An external magnetic field inverting apparatus for a magneto-optical disc apparatus

Abstract: The present invention relates to an external magnetic field inverting apparatus for a magneto-optical disc apparatus in which a permanent magnet (15) is used as external magnetic field generating means and a winding (25) is located so that upon supply of a current to that winding the said permanent magnet (15) can be rotated. A magnetic member (30) is located near the said permanent magnet (15) in such a manner that a magnetic flux generated from said winding (25) crosses that permanent magnet (15) with an inclination of a pretermined angle relative to an axis perpendicular to the longitudinal axis of the permanent magnet (15). Thereby the apparatus according to the invention can be reduced in cost, increased in reliability and miniaturized in size.

Description: The present invention relates to an external magnetic field inverting apparatus for a magneto-optical disc apparatus having the features according of the preamble of claim 1. There is already known an apparatus for providing a record erasing magnetic field for a photomagnetic recording medium (Patent Abstracts of Japan, vol. 8, number 282, (P-323) (1719), December 22, 1984 (JP-A-59 146 408)) whereby windings of two separate electromagnets for turning a permanent magnet are disposed rectangularly to each other and parallel to the longitudinal axis of the permanent magnet. The said windings have such sizes that they extend over the length of the permanent magnet. By supplying currents to the windings of said electromagnets the permanent magnet can be turned in such a manner that its magnetic field in the one direction or in the other direction is effective onto a photoelectric magnetic recording of a photoelectric magnetic recording medium. However, the expenditure of the said known apparatus is relative high. Furthermore a magneto-optical recording- and -reproducing device is known (GB-A-20 83 677), operating on a recording disc which comprises a substrate having magnetic thin films formed thereon. The magnetic easy directions of the films are perpendicular to the plane of the substrate, both films being magnetized in the same direction. An optical converging lens and a rotatable permanent magnet which is movable parallel to the plane of the recording disk are disposed on the opposite sides of the disk. However, in this connection there is no detailed information obtainable concerning the mounting of the permanent magnet. 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). Furthermore, FR-A-249475 describes an improved apparatus for premagnetizing a rotor of a motor for miniature clocks. 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°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 shoving 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 controlled on the basis of a drive signal from a system controller (not shown) and the permanent magnet 5 is half-rotated on the basis of the rotation of the motor 7. The half-rotated condition of the permanent magnet is detected by a pair of switches 11 and 12 shown in Fig. 4. To this end, as shown in Fig. 4, a projected member 13A is attached to a holder 13 which incorporates the permanent magnet 5 and the pair of switches 11 and 12 are located respectively at the positions to which the permanent magnet 5 is rotated by 180°. Then, the supply of the drive signal to the motor 7 is stopped by a signal obtained when the projected member 13A contacts with the switches 11 and 12. Thus, the half-rotated condition of the permanent magnet 5 can be stabilized. When the external magnetic field inverting apparatus 10 is constructed by using the permanent magnet instead of the electromagnet as described above, there arise the following problems. Since the external magnetic field inverting apparatus 10 employs the stepping motor 7 as a drive source for inverting the permanent magnet 5, it requires, in addition to the motor 7, circuits such as a driver and so on. This increases the manufacturing cost of the apparatus on the whole. Further, since the apparatus is constructed by using parts for consumption such as the motor 7, the pair of switches 11, 12 and so on, the apparatus is short in life span, poor in reliability and can not be miniaturized because of attaching the motor 7 and the like. DISCLOSURE OF INVENTION It is therefore an object of the present invention to provide an external magnetic field inverting apparatus as is defined in the preamble of claim 1 which can be made low in cost, high in reliablity and miniaturized in size. According to the present invention the afore mentioned object is attained by the characterizing feature of claim 1. According to the invention, since the repulsive forces generated between the magnetic fields resulting from supplying the current to the winding and the magnetic field of the permanent magnet itself are different at the center of the rotation of the permanent magnet, it is possible to rotate the permanent magnet in the desired direction (clockwise direction or counter-clockwise direction) by the difference of the repulsive forces. If the winding remaines as is conducted, the permanent magnet is stabilized under the half-rotated state. The reason for this is that the magnetic field of the permanent magnet and the magnetic field of the winding become same in direction, and hence the repulsive force applied to the permanent magnet disappears. As a result, the direction of the external magnetic field passing through the disc is inverted. When inverting the direction of this external magnetic field next time, if a current opposite to the above mentioned current is flowed to the winding, the permanent magnet is further half-rotated and stabilized in that state due to the similar reason. If the magnetic field of the permanent magnet is utilized positively and only the magnetic field is generated from the winding at a necessary time, it is possible to freely alter the opposing polarity of the permanent magnet relative to the disc surface. According to the arrangement of the invention in which the rotation force given to the permanent magnet is formed by the magnetic field of the permanent magnet and the magnetic field of the winding, the apparatus can be miniaturized in size and the apparatus can be made high in reliability. Brief description of the drawings: Figs. 1 and 2 are conceptual explanatory diagrams for known magneto-optical recordings, Fig. 3 is a constructional diagram showing an example of a prior art external magnetic field inverting apparatus, Fig. 4 is a partial diagram showing the operation state thereof, Fig. 5 is a side view showing an embodiment of the present invention, Fig. 6 is a schematic cross-sectional view of a main portion in Fig. 5. Best mode for carrying out the invention A first embodiment of an external magnetic field inverting apparatus 20 according to the present invention will be described in detail with reference to Fig. 5. As shown in Fig. 5, a short circuit winding (33) is mounted on an attaching plate (23). As shown in the figure, the permanent magnet 15 is located along the center Lc of the winding 25 and the short-circuit winding 33 is located in opposing relation to one surface of the permanent magnet 15. That is, in this embodiment as shown in Fig. 6, the short-circuit winding is located with a predetermined distance from the permanent magnet 15 at the upper surface side of the permanent magnet 15 and at the left of the rotary shaft 22 of the permanent magnet. When the apparatus is constructed as described above, the magnetic flux from the winding 25 partially crosses the short-circuit winding 33 so that an electromotive force is induced therein. Then, on the basis of this electromotive force, a predetermined magnetic field is generated from the short-circuit winding 33. The composed magnetic field of this magnetic field and the magnetic field of the winding 25 is inclined by a predetermined angle, for example, . As a result, a rotation force is applied to the permanent magnet 15 and the permanent magnet 15 can be rotated. According to the embodiment, as shown in Fig. 9 of EP-Application 86 902 518.9, the length of the permanent magnet 15 is selected to be substantially equal to the length of the track number that can be recorded on a disc. When a data is recorded on a predetermined track, the optical pickup apparatus is moved to the corresponding track. This is only one example. In order to check whether or not the permanent magnet 15 is inverted correctly, magnetic field inversion detecting means, for example, Hall element is attached to the main attaching plate 23 opposing to the permanent magnet 15 in facing relation to an elongated opening as shown in Fig.9 of the afore mentioned EP-Application. Since the polarity and the detection level of the detection output from this Hall element are changed dependent on the fact that the polarity of the permanent magnet 15 opposing to the Hall element is the N pole or S pole and also whether or not the external magnetic field Hm passes perpendicularly the Hall element from the permanent magnet 15, by this detection output, it is possible to check whether or not the permanent magnet 15 is inverted correctly and to detect the polarity thereof. The detection output is supplied to a system controller and the irradiation condition of the laser is controlled on the detection output therefrom. INDUSTRIAL APPLICABILITY The external magnetic field inverting apparatus for magneto-optical disc apparatus according to the present invention inverts the permanent magnet by the magnetic field generated from the electromagnet winding so that this invention is suitable for use with a magneto-optical recording and reproducing apparatus such as a disc memory and the like.

Claims: An external magnetic field inverting apparatus for a magneto-optical disc apparatus comprising a rotatable permanent magnet (15) located with a predetermined distance from the surface of a magneto-optical disc (1) in opposing relation thereto and for generating an external magnetic field Hm passing through said disc surface perpendicularly and being rotatably mounted to a rotary shaft (22) having an axis being parallel to said disc surface, a winding (25) producing a magnetic field Hc upon supply of current to said winding for rotating said permanent magnet (15) by a rotation force generated on the basis of a repulsive force occurring between both of said magnetic fields and applied to said permanent magnet (15) whereby to invert the direction of the external field generated by said permanent magnet, said permanent magnet (15) being supported rotatably on a frame through said rotary shaft, characterized in that said frame is provided with a short-circuit winding (33), and a composed magnetic field of a magnetic field generated from said short-circuit winding (33) and a magnetic field generated from said winding (25) crosses said permanent magnet (15) with an inclination of a predetermined angle relative to an axis perpendicular to said rotary shaft (22) of said permanent magnet (15) as well as to said disc surface.

Inventors: NAITO TAKASHI, TOSAKA SUSUMU, NAITO, TAKASHI, TOSAKA, SUSUMU
Applicants: SONY CORP, SONY CORPORATION
Application year: 1986
Main classification: G11B11
IPC codes: G11B11