JPS63244431A - Optical disk device - Google Patents

Abstract

PURPOSE:To decrease the leakage magnetic field of a magnetic field radiating part, to improve the magnetism utilizing efficiency and to reduce the power consumption by forming a cross section of a magnetic flux radiation part to be a wedge shape whose cross section is decreased along the major axis from the coupling part with a magnetic core part. CONSTITUTION:Magnetic flux leadout part 37 is formed to be a wedge shape in a way that the thickness is decreased along the major axis from the center being the coupling part of the magnetic core part 34 toward the tip and has a length corresponding nearly to the radius of an optical disk 20. That is, the magnetic flux radiating face 37A is prolonged at the outside of the range corresponding to the region on a magneto-optical recording film 24 capable of being radiated with a light beam focused by an objective lens 25 and the magnetic flux radiating face 37A being a flat lower face at the recording or erasure of information is opposed to the light beam radiation enable region of the magneto-optical recording film 24. Since the cross section of the magnetic flux radiating part 37 is formed to be a wedge shape in a way that the thickness is decreased along the major axis from the coupling part with the magnetic core 34, the magnetic field leaked to the magnetic flux radiating part 37 is small, the magnetism utilizing efficiency is improved and the power consumption is made small.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an optical disk device that records information on or erases information from a recording medium using a light beam while applying a magnetic field to the recording medium. The present invention relates to a magnetic field generating device including an improved magnetic field generating device that generates a magnetic field.

(Prior art) Information recording/reproducing device using magneto-optical recording, that is, an optical disk device such as an external memory of a computer, a rewritable video disk device, an image file device, an AD type compact disk device capable of playback/recording, or a rewritable one. There are high-density recording magnetic cards, and their development has been progressing recently. In this magneto-optical information recording/reproducing device, a static magnetic field is applied perpendicularly to the recording surface of the information recording medium, and a focused light beam is irradiated onto the recording film surface of the information recording medium to raise the temperature to over the Curie point or Information is recorded or erased by heating to a temperature where the coercive force becomes smaller than the external magnetic field and reversing the magnetic moment of the magnetic domain in that region. In such devices, methods for applying a magnetic field to a recording medium include the J method, in which a focused light beam is irradiated, and a magnetic field is applied locally only around the area where a beam spot is formed, and the information access method. Therefore, there is a method in which a convergent light beam is moved and a magnetic field is continuously applied over the entire range that can be irradiated with a four-flux light beam.

In a conventional magnetic field generation device that employs a local magnetic field application method, an electromagnetic coil is wound around a magnetic core portion that protrudes into a yoke that serves as a box-shaped magnetic feedback portion. In this magneto-optical field generator, the end faces of the magnetic core and the yoke are arranged to face the recording film surface of the magnetic recording medium, and when a current is supplied to the electromagnetic coil, the magnetic flux is emitted from the end face of the magnetic core as a magnetic flux emitting part. The magnetic flux spreads through the recording film surface of the magneto-optical recording medium and is returned to the end face of the yoke surrounding the end face of the magnetic core. Therefore, a magnetic field perpendicular to the recording film surface of the magneto-optical recording medium is locally applied to this recording film surface. When a local magnetic field application method is adopted, the length of the magnetic core end face and yoke end face of the magnetic field generator in the longitudinal direction is determined to be the length of the local area to which the magnetic field is to be applied, and the magnetic field generator itself can be made compact. has been done.

On the other hand, in a conventional magnetic field generating device that employs a full-range magnetic field application method, as shown in FIG.
An electromagnetic coil 16 is wound around a magnetic core 14 extending substantially parallel to the magnetic core 14 . In this magnetic field generating device, similarly, the end face 14A of the magnetic core 14 and the yoke 12 is arranged in parallel.
112A is arranged to face the recording film surface of the magneto-optical recording medium, and when a current is supplied to the electromagnetic coil 16, the magnetic flux emitted from the end surface 14A of the magnetic core 4 as a magnetic flux emitting section is used for magneto-optical recording. The end faces 12 of the yoke 12 are arranged on both sides of the end face 1.4A of the magnetic core portion 14, penetrating the recording film surface of the medium.
Returned to A. Therefore, similarly, a magnetic field perpendicular to the recording film surface of the magneto-optical recording medium is applied to the entire range of the recording film surface that can be irradiated with the light beam. When the full range magnetic field application method is adopted, the magnetic core end face and yoke end face 1 of the magnetic field generating bag device are
The width and length of 4A112A are determined to be approximately equal to each other, and the magnetic core end face and yoke end face 14 of the magnetic field generator
The lengths of A and 12A in the longitudinal direction are set to be larger than the length of the magnetic field of the magneto-optical recording surface of the information recording medium, and the magnetic field generating device itself is formed relatively large.

(Problem to be solved by the invention) In the conventional magnetic field generation device that employs a local magnetic field application method, the magnetic field is applied locally, so as the light beam moves, this magnetic field generation device also There is a problem in that it requires movement and the movement mechanism becomes complicated. On the other hand, a conventional magnetic field generating device as shown in FIG. 9 which employs a full range magnetic field application method does not require the magnetic field generating device to be moved, but has the following problems.

(1) There is a problem of high power consumption. In other words, in order to apply a large magnetic field to an information recording medium, it is necessary to generate a large magnetomotive force from the electromagnetic coil, but this magnetomotive force is determined by the total number of turns N of the electromagnetic coil and the amount of power flowing through the electromagnetic coil. It is determined by the product NXI of current l. Further, the power consumption P consumed by this electromagnetic coil is P=IXR2 when the resistance R of the electromagnetic coil is. In the magnetic field generator shown in FIG. 6, the length of the magnetic core in the longitudinal direction is determined corresponding to the length of the recording film surface of the magneto-optical recording medium, so the length of the outer circumference is relatively long. determined. Therefore,
The total length of the conductive wire of the electromagnetic coil wound N turns around the magnetic core 14 becomes extremely long, and the resistance value R of the electromagnetic coil increases accordingly, and the required power consumption also increases. If the linearity of the conducting wire is increased in order to reduce the resistance R of the electromagnetic coil, there is a problem in that the number of turns N becomes smaller if the size of the space in which the electromagnetic coil is accommodated is predetermined. Also, the number of turns N
When trying to obtain a specified magnetomotive force when becomes small,
There is a problem that a large current must be supplied to the electromagnetic coil, resulting in increased power consumption.

(2) There is a problem that the amount of heat generated is large. That is, when the power consumption is large as in a series of -1s, the amount of heat generated also increases accordingly. The coil, which is the heat generating part of the magnetic field generator, and the magnetic core and yoke to which heat is transferred from the coil are opposed to the magneto-optical recording medium in sufficient proximity to the magneto-optical recording medium, so the heat from the magnetic field generator is transferred to the magneto-optic There is a risk that the information may be transmitted to the recording medium, and the magneto-optical recording medium may be thermally deformed, or the recorded information may be lost.

(3) There is a problem in that the size of the magnetic field generator increases. In particular, there is a problem in that the height of the magnetic field generator along the direction perpendicular to the optical recording surface increases. In order to increase the magnetic density on the same recording surface, it is necessary to make the width of the magnetic core sufficiently small and the height of the magnetic core and yoke sufficiently high so that each turn of the electromagnetic coil is aligned perpendicular to the optical recording surface. Sequencing is required. In such a structure, there is a problem that the height of the device inevitably becomes large. When a magnetic field generator with a height is placed above the magnetic recording medium,
This leads to an increase in the size of the information recording and reproducing device itself, and it is subject to design constraints.

[Structure of the Invention] (Means for Solving the Problem) According to the present invention, there is provided a light source, an optical means for focusing a light beam from the light source toward an information recording medium, and a method for storing at least information on the information recording medium. It consists of a magnetic field generator that applies a magnetic field during recording. A magnetic flux made of a magnetic material that is connected to a magnetic core and has a wedge-shaped cross section that decreases along its long axis from the connection. A yoke portion magnetically connected to the other end of the magnetic core portion to which the magnetic flux emitted from the magnetic core extension portion is returned through a space where an information recording medium is to be placed. An optical disc device is provided.

(Function) Since the cross section of the magnetic flux emitting part is formed in a wedge shape that decreases from the joint with the magnetic core part along its long axis, the leakage magnetic field of the magnetic field emitting part is small and the efficiency of magnetic utilization can be increased. It is possible to reduce power consumption. Further, since the electromagnetic coil can be formed into an elongated shape and the wire length required for one turn can be reduced, a large magnetomotive force can be obtained with small power consumption. In addition, since the electromagnetic coil can be made elongated, the heat dissipation effect can be increased.
+111 does not heat up even if the power is turned on for a long time. Furthermore, since the magnetic field generator is compact, the optical disk device itself can be made smaller.

(Embodiments of the invention) Examples of the invention will be described below with reference to the drawings.

As shown in FIG. 1, the optical disk 20 as a magnetic recording medium has a structure in which a pair of transparent substrates 22 are faced and bonded together, and a magneto-optical recording film 24 is formed on the inner surface of the substrate. A tracking guide (not shown) is formed on the recording film 24 in advance. Usually, this information recording medium is formed in the shape of a disk so as to be called an optical disk, but it is not limited to this and can take various shapes such as a card shape. Further, the information recording medium 2o is a first
As shown in FIGS. 4 and 5, the cassette 26 is stored and protected, and when installed in the information recording and reproducing apparatus, a loading mechanism (not shown) is used to insert the information recording and reproducing apparatus together with the cassette. When inserted from the mouth (not shown) and ejected from the information recording/reproducing device,
The information recorder 1 is ejected together with this cassette 26 from the insertion slot of the main device.

As shown in FIG. 5, the cassette 26 is provided with two and lower windows 26B and 26C extending along the radial direction of the optical disk 20 in the upper and lower plate parts of a thin rectangular cassette case 26A. is provided with a shutter 19 that is slidable in the direction of arrow I. When the cassette 26 is loaded into an optical disc device as an information recording/reproducing device, one shutter is opened by an opening/closing mechanism (not shown) during the loading operation of the cassette 26, and the second part of the cassette case 26A and the lower window 26B are opened.

26C is opened, and when the cassette 26 is attached to and detached from the information recording/reproducing apparatus, the shutter 19 is closed by a spring mechanism (not shown) during the operation of attaching and detaching the cassette 26, and the upper and lower windows 26B and 26C of the cassette case 26A are opened. is closed. As shown in FIG. 1, when the cassette 26 is installed in the optical disc device, the windows 26B and 26C of the cassette 26
The lower stamper 52B connected to the motor 50 via the spindle 51 and the upper stamper 52A lowered from above the optical disc 20 stamp the optical disc 20.
is clamped and fixed, and the objective lens 25 of the optical head 28 is placed under the optical disk, and the optical head 28 is inserted through the lower window 26C.
The laser beam is maintained in a state capable of being focused from the objective lens 25 of No. 8.

Furthermore, when the cassette 26 is installed in the optical disc device,
” The magnetic flux deriving part 37 of the magnetic field generator 30 is located inside the two-part window 26B.
The magnetic flux emitting surface 37A is opposed to the optical disk 20, and information can be reproduced, recorded, or erased from the optical disk 20. As shown in FIG. 4, when the cassette 26 is removed or inserted into the optical disk device, the two-part stamper 52A is raised to one side, and the magnetic field generator 30 is placed outside the window 26B. The magnetic flux guiding portion 37 is withdrawn, and the magnetic field generating device 30 is moved by the moving mechanism, so that the magnetic field generating device 30 is deflected upward from the lower stamper 52B together with the cassette 26.

In this state, the cassette 26 is attached and detached.

As shown in FIG. 2, the magnetic field generating device 30 includes a prismatic magnetic core portion 34 to which an electromagnetic coil 32 as shown in FIG. 7 is attached.
and a magnetic flux deriving part 37 as shown in FIG.
and a yoke portion 39 in the shape of an opening, the other end of which is connected to the inner surface of the magnetic core portion 34, and from which the magnetic flux emitted from the magnetic flux emitting surface 37A is returned. here,
The magnetic flux deriving part 37 is formed in a wedge shape whose thickness decreases as it goes from the center part, which is the connection part of the magnetic core part 34, toward its tip along its long axis, and has a length corresponding to approximately the radius of the optical disc 20. have. That is, the magnetic flux emitting surface 37
A extends outside the area corresponding to the area on the magneto-optical recording film 24 that can be irradiated with the light beam focused by the objective lens 25, and when information is reproduced, recorded, or erased, its flatness is The magnetic flux emitting surface 37A, which is the lower surface, faces the light beam irradiable area of the magneto-optical recording film 24.

The magnetic core portion 34 extending from the inner surface of the three mouth-shaped yokes has a cross section smaller than the area of the magnetic flux emitting surface 37A of the magnetic flux deriving portion 37, and the cross-sectional area of the magnetic core portion 34 is It is determined to be sufficiently small so that its cross section can take a value close to the saturation magnetic flux density Bs, and the outer circumferential length of the magnetic core portion 34 is determined to be small. As a result, the wire length required for one turn of the electromagnetic coil 32 is reduced, and the resistance value of the electromagnetic coil 32 as a whole is determined to be small. Further, the cross-sectional area of the magnetic flux deriving portion 37 perpendicular to its longitudinal direction is similarly determined to be sufficiently small to the extent that the cross-section can take a value close to the saturation magnetic flux density Bs during operation, and the surface area is small. It is being saved. The magnetic flux passing through the magnetic flux deriving portion 37 near the magnetic core 34 is equal to the integrated amount of magnetic flux emitted from the surface closer to the magnetic core 34 . Therefore, the magnetic flux deriving portion 37 is shaped such that its cross-sectional area becomes larger as it approaches the magnetic core portion 34 from a certain point. In order to reduce the total amount of magnetic flux passing through the magnetic core part 34 and to make the magnetic field distribution near the magnetic flux emitting surface 37A uniform in the longitudinal direction, the magnetic flux deriving part 37 is connected at its center to the magnetic core 34. ing.

The optical head 28 is movably held by a guide mechanism 21'' on a base 27 extending in the radial direction of the optical disc 20, and the objective lens 25 is supported so as to be movable toward and away from the optical disc 20.

” In a magnetic field generator such as a series, the electromagnetic coil 3
When current is supplied to 2 and the electromagnetic coil 32 is energized,
The magnetic flux is transferred from the magnetic core part 34 to the magnetic core deriving part 3 via the connecting part 38.
7 and is emitted from the magnetic flux emitting surface 37A of the magnetic core lead-out portion 37 toward the light beam irradiable area of the magneto-optical recording film 24. Therefore, the magneto-optical recording film 24 is exposed to magnetic flux perpendicular to its surface. The magnetic flux that has penetrated the magneto-optical recording film 24 passes through space, enters the yoke 39, and is returned to the magnetic core 34 that is magnetically and mechanically connected to the yoke.

The magnetic field generating device 3'0 described above has a configuration in which the magnetic flux deriving part 37 is formed in a wedge shape whose thickness decreases from the center toward both ends, and the total surface area thereof becomes smaller. . Therefore, the leakage magnetic field from the surface of the magnetic flux emitting portion 37 is kept small, and the generated magnetic flux can be efficiently utilized. In addition, the magnetic flux deriving part 37 has the largest cross section in the width direction at the center where the connecting part 38 into which the magnetic flux is introduced is connected, and the cross section decreases by i-1 toward the 8th edge of the image. . When converted into cash, the surface area decreases toward both ends, the leakage magnetic flux also decreases, and the magnetic flux guided through the magnetic flux deriving portion 37 also decreases toward both ends.

Therefore, the magnetic flux emitted from the magnetic field emitting surface is kept uniform, and uniform magnetic flux can be applied to the magneto-optical recording film 24. Furthermore, since the electromagnetic coil 32 has an elongated shape as shown in FIG. 7, a large magnetomotive force can be generated with small power consumption. That is, the magnetomotive force of the magnetic flux generated by the magnetic field generator 30 is determined by the product of the number of turns of the electromagnetic coil 32 and the current supplied there, or the resistance value of the electromagnetic coil 32 is determined by the length of the wire required for one turn. The power consumption in the electromagnetic coil 32 is proportional to the overall resistance value. Therefore, by making the electromagnetic coil 32 elongated in shape, the number of turns for a given resistance value can be increased.

The magnetic field generating device described above has a magnetic core 3 as shown in FIG.
The magnetic field may be derived from the magnetic field deriving part 37 along the long axis of the magnetic core part 34 from 4. Even in this embodiment, the magnetic flux deriving section 3
7 is formed into a wedge shape in which the thickness decreases as it goes from the center part, which is the connecting part of the magnetic core part 34, toward the tip along its long axis. can be obtained.

The optical disk device as an information recording device shown in FIG. 1 has an optical system as shown in FIG. 5, for example, and such an optical system is incorporated in the optical head 28. Fifth
In the optical system shown in the figure, a laser beam generated from a semiconductor laser 60 is collimated by a collimator lens 6], and this collimated laser beam is introduced into a beam splitter 62. The racer ejected from the beam splitter 62
The beam is directed to the magneto-optical recording film 2 by an objective lens 25 supported movably in the direction of its optical axis by a voice coil 71.
Focused on 4. In regeneration mode, the magnetic field generator 30 is kept inactive and the regeneration racer beam is
In the area on the magneto-optical recording film 24 where information is recorded as an inverted magnetic domain, the plane of polarization is rotated and reflected from the magneto-optical recording film 24. In the recording mode, the magnetic field generator 30 is maintained in an operating state, and a laser beam with a relatively high intensity for recording is applied to the magneto-optical recording film 24 to which a magnetic field is applied from the magnetic field generator 30, and the recording is performed. The magnetic domain of the area on the magneto-optical recording film 24 to be recorded is reversed according to the information to be recorded, and the information is recorded. In the erasing mode, the magnetic field generator 30 is maintained in an activated state, and an erasing laser beam having an intensity lower than that of the recording laser beam is emitted from the magnetic field generator 30. The magnetic domain in the region of the magneto-optical recording film 24'' which is applied to the magnetic recording film 24 and is to be erased is reversed again, and the information is erased. In the recording mode and the erasing mode as well, the light is reflected from the magneto-optical recording film 24 and introduced into the deflection beam splitter 62 via the objective lens 25 in the same way as in the reproduction mode. The laser beam reflected by the semi-transparent mirror surface 63 in the splitter 62 passes through a ]/2 wavelength plate 64 and is introduced into a prism body 66 for separating polarized components. ]/2 wavelength plate 6
When the laser beam passes through 4, the deflection plane of the laser beam is rotated by 45 degrees, and the ratio of the deflection components is changed. The prism body 66 for separating deflection components is formed by joining a first rectangular prism 68 and a second prism 67, and a deflection surface 72 is defined at the joint that is the boundary between the two prisms. Further, on the back surface of the second prism 67, two reflective surfaces 67A are inclined and contact each other through a boundary.

67B is formed. Here, the reflective surface 67A.

The boundary between 67B is determined to extend in the direction in which the trough guide or its image extends. Therefore, the P-polarized component of the laser beam introduced into the prism body 66 is reflected by the deflection surface 72, focused by the projection lens 69, and is further given astigmatism by the cylindrical lens 70, so that the P-polarized component of the laser beam introduced into the prism body 66 is The light is incident on the first detection area 80B. The S-polarized component of the laser beam introduced into the prism body 66 is transmitted through the deflecting surface 72 and reflected by the reflecting surfaces 67A and 67B. When the S-polarized component of the laser beam is reflected by the reflecting surfaces 67A and 67B, this S-polarized component is reflected by the first and second laser beams.
Split into beam. The first and second S-polarized laser beams are focused by a projection lens 69 and further given astigmatism by a cylindrical lens 70, and are incident on a second detection area 80B of a photodetector 80. A reproduced signal is obtained by adding the signals from the first photodetector region 80B, similarly adding the signals from the second photodetector 80A, and comparing the two. A focus signal is generated by processing the signal from the first photodetection area 80B, and
A tracking signal is obtained by processing the signal from the second photodetector 80A. In this optical system, an astigmatism method is used as a focus detection method to obtain a focus signal, and tracking is used to obtain a tracking signal. Although the Naifetsu method is known as a focus detection method, it is clear that the Naifetsu method may also be employed. The voice coil 71 is driven according to the focus signal, the objective lens 25 is maintained in a focused state, and the head 28 is moved on the guide 21 according to the I-racking signal, so that the convergence emitted from the objective lens 25 is A laser beam is precisely directed onto the tracking guide, thereby maintaining the information in a state where it can be reproduced, recorded or erased.

As described above, according to the present invention, it is possible to provide a magnetic field generating device that has low power consumption, a correspondingly low heat generation amount, and a small height that can improve mounting efficiency.

Next, the function and operating principle of the magnetic field generator will be explained with reference to FIG. As shown in Figure 6, the electromagnetic coil 3
When the number of turns of 2 is N, and the current supplied to the electromagnetic coil 32 is I, a magnetomotive force Vm=IN is generated from the electromagnetic coil 32 in the magnetic flux deriving section 37. Magnetic flux is emitted from the surface of the magnetic flux emitting part 37A of the magnetic flux deriving part 37, and the lines of magnetic force reach a space quite far away from the magnetic flux deriving part 37. The lines of magnetic force diverged in space travel in a closed loop toward a yoke 39 serving as a magnetic feedback section, and are returned to the magnetic flux deriving section 37 via this yoke 39.

In such a magnetic field distribution, the flat magnetic flux emitting surface 37
Perpendicular lines of magnetic force are generated from A, and these lines of magnetic force are applied perpendicularly to the magneto-optical recording film 24 of the information recording medium 20. In the magnetic recording medium 20 (as already explained), the magnetic recording film 24 is formed on the transparent substrate 22, and the magnetic flux emitting surface 37A is separated from the magnetic recording film 24 by a distance. Usually small, 2.5 to 4.0 mm, and magnetic flux emitting surface 37
A has a relatively wide appropriate width, for example, 3 mm or more, and an appropriate length, for example, 20 mm or more, which is longer than the length of the front beam irradiation area of the magneto-optical recording film 24, so that the magneto-optical recording film 24 is efficient. The magnetic flux can be applied perpendicularly to the film surface, and lines of magnetic force having approximately equal strength are applied to all areas of the magneto-optical recording film 24 that can be irradiated with the light beam. A particularly strong magnetic force is generated in the area on the recording film 24 that is to be irradiated with the beam. The width of the magnetic flux emitting surface 37A is determined in consideration of the vertical movement of the magneto-optical recording film 24 due to surface wobbling of the transparent substrate 22 that occurs during rotation of the information recording medium 20.

That is, the magnetic flux is derived as a range in which the downward movement of the magneto-optical recording film 24 does not increase the magnetic field on the magneto-optical recording film 24, and the magnetic flux passing through the magnetic flux deriving section 37 does not become larger than necessary. The width of the portion 37 is determined in the range of 2 to 30'mm.

The difference in magnetic potential potency between the magnetic core extension part 36 and the yoke 38, that is, the magnetomotive force, is determined by Vm=IN or the yoke 39
The magnetic potential of a surface is determined as a function of its surface area. Here, when S is the magnetic resistance Rm or surface area from each surface of the yoke 39 to infinity where the magnetic potential is zero, Rm-1/2 u of fTl (however, C,
In the G, S emu unit system, Rm = 1 from μo-1
．． / 2 J- If it is assumed that "3-)", the smaller the surface area of the magnetic flux deriving part 37, the larger the magnetic potential becomes. It is emitted from the magnetic flux deriving part 37 and returns to the three yokes from a distant space. Since the total magnetic flux generated is constant, the smaller the surface area of the magnetic flux emitting portion 37, the greater the magnetic flux density.

” The contents of the two series are explained mathematically using a simple model below. The surface areas of the magnetic flux emitting part 37 and the yoke 39 are respectively Sc Sy, and the magnetic resistances from the magnetic flux emitting part 37 and the yoke 38 to infinity where the magnetic potential is zero are Rll, respectively.
1e, Rmy. Further, the magnetic flux along the direction from the magnetic flux emitting portion 37 toward the yoke 38 is expressed as Φtotal, and the magnetic flux density on the surface of the magnetic flux emitting portion 37 is expressed as B c (0).

However, the 11th place is C, G, S eIIlu 231 Use a system of units. As mentioned above, magnetoresistance RmC.

Assume that Rmy is expressed by the following equations (1) and (2).

Rmc-1/2 YarT11... (1) RITly-
1/2F Roro... (2) Here, Rm = 1/
4μπ. It was considered as 'O' + rQ -f7■ko.

The magnetic flux Φtotal is expressed by the following equation (3).

Φtotal = V+n X (Rmc+R+ny)
-1-2J〒VmX (1, /F 澗+1/n line) -1...
...(3) Here, Vllll is magnetomotive force (V+n=NI).

Further, the magnetic flux density B e (0) is expressed by equation (4).

Be (0) = ΦLoLal + 5e -2π* Vm (1, /zρSc + 1 / completed at ρ)
' / S e ...(4) Here, the total area S (d) of equipotential surfaces in a space a distance I4d away from the magnetic flux deriving part 37 is 5(d) = 4π(r
o+d) 2=4π(Fq positive/4y+d)2=(
fI]+J1*d)2, the magnetic flux density Bc(d) in that space is expressed by equation (5).

Be(d)=Φtotal+S(d)=2π・V
ra・(d怀+f■1・d)−2・(1/F5+
1/F5)-1 =2π・v[ll-8c゛1 ・(1+F"77Sc
'd ) ' ” (]/z”; e 士l/〜”S了fu)1...(5) In equation (5), when Sc>'>4πd2, (4
). Furthermore, the spatial magnetic field strength H(d) is μo=1
From H(0) = B(0), H(d) = B(d)
It can be obtained with S c >> 4π d2 and S
When y >> S c, the equation (5) becomes the equation (6), and the maximum magnetic field is determined by the magneto-optical recording film 24 of the information recording medium 20.
can be given to

H(d)=70 ×■■ ・ ・ ・ ・(6) However, as Sy becomes smaller, H(d) decreases, and 5
When y=ScL or 5C)4πd2, equation (5) becomes equation (7), which becomes half of the maximum magnetic field shown by equation (6).

H (d) ÷ F "Sweat x Vrrl (7) = 25- As is clear from the above analysis, Sc≦Sy, that is, the surface area of the magnetic flux emitting part 37 needs to be smaller than the surface area of the three yokes. It is understood that there is. Also, equation (6) and (
From formula 7), it is better to make Sc as small as possible, but
If Sc is made smaller than necessary, it becomes smaller than 4π d2, so Sc cannot be made that small.

Next, the shape and power consumption of the electromagnetic coil 32 will be considered. As shown in FIG. 6, the length η of the coil, the layer thickness λ of the coil formed by winding the conducting wire, the width W and the thickness t of the magnetic core portion 34 are assumed. (All units are am.) Also,
The maximum allowable temperature rise value when continuing to supply current to the electromagnetic coil 32 is ΔT [unit: °C], and the heat conduction coefficient is h = 2.
50/degree*cn+2, the maximum power consumption Pmax [W] is given by the following equation (8). (Nanto Hirano et al.; Electronics and Communication Academic Journal vol. 1160-
C, No.11. P [see i84.1977) Pmax=f2hΔT/(1×104Xπ)・η (W
(8) Furthermore, the conductor wire diameter of the coil conductor is d [ll1l], the outer diameter of the conductor including the coating is d [mm], and the volume resistivity of the coil conductor is ρ. [Ω-
cm ] and the total number of turns of the coil is N, the resistance value Re of the coil conducting wire is expressed by equation (9).

Re = f800ρN (W + 2λ) / (π
d2) ...(9) (8) formula and (9
), the maximum 811 capacity current of the electromagnetic coil 32 is 1 max
is expressed by the following formula (lO), and the maximum magnetomotive force maxV
m is expressed by equation (11).

Imax = 11. / (2x 10') l
・JhΔT/ρ・ (d2/Jλ) ・・・
・(10)max Vm=N Imax=(1/2
00) ・JhΔT/ρ・ηJλ/) ・・・・
(11) However, N8 (d) 2/100-λη was used.

A method for obtaining a large magnetomotive force with low power consumption will be considered from equations (8) and (11).

From equation (11), the maximum magnetomotive force fflaXVm is calculated from the magnetic core 3
It is understood that this does not depend on the outer diameter dimensions (W, t') of No. 4. Therefore, the first method for suppressing heat generation is to reduce the value of (W+t) in equation (8) or to reduce power consumption. However, when the saturation magnetic flux density of the material forming the magnetic core part 34 is Bs, W t B s≧ΦLO
Must be 1al. Therefore, it is necessary to suppress power consumption by minimizing Φtotal. Therefore, the length of the magnetic flux emitting section 37 is set to be slightly longer than the length of the recording area of the information recording medium to be searched by the light beam.
It is necessary to keep the portion that generates extra magnetic flux as small as possible. If magnetic flux leaks from the surface of the connecting part between the effective magnetic flux deriving part and the connecting part, the total magnetic flux Φtotal will increase, so as shown in FIG. 34 and arrange the electromagnetic coil 32 in this magnetic core part 34, and thereby the magnetic flux emitting surface 37A is substantially defined as an effective magnetic flux emitting part.

The magnetic flux deriving portion 37 is formed into a wedge shape as described above. This is based on the following reason. Generally, the area of the cross section perpendicular to the long axis of the magnetic flux deriving part 37 is larger than the total amount of magnetic flux emitted from the outer surface from that point to the center and the tip divided by the saturation magnetic flux density Bs. cannot be made smaller. For this reason, the magnetic flux emitting portion 37 is formed so as to have a structure in which the cross-sectional area decreases toward the tip and the area of the outer surface decreases, thereby minimizing the magnetic flux Φtotal emitted into space. Here, the cross-sectional area can also be reduced by changing the width of the magnetic flux emitting part 37, but when reducing the width, it is necessary to ) and in the left-right direction (the direction of movement along the circumference on the optical recording film 24), the magnetic field intensity changes sharply, which is undesirable because the requirement for precision in positioning the beam with the search area increases.

Even if efforts are made to reduce the value of the total magnetic flux Φtotal as described above, there is a limit to reducing (W+t). As is clear from comparing equations (8) and (II), power consumption is reduced by reducing the amount of temperature rise ΔT during energization of the electromagnetic coil 32, and in contrast to 29, the electromagnetic coil 34 The efficiency of the magnetomotive force can be improved by devising the shape of the magnetomotive force. It is understood from equation (11) that a change in the value of the coil length η changes the magnetomotive force more than a change in the thickness λ of the electromagnetic coil. Therefore, in the magnetic field generating device of the present application, the coil length η is set larger than the thickness λ of the electromagnetic coil. That is, magnetomotive force Vm=NI
is proportional to the number of turns N, or if the length of the wire required for one turn is long, the resistance value per turn of the wire increases, and the power consumption also increases. Therefore, instead of winding the wire in many layers and increasing the length of each turn on the outer periphery, we reduce the number of layers and make the length of the turns as small as possible to improve the magnetomotive force. .

[Effects of the Invention] As described in 2 below, according to the present invention, since the cross section of the magnetic flux emitting portion is formed in a wedge shape that decreases from the coupling portion with the magnetic core portion along its long axis, the magnetic field is emitted. Since the leakage magnetic field of the magnetic field is small, the magnetic utilization efficiency can be increased, and the power consumption can be reduced. Further, since the electromagnetic coil can be formed into an elongated shape and the wire length required for one turn can be reduced, a large magnetomotive force can be obtained with small power consumption. Furthermore, since the electromagnetic coil is long and thin, the heat dissipation effect can be increased, and the electromagnetic coil will not be heated even if it is energized for a long time.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing a magnetic field generating device for an optical disk device according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of the magnetic field generating device shown in FIG. 1 and its peripheral mechanism. The partially cutaway oblique view shown in FIG. FIG. 5 is a plan view showing the arrangement of the magnetic field generator with respect to the magneto-optical recording medium when the cassette containing the magneto-optical recording medium is installed in the optical disk device. , FIG. 6 is a schematic configuration diagram showing the optical system of an optical disk device in which the magnetic field generating device shown in FIG. 1 is incorporated, and FIG. 7 shows another embodiment of the magnetic field generating device of the optical disk device of the present invention. FIG. 8 is a perspective view showing the conventional magnetic field generating device shown in FIG. 1. 19... Shutter, 20... Destination disk, 21.
...Guide, 28...Optical head, 26...Set, 3
0... Magnetic field generator, 32... Electromagnetic coil, 34.
...Magnetic core part, 37...Magnetic field derivation part. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 3 Figure 7

Claims (1)

[Claims] (1) Consists of a light source, an optical means for focusing a light beam from the light source toward an information recording medium, and a magnetic field generating device that applies a magnetic field to the information recording medium at least when recording information, and this magnetic field generating device The magnetic core has a magnetic core made of a magneto-optical material, a coil wound around the magnetic core, and a magnetic field emission surface that extends in the width direction of the recording area of the information recording medium and is to be opposed to the magnetic core. A magnetic flux lead-out part made of a magnetic material and formed in a wedge shape whose cross section decreases along the long axis from the connecting part to the magnetic core through the space where the information recording medium is to be placed. An optical disk device comprising: a yoke portion magnetically connected to the other end of the magnetic core portion to which magnetic flux emitted from the extension portion is returned.