JPS63124203A - Bias magnetic field generator - Google Patents

Abstract

PURPOSE:To almost fix the position of a magnetic field applied to an optional spot of a medium based on an optional access position of an optical head by magnetically saturating a coil winding part to suppress an output from a magnetic field at a position separated from the center part of an access range of the optical head. CONSTITUTION:A winding part 6a of an exciting coil 7 is formed so that its width is most expanded at a position corresponding to the intermediate point in the access range of the optical head and narrowed in accordance its separation along the access direction. Thereby, the distribution of magnetic field intensity obtained on the recording face of the medium corresponding to the access position is constituted so that the magnetic field intensity on both end parts of the access range are almost the same as that of the center part without being increased. Since magnetic saturation is generated by a low current value in accordance with the efficiency of an output magnetic field to a driving current, the output magnetic field can be suppressed. Consequently, the magnetic field applied to the optical spot position of the medium can be almost fixed about an optional access position of the optical head.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a bias magnetic field generating device used in a magneto-optical recording and reproducing device used in an external storage device of an electronic computer, a recording and reproducing device for music and video signals, and other information. It is related to.

BACKGROUND OF THE INVENTION In recent years, with the development of electronic computers and means of high-speed mass transmission of information, there has been a demand for low-cost, high-density, large-capacity, non-volatile storage devices with high-speed transmission capabilities, and magnetic disk devices are often used. However, there are problems such as low recording density, high price per unit of information, and especially in fixed magnetic disk drives, it is difficult to exchange the medium. Optical recording is currently in the spotlight as a technology that can solve these problems, and rewritable magneto-optical recording in particular has high expectations in many fields.

A conventional bias magnetic field generator is disposed opposite an optical head with a magneto-optical recording medium in between, has a length that covers the access range of the optical head, and has a length parallel to the recording surface of the magneto-optical recording medium. The width of the cross-sectional shape of the winding portion of the excitation coil cut along the plane in the tangential direction of the magneto-optical recording medium is constant in the access range of the optical head regardless of the radial position of the magneto-optical recording medium of the optical head. (For example, Japanese Patent Application Laid-Open No. 119507/1983).

Hereinafter, a conventional bias magnetic field generating device as described above will be explained with reference to the drawings.

6, 7 and 8 show a conventional bias magnetic field generating device, and FIG. 6 shows the arrangement in a magneto-optical recording device,
FIG. 7 shows the structure, and FIG. 8 shows the flow of magnetic flux generated by the bias magnetic field generator.

In Fig. 6, 1 is a magneto-optical recording medium, 2 is an optical head, and the 6th
The objective lens actuator is accessed in the direction of the arrow in the figure, and controls the light spot emitted from the objective lens 3 to focus on the recording surface of the magneto-optical recording medium 1, and outputs the light spot. A laser light source necessary for this purpose and an optical system for guiding this laser light to an objective lens 3 are built-in. Reference numeral 4 denotes a bias magnetic field generating device for applying the perpendicular force necessary for recording and erasing information to the magneto-optical recording medium 1, which is disposed at a position facing the optical head 2 with the magneto-optical recording medium 1 in between. , a par-shaped center yoke 16 having a length equivalent to covering the access area of the optical head 2 along the access direction of the optical head 2, an excitation coil 17 wound around the center yoke 16, and a center yoke. It is composed of a channel-shaped outer yoke 16 surrounding the outer yoke 16. Further, the front end surface of the center yoke 16 and the medium facing end surface of the outer yoke 16 are on the same plane, and are opposed in parallel to the magneto-optical recording medium 1 with a distance d between them. The cross-sectional shape of the center yoke 15 taken along a plane parallel to the magneto-optical recording medium 1 has a constant width in the area that corresponds to the access range of the optical head.

Regarding the magneto-optical recording and reproducing device configured as above,
The operation will be explained below.

First, when the excitation coil 17 is energized, a magnetic flux φ flows through a magnetic path consisting of the center yoke 16 and the outer yoke 16, as shown in FIG. 8, and passes through the magneto-optical recording medium 1 as shown in the figure. At this time, if the distance d is made sufficiently small, the magneto-optical recording medium 51
A sufficient magnetic field with a component perpendicular to can be applied. In this state, if a light spot corresponding to the information is applied from the optical head 2 to the magneto-optical recording medium 1 through the objective lens 3, information is recorded. In the case of erasing, the direction of the magnetic field is reversed to provide a light spot.

Since the center yoke 16 of the bias magnetic field generator has a length sufficient to cover the access range of the optical head 2, recording is possible no matter where the optical wad 2 accesses in the direction of the arrow in FIG. , it is possible to obtain a magnetic field strong enough for erasing.

Problems to be Solved by the Invention However, the above configuration has the following problems.

As shown in FIG. 7, if the width of the center yoke 16 is constant regardless of the access position of the optical head, the magnetic field strength distribution in the access direction on the medium will be as shown in FIG. Near both ends of the access range P, Q
The maximum value is taken at the point, and the minimum value is taken at the 0 point in the center. This phenomenon in which the magnetic field strength increases at both ends is caused by magnetic leakage from the center yoke 15 to the base portion of the outer yoke 16 at both ends in the direction of the arrow in the bias magnetic field generator shown in FIG. Therefore, the conventional bias magnetic field generator is
It is necessary to flow a current sufficient to obtain the minimum magnetic field HR required for recording or erasing at the central 0 point, which has the lowest efficiency. However, in case 4, an unnecessarily large magnetic field is applied to the medium at both end points P and Q.

Such an excessive bias magnetic field increases the diameter of information bits formed during recording, affects adjacent pits, and degrades the reliability of information.

Conventionally, methods used to solve these problems include estimating the magnetic field strength on the medium from the output of a sensor installed on the optical side and controlling the current of the excitation coil. However, magnetic leakage from the objective lens actuator built into the optical head does not cause disturbance to the sensor, and the system becomes complicated and expensive for accurate control. Further, there were drawbacks such as difficulty in installing a sensor due to the structure.

In view of the above-mentioned problems, the present invention provides that the magnetic field intensity generated by the bias magnetic field generator at the position where the optical spot provided by the optical head is concentrated on the magneto-optical recording medium (over the access range of the optical head) is approximately constant. The present invention provides a bias magnetic field generating device capable of generating a bias magnetic field.

Means for Solving the Problems In order to achieve this object, the bias magnetic field generating device of the present invention provides a magneto-optical recording medium at a position opposite to an optical head that provides a light spot for recording, reproduction and erasing on the magneto-optical recording medium. The magneto-optical recording device has a length that covers the moving range of the optical spot, and has a cross-sectional shape of a winding portion of the excitation coil cut along a plane parallel to the recording surface of the magneto-optical recording medium. An electromagnet whose width in a tangential direction of the medium is widest at a position corresponding to a midpoint of a movement range of the optical spot, and narrows as it moves away from a position corresponding to the midpoint along a movement direction of the optical head. It is made up of.

Effect: With this configuration, the output of the magnetic field at a position far from the center of the access range of the optical head can be suppressed by causing magnetic saturation in the coil winding, and the output of the magnetic field can be suppressed at a position away from the center of the access range of the optical head. The applied magnetic field can be made substantially constant for any access position of the optical head.

EXAMPLE An example of the present invention will be described below with reference to the drawings. 1 and 2 show a bias magnetic field generator according to an embodiment of the present invention. FIG. 1 is a partially cutaway perspective view showing the structure, and FIG. 2 is a winding of the excitation coil 7. FIG. 2 is a half cross-sectional view taken along a plane parallel to the medium recording surface of the center yoke 6, which is a section, and a cross-sectional view showing the shape of a cross section perpendicular to the access direction of the optical end. In FIG. 1, reference numeral 6 denotes an outer yoke with a T-shaped cross section that is long enough to cover the access range of the optical head, and as shown in FIG. 2a, the winding portion 6a of the excitation coil 7 is The width is widest at a position corresponding to the midpoint of the access range of the optical head, and becomes narrower as it moves away from the midpoint along the access direction of the optical head. Figure 2, c.

d shows a cross section taken along line B-B, line C-C, and line D-D in FIG. 2a, and shows that only the width of the center yoke 6 changes with respect to the access position of the optical head. There is.

In FIG. 1, the outer yoke 5 is a channel-shaped member surrounding the center yoke 6.

The operation of the bias magnetic field generating device configured as described above will be explained below. In FIG. 1, when a current is applied to the excitation coil 7, a magnetic field is applied to the recording surface of the magneto-optical recording medium, but as shown in the conventional example, the efficiency of the output magnetic field with respect to the drive current varies depending on the access position of the optical head. Its efficiency improves as it approaches both ends of the access range of the optical head. However, as shown in FIG. 2, the center yoke 6 has a structure in which magnetic saturation is more likely to occur as it is closer to both ends of the access range of the optical head, and excessive magnetic field output is more likely to be suppressed as it is closer to both ends.

FIG. 3 shows the relationship between the drive current and the magnetic field strength on the medium at each cross section in FIG. 2. In FIG. 3, b is a cross section taken along the line B-B, and C is a cross section taken along the line C-C.

d indicates the characteristics in the cross section taken along the line D-D. As shown in Fig. 3, at low current values, characteristic C1 is more efficient than characteristic C, but characteristic d is more efficient than characteristic C1 due to the shape characteristics of the center yoke 6. drive current during recording or erasing operations, resulting in reduced efficiency.
The magnetic field strength applied to the medium at any point is the same magnetic field strength HR for recording or erasing. That is, the distribution of the magnetic field strength obtained on the recording surface of the medium with respect to the access position of the optical head is as shown in FIG. 4, and the distribution is as shown in FIG.

The magnetic field strength does not increase at the 9 points, and becomes almost the same as the magnetic field strength at the 0 point in the center.

As described above, according to this embodiment, the width of the cross-sectional shape of the center yoke 6 taken along a plane parallel to the recording surface of the magneto-optical recording medium in the tangential direction of the magneto-optical recording medium is the access range of the optical head. It is widest at the position corresponding to the midpoint of
Since the width becomes narrower as it moves away from the position corresponding to the midpoint along the moving direction of the optical head, the more efficient the output magnetic field is with respect to the drive current, the more magnetic saturation occurs at a lower current value, and the output magnetic field is suppressed. be done. As a result, the magnetic field applied to a certain position of the optical spot on the medium can be made approximately constant for any access position of the optical head.

Other embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 shows another embodiment of the bias magnetic field generating device of the present invention. In the figure, the main yoke 8 corresponds to the center yoke 6 of the first embodiment, and the side yokes 9 correspond to the outer yoke 5 of the first embodiment. The main yoke 8 is a member with an L-shaped cross section that is long enough to cover the access range of the optical head, and is wound with the same excitation coil 7 as in the first embodiment.
The winding portion is formed so that its width is widest at a position corresponding to the midpoint of the access range of the optical head, and becomes narrower as it moves away from the position corresponding to the midpoint along the access direction of the optical head. has been done. However, unlike the center yoke 6 of the first embodiment, the winding portion of the exciting coil 70 facing the side yoke 9 is flat. Usage is first
This is similar to the embodiment.

This embodiment has the same effect as the first embodiment, but since the side of the winding portion of the excitation coil 7 of the main yoke 8 that faces the side yoke 9 is flat, the side from the winding portion of the excitation coil 7 to the side Magnetic leakage to the yoke is reduced. That is, the influence of the magnetic leakage on the magnetic field strength distribution can be ignored, and the shape adjustment only needs to be done on one side, so that it is easier to control the magnetic field strength distribution by adjusting the cross-sectional shape of the main yoke.

Effects of the Invention The present invention provides a magneto-optical recording medium that is disposed across the magneto-optical recording medium at a position facing an optical head that provides a light spot for recording, reproduction and erasing on the magneto-optical recording medium, and has a length that covers the access range of the optical head. , and the width of the cross-sectional shape of the winding portion of the excitation four coils cut along a plane parallel to the recording surface of the magneto-optical recording medium in the tangential direction of the magneto-optical recording medium is within the access range of the optical head. By having a structure in which the width is widest at the position corresponding to the midpoint and becomes narrower as it moves away from the position corresponding to the midpoint along the moving direction of the optical head,
The output of the magnetic field at a position away from the center of the access range of the optical head in the access direction can be suppressed by causing magnetic saturation in the coil winding, and the magnetic field applied to the position of the optical spot on the medium can be suppressed. can be made approximately constant for any access position of the optical head. As a result,
Since the magnitude of the bias magnetic field is stabilized and the sizes of the information bits are uniform, the adjustment of the information detection means is facilitated, and the reliability of the information is improved. Further, it is possible to realize a bias magnetic field generating device that can obtain a number of excellent effects such as eliminating the need for the conventionally used magnetic sensor and reducing the cost of the magneto-optical recording and reproducing device.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing the structure of a bias magnetic field generating device in an embodiment of the present invention, FIG. 2 a is a half sectional view of the bias magnetic field generating device of FIG. 1, and FIGS. BB, 0-C, respectively of the bias magnetic field generating device in FIG. 2a.
3 is a characteristic diagram showing the relationship between the drive current and the magnetic field strength applied to the medium at each cross section of the bias magnetic field generator shown in FIG. 2, and FIG. FIG. 6 is a distribution diagram of the magnetic field strength in the radial direction of the recording medium obtained at the position of the optical spot on the magnetic recording medium, and FIG. 6 is a partial cross-sectional view of a bias magnetic field generator in another embodiment of the present invention. 7 is a perspective view showing the structure of the bias magnetic field generator shown in FIG. 6. FIG. 9 is a cross-sectional view showing the flow of magnetic flux in the device, and FIG. 9 is a distribution diagram of the magnetic field strength in the radial direction of the medium obtained by the bias magnetic field generating device of FIG. 7 at the position where the optical spot hits the magneto-optical recording medium. It is. DESCRIPTION OF SYMBOLS 1... Magneto-optical recording medium, 2... Optical head, 3... Objective lens, 4... Bias magnetic field generator, 5...・Outer yoke, 6...
... Center yoke, 7 ... Excitation coil, 8
...Main yoke, 9...Side yoke. Name of agent: Patent attorney Toshi Nakao, 1 person, 5-
11 Datoi EX Yoke 6 Mountains - Hakuen Shigo 2 Figure 3 (b) Figure 3 Figure 4 Optical head axle fLi 7---Excitation coil 8-m-Main yaw 7 9---Duid yoke Figure 5 Figure 8 Figure 9 P o a Kyuei head access eyebrow Σ transfer.

Claims (1)

[Claims] The magneto-optical recording medium is disposed across the optical head at a position facing the optical head that provides a light spot for recording, reproducing and erasing on the magneto-optical recording medium, and has a length that covers the access range of the optical head. The width of the cross-sectional shape of the winding portion of the excitation coil taken along a plane parallel to the recording surface of the recording medium in the tangential direction of the magneto-optical recording medium is widest at a position corresponding to the midpoint of the access range of the optical head. . A bias magnetic field generating device comprising an electromagnet that becomes narrower as it moves away from a position corresponding to the midpoint along the moving direction of the optical head.