External magnetic field generation apparatus and a magneto-optical recording apparatus

Abstract: An external magnetic field generation apparatus is used for a recording and reproduction apparatus which records information on a magneto-optical recording medium based on the magnetic field modulation system and the light modulation system, and applies a magnetic field to the portion of the magneto-optical recording medium where the light beam is projected. The apparatus has the first electro-magnet, used for the magnetic field modulation system, for generating an a.c. magnetic field which is reversed at a high speed. The apparatus has the second electro-magnet, used for the light modulation system, for generating a strong d.c. magnetic field such that power consumption coincides with that of the first electro-magnet. The second electro-magnet is integral with the first electro-magnet. The apparatus has a driver for selecting one of the electro-magnets in response to a switching signal, and the driver supplies power to the selected electro-magnet.

Description: FIELD OF THE INVENTION The present invention relates to an external magnetic field generation apparatus for use in a magneto-optical recording and reproduction apparatus which records, reproduces, or erases information on or from a magneto-optical recording medium such as a magneto optical disk. BACKGROUND OF THE INVENTION Information is recorded on a magneto-optical recording medium as follows. Namely, a light beam is converged on the magneto-optical recording medium so as to become a light spot having a diameter of about 1 micron. As a result, the temperature of the portion of the magneto-optical recording medium on which the light spot is located rises up to a Curie point, thereby decreasing a coercive force of the portion. After that, a magnetic field is applied to the portion where the coercive force is decreased. A magnetization direction of the portion where the light spot is oriented according to the applied magnetic field and the recording of information thus performed. There are two kinds of systems for recording information like above based thereon, i.e., the light modulation system and the magnetic field modulation system. According to the light modulation system, information is recorded in the following manner: (1) erasure is performed by applying a magnetic field having a predetermined direction to the magneto-optical recording medium, this initialization operation causes all the recording area having the same magnetization direction as the applied magnetic field, and thereafter (2) information is recorded by applying a magnetic field having the opposite direction to the portion while changing an intensity of laser light according to desired recording information, thereby forming a predetermined recording bit on the magneto-optical recording medium. In contrast, according to the magnetic field modulation system, information is recorded in the following manner: a modulated magnetic field is applied to a portion of the magneto-optical recording medium where information is to be recorded, a direction of the modulated magnetic field being changed into the opposite direction in response to recording information, thereby forming a predetermined recording bit on the magneto-optical recording medium. A magnetic head for use in the light modulation system is required to generate a strong d.c. magnetic field from an N-pole and a S-pole of a magnet since, using the strong d.c. magnetic field from the N-pole and S-pole, information should be recorded twice on the same track for accuracy while tracing the desired track. Accordingly, a magneto-optical recording medium for use in the light modulation system which has a standard wherein a magnetic field between 200 0e and 300 0e should be used during recording is available in the market. In contrast, a magnetic head for use in the magnetic field modulation system is required to switch a modulated magnetic field at a high speed, i.e., in a short cycle of 10 ns order. The magnetic head is thus designed to have a low inductance. The magneto-optical recording medium for use in the magnetic field modulation system is, therefore, improved in the sensitivity for magnetic field in order to be able to record information with a magnetic field of about 150 0e, since the magnetic head having the low inductance can generate a low magnetic field of 100 0e to 200 0e. As discussed above, the functions required for the respective systems, i.e., a strong d.c. magnetic field for the light modulation system and switching the modulated magnetic field at a high speed for the magnetic field modulation system, conflict with each other. Namely, the magnetic head for use in the magnetic field modulation system cannot record information on the magneto-optical recording medium for use in the light modulation system because the intensity of the generated magnetic field from this head is too weak to record. Further, the magnetic head for use in the light modulation system cannot record information on the magneto-optical recording medium for use in the magnetic field modulation system because this head cannot reverse the modulated magnetic field at such a high speed. As discussed above, the magnetic head for one system cannot record information on the magneto-optical recording medium used for the other system. Therefore, two kinds of magnetic heads should be prepared in a single recording and reproduction apparatus in order that the single apparatus can record information based on the respective systems, thereby resulting in that the apparatus becomes massive. In order to meet the deficiency, external magnetic generation apparatuses which have respective complexed magnetic heads including both a magnetic head capable of generating a strong d.c. magnetic field and a magnetic head capable of switching a modulated magnetic field at a high speed, both magnetic heads being integrated with each other, are disclosed in the Japanese unexamined patent publications JP-A-3-216836 and JP-A-3-268253. With this arrangement, the apparatus can avoid being massive. However, in the respective external magnetic generation apparatuses disclosed in these publications, the magnetic heads of the complexed magnetic head differ in their power consumptions from each other. Accordingly, the external magnetic generation apparatus is required to have two drivers, i.e., one is for the magnetic field modulation system and the other is for the light modulation system, for supplying power to the corresponding magnetic head. Namely, two drivers are required for a single apparatus, thereby making it impossible for the apparatus to be a small size though the apparatus is required to be more compact. The Japanese unexamined patent publication JP-A-3-228201 discloses a magnetic field supply device for a magneto-optical recording apparatus, the device having two coils which can be driven individually or together according to whether magnetic field or optical modulation is desired in recording. SUMMARY OF THE INVENTION It is an object of the present invention to provide an external magnetic field generation apparatus which can further miniaturize a recording apparatus. The present invention provides the external magnetic field generation apparatus defined by claim 1 and the magneto-optical recording apparatus defined by claim 10. According to the invention, it is not necessary to have two power supply means, i.e., one power supply means associated with the magnetic field modulation system and another power supply means associated with the light modulation system. This is based on the fact that power consumption of the first magnetic field generation means coincides with that of the second magnetic field generation means, whereby a single power supply means can be used for recording of information based on the two systems. As a result, the apparatus is further miniaturized as compared with the case where the two power supply means corresponding to the respective modulation systems are provided. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 through 4 show one embodiment of the present invention wherein: Fig. 1 is a schematic explanatory diagram showing the structure of a magnetic head of the present invention; Fig. 2 is a schematic explanatory diagram showing the structure of a magneto-optical recording and reproduction apparatus of the present invention; Fig. 3 is a block diagram showing the configuration of a driver of the present invention; and Fig. 4 is an explanatory diagram showing the structure of another magnetic head of the present invention. DESCRIPTION OF THE EMBODIMENTS The following description describes one embodiment of the present invention with reference to Figs. 1 through 4. A magneto-optical recording and reproduction apparatus of the present embodiment, as shown in Fig. 2 for example, has (a) a motor 2 for rotating a magneto-optical disk 1 containing therein a magneto-optical recording layer 1a, (b) an optical pickup 3 for projecting a light beam onto the magneto-optical disk 1, and (c) an external magnetic field generation apparatus 6 for applying a magnetic field to the magneto-optical disk 1. The external magnetic field generation apparatus 6 is composed of (a) a complex magnetic head 4 which is opposite to the optical pickup 3 through the magneto-optical disk 1 and (b) a driver 5, connected to the complex magnetic head 4, for supplying power to the complex magnetic head 4. The optical pickup 3 is integral with the complex magnetic head 4 and moves to a radial direction of the magneto-optical disk 1. The optical pickup 3 has (a) an objective lens 3a for converging a light beam to the magneto-optical disk 1 and (b) an actuator (not shown) for moving the objective lens 3a in two axes. The actuator is arranged such that the objective lens 3a converges the light beam to a desired track of the magneto-optical disk 1 based on a servo control. The complex magnetic head 4 is mounted on a floating slider (not shown) for example and is arranged such that a magnetic field is applied to the portion where the light beam is converged. During applying of the magnetic field, a distance between the magneto-optical disk 1 and the complex magnetic head 4 is kept substantially constant. The driver 5 (power supply means) which supplies power to the complex magnetic head 4, as shown in Fig. 3, has (a) a pair of current output means, i.e., a first current output section 10a and a second current output section 10b, which are connected to a voltage source Vcc, (b) a current output switching section 16 (current output switching means) to which a recording signal is inputted, and (c) a magnet switching section 17 (magnet switching means) to which a switching signal is inputted. The first current output section 10a has a current source 11a, a resistor 12a, and a coil 13a. The second current output section 10b has a current source 11b, a resistor 12b, and a coil 13b. The current output switching section 16 has diodes 14a, 14b, and switches 15a, 15b which are switched in response to the recording signal. The diode 14a is connected to the first current output section 10a and is also connected to the ground through the switch 15a. The diode 14b is connected to the second current output section 10b and is also connected to the ground through the switch 15b. The recording signal is inputted to the switch 15a as a control signal for switching thereof, while the inverted recording signal by a inverter 18 (current output switching means) is inputted to the switch 15b as a control signal for switching thereof. The first and second current output sections 10a and 10b are respectively connected to the magnet switching section 17. The magnet switching section 17 has a pair of switches 17a and 17b by which the first and second current output sections 10a and 10b are connected from an electro-magnet 4a (first magnetic field generation means) to an electro-magnet 4b (second magnetic field generation means) or vice versa according to a switching signal. A common terminal of the switch 17a is connected to a connecting point between the coil 13a and the diode 14a. A common terminal of the switch 17b is connected to a connecting point between the coil 13b and the diode 14b. With the arrangement, a current is supplied to one of the common terminals of the switches 17a and 17b from one of the first and second current output sections 10a and 10b according to the recording signal and the inverted recording signal, and the other common terminal of the switches 17a and 17b is connected to the ground. One of the output terminals of the switch 17a and a corresponding output terminal of the switch 17b are respectively connected to ends of a lead wire of the electro-magnet 4a (used for the magnetic field modulation system) of the complex magnetic head 4. The other output terminals of the switch 17a and the switch 17b are respectively connected to ends of a lead wire of the electro-magnet 4b (used for the light modulation system) of the complex magnetic head 4. With the arrangement, the magnet switching section 17 can select one of the electro-magnet 4b for the light modulation system and electro-magnet 4a for the magnetic field modulation system in accordance with the switching signal. Accordingly, the driver 5 can apply a modulated magnetic field having a direction in accordance with the recording signal to the recording portion of the magneto-optical recording layer 1a when the electro-magnet 4a is selected in response to the switching signal and when the recording signal is arranged so as to correspond to the information to be recorded on the magneto-optical disk 1, thereby enabling to record the information based on the magnetic field modulation system. It is also possible to record information based on the light modulation system when the electro-magnet 4b is selected in response to the switching signal and the driver 5 reverses the magnetic field according to the recording signal indicating an erasing or recording phase. The driver 5 defined as above is arranged such that a signal associated with the recording signal is amplified and a current of hundreds of milliamperes (mA) is outputted and is also arranged such that an output current is reversed within tens of nanoseconds (ns) when the electro-magnet 4b has an inductance of a few microhenries (µ H). The driver 5 is further arranged so as to output substantially the same amplitude of current. This is based on the fact that the driver 5 has a frequency characteristic over the wide-band from d.c. frequency to the modulated frequency. Namely, tens of microseconds (µ s) are required as the rise time of the output current since the frequency band of the output current is likely to decrease in proportion to the increase of the inductance of the electro-magnet 4b. In contrast, the current in the range of d.c. frequency is not changed in its amplitude. The complex magnetic head 4 which is connected to the driver 5, as shown in Fig. 1, has both the electro-magnet 4a for the magnetic field modulation system and the electro-magnet 4b for the light modulation system, wherein the electro-magnet 4a is designed to consume the same power as the electro-magnet 4b. The complex magnetic head 4 has an U-shaped magnetic core 7 of high permeability which is made of Mn-Zn ferrite for example, and is arranged such that lead wires are wound around respective ends of the magnetic core 7, thereby defining the respective electro-magnets 4a and 4b. Note that the lead wire associated with the electro-magnet 4b is designed so as to have the same resistance as the lead wire associated with the electromagnet 4a by adjusting the respective wire lengths and the respective wire diameters. In the concrete, the electro-magnet 4a is defined by winding by 20 turns around one end of the magnetic core 7 with a lead wire having a diameter of 70 micron (µ m). The electro-magnet 4b is defined by winding by 32 turns around the other end of the magnetic core 7 with a lead wire having a diameter of 90 micron (µ m), thereby coinciding with the resistance of the electro-magnet 4a. The electro-magnet 4a defined by 20 turns of the lead wire having a diameter of 70 micron (µ m) has inductance L 1 of 2 µ H. The electro-magnet 4b defined by 32 turns of the lead wire having a diameter of 90 micron (µ m) has inductance L 2 of 5 µ H. Inductance L 2 is 2.5 times as large as inductance L 1 though both resistances are equal with each other. When recording information on the magneto-optical disk 1 is performed based on the magnetic field modulation system by using the magneto-optical recording and reproduction apparatus having the above-mentioned external magnetic field generation apparatus, the electro-magnet 4a is first connected to the driver 5 in response to the switching signal. Then, the light beam having a constant intensity is projected onto the magneto-optical disk 1 from the optical pickup 3 and the magnetic field from the electro-magnet 4a is reversed according to the recording signal, thereby perfoming the recording of information. At this time, the driver 5 can drive a reversed current of ± 200 mA in a period of 20 ns within the frequency range of about 10 Mhz, and the complex magnetic head 4 can generate ± 160 0e. In contrast, when recording information on the magneto-optical disk 1 is performed based on the light modulation system, the electro-magnet 4b is connected to the driver 5. Then, the electro-magnet 4b applies a constant magnetic field to the magneto-optical disk 1 while changing the intensity of the light beam in accordance with the recording signal, thereby perfoming the recording of information. At this time, the electro-magnet 4b can generate a d.c. magnetic field of ± 250 0e for example according to the current of ± 200 mA from the driver 5, and the rise time of the magnetic field from 0 0e to ± 250 0e can be about tens of µ s. With the arrangement, the current outputted from a single driving source (driver 5) to the electro-magnets 4a and 4b is switched by the magnet switching section 17, and the current is applied to either the electro-magnet 4b or the electro-magnet 4a, since the power consumption of the electro-magnet 4a is equal to that of the electro-magnet 4b and one of the electro-magnets 4a and 4b can be selected according to the usage by only supplying the switching signal to the magnet switching section 17. When reproduction of the recorded information from the magneto-optical disk 1 by using the magneto-optical recording and reproduction apparatus, a light beam of low intensity from the optical pickup 3 is projected onto the magneto-optical disk 1. Reproduction is performed based on the reflected light beam from the magneto-optical disk 1 by using the magneto-optical effect. The complex magnetic head 4, as shown in Fig. 4, is preferably arranged such that a magnetic core 8 is wound with a lead wire having a diameter of 70 µ m to define an inner electro-magnet, i.e., an electro-magnet 4c and this magnetic core 8 is further wound with a lead wire having a diameter of 90 µ m to define an outer electro-magnet, i.e., an electro-magnet 4d. Note that the magnetic core 8 is formed around the electro-magnet 4d. In addition, the magnetic field can be changed by adjusting the winding turns of the lead wire in accordance with the embodiment, but the magnetic field can also be changed by controlling the driver 5 such that the driving current of the driver 5 changes in its amplitude. In the external magnetic field generation apparatus of the invention it is not necessary to have two drivers for supplying power to the respective electro-magnets 4a and 4b, i.e., one driver associated with the magnetic field modulation system and the other driver associated with the light modulation system. This is based on the fact that power consumption of the electro-magnet 4a coincides with that of the electro-magnet 4b. Accordingly, a single power supply means can be used for recording information based on the two systems in accordance with the present external magnetic field generation apparatus, thereby miniaturizing the driver more than the case where the two drivers corresponding to the respective modulation systems are provided. The present recording and reproduction apparatus, thus, can be miniaturized as a whole.

Claims: An external magnetic field generation apparatus for use in a recording apparatus which records information on a magneto-optical recording medium (1) based on a magnetic field modulation system and a light modulation system, said external magnetic field generation apparatus applying a magnetic field to a portion of the magneto-optical recording medium where a light beam is projected, and comprising: first magnetic field generation means (4a;4c) for generating an a.c. magnetic field which is reversed at a high speed, said first magnetic field generation means being used for the magnetic field modulation system; and second magnetic field generation means (4b;4d) for generating a strong d.c. magnetic field, said second magnetic field generation means being integral with said first magnetic field generation means, said second magnetic field generation means being used for the light modulation system; characterized by: the power consumption of said first magnetic field generation means (4a) being substantially the same as that of said second magnetic field generation means (4b); and a single power supply means (5, 16, 17, 18) for selectively supplying power to one of said first magnetic field generation means (4a) and said second magnetic field generation means (4b) in response to a switching signal. The external magnetic field generation apparatus as set forth in claim 1, wherein said first and second magnetic field generation means (4a,4b) are defined by respective windings of first and second lead wires around a magnetic core (7;8) of high permeability, and said first lead wire associated with said first magnetic field generation means has the same resistance as said second lead wire associated with said second magnetic field generation means by adjusting the respective wire lengths and wire diameters. The external magnetic field generation apparatus as set forth in claim 2, wherein said first magnetic field generation means (4a) is defined by a winding around one end of said magnetic core (7) of said first lead wire, and said second magnetic field generation means (4b) is defined by a winding around the other end of said magnetic core (7) of said second lead wire. The external magnetic field generation apparatus as set forth in claim 2 or claim 3, wherein said magnetic core is made of Mn-Zn ferrite. The external magnetic field generation apparatus as set forth in claim 1, wherein said first magnetic field generation means (4c) is defined by a winding of a first lead wire around a magnetic core (8), and said wound magnetic core (8) is further wound with a second lead wire (4d). The external magnetic field generation apparatus as set forth in any preceding claim, wherein said power supply means (5) includes: first and second current output means (10a,10b) connected to a voltage source, for outputting predetermined currents respectively; current output switching means (16,18) for permitting one of said pair of current output means to output the predetermined current while connecting the other current output means to ground, in response to a recording signal; and magnet switching means (17) for selecting one of said first and second magnetic field generation means (4a,4b;4c,4d) in response to a switching signal, and for connecting ends of the lead wire of said selected magnetic field generation means to respective outputs of said pair of current output means. The external magnetic field generation apparatus as set forth in claim 6, wherein each said current output means (10a,10b) includes a current source (11a,11b), a resistor (12a,12b), and a coil (13a,13b), these elements being connected in series. The external magnetic field generation apparatus as set forth in claim 7, wherein said current output switching means (16,18) includes: first and second diodes (14a,14b) connected to said respective first and second current output means; a first switch (15a), which is opened or closed in response to the recording signal, for connecting said first current output means to ground through said first diode during closing; an inverter circuit means (18) for outputting a reversed recording signal upon reception of the recording signal; and a second switch (15b), which is opened or closed in response to the inverted recording signal, for connecting said second current output means to ground through said second diode during closing. The external magnetic field generation apparatus as set forth in claim 8, wherein: said magnet switching means (17) includes third and fourth switches (17a,17b) for switching in response to the switching signal, each switch (17a,17b) having first and second output terminals; a common terminal of said third switch (17a) is connected to a connecting point between said first current output means (10a) and said current output switching means (16) while a common terminal of said fourth switch (17b) is connected to a connecting point between said second current output means (10b) and said current output switching means (16); and said respective first output terminals of said third and fourth switches (17a,17b) are connected to said first magnetic field generation means (4a) while said respective second output terminals of said third and fourth switches (17a,17b) are connected to said second magnetic field generation means (4b). A magneto-optical recording apparatus capable of performing recording operations selectively according to the so-called magnetic field modulation method and the so-called light modulation method, the apparatus including an external magnetic field generation apparatus according to claim 1.

Inventors: ISHII MITSUO, MIYAKE TOMOYUKI, ISHII, MITSUO, MIYAKE, TOMOYUKI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1992
Main classification: G11B11
IPC codes: G11B11, G11B5