Magneto-optical recording apparatus

Abstract: A magneto-optical recording apparatus includes an actuator for driving an objective lens for focusing a light beam on a magneto-optical disk to effect focusing and tracking, a magnetic head for applying a magnetic field to a portion irradiated by the light beam on the magneto-optical disk, which has a substantially U-shaped core with a main pole facing the magneto-optical disk and an opposed pole opposed thereto, and a linear motor for performing a seek operation to move the objective lens and magnetic head in a radial direction of the magneto-optical disk. In an embodiment, a direction of a composite field of leaking fields from the actuator and from the linear motor is substantially parallel to a diagonal line connecting between a corner of the opposed pole of the core near the magneto-optical disk and a corner located diagonal thereto. The apparatus may be so arranged in another embodiment that leaking fields from the actuator and from the linear motor cancel each other with respect to parallel components to the magneto-optical disk near the magnetic head.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a magneto-optical recording apparatus operated in the magnetic modulation method. Related Background Art There are heretofore well known magneto-optical recording apparatus which can record information signals in a magneto-optical disk by the magnetic modulation method. Fig. 1 shows the schematic construction of a conventional magneto-optical recording apparatus of such type. In Fig. 1, reference numeral 1 designates a disk, 2 an optical head, and 3 a magnetic head. The magnetic head 3 is a floating magnetic head provided with a slider, which is held above the upper surface of disk 1 by a load beam 6. Also, the magnetic head 3 is incorporated with the optical head 2 located below the lower surface of disk 1 through a connecting member 4 so that a linear motor 5 may drive to move them in the radial direction of disk 1. The disk 1 is rotated by a spindle motor 7. The optical head 2, the magnetic head 3 and the linear motor 5 will be further detailed in the following. Fig. 2 illustrates the optical head 2 and the linear motor 5 as the top plan view thereof. Also, Fig. 3 shows cross sections of the optical head 2, the magnetic head 3, the disk 1 and the linear motor 5 (along the radial direction of disk). The optical head 2 has an unrepresented laser source, which emits a light beam. The objective lens 103 focuses the light beam to form a fine spot on a recording layer la in the disk 1. Focusing coils 105 and tracking coils 104 are mounted on a lens holder 107 for holding the objective lens 103 in a supported state by plate springs 108. When a current is supplied to the tracking coils 104 and the focusing coils 105, a magnetic force acts between the coils and actuator magnets 109 or actuator yokes 106 fixed on a base 100. The magnetic force moves the objective lens to scan the beam thereby so that the fine spot may accurately trace a recording track formed on the recording layer la in disk 1, performing so-called tracking operation and focusing operation. The thus arranged actuator is mounted on a carriage 101. The linear motor 5 is constructed of linear motor yokes 200 to each of which a linear motor magnet 201 is attached, guides 203, and linear motor coils 202 attached to the carriage 101 for the actuator. When a current is supplied to the linear motor coils 202, a magnetic force acts between the coils and the linear motor magnets 201 or the linear motor yokes 200. The magnetic force moves the carriage 101 in the radial direction of disk 1 to perform the seek operation. The carriage 101 is arranged to move on the guide rails 203 through rollers 102. The magnetic head 3 is composed of a U-shaped core 3a made of a magnetic material, a coil 3b wound around a main pole of the core 3a, and a slider 3c made of a hard material such as ceramics. In this case, the main pole and opposed pole of core 3a are arranged to face the disk. In recording an information signal, a current modulated according to the information signal is supplied to the coil 3b in magnetic head 3, whereby a bias field modulated according to the information signal is applied from the main pole to the recording layer la in disk 1 in the direction normal thereto. As described above, the optical head 2 focuses the light beam to form a fine spot irradiating a region to which the bias field is applied on the recording layer 1a. The temperature increases in the portion irradiated by the light beam in the recording layer la to suddenly decrease the coercive force therein. Then magnetization is recorded corresponding to the direction of applied bias field. As the disk is further rotated, the thus magnetized portion leaves the irradiated portion by the light beam, whereby the temperature again decreases. With the temperature decrease, the coercive force suddenly increases to maintain the recorded magnetization. In this manner, information is recorded in a pattern of magnetization corresponding to the information signal. As described above, electromagnetic drive means is used in general as the actuator or the linear motor for optical head in magneto-optical recording apparatus. In this arrangement, magnetism could leak from magnets in the drive means, and the leaking magnetism sometimes acts near the magnetic head in recording the information signal. It was pointed out heretofore as a problem that such leaking field had components in the direction perpendicular to the disk which was added as offset to the modulated field generated by the magnetic head and that poor signal recording could result if the recording of information signal was carried out in the state that the field with offset was applied to the disk. A solution to this problem was already proposed (as in Japanese Laid-open Patent Application No. 3-259444). Inventors investigated such problem in detail and found that influence was greater on the disk from a magnetic field caused by magnetization induced inside the core in the leaking field rather than the direct effect of the leaking field itself on the disk, for some shapes of core. In addition, according to the investigation by Inventors, in case a core asymmetric in shape with respect to the main pole is employed, such as the substantially U-shaped core as described above, the poor signal recording is caused not only by the perpendicular components of the leaking field acting near the magnetic head to the disk but also by the magnetization induced inside the core by horizontal components. This will be described referring to Fig. 4 and Fig. 5. Fig. 4 shows a case in which a pair of actuator magnets 109 and a pair of linear motor magnets 201 are arranged with opposed faces being opposite magnetic poles (i.e., such that N-pole of right magnet 109b or 201b is opposed to S-pole of left magnet 109a or 201a), in which broken lines represent schematic lines of magnetic force of leaking fields from the magnets. Fig. 5 is an enlarged drawing to show the state of the leaking fields near the core 3a in the magnetic head shown in Fig. 4. When the arrangement of magnets as shown is employed, the direction of leaking fields as shown by broken lines is parallel to the disk 1 in the vicinity of the core 3a but there are little perpendicular components to the disk 1. In such leaking fields, magnetization is induced inside the core 3a while distributed on the sides of main pole 3mp and opposed pole 3sp as shown by signs + and - in Fig. 5. A magnetic field caused by this magnetization has lines of magnetic force as shown by solid lines in Fig. 5, which leave the ends of main pole 3mp of core 3a and reach the ends of the opposed pole 3sp. This magnetic field acts in the perpendicular direction to the portion irradiated by the light beam in the recording layer la in disk 1 immediately below the main pole 3mp. Consequently, even if the leaking fields from the actuator magnets and from the linear motor magnets have only the parallel components but no perpendicular components to the disk, the magnetic field caused by the magnetization of core acts also in the perpendicular direction to the disk, which is added as offset in recording the information signal and therefore could be a cause of the poor signal recording. The above phenomenon appears outstanding if the shape of core is asymmetric with respect to the main pole. Actually, the shape of core is not symmetric with respect to the main pole in most cases because of issues in production. For example, the core is usually formed approximately in a U shape, as shown, including a ring head. Therefore, such problem is very serious. Here, if the main pole and the opposed pole in the approximately U-shaped core are aligned in the tangential direction of disk as in the above example, the above problem is rarely caused by a radial component on the disk (which is a component perpendicular to the plane of Fig. 4 or Fig. 5) among the parallel components to the disk in the leaking field. The above problem is mainly caused by a tangential component to the disk (which is a parallel component to the plane of Fig. 4 or Fig. 5). JP-A-3-295004 reflecting the preamble of the appended independent claim discloses a magneto-optical recording apparatus of the type described above including an actuator for driving an objective lens and a linear motor for moving the objective lens and a magnetic head in a direction parallel to a magneto-optical recording medium. The magnetic head is constituted by an electromagnet in the form of a coil surrounding a core. The magnets of the linear motor are arranged such that the reverse poles of the magnets oppose each other such that the respective magnetic fields are in the same direction, thereby forming a closed magnetic path. US-A-4939711 also discloses a magneto-optical recording apparatus of the type described above. The magnetic circuits of the actuator and the linear motor are arranged such that the magnetic fields are directed in mutually opposite directions in the region of the irradiated portion of the magneto-optical recording medium. This enables cancellation of the leakage magnetic field. SUMMARY OF THE INVENTION The present invention has been accomplished taking the above points into consideration. According to the present invention, there is provided a magneto-optical recording apparatus comprising an actuator for driving an objective lens for focusing a beam of radiation on a magneto-optical medium; a magnetic head for applying a magnetic field to the irradiated portion of said magneto-optical medium, a linear motor for moving the objective lens and magnetic head in a direction parallel to said magneto-optical medium; the apparatus being characterised in that said magnetic head has a substantially U-shaped core comprising two leg portions arranged, in use of the apparatus, to face the medium, and a connecting portion remote from the medium; are leg portion forming a main pole arranged to face the irradiated portion of the magneto-optical medium and the other leg portion forming an opposed pole; and the direction of the composite field in the vicinity of the core produced by leaking fields from said actuator and from said linear motor is substantially parallel to the diagonal line connecting a corner of one of the leg portions of said core which are arranged to face said magneto-optical medium and the edge portion of the portion of the core located diagonally to said corner. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a drawing to show the schematic construction of a magneto-optical recording apparatus; Fig. 2 is a drawing to show the detailed construction of actuator, linear motor and magnetic head; Fig. 3 is a drawing to show the detailed construction of actuator, linear motor and magnetic head; Fig. 4 is a drawing to show the scheme of leaking fields in a conventional magneto-optical recording apparatus; Fig. 5 is an enlarged drawing near the core in Fig. 4; Fig. 6 is a drawing to show the scheme of leaking fields in a magneto-optical recording apparatus in an embodiment of the present invention; Fig. 7 is an enlarged drawing near the core in Fig. 6; Fig. 8 is a drawing to show the scheme of leaking fields in a magneto-optical recording apparatus in another embodiment of the present invention; and Fig. 9 is an enlarged drawing near the core in Fig. 8. DESCRIPTION OF THE PREFERRED EMBODIMENTS The magneto-optical recording apparatus of the present invention will be described in detail with reference to embodiments as shown in Fig. 6 to Fig. 9. Fig. 6 shows an example in which a pair of actuator magnets 109 are arranged to have mutually opposed faces as same magnetic poles (N-poles opposed to each other in the present embodiment) and a pair of linear motor magnets 201 are arranged to have mutually opposed faces as different magnetic poles (N-pole of right magnet 201b and S-pole of left magnet 201a opposed to each other in the present embodiment), in which broken lines show approximate lines of magnetic force of leaking fields. As shown in Fig. 6, a leaking field from the actuator magnets 109 is perpendicular to the disk 1 near the core 3a in a magnetic head (as directed upward) and a leaking field from the linear motor magnets 201 is parallel to the disk 1 near the core 3a in the magnetic head (as directed from right to left). Consequently, a composite field of the leaking fields from the actuator magnets 109 and from the linear motor magnets 201 is oblique from right bottom to left top, as shown in Fig. 7 (which shows an enlarged state near the core 3a). The point here is that the direction of the composite field is approximately parallel to a diagonal line A connecting between a bottom corner of opposed pole 3sp of core 3a and a top corner located diagonal thereto in the core 3a. In such leaking fields, magnetization is induced inside the core 3a as distributed as shown by signs - and + in Fig. 7 near the corner of opposed pole 3sp and near the corner located diagonal thereto. This magnetization produces a magnetic field with lines of magnetic force as shown by the solid lines in Fig. 7, which are concentrated near the corner of opposed pole 3sp and near the corner located diagonal thereto where the above magnetization is distributed. Further, the magnetization produces no magnetic field at the free end of main pole 3mp where the magnetization distribution is rare. In this arrangement, even if the actuator magnets and the linear motor magnets produce the leaking fields perpendicular and parallel to the disk, there is no magnetic field acting as offset in the irradiated portion by the light beam on the disk in recording an information signal, which enables excellent information recording accordingly. Next described is another example of arrangement of actuator magnets and linear motor magnets. Fig. 8 shows an example in which a pair of actuator magnets 109 are arranged to have mutually opposed faces as different magnetic poles (S-pole of right magnet 109b and N-pole of left magnet 109a opposed to each other in the present embodiment) and a pair of linear motor magnets are arranged to have mutually opposed faces as same magnetic poles (S-poles opposed to each other in the present embodiment), in which broken lines represent approximate lines of magnetic force of leaking fields. As shown in Fig. 8, a leaking field from actuator magnets 109 is parallel to the disk 1 near the core 3a in magnetic head (as directed from left to right) and a leaking field from linear motor magnets 201 is perpendicular to the disk 1 near the core 3a in magnetic head (as directed downward). Consequently, a composite field of the leaking fields from the actuator magnets 109 and from the linear motor magnets 201 is oblique from left top to right bottom as shown in Fig. 9 (which shows an enlarged state near the core). Also in this example, similarly as in the previous embodiment, the direction of the composite field is approximately parallel to a diagonal line A connecting between the bottom corner of opposed pole 3sp of core 3a and the top corner located diagonal thereto. In such leaking fields, magnetization is induced inside the core 3a as distributed as shown by signs + and - in Fig. 9 near the bottom corner of opposed pole 3sp and near the top corner located diagonal thereto. This magnetization produces a magnetic field having lines of magnetic force as shown by the solid lines in Fig. 9, which are concentrated near the corner of opposed pole 3sp and near the corner located diagonal thereto where the above magnetization is distributed. There is no magnetic field produced at the free end of magnetic pole 3mp where the magnetization distribution is rare. In this arrangement, even if the actuator magnets and the linear motor magnets produce the leaking fields parallel and perpendicular to the disk, there is no magnetic field acting as offset in the irradiated portion by the light beam on disk in recording an information signal, thus enabling excellent information recording. In the above embodiments, the important point is that the direction of composite field of leaking fields from the actuator magnets and from the linear motor magnets is substantially parallel to the diagonal line connecting between the corner of opposed pole 3sp and the corner located diagonal thereto in the vicinity of the core in magnetic head, but it is inessential whether the direction of magnetic field is directed from left top to right bottom or from right bottom to left top. Therefore, the embodiment shown in Fig. 6 may be modified such that the S-poles in the actuator magnet 109 are arranged to be opposed each other, and the S-pole of the right magnet 201b in the linear motor magnet 201 is opposed to the N-pole of the left magnet 201a in the linear motor magnet 201. Also, the embodiment shown in Fig. 8 may be modified such that the N-poles in the linear motor magnet 201 are mutually opposed and the N-pole of the right magnet 109b in the actuator magnet 109 is opposed to the S-pole of the left magnet 109a in the actuator magnet 109. In respect of the effect, the optimum direction of composite field is not always parallel to the diagonal line connecting between the corner of opposed pole and the corner located diagonal thereto. The optimum direction of field is related to the shape of core and should be considered to drop within the range of about ±30° with respect to the diagonal line. For example, in case a ratio of height to width of core is 1:1, the optimum direction of composite field of leaking fields is about 20° closer to the disk than the diagonal line, approaching the parallel direction to the disk (whereby the incident angle of magnetic field is about 25° to the disk). For reference, if the direction of composite field of leaking fields were approximately parallel to the other diagonal line connecting between a corner of main pole of core and a corner located diagonal thereto, different from the arrangement in the present invention, magnetization would be induced at the distal end of main pole where lines of magnetic force of produced magnetic field are concentrated. Therefore, this arrangement should be avoided in designing. It should be noted that the construction of actuator and linear motor as described was shown as an example and that the arrangement of the present invention can be applicable to any of various conventional constructions of actuator and linear motor. Specifically, the invention can be applied to an example employing an actuator and a linear motor each having at least a pair of permanent magnets located on the both sides of magnetic head. This example has a great degree of freedom in designing. Further, the example permits the permanent magnets to be properly arranged in position, whereby such an arrangement can be easily achieved that one pair of permanent magnets produce a leaking field approximately parallel to the disk near the magnetic head while another pair of permanent magnets produce a leaking field approximately perpendicular to the disk near the magnetic head and that a composite field of the leaking fields produced by the two pairs of permanent magnets is approximately parallel to a diagonal line connecting a corner of opposed pole of core and a corner located diagonal thereto near the magnetic head. As described above, according to the present invention, a magneto-optical recording apparatus comprises an actuator for electromagnetically driving an objective lens for focusing a light beam to form a fine spot on a magneto-optical disk so as to effect focusing and tracking, a magnetic head for applying a magnetic field to a portion irradiated by the light beam on the magneto-optical disk, and a linear motor for electromagnetically driving the objective lens and the magnetic head in a united or synchronized manner to effect the seek operation in the radial direction of magneto-optical disk, in which the magnetic head is provided with a substantially U-shaped core having a main pole facing the magneto-optical disk and an opposed pole opposed to the main pole and in which a direction of a leaking field produced by the actuator and the linear motor is substantially parallel near the magnetic head to a diagonal line connecting between a corner of the opposed pole of the core and a corner located diagonal thereto. Therefore, the leaking fields do not induce magnetization at the distal end of main pole of core, so that there is no magnetic field acting as offset in the irradiated portion by the light beam on disk in recording the information signal, thus enabling excellent information recording. In the embodiments as shown in Fig. 6 to Fig. 9, a requirement is that a composite field of the leaking field from the actuator magnets and the leaking field from the linear motor magnets is oblique in the vicinity of core 3a. Therefore, depending upon the strength of each leaking field, a combination of two leaking fields could be different from the combination of the perpendicular leaking field and parallel leaking field. Also, although the above embodiments employed the substantially U-shaped magnetic head, the present invention is of course applicable to apparatus employing a ring head with a gap provided in a part of magnetic path.

Claims: A magneto-optical recording apparatus comprising: an actuator (106) for driving an objective lens (103) for focusing a beam of radiation on a magneto-optical medium (1); a magnetic head (3) for applying a magnetic field to the irradiated portion of said magneto-optical medium (1), a linear motor (5) for moving the objective lens (103) and magnetic head in a direction parallel to said magneto-optical medium (1); the apparatus being characterised in that: said magnetic head has a substantially U-shaped core (3a) comprising two leg portions arranged, in use of the apparatus, to face the medium (1), and a connecting portion remote from the medium (1), one leg portion forming a main pole (3mp) arranged to face the irradiated portion of the magneto-optical medium and the other leg portion forming an opposed pole (3SP); and the direction of the composite field in the vicinity of the core (3a) produced by leaking fields from said actuator (106) and from said linear motor (5) is substantially parallel to the diagonal line connecting a corner of one of the leg portions of said core (3a) which are arranged to face said magneto-optical medium (1) and the edge portion of the portion of the core (3a) located diagonally to said corner. A magneto-optical recording apparatus according to Claim 1, wherein each of said actuator (106) and linear motor (5) has a pair of permanent magnets (109a, 109b; 201a, 201b) and wherein said permanent magnets (109a, 109b; 201a, 201b) are arranged such that in use of the apparatus the leaking field caused by one of the pairs of permanent magnets is substantially parallel to the portion of the surface of the magneto-optical medium (1) which faces said magnetic head (3) and such that the leaking field caused by the other of the pairs of permanent magnets is substantially perpendicular to the portion of the surface of the magneto-optical medium (1) which faces said magnetic head (3). A magneto-optical recording apparatus according to Claim 2, wherein the pair of permanent magnets in one of the actuator (106) and the linear motor (5) have corresponding poles facing each other, and the pair of permanent magnets in the other of the actuator (106) and the linear motor (5) have mutually opposite poles facing each other. An apparatus according to Claim 3, wherein the pair of permanent magnets (109a, 109b) in said actuator (106) have N-poles facing each other, and the pair of magnets in said linear motor (5) have a N-pole and a S-pole facing each other, wherein the N-pole of said linear motor (5) is located closer to said opposed pole (3sp) of the core (3a) than to the main pole (3mp) of the core (3a). A magneto-optical recording apparatus according to Claim 3, wherein the pair of permanent magnets (109a, 109b) in said actuator (106) have a N-pole and a S-pole facing each other, and the pair of magnets (201a, 201b) in said linear motor (5) have S-poles facing each other, wherein the S-pole of said actuator (106) is located closer to said opposed pole (3sp) of the core (3a) than to the main pole (3mp) of the core (3a). A magneto-optical recording apparatus according to Claim 3, wherein the pair of permanent magnets (109a, 109b) in the actuator (106) have S-poles facing each other, and the pair of magnets (201a, 201b) in the linear motor (5) have a N-pole and a S-pole facing each other, wherein the S-pole of the linear motor (5) is located closer to said opposed pole (3sp) of the core (3a) than to the main pole (3mp) of the core (3a). A magneto-optical recording apparatus according to Claim 3, wherein the pair of permanent magnets (109a, 109b) in the actuator (106) have a N-pole and a S-pole facing each other, and the pair of magnets (201a, 201b) in the linear motor (5) have N-poles facing each other, wherein the N-pole of said actuator (106) is located closer to said opposed pole (3sp) of the core (3a) than to the main pole (3mp) of the core (3a). A magneto-optical recording apparatus according to any one of the preceding claims wherein no magnetisation is induced in a portion of said other leg portion of the core (3a) arranged to face the magneto-optical recording medium due to said leaking fields. A magneto-optical recording apparatus according to any one of the preceding claims wherein the magneto-optical recording medium is a magneto-optical disc, and the linear motor (5) is arranged to move the objective lens (103) in a radial direction of said magneto-optical disc.

Inventors: ISHII KAZUYOSHI, ISHII, KAZUYOSHI, ISHII, KAZUYOSHI, C/O CANNON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G11B11
IPC codes: G11B5, G11B11