Small magnetic disk cartridge

A small magnetic disk cartridge for use in a card disk drive to be loaded in electronic equipment. The magnetic disk cartridge comprises a housing, a disk-mounting hub rotatable within the housing by a spindle provided in the disk drive, and a flexible magnetic disk mounted at one point on the disk-mounting hub.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a small magnetic disk cartridge, and particularly to a small magnetic disk cartridge that can be exchangeably loaded in a card disk drive that can be loaded in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop personal computer, etc.

2. Description of the Related Art

To record or reproduce information, a wide variety of recording media are removably loaded in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop personal computer (PC), etc. Such recording media that are in practical use are a semiconductor memory type, a hard disk type, an optical disk type, a magnetic disk type (e.g., a floppy disk type), etc.

Among these recording media, the semiconductor memory type is most widely used, because it is easy to handle and has a relatively large recording capacity. However, the semiconductor memory type is relatively expensive. Therefore, in digital cameras employing the semiconductor memory type, it is repeatedly used by storing the photographed image data in a PC, etc., and then deleting the data from the semiconductor memory.

Although there are known some hard disks that can store 340 megabytes (MB) of data or 1 gigabytes (GB) of data, the hard disk type of memory is similarly expensive. Because of this, the hard disk type is repeatedly used by storing data in a PC, etc.

The optical disk type has a large recording capacity for its size. For example, an optical disk with a size of 35 mm×41 mm×11 mm can store 256 MB of data. Optical disks with a recording capacity of 512 MB are about to be realized. However, optical disks have the disadvantage that the recording speed is slow, because the writing time is time-consuming.

Small magnetic disks (e.g., floppy disks) with a size of about 50 mm×55 mm×2 mm are known that can be exchangeably loaded in a disk drive of a size that can be inserted in the card slot of a PC, etc. However, the recording capacity is as small as 40 MB and insufficient to store data photographed by a camera. In addition, the size is not suitable for digital cameras.

With the spread of PCs, digital cameras have spread rapidly in recent years because of the easy method of recording, enhancement of the picture quality due to the development of imaging devices, the possibility of data deletion and transmission, size of the recording capacity, etc. However, digital cameras are restricted in use, because recording media are restricted in cost and recording capacity, as described above. For instance, since recording media are very expensive, one camera is usually provided with one recording medium, which is repeatedly used. That is, when the recording medium is filled with data, the data is transferred to a PC and deleted from the recording medium. Because of this, there are cases where the recording medium is filled up during a trip. In addition, the recording medium cannot be stored as it is, with data recorded therein, nor can it be given away to a person.

Hence, there is a demand for the realization of a small recording medium which is large in recording capacity and low in cost so that the data photographed by a digital camera can be stored as is, or given away to a person. In PCs, there is also a demand for the realization of an inexpensive small large-capacity recording medium that can be handed to a person.

To meet the aforementioned demands, it is contemplated that the above-described small recording medium may comprise a card disk drive which is loaded in electronic equipment such as a PC and a digital camera, and a magnetic disk cartridge which is loaded in the small card disk drive. That is, it is contemplated that such a magnetic disk cartridge may comprise a housing with a shutter, and a flexible magnetic disk, rotatably supported within the housing, which is capable of high-density recording and has a recording capacity of 200 MB or larger. Examples of magnetic recording media with a high recording density are a recording medium with a thin metal film formed by vapor deposition or sputtering, and a recording medium employing barium ferrite powder or ferromagnetic magnetic powder. An example of a magnetic recording medium with a high recording density employing barium ferrite powder is disclosed in U.S. patent application Ser. No. 10/266,584.

The “magnetic recording medium with a high recording density employing barium ferrite powder” is a magnetic disk containing barium ferrite powder in a magnetic layer, and is formed from a material that is capable of a high recording density. The magnetic disk may be constructed of a magnetic recording medium disclosed. The disclosed magnetic recording medium has a non-magnetic substrate, a non-magnetic layer which includes both non-magnetic powder and a binder, and a magnetic layer which includes both ferromagnetic powder (which is hexagonal-system ferrite powder) and a binder. The non-magnetic layer and the magnetic layer are formed on at least one surface of the non-magnetic substrate in the recited order. In the non-magnetic layer, the quantity of carbon black whose average particle diameter is 10 to 30 nm is 10 to 50 weight parts with respect to 100 weight parts of the aforementioned non-magnetic powder. The thickness of the magnetic layer is 0.2 μm or less. According to an electron-beam microanalysis, the standard deviation (b) of the strength of an element with respect to an average strength (a) which results from ferromagnetic powder is 0.03≦b/a≦0.4. The center plane average roughness Ra of the magnetic layer is 5 nm or less, and the 10-point average roughness Rz is 40 nm or less. In a magnetic disk employing the above-described magnetic recording material, information is recorded or reproduced by employing a magnetic head, such as an MR head, a GMR head, or a TMR head, which is capable of a high recording density.

When the above-described magnetic recording medium is about 30 mm in diameter, it can have a high recording density of 200 MB or larger, preferably 500 MB or larger. Therefore, if a still image has about 1 MB of data per image, the magnetic recording medium can store 500 sheets. In the case of a motion picture, the magnetic recording medium can store image contents of about 30 minutes. Thus, the magnetic recording medium can store a motion picture photographed by a digital camera, or a motion picture transmitted by a portable telephone. As a result, users can conveniently use the magnetic recording medium. Furthermore, the magnetic recording medium can be conveniently used in PCs as an inexpensive large-capacity data storage medium. Thus, the convenience of the magnetic recording medium is great.

Note that card disk drives are loaded in electronic equipment such as a PC, a digital camera, etc. In the case of a PC shown inFIG. 1A, for instance, a card disk drive6is connected electrically with the socket4of the receiving portion of a card2that is inserted in the card slot of the PC. In the case of a digital camera3shown inFIG. 1B, a card disk drive6is connected electrically with the socket of the receiving portion5of the camera3. A small magnetic disk cartridge8is removably loaded in these card disk drives6.

Therefore, the above-described card disk drive6is extremely small in size and has, for example, a length of 38 to 55 mm, a width of 35 to 51 mm, and a thickness of 3 to 5 mm. The above-described magnetic disk cartridge8has, for example, a length and a width of 25 to 36 mm and a thickness of 1 to 3 mm. This magnetic disk cartridge8rotatably supports a flexible magnetic disk (indicated by a broken line inFIG. 1) within its housing.

With the advancement of a high recording density in magnetic disks, incidentally, the degradation of recording-reproduction characteristics due to a fluctuation in the spacing between a magnetic disk and a magnetic head, slight circumferential shift of narrowed data tracks, etc., have become problems.

A conventional small magnetic disk cartridge has, for instance, a structure such as that shown in FIG.5. In this structure, a flexible magnetic disk14is rotatably supported within a flat housing12. The housing12is constructed of an upper shell12aand a lower shell12b. The center portion of the magnetic disk12is mounted on a disk-mounting hub15, which is spun by a spindle provided in the above-described disk drive6. The lower shell12is provided with a spindle hole16through which the disk-mounting hub15is magnetically chucked by the above-described spindle. Note in all drawings that the dimensions, such as thickness, etc., of each part are shown at ratios differing from those of the actual dimensions to facilitate the understanding of the structure.

InFIG. 5, the disk-mounting hub15has a lower shaft portion15a, an intermediate flange portion15c, and an upper shaft portion15b. The lower shaft portion15ais magnetically chucked by the spindle provided in the disk drive6. The upper shaft portion15bis inserted in the center hole of the magnetic disk14. The inner circumferential portion of the magnetic disk14around the center hole of the disk14is mounted on the annular top face15dof the flange portion15c.

However, in the case where the magnetic disk14is mounted on the flange portion15cof the disk-mounting hub15, wrinkles and distortions tend to occur around the inner circumferential portion of the magnetic disk14mounted on the flange portion15cof the disk-mounting hub15.

On the other hand, a reduction in the size of the magnetic disk14shortens the radial distance between the disk-mounting hub15and the innermost circumference of the recording area of the magnetic disk14. Therefore, in a structure such as the one shown inFIG. 5, wrinkles and distortions produced in the magnetic disk14have a bad effect on the inner circumference of the recording area. If surface runout occurs during rotation, the touch of a magnetic head with the magnetic disk14will become unstable, and consequently, recording-reproduction characteristics will be greatly affected.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described circumstances. Accordingly, it is the primary object of the present invention to provide a small magnetic disk cartridge which is loaded in a card disk drive for electronic equipment, thin in thickness, and large in recording capacity, and which has stable rotation, a good head touch, and excellent recording-reproduction characteristics by preventing surface runout.

To achieve this end and in accordance with the present invention, there is provided a small magnetic disk cartridge for use in a card disk drive to be loaded in electronic equipment. The magnetic disk cartridge comprises a housing, a disk-mounting hub rotatable within the housing by a spindle provided in the disk drive, and a flexible magnetic disk mounted at one point of the center thereof on the disk-mounting hub.

In a preferred embodiment of the present invention, the diameter of the one mounting point on the disk-mounting hub is 20% or less of the diameter of that portion of the disk-mounting hub which faces the magnetic disk, preferably 10% or less, and more preferably 5% or less. When the diameter of that portion of the disk-mounting hub which faces the magnetic disk is, for example, 10 mm, the diameter of the one point on the disk-mounting hub is 2 mm or less, preferably 1 mm or less, and more preferably 0.5 mm or less.

In the small magnetic disk cartridge of the present invention, the aforementioned flexible magnetic disk may be mounted at one point on the disk-mounting hub by an adhesive agent. The flexible magnetic disk may also be mechanically mounted at one point on the disk-mounting hub by a pin.

According to the magnetic disk cartridge of the present invention constructed as described above, the small area of the center portion of the magnetic disk is mounted at one point on the disk-mounting hub. Therefore, wrinkles and distortions are less liable to occur around the center portion of the magnetic disk. As a result, the flatness of the magnetic disk can be maintained during rotation, and a magnetic head can touch the magnetic disk stably.

According to the magnetic disk cartridge of the present invention, the dimensional accuracy of the assembly of the disk drive and the dimensional accuracy of the assembly of the magnetic disk cartridge can be absorbed. Furthermore, the operation of mounting the magnetic disk on the disk-mounting hub is easier than the above-described conventional operation of annularly mounting the magnetic disk cartridge on the disk-mounting hub.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 2, there is shown a small magnetic disk cartridge8constructed in accordance with a first embodiment of the present invention. The magnetic disk cartridge8has a flat housing12in which a magnetic disk14is rotatably supported. This magnetic disk14has no center hole and is constructed of a material that has a recording capacity of 200 MB or larger. For example, the magnetic disk14is constructed of the above-described magnetic recording medium that has a magnetic layer with a high recording density containing barium ferrite powder.

A disk-mounting hub15has a shaft portion15awhich is magnetically chucked by the spindle of the above-described disk drive6, and a flange portion15cwhich has a flat top face15a. The lower shell12bof the housing12has a spindle hole16to expose the disk-mounting hub15. The center portion of the under side of the magnetic disk14is mounted at one point on the top face15dof the disk-mounting hub15by an adhesive agent18. The diameter of the one mounting point on the top face15dof the disk-mounting hub15is 20% or less of the diameter of the flange portion15cof the disk-mounting hub15, preferably 10% or less, and more preferably 5% or less. When the diameter of the flange portion15cof the disk-mounting hub15is, for instance, 10 mm, the diameter of the one point on the top face15dof the disk-mounting hub15is 2 mm or less, preferably 1 mm or less, and more preferably 0.5 mm or less.

Referring now toFIG. 3, there is shown a small magnetic disk cartridge8constructed in accordance with a second embodiment of the present invention. Note inFIG. 3that the same parts as the first embodiment ofFIG. 2are represented by the same reference numerals. The second embodiment is characterized in that the upper portion of a disk-mounting hub15is formed into a truncated cone15einstead of the above-described flange portion15c. The center portion of the under side of the magnetic disk14is mounted at one point on the top face of the truncated cone15eby an adhesive agent18.

Referring now toFIG. 4, there is shown a small magnetic disk cartridge8constructed in accordance with a third embodiment of the present invention. Note inFIG. 4that the same parts as the first embodiment ofFIG. 2are represented by the same reference numerals. The third embodiment is nearly the same as the first embodiment ofFIG. 2, but differs in that the center portion of a magnetic disk14is mounted mechanically at one point on the top face15dof the flange portion15cof a disk-mounting hub15by a pin20press-fitted in the flange top face15d. In addition to the pin20, the third embodiment may employ the adhesive agent18shown in FIG.2.

As set forth above, the magnetic disk cartridge8of the present invention has the following advantages:

(1) The small area of the center portion of the magnetic disk14is mounted at one point on the disk-mounting hub15. Therefore, wrinkles and distortions are less liable to occur around the center portion of the magnetic disk14. As a result, the flatness of the magnetic disk14is maintained during rotation, and a stable head touch can be assured. (2) In the case where the magnetic disk14is mounted on the top face of the truncated cone15eof the disk-mounting hub15, as in the second embodiment shown inFIG. 3, a recess in which the flexible magnetic disk14can move downward is present between the flexible magnetic disk14and the truncated cone15e. This recess can absorb the dimensional accuracy of the assembly of the disk drive6and the dimensional accuracy of the assembly of the magnetic disk cartridge8. (3) The operation of mounting the magnetic disk14on the disk-mounting hub15is easier than the conventional operation of annularly mounting the magnetic disk cartridge8′ on the disk-mounting hub15, shown in FIG.5.

While the present invention has been described with reference to the preferred embodiments thereof, the invention is not to be limited to the details given herein, but may be modified within the scope of the invention hereinafter claimed.