present invention, of the second core 34b, (b) of the first core 34a, (c) the core 33 combining them. It is a graph which shows the measurement result of the waveform of the cogging torque regarding each core. It is a graph which shows the measurement result of the cogging torque waveform of the conventional core used for the conventional spindle motor. (A) And (b) is a figure which shows the core of the spindle motor concerning the 3rd Embodiment of this invention. It is a perspective view which shows the principal part of the core of the spindle motor concerning other embodiment of this invention. It is sectional drawing of a core which shows the lamination | stacking and bending method of a core of the spindle motor concerning other embodiment of this invention. (A) And (b) is a figure which shows the core of the spindle motor concerning other embodiment of this invention. (A)-(c) is a figure which shows the spindle motor concerning the 4th Embodiment of this invention. (A) And (b) is a figure which shows the core of the conventional spindle motor.

Explanation of symbols

1. 2. Hard disk drive Spindle motor 103. Spindle motor 11. Hard disk 12. Housing 13. Head 14. Head assembly 21. Rotor hub 22. Bearing 23. Base plate 31. Stator 31a. Coil 32. Rotor magnet 33. Core 133. Core 330. Conventional core 33a. Core back 133a. Core back 33b. Magnetic pole teeth 133b. Magnetic pole teeth 34. Core plate 134. Core plate 34a. First core 34a1. Bent portion 34a2 (of the first core). Vertical portion 34a3 (of the first core). Second horizontal portion 34a11. Opposing surface 34a12. Second horizontal portion 34b. Second core 34b1. Opposing surface 34b2. 1st horizontal part 34b11. Bent part 34b12 (of the second core). Vertical part 34b13 (of the second core). First horizontal portion 34c. Inner peripheral surface 34d. Bent core board

Claims (11)

A rotor magnet having a cylindrical peripheral surface representing a circular cross section, and a plurality of magnetic poles arranged in a circumferential direction around a central axis;
A first core having an extension extending in a radial direction, and an end of the extension facing the circumferential surface of the rotor magnet in a radial direction is curved at a first radius of curvature;
The end facing the circumferential surface of the rotor magnet in the radial direction is curved at a second radius of curvature different from the first radius of curvature, and at least at the end relative to the end of the first core. A second core that is laminated in the axial direction to form the magnetic pole teeth together with the first core;
A coil attached to the magnetic pole teeth;
A rotor for holding the rotor magnet;
A bearing mechanism for rotatably supporting the rotor with respect to the core;
A motor consisting of The motor according to claim 1, wherein the first radius of curvature is larger than the second radius of curvature. A rotor magnet having a cylindrical peripheral surface representing a circular cross section, and a plurality of magnetic poles arranged in a circumferential direction around a central axis;
A first core having an extension portion extending in a radial direction and having a linear shape in which an end portion of the extension portion facing the circumferential direction of the rotor magnet in the radial direction extends in the circumferential direction;
The end facing the circumferential surface of the rotor magnet in the radial direction is curved with a predetermined radius of curvature, and is laminated in the axial direction at least at the end with respect to the end of the first core. A second core that constitutes the magnetic pole teeth together with the core of
A coil attached to the magnetic pole teeth;
A rotor for holding the rotor magnet;
A motor comprising a bearing mechanism that supports the rotor so as to be relatively rotatable with respect to the core. The rotor magnet is disposed radially outward of the stator;
The second radius of curvature is not less than 1.5 times and not more than 3 times the radius of the outer peripheral surface of the rotor magnet.
The motor according to claim 1 or 2, characterized in that: The rotor magnet is disposed radially outward of the stator;
The first radius of curvature is not more than 0.9 times the radius of the inner peripheral surface of the rotor magnet.
The motor according to claim 1, characterized in that: The first core is a single core plate having a vertical portion that is bent substantially perpendicularly toward one axial direction at an end facing the rotor magnet circumferential surface,
The second core is composed of one or more flat core plates, and is laminated on the other axial side of the first core.
The motor according to any one of claims 1 to 5, characterized in that. A rotor magnet having a cylindrical peripheral surface representing a circular cross section, and a plurality of magnetic poles arranged in a circumferential direction around a central axis;
A first core having a radially extending extension;
An extension part extending in a radial direction, and the extension part has a vertical part bent substantially perpendicularly toward one axial direction at an end part opposing the circumferential surface of the rotor magnet in the radial direction, A second core, which is laminated on the other surface in the axial direction of one core and constitutes a magnetic pole tooth with the first core;
A coil attached to the magnetic pole teeth;
A rotor for holding the rotor magnet;
A bearing mechanism for rotatably supporting the rotor with respect to the core;
Consists of
An end portion on one axial side of the bent portion of the second core protrudes from a surface on one axial side of the first core,
A motor characterized by things. A rotor magnet having a cylindrical circumferential surface showing a circular cross section, and a plurality of magnetic poles arranged in a circumferential direction around a central axis;
It has an extension part extending in the radial direction, and an end part on the rotor magnet side has a vertical part bent substantially perpendicularly toward one side in the axial direction, and the axial width of the vertical part is the center in the circumferential direction The first core, which becomes narrower toward the ends from
A second core comprising one or more flat core plates, laminated on the first core and constituting magnetic pole teeth together with the first core;
A coil attached to the magnetic pole teeth;
A rotor for holding the rotor magnet;
A bearing mechanism for rotatably supporting the rotor with respect to the core;
A motor consisting of The axial width of the vertical portion becomes narrower toward the both ends from the circumferential center,
The motor according to claim 6 or 7, characterized in that: The cogging force resulting from the magnetic interaction between the radial end of the first core and the peripheral surface of the rotor magnet exhibits a first waveform with respect to the rotation angle of the rotor magnet,
The cogging force resulting from the magnetic interaction between the radial end of the second core and the peripheral surface of the rotor magnet is the first waveform with respect to the rotation angle of the rotor magnet. Shows a second waveform that is out of phase with
The motor according to claim 1. A spindle motor comprising the motor according to claim 1 and a rotor hub that rotates integrally with the rotor;
A recording disk attached to the rotor hub;
An information access means having a function of reading information on the recording disk;
A housing for housing the spindle motor, the recording disk, and the information access means therein;
A recording disk drive device comprising:

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