JPS63266643A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To simplify a magnetic field switching circuit by providing a pair of coils for a focus and a coil for a track at both sides of an objective lens, arranging first and second magnetic circuits to give a magnetic field to respective coils and making non-symmetrical the polarity of a magnet used for the second magnetic circuit. CONSTITUTION:An inside surface 21a of one side magnet 18a comes to be an N pole, an outside surface 23a comes to be an S pole and in the direction shown by an arrow phia in a magnetic gap 22a, a magnetic field is formed. An inside surface 21b of other side magnet 18b comes to be the S pole, an outside surface 23b comes to be the N pole and in the direction shown by an arrow phib in a magnetic gap 22b, the magnetic field is formed. Thus, since the polarity of the magnet used for first and second magnetic circuits 17a and 17b is made non-symmetrical, the direction of the leaking magnetic flux at the spot position of the recording medium, in which a laser light is converged, comes to be in parallel to the recording medium. Consequently, the magnetic field vertical to the recording medium impressed to the spot position by a magnetic field impressing means is not influenced by the leaking magnetic flux. Thus, the switching circuit to switch the direction of the magnetic field, namely, the direction of the current is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an objective lens drive device for a rewritable magneto-optical disk device.

(Prior Art) In a so-called rewritable magneto-optical disk device, which can perform recording, reproduction, and erasing by applying a magnetic field to the recording medium and irradiating the medium surface with laser light, an objective lens is placed on the recording medium surface. an objective lens that is driven in a direction perpendicular to the recording medium to maintain appropriate convergence of the laser beam, and that tracks a spiral or concentric recording track by driving the objective lens in the radial direction, that is, in the radial direction of the recording medium. A lens driving device and a magnetic field applying means for applying a magnetic field perpendicular to the recording medium surface and reversing the direction of the applied magnetic field during recording and erasing are required.

A conventional objective lens driving device and magnetic field applying means will be explained below with reference to FIGS. 2(a) to 2(d).

FIG. 2(a) is an exploded perspective view of a movable coil of a two-dimensional drive system used in an objective lens drive device, and the movable coil 51
The two focusing coils 52a and 52 are formed into a mouth shape by bending both sides of a flat rectangular coil at right angles.
b, and two rectangular cylindrical track coils 53a and 53b.
It is constructed by integrating the two with adhesive or the like.

Therefore, the movable coil 51 is indicated by the arrow φ1. If the movable coil 51 is placed in a magnetic field indicated by φ2 and a current is passed through the focus coils 52a and 52b, it can be driven in the Ff or -Ff direction, and if a current is passed through the focus coils 53a and 53b, the movable coil 51 can be moved. The coil 51 can be driven in the Ft or -Ft direction.

FIG. 2(b) shows the φ1. The magnetic field of φ2 is applied to the moving coil 51.
FIG. 2(c) is a sectional view taken along the line X--X in FIG. 2(b). The magnetic circuit 54 includes two elongated magnets 55a arranged in parallel.

55b, yokes 56a, 56b, 57a, 57b, 58a, 58b that surround the magnets 55a, 55b in a rectangular shape, and elongated mutually formed spaces between the magnet 55a and the yoke 57a and between the magnet 55b and the yoke 57b. Parallel magnetic gap 59a.

59b, which are arranged in the radial direction of the recording medium. Also, the magnet 55a.

The polarity of 55b is such that each inner surface 60a, 60b is a north pole,
The outer surfaces 61a and 61b are S poles, and the magnetic gap 59
a, 59b, arrow φ1. A magnetic field in the φ2 direction is generated. C is the magnetic flux that passes through the yoke and forms a loop. Reference numeral 62 denotes a support whose both sides are loosely inserted into the magnetic gaps 59a and 59b and which has an objective lens 63 on its upper surface, and the movable coil 51 is integrally fixed to this support 62 with an adhesive or the like. The objective lens driving device 64 is configured as described above.

Therefore, the focusing coil 52 of the movable coil 51
By supplying current to the track coils 53a and 52b of the movable coil 51, the support 61 can be driven in a direction perpendicular to the surface of the recording medium to maintain proper convergence of the laser beam. By flowing the support body 61 in the radial direction of the recording medium, the recording track can be tracked (see Japanese Patent Laid-Open Nos. 59-11544 and 60-239943).

FIG. 2(d) shows a main part of the objective lens driving device and a vertically elongated magnetic field applying means disposed parallel to the objective lens driving device and the recording medium, extending in the radial direction of the recording medium. It is a cross-sectional view, and the magnetic field applying means 65 is attached to the support body 6.
2, an excitation coil 67 wound around the magnetic pole 66, and a yoke 68 having an opening-shaped cross section surrounding the magnetic pole 66. Therefore, by passing a current through the excitation coil 67, a magnetic field can be applied perpendicularly to the medium surface of the recording medium 69, and by reversing the direction of the current flowing through this excitation coil 67, the direction is reversed during recording and erasing. can be applied to the recording medium 69 (see Japanese Patent Laid-Open No. 119507/1983).

(Problems to be Solved by the Invention) By the way, the magnetic circuit 54 is connected to the broken line E in FIG. 2(c).
, F is always generated, and a part of this leakage flux is shown by the broken line J in FIG. 2(d).

As shown in K, it is in a state where it is attracted to the yokes 66 and 68 of the magnetic field applying means 65. Therefore, the magnetic field applying means 65
The strength of the magnetic field applied to the spot position G of the recording medium 69 where the laser beam is focused varies due to the influence of the leakage magnetic flux J.

FIG. 2(e) is a characteristic diagram showing the relationship between the current and the strength of the magnetic field, where the horizontal axis 1c represents the strength of the current flowing through the excitation coil of the magnetic field applying means 65, and the vertical axis Hg represents the spot position G. The strength of the magnetic field applied to each is shown, and Fig. 2 (
The direction of the arrow shown in d) is the positive direction of the vertical axis HG. Further, H2 shown by a solid line is a characteristic when the magnetic circuit 54 is used, that is, when leakage magnetic flux is generated.
Hl indicated by a broken line is connected to the magnets 55a, 5 from the magnetic device 54.
This is the characteristic when 5b is removed, that is, when no leakage flux is generated.

In this way, the characteristic H2 when leakage magnetic flux is generated is compared to the characteristic H1 when leakage magnetic flux is not generated.
The vertical axis - is equal to the strength HM of the magnetic field due to the leakage magnetic fluxes J and K.
It appears that the HG force direction has shifted. That is, the magnetic field strength HW required for recording and erasing is opposite in direction but approximately the same in magnitude;
When trying to obtain HE, in the case of characteristic H2, characteristic H1
Although the current 12E required to obtain the magnetic field HE is small compared to the above, the current IW2 required to obtain the magnetic field HW becomes large. Therefore, in the case of characteristic H2, a large power supply corresponding to the current IW is required, and the direction of the magnetic field,
That is, there is a problem in that the switching circuit that switches the direction of the current requires an enclosure that changes the magnitude of the current based on the leakage magnetic flux.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an objective lens drive device in a magneto-optical disk device, in which at least one pair of focusing coils and one pair of tracking coils are provided on each side of the objective lens. A first magnetic circuit and a second magnetic circuit are provided to apply a magnetic field to each coil, and the polarities of the magnets used in the first and second magnetic circuits are asymmetrical.

(Function) According to the present invention, since the polarity of the magnets used in the first and second magnetic circuits is asymmetric, the direction of leakage magnetic flux at the spot position of the recording medium where the laser beam is focused is directed to the recording medium. Therefore, the magnetic field perpendicular to the recording medium applied to the spot position by the magnetic field applying means is not affected by the leakage magnetic flux.

(Embodiment) FIGS. 1(a) to (C) show an embodiment of the present invention, in which FIG. 1(a) is a partially cutaway perspective view showing an objective lens driving device, and FIG. ) is a sectional view taken along line A-A in FIG. 1(a), and FIG. 1(c) is an exploded perspective view of the movable body. A movable body 1 that can move in two directions perpendicular to each other with respect to the recording medium W, that is, in a direction substantially perpendicular to the recording medium and in a radial direction of the recording medium, includes a holder 2 and an engaging body 3.
It is made up of. The holder 2 includes a cylindrical portion 5 having a through hole 4 on its side surface, support plates 6a and 6b provided at upper and lower positions of the cylindrical portion 5, and approximately the center of the support plate 6a above the cylindrical portion 5. It is composed of an objective lens 7 embedded in the position. Further, in the holder 2, two rectangular cylindrical track coils 8a and 8b sandwich the cylindrical portion 4 and support plates 5a.

5b, and four focusing coils 9a formed by bending a flat coil at right angles near the center.

9b, 9c, and 9d are fixedly arranged by adhesive or the like so as to cover two sides at four locations of a rectangular parallelepiped formed by the support plates 6a, 6b and the outer surfaces of the track coils 8a, 8b.

The engaging body 3 includes a cylindrical portion 11 having a through hole 10 on its side surface, a support base 13 provided at the lower end of the cylindrical portion 11 and having guide holes 12a and 12b on both sides, and a support base 13 disposed within the cylindrical portion 11. It consists of a 45@ inclined mirror 14. The cylindrical portion of the holder 1 is fitted into the cylindrical portion 11 of the engaging body 3 so that the through holes 4 and 10 match each other, and the guide hole 15 of the lower support plate 6b is fitted into the pin 16 of the support base 13. The movable body 1 is mounted so as to be slidable only in the vertical direction.

17a and 17b are a pair of magnetic circuits arranged in parallel on both sides of the holder 2. Magnetic circuits 17a, 17b
are vertically long magnets 111a and 18b and the magnets 18a and 18b.
Yoke members 19a, 19b, 20a that surround in a rectangular shape
, 20b, and the magnets 18a, 18
b inner surfaces 21a, 21b and yoke members 20a, 20b
elongated magnetic gaps 22a, 22b between the outer surface of the
and each form a closed magnetic path.

The polarity of the magnets 18a and 18b will be explained with reference to FIG. 3. The inner surface 21a of one magnet 18a is an N pole, and the outer surface 23 is an altS pole, so that the magnetic gap 2
A magnetic field is formed within 2a in the direction indicated by arrow φa. In addition, the inner surface 21b of the other magnet 18b is an S pole, and the outer surface 23b is an N pole, thus forming a magnetic gap 22b.
Inside, a magnetic field is formed in the direction indicated by arrow φb.

The movable body 1 includes track coils ga and 3 of the holder 2.
b is the yoke member 2Qa of the magnetic circuits 17a and 17b described above.
, 20b, and a portion of the tracking coils 8a, 8b and focusing coils 9a to 9d are disposed within each magnetic gap 22a, 2'2b, and the engaging body 3
The magnetic circuit 17a slides through the guide holes 12a and 12b via bearings or the like.

A pair of guide shafts 24a arranged parallel to 17b
, 24b in a slidable manner. In this way, a drive device capable of moving the above-mentioned movable body 1 in two directions perpendicular to each other with respect to the recording medium W is constructed.

Reference numeral 25 denotes an optical system disposed in front of the through holes 4 and 10, and the optical system 25 includes a semiconductor laser, a focus and tracking error detector, and a signal detector. Note that the magnetic devices 17a, 17b and the guide shafts 24a, 24
b and the optical device 25 are each fixed to a frame (not shown).

Next, the operation of the objective lens driving device described above will be explained.

A parallel laser beam 26 emitted from the optical device 25 passes through the through holes 4 and 9, is reflected at right angles by the mirror 14, and is focused onto the recording surface of the recording medium W by the objective lens 6. On the other hand, the reflected light 27 from the recording medium W returns to the optical device 25 via the objective lens 6 and mirror 14, and detection of focus and tracking errors and recording signal detection are performed.

Therefore, when a focus error is detected in the optical device 25, a control circuit (not shown) controls the focus coils 9a to 9 based on this focus error signal.
d, applying a driving force to the focusing coils 9a to 9d by the interaction of this current and the magnetic fields in the magnetic gaps 22a and 22b of the magnetic circuits 17a and 17b, respectively,
The holder 2 is moved along the cylindrical portion 11 of the engaging body 3 in a direction perpendicular to the medium surface of the recording medium W depending on the direction of the current at that time. That is, each of the focusing coils 9a to 9d has Ra 1°Rbl, Rcl, as shown in FIG. 1(c).
When a current flows in the direction indicated by Rdl, the magnetic circuit 1
Since the directions of the magnetic fields in the magnetic gaps 22a, 22b of Ra2. Rb2. Ra2. When a current is applied in the direction indicated by Ra2, the holder 2 moves in the direction of arrow -2, that is, in the direction away from the recording medium W. In this way, by controlling the direction, magnitude, and time of the current flowing through the focusing coils 9a to 9d, it is possible to drive the holder 2 along the cylindrical portion 11 of the engaging body 3 and perform focus control.

Further, when a tracking error is detected in the optical device 25, a control circuit (not shown) causes a current to flow through the tracking coils 8a and 8b based on this tracking error signal, and the current and the magnetic devices 17a and 17b are connected to each other. The tracking coil 8a by the action of the magnetic field in the magnetic gaps 22a, 22b.

8b is applied to move the holder 2 in the radial direction of the recording medium W along the guide shafts 24a and 24b depending on the direction of the current at that time.

That is, each of the track coils 8a and 8b is
When current is passed in the directions shown by Qal and Qbl as shown in FIG.
, 22b are φa, φb, so the holder 2 moves in the direction of arrow X, and Qa2
．． When a current is applied in the direction indicated by Qb2, the holder 2 moves in the direction of the arrow -X. in this way,
Track control can be performed by driving the holder 2 along the guide shafts 24a, 24b by controlling the direction, magnitude, and time of the current flowing through the tracking coils 8a, 8b.

Furthermore, access control is performed by controlling the track coils 8a and 8b by a control circuit based on the difference between the designated position and the current position.
holder 2 in the same way as the track control described above.
This is done by moving the recording medium W in the radial direction. The position detecting means at this time may be by counting the number of tracks crossed, or by using an external scale.

As described above, the movable body 1 is appropriately driven in a direction substantially perpendicular to the recording medium W and in a radial direction due to track and focus errors, differences from the target track, and the like.

FIG. 4 is a cross-sectional view of a main part showing the objective lens driving device and a vertically elongated magnetic field applying means arranged parallel to the objective lens driving device and the recording medium W, and extending in the radial direction of the recording medium W. 2, the magnetic field applying means 26 includes a yoke 27 having a length corresponding to the movable area of the movable body 1 in the radial direction, and an excitation coil 28 wound around the yoke 27.
and a yoke 29 having an opening-shaped cross section and surrounding the yoke 27. Therefore, by passing a current through the excitation coil 28, a magnetic field can be applied perpendicularly to the recording medium W.
Furthermore, by reversing the direction of the current flowing through the excitation coil 28, magnetic fields in opposite directions can be applied to the recording medium W during recording and erasing.

Incidentally, leakage magnetic flux naturally occurs in the magnetic circuits 17a and 17b as well. However, the magnetic circuits 17a, 1
7b, the directions of the magnetic fields are φa and φb, so the direction of the leakage magnetic flux O is parallel to the recording medium W near the spot position P where the laser beam of the recording medium W is focused.
Therefore, the strength of the vertical magnetic field necessary for recording and erasing does not vary due to the influence of the leakage magnetic flux O.

FIG. 5 is a characteristic diagram showing the relationship between the current flowing through the excitation coil 28 of the magnetic field applying means 26 and the strength of the magnetic field applied by the magnetic field applying means 26, and the horizontal axis IC represents the magnetic field applying means 26. The vertical axis HG represents the strength of the current applied to the excitation coil 28, and the strength of the magnetic field perpendicular to the recording medium W applied to the spot position P.

In this way, the characteristic H3 is symmetrical about the origin on the graph, and is approximately equal to the characteristic H1 shown in FIG. 2(e) where there is no leakage flux at all. That is, even when the magnetic fields HW and HE necessary for recording and erasing are generated at the spot position P, the required current IW3. The magnitude of IE3 may be the same, although in the opposite direction, and is not affected by leakage magnetic flux.

(Effects of the Invention) As described above, according to the present invention, in the objective drive device of a magneto-optical disk device, at least one pair of focusing coils and one pair of tracking coils are provided on both sides of the objective lens, and a magnetic field is applied to each coil. A first magnetic circuit and a second magnetic circuit are arranged to provide the first and second magnetic circuits.
Since the polarity of the magnet used in the magnetic circuit is asymmetric, the direction of leakage magnetic flux at the spot position of the recording medium where the laser beam is focused is parallel to the recording medium, and therefore the direction of the leakage magnetic flux at the spot position of the recording medium where the laser beam is focused is parallel to the recording medium. The applied magnetic field perpendicular to the recording medium is not affected by the leakage magnetic flux. This has the effect that the magnetic field switching circuit of the magnetic field applying means can be simplified and the power supply required for the magnetic field applying means can be made smaller.

In the above embodiment, the case where the two magnetic circuits were arranged independently was explained, but as shown in FIG. 2(b), even if the two magnetic circuits are connected by a yoke member, the spot Since the direction of the leakage magnetic flux at the position is parallel to the recording medium, the same effect as described above can be achieved.

Further, in the above embodiment, the two magnetic circuits include the objective lens, and are arranged approximately symmetrically with respect to a plane perpendicular to the recording medium in the access direction of the objective lens. If the direction of the magnetic poles is asymmetrical, the HM shown in Figure 2 (e) can be brought closer to the origin of the graph than if it is symmetrical, and the influence of leakage magnetic flux can be reduced. .

[Brief explanation of drawings]

FIG. 1(a) is a partially cutaway perspective view showing the objective lens driving device of the present invention, FIG. 1(b) is a sectional view taken along the line A-A in FIG. 1(a), and FIG. 2(c) is an exploded perspective view of the movable body of the present invention, FIG. 2(a) is an exploded perspective view showing a conventional moving coil, FIG. 2(b) is a perspective view showing a conventional objective lens drive device, 2(c) is a sectional view taken along the line X-X in FIG. 2(b), FIG. 2(d) is a sectional view of the main part of a conventional magneto-optical disk device, and FIG. A conventional current/magnetic field characteristic diagram, FIG. 3 is a cross-sectional view taken along the line B-B in FIG. 1(a),
FIG. 4 is a sectional view of a main part of the magneto-optical disk device of the present invention, and FIG. 5 is a current/magnetic field characteristic diagram of the present invention. 1... Movable body, 7... Objective lens, 8a, 8b...
・Track coil, 9a, 9b, 9c, 9d...Focusing coil, 1
7a, 17b...Magnetic circuit, 18a, 18b...Magnet, W...Recording medium. Patent applicant Oki Electric Industry Co., Ltd. Agent Patent attorney Yoshi 1) Yoshitaka 92 Figure (b) 2 w1 (C) Figure 2 ((1) Figure 2 (e) 3 WJ Hatake φ6 To the nine magnetic fields of the present invention Figure 4 is a side view of the main parts of the Suffu device.

Claims (3)

[Claims] (1) an objective lens, and a focusing coil for moving the objective lens in a direction substantially perpendicular to the surface of the recording medium;
and an objective lens drive device in a magneto-optical disk device, which has a movable body equipped with a tracking coil for moving in the radial direction, and a magnetic circuit that applies a magnetic field to the focusing coil and the tracking coil, on both sides of the objective lens. At least a pair of focusing coils and a tracking coil are each provided, and a first magnetic circuit and a second magnetic circuit are provided for applying a magnetic field to each coil, and the magnetic circuits are used for the first and second magnetic circuits. An objective lens drive device characterized by asymmetric polarity of a magnet. (2) The first and second magnetic circuits include an objective lens and are arranged substantially symmetrically with respect to a plane perpendicular to the recording medium in the access direction of the objective lens. The objective lens driving device described in . (3) The objective lens driving device according to claim 1, wherein the first and second magnetic circuits are connected by a yoke member.