JPH03152702A - Bias magnetic field generating device - Google Patents

Abstract

PURPOSE:To make the size of components small and to facilitate the control for reverse by using a permanent magnet for generating a bias magnetic field in common for a drive system for magnetic field inversion. CONSTITUTION:A permanent magnet 301 is contained in a groove part of a holder 306, adhered thereto, a cylindrical projection is provided at both ends and engaged with an inner race of a bearing 304. Moreover, the bearing 304 is coupled with a hole made to a case 307 containing the entire base magnetic field generating device and the case and the bearing constitute a rotary support device with a small load torque. Then the permanent magnet 301 is driven around a rotary center 305 with a small torque. Moreover, a drive coil 302 is fixed to the inner face of the case 307 and designed as close as possible to the permanent magnet in a contactless range when the permanent magnet is driven. Thus, the high speed and stable reversing is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bias magnetic field generation mechanism for a magneto-optical recording/reproducing device.

[Prior Art] In a magneto-optical recording/reproducing device, when recording and erasing information, it is necessary to create a magnetic field of several hundred oersteds at the focal point of a laser beam on a recording medium.

This magnetic field during recording and erasing is called a bias magnetic field or the like.

Methods for generating this bias magnetic field include methods using electromagnets and methods using permanent magnets, but permanent magnets are often used in small magneto-optical recording and reproducing devices.

Here are three examples of conventional methods using permanent magnets.

In FIG. 4, a permanent magnet 401 is placed close to an optical disk (magneto-optical recording medium) 403, and a rotation center 402
It is supported so that it can rotate. This permanent magnet is driven by a coaxially connected motor 404 and N
It has a structure that allows the pole and south pole to be reversed.

FIG. 5 shows an example in which an electromagnetic coil is used to reverse the magnet. FIG. 5(a) is a plan view, and FIG. 5(b) is a sectional view taken along line AA in FIG. 5(a).

As shown in FIG. 5(a), a rod-shaped permanent magnet 501 magnetized in the same manner as the example shown in FIG. 4 is rotatably supported by rotary supports 502 at both ends. And 50 pieces of iron
Due to the attractive force with 4, both magnetic poles of the permanent magnet are
It is designed to stop stably in the direction above or below. A drive coil 503 is placed so as to surround this permanent magnet 501. When a current is passed through the drive coil 503, a vertical magnetic field is generated as shown in FIG. 5(b), so
Permanent magnet 501 reverses its polarity according to the direction of this magnetic field.

FIG. 6 shows an example in which two drive coils are used to reverse the magnets. Figure 6(a) is a plan view, Figure 6(a) is a plan view;
b) is a sectional view taken along line AA in FIG. 6(a). The structure is the same as the example shown in FIG. 5, except for the number and arrangement of drive coils. Figure 6 (+) with two drive coils 602 and 603
When a current is passed in the direction of arrows 605 and 606, the result in Figure 6 (b
), a magnetic field is generated in the direction of arrow 607. This causes the permanent magnet 601 to rotate 90 degrees. Then, when the current is turned off at a good timing, the 180 degree reversal is completed with the help of the attraction force with the iron piece 604.

[Problems to be solved by the invention] Among conventional methods, the use of a motor to rotate a permanent magnet increases the overall cost due to the use of the motor.
It also has the disadvantage that it is difficult to miniaturize.

In an example using one drive coil, the permanent magnet has a structure that is stable in two directions, so the maximum torque is required at the beginning of rotation when reversing, but the torque generated by the drive coil is extremely small at the beginning of rotation. For this reason, the coil has to be large in size, making it difficult to save power and downsize.

In an example using two drive coils, the torque generated by the coils is up to 90 degrees, so current control at delicate timing is required in order to rotate 180 degrees.

For this reason, it is difficult to perform stable and high-speed reversal. Also,
Since two coils are used, miniaturization is also difficult.

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide a structure that reduces the number of parts, downsizes the parts, facilitates control for reversal, and easily shortens reversal time.

[Means for Solving the Problems] A bias magnetic field generating mechanism of the present invention is a magneto-optical recording/reproducing device, and is a bias magnetic field generating mechanism that is a means for generating a magnetic field on a recording medium surface when recording or erasing information. , (a) a bar-shaped permanent magnet magnetized in the thickness direction, (b) a rotation support mechanism that supports the permanent magnet so that it can rotate around the longitudinal direction, (c) an electromagnetic coil wound in a long and thin manner, It is characterized by being constituted by a drive coil whose two sides are placed along the permanent magnet, and whose two sides are arranged in a positional relationship that is approximately 90 degrees from the rotation center of the permanent magnet. .

[Operation] FIG. 1 is a perspective view showing the shapes of main components in an embodiment of the present invention. The permanent magnet 101 is supported by a rotation support mechanism (not shown in the figure) and is rotatable about a rotation center 104. A coil 102 is placed along the permanent magnet 101, and an iron piece 103 made of a soft magnetic material is placed at the top.

FIGS. 2(a), 2(b), and 2(c) are operational diagrams in an embodiment of the present invention, and are diagrams showing a cross section in a plane perpendicular to the center of rotation of the permanent magnet. Permanent magnet 201 can freely rotate around rotation center 205. The current flowing through the drive coil is
The flow flows through the coil cross section A 202 and the coil cross section B2O3 in a direction perpendicular to the plane of the paper, and the directions are opposite to each other.

The torque acting on the permanent magnet will be explained using these figures.

First, consider the torque generated when current flows through the drive coil. The direction of the current is assumed to be toward the front of the paper at the coil cross section A202, and toward the front of the paper at the coil cross section B2O3.

When the permanent magnet is in the position shown in Figure 2 (a), the coil cross section is A20.
The magnetic field created by the current flowing through 2 is indicated by the arrow 206 with respect to the N magnetic pole.
gives a force in the direction of Since the S magnetic pole is far away and the force it receives is small, it is ignored. At this time, the direction of the torque acting on the permanent magnet is clockwise. The force exerted on the permanent magnet by the magnetic field created by the current flowing through the coil cross section B2O3 is symmetrical between the N and S magnetic poles, and no torque is generated.

Considering the same way, in FIG. 2(b), since the force acting on the S magnetic pole is in the direction of arrow 207, the direction of the torque acting on the permanent magnet is also clockwise.

In addition, during the clockwise rotation from FIG. 2(a) to FIG. 2(b), the torque received from the magnetic field created by the current flowing through the fill cross section A202 decreases, and the coil cross section B2O3
As the torque received from the magnetic field created by the current flowing through the coil increases, a nearly constant clockwise resultant torque acts (depending on the coil shape).

Next, in FIG. 2(c), the combined magnetic field created by the currents flowing through the coil cross section A202 and the coil cross section B2O3 is in the opposite direction to the arrow 208, so the force acting on the S magnetic pole is as indicated by the arrow 208.
It becomes 8. Therefore, the torque acting on the permanent magnet is zero.

However, if the permanent magnet shifts slightly clockwise or counterclockwise, a torque is applied to return it to the position shown in the diagram.

Next, consider the force acting between the iron piece 204 and the permanent magnet 201. Since an attractive force is always acting on the N and S magnetic poles in the direction of bringing them closer to the iron piece, it is stable at the position shown in Figure 2 (8) or the position where the N% S magnetic poles are swapped by rotating 180 degrees, and from these directions. If it shifts, a torque is generated to try to return it to its original position.

Figure 2 (1)) position or rotate 180 degrees to N.
At the position where the S magnetic poles are swapped, the torque is 0, but it is an unstable position, and when the position deviates from this direction, the torque acts in a further deviated direction. Therefore, a clockwise force acts at the position shown in FIG. 2(c).

The process of actually reversing the permanent magnet 201 will be explained keeping in mind that the above torque moves.

First, assume that the permanent magnet is in the position shown in FIG. 2(a) with no current flowing through the drive coil.

The permanent magnet 201 is stabilized by magnetic attraction with the iron piece 204. Next, consider a case where a current is passed through the coil cross section A202 toward the side of the page and through the coil cross section B2O3 toward the side of the page. Due to the magnetic field created by the current, the permanent magnet 201
A clockwise torque is generated. If the current flowing through the coil is of sufficient magnitude, this torque will exceed the attractive force generated between the iron piece 204 and the magnetic pole, and the two permanent magnets will begin to rotate clockwise. While constantly receiving clockwise torque, it reaches the position shown in Figure 2 (b), and rotates further to reach the position shown in Figure 2 (
It will be in position c). Even in this position, the attraction force with the iron piece acts as a clockwise torque, but the torque generated by the drive coil changes counterclockwise, so when the current is cut off at this time, the S magnetic pole is at the top position due to the attraction force with the iron piece. It rotates until it stabilizes. With the above, the NSS magnetic pole is reversed.

In order to rotate it again so that the north pole is on top, the direction of the current flowing through the drive coil can be reversed and the process can be reversed in the same manner as described above.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 3(a) is a bottom view showing an embodiment of the bias magnetic field generating mechanism of the present invention. Also, Fig. 3(b) is similar to Fig. 3(a).
) is a sectional view taken along line A-A.

The length of the permanent magnet in the longitudinal direction is determined according to the width of the recording area of the optical disk. For example, when used in a magneto-optical recording/reproducing device for an optical disk with a diameter of 5.25 inches, the thickness may be approximately 35 mm. The permanent magnet 301 is housed in the groove of the holder 306 and bonded. Holder 3
Cylindrical projections are provided at both ends of the bearing 304 and engage with the inner ring of the bearing 304.

Further, this bearing 304 is engaged with a hole made in a case 307 that houses the entire bias magnetic field generation mechanism. This case and bearings constitute a rotational support mechanism with low load torque. As a result, the permanent magnet 301
has a structure that allows rotation with a small torque around the rotation center 305. Further, if the drive coil 302 is fixed to the inner surface of the case 307, it is preferable to design the drive coil so that it comes as close to the permanent magnet as possible without coming into contact with the permanent magnet when the permanent magnet rotates.

This is to reduce the power required to obtain the required torque. Further, since the drive coil applies torque to the permanent magnet when energized and at the same time receives a reaction thereof, it is desirable to fix it by a reliable method such as adhesive, thereby suppressing vibrations and the like. The iron piece 303 is fixed to the outside of the case, and the permanent magnet is attracted by the attraction force with the permanent magnet.
I try to keep it stable in direction. It is important to select an appropriate size and thickness for this iron piece according to the distance from the permanent magnet, and to design it to obtain the optimum attractive force.

Furthermore, although not shown in the figure, by attaching a Hall element or similar device to an appropriate position, it is possible to monitor the polarity of the bias magnetic field, and this can be used to optimize the timing of cutting off the current. Is possible. Optimization of this timing contributes to shortening the inversion time. Furthermore, in order to speed up the reversal time, it is also effective to detect the rotation angle of the permanent magnet, generate a torque in the opposite direction to the rotation direction, and apply the brake.

In the embodiment described above, magnetic attractive force with the iron piece is used to stabilize the permanent magnet in two directions, but this can also be achieved by a mechanical structure.

[Effects of the Invention] The bias magnetic field generation mechanism of the present invention has the following special effects.

That is, this method uses a permanent magnet to generate a bias magnetic field, and there is no need to apply electricity except during reversal, so even if continuous erasing is performed, there is no need to worry about heat generation and the power consumption is low.

Since the permanent magnet for generating the bias magnetic field also serves as the drive system for reversing the magnetic field, it is extremely compact. In particular, since the drive coil improved by the present invention is extremely space-saving compared to similar systems, it is very effective for making magneto-optical recording and reproducing devices smaller and thinner.

The particularly devised shape and arrangement of the drive coil of the present invention not only generates a large starting torque but also generates continuous torque while the magnet rotates 135 degrees, enabling high-speed and stable reversal operation.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the main components of an embodiment of the bias magnetic field generating mechanism of the present invention. FIGS. 2(a), 2(b), and 2(c) are operational diagrams of an embodiment of the bias magnetic field generating mechanism of the present invention. FIG. 3(a) is a plan view of an embodiment of the bias magnetic field generating mechanism of the present invention. FIG. 3(b) is a sectional view of an embodiment of the bias magnetic field generating mechanism of the present invention. FIG. 4 is a perspective view of a conventional example using a motor. Figure 5(a) is a plane view of a conventional example using one drive coil. Figure 5(b) is a cross section of a conventional example using one drive coil. Figure 6(a) is a plane view of a conventional example using two drive coils. The plane milk of the example shown in FIG. 6(b) is a cross section of a conventional example using two drive coils, 1 1 0 1° 401. 102. 602. 103. 504. 304 ・ 306 ・ 307 ・ 308, 011 011 302. 603 ・204. 604 @ 403 Naki 011 601 ・ 503. 303, ...Permanent magnet, drive coil, iron piece Φ bearing, holder, case, optical disk or more

Claims (1)

[Claims] In a magneto-optical recording/reproducing device, a bias magnetic field generating mechanism, which is a means for generating a magnetic field on the surface of a recording medium when recording or erasing information, includes: (a) a rod-shaped magnetic field magnetized in the thickness direction; a permanent magnet; (b) a rotation support mechanism that supports the permanent magnet so that it can rotate around the longitudinal direction; (c) an electromagnetic coil wound in a long and thin manner, the two sides of which are placed along the permanent magnet. A bias magnetic field generating mechanism characterized in that the bias magnetic field generating mechanism is constituted by a drive coil arranged in a positional relationship such that two sides thereof are approximately 90 degrees from the center of rotation of the permanent magnet.