Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Patent
1986-12-29
1988-05-31
Cardillo, Raymond F.
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
360114, 360 59, 365122, G11B 503, G11B 1304, G11B 1114
Patent
active
047486066
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an external magnetic field inverting apparatus for use with a magneto-optical disc apparatus. Particularly, this invention uses a permanent magnet as external magnetic field forming means and locates a winding so as to surround the permanent magnet, wherein when a rotation force generated on the basis of a repulsive force between an external magnetic field formed by the permanent magnet and a magnetic field resulting from supplying a current to the winding is applied to the permanent magnet, the permanent magnet can be half-rotated in a desired direction. Thus, an external magnetic field inverting apparatus which is inexpensive, reliable and small in size can be made.
2. Background Art
There is already known a magneto-optical disc apparatus which can record and reproduce a data by using a magneto-optical disc (for example, Japanese laid-open patent application No. 58-14306 and Japanese laid-open patent application No. 57-133537).
The fundamental concept of this magneto-optical disc apparatus will be described with reference to FIGS. 1 and 2. In FIG. 1, reference numeral 1 designates a magneto-optical disc. Before a data is recorded on the magneto-optical disc, it is magnetized uniformly in the same direction (downward direction) as, for example, shown in the Figures. An optical pickup apparatus 2 is located in opposing relation to one surface of the disc 1 to record the data on the disc surface and to reproduce the data therefrom. It is known that the optical pickup apparatus 2 utilizes a laser (semiconductor laser and the like) to record and to reproduce the data. The laser is converged by an objective lens 3 on the disc surface as an optical path 3a.
An electromagnet 5 as the external magnetic field forming means is located at the disc surface opposite to the optical pickup apparatus 2 in facing relation to the optical pickup apparatus 2. This electromagnet 5 generates an external magnetic field H vertical to the disc surface as shown in the figures.
When the optical pickup apparatus 2 is moved to a predetermined disc surface and irradiates a laser thereon so that the disc surface is heated to a temperature (for example, 400.degree. C.) higher than Curie temperature, the magnetic domains in the heated portion become irregular. Under this condition, when a predetermined current is flowed to the electromagnet 5 such that an external magnetic field H (FIG. 2) opposite to the external magnetic field H shown in FIG. 1 is applied to the disc, the magnetization direction of the heated portion within the disc 1 becomes the same direction as that of the external magnetic field H as indicated by a broken line. Accordingly, under this condition, if the irradiation of the laser is stopped, the internal magnetic field is kept as shown by the broken line. In order to invert the direction of the internal magnetic field next time, it is sufficient that the external magnetic field H is inverted as shown in FIG. 1 and the above mentioned scanning is executed. Then, "0" assumes, for example, the magnetization direction shown in FIG. 1 and "1" the magnetization direction shown by the broken line in FIG. 2. Under this assumption, if the magnetization scanning is carried out sequentially at a predetermined pitch in the circumferential direction of the disc 1, it is possible to record (including re-recording) the data "0" and "1" on the disc along the circumferential direction thereof.
The external magnetic field forming means is not limited to the electromagnet but can use a permanent magnet. FIG. 3 is a diagram showing an example of an external magnetic field inverting apparatus 10 which uses a permanent magnet 5 as the external magnetic field forming means. The flat rectangular solid-shaped permanent magnet 5 that is magnetized with the illustrated polarities is located in opposing relation to the disc 1 and rotatably mounted to the apparatus. Its rotary shaft 6 is coupled to the rotary shaft of a stepping motor 7 through coupling means 8.
The motor 7 is contr
REFERENCES:
patent: 4701895 (1987-10-01), Vansant
Naito Takashi
Tosaka Susumu
Cardillo Raymond F.
Nguyen Hoa T.
Sony Corporation
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