JPS63244717A - Magnetic field generating device - Google Patents

Abstract

PURPOSE:To improve the magnetic generation efficiency as well as a heat radiation effect and to elevate the magnetic utilization efficiency by forming a slender magnetic coil which is wound at a magnetic core part and by making a magnetic flux discharge part and the magnetic core part have structures comprising stepped parts. CONSTITUTION:When a magnetic coil 32 is energized by supplying a current, magnetic flux is supplied from a magnetic core part 34 to a magnetic flux leading out part 37 through a coupling part 38 and is discharged toward a region where the light beam of a photo- electromagnetic recording film 24 can be irradiated from a magnetic flux discharge plane 37A located at a lower plane of the magnetic flux leading out part 37. Then, the photoelectro- magnetic recording film 24 is exposed to magnetic flux that is perpendicular to its plane. Magnetic flux which is passing through its film 24 enters into a yoke 39 through a space and is feedback to the magnetic core part 34 which is magnetically and mechanically coupled to the yoke. In such a structure, the magnetic coil 32 is so slender that a great magnetomotive force is obtained by less electricity consumption and its heat radiation effect is also excellent. Since the magnetic flux leading out part 37 and the magnetic core part 34 have stepped parts, its configuration allows the magnetic flux discharge plane 37A to approach sufficiently an information recording medium 20 and the magnetic utilizastion efficiency can be elevated.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention relates to magneto-optical technology that records information on a recording medium 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 improvements in magnetic field generating devices that generate magnetic fields used in recording and reproducing devices.

(Prior art) Information recording and reproducing devices using magneto-optical recording include external memory for computers, rewritable video disk devices, image file devices, AD type compact disk devices capable of playback and recording, and rewritable high-density recording. There are magnetic cards, and these are being developed 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 a device, a method of applying a magnetic field to a recording medium is to apply a focused light beam locally only around the area where a beam spot is formed, and a method of applying a magnetic field locally to a recording medium for accessing information. the light beam is moved,
There is a method of continuing to apply a magnetic field over the entire range that can be irradiated with a focused 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 light generating device, 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 end faces of the magnetic core as a magnetic flux emitting part The emitted magnetic flux spreads through the recording film surface of the magneto-optical recording medium and is returned to the end surface of the yoke surrounding the end surface 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 formed by being wound around a magnetic core portion 14 that extends 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 disposed facing 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 14 serving as a magnetic flux emitting section is applied to the magneto-optical recording medium. The light passes through the recording film surface and is returned to the end surface 12A of the yoke 12, which is disposed on both sides of the end surface 14A of the magnetic core portion 14. 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 14A112 of the magnetic field generator
The width and length of A are determined to be approximately equal to each other,
Core end face and yoke end face 14A, 12A of the magnetic field generator
The length in the longitudinal direction is set to be larger than the length of the magnetic field on 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. 7 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 that power consumption is large. 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 number of turns flowing through the electromagnetic coil. It is determined by the product NXI of current I. Moreover, the power consumption P consumed by this electromagnetic coil is P-IXR2 when it is the resistance R of the electromagnetic coil. 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, 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, as described above, when the power consumption is large, 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 will be transmitted to the recording medium and the magneto-optical recording medium will be thermally deformed or the recorded information will be erased.

(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 recording surface, it is necessary to make the width of the magnetic core sufficiently small, the height of the magnetic core and yoke sufficiently high, and arrange each turn of the electromagnetic coil along the direction perpendicular to the optical recording surface. It is necessary to do so. In such a structure, there is a problem that the height of the device inevitably becomes large. When a magnetic field generating device having a height is placed on a magnetic recording medium, the information recording/reproducing device itself becomes larger and is subject to design constraints.

[Structure of the Invention] (Means for Solving the Problem) According to the invention, a magnetic core made of a magnetic material, a coil wound around the magnetic core, and a magnetic core in the width direction of a recording area of an information recording medium are provided. a magnetic flux guide made of a magnetic material, which extends substantially parallel to the direction in which the magnetic core extends, has a magnetic field emitting surface to be opposed to the magnetic core, is connected to one end of the magnetic core, and extends substantially parallel to the direction in which the magnetic core extends; a magnetic field generator comprising: a yoke portion magnetically connected to the other end of the magnetic core portion to which magnetic flux emitted from the magnetic core extension portion is returned through a space in which an information recording medium is disposed; is provided.

[Operation] Since the electromagnetic coil has an elongated shape, a large magnetomotive force can be obtained with small power consumption.

In addition, since the electromagnetic coil is long and thin, it has a high heat dissipation effect and does not get heated even if it is energized for a long time. Furthermore, since the magnetic flux emitting part and the magnetic core part have a stepped structure, even when an information recording medium is stored in a cassette, the magnetic flux emitting surface of the magnetic flux deriving part can be kept sufficiently close to the information recording medium. It is possible to increase the magnetic utilization efficiency.

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

FIG. 1 is a cross-sectional view schematically showing a magnetic field generating device according to an embodiment of the present invention. The arrangement of the magnetic field generator with respect to the magneto-optical recording medium is shown when data is erased from the recording medium. 2 is a partially cutaway perspective view schematically showing the magnetic field generating device shown in FIG. 1 and its peripheral mechanism, and FIG. 3 is a partially cutaway perspective view of the magnetic field generating device shown in FIG. FIG. 4 is a sectional view schematically showing the arrangement relationship in the case where a magnetic field is generated on the magneto-optical recording medium when the cassette containing the magneto-optical recording medium is installed in an information recording/reproducing apparatus. FIG. 5 is a schematic diagram showing an optical system of an information recording/reproducing apparatus in which the magnetic field generating device shown in FIG. 1 is incorporated.

The magnetic recording medium 20 has a structure in which a pair of transparent substrates 22 are faced and bonded together as shown in FIG. 1, and a magneto-optical recording film 24 is formed on the inner surface of the substrate. A tracking φ guide (not shown) is formed in advance on 24 . Usually, the information recording medium 20 is formed in a disk shape so as to be called an optical disk, but the information recording medium 20 is not limited to this, and may take various shapes such as a card shape.

Further, the information recording medium 20 is housed and protected in a cassette 26 as shown in FIGS. 1, 3, and 4, and when installed in an information recording/reproducing apparatus, a loading mechanism (not shown) The cassette 26 and the cassette 26 are inserted into the insertion slot (not shown) of the information recording/reproducing apparatus, and when the cassette 26 is ejected from the information recording/reproducing apparatus, the cassette 26 is ejected from the insertion opening of the information recording/reproducing apparatus.

As shown in FIG. 4, the cassette 26 has upper and lower windows 26B and 26C extending along the radial direction of the optical disc 20 in the upper and lower plate parts of a rectangular thin cassette case 26A. is provided with a shutter 19 that is slidable in the direction of arrow I. When loading the cassette 26 into the information recording/reproducing apparatus, the shutter 19 is opened by an opening/closing mechanism (not shown) during the loading operation of the cassette 26, the upper and lower windows 26B and 26C of the cassette case 26A are opened, and the cassette 26 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 26 of the cassette case 26A are closed.
B, 26C is closed. As shown in FIG. 1, when the cassette 26 is inserted into the information recording/reproducing apparatus,
windows 26B and 26C are opened, and the optical disc 20 is clamped and fixed by a lower stamper 52B connected to the motor 50 via the spindle 51 and an upper stamper 52A lowered from above the optical disc 20, and the objective lens 25 of the optical head 28 is is placed under the optical disk and the lower window 26C
The laser beam is emitted from the objective lens 25 of the optical head 28 via the
The beam remains focused. Further, when the cassette 26 is installed in the information recording/reproducing device, the upper window 26B
The magnetic flux deriving section 37 of the magnetic field generating device 30 is inserted into the inside, and the magnetic flux emitting surface 37A is opposed to the optical disk 20, so that information can be reproduced, recorded, or erased on the optical disk 20. At the time of this insertion, the magnetic field generating device 30
It has a structure that can be separated by a separation mechanism (not shown) so as not to impede insertion and ejection operations of the information recording medium 20 during ejection. Therefore, as shown in FIG. 3, when the cassette 26 is detached or attached to the information recording/reproducing apparatus, the upper stand bar 52A is lifted upward, and the upper window 26
The magnetic flux deriving portion 37 of the magnetic field generating device 30 is withdrawn to outside B, and the magnetic field generating device 30 is separated by the separation mechanism, and the magnetic field generating device 30 is deflected upward from the lower stand bar 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 or plate-shaped magnetic core 34 on which an electromagnetic coil 32 as shown in FIG. A magnetic flux deriving part 37 having an extending magnetic flux emitting surface and a magnetic flux deriving part 37 extending substantially perpendicularly to the extending direction of the magnetic core 34 in order to provide a step between the magnetic core part 34 and the magnetic flux deriving part 37, and one end of the magnetic core part 34. and a triangular pyramid-shaped connecting portion 38 that connects the upper surface of the center portion of the magnetic flux deriving portion 37, and a yoke portion 3 that extends from the other end of the magnetic core portion 34 and returns the magnetic flux emitted from the magnetic flux emitting surface 37A.
It consists of 9. Here, the magnetic flux deriving section 37 is
It is formed into a wedge shape whose thickness decreases from the center toward the front edge of the image, and has a length approximately corresponding to the radius of the optical disc 20. That is, the magnetic flux emitting surface 37A extends outside the range 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 is used for reproducing and recording information or During erasing, the flat lower surface of the magnetic flux emitting surface 37A is opposed to the light beam irradiable area of the magneto-optical recording film 24. The magnetic core portion 34 extending from the yoke 39 is connected to the connecting portion 38 at the approximate center of the magnetic flux deriving portion 37, so its length is set to be relatively long. The shape is elongated.

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

In the magnetic field generating device as described above, the electromagnetic coil 32
When a current is supplied to energize the electromagnetic coil 32, magnetic flux is transmitted from the magnetic core portion 34 to the magnetic core extension portion 36 via the connecting portion 38.
The magnetic flux emitting surface 37A on the lower surface of the magnetic core extension 36
The light beam is emitted from the magneto-optical recording film 24 toward the area where the light beam can be irradiated. 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.

In the embodiment described above, the magnetic field generating device 30 has a structure in which the yoke portion 39 is separable, but the magnetic core portion 34
may be separated from the yoke portion 38.

The magnetic field generating device 30 described above has a shape in which the magnetic flux deriving portion 37 is formed in a wedge shape whose thickness decreases from the center toward both ends, and the overall surface area thereof decreases. Therefore, the leakage magnetic field from the surface of the magnetic flux deriving portion 37 is kept small, and the generated magnetic flux can be efficiently utilized. Further, the magnetic flux deriving portion 37 has the largest cross section in the width direction at the center where the connecting portion 38 into which the magnetic flux is introduced is connected, and the cross section decreases toward both ends thereof. In other words, 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. 6, 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 71i current supplied thereto, but the resistance value of the electromagnetic coil 32 is determined by the amount of wire required for one turn. The power consumption in the electromagnetic coil 32 is proportional to the length, and the power consumption in the electromagnetic coil 32 is proportional to the overall resistance value. Therefore, by defining the shape of the electromagnetic coil 32 to be elongated, it is possible to increase the number of turns for a predetermined resistance value.

The information recording apparatus shown in FIG. 1 has, for example, an optical system as shown in FIG. 5, and such an optical system is incorporated in the optical head 28. In the optical system shown in FIG.
The beam is collimated by a collimator lens 61 and this collimated laser beam is introduced into a beam splitter 62. The laser beam emitted from the beam splitter 62 is focused onto the magneto-optical recording film 24 by the objective lens 25, which is supported movably in the front axis direction by the voice coil 71. In the reproduction mode, the magnetic field generator 30 is kept inactive and the reproduction laser beam has its plane of polarization rotated in the region on the magneto-optical recording film 24 where information is recorded as reversed magnetic domains. It is reflected from the magneto-optical recording film 24 as a lever. 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 erase mode, the magnetic field generator 30 is maintained in an operating state, and an erase laser beam having a lower intensity than the recording laser beam is applied to the magneto-optical recording film 22 to which a magnetic field is applied from the magnetic field generator 30. The magnetic domain of the area on the magneto-optical recording film 24 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 1/2 wavelength plate 64 and is introduced into a prism body 66 for separating polarized components. When the laser beam passes through the half-wave plate 64, the plane of deflection of the laser beam is rotated by 45 degrees, and the ratio of the polarized components is changed.

The prism body 66 for separating deflection components is formed by joining a first rectangular prism 68 to a second prism 67, and a deflection surface 72 is defined at the joint surface that is the boundary between both prisms. Further, on the back surface of the second prism 67, two reflective surfaces 67A and 67B are formed which are inclined and contact each other through a boundary.

Here, the boundary between the reflective surfaces 67A and 67B is determined to extend in the direction in which the tracking guide extends or in the direction in which its image extends. Therefore, the prism body 6
The P-polarized component of the laser beam introduced into the laser beam 6 is reflected by a deflection surface 72, focused by a projection lens 69, and further given an astigmatism by a cylindrical lens 70, and then detected by the first detection by a photodetector 80. The light is incident on the region 80B. The S-polarized component of the laser beam introduced into the prism body 66 is transmitted through the deflection surface 72 and is reflected by the reflection surface 67A.

It is reflected by 67B. When the S-polarized component of the laser beam is reflected by the reflective surfaces 67A, 67B, the S-polarized component is split into first and second laser beams. The first and second S-polarized laser beams are
The light is focused by the projection lens 69, is given astigmatism by the cylindrical lens 70, and is incident on the second detection area 80A of the photodetector 80. A reproduced signal is obtained by adding the signals from the first photodetector area 80A, and similarly adding the signals from the second photodetector 80B, and comparing the two. A focus signal is generated by processing the signal from the first photodetection area 80A, and a focus signal is generated from the second photodetector 80A.
A tracking signal is obtained by processing the signal from 0B. In this optical system, an astigmatism method is used as a focus detection method to obtain a focus signal, and a push-pull method is used as a tracking guide detection method to obtain a tracking signal. Although the Naifezi method is known as a focus detection method, it is clear that the Naifezi method may also be employed. Voice coil 71 according to the focus signal
is driven, the objective lens 25 is maintained in focus, the optical head 28 is moved on the guide 21 according to the tracking signal, and the focused laser beam emitted from the objective lens 25 is accurately guided to the tracking guide. This maintains the state in which information 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 1, a magnetomotive force Vm-IN is generated from the electromagnetic coil 32 in the magnetic flux deriving section 37 . The magnetic flux is diverged from the magnetic flux emitting surface 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, perpendicular lines of magnetic force are generated from the flat magnetic flux emitting surface 37A, and these lines of magnetic force are applied perpendicularly to the magneto-optical recording film 24 of the information recording medium 20. As already explained, the magnetic recording medium 2
0, the magneto-optical recording film 24 is formed on the transparent substrate 22, and the magnetic flux emitting surface 37A is slightly separated from the magneto-optical recording film 24, but this distance is usually 2.5 to 4. 0 mm, and the magnetic flux emitting surface 37A has a relatively wide appropriate width, for example, 3 mm or more, and an appropriate length that is longer than the length of the light beam irradiable area of the magneto-optical recording film 24, for example, 2 mm.
0 mm or more, magnetic flux can be efficiently applied to the magneto-optical recording film 24 perpendicular to the film surface, and the magnetic flux can be applied almost evenly to the entire area of the magneto-optical recording film 24 that can be irradiated with the light beam. Because strong magnetic lines of force are applied,
A particularly strong magnetic force is applied to the region on the magneto-optical recording film 24 that is to be irradiated with the light beam. The width of the magnetic flux emitting surface 37A is
This is determined in consideration of the fact that the magneto-optical recording film 24 is moved up and down due to surface wobbling of the transparent substrate 22 that occurs during rotation of the information recording medium 20. That is, the width of the magnetic flux derivation section 37 is set as a range in which the magnetic field on the magneto-optical recording film 24 does not increase to that extent due to the vertical movement of the magneto-optical recording film 24, and the magnetic flux passing through the magnetic flux derivation section 37 does not need to be increased more than necessary. is determined in the range of 2 to 30 mm.

The difference in magnetic potential between the magnetic core extension portion 36 and the yoke 38, that is, the magnetomotive force, is determined by Vmm I N, while the magnetic potentials of the surfaces of the connecting portion 38 and the yoke 39 are determined as a function of their surface areas. Here, when the magnetic resistance Rm from each of the surfaces of the connecting portion 38 and the yoke 39 to infinity where the magnetic potential is zero is the surface area S, Rm-1/2
If it is assumed that μ(IfTl (however, in the C, G, Seo+u unit system, Rm = 1/2 f7 from μo-1), the smaller the surface area of the magnetic flux deriving part 37, the more the magnetic potential. Magnetic flux deriving section 3
Since the total magnetic flux emitted from the yoke 7 and returned to the yoke 39 from a distant space is constant, the smaller the surface area of the magnetic flux deriving part 37, the greater the magnetic flux density thereon can be.

The above content will be explained mathematically using a simple model below. Connecting portion 38, magnetic flux deriving portion 37, and yoke 39
Let the surface areas of Sc and Sy be respectively, and let the magnetic resistances from the connecting portion 38, the magnetic flux deriving portion 37 and the yoke 38 to infinity where the magnetic potential is zero be Rme and Rff1y, respectively. Further, from the connecting portion 38 and the magnetic flux deriving portion 37 to the yoke 3
The magnetic flux along the direction toward
). However, the units used are C, G, and Semu units. As mentioned above, the magnetic resistances Rme and Ro+y are assumed to be based on the following equations (1) and (2).

Rwc-1/2 J block lower --- (1) R11y-1/
2Fr rent...(2) Here, Rm=1/4μπo
It was considered as ro, ro■f7TT.

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

Φtotal-VIIX (Rwc+Rmy) -”-
2-r'; i-V ts X (1/ fl lower + 1/
fl7)-1...(3) Here, Va+ is the magnetomotive force (Vm-Nl).

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

Be(0)-Φtotal + S c-2fi-V
Ia (1/ J■τ+ 1 /-1' below) -1/
S c ... (4) Here, the total area S (d) of equipotential planes in a space separated by a distance d from the magnetic flux deriving part 37 is 5 (d) - 4π (ro + d
) 2-4π(7l7/4x-z)2-(,7'dτ
+fTT-d)2, the magnetic flux density Bc(d) in that space is expressed by equation (5).

Bed-Φtotal + S (d)-2(i-Vl
@ (f1 lower + fτ1・d) −2・(1/ fI lower +1/−1”;'T )−'w2π−vl conflict 5c−1Φ (1+f positive 77Tτ・d) −2・<1/J”Xτ+1 /v'cho7)-1・・・・・(
5) When Sc>'>4πd2 in equation (5), equation (4) is obtained. Furthermore, the spatial magnetic field strength H(d) is μ
. From −1, H(0) −B(0) , H(d) −B(
d). Sc>)4πd2 and 5ySc
In this case, equation (5) becomes equation (6), and the maximum magnetic field can be applied to the magneto-optical recording film 24 of the information recording medium 20.

H(d)-JgokozKcho×VIl ・ ・ ・ ・(6
) However, as sy becomes smaller, H(d) decreases, and when 5y-ScL, 5C)4π d2, equation (5) becomes equation (7), and the maximum shown by equation (6) It becomes half of the magnetic field.

H(d)-f 1×vII ・ ・ ・ ・ (7) As is clear from the above analysis, Sc≦Sy, that is, the surface area of the magnetic flux deriving part 37 needs to be smaller than the surface area of the yoke 39. is understood. Also, equation (6) and (7
) From the formula, it is better to make Sc as small as possible, but if it is made smaller than necessary, it will become smaller with respect to 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. (Both units are cIl.) Also, the maximum allowable temperature rise value when continuing to supply current to the electromagnetic coil 32 is ΔT [unit: °C], and the thermal conductivity coefficient is h-2.
50/degree-CI2 and maximum power consumption P
max [W is given by the following equation (8). (Yoshiyuki Hirano “etc.; Electronics and Communication Academic Journal vol. 1. J [10-
C, No.11. P2S5.1977) Pmax-(2hΔT/(1x104xπ)・η(W+
t +2λ)...(8) Furthermore, the diameter of the conductor wire of the coil conductor is d[■], and the outer diameter of the conductor including the coating is d[1
ml], and the volume resistivity of the coil conductor is ρ[Ω-Ca+
], 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 = (800ρN (W+t +2
λ))/(πd2) ・ ・
・ ・ (9) From equations (8) and (9), electromagnetic coil 3
The maximum allowable current Iwax of 2 is shown by the following equation (10), and the maximum magnetomotive force fflaXVm is shown by the equation (11).

ll1ax = (1/ (2X10')l ・L
"τT77・ (d2/JT) ... (10) wax Vm-N Ifllax - (1/200)
φfYτT7f・ηJT/Ni) (11) However, N8(Nid)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 1aXVIIl is calculated from the magnetic core 3
It is understood that it does not depend on the outer diameter dimensions (W, t) of No. 4. Therefore, reducing the value of (W+t) in equation (8) is the first method for reducing power consumption and suppressing heat generation. However, when the saturation magnetic flux density of the material forming the magnetic core part 34 is Bs, W t B s≧Φtot
It must be al. Therefore, it is necessary to suppress power consumption by minimizing Φtotal. Therefore, it is necessary to keep the length of the magnetic flux deriving section 37 slightly longer than the length of the recording area of the information recording medium to be searched by the light beam, and to keep the portion that generates extra magnetic flux as small as possible. It is. 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. It is preferable to provide a portion 34 and arrange the electromagnetic coil 32 in this magnetic core portion 34.

The magnetic flux deriving portion 37 is formed into a wedge shape as described above, and this is based on the following reason. Generally, the area of the cross section perpendicular to the long axis of the magnetic flux deriving portion 37 at any point is smaller than the value obtained by dividing the total amount of magnetic flux emitted from the outer surface from that point, from the center to the tip, by the saturation magnetic flux density Bs. Can not do it. For this reason, the magnetic flux deriving 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, so that the magnetic flux Φtotal released into space is made as small as possible. Here, the cross-sectional area can also be reduced by changing the width of the magnetic flux deriving portion 37, but when reducing the width, it is necessary to This is preferable because the magnetic field strength changes sharply in the direction) and in the left-right direction (the direction of movement along the circumference on the magneto-optical recording film 24), and the requirement for precision in positioning the beam with the search area increases. do not have.

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 (11), power consumption is reduced by reducing the amount of temperature rise ΔT when the electromagnetic coil 32 is energized;
The efficiency of magnetomotive force can be improved by devising the shape of 4. 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, the magnetomotive force Vm-Nl is proportional to the number of turns N, but
- If the length of the wire required for winding is long, the resistance value per turn of the wire increases, and the power consumption also increases. For that reason,
Instead of winding the wire in many layers and increasing the length of each turn on the outer periphery, the number of layers is reduced and the length of the turns is made as small as possible to improve the magnetomotive force.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an information recording/reproducing device that can be downsized.

Moreover, according to the present invention, since the electromagnetic coil has an elongated shape, a large magnetomotive force can be obtained with small power consumption. In addition, since the electromagnetic coil is long and thin, it has a high heat dissipation effect and does not get heated even if it is energized for a long time. Furthermore, since the magnetic flux derivation part and the magnetic core part have a structure in which there is a step difference, even when an information recording medium is stored in a cassette, the magnetic flux emitting surface of the magnetic flux derivation part can be kept sufficiently close to the information recording medium. It is possible to increase the magnetic utilization efficiency.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing a magnetic field generating device according to an embodiment of the present invention, and FIG. 2 is a partial diagram schematically showing the magnetic field generating device shown in FIG. 1 and its peripheral mechanism. A broken perspective view, FIG. 3, is a sectional view schematically showing the arrangement relationship when the magnetic field generating device shown in FIG. 1 is lifted, and FIG.
The figure is a plan view showing the arrangement of the magnetic field generating device with respect to the magneto-optical recording medium when the cassette containing the magneto-optical recording medium is installed in the information recording and reproducing apparatus. 6 is a perspective view showing the electromagnetic coil of the magnetic field generating device shown in FIG. 1, and FIG. FIG. 2 is a perspective view showing a magnetic field generating device of FIG. 19... Shutter, 20... Optical disc, 2
Part 1: Urn guide, 28, -φ conflict light, Sodo, 26...
...Cassette, 30...Magnetic field generator, 32...
- Electromagnetic coil, 34... magnetic core section, 38... connecting section, 37... magnetic field deriving section. Applicant's agent Patent attorney Takehiko Suzue Figure 3 Figure 5 Figure 6 Figure 7

Claims (4)

[Claims] (1) It has a magnetic core made of a magnetic material, a coil wound around the magnetic core, and a magnetic field emitting 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 guide portion made of a magnetic material connected to one end of the magnetic core portion and extending substantially parallel to the direction in which the magnetic core portion is extended; A magnetic field generating device comprising: a yoke portion magnetically connected to the other end of the magnetic core portion to which magnetic flux emitted from the magnetic core portion is returned. (2) The magnetic field generating device according to claim 1, wherein the magnetic core portion and the magnetic flux deriving portion are connected by a connecting portion with a step. (3) The magnetic field generating device according to claim 1, wherein the magnetic side extension part extends partially between the magnetic core part and the magneto-optical information recording medium. (4) The magnetic field generating device according to claim 1, wherein the magnetic flux deriving portion is formed in a wedge shape whose cross section decreases from the center portion along the long axis.