Magnetic field generating device

There is disclosed a magnetic field generating device for use in a magnetooptical recording apparatus of a magnetic field modulation method. The device includes a planar spiral coil, of which coil pitch is smaller in the peripheral area than that in the central area thereof, thus realizing a relatively wide area of magnetic field of uniform intensity, with a low inductance. Because of the planar structure, the device can be positioned very close to the recording medium, and can achieve the high speed switching required in the magnetic field modulation method, without a large power source.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic field generating device for 
applying a bias magnetic field to a recording layer of a magnetooptical 
recording medium in the magnetooptical recording method. 
2. Related Background Art 
FIG. 1 illustrates a conventional bias magnetic field generating device 
employed in the magnetooptical recording method of light modulation type. 
The bias magnetic field generating device 52 is provided on a 
magnetooptical recording medium, or a magnetooptical disk 50, so as to 
generate a substantially uniform magnetic field over the entire 
information recording area in which an optical head 51 is moved under 
tracking control. A bias field generating power source 53 supplies current 
to a coil wound on a core of the bias field generating device 52, and the 
magnetooptical disk 50 is rotated by a spindle motor 55. 
In such magnetooptical recording of a light modulation method, record bits 
(portions of inverted magnetization) are formed by the intensity change of 
a light beam from the optical head, and the external field from the bias 
field generating device is used as a supplement. The recording, 
reproduction and erasure of information are achieved by intensity change 
of the light beam. Thus the light beam from the optical head is modulated 
according to the recording signal. 
In such structure, the bias field generating device and the power source 
therefor are inevitably bulky and heavy since the bias magnetic field has 
to be generated for the entire information recording area 54. Also because 
of the difficulty of application of a uniform bias field over the entire 
information recording area 54, the record pits formed in the 
magnetooptical disk at recording become uneven in size and shape, 
eventually giving rise to errors in information reading. Furthermore, 
because of the significant electric power required for generating the bias 
magnetic field, the bias field generating device 52 causes temperature 
increase of the magnetooptical disk 50, thereby affecting the conditions 
of information recording and eventually leading to errors. 
For this reason there is also proposed a bias field generating device for 
applying a bias field only to an area currently subjected to 
magnetooptical recording by the optical head, and this is called the 
magnetooptical recording of a magnetic field modulation method. FIG. 2 
illustrates such recording, wherein a bias field generating device 62 is 
linked, by a support member 66, to an optical head 61 positioned across a 
magnetooptical disk 60, and said device 62 and optical head 61 are 
mutually so positioned that the light beam 67 for information recording 
and reproduction from the optical head 61 substantially coincides with the 
center of the bias field generated by the device 62. Consequently the bias 
field generating device 62 can follow the movement of the optical head 61 
when it is moved in the information recording area 64 under tracking 
control. 
In such magnetooptical recording of the magnetic field modulation method, 
the recording signal is introduced into the external magnetic field of the 
bias field generating device. At the information recording, the light beam 
from the optical head has a constant intensity and is used as a 
supplement. Thus the external field from the bias field generating device 
is modulated according to the recording signal. 
In such magnetooptical recording, the support member 66 linking the bias 
field generating device 62 and the optical head 61 is provided, in a part 
A, with a spring of desired properties, and said bias field generating 
device 62 is made to float with a small spacing from the surface of the 
magnetooptical disk 60, utilizing the air flow generated by the rotation 
of the magnetooptical disk 60 on said surface. 
Thus the bias field generating device shown in FIG. 2 can avoid the 
drawbacks of the bulk, weight and large power consumption associated with 
the device generating the magnetic field over the entire recording area as 
shown in FIG. 1, and can therefore eliminate the causes of errors. 
However the bias field generating device shown in FIG. 2 is still 
associated with the following drawbacks. In such a device, since the 
generated bias field has only a narrow uniform area, so that the light 
beam 67 from the optical head 61 has to be exactly aligned with the center 
of the magnetic field generated by the device 62. For this reason there 
are required highly precise designing, manufacture and alignment, which 
lead to increased costs. 
Also, the bias field generating device can follow the movement of the 
optical head through the support member 66, when said optical head is 
moved by a large amount under tracking control, but, in the course of 
scanning with the light beam, there is required correction control for the 
vibration of the light beam 67 resulting from vibration of an optical head 
actuator or for the aberration between the light beam 67 and the center of 
the bias field resulting from the vibration of the generating device 62. 
Particularly, in the tracking control of the light beam 67 by a fine 
tracking control actuator in the optical head 61, the correction control 
is indispensable for the positional aberration of said bias field 
generating device 62. 
It is therefore conceivable to maintain the uniform area of the bias 
magnetic field of the generating device at a certain size, thereby 
enlarging the tolerance of said positional aberration and practically 
dispensing with said correction control. However, in the above-mentioned 
bias field generating device, the cylindrical coil employed therein 
requires a considerable number of turns for generating a required magnetic 
field, and the magnetic field is difficult to concentrate as the coil 
requires a certain distance in a direction perpendicular to the 
magnetooptical disk. Therefore if the magnetic pole is made larger for 
enlarging the uniform area of the necessary magnetic field, the high 
frequency drive becomes difficult due to the increase in inductance, and 
the bias field generating device inevitably becomes bulky and heavy. 
SUMMARY OF THE INVENTION 
In consideration of the foregoing, the object of the present invention is 
to provide a bias magnetic field generating device which is compact in 
size and light in weight, and provides a uniform area of the bias field 
sufficient for accommodating the positional aberration of the light beam, 
without increase in inductance. 
According to an aspect of the present invention, there is provided a 
magnetic field generating device comprising: 
a substrate; 
a magnetic field generating coil provided on said substrate and having 
different coil pitches in the central area and in the peripheral area; and 
drive means for driving said magnetic field generating coil. 
Also there is provided a magnetooptical recording apparatus utilizing the 
magnetic field generating device of the present invention, comprising: 
an optical head for irradiating a magnetooptical recording medium with a 
light beam; and 
a magnetic field generating device for applying a magnetic field to said 
magnetooptical recording medium, including a substrate, a magnetic field 
generating coil provided on said substrate and having different coil 
pitches in the central area and in the peripheral area, and drive means 
for driving said magnetic field generating coil. 
According to another aspect of the present invention, there is provided a 
magnetic field generating device comprising: 
a substrate; 
a magnetic field generating coil formed on a first face of said substrate; 
terminals formed on a second face different from said first face and 
connected to said magnetic field generating coil through conductive 
portions; and 
drive means connected to said terminals for driving said magnetic field 
generating coil. 
Also there is provided a magnetooptical recording apparatus utilizing the 
magnetic field generating device of the present invention, comprising: 
an optical head for irradiating a magnetooptical recording medium with a 
light beam; and 
a magnetic field generating device for applying a magnetic field to said 
magnetooptical recording medium, including a substrate, a magnetic field 
generating coil formed on a first face of said substrate, terminals formed 
on a second face different from said first face and connected to said 
magnetic field generating coil through conductive portions, and drive 
means connected to said terminals for driving said magnetic field 
generating coil. 
According to still another aspect of the present invention there is 
provided a magnetic field generating device comprising: 
a substrate; 
a magnetic field generating printed coil formed on said substrate and 
having different sizes in two perpendicular directions; and 
drive means for driving said magnetic field generating printed coil. 
Also there is provided a magnetooptical recording apparatus utilizing the 
magnetic field generating device of the present invention, comprising: 
an optical head for irradiating a magnetooptical recording medium with a 
light beam; and 
a magnetic field generating device for applying a magnetic field to said 
magnetooptical recording medium, including a substrate, a magnetic field 
generating printed coil formed on said substrate and having different 
sizes in two perpendicular directions, and drive means for driving said 
magnetic field generating printed coil. 
According to still another aspect of the present invention there is 
provided a magnetic field generating device comprising: 
a substrate provided with a plurality of magnetic field generating printed 
coils; and 
drive means for driving said magnetic field generating printed coils. 
Also there is provided a magnetooptical recording apparatus utilizing the 
magnetic field generating device of the present invention, comprising: 
an optical head for irradiating a magnetooptical recording medium with a 
light beam; and 
a magnetic field generating device for applying a magnetic field to said 
magnetooptical recording medium, including a substrate provided with a 
plurality of magnetic field generating printed coils, and drive means for 
driving said magnetic field generating printed coils. 
According to still another aspect of the present invention, there is 
provided a magnetic field generating device comprising: 
first plural magnetic field generating coils formed on a first face; 
second plural magnetic field generating coils formed on a second face 
different from said first face; and 
drive means for driving said first and second magnetic field generating 
coils. 
Also there is provided a magnetooptical recording apparatus utilizing the 
magnetic field generating device of the present invention, comprising: 
an optical head for irradiating a magnetooptical recording medium with a 
light beam; and 
a magnetic field generating device for applying a magnetic field to said 
magnetooptical recording medium, including first plural magnetic field 
generating coils formed on a first face, second plural magnetic field 
generating coils formed on a second face different from said first face, 
and drive means for driving said first and second magnetic field 
generating coils. 
There is also provided a magnetooptical recording apparatus utilizing the 
magnetic field generating device of the present invention, comprising: 
an optical head for irradiating a magnetooptical recording medium with a 
light beam; and 
a magnetic field generating device for applying a magnetic field to said 
magnetooptical recording medium, including a substrate provided with 
plural magnetic field generating printed coils, and drive means for 
driving said magnetic field generating printed coils; and 
regulation means for regulating the distance between said magnetic field 
generating device and said magnetooptical recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now the present invention will be clarified in detail by embodiments 
thereof shown in the attached drawings. 
In the following description, there will only be described the bias field 
generating device of the present invention, since the entire structure of 
the magnetooptical recording apparatus is similar to the aforementioned 
conventional example, shown in FIG. 2, based on the magnetic field 
modulation method. The bias field generating device of the present 
invention is formed, by thin film technology as shown in FIGS. 3A and 3B, 
by forming a conductive pattern 8 on a block 1 of a magnetic material 
constituting a substrate, depositing an insulating layer 7 except for 
connection points 5, 6 at the both ends of said conductive pattern 8, and 
forming, on the upper surface of said insulating layer 7, a spiral printed 
coil 2, a terminal 3 connected to the outer end of said coil 2 and a 
terminal 4 connected to said conductive pattern 8 at said point 6 by 
conductive patterns. The inner end of said coil 2 is connected to said 
point 5. If necessary there may be provided a protective insulating layer 
on said insulating layer 7, so as to cover the printed coil 2. 
The magnetic block 1 is preferably composed of a magnetic material with 
satisfactory high frequency characteristics, such as high frequency 
ferrite, having a low high-frequency loss and a high magnetic 
permeability. In the present embodiment, the printed conductors such as 
the conductive pattern 8 and the printed coil are preferably formed by 
evaporation or sputtering, with a highly conductive material such as 
copper. There may also be employed a method of leaving the desired 
pattern, such as etching. 
Printed coil 2 is so constructed that the pitch thereof decreases gradually 
or stepwise in certain zones, in comparison with that in the central area. 
The width of the conductor of the coil 2 can be constant. Also the 
external diameter of said coil 2 is preferably so selected that the 
uniform area of the bias magnetic field in the vertical direction 
generated by said coil 2 covers the movable range of the light beam moved 
by the precise tracking actuator of the optical head. 
Such a bias field generating coil generates a magnetic field in a direction 
+Z or -Z respectively when current is supplied from the terminal 3 to 4 or 
from 4 to 3, by a power source 9. The information recording is achieved by 
such modulation of the external magnetic field. 
FIG. 4 illustrates the distribution of the bias magnetic field generated by 
the bias field generating device explained above, and shows, in the 
ordinate, the magnitude of a vertical magnetic field component applied to 
the recording layer of the magnetooptical disk, as a function of the 
distance from the center of the printed coil in the abscissa. In FIG. 4, a 
curve A represents the distribution of the magnetic field generated by the 
bias field generating device of the present invention, while a curve B 
represents that of the magnetic field generated by a spiral coil of the 
same diameter with a constant coil pitch. A line C indicates the minimum 
bias field required for recording. Thus, in consideration of the alignment 
error between the optical head and the bias field generating device, there 
is required a magnetic field of at least 200 Oe in a range (for example 
+200 .mu.m) including the movable range of the light beam by the tracking 
actuator, and the present invention can provide a uniform magnetic field 
of a wide area sufficiently satisfying this condition. Also, the bias 
field generating device can be made more compact and lighter, because it 
can provide the uniform magnetic field of a given size by a coil of 
smaller diameter, in comparison with a cylindrical coil or a planar 
printed coil with a constant coil pitch. Furthermore, an excellent high 
frequency switching property can be obtained as the inductance of the coil 
can be reduced. 
FIG. 5 shows another embodiment of the bias field generating device of the 
present invention, in a plan view of an upper printed coil 31. Coil 31 is 
formed as a square spiral coil with the coil pitch smaller in the 
peripheral area than in the central area. There are also shown a magnetic 
block 32; terminals 33, 34; and connection points 35, 36. 
FIGS. 6A and 6B show still another embodiment of the bias field generating 
device of the present invention, in which the upper printed coil 41 is 
similar to that shown in FIG. 3, but the conductor pattern 8 is replaced 
by a lower printed coil 46 wound inversely to said upper coil 41 and 
connected thereto at a point 5. Thus the number of turns of the coil is 
doubled, and a doubled magnetic field can be generated with the same 
driving current. Such structure is effective in case the bias field 
generating device cannot be positioned close to the magnetooptical disk, 
or in case a large bias magnetic field is required, or for any other 
reason. 
The printed coil in the foregoing embodiments is circular or square, but it 
may also be formed in other shapes such as oval or rectangular. 
As explained in the foregoing, according to the present invention, in the 
magnetooptical recording method in which a magnetooptical recording medium 
is heated with a light beam from an optical head and is subjected 
simultaneously to the application of a bias magnetic field so as to 
represent information by the direction of magnetization of a magnetic 
domain, a magnetic field generating coil having a main field component 
perpendicular to the recording layer of said recording medium is formed in 
a plane close to said recording medium with the coil pitch smaller in the 
peripheral area than in the central area. 
In each of the foregoing embodiments there is employed a coil, but there 
may be employed plural magnetic field generating coils. 
FIG. 7 shows an embodiment in which plural magnetic field generating coils 
are provided on the same substrate 75 composed of a magnetic block. A 
power source 76 is provided for driving said magnetic field generating 
coils. In FIG. 7, a direction X is the direction of tracking control of 
the optical head, and a direction Y is the direction of relative movement 
between the magnetic field generating device and the recording medium. 
FIG. 8 shows a magnetooptical recording apparatus employing the bias field 
generating device of the present invention, shown in FIG. 7. A bias field 
generating device 70 of the present invention is positioned opposite to an 
optical head 51, across a magnetooptical disk 50 constituting a recording 
medium, so as to generate a bias magnetic field over the entire 
information recording area 54 in which the optical head 51 moves under 
tracking control. A coil of said device 70 receives current from a bias 
field generating power source 53, and the magnetooptical disk 50 is 
rotated by a spindle motor 55. Naturally, in the bias field generating 
device 70 of the present invention, the magnetic field generating coil has 
different coil pitches between the peripheral area and the central area as 
explained before. There are also shown a linear motor 71 for moving the 
optical head 51 in the direction of tracking control; a control unit 72 
for controlling the functions of the bias field generating device 70, 
optical head 51, linear motor 71 and spindle motor 55; and a process unit 
73 for sending or receiving signals to or from the control unit 72. When 
plural coils are provided as explained above, over the entire information 
recording area in which the optical head moves under tracking control, a 
coil corresponding to the position of the optical head is driven for 
modulation at the recording, as the optical head moves. 
According to the present invention, as detailedly explained in the 
foregoing, the magnetic field generating coil is formed on a plane close 
to the recording medium, with the coil pitch smaller in the peripheral 
area than in the central area of the coil. Consequently, in the tracking, 
since a uniform magnetic field area can be easily obtained to cover the 
movable range of the light beam from the optical head, there can be 
dispensed with the relative alignment between the optical head and the 
bias field generating device. This fact is advantageous in structure and 
in control, and can reduce the cost and the errors in the recording 
operation. Also since a uniform area of magnetic field can be obtained 
with a necessary intensity, without the use of an enlarged magnetic pole, 
there is obtained a bias field generating device of low inductance, 
enabling high frequency switching operation. Also the more compact bias 
field generating device ensures high speed movement of the optical head 
for example in the seeking operation, and ensures excellent response to 
transient variation in the air flow in a floating structure, reduced 
vibration, satisfactory stability and high reliability. 
In the following there will be explained a structure of the bias field 
generating device that can expand the uniform area of magnetic field 
without an increase in the inductance and can be supported in a floating 
mechanism. 
As shown in FIG. 9, there can be conceived a bias field generating device 
employing a spiral coil, thereby expanding the necessary uniform area of 
magnetic field without increasing the inductance. A printed coil 87 
patterned by a thin film etching technology on a magnetic block 81 
receives a driving current from an unrepresented power source through lead 
wires 84, 89 to generate a perpendicular magnetic field in the 
Z-direction. Coil 87 is formed on an insulating layer 85 provided on the 
magnetic block 81, and is covered by a protective film 86. On both sides 
of said printed coil 87 on the magnetic block 81, there are formed 
terminal patterns 80, 82 to which said lead wires 84, 89 are connected by 
soldering or bonding. 
Such structure is associated with a decisive defect that, as will be clear 
from FIG. 9A, the soldered or bonded portions 83, 88 protrude upwards on 
the terminal patterns 80, 82 by a height t beyond the surface of the 
protective film 86, whereby the bias field generating device, particularly 
the printed coil 87 thereof cannot be positioned close enough to the 
surface of the magnetooptical disk. 
This fact hinders the intension of obtaining an expansion in the uniform 
area of a necessary magnetic field without an increase in the inductance, 
and becomes a structural disturbance in the floating support for the bias 
field generating device shown in FIG. 9. 
In practice, it is difficult to reduce such protrusion of soldering or 
bonding below 100 .mu.m even under highly sophisticated connection 
technology. Consequently the floating mechanism is unemployable, in 
consideration of the fact that the gap between said bias field generating 
device and the surface of the magnetooptical disk in the floating system 
has to be in the range of 3-4 .mu.m. 
In the following there will be explained an embodiment of the magnetic 
field generating device of the present invention, taking the 
above-explained facts into consideration. 
Now said embodiment will be explained in detail with reference to FIGS. 10A 
and 10B, which show a bias field generating device for generating a bias 
magnetic field by a printed coil 93 formed by a thin film technology on a 
magnetic block 91 constituting a substrate and having lowered portions 
91a, 91a' on both sides. Said magnetic block 91 is composed of a material 
of satisfactorily high frequency properties such as high frequency 
ferrite, which should preferably be provided with a low high-frequency 
loss and a high magnetic permeability. Magnetic block 91 has a stepped 
surface consisting of said lower portions 91a, 91a' and a central upper 
portion 91c mutually connected by sloped portions 91b, 91b'. Terminal 
areas 94, 95 are formed on said lower portions 91a, 91a' and on said 
sloped portions 91b, 91b', and a conductive portion 99 is extended inwards 
in the central upper portion 91c. An insulating layer 97 is laminated on 
said upper portion 91c, excluding a connection point 96 at the end of said 
conductive portion 99, and the aforementioned printed coil 93 is provided 
on said insulating layer. Said printed coil 93 is formed as a spiral, of 
which the internal end is connected to said connection point 96 while the 
external end is connected to said terminal area 95 through a conductive 
portion 100. An insulating layer 92 is formed thereon for protecting the 
coil 93. 
The above-explained bias field generating coil generates a magnetic field 
in a direction +Z or -Z respectively when current is supplied from the 
terminal 94 to 95 or from 95 to 94 by a power source 101 for driving said 
coil. The plane of the terminals 94, 95 is more separated, than the 
surface of the upper portion 91c on which the coil 93 is provided, from 
the surface of the magnetooptical recording medium (not shown), which is 
positioned above the insulating layer 92 in FIG. 10B. For this reason, the 
soldering or bonding used for connecting the lead wires from the power 
source 101 to said terminals 94, 95 does not protrude from the plane of 
the printed coil 93 toward the magnetooptical recording medium. Stated 
differently, the step between the plane of the printed coil 93 and the 
lower portions 91a, 91a' on which the terminals 94, 95 are formed can be 
selected at a value, for example 0.25 mm, exceeding the expected thickness 
of solder, for example 0.2 mm. 
In consideration of a fact that evaporation or sputtering will be employed 
for forming the terminals 94, 95 also on the sloped portions 91b, 91b', 
the angle .theta. of said sloped portions 91b, 91b' with respect to the 
central upper portion 91c is preferably selected in excess of 90.degree., 
for example 135.degree. as shown in FIG. 10B. 
Now reference is made to FIG. 11 for explaining the manufacturing process 
of the bias field generating device explained above. At first a magnetic 
block 91 having the upper portion 91c, sloped portions 91b, 91b' and lower 
portions 91a, 91a' on the surface as shown in 11A, 11A' is formed by 
shaping from a block or by press molding. Then, as shown in 11B, 11B', a 
conductor pattern 98 constituting the conductive portion 99 is formed by 
evaporation or sputtering on the upper portion 91c. Then the insulating 
layer 97 is formed on the upper portion 91c as shown in 11C, 11C', and a 
hole 97a is formed in a position corresponding to the connection point 96 
as shown in 11D, 11D', thereby exposing a part of the conductor pattern 98 
in the bottom thereof. Then, as shown in 11E, 11E', the printed coil 93 is 
formed by a conductor pattern, and the internal end of said coil is 
connected to the conductive portion 99 at the connection point 96. Also at 
the external end there is formed the conductive portion 100, which extends 
beyond the edge of the insulating layer 100 to the edge of the upper 
portion 91c. In this state the insulating layer 92 is formed for 
protecting the printed coil 93 as shown in 11F, 11F', and a mask M is 
formed excluding the terminal patterns as shown in 11G, 11G'. The 
terminals 94, 95 are formed in this state by evaporation or sputtering, 
and said mask M is removed to obtain a bias field generating device of the 
structure shown in 11H, 11H'. 
FIGS. 12A and 12A' show the mode of mounting, on such a bias field 
generating device, lead wires 105 to the terminals 94, 95 by soldering or 
bonding 106. As shown in FIG. 12B, the soldering or bonding 106, being 
formed on the lower portions 91a, 91a', does not reach the upper portion 
91c on which the printed coil 93 is provided. 
FIGS. 13A and 13B show the state of supporting the bias field generating 
device with support members 107 functioning also as lead wires. Support 
members 107 are preferably composed of elastic members and may be designed 
to serve as arms for supporting the bias field generating device in a 
floating state. The terminals 94, 95 are electrically connected to said 
support members 107. 
The above-explained bias field generating device having a coil on a first 
plane and terminals, connected to said coil through conductive portions, 
on a second plate spaced by a predetermined amount from said first plane 
may be employed in the magnetooptical recording apparatus shown in FIG. 2, 
in place of the bias field generating device 62. 
In each of the foregoing embodiments shown in FIGS. 10 to 13, there is 
employed a coil, but there may be employed plural magnetic field 
generating coils. 
FIG. 14 shows an embodiment in which plural magnetic field generating coils 
are provided on the same substrate 108 composed of a magnetic block. A 
power source 109 is provided for driving said magnetic field generating 
coils. In FIG. 14, a direction X is the direction of tracking control of 
the optical head, and a direction Y is the direction of relative movement 
between the magnetic field generating device and the recording medium. The 
magnetic field generating device shown in FIG. 14 may naturally be 
employed instead of the device 70 shown in FIG. 8. 
As explained in the foregoing, according to the present invention, in the 
magnetooptical recording method in which a magnetooptical recording medium 
is heated with a light beam from an optical head and is subjected 
simultaneously to the application of a bias magnetic field so as to 
represent invention by the direction of magnetization of a magnetic 
domain, a magnetic field generating coil having a main field component 
perpendicular to the recording layer of said recording medium is formed in 
such a manner that the coiled portion thereof is formed on a plane close 
to said recording medium and the terminals, connected to said coiled 
portion through conductors, are formed on a second plane which is more 
spaced than the first-mentioned plane from said recording medium. 
Therefore, even when the lead wires are connected to said terminals by 
soldering or by bonding, the coiled portion of said magnetic field 
generating coil can be positioned very close to the surface of the 
recording medium. Consequently the magnetic field generating device of the 
present invention can sufficiently provide a uniform area of necessary 
magnetic field, ensures the reliability of recording and enables the use 
of a floating mechanism despite a small inductance. Also the low 
inductance enables a high frequency switching operation, a high transfer 
rate and a high density recording. 
In the following there will be explained still another embodiment of the 
magnetic field generating device of the present invention, with reference 
to the attached drawings. Since the entire structure of the magnetooptical 
recording apparatus is similar to that shown in FIG. 2, the explanation 
will be concentrated on the structure of the bias field generating device 
of the present invention. The bias field generating device of the present 
embodiment is formed by thin film technology, as shown in FIGS. 15A and 
15B, by forming a conductive pattern 208 on a block 201 of a magnetic 
material constituting a substrate, depositing an insulating layer 207 
except for connection points 205, 206 at the both ends of said conductive 
pattern 208, and forming, on the upper surface of said insulating layer 
207, a spiral printed coil 202, a terminal 203 connected to the outer end 
of said coil 202 and a terminal 204 connected to said conductive pattern 
208 at said point 206 by conductive patterns. The inner end of said coil 
202 is connected to said point 205. If necessary there may be provided a 
protective insulating layer on said insulating layer 207, so as to cover 
the printed coil 202. 
The magnetic block 201 is preferably composed of a magnetic material with 
satisfactorily high frequency characteristics, such as high frequency 
ferrite, having a low high-frequency loss and a high magnetic 
permeability. In the present embodiment, the printed conductors such as 
the conductive pattern 208 and the printed coil 202 are preferably formed 
by evaporation or sputtering, with a highly conductive material such as 
copper. There may also be employed a method leaving the desired pattern, 
such as etching. 
The printed coil 202 is formed as a spiral of oval form having different 
sizes in mutually perpendicular two directions, longer in the y-direction 
(direction of the information track on the recording medium) and shorter 
in the x-direction (direction of tracking control of the optical head, 
perpendicular to said track). Consequently the mounting direction of said 
bias field generating device has to be adjusted in the magnetooptical 
recording apparatus, with respect to the recording medium. 
Thus the bias field generating coil shown in FIG. 15 generates a magnetic 
field in a direction +Z or -Z respectively when a current is supplied from 
the terminal 203 to 204, or from 204 to 203 by a magnetic field generating 
power source 209 for driving said coil. 
FIG. 16 illustrates the distribution of the bias magnetic field generated 
by the bias field generating device explained above, and shows, in the 
ordinate, the magnitude of the vertical magnetic field component applied 
to the recording layer of the magnetooptical disk, as a function of the 
distance from the center of the printed coil in the abscissa. In FIG. 16, 
a curve A represents the distribution in the x-direction, while a curve B 
represents the distribution in the y-direction, and a line C indicates the 
minimum bias field required for recording. The chart indicates that, in 
the x-direction of tracking control of the optical head, the magnetic 
field has to be at least equal to 200 Oe in a range for example of .+-.200 
.mu.m including the possible alignment error between the optical head and 
the bias field generating device and the movable range of the light beam 
by the tracking actuator. Also in the direction perpendicular to the 
moving direction of the tracking actuator, the magnetic field needs to be 
at least 200 Oe in a range for example of .+-.100 .mu.m capable of 
covering the possible alignment error between the light beam from the 
optical head and the center of the bias field generating device in the 
y-direction and the positional aberration by vibration or time-dependent 
change. Thus the area of the main component of the magnetic field to be 
applied to the recording layer of the magnetooptical recording medium is 
significantly different between the tracking direction of the optical head 
and the perpendicular direction. In fact, that area can be made as small 
as possible in the direction of an information track of said recording 
medium, and can be so selected, in the tracking direction, that the 
uniform area of said magnetic field covers the movable range of said light 
beam in the fine tracking operation. 
As explained in the foregoing, the bias field generating device of the 
present embodiment can generate a uniform magnetic field in a sufficiently 
wide area in the moving direction of the light beam by the fine tracking 
actuator but does not generate the magnetic field in an unnecessarily wide 
area in the perpendicular direction of the information track, thereby 
reducing the variation in the record pits resulting from unevenness of the 
magnetic field and drastically lowering the frequency of generation of 
errors. Also since a large magnetic field is not applied to the area not 
subjected to recording, the recorded information is changed, so that the 
reliability can be ensured for a prolonged period. Also the present 
embodiment is advantageous for compactization and weight reduction of the 
bias field generating device, since the length of the magnetic block can 
be minimized particularly in the y-direction. Also since the coil pitch 
can be reduced in the y-direction, the coil 202 can further reduce the 
inductance, thereby further improving the high frequency switching 
performance. 
FIG. 17 shows another embodiment of the magnetic field generating device of 
the present invention, in a plan view of an upper printed coil 231. The 
coil 231 is formed as a rectangular spiral, longer in the x-direction. 
There are also shown a magnetic block 232, terminals 233, 234, and 
connection points 235, 236. 
FIGS. 18A and 18B show still another embodiment of the magnetic field 
generating device of the present invention, in which the upper printed 
coil 241 is similar to that shown in FIG. 15, but the printed conductor 
pattern 208 is replaced by a lower printed coil 246 wound inversely to 
said upper coil 241 and connected thereto at the connection points 244, 
245. Thus the number of turns of the coil is doubled, and a doubled 
magnetic field can be generated with the same driving current. Such 
structure is effective in case the bias field generating device cannot be 
positioned close to the magnetooptical disk, or a large bias magnetic 
field is required, for any reason. The form of the spiral coil is not 
limited to rectangular form but can naturally be modified in other forms 
such as an oval form. 
In each of the foregoing embodiments there is employed a coil, but there 
may be employed plural magnetic field generating coils. 
FIG. 19 shows an embodiment in which plural magnetic field generating coils 
are provided on the same substrate 250 composed of a magnetic block. A 
power source 251 is provided for driving said magnetic field generating 
coils. In FIG. 19, a direction X is the direction of tracking control of 
the optical head, and a direction Y is the direction of relative movement 
between the magnetic field generating device and the recording medium. The 
magnetic field generating device shown in FIG. 19 may naturally be 
employed in place of the bias field generating device 70 shown in FIG. 8. 
As explained in the foregoing, according to the present invention, in the 
magnetooptical recording method in which a magnetooptical recording medium 
is heated with a light beam from an optical head and is subjected 
simultaneously to the application of a bias magnetic field so as to 
represent information by the direction of magnetization of a magnetic 
domain, a magnetic field generating coil having a main field component 
perpendicular to the recording layer of said recording medium has such a 
main magnetic field distribution that is narrow in the direction of an 
information recording track of said magnetooptical recording medium but 
has an intensity enough for inverting the direction of magnetization of 
the domain heated by light irradiation, and is wider in the direction of 
tracking control which is perpendicular to said track direction so as to 
cover the movable range of the light beam by fine tracking. 
Consequently, these embodiments no longer require the control for mutual 
alignment of the optical head and the bias field generating device in the 
fine tracking, and are therefore advantageous in structure and control. 
Thus said embodiments can reduce the cost and the error generation at 
information recording. Also since the magnetic field is not applied to an 
unnecessary area at information recording, the recorded information is not 
changed, and the reliability of recorded information can be secured for a 
prolonged period. Furthermore, since the coil can be minimized in the 
direction of a track, the bias field generating device can be compactized 
and provides other advantages such as the applicability in a floating 
mechanism. It is thus rendered possible to ensure high speed movability 
for example in the seeking operation of the optical head, to reduce 
vibration and to obtain stability and high reliability. 
In the following there will be explained still another embodiment of the 
magnetic field generating device of the present invention, with reference 
to the attached drawings. In said embodiment, since the entire structure 
of the magnetooptical recording apparatus is similar to that shown in FIG. 
8, the following description will be concentrated on the structure of the 
bias field generating device of the present invention. In the present 
embodiment, as shown in FIGS. 20A and 20B, conductor patterns are formed 
by a thin film technology to constitute plural printed coils 302a, 302b, . 
. . for generating magnetic field, in the direction of tracking control of 
the optical head, on an oblong magnetic block 301 constituting the 
substrate and extending over the entire recording area of a magnetooptical 
disk serving as the magnetooptical recording medium. On both ends of said 
magnetic block 301, there are provided terminals 320, 321; 322, 323; . . . 
; 330, 331 respectively connected to the ends of said printed coils 302a, 
302b, . . . . Such structure can be obtained by forming at first conductor 
patterns connecting the central connection points of the printed coils 
302a, 302b, . . . with the terminals 321, 323, . . . , 331, then forming 
an insulating layer thereon except said connection points, and forming 
said printed coils 302a, 302b, . . . , and terminals 320, 321; 322, 323; . 
. . ; 330, 331 on said insulating layer. 
The magnetic block 301 is preferably composed of a magnetic material with 
satisfactorily high frequency characteristics, such as high frequency 
ferrite, having a low high-frequency loss and a high magnetic 
permeability. In the present embodiment, the conductor patterns are 
preferably formed by evaporation or sputtering, with a highly conductive 
material such as copper. There may also be employed a method leaving the 
desired pattern, such as etching. A power source 350 is provided for 
driving the printed coils. 
Printed coils 302a, 302b, . . . are so sized that the areas of magnetic 
field of the intensity required for inversion of the magnetic domain are 
not continuous between the adjacent coils, but are so constructed as to 
generate a magnetic field enough for inverting the magnetic domain between 
the magnetic fields corresponding to adjacent coils when they are 
simultaneously driven, and are so driven that said magnetic fields become 
continuous in the direction of tracking control of the optical head. Also 
said area is so sized as to cover the movable range of the light beam by 
the fine tracking actuator of the optical head and the range of eventual 
positional aberration by vibration. For example, if said range including 
the movable range of said tracking actuator and the alignment error 
between the optical head and the bias field generating device is .+-.300 
.mu.m, said coil is so sized as to provide the necessary perpendicular 
magnetic field in an area of at least .+-.300 .mu.m. 
FIGS. 21A and 21B show the distribution of the magnetic fields generated by 
the above-explained bias field generating device, wherein the abscissa 
indicates the distance from the center of the magnetooptical disk while 
the ordinate indicates the magnitude of the perpendicular magnetic 
component applied to the recording layer of said magnetooptical disk. 
Curves Aa, Ab, . . . indicate the distributions of the magnetic fields 
respectively generated by the printed coils 302a, 302b, . . . , and a line 
Hb indicates the minimum value of the bias magnetic field required for 
information recording. In the present embodiment, the magnetic field 
generated by each of the printed coils 302a, 302b, . . . is weaker than 
the level Hb in a position between the adjacent coils, but, when the 
optical head is moved to such position, the adjacent printed coils, for 
example 302a and 302b, are simultaneously activated by the driving means 
to be explained later, whereby the added magnetic fields a+b become 
stronger than the level Hb. Consequently the area of magnetic field enough 
for inversion of the magnetic domain becomes practically continuous, and 
the intensity of the magnetic field is made uniform. 
FIG. 22 shows control means for energizing each or an adjacent two of the 
printed coils 302a, 302b, . . . corresponding to the movement of the 
optical head. Switches Sa1, Sa2; Sb1, Sb2;, . . . are serially connected 
to both ends of the printed coils 302a, 302b, . . . and are connected 
between the junction point between driving transistors Q1, Q2 and that 
between driving transistors Q3, Q4. Transistors Q1 and Q2, and those Q3 
and Q4 are serially connected to a power source Vcc, and control voltages 
V1, V2, V3 and V4 are respectively applied to the bases of said 
transistors. In the case of generating the magnetic field in a direction 
+Z the transistors Q1 and Q4 are turned on while those Q2 and Q3 are 
turned off. In the case of generating the magnetic field in a direction 
-Z, the transistors Q2, Q3 are turned on while those Q1, Q4 are turned 
off. 
Consequently, as said switches Sa1, Sa2; . . . are selectively closed with 
the timing shown in FIG. 23, the printed coils 2a, 2b, . . . are energized 
corresponding to the moving position of the optical head. Thus the driving 
means for the coils are controlled corresponding to the irradiating 
position of the light beam. In the present embodiment, in order to obtain 
a desired distribution of the bias magnetic field with six printed coils 
in a radius of 20-40 mm, each coil should provide the perpendicular field 
in an area of about 2.5 mm, with the assumption that the adjacent printed 
coils are simultaneously energized over a range of about 1 mm. The 
position of the optical head can be determined from the signal of a 
position sensor mounted in the radial direction of the magnetooptical 
disk, or by calculation from the track signal at the access. 
In the above-explained embodiment, an insulating layer is provided on the 
printed conductors for the terminals 321, 323, . . . , 331, and the 
printed coils 302a, 302b, . . . are formed on said insulating layer, but 
it is also possible to form on said insulating layer, but it is also 
possible to form other coils of inverse winding on the magnetic block 301, 
to connect the centers of said printed coils, through the connection 
points, to the printed coils formed on the insulating layer, and to 
connect the outer ends of said printed coils to the terminals 320, 321; 
322, 323; . . . . In this case the intensity of the magnetic field is 
doubled as the length of the coil is practically doubled. Such structure 
is effective in case the bias field generating device cannot be positioned 
close to the magnetooptical disk or a strong magnetic field is required, 
for any reason. 
In the foregoing embodiment, a non-magnetic protective film may be provided 
on the insulating layer for protecting the printed coils. 
According to the present invention, as explained above, in a magnetooptical 
recording apparatus in which a magnetooptical recording medium is heated 
by the light beam from the optical head and is subjected to the 
application of a perpendicular magnetic field by the bias field generating 
device thereby representing the information by the direction of 
magnetization of a magnetic domain, said bias field generating device is 
provided with plural magnetic field generating coils so positioned that 
the main magnetic component is perpendicular to the recording layer of 
said recording medium, wherein said coils are arranged on a plane close to 
said recording medium over the entire recording area of said recording 
medium in the direction of tracking control of the optical head and 
adapted to generate a magnetic field enough for inverting the 
magnetization of said domain in a desired area of the magnetic field, and 
with driving means for energizing each of said coils or an adjacent two of 
said coils to generate a magnetic field area of necessary intensity, 
corresponding to the movement of the optical head. 
Such structure can reduce the electric power consumption for bias field 
generation, since only one or two of the magnetic field generating coils 
need to be energized for securing a magnetic field area necessary for the 
inversion of magnetization, corresponding to the movement of the optical 
head. Also the form and size of the coils can be easily designed since 
each coil can have a relatively narrow magnetic field, as a necessary 
magnetic field can be maintained in the area between the adjacent coils, 
by the cooperation of said coils. 
Also since the magnetooptical recording medium is not affected by the 
temperature increase in the bias field generating device, the recording 
conditions can be stabilized and the error generation can be prevented. 
Furthermore, since the magnetic field generating coils can be formed, for 
example by a printing method, on a plane close to the magnetooptical 
recording medium, they can generate a perpendicular magnetic field of an 
intensity enough for inverting the magnetization of the domain in an area 
capable of covering the vibration of the light beam resulting for example 
from the vibration of the actuator despite the small size of said coils. 
For this reason the bias field generating device can be made smaller in 
size and in weight, sufficiently for example for being supported in a 
floating mechanism, and can therefore stabilize the recording conditions. 
Also since a desired bias field can be obtained with a relatively small 
current, an increase in the inductance is not required, and the high 
frequency switching is therefore rendered possible. Besides, in the 
tracking control of the optical head, correction control is not required 
for the positional aberration with the bias field generating device. 
Consequently there is provided a magnetooptical recording apparatus of 
high performance and high reliability. 
In the following there will be explained still another embodiment of the 
magnetic field generating device of the present invention, with reference 
to the attached drawings. In said embodiment, as the entire structure of 
the magnetooptical recording apparatus is similar to that shown in FIG. 8, 
the following description will be concentrated on the structure of the 
bias field generating device. In the present embodiment, as shown in FIGS. 
24A to 24C, conductor patterns are formed by thin film technology so as to 
constitute plural magnetic field generating printed coils 402a, 402b, . . 
. , 402e; 402f, 402g and 402i on upper and lower planes of a magnetic 
block 401 constituting a substrate and extending over the entire recording 
area of a magnetooptical disk, in arrays in the direction of tracking 
control of the optical head. Said planes are mutually parallel, and have 
an insulating layer 403 therebetween. Terminals 410, 411; 412, 413; . . . 
; 418, 419 connected to the ends of said printed coils 402a, 402b, . . . , 
402e are provided on said lower plane, while terminals 420, 421; 422, 423, 
. . . , 426, 427 connected to the ends of said coils 402f, 402g, . . . , 
402i are provided on said upper plane. In practice, such structure can be 
obtained by forming conductor patterns connecting the terminals 411, 413, 
. . . , 419 and the central connection points of the coils 402a, 402b, . . 
. , 402e on said magnetic block 401, then forming an insulating layer 
thereon excluding said central connection points, forming the printed 
coils 402a, 402b, . . . , 402e and the terminals 410, 411; 412, 413; . . . 
; 418, 419 on said insulating layer, further forming conductor patterns 
connecting the terminals 421, 423, . . . , 427 and the central connection 
points of the coils 402f, 402g, . . . , 402i on said insulating layer 403, 
forming another insulating layer thereon excluding said central connection 
points, and forming thereon the printed coils 402f, 402g, . . . , 402i and 
terminals 420, 421; 422, 423; . . . ; 426, 427. There is also provided a 
magnetic field generating power source 450. 
The magnetic block 401 is preferably composed of a magnetic material with 
satisfactorily high frequency characteristics, such as high frequency 
ferrite. Also said magnetic block 401 and insulating layer 403 are 
preferably provided with a low high-frequency loss and a high magnetic 
permeability. In the present embodiment, the printed conductors are 
preferably formed by evaporation or sputtering, with a highly conductive 
material such as copper. There may also be employed a method of leaving 
the desired pattern, such as etching. 
Printed coils 402a, 402b, . . . , 402e are so sized that the magnetic field 
areas of the intensity enough for inverting the magnetization are not 
continuous between the adjacent coils, but said areas become continuous in 
the direction of tracking control of the optical head since the printed 
coils 402f, 402g, . . . , 402i arranged on the other plane are displaced 
by a half pitch from the above-mentioned coils 402a, 402b, . . . , 402e. 
Also said magnetic field area is so selected as to cover the movable range 
of the light beam by the fine tracking actuator of the optical head and 
the positional aberration by vibration. For example the coil is so sized 
to generate the necessary magnetic field at least in an area of .+-.300 
.mu.m, if the sum of the movable range of said tracking actuator and the 
alignment error between the optical head and the bias field generating 
device is .+-.300 .mu.m. 
Also the number of coils arranged in the x-direction is determined from the 
length of the recording range in the radial direction of the 
magnetooptical disk, in consideration of the magnetic field area covered 
by a coil and the overlapping of coils in the upper and lower planes. For 
example, for a size of each coil of 1 mm, an overlapping length of 0.1 mm 
and a radial range of recording area of 20-40 mm, there can be provided 12 
coils on the first (lower) plane and 11 coils on the second (upper) plane. 
The first magnetic field generating coils provided on said first (lower) 
plane are arranged linearly, and the second magnetic field generating 
coils provided on said second (upper) plane are arranged linearly, 
parallel to the direction of arrangement of said first coils. Said first 
and second coils are so arranged that the centers thereof do not mutually 
coincide. 
FIGS. 25A and 25B show the distribution of the magnetic fields generated by 
the above-explained bias field generating device, wherein the abscissa 
indicates the distance from the center of the magnetooptical disk while 
the ordinate indicates the magnitude of the perpendicular magnetic 
component applied to the recording layer of said magnetooptical disk. 
Curves Aa, Ab, . . . indicate the distributions of the magnetic fields 
respectively generated by the printed coils 402a, 402b, . . . , and a line 
Hb indicates the minimum value of the bias magnetic field required for 
information recording. In the present embodiment, the magnetic field 
generated by each of the coils in the group 402a, 402b, . . . , 402e and 
the group 402f, 402g, . . . , 402i is weaker than the level Hb in the 
positions of overlapping of solid lines or broken lines between the 
adjacent coils, but the magnitude of the magnetic field can be made 
stronger than the level Hb by the combination of said groups. Consequently 
the areas of magnetic field enough for the inversion of domain become 
practically continuous, and there is obtained a uniform intensity of the 
magnetic field. 
FIG. 26 shows control means for individually energizing the printed coils 
402a, 402f, 402b, 402g, 402c, . . . corresponding to the movement of the 
optical head. Switches Sa1, Sa2; Sb1, Sb2; . . . ; Si1, Si2 are serially 
connected to both ends of the printed coils 402a, 402b, . . . , 402i and 
are connected between the junction point between driving transistors Q1, 
A2 and that between driving transistors Q3 and Q4. Transistors Q1 and Q2, 
and those Q3 and Q4 are serially connected to a power source Vcc, and 
control voltages V1, V2, V3 and V4 are respectively supplied to the bases 
of said transistors. In a case of generating the magnetic field in a 
direction +Z, the transistors Q1 and Q4 are turned on while those Q2 and 
Q3 are turned off. In a case of generating the magnetic field in a 
direction -Z, the transistors Q2, Q3 are turned on while those Q1, Q4 are 
turned off. 
Consequently, as said switches Sa1, Sa2; . . . are selectively closed with 
the timing shown in FIG. 27, the printed coils 402a, 402b, . . . are 
energized corresponding to the moving position of the optical head. Thus 
the driving means for the coils are controlled corresponding to the 
irradiating position of the light beam. In the present embodiment, in 
order to obtain a desired distribution of the bias magnetic field with 9 
coils over a radial range of 20-40 mm, each coil should cover an area of 
about 2.3 .mu.m. The position of the optical head can be determined from 
the signal of a position sensor mounted in the radial direction of the 
magnetooptical disk, or by calculation from the track signal at the 
access. 
In the foregoing embodiment, the printed coils 402a, 402b, . . . , 402e of 
the first plane are formed on an insulating layer provided on the 
conductors for the terminals 411, 413, . . . , 419, and those 402f, 402g, 
. . . , 402i of the second plane are likewise formed on an insulating 
layer provided on the conductors for the terminals 421, 423, . . . , 427. 
However it is also possible to form, on the magnetic block 401 and the 
insulating layer 403, inversely wound printed coils and connect the 
centers thereof, through connection points, with the above-mentioned coils 
402a, 402b, . . . , 402e and 402f, 402g, . . . , 402i. The outer ends of 
the printed coils are connected to the terminals 410, 411;, 412, 413, . . 
. and 420, 421; 422, 423; . . . . In this case the intensity of the 
concentrated magnetic field is doubled, since the length of each coil is 
practically doubled. Such structure is advantageous in case the bias field 
generating device cannot be positioned close to the magnetooptical disk or 
a strong magnetic field is needed, for any reason. 
If the objective lens of the optical head is supported on an end of an arm 
and performs an arc-shaped scanning motion, with a radius from the rotary 
shaft of said arm to said objective lens, at the tracking control, the 
bias field generating device is constructed as shown in FIGS. 28A, 28B and 
28C, in which the magnetic field generating coils are arranged along said 
arc. There is provided a power source 451 for energizing said coils. 
In the foregoing embodiment, a non-magnetic protective film may be provided 
for protecting the printed coils 402f, 402g, . . . , 402i on the upper 
insulating layer. 
According to the present invention, as explained in the foregoing, in a 
magnetooptical recording apparatus in which the magnetooptical recording 
medium is heated with the light beam from the optical head and is 
simultaneously subjected to the perpendicular magnetic field of the bias 
field generating device so as to represent the information by the 
direction of magnetization the magnetic domain, said bias field generating 
device is provided with plural magnetic field generating coils having a 
main magnetic field component perpendicular to the recording layer of said 
recording medium. Said coils are arranged on two planes close to said 
recording medium, along the direction of tracking control of the optical 
head and over the entire recording range of said recording medium, in such 
a manner that the coils on one plane and those on the other are mutually 
displaced by a half pitch and that the areas of magnetic field of the 
intensity required for inversion of magnetization become continuous 
between the mutually overlapping coils respectively on both planes. Also 
there is provided means for energizing said magnetic field generating 
coils corresponding to the movement of the optical head. 
Such structure can reduce the electric power consumption for generation of 
the bias magnetic field, since only one or two magnetic field generating 
coils are energized corresponding to the movement of the optical head. 
Because of this fact, the magnetooptical recording medium is not affected 
by the heat of the bias field generating device, so that the recording 
conditions can be stabilized and the formation of errors at recording can 
be prevented. Particularly in the direction of tracking control, the 
magnetic field generating coils are arranged on two planes with mutual 
displacement of a half pitch in such a manner that the areas of required 
magnetic field mutually overlap between the vertically overlapping 
adjacent coils, so that the intensity of the perpendicular magnetic field 
is made uniform by successive energization of said coils, whereby the 
recording conditions are further improved. Consequently the bias field 
generating device can be made smaller in size and weight, and the high 
speed access is rendered possible. Besides, as the magnetic field 
generating coils can be prepared, for example by printing technology, on 
two planes positioned close to the magnetooptical recording medium, they 
can provide an area of perpendicular magnetic field of an intensity enough 
for inverting the magnetization of the magnetic domain and a size not 
affected by the vibration of the light beam resulting for example from the 
vibration of the actuator of the optical head, despite the limited size of 
said coils. Furthermore, since the required bias field can be obtained 
with a relatively small current, there is not required an increase in the 
inductance, and the high frequency switching operation can be therefore 
rendered possible. Also the tracking control of the optical head does not 
require the correction control for the alignment error with the bias field 
generating device. Thus there is provided a magnetooptical recording 
apparatus of high performance and high reliability. 
In a magnetooptical recording apparatus, the overwriting can be achieved 
either by a light modulation method in which information recording is 
conducted by applying the recording signal on the laser beam from the 
optical head, or by a magnetic field modulation method in which 
information recording is conducted by applying the recording signal on the 
bias magnetic field. 
For achieving the overwriting by the magnetic field modulation method, 
there is required an electromagnet with a coil of small inductance, in 
order to modulate the direction of the bias magnetic field at a high 
speed. 
However, there has been required a complicated control for using an 
electromagnet with a coil of small inductance and moving such a magnet 
corresponding to the movement of the optical head, and such structure has 
been inconvenient for replacing the recording medium. 
For this reason, the present applicant proposes to prevent such drawbacks 
by a magnetooptical recording apparatus in which bias field applying means 
consisting of a linear array of plural coils of a limited number of turns 
is arranged perpendicularly to the scanning direction of the recording 
medium (radial direction in the case of a disk-shaped recording medium) 
and the magnetic field is applied by selectively energizing said coils 
corresponding to the movement of the light beam. 
In such structure, the magnetic field is weak because of the limited number 
of turns of said coils, and the bias field generating coils have to be 
positioned at a distance of several tens of microns from the surface of 
the recording medium, in order to obtain a magnetic field of several 
hundred Gausses on the recording medium for recording or erasing the 
information. 
However, a vibration of 100-200 .mu.m is inevitable in the rotating medium, 
and the bias field generating coils have to follow such vibration, 
maintaining said distance of several tens of microns. Such control, if 
conducted by an independent servo mechanism, requires a complex and 
expensive circuit. 
In the following there will be explained an embodiment of the present 
invention, capable of solving the above-mentioned drawbacks. 
FIG. 29 is a schematic view of the magnetooptical recording apparatus of 
the present invention. 
A system controller 501 executes data exchange between a host computer 
overall system control and a drive controller 503, which executes the 
recording and reading of data by controlling the drive and the optical 
head. Controller 503 sends signals to a drive selector at the recording 
and erasing of data, in relation to the movement of the optical head 506. 
There are further shown a drive selector 504 for selection of the unit 
coils of a bias field generating device 505 according to the signal from 
the drive controller 503; a bias field generating device 505 having plural 
unit coils arranged on a rectangular substrate as shown in FIG. 20; an 
optical head 506; and an objective lens 507 thereof; and an auto 
tracking/auto focusing (AT/AF) circuit 508 incorporated therein. 
An applied voltage adjusting circuit 509 calculates and adjusts the voltage 
applied to the piezoelectric ceramic material, based on a focus error 
signal from said AF circuit and in consideration of the hysteresis 
(voltage-displacement characteristics) of said piezoelectric ceramic 
material). The adjustment conducted by said circuit 509 includes, for 
example, the inversion of the focus error signal in a case when the 
optical head 506 and the bias field generating device 505 are positioned 
across the magnetooptical disk 510. Also there is conducted, if necessary, 
a process of reducing the variation in the auto focusing error signal from 
the optical head 506, detected by the laser spot, so as to adapt to the 
movement of the rectangular bias field generating device 505, in order to 
avoid the eventual contact between said device 505 and the magnetooptical 
disk 510 resulting from vertical warpage thereof. 
There are further shown a magnetooptical disk 510 constituting a recording 
medium, and a motor 511 for rotating said disk 510. 
When receiving an instruction for data recording or erasing from the host 
computer 501, the drive controller 503 shifts the optical head 506 to a 
designated sector of a designated track on the disk, and drives a 
semiconductor laser with a recording or erasing power. At the same time, 
the drive selector 504 sends a signal for selecting a corresponding coil 
to the bias field generating device 505, whereby said coil effects 
modulation according to the recording signal in a case of recording, or 
generates the magnetic field in an opposite direction in a case of 
erasing. In this state the optical head 506 executes AT/AF control by the 
AT/AF circuit 508, and the obtained auto focusing signal is supplied, 
after calculation and adjustment in the applied voltage adjusting circuit 
509 as explained above, to gap regulating means in the bias field 
generating device 505. In this manner the distance between the coils and 
the disk is indirectly detected by the AF signal for detecting the 
distance between the optical head and the disk. 
FIG. 30 is a magnified view of an embodiment of the bias field generating 
device 505 of the present invention. 
On a rectangular substrate, there are provided plural magnetic field 
generating coils 516 which are respectively connected with the drive 
selector 504. 
A non-contact sensor 520 is provided for maintaining the entire device 505 
at a predetermined distance from the magnetooptical disk 510, and serves 
to control the distance of said device 505 based on the focus error signal 
from the AF circuit when the distance becomes shorter than said 
predetermined value. 
Piezoelectric ceramic plates 518 serve as the gap regulating means for 
regulating the gap between the bias field generating device and the disk 
510. Two rectangular ceramic plates 518 are placed on both sides as shown 
in FIG. 30, and the rectangular substrate, supporting the magnetic field 
generating coils 516, is placed thereon. As said piezoelectric ceramic 
plates 518 execute deformation substantially in proportion to the applied 
voltage, the gap between the magnetooptical disk 510 and the bias field 
generating device 505 can be easily maintained at a constant value, by 
means of the focus error signal from the AF circuit. 
In the foregoing embodiment, piezoelectric ceramic plates are employed for 
regulating the gap between the bias field generating device and the 
magnetooptical disk 510, but there may be employed other means for this 
purpose. 
Also in case the optical head 506 and the bias field generating device 505 
can be positioned on the same side of the disk, as shown in FIG. 31, for 
example by a multi-layered structure of the recording medium, the focus 
error signal from the optical head can be substantially directly utilized. 
In the foregoing description, the magnetic field generating means 
positioned close to the recording medium for modulating the magnetic field 
according to the recording signal is provided with a plurality of unit 
magnetic field generating means, but the concept of the present invention 
for controlling the position of the magnetic field generating means with 
respect to the recording medium, by means of the focus error signal from 
the auto focusing circuit, is applicable also to the conventional magnetic 
field generaitng means with a single coil of a small number of turns. 
According to the present invention, as explained in the foregoing, in a 
magnetooptical recording apparatus provided with an optical head for 
irradiating a magnetooptical recording medium with light and focus signal 
detecting means for detecting the distance between said medium and said 
optical head, there are provided magnetic field generating means 
positioned close to said recording medium and equipped with a plurality of 
unit magnetic field generating means for modulating the magnetic field 
according to the recording signal, and distance regulating means for 
regulating the distance between said magnetic field generating means and 
said magnetooptical recording medium, wherein said distance regulating 
means is driven by a focus signal from said focus signal detecting means. 
The present invention is also featured by a fact that said distance 
regulating means is composed of a piezoelectric ceramic material. 
The present invention is also featured by a fact that said distance 
regulating means and said optical head are positioned across said 
magnetooptical recording medium, and said distance regulating means is 
driven by a signal obtained by inversion and predetermined regulation of 
the focus signal from said focus signal detecting means. 
The present invention is also featured by a fact that said distance 
regulating means and said optical head are positioned in the same side of 
the magnetooptical recording medium, and said distance regulating means is 
driven substantially directly by the focus signal from said focus signal 
detecting means. 
The present invention is also featured, in a magnetooptical recording 
apparatus provided with an optical head for irradiating a magnetooptical 
recording medium with light and focus signal detecting means for detecting 
the distance between said medium and said optical head, by a fact that 
there are provided magnetic field generating means positioned close to 
said recording medium and adapted for modulating the magnetic field 
according to the recording signal, and distance regulating means for 
regulating the distance between said magnetic field generating means and 
said magnetooptical recording medium, wherein said distance regulating 
means is driven by a focus signal from said focus signal detecting means. 
As explained in the foregoing, the magnetooptical recording apparatus of 
the present invention provides an advantage of easily maintaining a 
constant distance between the recording medium and the bias field 
generating device, in the positioning of the bias field generating device 
in the focusing direction, utilizing a focus error signal from the auto 
focusing circuit of the optical head.