JPH0616322B2 - Bias magnetic field generator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias magnetic field generator used in a magneto-optical recording / reproducing apparatus used in an external storage device of an electronic computer, music and video signals, and other information recording / reproducing apparatus. It is a thing.

2. Description of the Related Art In recent years, along with the development of electronic computers and the means of high-speed mass transmission of information, there has been a demand for a low cost, high-density, large-capacity, and high-speed transmission permanent recording apparatus. However, there are problems that the recording density is low, the price per information unit is high, and the medium cannot be exchanged. Optical recording is currently in the spotlight as a technique for solving these problems, and rewritable magneto-optical recording is expected in many fields.

The conventional bias magnetic field generator has a length that covers the access range of the optical head and has a uniform magnetic gap width in the access direction of the optical head (for example, Japanese Patent Laid-Open No. 59-119507). .

Hereinafter, the conventional bias magnetic field generator as described above will be described with reference to the drawings.

FIGS. 4, 5, and 6 show a conventional bias magnetic field generator. FIG. 4 shows an arrangement in a magneto-optical recording / reproducing apparatus, FIG. 5 shows its structure, and FIG. 6 shows a bias magnetic field. 4 shows the flow of magnetic flux generated by the generator.

In FIGS. 4 to 6, 1 is a magneto-optical recording medium, 2 is an optical head, which is designed to be accessed in the direction of arrow A in FIG. 4, and the light spot emitted from the objective lens 3 is magneto-optical. A mechanism for controlling to focus on the recording surface of the recording medium 1, a laser light source necessary for emitting the light spot, and an optical system for guiding the laser light to the objective lens 3 are built in. Reference numeral 4 denotes a bias magnetic field generator for applying a vertical magnetic field required for recording and erasing information to the magneto-optical recording medium 1, which is arranged at a position facing the optical head 2 with the magneto-optical recording medium 1 interposed therebetween. A bar-shaped center yoke 5 having a length sufficient to cover the access area of the optical head 2 along the access direction of the optical head 2, and an exciting coil 7 and a center yoke 5 wound around the center yoke 5. It is composed of a channel-shaped outer yoke 6 that is surrounded. Further, the tip end surface of the center yoke 5 and the tip end surface of the outer yoke 6 facing the medium are on the same plane, and the magnetic gap width Lg at the tip surface is uniform in the entire cross section perpendicular to the A direction, and is separated by a distance d. It faces the magneto-optical recording medium 1 in parallel.

The operation of the bias magnetic field generator configured as described above will be described below.

First, when the exciting coil 7 is energized, as shown in FIG. 6, a magnetic flux φ is generated in the magnetic path formed by the center yoke 5 and the outer yoke 6.
Flow through the magneto-optical recording medium 1 as shown. At this time, if the distance d is made sufficiently small, a magnetic field of a component perpendicular to the magneto-optical recording medium 1 can be sufficiently given. In this state, information is recorded by applying a light spot corresponding to information to the magneto-optical recording medium 1 from the optical head 2 through the objective lens 3. At the time of erasing, the direction of the magnetic field is reversed to give a light spot.

Further, since the center yoke 5 has a length enough to cover the access range of the optical head 2, no matter where the optical head 2 in the direction of arrow A in FIG. It is possible to obtain a strong magnetic field.

Problems to be Solved by the Invention However, the above-mentioned method has the following problems. That is, as in the conventional example shown in FIG. 5, in the bias magnetic field generator in which the air gap magnetic flux width Lg is uniform over the entire cross section perpendicular to the access direction of the optical head, the magnetic field strength in the access direction of the optical head on the medium is increased. As shown in FIG. 7, the distribution takes a maximum value at points P and Q near both ends of the access range of the optical head, and a minimum value at a central point O.
The phenomenon that the magnetic field strength becomes large at both ends is due to magnetic leakage from the center yoke 5 to the base portion of the outer yoke 6 at both ends in the direction of arrow A in FIG. 5 of the bias magnetic field generator. Therefore, in the bias magnetic field generating device as in the conventional example, it is necessary to pass a current enough to obtain the minimum magnetic field strength required for the recording and erasing, at the central point O which is the least efficient. On the other hand, at both ends P and Q, an unnecessarily large magnetic field is applied to the medium. Such an excessive bias magnetic field increases the diameter of the information pit formed on the medium at the time of recording and affects adjacent pits, and deteriorates the reliability of information.

Conventionally, as a method for solving these problems, the magnetic field strength on the medium is estimated by the output of a sensor provided on the optical head side, the current of the exciting coil is closed-loop controlled, the known magnetic field strength distribution and the optical head A method of controlling the current of the exciting coil based on the current position was used, but it had a drawback that the system was complicated.

In view of the above problems, the present invention provides a bias magnetic field generator capable of giving a magnetic field whose magnetic field intensity on the magneto-optical recording medium is substantially constant over the access range of the optical head.

Means for Solving the Problems In order to achieve this object, a bias magnetic field generating device of the present invention is arranged at a position facing an optical head with a magneto-optical recording medium sandwiched therebetween, and a magnetomotive force source such as an exciting coil, A main magnetic pole and an auxiliary magnetic pole magnetically coupled to each magnetic pole of the magnetomotive force source are provided, and the main magnetic pole has a main magnetic pole facing surface having a length equal to or greater than an access range and facing substantially parallel to the magneto-optical recording medium. Then, the gap between the ridgeline of the main pole facing surface and the auxiliary pole ridgeline provided on the surface facing the magneto-optical recording medium is defined as the magnetic gap width, and the magnetic gap width corresponds to the midpoint of the access range within the access range of the optical head. It is configured so that it is the narrowest at the position where it is turned on, and becomes wider as it goes away from the position corresponding to the midpoint along the access direction of the optical head.

With this configuration, the present invention can reduce the component of the magnetic field in the access direction of the optical head at a position distant from the center of the access range of the optical head by expanding the magnetic gap width. The magnetic field strength distribution on the recording surface of the medium within the access range can be made substantially uniform.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a bias magnetic field generator according to an embodiment of the present invention. In FIG. 1, 11 is a bar-shaped center yoke having a length sufficient to cover the access range of an optical head (not shown), 12 is an exciting coil wound around the center yoke 11, and 13 is a center yoke. In the outer yoke that surrounds 11, the magnetic gap width Lg on the medium facing surface formed between the outer yoke and the center yoke 11 becomes minimum at a position corresponding to the vicinity of the midpoint of the access range of the optical head. It is formed so that it becomes wider toward the end of the access range of the head.

The operation of the bias magnetic field generator configured as described above will be described below. In FIG. 1, when a current is passed through the exciting coil 12, a magnetic field is applied to the recording surface of the magneto-optical recording medium 1. The magnetic gap width Lg on the medium facing surface of the bias magnetic field generator is shown in FIG. As described above, the bias magnetic field generator is narrow at the center and widens as it goes away from the center, so that the component of the magnetic field in the direction of arrow A that goes away from the center becomes smaller toward the end. Therefore, the magnetic field strength obtained on the recording surface of the magneto-optical recording medium is as shown in FIG. 2, and the increase in the magnetic field strength at the end points P and Q of the access range of the optical head described in the conventional example. It disappears and becomes almost the same as the magnetic field intensity at the center point O.

As described above, according to the present embodiment, the magnetic gap width Lg on the medium facing surface of the bias magnetic field generator is controlled by the shape of the outer yoke to be the narrowest in the central portion and widen as the distance from the central portion increases. The magnetic field strength on the recording surface can be made uniform with respect to an arbitrary optical head access position. Further, since the average magnetic gap width Lg of the bias magnetic field generator as a whole increases, the unnecessary magnetic coupling degree decreases and the self-inductance decreases, so that the reversal speed of the magnetic field improves.

FIG. 3 shows another embodiment of the bias magnetic field generator of the present invention, in which 14 is a center yoke, which has a length sufficient to cover the access range of an optical head (not shown), and is indicated by an arrow A. A member having a T-shaped cross section perpendicular to the direction. Reference numeral 15 is a channel-shaped outer yoke surrounding the center yoke 14, and 16 is an exciting coil wound around the center yoke 14. Further, the center yoke 14
The magnetic gap width Lg on the medium facing surface formed between the outer yoke 15 and the outer yoke 15 is controlled by controlling the shape of the head portion of the center yoke 14 so as to be in a position near the midpoint of the access range of the optical head. It becomes the minimum and becomes wider toward the end of the access range of the optical head. The usage is the same as in the first embodiment.

This embodiment has the same effect as the embodiment shown in FIG.
The structure of the outer yoke is simpler than that of the embodiment shown in FIG. 1, and the curved portion of the center yoke is relatively easy to mold, which facilitates the manufacture.

According to the present invention, the magnetic gap width on the medium facing surface of the bias magnetic field generator having a length equal to or longer than the access range of the optical head is the narrowest at the position corresponding to the midpoint of the access range, and corresponds to the midpoint. The magnetic field strength on the magneto-optical recording medium is controlled by controlling the shape of at least one of the two magnetic poles of the main magnetic pole and the auxiliary magnetic pole forming the magnetic gap so that the magnetic field strength becomes wider as the distance from the position Since a magnetic field that is almost constant can be applied over the head access range, stable information pits are formed in the entire recording effective area of the magneto-optical recording medium without requiring any special control means for the bias magnetic field generator. It is possible to improve the reliability of information. Furthermore, an excellent bias magnetic field generator that can obtain the effect that the average value of the magnetic gap width becomes wider than the magnetic gap width of the conventional bias magnetic field generator, the self-inductance is reduced, and the magnetic field reversal speed is improved. It can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view of a bias magnetic field generator in one embodiment of the present invention, FIG. 2 is a magnetic field strength distribution diagram on the recording surface of a medium by the same, and FIG. 3 is a bias in another embodiment of the present invention. FIG. 4 is a perspective view of a magnetic field generator, FIG. 4 is a configuration diagram showing an arrangement state of a conventional bias magnetic field generator in a magneto-optical recording / reproducing device, and FIG. 5 is a perspective view of a conventional bias magnetic field generator. FIG. 6 is a state diagram showing magnetic flux generated by the bias magnetic field generator of FIG. 5, and FIG. 7 is a magnetic field strength distribution diagram on the medium recording surface by the bias magnetic field generator of FIG. 1 ... Magneto-optical recording medium, 2 ... Optical head, 3 ... Objective lens, 4 ... Bias magnetic field generator, 11, 14 ...
Center yoke, 12, 16 ... Excitation coil, 13, 15
…… Outer yoke.

Claims (1)

[Claims] 1. A magneto-optical recording / reproducing device having at least an optical head for giving a light spot for recording / reproducing / erasing to / from the magneto-optical recording medium while performing a relative movement of a predetermined access trajectory with respect to the magneto-optical recording medium within a predetermined access range. A bias magnetic field generator arranged to sandwich the magneto-optical recording medium at a position facing the optical head in order to apply a vertical magnetic field used in the apparatus to the magneto-optical recording medium, the bias magnetic field generating apparatus generating a magnetic field. A magnetomotive force source; a main magnetic pole having a main magnetic pole facing surface that faces the magneto-optical recording medium, which is a magnetic body magnetically coupled to one magnetic pole of the magnetomotive force source, in a substantially parallel manner; An auxiliary magnetic pole having an auxiliary magnetic pole ridge line substantially juxtaposed to the main magnetic pole facing surface, which is a magnetic material magnetically coupled to the other magnetic pole, the main magnetic pole facing surface is along the access trajectory. And the center line of the main magnetic pole facing surface is substantially the same shape as the access track, and the length of the main magnetic pole facing surface is greater than or equal to the access range. The magnetic gap between the auxiliary magnetic pole ridge and the auxiliary magnetic pole ridge has a magnetic gap width that is the width of the magnetic gap in the direction parallel to the main pole facing surface and substantially perpendicular to the center line. The bias magnetic field generating device is characterized in that the width is narrowest in the center of the access range, and the magnetic gap width is expanded as it goes away from the center of the access range.