JP2710163B2 - Spindle motor used for disk drive - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates generally to the field of disk drives,
More particularly, it relates to an improved spindle motor structure for a disk drive.

The present invention is hereby incorporated by reference.
It is particularly useful as a spindle motor for use in a rotary actuator of the type disclosed in U.S. Patent Application Ser.

2. Description of the Related Art A disk drive device stores information on a concentric circular track of a magnetic disk and reproduces the recorded information. These recording disks are driven at a constant rotational speed by a spindle motor, during which a transducer is selectively positioned at the position of the disk where the information to be accessed is stored, so that the information stored on the disk can be quickly and accurately stored. Is accessible. Therefore, it is important to provide a spindle motor that can quickly bring a disk to a constant rotational speed and maintain the constant rotational speed for a long time.

It is difficult to properly design such motors as disk drives are becoming smaller in size. As disk drives are becoming thinner and thinner, it is necessary to adopt many novel design techniques to realize highly efficient thin DC spindle motors. One solution to such a motor problem is to use what is commonly referred to as a pancake type motor. A structural feature common to pancake motors is that a plurality of air-core flat axial coils are fixed to a printed circuit board to form a motor stator. These coils are regularly spaced axially around a motor shaft extending through the printed circuit board. One end of the shaft is mounted on a bearing and extends upward through the casting base of the disk drive, and the top of the shaft supports the hub. The hub supports one or more disks for constant rotation. The other end of the shaft supports a shallow cup-shaped element, which includes an annular permanent magnet that forms the rotor of the motor. The rotor and stator are operated in combination to form a brushless DC motor particularly suitable for disk drives.

As the coils are sequentially energized, the current flowing in the coils, combined with the magnetic flux from the permanent magnets, generates torque to rotate the motor shaft. In some such motors, it is known to provide a fixed annular return path on the side of the coil opposite the flat rotating magnet.

The use of such fixed return magnetic paths is already known in the art. However, such fixed magnetic paths are usually stamped from a magnetic steel plate.
Since the direction of the magnetic flux in the steel extends perpendicular to the stacking direction, a large current loss is induced, resulting in a significant loss of output. Such eddy currents occur when the magnetic field in a steel plate changes as a function of time. In the case of motors of the type described above, when the magnetic field is reversed (which occurs relatively frequently), eddy currents are induced in a direction that produces a magnetic field that opposes the change. That is, remarkable eddy current loss is caused.

In order to reduce eddy current losses, efforts have been made in the past to attempt to use return magnetic paths made of powdered metal, for example 3% silicon steel. This allows
Although the loss is reduced to some extent, it is not only difficult to make a thin plate with powdered metal, but materials with good high frequency performance tend to become brittle when made into such a thin plate.

Accordingly, it is an object of the present invention to provide an improved spindle motor for use in a disk drive. More specifically, an object of the present invention is to provide a spindle motor that incorporates a return magnetic path with low eddy current loss.

It is an object of the present invention in this context to provide a spindle motor that is easier to assemble than known spindle motors used in disk drives.

Yet another object of the present invention is to provide a disk drive design suitable for quick and accurate assembly.

SUMMARY OF THE INVENTION These and other objects are to use a single printed circuit board to support a plurality of flat air-core coils arranged axially around a motor shaft, and to use these coils for mounting. This is achieved by providing a pancake-type spindle motor in which the supporting printed circuit board is opposed to a shallow cup-shaped element supporting an annular permanent magnet. The opposite side of the printed circuit board supports an annular return magnetic path. The return path is comprised of a thinly sliced sheet steel spiral wound coil. The return magnetic path taped in this manner allows the magnetic flux to easily flow in the peripheral direction, while preventing the eddy current from flowing in the radial direction and significantly reducing the eddy current loss. In a preferred form, the steel is 0.004 inches thick and 0.060 inches wide and is formed by wrapping the core in a suitable size. The coil wound in this manner is mechanically strong and has low manufacturing costs. By providing the coils on a surface opposite to the surface of the printed circuit board supporting the flat stator coils, and including all the electronic components necessary for axial coil commutation and rotor position sensing By designing a spindle motor, a spindle motor that is very efficient and easy to manufacture and assemble is realized.

Embodiments The features and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention and the problems solved by it, a flat brushless DC motor according to the invention
First, FIG. 1 showing a longitudinal section of FIG. 10 will be described. This low-profile spindle motor 10 uses bearings 12 and 14 that are directly incorporated into a casting base 16 of the disk drive to rotatably support a shaft 18. Shaft 18
The hub 20 supported at the tip of the disk supports one or more disks 22 in rotation. By arranging a spring 24 between the bearings 12, 14, these bearings are maintained under a suitable load in advance. This spring creates a pre-loaded condition known in the art as DB, which provides the greatest stability to the bearing system in the casting base 16.

One printed circuit board 26 supported from the casting base 16
The electronic circuit of the motor is mounted on top. In particular, the casting base 16 has shoulders 30 and 32, which define a central bore in which the bearings 12, 14 supporting the shaft 18 are located. An opening 16a used to connect the inner end 36 of the printed circuit board 26 to the casting base 16 is disposed on the outer surface of the shoulder 32. The outer end 38 of the printed circuit board is similarly supported from the casting base 16.

The end of the shaft 18 supports a shallow cup-shaped element 40 having an upwardly bent end 42, which forms a support for the rotor of the motor. The cup-shaped element 40 is
It supports an annular permanent magnet 43 bonded to its inner surface. In the preferred embodiment, the annular magnet 43 is configured to have eight pie-shaped sectors of alternating magnetic poles, which are affixed to a printed circuit board as shown in FIG. 2A. 6 flat axial air core coils 44A-
It is designed to face F. As is evident from FIG. 1, the coil 44 is aligned with the annular magnet 43 so as to lie thereon, and when the coil 44 is sequentially selectively energized,
A magnetic path is completed from one polarity magnet section and back through one of the coils to the opposite polarity section of magnet 43. Thus, by sequentially energizing the coils, rotation of the magnet and its rotor 40, and thus rotation of the shaft 18, is achieved.

It is well known in the art to provide a return magnetic path 50 to efficiently complete a magnetic circuit. However, as mentioned above, such return magnetic paths are typically formed from steel sheets or powdered metal and are therefore prone to significant eddy current losses. In particular, as shown in FIG. 4A, the eddy currents indicated by arrows 52 in FIG. 4A are significantly greater in the return path of solid steel. This is because such a magnetic path does not obstruct the flow of current.

FIG. 4B illustrates one embodiment of the present invention in which the return path is formed of a coarsely wound or relatively thick helical steel. As indicated by arrow 54B, eddy currents are significantly reduced because current flows only in a limited area. FIG. 4C shows a more finely wound return magnetic path element, which can further limit eddy currents, as indicated by arrow 54C.

In a preferred embodiment of the invention shown in FIG.
The return magnetic path is formed by winding a steel tape 60 having a thickness of about 0.004 inches and a width of about 0.060 inches. The eddy current is extremely small because the path through which the current flows is extremely limited (see FIG. 4C). Therefore, in such a state where the eddy current path is subdivided, the eddy current is remarkably reduced, and the motor design efficiency and output can be maximized.

It is 2A that further efficiency can be obtained in the design of the present invention.
It will be clear from the figure and FIG. 2B. As shown in these figures, the step motor 70 and the spindle motor 10
All discrete components, such as the drive speed control electronics for both (shown in more detail in FIG. 5) and the LSI type electronics, are mounted on a single printed circuit board 26. FIG. 2A shows the front (principal) surface 59 of the printed circuit board 26 with six annularly disposed air core axial coils 44A-F mounted thereon, and when these coils are selectively energized, The rotor of the motor is rotated. Posts 61 are provided and molded on the surface 59 of the circuit board to maintain the correct alignment of the shape and annular arrangement of each coil 44.

The Hall effect devices 64A-C required to control the selective energization of the motor coils are located on the same printed circuit board surface 59, which in turn is adjacent to the stepper motor area 75. All other electronic components required to control the stepper motor are also located in the spindle motor electronics 77 adjacent to the electronics section 73 and the area 79 for mounting the spindle motor. In this way, the motor is easy to assemble and maximum integration over the entire structure is obtained. Moreover, the Hall effect devices 64A-C can be accurately positioned with respect to the assembled spindle motor.

The other side 63 of the molded circuit board (shown in FIG. 2B) is a coil just below the cast base 16 shown in FIG.
Support 60. The casting base 16 itself is shown in its longitudinal section in FIG. 5A and in plan view in FIG. 5B. This figure shows a relative positional relationship between the position 79 of the spindle motor and the position 75 of the step motor. The molded printed circuit board shown in FIG. 5B lies below the entire area designated for the spindle motor and is adjacent to the area designated for the stepper motor. The use of this circuit board to support the coil 60, the core 44 and the electronic circuits 73, 77 expedites assembly, precisely aligns all the elements of the spindle motor, and furthermore, the space in the disk drive. Can be used effectively.

From the above description, other features and advantages of the invention will be apparent to those skilled in the art. Accordingly, the invention is to be limited only by the following claims.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a spindle motor according to the present invention. FIGS. 2A and 2B are diagrams showing a single printed circuit board used to support both a coil and a return magnetic path of a disk drive. FIG. 3 shows the steel core coil forming the return magnetic path of the present invention, FIGS. 4A, 4B and 4C show the improvement of the present invention with respect to the reduction of the eddy current, and FIGS. FIG. 5B is a longitudinal sectional view and a plan view, respectively, when the circuit board according to the present invention is supported by a casting base. 10 ... Spindle motor 12,14 ... Bearing 16 ... Cast base 18 ... Shaft 24 ... Spring 26 ... Printed circuit board 30,32 ... Shoulder 40 ... Cup element 43 ... Circular permanent magnet 44A -F ... air-core coil 50 ... return magnetic path 70 ... step motor

Continued on front page (72) Inventor Miles Leonard Peterson United States of America 95124 San Jose Constock Lane 1793 (72) Inventor Charles Glen Norwalk Jr. United States of America 95003 Aptos Vista del Mar 441 (56) Reference Document JP-A-64-16243 (JP, A) JP-A-65-156477 (JP, U)

Claims (10)

(57) [Claims] 1. A spindle motor for use in a disk drive including a casting base, the spindle motor including a shaft and an axial air gap motor for controlling rotation of the shaft, wherein the shaft includes the casting base. A hub that penetrates through and supports one or more disks for rotation, and is mounted on the casting base for rotation by one or more bearings, the axial air gap motor comprising: A flat printed circuit board connected to the shaft and extending parallel to the casting base of the housing, the rotor comprising a magnet supported by a rotor support plate supported at an end of the shaft. Prepared,
The stationary printed circuit board is supported to have first and second surfaces that are essentially out of contact with the rotor support plate and the casting base, wherein the stationary printed circuit board has one of the surfaces. On its surface, around the shaft and in a plane parallel to the magnets, in a ring to support a plurality of axially arranged coils, and on its other surface, the rotor A plurality of helical windings of a thinly sliced steel sheet, which support an annular return magnetic path element mounted on the opposite side of the plurality of axially disposed coils as viewed from above. , Wherein the overcurrent path is cut to reduce the overcurrent of the magnetic return path element formed as a single plate, whereby the magnet, the coil and the return A spindle motor for use in a disk drive, wherein a thin magnetic spindle motor having increased power and efficiency as a result of a reduction in overcurrent loss is formed by forming a magnetic path including a magnetic path element. 2. A spindle motor for use in a disk drive including a casting base, the spindle motor including a shaft and an axial air gap motor for controlling rotation of the shaft, wherein the shaft includes the casting base. A hub that penetrates through and supports one or more disks for rotation, and is mounted on the casting base for rotation by one or more bearings, the axial air gap motor comprising: A flat rotor connected to the shaft and extending parallel to the casting base of the housing and a stationary printed circuit board, the rotor being supported by a rotor support plate supported at the end of the shaft. The stationary printed circuit board is provided on one surface thereof with a magnet around the shaft. And in a plane parallel to the magnets as an annular path to support a plurality of axially arranged coils, and on its other surface, the plurality of coils as viewed from the rotor. It supports an annular return path element mounted on the opposite side of the axially disposed coil, the return path element comprising a coil consisting of a number of helical turns of a thinly sliced steel sheet. Limiting the overcurrent path to reduce the overcurrent of the magnetic return path element formed as a single plate, the stationary printed circuit board supported by the disk drive being supported by the rotor support The stationary printed circuit board is supported to have first and second surfaces that are essentially out of contact with the plate and the casting base, and the stationary printed circuit board is mounted on the plurality of axially disposed cores. A first depression in the first surface for supporting the magnetic return path element and a second depression in the second surface for supporting the magnetic return path element. The first and second depressions are in the area of the stationary printed circuit board assigned to the spindle motor, the first depressions receiving the axially disposed coils, and The second recess receives the magnetic return path element, thereby achieving quick assembly of the spindle motor, accurate alignment of the spindle motor elements, and reducing the thickness of the spindle motor. A spindle motor for use in a disk drive. 3. A spindle motor for use in a disk drive according to claim 1, wherein the return path element is formed from steel having a thickness of about 0.004 inches. 4. A spindle motor for use in a disk drive according to claim 1, wherein the return magnetic path element is formed from steel having a width of about 0.060 inches. 5. A spindle motor for use in a disk drive according to claim 1, wherein control electronics for controlling the rotation of said shaft is mounted on said printed circuit board adjacent to said coil. 6. The method of claim 1, wherein the outer surface of the shoulder of the casting base hole through which the shaft extends has an opening for mounting the inner end of the printed circuit board on the side of the casting base opposite the disk. A spindle motor used for the disk drive described. 7. A spindle motor for use in a disk drive according to claim 6, wherein said casting base supports the periphery of said stationary printed circuit board. 8. A method for mounting the coil adjacent to a plurality of annularly arranged posts molded on the stationary printed circuit board to maintain the shape of the coil and to align the annular array. A spindle motor used in the disk drive according to claim 1. 9. A stationary printed circuit board having a first recess formed in a first surface of said stationary printed circuit board for receiving and supporting said plurality of axially disposed coils. A second recess formed in the second surface of the coil to receive and support said return magnetic path elements, said recesses comprising said plurality of axially disposed coils, said stationary printed circuit board; 2. The spindle motor according to claim 1, wherein said return magnetic path element is assembled so that the thickness of said spindle motor can be reduced. 10. The spindle motor used in a disk drive according to claim 9, wherein said first and second recesses are formed in a printed circuit board by molding of said stationary printed circuit board.