JPS63164004A - Magnetic field generator - Google Patents

Abstract

PURPOSE:To generate a sufficiently strong magnetic field, to reduce power consumption and heat and to improve the mount efficiency by decreasing the surface area of a magnetic core extension part more than the surface area of a yoke part. CONSTITUTION:A magnetic field generator 30 giving a magnetic field perpendicular to a magneto-optical recording medium 20 consists of a magnetic core mounted with an electromagnetic coil 32, a magnetic core extension part 36 of wedge form and a yoke part 38. Then the surface area of the magnetic core extension part 36 is selected so as to be smaller than the surface area of the yoke part 38. Thus, the magnetic potential of the magnetic core extension part 36 is selected sufficiently higher and a sufficiently strong magnetic field is given to a recording medium 20. Since a heat sink 42 is provided to the magnetic core extension part 36, the temperature rise in energizing the coil 32 is suppressed, the power consumption is decreased attended therewith and the height is small and the mount efficiency is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to a magneto-optical recording/reproducing 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 an improvement of a magnetic field generating device that generates a magnetic field.

rPrior art 1 Information recording and reproducing devices using magneto-optical recording, external memory for computers, rewritable video disc devices, etc.
There are image zero file devices, AD type compact disk devices capable of playback and recording, and J4 exchangeable J4 density recording magneto-optical cards, and these have been recently developed. This magneto-optical information recording/reproducing device J5 applies a static magnetic field perpendicularly to the recording surface of the information recording medium, and further illuminates the recording film surface of the information recording medium with an east-focused light beam. Fi information is recorded or erased by heating to a temperature exceeding the Curie point or to a temperature at which 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 generating device that employs a local magnetic field application method, as shown in FIG.
It is formed by completely winding.

In this magneto-optical field generator, the end faces 14A and 12A of the magnetic core 14 and the yoke 12 are disposed to face the recording film surface of the magnetic recording medium, and when a current is supplied to the electromagnetic coil 16, the end faces 14A and 12A of the magnetic core 14 and the yoke 12 are arranged to face the recording film surface of the magnetic recording medium. The magnetic flux emitted from the end surface 1/IA of the magnetic core section 14 spreads through the recording film surface of the magneto-optical recording medium and is returned to the end surface 12A of the yoke 12 surrounding the end surface 14A of the magnetic core section 14. Therefore, the recording n of the magneto-optical recording medium
On page 9! A direct magnetic field is locally applied to this recording film surface. When the local magnetic field application method is adopted, the magnetic core end face and yoke end face 14A, 12 of the magnetic field generator
The length in the longitudinal direction of A is determined to be the length of a local area to which a magnetic field is to be applied, and the magnetic field generating device itself is formed in a small size.

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 .

At this magnetic field generation position tA, the parallel end faces 14A and 12A of the magnetic core 14 and yoke 12 are arranged to face the recording film surface of the magneto-optical recording medium, and the electromagnetic coil 16
When a current is supplied to the magnetic core part 14 as a magnetic flux emitting part,
The magnetic flux emitted from the end surface 14A of the magneto-optical recording medium passes through the recording film surface of the magneto-optical recording medium and is returned to the end surface 12A of the yoke 12 disposed on both sides of the end surface 14A of the magnetic core 14. Therefore,
At 4'j, 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 determined to be much 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.

[Problems to be Solved by the Invention] In the conventional magnetic field generating device shown in FIG. 5, which adopts a local magnetic field application method, since the magnetic field is applied locally, there is a problem with the movement of the light beam. This magnetic field generating device is required to be moved, and there is a problem in that the horizontal movement 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 N of electromagnetic coils and the magnetic coil. It is determined by N×I of the current I to flow. 8 again with this electromagnetic coil! When the power of lightning P calculated by iX1 is the resistance R of the electromagnetic coil, P=IXR2. 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 conductor 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. Put it away. In order to reduce the resistance R of the electromagnetic coil, if the linearity of the 'IJ line is increased, if the size of the space in which the electromagnetic coil is accommodated is predetermined.

There is a problem that the number of turns N becomes small. Furthermore, in order to obtain a predetermined magnetomotive force when the number of turns N becomes small, a large current must be supplied to the electromagnetic coil.
Me ¥! There is a problem that the power consumption increases.

(2) There is a problem that the heat generating part is large. That is, as described above, when the power consumption is large, the heat generating portion also becomes larger. The coil, which is the heat generating part of the magnetic field generating HfR, and the magnetic core and yoke to which the heat from the coil is transferred are opposed to the magneto-optical recording medium sufficiently close to each other, so that the heat from the magnetic generator is transferred to the magneto-optical recording medium. There is a risk that the information will be transmitted to the recording medium, causing the magneto-optical recording medium to be thermally deformed, or that the recorded information will be interrupted.

(3) There is a problem that the size of the magnetic field generator increases. In particular, there is a problem that the height of the magnetic field generator along the direction perpendicular to the optical recording surface increases.Magnetic density on the recording surface 8, it is necessary to make the width of the magnetic core sufficiently small, the thickness 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. In such a four-frame structure, there is a problem that the device inevitably becomes bulky.When a magnetic field generating device with a height is placed above the magnetic recording medium,
This increases the size of the information recording and reproducing apparatus itself, and is subject to design constraints.

[Means for solving the problem] The magnetic field generating device of the present invention includes 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. a magnetic core extension made of a magnetic core, and a space that is magnetically connected to the other end of the magnetic core and in which an information recording medium on which information can be recorded or removed is placed. The yoke part to which the magnetic flux emitted from the magnetic flux is returned is FJ, and the human face area of the magnetic core extension part is set to be 6 smaller than the surface area of the yoke part in 11α. In a preferred embodiment, the core extension includes a heat sink. 1rKJ magnetic core part, magnetic core extension part, and yoke part have a structure in which the magnet 4"4 is separable, and at least when the coil is energized, the magnetic core part, +iQ magnetic core extension part, and yoke part are connected. The magnetic structure is maintained in this state, and the magnet structure is separated when the information recording medium is attached or detached.Furthermore, in order to form the 7a shape, the flat lower surface of the magnetic core extension part 34 and the magnet part 34 are made to be approximately parallel to each other, but they are staggered. It's a desk.

"Effect J Since the surface area of the magnetic core extension is determined to be smaller than the surface area of the yoke, the magnetic potential IP of the magnetic core extension
It is possible to maintain a sufficiently high magnetic field, and a sufficiently strong magnetic field can be applied to the information recording medium. In addition, since the magnetic core extension part is equipped with a heat dissipation part, it is possible to suppress the temperature of the magnetic core extension part when electricity is applied to the electromagnetic coil, and to efficiently transfer the magnetic field to the information recording medium. be able to. Furthermore, since the magnet structure consisting of the magnetic core part, the magnetic core extension part, and the yoke part has a separable structure, it becomes easy to attach the n-report 8 medium to the magnetic field generator.

(Embodiment 1 of the Invention An embodiment of this light 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, and is used when information is recorded on a magneto-optical recording medium in an information recording/reproducing device, or when information is optically recorded. It shows the arrangement of the magnetic field generating device with respect to the magneto-optical recording medium when it is lubricated by the magnetically distributed Q medium. Also,
FIG. 2 is a partially cutaway perspective view of the information recording and reproducing device showing the magnetic field generating device shown in FIG. 1 and its surroundings, and FIG. FIG. 2 is a cross-sectional view schematically showing the generator, 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 attached to and removed from the information recording/reproducing apparatus. It shows. As shown in FIG. 1, the magneto-optical recording medium 20 has a sandwich Ra structure in which a pair of transparent substrates 22 are bonded to each other with an air gap in between, and a magneto-optical recording film 24 is formed on the inner surface of the substrate. ing. In some cases, the air gap is filled with adhesive. 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, it is expected that the information recording medium 20 will have various structures other than the supplementary one shown in FIG. This information recording medium 20 is transferred to a cassette 26 as shown in FIG.
Alternatively, the optical disc may be inserted as is from the insertion port of the information recording/reproducing apparatus, placed on the objective lens 25 of the optical head 28, and then ejected from the insertion port. Magnetic field generator 3
0 has a tub structure that allows leakage to occur with a separate tub (not shown) so as not to overstate the insertion and ejection operations of the information recording medium 20 at the time of insertion or ejection. That is,
This magnetic field generating device consists of an electromagnetic coil 3 as shown in FIG.
2 attached thereto, and a wedge-shaped magnetic core extension part that has the function of emitting a magnetic field to the information recording medium 20 and extends from this center and decreases in J7 toward the tip. 36 is integrally formed with a magnetic material as a magnetic flux deriving part 37, and one end of this magnetic flux deriving part 37 is configured to be removably attached to the upper surface of a yoke part 38 serving as a pedestal to which the magnetic flux emitted from the magnetic core extension part is returned. When the information recording medium 20 is inserted or ejected, the magnetic flux deriving section 37 is separated from the yoke section 38 and biased upward. When the information recording medium 20 is stored in the cassette I/26,
During the insertion operation, the cassette window 40 of the cassette 26 opens, the cassette 26 is inserted into the information recording and reproducing apparatus, and the information recording medium 20 is placed on the turntable 42.
and is rotatably supported.

When the mounting operation of the cassette 1-26 is completed, the magnetic flux deriving section 3
7 is lowered, and the magnetic flux deriving section 37 enters into the cassette window 40, making it possible to erase or record. In this erasing or recordable state, the objective lens 25 is opposed to the magneto-optical recording film surface 24 of the information recording medium 20, and then the objective lens 25 moves on the guide support 21 so that the objective lens 25 The magnetic core extension part 36 extends outside the area corresponding to the area on the magneto-optical recording film 24 that can be irradiated with the focused light beam, and its flat lower surface is exposed to the light of the magneto-optical recording film 24. It faces the beam irradiation area.

When current is supplied to the electromagnetic coil 32 in this state and the electromagnetic coil 32 is energized, magnetic flux is supplied from the magnetic core 34 to the magnetic core extension 36, and the magneto-optical recording film 24 is exposed from the bottom surface of the magnetic core extension 36. The light beam is emitted toward the irradiable area.

Therefore, the magneto-optical recording film 24 is exposed to magnetic flux perpendicular to its surface. The magnetic flux that has passed through the magneto-optical Q film 24 C5 passes through the space, enters the yoke 38, and is returned to the magnetic core 34 that is magnetically and mechanically connected to this yoke.

In addition, in the embodiment described above, if the magnetic core and the flat lower surface of the magnetic core extension part 36 are made substantially parallel, a step is provided at 6 and the flat lower surface of the magnetic core extension part 36 is placed close to the lower surface of the electromagnetic coil 32. By doing so, the overall thickness can be reduced.

In the above-mentioned embodiment, the magnetic field generating device has a supplementary structure in which the magnetic flux deriving part 37 is separated from the yoke part 38, but the magnetic flux deriving part 37 is not limited to such a structure. A part of the magnetic core extension part 36 of the magnetic flux deriving part 37 may be configured to be separable, and the magnetic core part 3/
I, the magnetic core extension part 36, and B may be separably coupled.

Furthermore, the yaw portion itself may have a 411i structure that can be separated. Further, in order to generate magnetic flux perpendicular to the magneto-optical recording film 24, the magnetic core extension part 36 is preferably formed in a plate shape with a flat lower surface as shown in the figure, but is not limited to a plate shape, and has an angular shape. It may be formed into a columnar shape or a columnar shape.

Next, the operation of the magnetic field generator and the principle of operation will be explained with reference to FIG. If the number of turns of the electromagnetic coil 32 is N, and the current supplied to the electromagnetic coil 32 is I and 1, then a magnetomotive force Vm=[N is generated from the electromagnetic coil 32 in the magnetic flux deriving section 37. Magnetic flux is emitted from the surface of the magnetic core extension part 36 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 the space travel to the yoke 38 as a magnetic return member so as to draw a closed loop, and then flow through the yoke 38 to the magnetic flux derivation unit 3.
He will be returned on 7th. In this magnetic field distribution, magnetic lines of force perpendicular to the flat lower surface are generated in the vicinity of the lower surface of the magnetic flux deriving portion 37, and these lines of magnetic force are applied perpendicularly to the magneto-optical recording film 24 of the information recording medium 20. J, which has already been explained,
In the magnetic recording medium 20, the magnetic recording film 24 is formed on the transparent substrate 22, and the lower surface of the magnetic flux deriving part 37 is slightly spaced from the magnetic recording film 24, but this distance is usually 2.
゜5～4: ○mrT1 and small size, but magnetic flux derivation part 37
Since the lower surface has a relatively wide appropriate width, for example, 3 mm or more, and an appropriate length 1, for example, 20 mm or more, which is longer than the length of the light beam irradiable area of the magneto-optical recording 11924, the magneto-optical recording film 24 can be efficiently In other words, magnetic flux can be applied perpendicularly to this film surface, and lines of magnetic force with equal strength are applied to all areas of the magneto-optical distribution 24 that can be irradiated with the light beam. The width of the magnetic flux deriving portion 37 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, by vertically moving the magneto-optical recording film 24, the magneto-optical recording film 24 is moved up and down. The width of the magnetic flux deriving part 37 is set in a range of 2 to 3 Qmm so that the magnetic field on the 8 film 24 does not increase to that extent and the magnetic flux passing through the f11 flux deriving part 37 does not need to be increased more than necessary.

The difference in magnetic potential between the magnetic core extension 36 and the yoke 38, that is, the magnetomotive force, is determined by Vrn=INτ', but the magnetic potential P on the surfaces of the magnetic core extension 36 and the yoke 38 is determined as a function of their surface areas. .

Here, when the surface area of magnetic resistance Rm from each of the magnetic core extension part 36 and yoke 38 surface to infinity with zero magnetic potential is S, Rm=1/2 μo J7rS (However, in C, G, S eIlu units) In the system, if it is assumed that Rm=1/2JπS from μo=1), the smaller the surface area of the magnetic core extension 36, the larger the magnetic potential potency P becomes. Since the total magnetic flux emitted from the magnetic core extension part 36 and returned to the yoke 38 from the female space is constant, the smaller the surface area of the magnetic core extension part 36, the greater the magnetic flux density on the magnetic core extension part 36. can do.

The above content will be explained mathematically using a simple model below. The surface area of the magnetic core extension 36 and the yoke 38 is
c Sy, and the magnetic resistance from the magnetic core extension gs 36 and yoke 38 to infinity of zero magnetic potential is Rn, respectively.
c. RIIV. Also, from the magnetic core t1 part 36]-
The magnetic flux along the direction 38 is defined as Φtotal, and the magnetic flux density at J3 on the surface of the magnetic core extension 36 is expressed as BC(0). However, the units used are C, G, and SeI'llu units. As mentioned above, the magnetic resistance Rmc.

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

R11c=1/277C8c...(1) R1y=
1/2JyrSy...(2) Here, R1=1
/4μ口πro.

It was assumed that r = (S/4π).

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

Φtotal = Vm x (Rrnc+RIlly)
−1=2”7rVIII X (1/JSc + 1
．． 'rsy)-' (3) Here, Vn is the magnetomotive force (■In-NI).

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

Bc(0)-Φtotal-knee5c=2(π xVI (1/JSc +1/J'Sr)-'/Sc
−・・・・・・・・・(,1) Here, the distance d from the magnetic core is d(g!?rH in the space away from the magnetic core 36). )=4
π (ro+d)2 = 4π (JSc/4rr+d)2=<JSc+J
Assuming that 4π·d)2, the magnetic flux density Bc(d) in the air 17B is expressed by equation (5).

Bc(d)=Φtotal ÷5(d)=2s/”yr
・Vl# (-ysc +v'47r ・d)'x
(1/JSc +1/Jsy)-1=2π-Vn+
-8c -1 X (1+J47[/SC-d)'2x (1/
JSc + 1/JSy) °5...(
5) Furthermore, the spatial magnetic field intensity H(d) is H(0) from μG=1.
=B(0), H(d) =B(d).

5c) 4πd2 and Sy (sc and Kiniha, (
5] Equation becomes Equation (6), and the maximum magnetic field is determined by the information recording medium 2.
0 can be applied to the magneto-optical recording film 24.

! ((d) = J4π/Sc xVn+ --- (6
) However, as Sv becomes smaller, H(d) decreases, and when 5v=Sc and Sc:>4yrd2, equation (5) becomes equation (7), which is shown by equation (6). It becomes half of the maximum magnetic field.

H(d)=J7r/SCXVI ・---(7) As is clear from the above analysis, Sc≦Sy, that is, the magnetic core extension 3
It is understood that the surface area of 6 needs to be smaller than the surface area of yoke 38. Further, from equations (6) and (7), it is better to make Sc as small as possible, but if it is made smaller than necessary, it will become smaller than 4πd2, so 3c cannot be made that small.

Next, the shape and power consumption of the electromagnetic coil 32 will be considered. As shown in FIG. 4, 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. The compression unit is CI. )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 = 25.
0/deQree -cm2 and maximum power consumption P
Iax [W] is given by the following equation (8).

(Yoshiyuki Hirano et al.; Electronics and Communication Academic Journal vol. 1. J60-
C, No.11. (See PG84, 1977) Plax=
(2hΔT/<lX10'Xπ))・Xη (W+ t
+ 22) ・ ・ ・ ・ (8) Furthermore, the diameter of the conductor wire of the coil conductor is d[lll1], the outer diameter of the conductor including the coating is d[+mn], and the volume resistivity of the coil conductor is ρ. When the number of turns a of the coil is N in [Ω-cn+], the resistance value Rc of the coil conducting wire is expressed by equation (9).

Rc = (800ρN(W+t+2λ))/(πd...(9) From equations (8) and (9), the maximum allowable current ■lax of the electromagnetic coil 32 is shown by equation (10) below, or The lζ maximum magnetomotive force laxVm is expressed by equation (11).

l1lax = (1/ (2xlO'))x, rh
ΔT/ρ・(d2/Jλ)・・・(10) nax Vm=N Inax = (1/200>×(
[1ΔT/ρ・η×λ/）・・・(11) However, N
8(d)2/100=λη.

From equations (8) and (11), a large magnetomotive force can be generated with a small Fi cost power of 1! Consider how to do this.

It is understood from equation (11) that the maximum magnetomotive force maxVm does not depend on the outer diameter dimension (W, l:) of the magnetic core portion 34. 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 Ss, WtBS≧Φt
Must be otal. Therefore, it is necessary to suppress the mechanical cost and lightning force by minimizing Φtotal. Therefore, the length of the magnetic core extension 36 is the information 9g to be searched by the light beam.
It is necessary to make it only slightly longer than the length of the recording area of the X body, and to keep the portion that generates extra magnetic flux as small as possible. When magnetic flux leaks from the surface of the connecting part between the effective magnetic flux emitting part and the magnetic core part, the total daily flux Φtota
1, the magnetic core 34 is provided on the extension line of the magnetic core extension 36 and close to the magnetic core extension 36, as shown in FIG.
2, which substantially defines the core extension 36 as an effective flux emitting section. In order to make this possible, the flat lower surface of the magnetic core extension portion 36 and the magnetic core portion 34 may be made substantially parallel to each other, and may be arranged slightly offset from each other.

Since the optical recording film 24 of the information recording medium 20 is given the magnetic flux emitted from the magnetic core extension part 36 as described above, the distance between the magnetic core extension part 36 and the yoke 38 is determined by the magnetic core extension part 36. The distance between the magnetic core portion 34 and the magnetic core portion 34 is made larger than that between the magnetic core portion 34 and the magnetic core portion 34. As a result, no gap is created between the magnetic core extension 36 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 Φjojal can be made as small as possible.

The magnetic core extension portion 36 is formed into a wedge shape as described above, and this is due to the following reasons. Generally, the area of the cross section of the magnetic core extension 36 perpendicular to the long axis at any point of the magnetic core extension 36 is the saturation magnetic flux, which is the total amount of magnetic flux emitted from the outer surface from that point to the tip opposite to the magnetic core 34. It cannot be made smaller than the value divided by the density 3s. 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 Φtota1 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 core extension part 36, 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.

As described above, there is a limit to how b (W+ t ) can be reduced by devising ways to reduce the value of the total magnetic flux Φtotal. As is clear from comparing equations (8) and (11), the power consumption is reduced by reducing the thirst increase mother Δd when the electromagnetic coil 32 is energized; The efficiency of magnetomotive force can be improved by devising the shape. 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 generator of the present application,
The 6-coil length is set larger than the thickness λ of the electromagnetic coil. That is, the magnetomotive force VIa=NI is proportional to the number of turns N, but if the length of the wire required for -turning is long, the resistance value per turn of the wire increases, and 21! The cost of electricity 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 is made of a material having a small temperature rise but preferably has a thermal conductivity of 13 as shown in FIGS. 1 to 3, for example made of aluminum. A heat sink is provided on the magnetic core extension 36. As shown in the figure, a large number of vortices are formed in the heat radiating portion 42 to form a fin 41 structure. Therefore, when electricity is applied, it is possible to prevent the temperature of the magnetic core extension from increasing.

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 calorific value, and is capable of improving mounting efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a magnetic field generating device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the operation when attaching or detaching information records and media in the device shown in FIG. 3 is a perspective view of the magnetic field generator shown in FIG. 1, and FIG. 4 is a perspective view of the magnetic field generator shown in FIG. 1. FIGS. 5 and 6 are perspective views showing a conventional magnetic field generating device, without showing the coil. 20... Information recording medium, 25... Objective lens, 28... Optical head, 34... Magnetic core, 36...
...Magnetic core extension part, 37...vA flux derivation part, 38...
... Yoke part, 40 ... Heat dissipation part Applicant's agent Patent attorney Takeshi Suzue β No. 5 Inwaki Fig. 6

Claims (1)

[Claims] (1) A magnetic core made of a magnetic material, a coil wound around the magnetic core, and a magnetic core extension made of a magnetic material extending from one end of the magnetic core. , a yoke portion that is magnetically connected to the other end of the magnetic core portion and returns the magnetic flux emitted from the magnetic core extension portion through a space in which an information recording medium capable of recording or erasing information is placed; A magnetic field generating device (2) characterized in that the surface area of the magnetic core extension part is smaller than the surface area of the yoke part.
(3) The magnetic field generating device according to claim 1, wherein the magnetic core extension has at least one surface parallel to the magnetic core. (4) The magnetic field generating device (4) according to claim 1, wherein the heat dissipation section is made of a non-magnetic material (5) The magnetic core , the magnet structure including the magnetic core extension and the yoke has a separable structure, the magnetic core, the magnetic core extension and the yoke are maintained in a connected state at least when the coil is energized, and the information The magnetic field generating device according to claim 1, wherein the magnetic structure is separated when the recording medium is attached or detached. (6) The magnetic field generating device according to claim 1, wherein the magnetic core part is separated from the yoke part. (7) The magnetic field generating device according to claim 4, wherein the magnetic core extension portion is separated from the magnetic core portion. (8) The magnetic field generating device according to claim 4, wherein the yoke portion is separated. A magnetic field generating device (9) according to claim 4, characterized in that the magnetic field generating device (9) has a structure in which the magnetic core extension part has a separable structure. magnetic field generator