JPS63244719A - Magnetic field generating device - Google Patents

Abstract

PURPOSE:To reduce a wire length required for winding a coil and obtain large magnetomotive force at the least consumption of electricity: besides, to improve a heat radiation effect by forming a lengthy magnetic coil along its long axis of a magnetic core part which is larger than the thickness of its layer. CONSTITUTION:When a current is supplied and then a magnetic coil 32 is energized, magnetic flux is discharged from a magnetic core part 34 through a coupling part 38 toward a region where the light beam of a photoelectro-magnetic 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 34 which is magnetically and mechanically coupled to the yoke. Although magnetomotive force generated at this stage is determined by the product of the number of turns of the magnetic coil 32 and a current supplied herewith, the resistance value of the magnetic coil 32 is in proportion to the length of wire materials required for a coil and the consumption of electricity in the coil 32 is proportional to the resistance value. Thus less electricity consumption may generate great magnetomotive force.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) This invention relates to magneto-optical technology 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 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 film devices, AD type compact disk devices capable of playback and recording, and rewritable high-density recording. There are magneto-optical 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 uniformly applying 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 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 the conventional magnetic field generating device that adopts the full range magnetic field application method, as shown in Fig. 8, a magnetic feedback section with a U-shaped cross section protrudes into the yoke and extends approximately parallel to the yoke. It is formed by winding an electromagnetic coil around a magnetic core. In this magnetic field generator, similarly, the parallel end faces of the magnetic core and the yoke are arranged to face the recording film surface of the magneto-optical recording medium, and when a current is supplied to the electromagnetic coil, the magnetic core as the magnetic flux emitting part The magnetic flux emitted from the end face of the magnetic core passes through the recording film surface of the magneto-optical recording medium and is returned to the end face A of the yoke disposed on both sides of the end face of the magnetic core. 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 width and length of the magnetic core end face and yoke end faces 14A and 12A of the magnetic field generator are determined to be approximately equal to each other, and the magnetic core end face and yoke end face 14A of the magnetic field generator, The length in the longitudinal direction of 12A 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 generating device as shown in FIG. 5, which adopts a local magnetic field application method, since the magnetic field is applied locally, This magnetic field generating device also needs to be moved, which poses a problem in that the moving mechanism becomes complicated.

On the other hand, a conventional magnetic field generating device as shown in FIG. 6 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. 7, 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 are reports that the size of the magnetic field generator will increase. In particular, there are trends in which the height of the magnetic field generator increases along the direction perpendicular to the optical recording surface. 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 present invention, a magnetic core made of a magnetic material, a coil wound around the magnetic core, and a coil extending from one end of the magnetic core are provided. , a magnetic flux derivation section made of a magnetic material is magnetically connected to the other end of the magnetic core section, and the magnetic flux emitted from the magnetic flux derivation section is returned through a space in which an information recording medium is to be placed. In the magnetic field generating device including a yoke portion, the electromagnetic coil has a coil length along the long axis of the magnetic core portion that is greater than the thickness of the layer thereof.

(Function) Since the electromagnetic filter 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 can be made elongated, the heat dissipation effect can be enhanced, and the coil will not be heated even if it is energized for a long time. In addition, since the surface area of the magnetic core extension is smaller than the surface area of the yoke, it is possible to maintain the magnetic potential of the magnetic core extension sufficiently high, making it sufficiently strong for information recording media. A magnetic field can be applied. 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, reducing consumption. Power can also be reduced.

(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 2o as a magneto-optical recording medium has a structure in which a pair of transparent substrates 22 are bonded to each other with an air gap in between, and magneto-optical recording is performed on the inner surface of the optical disk 2o. Generally, this magneto-optical recording film 24
A tracking guide (not shown) is formed in advance. Usually, this information recording medium is formed in a disk shape 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 optical disc 2o is housed and protected in a cassette 26 as shown in FIGS. 1 and 2.
In this cassette case 26, upper and lower windows 26B and 26C extending along the radial direction of the optical disc 2o are bored in the upper and lower plate parts of a thin rectangular cassette case 26A.
A is provided with a shutter 19 that is slidable in the direction of arrow (■). When loaded into the information recording/reproducing apparatus, the optical disc 20 is inserted together with the cassette from the insertion slot (not shown) of the information recording/reproducing apparatus by a loading mechanism (not shown), and is ejected from the information recording/reproducing apparatus. When the cassette 26 is loaded, the cassette 26 is ejected from the insertion slot of the information recording/reproducing apparatus. When the cassette 26 is installed in the information recording/reproducing apparatus, the shutter 39 is opened by an opening/closing mechanism (not shown) during the installation operation of the cassette 26, and the upper and lower windows 26B of the cassette case 26A 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 information recording/reproducing apparatus, the windows 26B, 26
C is opened, and the optical disc 2 is stamped by 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.
0 is clamped and fixed, and the objective lens 25 of the optical head 28 is disposed below the optical disk to maintain a state in which the laser beam can be focused from the objective lens 25 of the optical head 28 through the lower window 26C. Furthermore, when the cassette 26 is installed in the information recording and reproducing apparatus, the magnetic flux deriving section 37 of the magnetic field generating device 30 is inserted into the upper window 26B, and the magnetic flux emitting surface 37A is opposed to the optical disk 20, so that information is not transmitted to the optical disk 20. It becomes possible to play, record, or erase. Fourth
As shown in the figure, when the cassette 26 is detached or attached to the information recording/reproducing apparatus, the upper stand bar 52A is lifted upward, and the magnetic flux deriving section 37 of the magnetic field generator 30 is exited out of the upper window 26B. At the same time, the magnetic field generating device 30 is moved by the moving 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.

The magnetic field generating device 30 has a structure that can be separated by a separation mechanism (not shown) so as not to hinder the insertion and ejection operations of the optical disk 20 during insertion and ejection. That is, this magnetic field generating device includes a prismatic or plate-shaped magnetic core portion 34 equipped with an electromagnetic coil 32 as shown in FIG. A wedge-shaped magnetic core extension portion whose thickness decreases toward the tip is formed integrally with the magnetic core as a magnetic flux deriving portion 37 using a magnetic material, and the magnetic coil 32
has a coil length along the long axis of the magnetic core section 34 that is larger than the thickness of the layer, and one end of the magnetic flux deriving section 37 is a yoke section serving as a pedestal to which the magnetic flux emitted from the magnetic core extension section is returned. The magnetic flux deriving part 37 is detachably attached to the upper surface of the yoke part 38, and when the optical disc 20 is inserted or ejected, the magnetic flux deriving part 37 is separated from the yoke part 38 and biased upward.

In this erasure or recordable state, the objective lens 25 is opposed to the magneto-optical recording film surface 24 of the optical disk 20, and the objective lens 25 moves on the guide mechanism 21 to collect the light focused by the objective lens 25. The magnetic core extension 36 extends outside the area corresponding to the area on the magneto-optical recording film 24 that can be irradiated with the beam, and its flat lower surface corresponds to the area of the magneto-optical recording film 24 that can be irradiated with the light beam. is facing.

The cross section of the magnetic core part 34 is set to be smaller than the area of the magnetic flux emitting part 37A of the magnetic flux deriving part 37, and the cross-sectional area of the magnetic core part 34 has a value close to the saturation magnetic flux density Bs in the cross section during operation. It is determined to be sufficiently small to the extent that it can be taken, 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 wire of the electromagnetic coil 32 is reduced, and the resistance value of the electromagnetic coil 32 as a whole is determined to be small. In addition, the magnetic flux deriving section 37
Similarly, the cross-sectional area of the cross-section perpendicular to the longitudinal direction is 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 its surface area is kept small.

The magnetic flux passing through the magnetic flux deriving section 37 near the magnetic core section 34 is
It is equal to the cumulative 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.

As shown in FIG.
The objective lens 25 is movably held on a guide mechanism 21 on a base 27 extending in the radial direction of the optical disc 2.
It is supported so that it can be moved into and out of contact with 0.

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 flat lower surfaces of the magnetic core section 34 and the magnetic flux emitting section 37 are made substantially parallel to each other, and a step is provided so that the flat lower surface of the magnetic flux deriving section 37 is arranged close to the lower surface of the electromagnetic coil 32. This allows the overall thickness to be reduced.

In the embodiment described above, the magnetic field generating device has a structure in which the magnetic flux deriving part 37 is separated from the yoke part 38, but the structure is not limited to such a structure. A part of the magnetic flux deriving portion 37 may be configured to be separable, or the magnetic core portion 34 and the magnetic flux deriving portion 37 may be separably coupled. Furthermore, the yoke part itself may have a separable structure. In addition, the magneto-optical recording film 2
A magnetic flux deriving section 37 is used to generate magnetic flux perpendicular to 4.
is preferably formed into a plate shape with a flat lower surface as shown in the figure, but is not limited to the plate shape and may be formed into a prismatic or cylindrical shape.

The above-described magnetic field generating device 30 has a shape in which the magnetic flux deriving portion 37 is formed in a wedge shape whose thickness decreases toward its tip, and its overall surface area decreases. 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.

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 magnetic field generator 3
The magnetomotive force of the magnetic flux generated at zero is determined by the product of the number of turns of the electromagnetic coil 32 and the current supplied there, but the resistance value of the electromagnetic coil 32 is proportional to the length of the wire required for one turn,
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 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 optical 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 record 11124 of the 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 3o, and the recording is performed. Magneto-optical recording film 2
The magnetic domains in the area above 4 are reversed according to the information to be recorded, and the information is recorded.

In the erase mode, the magnetic field generator 3o is maintained in an operating state, and an erase laser beam having lower intensity than the recording laser beam is applied to the magneto-optical recording film 20 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(Q) component of the laser beam introduced into the laser beam 6 is reflected by the deflection surface 72, focused by the projection lens 69, and further given astigmatism by the cylindrical lens 70, and The S-polarized component of the laser beam introduced into the prism body 66 is transmitted through the deflection surface 72 and is reflected on 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 focused by a projection lens 69 and further by a cylindrical lens 7.
Astigmatism is given at 0, and the light is incident on the second light detection area 80B of the photodetector 80. A reproduced signal is obtained by adding the signals from the first photodetection area 80A, similarly adding the signals from the second photodetection area 80B, and comparing the two. A focus signal is generated by processing the signal from the first photodetection area 80A, and a tracking signal is obtained by processing the signal from the second photodetection area 80B. 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.

The Naifetsu method is known as a focus detection method, but the fact that this Naifetsu method may be adopted is as follows.
It's obvious. Voice coil 7 according to the focus signal
1 is driven, the objective lens 25 is maintained in focus,
The optical head 28 is moved on the guide 21 in accordance with the tracking signal, and the focused laser beam emitted from the objective lens 25 is accurately directed toward the tracking guide, thereby making it possible to reproduce, record, or erase information. maintained in good condition.

Next, the function and operating principle of the magnetic field generator will be explained with reference to FIG. The number of turns of the electromagnetic coil 32 is N,
Assuming that 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 . Magnetic flux is emitted from the surface 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 head towards the yoke 38 as a magnetic return part so as to draw a closed loop, and the yoke 38
The magnetic flux is fed back to the magnetic flux deriving section 37 via. In such a magnetic field distribution, lines of magnetic force perpendicular to the flat lower surface are generated in the vicinity of the magnetic field deriving surface 37A of the magnetic flux deriving section 37, and these lines of magnetic force are applied perpendicularly to the magneto-optical recording film 24 of the information recording medium 20. It will be done. As already explained, in the magnetic recording medium 20, the magneto-optical recording film 24 is formed on the transparent substrate 22, and the magnetic field deriving surface 37A of the magnetic flux deriving section 37 is connected to the magneto-optical recording film 24.
This distance is typically 2.5~
4. Qmm, and the magnetic flux deriving surface 37A has a relatively wide appropriate width, for example, 3 mm or more, and the magneto-optical recording film 2
Since it has an appropriate length, for example, 20 mm or more, which is longer than the length of the light beam irradiable area of No. 4, magnetic flux can be efficiently applied to the magneto-optical recording film 24 perpendicular to the film surface. Magneto-optical recording film 24 that can be irradiated with a light beam
Magnetic lines of force with equal strength are applied to all regions of . The width of the magnetic flux deriving portion 37 is determined by the width of the magneto-optical recording film 24 due to surface buffing of the transparent substrate 22 that occurs during rotation of the information recording medium 20.
It is determined taking into account the fact that it is moved up and down. That is, the magnetic flux derivation section 3 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 become larger than necessary.
The width of 7 is determined in the range of 2 to 3 Qmm.

The difference in magnetic potential between the magnetic flux deriving part 37 and the yoke 38, that is, the magnetomotive force, is determined by Vm-IN, but the magnetic potentials of the surfaces of the magnetic flux deriving part 37 and the yoke 38 are determined as a function of their surface areas.

Here, when the magnetic resistance Rm from each of the surfaces of the magnetic core deriving part 37 and the yoke 38 to infinity with zero magnetic potential has a surface area of S, Rm -1/2 μo fTl (however, C, G, S
In the emu unit system, μ. -1 from Rm-1/2J-1)
Assuming that, the smaller the surface area of the magnetic flux deriving section 37, the larger the magnetic potential becomes.

The magnetic flux is emitted from the magnetic flux deriving part 37 and the yoke 3 is emitted from a distant space.
Since the total magnetic flux fed back to the magnetic core 8 is constant, the smaller the surface area of the magnetic flux deriving part 37, the greater the magnetic flux density on the magnetic core extension part 36 can be increased.

The above content will be explained mathematically using a simple model below. The surface areas of the magnetic flux deriving portion 37 and the yoke 38 are respectively Sc
Sy, and the magnetic resistance from the magnetic flux deriving part 37 and yoke 38 to infinity where the magnetic potential is zero is Rmc, respectively.
RIIY. Further, from the magnetic flux deriving section 37 to the yoke 38
The magnetic flux along the direction is Φtotal, and the magnetic flux deriving section 37
The magnetic flux density at the surface of is expressed as Be(0). However, the units used are C, G, and Se■U. As mentioned above, the magnetic resistances Rme and RB are assumed by the following equations (1) and (2).

RIlc-1/2Frn... (1) RIIly-1
/2F11...(2) Here, R1-1/4μ.

πrQ.

It was considered as ro-1 cho 7 go 1.

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

Φtotal −Vi X (Ra+c+Rmy) −
'-2 convex V 1IIX (1/-1"H lower +1/F
-1...(3) Here, vm is the magnetomotive force (Vm-NI).

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

B c(0)-Φtotal +S c-2-r;1-
Va+ (1/Fn+1/v'T lower)-1/Sc
(4) Here, the total area S (d) of equipotential surfaces in a space separated by a distance d from the magnetic flux deriving section 37 is S (d) = 4 y
r (ro+d) 2-4π(f d τ711+d)
Assuming that 2 - (7 tau+f■]・d)2, the magnetic flux density Be(d) in that space is (
5) It is shown by the formula.

B e (d) - Φtotal + S (d) - 2fT
−Vlm・(nτ+fT1・d)−2X (1/ F
■+ 1 / J1 completion) -1-2 (i--Vm-Sc-
1・(1+ 4x Sc ・d)-2X (1
/ F5+1/ f)7)-' ...(5) Furthermore,
The spatial magnetic field strength H(d) is H(0) −B from μo−1
(0) , H(d) −B (d).

5c) When 4π d2 and Sy multi-Sc,
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)myr cxVm ・・＊・(6)
However, as sy becomes smaller, H(d) decreases, and when 5y-ScL, 5c)4πd2, (
Equation 5) becomes Equation (7), which becomes half of the maximum magnetic field shown by Equation (6).

H(d)÷r'7]1×v11 (7) As is clear from the above analysis, Sc≦Sy, that is, the magnetic flux deriving unit 3
It is understood that the surface area of 7 needs to be less than the surface area of yaw 38. Also, from equations (B) and (7), 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 C shoes.) Also,
The maximum allowable temperature rise value when current is continued to be supplied to the electromagnetic coil 32 is ΔT [unit: °C], and the thermal conductivity coefficient is h-2.
50/degree-cI112, the maximum power consumption Pa+ax [W] is given by the following equation (8). (Yoshiyuki Hirano et al.; Electronics and Communication Academic Journal vol. 1. J60
-C, No.11. P684.1977) Piax-(2hΔT/ (IXIO' Xyr))-
η(W+t +2λ)...(8) Furthermore, the conductor wire diameter of the coil conductor is d[ll11], the outer diameter of the conductor including the coating is d[ll1], and the volume resistivity of the coil conductor is When the total number of turns of the coil is N in ρ[Ω-CIl], the resistance value Re of the coil conducting wire is expressed by equation (9).

Re −1800ρN (W+t+2λ))/(πd2
)...(9) From equations (8) and (9), the maximum allowable current 1 max of the electromagnetic coil 32 is given by the following equation (10), and the maximum magnetomotive force 111aXVm is given by the equation (11). shown.

Imax - (1/ (2X 10') ) x f〒τ
Lower 77・ (nia2/lT> ・ ・ ・ ・ (lO) a+ax Vm-N Imax -(1/200)
×J11 ``lower f'r・ηd/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 +1aXV11 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, WtBs≧Φtota
It must be l. Therefore, it is necessary to suppress power consumption by minimizing Φtotal. Therefore, it is necessary to make the length of the magnetic core extension part 36 only 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. be. When magnetic flux leaks from the surface of the connecting part between the effective magnetic flux deriving part and the magnetic core part, the total magnetic flux Φtotal increases, so as shown in FIG. It is preferable that a magnetic core portion 34 be provided adjacent to the extension portion 36 and that the electromagnetic coil 32 be disposed on the magnetic core portion 34 . In order to make this possible, the flat lower surface of the magnetic core extension part 36 and the magnetic core part 34 may be made substantially parallel to each other, and arranged with a slight offset.

Since the magneto-optical recording film 24 of the information recording medium 20 is given the magnetic flux emitted from the magnetic flux deriving section 37 as described above, the distance between the magnetic flux deriving section 37 and the yoke 38 is determined by the distance between the magnetic flux deriving section 37 and the magnetic core. The distance between the two parts 34 and 34 is increased. As a result, no gap is created between the magnetic flux guide portion 37 and the yoke 38. Therefore, unnecessary magnetic flux that is not applied to the magneto-optical recording film 24 through the small gap of magnetoresistance is not generated, and the total magnetic flux Φtotal can be made as small as possible.

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 of the magnetic flux deriving part 37 perpendicular to the long axis at any point of the magnetic flux deriving part 37 is the total amount of magnetic flux emitted from the outer surface from that point to the tip opposite to the magnetic core part 34. It cannot be made smaller than the value divided by the density Bs. From this, the magnetic core extension part 3 is designed to have a structure in which the cross-sectional area decreases toward the tip and the outer surface area decreases.
6, and the magnetic flux Φtotal emitted 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 during energization of the electromagnetic coil 32, and in contrast, the shape of the electromagnetic coil 32 The efficiency of magnetomotive force can be improved by devising the following. 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 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. .

In the present application, the heat dissipation part 42 has a configuration with a small temperature rise, but is preferably made of a material with high thermal conductivity, as shown in FIGS. 1 to 3. A plate is provided on the magnetic flux lead-out section 37. As shown in the figure, the heat dissipation section 42 has a fin structure with a large number of grooves formed therein. Therefore, when electricity is applied, it is possible to prevent the temperature of the magnetic core extension from increasing.

[Effects of the Invention] 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 can be made elongated, the heat dissipation effect can be enhanced, and the coil will not be heated even if it is energized for a long time. In addition, since the surface area of the magnetic core extension is smaller than the surface area of the yoke, it is possible to maintain the magnetic potential of the magnetic core extension sufficiently high, making it sufficiently strong for information recording media. A magnetic field can be applied. Since the cross section of the magnetic flux lead-out part is formed in a wedge shape that decreases from the joint part with the magnetic core part along its long axis, the leakage magnetic field of the magnetic field lead-out part is small, and the magnetic utilization efficiency can be increased, reducing consumption. Power can also be reduced.

[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. FIG. 2 is a perspective 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 information recording/reproducing apparatus, and FIG. A side view showing the magnetic field generator shown in FIG. 1, No. 4
The figure is a sectional view schematically showing the arrangement relationship when the magnetic field generator shown in FIG. 1 is lifted, and FIG.
FIG. 1 is a schematic configuration diagram showing an optical system of an information recording/reproducing device in which the magnetic field generating device shown in FIG. 1 is incorporated; FIG. 6 is a perspective view showing an electromagnetic coil of the magnetic field generating device shown in FIG. 1; FIG. 7 is a perspective view showing a conventional magnetic field generating device. 20... Optical disc, 21... Guide, 28...
Optical head, 26... Cassette, 30... Magnetic field generator, 32... Electromagnetic coil, 34... Magnetic core, 37...
...Magnetic field derivation section. Applicant's agent Patent attorney Takehiko Suzue Figure 5 Figure 6 Figure 7

Claims (7)

[Claims] (1) A magnetic core made of a magnetic material, a coil wound around the magnetic core, a magnetic flux lead-out part made of a magnetic material extending from one end of the magnetic core, and other parts of the magnetic core. In the magnetic field generating device, the electromagnetic coil includes a yoke part that is magnetically connected to an end thereof and returns the magnetic flux emitted from the magnetic flux deriving part through a space in which an information recording medium is to be placed. A magnetic field generator characterized in that the coil length along the long axis of the magnetic core is greater than the thickness of the magnetic field generator. (2) The magnetic field generating device according to claim 1, wherein the magnetic flux deriving section has a magnetic flux emitting surface parallel to the magnetic core section. (3) The magnet structure consisting of the magnetic core, the magnetic flux deriving part, and the yoke has a separable structure, and the magnetic core, the magnetic flux deriving, and the yoke are in a connected state at least when the coil is energized. The magnetic field generating device according to claim 1, wherein the magnetic field generating device is maintained and the magnetic structure is separated when the information recording medium is attached or detached. (4) The magnetic field generating device according to claim 3, wherein the magnetic core portion is separated from the yoke portion. (5) The magnetic field generating device according to claim 3, wherein the magnetic flux deriving section is separated from the magnetic core section. (6) The magnetic field generating device according to claim 3, wherein the yoke portion has a separable structure. (7) The magnetic field generating device according to claim 3, wherein the magnetic flux deriving section has a separable structure.