BRUSHLESS MOTOR HAVING CHUCKING MECHANISM, AND DISK DRIVING DEVICE HAVING THE BRUSHLESS MOTOR

Abstract

A space for accommodating therein a portion of an optical pickup mechanism is arranged below a disk loading portion of a turn table member of a chucking mechanism of the present invention. The space is arranged axially below a disk mounting surface. Since such space is provided, a recording/reproducing portion will be allowed to move closer to a brushless motor, and therefore a second lens arranged further away from the brushless motor will be allowed to move radially inward of a recording/reproducing area of an optical disk.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of a brushless motor according to a preferred embodiment of the present invention.

FIG. 2 is an enlarged and cross sectional view of a chucking mechanism and an upper portion of a rotor portion of the brushless motor according to the preferred embodiment of the present invention.

FIG. 3 is plan view of a turn table member of the brushless motor as seen from below according to the preferred embodiment of the present invention.

FIG. 4 is a graph showing a level of vibration with respect to rpm of the brushless motor according to the preferred embodiment of the present invention and that of a conventional brushless motor.

FIG. 5 is a schematic cross sectional view of disk driving device according to a preferred embodiment of the present invention.

FIG. 6 a is a plan view of an optical pick up mechanism.

FIG. 6 b is a schematic cross sectional view of the chucking mechanism provided to illustrate a positional relationship between the optical pick up mechanism shown in FIG. 6a and the chucking mechanism.

FIG. 7 is a cross sectional view of an embodiment of the conventional brushless motor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Structure of Brushless Motor

Note that in the description of a preferred embodiment of the present invention herein, words such as upper, lower, left, right, upward, downward, top and bottom for describing positional relationships between respective members and directions merely indicate positional relationships and directions in the drawings. Such words do not indicate positional relationships and directions of the members mounted in an actual device. Also note that reference numerals, figure numbers and supplementary descriptions are shown below for assisting the reader in finding corresponding components in the description of the preferred embodiment below to facilitate the understanding of the present invention. It is understood that these expressions in no way restrict the scope of the present invention. Note that reference numerals, figure numbers and supplementary explanations are shown in parentheses below for assisting the reader in finding corresponding components in the description of a preferred embodiment below to facilitate the understanding of the present invention. It is understood that these parenthetic expressions are in no way intended to restrict the scope of the invention.

Hereinafter, a structure of the brushless motor according to the preferred embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is a cross sectional view of the brushless motor according to the preferred embodiment of the present invention.

Hereinafter, a stator portion of the brushless motor will be described with reference to FIG. 1.

A housing 10 formed by a deformation process (e.g., pressing) performed on a steel plate includes a cylindrical portion 11 concentric with a central axis J1 extending in an axial direction, a bottom surface portion 12 arranged at a bottom end of a cylindrical portion 11 for closing the cylindrical portion 11. The housing 10 has an opening at an axially top end thereof. A step portion 13 is arranged at a connecting portion between the cylindrical portion 11 and the bottom surface portion 12 in the housing 10. A washer 20 of an annular shape made of a resin material is arranged on a top surface of the step portion 13. A substantially cylindrically shaped sleeve 30 is arranged attached to a top surface of the washer 20 and to an inner circumferential surface of the cylindrical portion 11 of the housing 10. The sleeve 30 is a sintered object impregnated with oil. A washer 40 is arranged on a top surface of the sleeve 30 so as to prevent an oil leakage via a top portion of the sleeve 30. A thrust plate 50 made of a resin material having a superior abrasion quality and slidability is arranged on a top surface of the bottom surface portion 12. Also, a radially extending portion 14 extending in the radial direction is arranged on a top end of the cylindrical portion 11.

A stator 60 is arranged on an outer circumferential surface of the cylindrical portion 11. The stator 60 includes: a plurality of stator cores 61 each having a core back portion 61a of an annular shape made of a thin plate and a plurality of tooth portions 61b each extending in the radial direction and arranged evenly apart from one another in a circumferential direction, wherein the plurality of stator cores 61 each are flat-rolled magnetic steel sheet laminated on top of another in the axial direction to form a layer thereof; an insulating coating (not shown) arranged on a surface of the stator core 61; and a coil 61 formed by winding a multiple layers of wire around each tooth portion 61.

Also, an attachment board 70 formed by a deformation process (e.g., pressing) performed on a steel plate is arranged on an outer circumferential surface of the housing 10 axially below the stator 60. The attachment board 70 includes an attachment portion 71 of a substantially cylindrical shape is arranged at a portion thereof making contact with the outer circumferential surface of the cylindrical portion 11. A circuit board 80 is arranged on a top surface of the attachment board 70 via an insulating layer (not shown) in order to electrically insulate one from another. On the circuit board 80, a plurality of Hall elements 81 (3 in the present embodiment) are arranged in the circumferential direction as a detection means for a high speed rotation. As a detection means for a low speed rotation, an optical element 82 is arranged. The optical element 82 is arranged axially on top of a resin layer 83 arranged on top of the circuit board 80. The optical element 82 is arranged radially outward of the Hall element 81. The optical element 82 detects a pattern formation portion (not shown) arranged radially inward of the recording/reproducing portion of the optical disk in order to detect the rotation of the optical disk.

Hereinafter, a rotor portion of the brushless motor will be described.

A shaft 90 concentric with the central axis J1 is inserted into the sleeve 30 and is rotatably supported by the inner circumferential surface of the sleeve 30. A rotor holder 100 formed by a deformation process (e.g., pressing) performed on a steel plate is affixed to the shaft 90 at a portion thereof axially above the sleeve 30. The rotor holder 100 includes a flat lid portion 102 radially extending outward of the shaft 90, and a cylindrical portion 101 extending in the axially downward direction from a radially outer area of the lid portion 102. The rotor holder 100 surrounds the stator 60. A rotor magnet 110 is arranged at an inner circumferential surface of the cylindrical portion 101. The rotor magnet 110 is arranged facing an outer circumferential surface of the tooth portions 61b via a gap therebetween. A pressuring magnet 120 is arranged at a bottom facing surface of the lid portion 102 and axially facing the radially extending portion 14.

Hereinafter, a chucking mechanism 130 will be described.

The chucking mechanism 130 includes: a turn table member 131 of a substantially cylindrical shape made of a resin material arranged on the top surface of the lid portion 102; a cone shaped member 132 made of a resin material having a slidable portion 132a of a substantially cylindrical shape sliding with the shaft 90 and arranged axially above the turn table member 131, and a disk contacting portion 132b contacting with an optical disk (not shown); an elastic member 133 (coiled spring in the present embodiment) arranged at a space between the turn table member 131 and the cone shaped member 132 for retaining an axial position of the cone shaped member 132; and a yoke member 134 which is a magnetic substance arranged to restrict an axial movement of the cone shaped member 132.

A hollow portion 131a of a substantially annular shape is arranged at a radially outward portion of the turn table member 131. A balance member 135 (a plurality of steel balls in the present embodiment) is arranged at the hollow portion 131a.

Structure of Chucking Mechanism and Rotor Portion

Hereinafter, a detailed structure of the chucking mechanism 130 and that of the rotor portion according to the preferred embodiment of the present invention will be described with reference to FIGS. 2 and 3. FIG. 2 is an enlarged cross sectional view of the chucking mechanism 130. FIG. 3 is a plan view of a turn table member as seen from below according to the preferred embodiment of the present invention.

According to FIG. 2, an indented receiving portion 131b for receiving a portion of the cone shaped member 132 is arranged at a center of the turn table member 131 of the chucking mechanism. The indented receiving portion 131b includes a first accommodating portion 131b1 arranged at a radially outermost area of the indented receiving portion 131b for receiving the disk contacting portion 132b of the cone shaped member 132, a second accommodating portion 131b2 arranged radially inward of the first accommodating portion 131b1 making contact with the elastic member 133, and a third accommodating portion 131b3 arranged radially inward of the second accommodating portion 131b2 for receiving the slidable portion 132a of the cone shaped member 132. An inner circumferential edge of the third accommodating portion 131b3 and the outer circumferential surface of the shaft 90 are affixed to one another. The first accommodating portion 131b1 is arranged axially above the other accommodating portions, while the third accommodating portion 131b3 is arranged axially lowest.

The hollow portion 131a of an annular shape in the circumferential direction is arranged at a radially outer area of the first accommodating portion 131b1. The hollow portion 131a has an opening facing axially below thereof. The hollow portion 131a includes an inner circumferential wall 131a2 at radially inward thereof, an outer circumferential wall 131a3 at radially outward thereof, and a lid surface 131a5 radially connecting the inner circumferential wall 131a2 and the outer circumferential wall 131a3. The hollow portion 131a is radially adjacent to the first accommodating portion 131b1. That is, the inner circumferential surface of the first accommodating portion 131b1 and the outer circumferential surface of the inner circumferential wall 131a2 are arranged at substantially the same position in the radial direction. Also, an axial position of the lid surface 131a5 connecting the inner circumferential wall 131a2 and the outer circumferential wall 131a3 of the hollow portion 131a is substantially the same as a bottom portion of the first accommodating portion 131b1. An inclined surface is arranged at a corner portion 131a1 at radially inward and axially upper area of the hollow portion 131a. If such inclined surface is not arranged (see a dotted line in FIG. 2) at the corner portion 131a1, a radial width of the inner circumferential wall 131a2 between the first accommodating portion 131b1 and the hollow portion 131a will be unfavorably thin, thereby severely deteriorating a flow of the resin material when injected in a mold for shaping the elements of the motor and consequently affecting the manufacturing efficiency. On the other hand, due to the inclined surface arranged at the corner portion 131a1, preferable radial width of the inner circumferential wall 131a2 will be arranged between the first accommodating portion 131b1 and the hollow portion 131a, thereby improving the flow of the resin material. The inclined surface of the corner portion 131a1 is arranged axially above a center of the steel ball. In particular, according to the preferred embodiment of the present invention an angle generated between the inclined surface of the corner portion 131a1 and the central axis J1 is approximately 45 degrees.

Also, an indent portion 131c of a substantially annular shape in the circumferential direction is arranged at the inner circumferential area of the inner circumferential wall 131a2 wherein the indent portion 131c has an opening facing axially downward.

A diameter of the outer circumferential wall 131a3 is substantially equal to the external diameter of the cylindrical portion 101 of the rotor holder 100. Also, a disk loading portion 131d radially extending off the outer circumferential wall 131a3 is arranged at an upper area of the turn table member 131. A disk mounting surface 131e of a substantially annular shape made of a material having a great frictional property (e.g., rubber) is arranged on the top surface of the disk loading portion 131d. Also, at an upper portion of the outer circumferential wall 131a3, an inclined surface extending toward the outer end of the disk mounting surface 131e is arranged.

A plate 136 of a substantially annular shape made of a thin metal plate by a deformation process (e.g., pressing) for sealing the hollow portion 131a is arranged at the opening of the hollow portion 131a axially below thereof. A hook portion 136a of a substantially cylindrical shape extending upward is arranged at a radial end of the plate 136, wherein an outer circumferential surface of the hook portion 136a and the inner circumferential surface of the inner circumferential wall 131a2 are affixed to one another by a press fit. The outer circumferential wall 131a3 includes a step portion 131a4 at the inner circumferential portion thereof whereby an outer end of the plate 136 makes contact therewith so as to determine the axial position of the plate 136. The outer circumferential wall 131a3 extends axially lower than the bottom facing surface of the plate 136. The inner circumferential surface of the outer circumferential wall 131a3 makes contact with the outer circumferential surface of the plate 136. By virtue of such configuration, the hollow portion 131a is sufficiently sealed, and therefore sound which is generated therein due to movement of the balance member 135 will well be contained. Further, since the outer circumference of the outer circumferential wall 131a3 extends axially lower than the bottom facing surface of the plate 136, the hollow portion 131a will be sufficiently sealed. Furthermore, the outer circumference of the outer circumferential wall 131a3 extends axially lower than the top surface of the lid portion 102 of the rotor holder 100.

An adjuster 137 of an annular shape made of a thin plate is arranged above the plate 136 within the hollow portion 131a in which the balance member 135 moves. The adjuster 137 absorbs the noise generated when the balance member 135 moves due to a rotary force of the rotor portion.

With reference to FIG. 3, an adhesive filling portion 131f having an opening facing axially downward is arranged on a bottom facing surface of the turn table member 131. The adhesive filling portion 131f includes a first indent portion 131f1 of a substantially annular shape, and a plurality of second indent portions 131f2 (6 in the present embodiment) each extending in the radial direction from the first indent portion 131f1. The second indent portions 131f1 each are connected to the indent portion 131c.

With reference to FIG. 3, the first indent portion 131f1 is axially opposed to a portion of the lid portion 102. By virtue of such configuration, the turn table member 131 and the lid portion 102 are securely affixed to one another via adhesive. Further, since the second indent portions 131f2 are connected to the first indent portion 131f1, any amount of adhesive in excess of the space generated between the first indent portion 131f1 and the lid portion 102 will flow to the second indent portion 131f2.

The disk contacting portion 132b of the cone shaped member 132 is shaped such as to make contact with a substantially entire inner circumferential surface of the central opening of the optical disk (not shown). An outer circumferential surface of the disk contacting portion 132b includes at a top portion thereof a disk guiding surface 132b1 which makes contact with the inner circumferential surface or a bottom surface of the central opening of the optical disk and guides the optical disk toward a center of rotation of the brushless motor, and at a bottom portion thereof disk aligning surface 132b2 which is connected with the disk guiding surface 132b1 and aligns the rotation of the disk with that of the brushless motor. An inner wall 132b3 of a substantially annular shape extending in the axial direction is arranged radially inward of the disk contacting portion 132b. A connecting portion 132c extending radially inward is arranged so as to connect the inner wall 132b3 with the slidable portion 132a. An annular open portion 132b4 is arranged radially between the inner wall 132b3 and the disk aligning surface 132b2. The elastic member 133 which is compressed to a predetermined level is arranged so as to make contact with a bottom surface of the annular open portion 132b4 and a top surface of the second accommodating portion 131b2.

Also, since the disk aligning surface 132b2 makes contact with a substantially entire inner circumferential surface of the central opening of the optical disk, aligning quality of the disk with brushless motor and the retaining strength of the optical disk will be improved.

Also, since a step portion 103 is arranged at a portion connecting the lid portion 102 and the cylindrical portion 101 of the rotor holder 100, wherein the rotor holder 100 is radially indented, deformation of the lid portion 102 which lacks rigidity particularly at the joint thereof with the cylindrical portion 101 will be minimized.

Also, the hollow portion 131a is arranged at an outer circumferential area of the lid portion 102 and the plate 136 makes contact with the lid portion 102. Also, since the step portion 103 is arranged at the outer circumferential area of the lid portion 102 minimizing the risk of deforming the lid portion 102, deformation of the plate 136 caused due to the deformation of the lid portion 102 will be minimized. By virtue of such configuration, the preferred embodiment of the present invention is able to reduce the level of vibration and noise caused due to deformation of the travel passage of the balance member 135 which is caused by deformation of the lid portion 102.

Also, an outer circumferential area of the outer circumferential wall 131a3 of the hollow portion 131a and the step portion 103 are arranged at substantially the same position in the radial direction, while a bottom end of the outer circumferential wall 131a3 is arranged axially below the top surface of the lid portion 102. By virtue of such configuration, the bottom end of the outer circumferential wall 131a3 will make no contact with the lid portion 102, and therefore, while the radial position of the outer circumferential wall 131a3 is same as that of the cylindrical portion 101 of the rotor holder 100, the lid portion 102 and the plate 136 make contact with one another in a preferable manner.

Hereinafter, a comparison will be made with reference to FIG. 4 between a level of vibration with respect to rpm of the brushless motor according to the preferred embodiment of the present invention and that of a conventional brushless motor which includes a balance member having a plurality of aligning claws are arranged in the circumferential direction. FIG. 4 is a diagram showing a level of vibration with respect to rpm of the brushless motor according to the preferred embodiment of the present invention and that of the conventional brushless motor. Note that the horizontal axis of the diagram indicates rpm and the axial axis indicates the level of vibration (Grms). Also note that the value for the vibration with respect to rpm of the brushless motor according to the preferred embodiment of the present invention is denoted by a solid line, while that of the conventional brushless motor is denoted by a dotted line.

According to FIG. 4, the level of vibration shifts in a uniformed manner for both brushless motor of the present invention and the conventional brushless motor until rpm reaches approximately 3,000 at which point the level of vibration drops which indicates that the balance member (steel balls) is arranged at an appropriate position of each motor. When rpm reaches approximately 6,000, the difference between the brushless motor according to the preferred embodiment of the present invention and the conventional brushless motor becomes apparent where the level of vibration for the conventional brushless motor becomes greater than that of the brushless motor according to the preferred embodiment of the present invention. This indicates that at approximately 6,000 rpm and thereafter a centrifugal force originally generated due to an imbalance of the optical disk forcing the optical disk to be removed from the chucking mechanism becomes greater than a retaining strength of the aligning claws of the conventional brushless motor, thereby misaligning the optical disk. That is, the rotation of the optical disk will be misaligned from the rotation of the brushless motor. Consequently, the greater the misalignment between the optical disk and the brushless motor, the greater the level of the vibration of the brushless motor becomes. On the other hand, the cone shaped member 135 of the brushless motor according to the preferred embodiment of the present invention makes contact with substantially the entire inner circumferential surface of the central opening of the optical disk and therefore, the optical disk will be retained more securely. Consequently, as shown in FIG. 4, misalignment of the optical disk is minimized even at 6,000 rpm for the brushless motor according to the preferred embodiment of the present invention. Thus, the brushless motor according to the preferred embodiment of the present invention is suitable for recording data on the optical disk and reproducing data from the optical disk when the rotation of the optical disk reaches approximately 6,000 or higher.

Disk Driving Device

Hereinafter, a disk driving device according to the preferred embodiment of the present invention will be described with reference to FIGS. 5, 6a and 6b. FIG. 5 is a schematic cross sectional view of the disk driving device. FIG. 6a is a plan view of an optical pick up mechanism. FIG. 6b is a schematic cross sectional view of the chucking mechanism provided to illustrate a positional relationship between the optical pick up mechanism shown in FIG. 6a and the chucking mechanism.

According to FIG. 5, a disk driving device 200 includes a brushless motor 220 for rotating an optical disk 210, an optical pickup mechanism 230, for recording on the optical disk 210 and reproducing data from the optical disk 210, which moves freely in the radial direction within a predetermined circumferential direction, a loading mechanism 240 for loading and unloading the optical disk 210 to the disk driving device 200, and a housing 250 of a cuboid shape for accommodating therein the brushless motor 220, the optical pickup mechanism 230 and the loading mechanism 240.

The loading mechanism 240 is arranged axially above the brushless motor 220 and includes a disk accommodating portion 241 having a concaved area facing axially upward on which the optical disk 210 is to be loaded. The loading mechanism 240 includes at a radially outermost portion thereof an outer wall 242 which becomes a portion of the housing 250. When the loading mechanism 240 shifts such that the outer wall 242 aligns with the housing 250 in the axial direction, the center of rotation of the brushless motor 220 aligns with the center of the central opening of the optical disk 210.

The optical pickup mechanism 230 includes a recording/reproducing portion 231 for recording data on the optical disk 231 and reproducing data from the optical disk 210, and an optical pick up moving portion 232 for moving the recording/reproducing portion 231 in the radial direction. The recording/reproducing portion 231 includes two object lenses in the radial direction. One of the object lenses arranged nearer to the brushless motor will be referred to as a first lens 233a and the other lens will be referred to as a second lens 233b. These two lenses will be used when recording data on and reproducing data from different types of optical disk (e.g., HD-DVD and Blu-ray disk). Also, the optical pick up transport portion 232 includes a plurality of gear mechanisms 234 which engage with the recording/reproducing portion 231 and a gear driving motor 235 for driving the gear mechanism 234.

The housing 250 includes an opening portion 251 allowing the loading mechanism 240 to move therethrough.

Hereinafter, a positional relationship between the recording/reproducing portion 231 and the brushless motor 220 will be described with reference to FIG. 5. In FIG. 5, a dotted line denotes the optical disk 210 while an alternate short and long line denotes a radially inner most portion of a recordable and reproducible region of the optical disk 210.

When the second lens 233b of the recording/reproducing portion 231 is used to reproduce the data stored at an area further radially inward of a recording/reproducing area 211 which is an area of the optical disk 210, the first lens 233a will be at an area very close to the brushless motor 220 (i.e., further inward of the recording/reproducing area 211). Therefore, a space to accommodate a portion of the recording/reproducing portion 231 will be required underneath the disk loading portion 131d. According to the brushless motor 210 of the present invention, the outer circumferential wall 131a3 of the hollow portion 131a which is underneath the disk loading portion 131d is arranged at an area radially inward of the disk mounting surface 131e, and therefore, a space (accommodating portion 260) to accommodate therein the portion of the storing/reproducing portion 231 is arranged. By virtue of such configuration, it becomes possible to execute a recording and reproducing of data at the area further radially inward of the recording/reproducing area 211.

While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention.

For example, although the present embodiment assumes that the inclined surface of the corner portion 131a1 of the turn table member 131 to be flat, the present invention is not limited thereto; the inclined surface can be curved with respect to the axial direction.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Claims

1. A brushless motor having a chucking mechanism operable to detachably place thereon an optical disk including a central opening portion, the brushless motor comprising: a shaft being a rotary axis;a rotor magnet rotating along with the shaft; anda rotor holder including therein a cylindrical portion retaining the rotor magnet and a flat lid portion extending from the cylindrical portion to the shaft, whereinthe chucking mechanism is arranged on a top surface of the lid portion, andthe chucking mechanism includes: a cone shaped member having a slidable portion of a substantially cylindrical shape with an inner circumferential surface movable in an axial direction with respect to the shaft, and a disk contacting portion of a substantially annular shape expanding downwardly in the axial direction making contact with an inner circumferential surface of the central opening portion;a turn table member having a disk mounting surface making contact with a bottom surface of the optical disk, a hollow portion arranged axially below the disk mounting surface, having a substantially annular shape with an opening facing downward, an inner circumferential wall and an outer circumferential wall, and at least one balance member accommodated in the hollow portion;an elastic member, arranged at an axial space between the turn table member and the cone shaped member, retaining an axial position of the cone shaped member; anda yoke member arranged axially above the slidable portion restricting axial movement of the cone shaped member, andan outer circumferential surface of the outer circumferential wall is arranged radially at a same position as the cylindrical portion or radially inward of the cylindrical portion.

2. The brushless motor according to claim 1, wherein the outer circumferential surface of the outer wall is arranged at radially a same position or inward of an inner end of the disk mounting surface.

3. The brushless motor according to claim 1, wherein an inner circumferential surface of the outer wall is arranged radially inward of an inner edge of the disk mounting surface.

4. The brushless motor according to claim 1, wherein the disk mounting surface includes a portion arranged radially outward of the outer circumferential wall, andthe outer circumferential wall includes an inclined surface extending radially outward and axially upward.

5. The brushless motor according to claim 1, wherein the inner circumferential wall includes at an outer circumferential surface thereof an inclined surface such as to expand in an upward direction.

6. The brushless motor according to claim 5, wherein the balance member is a steel ball, andthe inclined surface is arranged axially above a center of the steel ball.

7. The brushless motor according to claim 5, wherein an angle generated between the inclined surface and the central axis is approximately 45 degrees.

8. The brushless motor according to claim 6, wherein an angle generated between the inclined surface and the central axis is approximately 45 degrees.

9. The brushless motor according to claim 1, wherein the turn table includes an indented receiving portion of a substantially annular shape receiving a portion of of the cone shaped member,the indented receiving portion includes a first accommodating portion receiving a portion of the disk contacting portion and a second accommodating portion arranged radially inward of and axially lower than the first accommodating portion receiving the elastic member, and

10. The brushless motor according to claim 9, wherein an axial position of a lid surface connecting the inner circumferential wall and the outer circumferential wall is a substantially same or lower than that of the first accommodating portion.

11. The brushless motor according to claim 1, wherein the turn table member includes an indented receiving portion of a substantially annular shape receiving a portion of the cone shaped member,the indented receiving portion includes a first accommodating portion accommodating a portion of the disk contacting portion and a second accommodating portion arranged radially inward of and axially lower than the first accommodating portion receiving a portion of the elastic member,an inner circumferential surface of the first accommodating portion is arranged at a substantially a same radial position as an outer circumferential surface of the inner circumferential wall of the hollow portion,an axial position of a lid surface connecting the inner circumferential wall and the outer circumferential wall of the hollow portion is substantially a same as a bottom portion of the first accommodating portion, andthe inner circumferential wall of the hollow portion includes an inclined surface connecting the lid surface and the inner circumferential surface of the hollow portion.

12. The brushless motor according to claim 11, wherein the balance member is a plurality of steel balls, andthe inclined surface is arranged axially above a center portion of each steel ball in the hollow portion.

13. The brushless motor according to claim 11, wherein an angle generated between the inclined surface and the central axis is approximately 45 degrees.

14. The brushless motor according to claim 1, wherein the outer circumferential wall is arranged radially outward of the lid portion andthe rotor holder includes at a portion connecting the lid surface and the cylindrical portion a step portion radially indenting inward.

15. The brushless motor according to claim 1, wherein a flat plate of a substantially annular shape is arranged below the inner circumferential wall and the outer circumferential wall of the turn table member, anda bottom surface of the plate makes contact with a top surface of the lid surface of the rotor holder.

16. The brushless motor according to claim 14, wherein a flat plate of a substantially annular shape is arranged below the inner circumferential wall and the outer circumferential wall of the turn table member, anda bottom surface of the plate makes contact with a top surface of the lid surface of the rotor holder.

17. The brushless motor according to claim 14, wherein a bottom end of the outer circumferential wall is arranged axially lower than the top surface of the lid portion.

18. The brushless motor according to claim 16, wherein a bottom end of the outer circumferential wall is arranged axially lower than the top surface of the lid portion.

19. The brushless motor according to claim 1, wherein an adhesive is arranged at an axial space between the turn table member and the rotor holder,the turn table includes, at a portion thereof opposite to the top surface of the lid portion, a hollow portion having an opening facing axially downward, andan adhesive is arranged between the top surface of the lid portion and the hollow portion.

20. The brushless motor according to claim 19, wherein the hollow portion includes a first hollow portion of a substantially annular shape, and a plurality of second hollow portions radially extending from the first hollow portion arranged in a circumferential direction.

21. The brushless motor according to claim 1, wherein the brushless motor stores data on the optical disk and reproduces data from the optical disk at at least substantially 6,000 rpm.

22. A brushless motor having a chucking mechanism operable to detachably place thereon an optical disk including a central opening portion, the brushless motor comprising: a shaft being a rotary axis;a rotor magnet rotating along with the shaft;a rotor holder including a cylindrical portion retaining the rotor magnet, and a flat lid portion extending from the cylindrical portion to the shaft, whereinthe chucking mechanism is arranged on a top surface of the lid portion, andthe chucking mechanism includes: a cone shaped member having a slidable portion of a substantially a cylindrical shape with an inner circumferential surface movable in an axial direction with respect to the shaft, and a disk contacting portion of substantially an annular shape expanding downwardly in the axial direction making contact with an inner circumferential surface of the central opening portion;a turn table member having a disk mounting surface making contact with a bottom surface of the optical disk, a hollow portion arranged axially below the disk mounting surface, having substantially an annular shape with an opening facing downward, an inner circumferential wall and an outer circumferential wall, and at least one balance member accommodated in the hollow portion;an elastic member, arranged at an axial space between the turn table member and the cone shaped member, retaining an axial position of the cone shaped member; anda yoke member arranged axially above the slidable portion restricting axial movement of the cone shaped member, andthe brushless motor stores data on the optical disk and reproduces data from the optical disk at at least substantially 6,000 rpm.

23. A disk driving device storing data and reproducing data on the optical disk comprising: an optical pickup mechanism including a recording/reproducing portion recording data on the optical disk and reproducing data from the optical disk, and an optical pick up transport portion moving the recording/reproducing portion, andthe brushless motor according to claim 1.

24. The disk driving device according to claim 23, wherein the recording/reproducing portion is operable to move such that at least a portion thereof axially overlaps with the disk mounting surface.

25. The disk driving device according to claim 23, wherein the recording/reproducing portion includes a plurality of lenses each emitting an optical light toward a bottom surface of the optical disk.

26. The brushless motor according to claim 1 further comprising a rotation detection means for high speed rotation, and a rotation detection means for low speed detection.

27. The brushless motor according to claim 26, wherein the rotation detection means for low speed rotation detects a pattern formation portion arranged on a bottom surface of the optical disk.