JPH0410258A - Magneto-optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To enable the reproducing under high C/N condition by making the temp. of the pickup side of a magneto-optical disk approximately equal to or higher than the temp. of the other side. CONSTITUTION:Temp. measuring signals from temp. sensors 52 and 52b are inputted respectively via amplifiers 68a and 68b and A/D converters 69a and 69b to a CPU 67, and the operation/nonoperation of motors 62, 65a and 65b is controlled by the CPU 67 based on these temp. measuring signals. Consequently, when the temp. of the upper surface of the magneto-optical disk 54 is raised, an airflow control door 64b on the lower side is closed while an airflow control door 64a on the upper side is opened, and the revolving speed of the motor 62 for rotating a fan 63 is raised, so that the temp. of the upper surface side of the disk 54 is lowered, and then a temp. control is carried out to keep such temp. condition that a temp. difference between the disk upper surface and the disk lower surface should be zero or negative, thus setting such temp. condition to enable the C/N to be kept high when information recorded on the disk 54 is reproduced in the device 51.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording/reproducing device that performs recording/reproducing using a magneto-optical method.

[Prior Art] In recent years, optical (information) recording and reproducing devices that can record information on an optical recording medium and reproduce recorded information by condensing a light beam have been widely used. It became so.

In the above device, when a magneto-optical system is used, the recorded information can be erased and rewritten again, so the capacity can be increased compared to conventional magnetic recording and reproducing devices, and it is expected to be widely used in the future.

FIG. 11 shows a conventional magneto-optical recording/reproducing apparatus 1. As shown in FIG.

A magneto-optical pickup 4 is disposed facing one surface of a magneto-optical disk 3 which is rotationally driven by a spindle motor 2, and a field coil 5 is disposed on the other surface.

The field coil 5 is supplied with a current for applying bias magnetic fields of opposite polarity to the optical disk 3 from the field control circuit 6 during recording and erasing.

The magneto-optical pickup 4 is movable in the radial direction of the magneto-optical disk 3 by a voice coil motor (abbreviated as VCM) 7 having a voice coil 7a. This magneto-optical pickup 4 houses a laser diode 8 as a light beam generating means, and this laser light passes through a beam splitter 9, is reflected by a mirror 10, and is directed to an objective lens 11.
The light is then irradiated onto the magneto-optical disk 3.

The reflected light from the magneto-optical disk 3 passes through the objective lens 11, is reflected by the half mirror 10, is partially reflected by the beam splitter, and is received by the photodetector 12. The output signal is input to the focus/tracking servo circuit 13, which generates a focus error signal for performing focus control and a track error signal for performing tracking control. The focus error signal and the track error signal are supplied to a focusing coil 15 and a tracking coil 16 that constitute a lens actuator to which the objective lens 11 is attached, so that the spot of the light beam irradiated onto the magneto-optical disk 3 is brought into focus. and to be able to maintain tracking status.

The output signal of the photodetector 12 is also input to a demodulation circuit (not shown), and the information recorded on the magneto-optical disk 3 is reproduced.

When reading the information recorded on the magneto-optical disk 3,
It detects the magnetic Kerr rotation of the returned light depending on the magnetization direction of the magnetized film, and since this Kerr rotation angle is generally quite small, it is necessary that the C/N of the signal does not decrease. Become.

The magneto-optical disk 3 uses a transparent substrate in order to protect the magnetized film and prevent it from being deformed.The magnetized film is irradiated with light through the transparent substrate, and the magnetized film is exposed to light. The reflected light returns to the magneto-optical pickup through the transparent substrate again.

Therefore, if birefringence exists in the substrate, the C/N of the reproduced signal will be lowered due to the birefringence, resulting in negative effects such as read errors and deterioration of servo signals. For this reason, it is desirable that the birefringence of the substrate be as small as possible.

Further, the substrate needs to have mechanical strength so that the magneto-optical disk does not deform, and polycarbonate resin or the like is widely used.

In a conventional example such as the device 1 shown in FIG. 11, a magneto-optical pickup 4 and a VCM 7 for moving it are arranged on one surface (lower surface in FIG. 11) of a magneto-optical disk 3, and on the other surface (upper surface). A field coil 5 for applying a bias magnetic field to the magneto-optical disk 3 is disposed on the side. For example, when moving the pickup 4 toward the inner or outer circumference, V
Since the drive current is supplied to CM7, VCM7 generates heat.

Furthermore, when erasing or writing information, a large current is supplied to the field coil 5, which generates heat.

Further, the objective lens 11 is configured, for example, in a focusing direction (
Servo is applied in the direction perpendicular to the surface of the magneto-optical disk 3) and in the direction across the tracks.
The coils 15 and 16 that drive the motor also generate heat.

Therefore, since the magneto-optical disk 3 is surrounded by such heating elements, it may be exposed to considerably high temperatures. In connection with this, the present applicant reported in Japanese Patent Application No. 1-99200 that there is a phase difference that gives the highest value of C/N.

Also, Fujiwara, Yoshizawa, "Analysis of elliptically polarized light reflected from a magneto-optical disk" Magnetics Study Group MAG-8 of the Institute of Electrical Engineers of Japan
9-229, as the temperature increases, the retardation increases, especially in the case of polycarbonate substrates.

Strictly speaking, this temperature is the temperature of the recording film sandwiched between the upper and lower substrates.

[Problems to be Solved by the Invention] In conventional magneto-optical recording and reproducing devices including the device 1 shown in FIG. 11, the heat source around the magneto-optical disk is not uniform, and the flow of cooling air It is complicated, and the temperature around the magneto-optical disk is not uniform.

Therefore, the temperature may be different between the top and bottom surfaces of the magneto-optical disk.

In these situations, it is desirable to be able to set the C/N as high as possible.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a magneto-optical recording and reproducing device that has a simple configuration and is capable of setting a high C/N and performing reproduction using a magneto-optical method. shall be.

[Means and effects for solving the problems] The present invention changes the temperature of one side of the magneto-optical disk on the pickup side and the other side of the field coil side, thereby increasing the temperature of the magneto-optical disk.
By checking the phase difference that gives the highest value of /N, it is possible to make the temperature of the pickup side almost equal to that of the other side, or
Based on this knowledge, by not lowering the pick-up side surface than the other surface, the highest C/N value can be increased by increasing the C/N value.
We are trying to make sure that you can get the following.

[Example] Hereinafter, the present invention will be specifically explained with reference to the drawings.

FIGS. 1 to 8 relate to the first embodiment of the present invention.
The figure is a schematic diagram of the first embodiment, and the figure 2 shows the C/C ratio at each temperature.
Figure 3 is a diagram showing the configuration of the measuring device that measures the N characteristic. Figure 3 is an explanatory diagram showing that there are variations in the phase difference of the pickup.
Figures 7 through 7 are characteristic diagrams of C/N measured under different temperature conditions using the measuring device shown in Figure 2, and Figure 8 shows a summary of the data obtained by the measuring device shown in Figure 2. It is a graph.

First, with reference to FIG. 2, a measuring device and measurement results that support the effectiveness of the present invention will be explained, and then each embodiment of the present invention will be explained.

Figure 2 (B) shows the C with respect to the temperature change of the magneto-optical disk.
/N measuring device 21 is shown.

As shown in FIG. 2(B), a magneto-optical pickup 24 is arranged opposite to one surface (lower surface) of a magneto-optical disk 23 which is rotationally driven by a spindle motor 22. As shown in FIG. Furthermore, temperature sensors 25a and 25b are disposed near the upper and lower surfaces near the innermost circumference of the magneto-optical disk 23, and the temperatures Ta, T near the upper and lower surfaces of the magneto-optical disk 23 are measured.
b.

The magneto-optical disk 23 used for this measurement was 1.2 m long.
Single-plate magneto-optical disks were bonded together with adhesive so that the recording film side could be overlapped, and the disks had a thickness of 2.5 mm and had symmetrical upper and lower surfaces. The measurement results were similar for the veneer type.

The magneto-optical pickup 24 has a semiconductor laser 31, as shown in FIG. incident on the prism 33,
After being shaped, the half mirror 34 separates the light into transmitted light and reflected light. The transmitted light enters the polarizing beam splitter 35, and the light transmitted through the polarizing beam splitter 35 is totally reflected by the total reflection mirror 36, and then condensed by the objective lens 37 as shown in FIG. 2(B). magneto-optical disk 23
is irradiated.

The light reflected by the magneto-optical disk 23 becomes polarized light that undergoes Kerr rotation according to the polarity of the magnetized film, and is transmitted through the objective lens 37.
, and enters the polarizing beam splitter 35 via the total reflection mirror 36.

The light reflected by the polarizing beam splitter 35 passes through the phase compensation plate 38 and is further incident on the polarizing beam splitter 39. This polarizing beam splitter 39 splits the transmitted light and reflected light into collimator lenses 41.4 and 41.4.
2 and a photodetector 4344. The photoelectric conversion outputs of these photodetectors 43 and 44 are differentially amplified by a differential amplifier 45 and then input to a spectrum analyzer 46.
The C/N is detected by measuring carrier and noise levels.

The temperature of the upper and lower surfaces of the magneto-optical disk 23 can be heated by a heating device (not shown).

In the measuring device 221, the temperature of the upper surface and lower surface of the magneto-optical disk 23 is changed, and the phase compensator 3 is
By changing the phase by 8 and changing the phase difference of the pickup 24 and measuring the C/N, the temperature dependence characteristic of the C/N can be determined.

Further, FIG. 3 is a diagram showing why the change in C/N with respect to the phase difference of the pickup becomes a problem.

For the magneto-optical disk 23A, the range of the phase difference of the pickup whose C/N exceeds 45 dB, which is the standard for magneto-optical disks, is from 130 degrees to +65 degrees, whereas for the magneto-optical disk 23B, it is -5 degrees. It's +80 degrees from here. On the other hand, although it is desirable that the phase difference of the pickup be zero, variations inevitably occur at the production level, and the standard for this is said to be +15 degrees. Therefore, this ±
Considering that a pickup with a phase difference of about 15 degrees is used, the magneto-optical disk 23A can ensure a C/N of 45 dB or more in any pickup, whereas the magneto-optical disk 23B has a phase difference of 15 degrees. If it deviates more to the negative side, the C/N will fall below 45 dB, resulting in a drawback that the occurrence of reading errors will increase.

Therefore, for this reason, it is desirable that the change in the phase difference that gives the peak position of C/N be small in response to the change in the temperature of the magneto-optical disk 23 described above (the change in the phase difference is small and the phase difference that reaches the peak is It is more desirable that the value of is also small).

For example, a magneto-optical disk indicated by 23A in FIG. 3 at room temperature changes to 23B at high temperature, making it practically unusable.

Furthermore, securing a C/N of 45 dB is most problematic at the innermost circumference where the signal level is lowest.

Therefore, when measuring such temperature characteristics, the measurement should be made at the innermost circumference, and the C/N at the innermost circumference should be considered.

Under such conditions, the pickup phase difference is +15 degrees,
The temperature change range that can ensure a C/N of 45 dB should be clarified and reflected in the design of actual recording/reproducing devices.

The measurement conditions were to record at 1800 rpm and at a recording frequency of 3.7 MHz on the innermost circumference of a radius of 30. When this recorded information was reproduced, the carrier level and noise level were detected by the spectrum analyzer 46, and the C/N was calculated. I asked for it.

a) First, as a comparative example, the relationship between the phase difference and C/N of the pickup when there is no temperature difference between the top and bottom of the magneto-optical disk 23 at room temperature (23°C) was measured, and the relationship between the phase difference and C/N of the pickup was measured, and Table 1 and a graph of this were The results shown in Figure 4 were obtained.

From Figure 4, the phase difference of the pickup that provides the C/N peak is 14 degrees, and the C/N of 45 dB can be secured by 12 degrees.
It ranges from 9 degrees to +57 degrees.

b) Next, the temperature Tb of the lower surface of the pickup side of the magneto-optical disk 23 is 53°C (Tb=53°C), and the temperature Ta of the upper surface of the opposite side is 60°C (Ta=60°C). The carrier level, noise level, and C/N when the phase difference is changed are as shown in Table 2 or a graph of this in FIG. 5.

In this case, the C/N peak position has shifted 15 degrees to the right (positive direction) compared to when there is no temperature difference between the top and bottom surfaces at room temperature (Ta = Tb = 23°C) in Figure 4. (In other words, the peak position has shifted from 14 degrees to 29 degrees.

), a C/N of 45 dB is ensured even with a pick-up phase difference of approximately -29 degrees at room temperature;
In the figure, the C/N becomes less than 45 dB from 19 degrees.

C) Next, the measured values of the carrier level, noise level, and C/N when the temperature Tb of the bottom surface of the pickup side is held at 59°C and the temperature Ta of the top surface is held at 49°C are shown in Table 3 or graphed. It will look like Figure 6.

In this case, the C/N peak is when the pickup phase difference is +18 degrees, and the pickup phase difference is +18 degrees.
A C/N of 45 dB is ensured from 1° to +56°. Furthermore, when looking at the shift in the C/N peak position, it can be seen that the shift is only 5 degrees compared to the case of room temperature in FIG. 4. In other words, it can be seen that the temperature condition C) is better than the temperature condition b).

The result is as shown in Table 3, and when this is graphed, it becomes as shown in Figure 7.

In this case, the phase difference of the pickup that gives the peak of the C/N is 22 degrees, and a C/N of 45 dB is ensured from the pickup phase difference of 122 degrees to +66 degrees.

d) Next, a state where there is almost no temperature difference between the upper and lower surfaces of the magneto-optical disk 23 (in this case, "ra=49°C, Tb=
Figure 8 of Table 4 shows the carrier level, noise level, and C/N level when held at 50°C), a), b),
The phase difference of the pickup ± at various temperatures such as c) and d)
C/N is 45d in the entire 15 degree range (-15 degrees to +15 degrees)
The temperature conditions where B could be ensured are indicated by O, and the temperature conditions where B could not be ensured are indicated by x.

The temperatures of the upper and lower surfaces of the magneto-optical disk are the temperatures detected by the temperature sensors 25a and 25b shown in FIG. 2, and as described above, the lower surface of the disk is the surface on which the pickup is placed facing.

From the results shown in Figure 8, the temperature Ta between the top and bottom surfaces of the disk is
, Tb is the same, and when the temperature Tb of the lower surface of the disk is higher than the temperature Ta of the upper surface of the disk, the shift amount of the C/N peak is smaller than when the temperature Tb of the lower surface of the disk is higher than the temperature Ta of the disk upper surface. A C/N of 45 dB can be secured over the range.

The temperature difference between the temperatures Ta and Tb between the top and bottom surfaces of the disk is 1
The limit is 5 degrees Celsius, and if it exceeds that, the amount of shift of the C/N curve becomes large, and the phase difference of the pickup is +15 degrees.
C/N of 45dB cannot be secured.

Next, FIG. 1 shows a magneto-optical recording/reproducing apparatus 51 of the first embodiment, which is provided with a temperature control means so as to ensure a C/N of 45 dB with a pickup phase difference of +15 degrees as described above.

The magneto-optical recording/reproducing device 51 of the first embodiment has a device exterior 52
A magneto-optical pickup 55 is disposed facing one surface of a magneto-optical disk 54 mounted on a turntable which is rotationally driven by a spindle motor 53, and an electromagnet 56 is disposed on the other surface.

The magneto-optical pickup 55 is constructed, for example, from the magneto-optical pickup 4 shown in FIG. 11 or the magneto-optical pickup shown in FIG. 2 without the phase compensation plate 38. This magneto-optical pickup 55 is movable in the radial direction of the magneto-optical disk 54 by a linear motor or voice coil motor (abbreviated as VCM) 57.

Further, the electromagnet 56 is supplied with magnetizing currents of opposite polarity during recording and erasing by the field control circuit 58.

Temperature sensors 59a and 5 are provided near the top surface of the magneto-optical disk 54 near the innermost track and the bottom surface of the disk.
9b are arranged to measure the temperatures Ta and Tb of the upper surface of the disk and the lower surface of the disk, respectively.

For example, an opening 61 is provided on one side of the device exterior 52 along the direction in which the magneto-optical pickup 55 moves, and a fan 6 rotated by a motor 62 is installed inside this opening 61.
3 is stored so that cooling air can be sent to the front magneto-optical disk 54 side. In front of the fan 63, a pair of air volume control doors 64a and 64b are arranged in the vertical direction so that the air volume blown by the fan 63 can be controlled. Each field 64a, 64b is rotatable around a pivot, and its opening/closing view, that is, the amount of air, can be controlled by motors 65a, 65b connected to each other via an opening/closing rod or the like.

The operations of the motors 62, 65a, and 665b are controlled by a CPU 67 via a motor control circuit 66.

Temperature measurement signals from temperature sensors 52a and 52b are input to this CPU 67 via amplifiers 68a and 68b and A/D converters 69a and 69b, respectively, and based on these temperature measurement signals, CP [J67 is the motor 62, 65a, 6
The operation/non-operation of 5b is controlled.

For example, when the temperature difference Ta-Tb between the temperatures Ta and Tb detected by the sensors 52a and 52b becomes positive, that is, when the temperature on the top surface of the disk becomes high, the lower air volume control door 6
4b and open the upper air volume control door 64a to increase the rotation speed of the motor 62 that rotates the fan 63, thereby cooling the upper surface of the disk and lowering the temperature of the upper surface.
Temperature (condition) control is performed to maintain a temperature condition such that the temperature difference Ta-Tb is approximately zero or negative.

It is also determined whether this temperature difference Ta-Tb satisfies Ta-Tb≦15, and if it deviates from this condition, the upper air volume control door 64a is closed, the other side door 64b is opened, and the lower side of the disk is closed. The temperature is also controlled to satisfy the condition of Ta-Tb≦15.

Since the temperature is controlled in this way, when reproducing information recorded on the magneto-optical disk 54 with this device 51, the desirable temperature conditions that can maintain a high C/N as shown in FIG. 8 are set. It is possible to perform highly reliable playback with few reading errors.

FIG. 9 shows a second embodiment of the invention.

In this embodiment, the magneto-optical drive unit 72 includes spindle motors 53 denoted by reference numerals 53 to 58 shown in FIG.
A field control circuit 58 is housed therein.

The exterior 74 of the drive unit 72 is provided with an open lower 5 above the top surface of the disk, and a fan 77 rotated by a motor 76 is disposed opposite the open lower 5. By rotating this fan 77, the air taken in from the open lower part 9 of the device exterior 78 housing this drive unit 72 cools the upper surface side of the disk preferentially, and From 80, it is discharged to the outside through an opening 81 around (or opposite to) the opening 81.

In this embodiment, the cooling air passing through the upper surface of the disk has a larger wind foot than the cooling air passing through the lower surface of the disk, so that the upper surface of the disk is always lower than the lower surface of the disk.

This embodiment makes it possible to realize an apparatus capable of reproducing in a high C/N state with almost no modification to the conventional apparatus.

FIG. 10 shows a third embodiment of the invention.

In this embodiment, there are two openings 9 in the exterior part on the top side of the disk.
2 and 93, and a motor 94 and a fan 95 rotated by the motor 94 are housed on the upper surface side of the disk. By rotating this fan 95, the air flowing in from one opening 92 is discharged from the other opening 93 by the fan 95 on the disk upper surface side, most of which passes through the disk upper surface side. Therefore, in this case as well, the upper surface of the disk is maintained at a lower temperature than the lower surface of the disk.

Other members that are the same as those in the first embodiment or the second embodiment are designated by the same symbols.

The effects of this third embodiment are almost the same as those of the second embodiment.

The graph regarding temperature conditions shown in Figure 8 is particularly effective when the magneto-optical disk uses a polycarbonate substrate, but since magneto-optical recording and reproducing devices are generally used with removable magneto-optical disks. As mentioned above, by controlling the temperature on the lower side of the disk (pickup side) to be higher (or equal) than on the upper side of the disk, a high C/N can be achieved no matter which magneto-optical disk is installed.
This ensures that playback with a low error rate is possible.

Incidentally, a temperature sensor or the like may be further provided in the second embodiment or the third embodiment, and a more appropriate temperature condition may be set according to the output of the temperature sensor.

In the first embodiment as well, there is a temperature difference where the lower surface of the disk is slightly higher than the upper surface of the disk (for example, Tb - Ta
=7°C).

Further, the temperature condition may be maintained at the above-mentioned temperature condition at least only during reproduction. It should be noted that it is necessary to identify whether the substrate used in the magneto-optical disk is a substrate that is affected by temperature, such as a polycarbonate substrate, and to maintain a high C/N as described above only in the case of these substrates. It may be possible to maintain the temperature conditions at a temperature that is possible.

Note that the phase difference of the magneto-optical pickup may be set to a positive value in advance or in response to a rise in temperature, etc., so as to be suitable for obtaining a high C/N.

[Effects of the Invention] As described above, according to the present invention, one surface of the magneto-optical disk facing the pickup side is prevented from being lower than the other surface, so it is possible to use a pickup with uneven phase difference. Even in the case of high C/N, reproduction can be performed with high C/N.

[Brief explanation of the drawing]

FIGS. 1 to 8 relate to the first embodiment of the present invention.
The figure is a schematic diagram of the first embodiment, and the figure 2 shows the C/C ratio at each temperature.
Figure 3 is a diagram showing the configuration of the measuring device that measures the N characteristic. Figure 3 is an explanatory diagram showing that there are variations in the phase difference of the pickup.
Figures 7 through 7 are characteristic diagrams of C/N measured under different temperature conditions using the measuring device shown in Figure 2, and Figure 8 shows a summary of the data obtained by the measuring device shown in Figure 2. Graph, FIG. 9 is a schematic diagram of the second embodiment of the present invention, FIG. 10 is a schematic diagram of the third embodiment of the present invention, and FIG.
The figure is a configuration diagram showing a conventional example. 21... C/N measuring device f 23... Magneto-optical disk 24... Magneto-optical pickups 25a, 25b... Temperature sensor 38... Phase compensation plate 43.44... Photodetector 51 ... magneto-optical recording/reproducing device 52a, 52b... temperature sensor 54... magneto-optical disk 55... magneto-optical pickup 56... electromagnet 62... motor 63...
Fan 64a, 64b = door 65a 6
5b-Motor 67-CPU Fig. 1 Fig. 2 Fig. 5 (A) (B) Fig. 5 Fig. 6

Claims (1)

[Claims] A magneto-optical recording and reproducing device capable of optically recording and reproducing data using a magneto-optical disk, characterized in that the temperature of the surface on the pickup side facing the magneto-optical disk is approximately equal to or higher than the temperature of the other surface. A magneto-optical recording and reproducing device.