Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-05-23
2004-03-02
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156320, C310S268000
Reexamination Certificate
active
06700247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a thin type permanent magnet generator, and more particularly to a thin type permanent magnet generator that can be incorporated in a diskette designed to be used by inserting into a floppy disk drive, and when a memory, such as a magnetic card, is installed in the diskette, serves as a power source for the memory to write and read data in the memory.
2. Description of the Related Art
Medical information, such as personal medical checkup results, is stored in an IC card, from which medical institutions can retrieve such information for use in the treatment of a patient, and can store in the card the contents of his case records after some medical treatments. Plans are also now under way to use IC cards as electronic money. Under the plans, data on a customer's bank account, password, and the balance of his account, if necessary, are stored in an IC card, by means of which payment is made on-line every time the card holder spends money.
It has been proposed that an enormous amount of video information handled by a digital camera be stored in a flash memory that has a capacity as large as several megabytes to 10 megabytes. A flash memory containing the video information taken by a digital camera can be connected to a personal computer for subsequent video processing. The use of a flash memory to record the video information taken by a digital camera may eliminate an additional external memory unit, such as MOs.
The widespread use of IC cards or flash memories, however, has been deterred by the need for special input/output (I/O) devices dedicated for such media. Since most commonly used I/O devices for personal computers are floppy disk drives, particularly 3.5″ floppy disk drives, the use of 3.5″ floppy disks as an I/O device for IC cards and flash memories could spur their proliferation. In fact, methods for writing and reading data into and from an IC card or flash memory are being studied, and adapters that can be inserted or incorporated in 3.5″ floppy disk drives have already been proposed. A conventional type of 3.5″ floppy disk drive has a magnetic head to read and write information from and into a 3.5″ diskette, and a drive shaft to cause the diskette to rotate at 300 rpm, but it has no power feeding terminals. In diskette-shaped adapters, a button battery is incorporated to power the built-in CPU. A battery, which depletes as it is used, has to be replaced with a new one every four to five months at the longest.
Introduction of a 3.5″ floppy disk in which a generator is incorporated and driven by the rotation of the drive shaft of a 3.5″ floppy disk drive would prove very useful, giving momentum to the proliferation of IC cards and similar media. In order to implement a diskette which serves as an information I/O device in conjunction with a memory card having magnetic stripes, such as an IC card, a space for housing a memory card must be provided in the diskette. The typical size of a standard memory card is 85 mm in length, 54 mm in width, and 0.8 mm in thickness. Since the thickness given above ignores the embossed part for raised letters of the memory card, its actual thickness is a little bit thicker. To provide a space for a memory card and a permanent magnet type generator in a 3.5″ diskette having a thickness of 3.5 mm and two 0.2 mm-thick covers on both sides, the thickness of the generator must be not more than 2.0 mm, allowing for the thickness of the memory card of 0.8 mm and some clearance for loading and unloading the card.
The thickness t allowed for the permanent-magnet generator to be incorporated in a 3.5″ diskette is 2.0 to 2.5 mm, as stated earlier. The size (width and length) allowed for the generator is up to the size of the 3.5″ diskette, or 90 mm in diagonal length d (mm) on the end face thereof. With t being 2.3 mm and d being 90 mm, the aspect ratio (t/d) is approximately 2.6%.
Commercially available motors or generators having a small thickness include spindle motors for FDD. Some of commercially available thin motors are shown in TABLE 1, where the diagonal length d, thickness t, and aspect ratio (t/d) thereof are also shown, together with the locations of gaps for the motor permanent magnets. As is evident from TABLE 1, the aspect ratio of a generator that can be incorporated in a 3.5″ diskette is extremely small, compared with commonly used thin motors and generators.
TABLE 1
Diagonal
Thick-
Aspect
length
ness
ratio
Type
Gap
d (mm)
t (mm)
t/d (%)
FDD spindle motor for notebook
Radial
18
4
22.2
computer
FDD spindle motor for notebook
Radial
60
3.2
5.3
computer
FDD spindle motor for notebook
Axial
40
3
7.5
computer
FDD spindle motor for desk-top
Radial
50
5
10.0
computer
FDD spindle motor for desk-top
Radial
50
8
16.0
computer
Cooling fan motor
Radial
30
15
50.0
Generator built into diskette
Axial
90
2.3
2.6
Incorporating a generator into a 3.5″ diskette has already been proposed, as in U.S. Pat. No. 5,159,182 and Published Japanese Translation of PCT International Publication for Patent Application Hei-7(1995)-500238.
U.S. Pat. No. 5,159,182 discloses that a generator is incorporated into a 3.5″ diskette, and that the generator has a rotor and a stator, but does not disclose any further details of its construction. In Published Japanese Translation of PCT International Publication for Patent Application Hei-7(1995)-500238, it is disclosed that a permanent magnet rotating together with a hub is provided as a generator built into a 3.5″ diskette; the hub having the permanent magnet is caused to rotate by the drive shaft of a floppy disk drive. It is also disclosed that the permanent magnet is of a cylindrical shape, and magnetized in the direction of the rotational shaft so that a large number of magnetic poles are provided on both end faces of the cylindrical permanent magnet. The magnetic poles on the stator yokes are arranged in such a manner as to sandwich the cylindrical permanent magnet, and a stator coil is provided between the stator yokes on both sides of the cylindrical permanent magnet.
Now, suppose a permanent magnet generator of a size that can be incorporated into a 3.5″ diskette, as disclosed in Published Japanese Translation of PCT International Publication for Patent Application Hei-7(1995)-500238, where a cylindrical rotor permanent magnet is magnetized in the direction of the rotational shaft so that a large number of magnetic poles are provided on both end faces of the cylindrical permanent magnet. In this case, stator magnetic poles are arranged on both sides of the end faces of the cylindrical permanent magnet via small magnetic gaps. Since the thickness allowed for the generator is 2.0 to 2.5 mm, the thickness allowed for the permanent magnet is only 0.5 to 0.8 mm. In a magnet having a short distance between the magnetic poles, even when a material having a large coercive force is used, the resulting magnet has a small magnetomotive force. Since both end faces of the cylindrical permanent magnet face stator magnetic poles, a gap of a few tenth of millimeters is needed to allow the rotor to rotate without mechanical interference with the stator magnetic poles. To ensure the gap of this size, the thickness of the stator magnetic poles must be not more than 0.5 mm, assuming that the thickness of the permanent magnet is 0.5 mm. This thickness is not enough to allow magnetic flux to pass. In Published Japanese Translation of PCT International Publication for Patent Application Hei-7(1995)-500238, furthermore, a long magnetic path is required because the stator coil is provided away from the stator magnetic poles. This, together with the use of thin stator magnetic poles, has led to an increased magnetic resistance, resulting in a generator having small output.
The present inventors already proposed a diskette incorporating a new permanent magnet generator that can be used for the above purpose, and filed an application for patent as U.
Kimura Fumio
Masuzawa Masahiro
Mita Masahiro
Takahashi Toshiko
Dougherty Thomas M.
Hitachi Metals Ltd.
Perez Guillermo
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