JPH04245001A - Magnetic field generation device - Google Patents

Abstract

PURPOSE:To enable a bias magnetic field to be inverted at high speed with a simple mechanism and a drive circuit and achieve a low power consumption by allowing a drive coil to be in a bent shape in a direction for approaching a magnetic rotary body along an axis which is in parallel to a rotary axis. CONSTITUTION:A drive coil 1 is mounted on a fixed base 2 and is in a shape which is bent in a direction for approaching a rotary body 4 along an axis which is in parallel to a rotary axis 4a of the magnetic rotary body 4. Also, the yoke 4 as a magnetic rotary body with the axis 4a at both edge portions is mounted on the base 2. Permanent magnets 3a and 3b for generating magnetic field which are magnetized in a same direction in a direction which crosses the axis 4a are applied to both surfaces of the yoke 4 in one piece. Then. when a current is allowed to flow to the coil 1, a magnetic field which is generated by it allows an asymmetrical magnetic field to be generated around a magnetic pole surface and Maxwell stress which is operated upon the magnetic pole surface generates a rotary torque.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias magnetic field generating device for a magneto-optical disk device.

0002

[Prior Art] In contrast to playback-only optical disk devices such as compact disks and optical video disks, magneto-optical disk devices that allow data to be rewritten use magneto-optical disks as data recording media. By changing the power of the emitted laser beam, data can be recorded, reproduced,
There is a method called a light modulation method that performs erasing. In this method, in addition to the laser beam, it is necessary to apply a bias magnetic field perpendicular to the surface of the recording medium, the direction of which varies depending on the case of recording and erasing.

Generally, an objective lens that focuses the laser beam into an extremely small spot is located close to one side of the recording medium surface, and a device that generates a bias magnetic field is usually placed on the opposite side of the recording medium. . FIG. 6 shows a conventional example.

A permanent magnet 12 is placed at a certain distance from the upper surface of the magneto-optical disk 14, and although not shown, an optical pickup device is moved in the radial direction of the magneto-optical disk 14 to the lower surface of the optical disk 14. Possibly located.

The permanent magnet 12 has a long shape in the radial direction of the magneto-optical disk 14, which uniformly applies a magnetic field to the data recording area of the magneto-optical disk 14, which is the same as the movable area of the optical pickup. Magnetized in orthogonal directions.

Furthermore, the permanent magnet 12 is rotated by a drive motor 13 with its longitudinal direction serving as a rotation axis, and the direction of the bias magnetic field applied to the recording medium is reversed.

[0007]

[Problems to be Solved by the Invention] However, in the past, relatively expensive mechanical parts such as the drive motor 13 are required, and in order to reverse the magnetic field at high speed, an extremely large driving force is required. , a motor with small rotational inertia is required, resulting in high cost.

In addition, in a miniaturized magneto-optical disk device that is packed with high density, a magnetic structural member is constructed in close proximity to the permanent magnet 12 that generates the bias magnetic field described above. A force is exerted on the magnet due to interaction with these magnetic bodies, and the magnet cannot be fixed in a predetermined position, requiring a large holding force from the drive motor. In addition, these interactions constitute a holding force, resulting in a mechanical system with extremely small damping force and easy to vibrate. Therefore, the device becomes large, and in order to reverse the magnetic field at high speed, there is a problem in that sophisticated position control and a power source that supplies a large amount of power are required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a compact magnetic field generating device that can quickly reverse the bias magnetic field applied to a magneto-optical disk using a simple mechanism and a drive circuit, and has low power consumption. shall be.

0010

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a magnetic rotating body having a rotating shaft, a permanent magnet attached to the magnetic rotating body and magnetized in a direction perpendicular to the rotating shaft. , a support part that rotatably supports a rotating shaft of the magnetic rotary body; a drive coil that rotates the magnetic rotary body supported by the support part by electromagnetic force; and a drive coil that positions the magnetic rotary body at a predetermined position by an attractive magnetic force. The drive coil is bent in a direction approaching the magnetic rotor along an axis parallel to the rotation axis of the magnetic rotor.

[0011]

[Operation] When a current is passed through the drive coil, a magnetic field is generated around the magnetic pole face of the permanent magnet of the magnetic rotating body, and rotational torque is generated. This rotational torque causes the magnetic rotating body to rotate and apply bias magnetic fields in different directions to the recording medium surface.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to an embodiment shown in FIGS. 1 to 5.

FIG. 1 shows a magnetic field generator, in which 1
is the drive coil. This drive coil 1 is attached to a fixed base 2, and has a shape bent in a direction approaching the magnetic rotor 4 along an axis parallel to a rotation axis 4a of the magnetic rotor 4, which will be described later. There is. In addition, the above fixed base
A yoke 4 as a magnetic rotating body having rotating shafts 4a, 4a at both ends is attached to the base 2. This yoke 4
Two permanent magnets 3a, 3b magnetized with the same polarity in a direction orthogonal to the rotating shafts 4a, 4a are attached to both sides of the rotating shafts 4a, 4a to form an integral structure.
a is a rotation bearing (ball bearing) 5 as a support part
It is rotatably supported by a and 5b. The rotary bearings 5a, 5a are preloaded in the direction of the rotary shafts 4a, 4a by preload seats 6a, 6b to eliminate looseness.

The rotation bearings 5a, 5a and preload seats 6a, 6b are supported by two U-shaped positioning yokes 7a, 7b constituting positioning means and fixed to the fixed base 2. .

The fixed base 2 is a component into which the driving coil 1 is insert-molded, and includes the rotating magnetic body 4, the rotating bearings 5a, 5a, the preload seats 6a, 6b, and the positioning yoke 7a. , 7b are inserted from the top and bottom of the drawing and fixed inside with fixing screws 11a and 11b. Next, the principle of magnetic field reversal operation of the present invention will be explained based on FIG. 3. Figure 3
A recording medium is placed below each cross section. In FIG. 3(a), the south pole faces the recording medium. Figure 3(a)
As shown in FIG. 2, when a current is passed through the drive coil 1, the magnetic field generated by the current generates an asymmetric magnetic field around the magnetic pole face. As a result, the Maxwell stress acting on the magnetic pole surface generates a force in the direction of the arrow in the figure, resulting in rotational torque.

This magnetic force can be thought of as a reaction to the electromagnetic force generated in the drive coil 1 by the magnetic field generated by the permanent magnet 3, and a larger torque can be generated if the drive coil 1 is as close to the magnetic pole surface as possible. In FIG. 3(b), the magnetic rotating body 4 is 90
Indicates a rotated state. The magnetic pole face N moves away from the drive coil 1, but in the case of the drive coil 1 according to the invention,
The opposite pole, the south pole, approaches the drive coil 1. Therefore, the rotational driving force does not decrease depending on the rotational position, and the driving force can be applied to the magnetic rotating body 4 very efficiently. FIG. 3(c) shows a state in which the magnetic field reversal has been completed with respect to the state in FIG. 3(a). Since the rotational movement is performed at extremely high speed, the kinetic energy of rotation is large.

This kinetic energy must be absorbed at high speed in the state shown in FIG. 3(c), but in the state shown in FIG. 3(c), the magnetic pole surface is closest to the drive coil 1, and a small amount of current It can generate large braking force. FIG. 4 shows a positioning yoke 7 placed at the end of the permanent magnet 3.
FIG.

The permanent magnet 3 is arranged in such a way that a magnetic circuit is formed with a gap at the end between the different magnetic pole faces, and the permanent magnet 3 has a structure that can serve both of the functions of positioning and fixing the bearing 5.

The end face of the permanent magnet 3 and the positioning yoke 7 are close to each other with a slight gap between them, and the magnetic positioning yoke 7 is guided by the permanent magnet 3.
A different polarity is generated from the magnetic pole end face. Therefore, as shown in FIG. 4, when the permanent magnet 3 is rotated to a position deviated from a predetermined position, a restoring force is generated in the direction shown by the arrow in the figure. Therefore, the rotating permanent magnet 3 can be positioned without passing current through the drive coil 1.

FIG. 5 schematically shows the output characteristics of the magnetic field strength detector 8 placed at the position shown in FIG. Since the position of the magnetic field strength detector 8 is shifted from the center of the magnetic pole surface at the neutral position, the output is at the neutral position in the characteristic portion where the output changes greatly according to the angle change. Therefore, the position of the magnetic pole surface can be detected, and by passing the output through a time differentiation circuit, a signal approximately proportional to the speed of movement can be extracted. Performing negative feedback control using this rotational speed signal is extremely effective in controlling rotational vibration due to the restoring force of the positioning yoke 7 near the neutral position. As a result, the period of unstable vibration near the end of the magnetic field reversal operation is short, and the time required to complete the magnetic field reversal operation can be shortened. As mentioned above, the drive motor
Since the permanent magnet for generating the magnetic field is rotated without using a magnet, the structure can be simplified and costs can be reduced. Also,
The only rotating parts are the bias magnetic field generating permanent magnets 3a and 3b and the yoke 4 that supports them, resulting in extremely low rotational inertia. Furthermore, the driving coil 7 includes permanent magnets 3a,
In the reversing operation of 3b, since the arrangement is extremely rational for generating driving force, a high-speed magnetic field reversing operation is possible.

The positioning yoke 7 also includes a permanent magnet 3a that rotates to apply the necessary magnetic field to the recording medium.
, 3b can be stabilized in a predetermined position, and can also be configured to support the bearing 5, generating sufficient position holding force while occupying a small space. It becomes possible to do so.

On the other hand, by placing the magnetic field strength detector 8 at a location offset from the predetermined position on the magnetic pole surface, it is possible to detect the polarity of the magnetic field applied to the recording medium surface and also to detect the speed of rotational motion. It becomes possible to detect this, and by using it as a signal for magnetic field reversal drive control, it is possible to provide damping properties to the rotational motion. Appropriately controlled damping motion achieves quick reversal action without vibration.

[0023]

[Effects of the Invention] As explained above, according to the present invention,
The magnetic field generator has an extremely simple configuration, is compact, has high reliability, and can perform magnetic field reversal operations at high speed with little electric power and with a simple drive circuit.

Furthermore, since the position of the magnetic pole of the rotatable permanent magnet is held by a closed magnetic field circuit, the holding force is large and the influence of interaction with other magnetic bodies in the optical disk device is small.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a magnetic field generator according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of the magnetic field generator shown in FIG. 1;

FIG. 3 is an explanatory diagram showing the operation of the magnetic field generator of FIG. 1.

FIG. 4 is an enlarged perspective view of a part of the magnetic field generator shown in FIG. 1;

FIG. 5 is a graph diagram showing the relationship between the rotation angle of the rotating body of the magnetic field generator of FIG. 1 and the output of the magnetic field strength detector.

FIG. 6 is a perspective view showing a conventional magnetic field generating device.

[Explanation of symbols]

1...Drive coil 3a...Permanent magnet 4a...Rotation axis 4...Magnetic rotating body 5...Ball bearing (support part) 7...Positioning means.

Claims (3)

[Claims] 1. A magnetic rotating body having a rotating shaft, a permanent magnet attached to the magnetic rotating body and magnetized in a direction perpendicular to the rotating shaft, and a support portion rotatably supporting the rotating shaft of the magnetic rotating body. a drive coil that rotates the magnetic rotor supported by the support part by electromagnetic force; and a positioning means that positions the magnetic rotor at a predetermined position by an attractive magnetic force, and the drive coil rotates the magnetic rotor by electromagnetic force. A magnetic field generating device characterized by having a shape bent in a direction approaching a magnetic rotating body along an axis parallel to the rotational axis of the body. [Claim 2] The positioning means is close to the magnetic pole face of the permanent magnet of the magnetic rotating body, determines the dynamically neutral position of the magnetic rotating body by the attraction force of the magnetic force, and fixes the support part that supports the magnetic rotating body. The magnetic field generating device according to claim 1, wherein the magnetic field generating device has a function of: 3. The magnetic field generating device according to claim 1, further comprising a magnetic field strength detector near the bend of the drive coil bent in a direction approaching the magnetic rotating body.