JPS63244326A - Af control method for optical head - Google Patents

Abstract

PURPOSE:To prevent the generation of a reproduced light deterioration by giving an offset through an autofocusing AF control loop, and controlling the size of a cast spot on a recording medium, to be larger than that at the time of a focusing, when the recording medium stands still. CONSTITUTION:An output from an amplifier 15 is processed by a phase compensation circuit 17 and an actuator driver circuit 18, and impressed to an actuator 6. When an AF draw-in operation is finished, an offset instructing signal is impressed to a servo circuit 8 from a system controller 4, and a switch circuit 15 comes conductive to V2, and the spot is expanded. Afterward, an insulation for selecting a track from the system controller 4 is sent to a head feeding driver. When the track selection is finished, the spot stands still in a state that the spot is expanded, and when information is recorded or reproduced, the offset is canceled. (i.e., the switch circuit 16 is energized to V1 side.) Thus, the problem of the reproduced light deterioration, after the AF drawing and in the standing still state of the light spot in a stand-by state till the recording and the reproducing, can be solved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for recording information by irradiation with a light beam.
In addition, the recording and reproducing method of optical recording media that can optically reproduce the information recorded in this way %] In recent years, electronic file systems using compact discs and write-once discs, or erasable optical Commercialization and research and development of optical information recording and reproducing devices such as optical disk systems using magnetic materials and phase change materials are active. Furthermore, a new optical information recording medium in the form of a card (of a size called wallet size) has appeared.

This card C (hereinafter referred to as an optical card) is easy to carry due to its form, and has a large information capacity considering its area (2
MBrte or higher), and its commercialization is expected.

[Problems to be solved by the invention] Unsolved problem 1 is the problem of reproduction light deterioration (optical changes such as reflectance of the medium due to information reproduction light) that occurs in optically recordable and reproducible (recordable and reproducible) media. It was designed to solve the problem.

Normally, information is recorded on an optical recording medium by irradiating it with light energy necessary to change its reflectance and form holes through dissolution. To reproduce information from an optical recording medium, the information recording section is traced with light energy that does not change the optical recording medium.
This is done by photoelectrically detecting changes in the amount of reflected or transmitted light.

For this reason.

Optical recording media are required to have clear threshold characteristics as shown by the solid line in FIG. However, general dye-based recording media, which have particularly strong durability against temperature and humidity, do not meet this requirement, as shown by the broken line in Figure 5. Furthermore, Figure 5 shows the characteristic curve ' of the optical recording medium. It shows,
The horizontal axis shows the irradiation energy, and the vertical axis shows the change in reflectance or the degree of hole formation.In other words, in a recording medium having the characteristics shown by the broken line, the irradiation light energy when reproducing information must be extremely small.

This limitation is due to the fact that the light train that enters the photodetector that detects changes in light intensity becomes very small, and the error signal for auto focusing (hereinafter referred to as AF multiplied signal, hereinafter referred to as auto Φ tracking error signal (hereinafter referred to as AT multiplied signal, information reproduction signal) This means that detection becomes difficult.

In the case of an optical disc, generally, AF, AT loop pull-in, information track selection (access), etc. are performed while the information medium, that is, the disc, is rotating. Therefore, the effective light energy of the area where the medium is irradiated decreases (even if the medium is irradiated with the same amount of light, the light energy density of the irradiated area is lower when the medium is moving than when it is stationary). In the disk system, the amount of light irradiated onto the medium can be increased, and as a result, the amount of light incident on the photodetector can be as much as necessary. That is, in optical discs, the problem of reproduction light deterioration is resolved by rotating the recording medium, or a balance is maintained between the deterioration and the quality of the detection signal (S/N ratio).

However, in the case of an optical recording medium in the form of a card, the AF
, AT pull-in, and access operations are performed with the optical card stationary to increase the reliability of the device. To help explain the reason for this, an optical card and a recording/reproducing device for the optical card will be described below.

An example of an optical card is shown in FIGS. 6 and 7. FIG. 6 is a plan view of the optical card, and the optical card 20 is provided with a recording area 21, in which the optical recording medium is coated. It is coated by vapor deposition means, etc. Further, the tracking track 22 is preformatted with irregularities or with a reflectance different from that of the surrounding area. Note that other preformat signals (eg, track number clock signal, etc.) are provided as necessary. The standard size of an optical card is approximately 85.8 m layers x 54 mm.

FIG. 7 is an example of a cross-sectional configuration of the optical card 20. As shown in FIG. A recording medium 24 is coated on the preformat side of a transparent substrate 23 on which a preformat pattern is provided with unevenness. Furthermore, an adhesive 25 is added for the purpose of protecting the recording medium.
A support substrate 26 is attached via. The light is focused by the lens 33, enters the optical card 20 from the transparent substrate 23 side, creates a spot of several ILm on the surface of the recording medium 24, and records and reproduces information.

FIG. 8 shows an example of the configuration of an optical head used for recording and reproducing information on the optical card 20. A light beam emitted from a semiconductor laser 27 or the like becomes a parallel light beam by a condenser lens 28. The cross-sectional shape of the light beam at this time has an elliptical distribution when a semiconductor laser is used as a light source. For this purpose, the refraction effect of the prism 29 is utilized to form the cross section into a circular shape. The luminous flux is split into three luminous fluxes of 0th order and ±1st order by a grating 30. After passing through a beam splitter 31, the direction is changed by a prism mirror 32, and an objective lens 33 produces a several gm spot on an optical card 20. The light is focused. The light beam reflected by the optical card 20 is returned to the objective lens 3.
3. The zero-reflection beam that passes through the prism mirror 32 and is separated from the incident beam by the beam splitter 31 is passed through the circular lens 34. The light passes through an analog optical system consisting of a cylindrical lens 35 and enters a photodetector 36.

With this optical head, an AF multiplication signal can be obtained using the well-known astigmatism method (Japanese Patent Publication No. 57-12188). or.

The AT multiplied signal can be obtained using the following principle.

As shown in Fig. 9, the luminous flux is divided into three parts 37, 38, 39
is focused by an objective lens, and at least three spots with a size of several 7zm are formed between different preformatted tracking tracks 22-1 and 22-2 and between them. Tracking track 22-1.22-
2 are parallel to each other, therefore, the photodetectors 36b and 36c (8th
The difference between the electrical signals from (Fig.) is the AT times signal. Normally, (Suboc) 37.38 is 20% compared to the light intensity of spot 39.
It is as follows.

Note that the spot 39 that is focused between the tracking tracks 22 is responsible for recording and reproducing information, so the information track exists in a part between the tracking tracks.

FIG. 10 shows an example of an optical card recording/reproducing device. optical card 2
0 is a card holding stand 4 called a shuttle from the insertion slot 40
1 is loaded. The optical head shown in Figure 8 is 4
2 and is moved along guides 43, 44 in a direction perpendicular to the tracks of the card under the drive of a pulse motor 45. The shuttle 41 is driven by a motor 46 and reciprocates in directions A and B via a belt 47.

An example of an optical card and a recording/playback device for the optical card has been briefly described above.

From the above explanation, it can be understood that the optical card basically moves back and forth to perform recording and playback. The biggest drawback resulting from this reciprocating motion is that vibrations are likely to occur when the motion is reflected.

Because of this vibration, there is a drawback that it is difficult to pull in the control of AT or AF if the card is moving. Furthermore, during track selection, ie, access operation, if the optical head is moved while the card is being moved, the access time becomes longer.

In order to suppress the vibration during reciprocating motion to a practical level, the moving speed must be at most several hundred millimeters per second.
When the speed is high, the acceleration generated during deceleration and acceleration during reversal becomes large, and therefore vibration becomes large. In contrast, in the case of an optical disc, the disc can run smoothly due to its rotational motion, and the linear velocity is usually on the order of several m/sec. Therefore, even if a track is selected by moving the optical head while rotating the disk, the beginning of the information track will be directly below the optical head in a short time. Therefore, in the case of optical discs,
The access time is dominated by the movement time of the head.

On the other hand, with an optical card, it takes time to bring the beginning of the information track directly below the optical head, resulting in a longer access time. Therefore, it is advantageous to select an information track while keeping the card in place.

FIG. 11 summarizes and explains the above.

In the case of an optical card, when the card 20 is loaded, first, the optical head is waiting in the home position stirrup 48, and at that point, the AF control is first pulled in. Next, the optical head is moved by a pulse motor. Move to the area where the tracking track exists and perform AT amount control pull-in.
The reason why AF pull-in is not performed in the area where the track exists is that the track information does not affect the AF multiplier signal, and reliable AF
Next, the optical head is moved to a desired track position 50 to perform Fel.

That is, the optical head is moved along the dashed-dotted line in FIG. 11 (the dashed-dotted line indicates the beginning of the information section of each track). Thereafter, the optical card is reciprocated for the first time to record and reproduce information. In other words, during the recording and reproducing operation of the optical card, the card may be in a stationary state. For this reason, the influence of playback deterioration is
In the case of optical card systems, this is an important issue.

The state at the time of AF pull-in will be explained using FIG. 13. FIG. 13 shows the AF error signal at the time of pull-in. The objective lens 33 is moved perpendicularly to the card using a moving means called a 7-cut unit. When the lens approaches the card from a far position, the AF error signal becomes S-shaped near the surface of the optical card, and then , it becomes S-shaped near the surface of the recording medium. Point B in Figure 13 indicates focus on the card surface, point A indicates focus on the recording medium surface, AF amount control,
Since it is necessary to perform this in the vicinity of point A, it is necessary to distinguish between the 8 characters on the card surface and the 8 characters on the medium surface. This distinction is the first
As shown by the one-dot chain line in FIG. 3, zero is carried out depending on whether the level of the error signal is higher than or equal to Vo. Normally, the reflectance on the surface of the card is 5% or less, and the reflectance on the surface of the recording medium is 10% or more.

The above method allows for differentiation. However, when the reflectance of the medium changes due to deterioration of the reproduction light and the amount of light entering the photodetector decreases, an error signal as shown by the dotted line is generated, making it impossible to distinguish between the card surface and the medium surface, and AF pull-in becomes impossible. .

Furthermore, what must be taken into account for reproduction light deterioration is the AF
, After AT has finished pulling in, select the track,
This is the waiting time until a command to record and play information arrives.

During the time until this command arrives, the characteristics of the medium change and the amount of one reflected light decreases, resulting in a decrease in servo gain. For this reason, it becomes vulnerable to external vibrations, etc. AF becomes easily off. In the example shown in Figure 8, the tracking spot has a light intensity ratio of AF.
During this waiting time, the AFF control loop is affected first because it is smaller than the active spot.

One solution is to lower the output of the semiconductor laser, but taking into account the stable oscillation of the semiconductor laser, the amount of light at the medium surface must be 0.1 mW or more, and the amount of reflected light itself must be Although it is difficult to avoid a decrease in servo gain because of the change in

FIG. 12 shows the state of reproduction light deterioration of a dye-based recording medium with a solid line. The dye shown in FIG. 12 is a polymethine dye, but the same was true for cyanine dyes.

In FIG. 12, the horizontal axis represents time, and the vertical axis represents changes in the amount of light received by the photodetector. Note that the measurement conditions were that the two cards were stationary, the spot diameter was φ3JLm, and the light amount was 0.21. Furthermore, it has been experimentally confirmed that this characteristic change changes with the illumination time even if the light is flickered intermittently.

When a dye-based recording medium is used with the configuration shown in Figure 7,
The reflectance on the surface of the recording medium is usually about 10% to 30%. Especially refractive index 1.8-2.0, absorption coefficient a0.8-1.0
The media film was 5% polymethine dye.

Furthermore, there are conditions under which 25 to 30% of the cyanine-based Ni complex dye can be obtained. The reflectance of the medium when no light is irradiated is RO
If the reflectance on the card surface is R1, then A F
The percentage of reflectance reduction allowed for rfA pull-in is:
It becomes R1/RO.

For example, when R1=5% and RO=12%, the allowable reflectance reduction rate is about 42%.

[Means for Solving the Problems] As described above, countermeasures against the deterioration of the reproduced light are essential in order to put the optical card system into practical use.

An object of the present invention is to provide a method for solving the above problem of reproduction light deterioration.

The purpose of the above is to provide an AFF control method for an optical head in which light from the surface of a recording medium is received by a photodetector to perform autofocusing (AF), and the recording medium is focused by irradiating light onto the recording medium. When using a recording medium whose characteristics change and the amount of light incident on the photodetector changes, when the recording medium is stationary, an offset is applied in the AFF control loop to adjust the size of the irradiation spot on the recording medium. This is achieved by an optical head AFF control method characterized by controlling the AFF to be larger than the focused state.

That is, in the present invention, when the optical recording medium is stationary, the AF
The problem of reproduction light deterioration is solved by giving an on set signal to the servo circuit and increasing the diameter of the light spot irradiated onto the surface of the recording medium.

For example, if the diameter of the optical spot is doubled, the optical energy density will be reduced to 1/4, which can significantly solve the problem of deterioration of the reproduced light, and according to this method, the total amount of light incident on the photodetector will not decrease. Therefore, the gain of the servo loop does not change.

Now, when the illumination light spot system is set to φ6 μm and the light energy density is set to 1/4, as shown by the broken line in Fig. 12,
Significant improvement was seen.

[Example] Hereinafter, the AFF control method for an optical head of the present invention will be described in detail based on a specific example.

FIG. 1 is a signal processing block diagram of an optical card recording/reproducing apparatus to which the optical head AFF control method of the present invention can be applied, and FIG. 2 is an example of a flowchart of its control.

i1 In the figure, 1 is an optical card, 2 is a photocoupler for determining whether the optical card is in a predetermined position, 3 is a pulse generator that receives the signal from the photocoupler 2 and sends a pulse signal to the system controller 4, 4 is a system controller that controls the entire optical recording/reproducing device; 5 is an optical head as shown in FIG. 8; 6 is an actuator that drives the optical head in the focusing direction and the tracking direction; and 7 is a system controller that controls the reflected light from the optical card. A photodetector for receiving light and obtaining an AF multiplied signal and an AT multiplied signal; 8, a servo circuit for controlling the actuator 6 based on the signal from the photodetector 7; 9;
1 is an optical head feed mechanism, 10 is a helad feed driver, 1
1 is a card feeding mechanism, and 12 is a card feeding driver.

FIG. 3 is a diagram schematically showing the servo circuit 8 of FIG. 1.

In FIG. 3, 13 is an AF front photodetector 14 which has a light receiving surface divided into four parts by the astigmatism method, and an AFF dynamic amplifier which takes the difference between these light receiving surfaces and obtains an autofocus error signal, 15 is an amplifier, and 16 17 is a switch circuit for applying voltages Ml and V2 to the amplifier; 17 is a phase compensation circuit; 18 is a switch circuit for applying voltages Ml and V2 to the amplifier;
is an actuator driver, and 6 is an actuator.

Next, the operation of the apparatus shown in FIG. 1 and the AFF control method of the optical head according to the present invention will be explained with reference to the flowchart shown in FIG.

First, an outline of the operation will be explained based on the flowchart in FIG. First, load the optical card into the device.
Step 31 in the figure), perform AF retraction (step S
2) In order to prevent the reflection characteristics of the recording medium from deteriorating due to the light spot on the card when the AF is retracted, the AFF
An offset is applied to the control loop (step S3), and then the seek operation is performed (step S4). At this time, the offset may be canceled before the seek operation is performed (
Step S3'), when the optical head reaches the predetermined recording or reproducing position (step S5), the recording or reproducing operation is performed as usual (step S6); however, when performing the operation of step 33', , the process moves to step S5 after performing an offset (step S4
').

Next, the operation will be explained in detail with reference to FIGS. 1 and 2.

In FIG. 1, for example, a photocoupler 2 detects that a card 1 has been loaded, and its output is sent to a pulse generator 3 (z-value conversion circuit), which is then sent to a system controller 4.
Sends a pulse signal to indicate the end of loading.

In response to this, the system controller
AF sends a signal to move the cutter 6 to the servo circuit 8
In the diagram showing the outline of the servo circuit that performs the pull-in operation, each horn detection element 13 of the photodetector 13/
a, 13b, L3c.

The output from 13d is the output of 13a, the output of 13d, and 1
After the output of 3b and the output of 13C are added, differential amplifier 1
3 is input. The differential amplifier 13 outputs (13a*13d)-(13b+13c) (7) fourth signal at a predetermined amplification factor.
The output signal shown in the figure (so-called 5-figure curve) is obtained.

This signal is further amplified by a predetermined amplification factor in the next amplifier 15, but an offset signal is added when the recording medium is stationary. The offset signal is the switch circuit 16
It can be changed at 7. In FIG. 3, in order to focus the light spot on the surface of the recording medium, a differential is applied at the potential O1, that is, at point A in FIG. 4, to enable servo control. In Fig. 3, for example, vl is O
In this case, when the switch circuit 16 is made conductive on the vl side, the servo operates at 0 potential. However, in order to cancel the offset component of one circuit, uneven sensitivity of the photodetector, etc., Vt is usually set to a value other than O. Potential V2 gives an offset to the servo loop, that is, A
Set the servo to operate at the point ′ and defocus (
DefocusSΔD) to widen (focus) the light spot on the medium surface.

The output from the amplifier 15 is processed by a phase compensation circuit 17 and an actuator driver circuit 18, and then sent to the actuator 6.
to be applied. When the AF pull-in operation is completed, an offset command signal is applied from the system controller 4 to the servo circuit 8, and the know-2-chi circuit 15 becomes conductive to (2).
Expand your spot. After that, the system for track selection.
When a command from the controller 4 is sent to the head feed driver and the RAD 5 is moved toward the light, it is moved as it is, or the offset is canceled once, and the head is moved in a focused state.

The former is a so-called open-loop head seek mode, and the latter is a seek mode that counts the number of track crossings. When the track selection is completed, the spot remains stationary in a spread state, and when recording or reproducing information, the offset is canceled (that is, the switch circuit 16 is made conductive to the vl side), and at the same time, The system controller 4 sends a signal to the card feed driver to make it reciprocate, and modulates the semiconductor laser or causes it to emit a constant amount of light to perform recording or reproduction.

With the above-described operation, 1K can be achieved which solves the problem of reproduction light deterioration in the stationary state of the optical spot after AF pull-in and in the standby state until recording and reproduction.

The present invention is not limited to the above-mentioned embodiments, and various modifications and applications are possible.

In the above embodiments, reproduction light degradation refers to a decrease in the amount of reflected light, but in the case of a multilayer structure such as a dye layer and a metal layer,
The phenomenon of reproduction light deterioration results in an increase in the amount of light. In this case, there is no disadvantage that it becomes difficult to distinguish from the surface, but there is a problem in that the servo gain changes. Therefore, this method is effective in this case as well.

In addition, as mentioned above, reproduction light deterioration is a special problem when using optical card-shaped recording media, but the situation is the same with reciprocating recording media such as optical tapes, and furthermore, reproduction light deterioration also occurs in optical discs. It is clear that the technical idea of the present invention can be applied even when using a recording material with a high degree of turbulence.

[Effects of the Invention] As explained above, according to the AF control method for an optical head of the present invention, it is possible to achieve the AF control method for an optical head according to the present invention by using the equipment device of operating the optical head without using any means such as improving the recording medium. It is possible to solve the problem of reproduction light deterioration in optical recording media, which has extremely great practical advantages.In addition, by carrying out the method of the present invention, the problem of reproduction light deterioration can be solved,
It has become possible to make the optical card system function in a desired sequence.

[Brief explanation of the drawing]

FIG. 1 is a signal processing block diagram of an example of the AFi1m method for an optical head according to the present invention. FIG. 2 is an example of a flowchart of the apparatus shown in FIG. FIG. 3 is a diagram schematically showing the servo circuit. FIG. 4 is a diagram illustrating the addition of bias to the AF signal. FIG. 5 is a sensitivity characteristic curve of the recording medium. FIG. 6 is a plan view of the optical card. Figure t57 is a sectional view of the optical card. FIG. 8 shows an example of an optical head. FIG. 9 is a diagram illustrating the function of the light spot on the card surface. FIG. 10 shows an example of an optical card recording/reproducing device. Figure ffllll is a diagram explaining a desirable sequence of the optical card system. FIG. 12 shows the characteristics of reproduction light deterioration. FIG. 13 is a diagram showing the influence of AF pull-in when there is reproduction light deterioration. l: Optical card 2: Photo coupler 3: Pulse generator 4 System controller 5: Optical head 6: Actuator 7: Photodetector 8: Servo circuit 9: Optical head feed mechanism 10: Head feed driver 11: Optical card feed Mechanism 12 2 Card feed driver 13: AF destination photodetector 4: Differential amplifier 15: Amplifier 16: Switch circuit 17: Phase compensation circuit 18: 7 Cut unit driver Agent Patent attorney Sekihira Yamashita Figure 1 Figure 2 Figure 3 Figure 4 AF error color difference ΔD Figure 5 Figure 6 Figure 7 Figure 8 Figure 11 Figure 12 Irradiation time Figure 13 AF error 4 episodes

Claims (2)

[Claims] (1) A photodetector receives the light from the surface of the recording medium, and
An AF control method for an optical head that performs focusing (AF), when a recording medium is used in which the characteristics of the recording medium are changed by irradiating the recording medium with light, and the amount of light incident on the photodetector is changed, An AF control method for an optical head, characterized in that when a recording medium is stationary, an offset is applied in an AF control loop to control the size of an irradiation spot on the recording medium to be larger than when in focus. (2) The AF control method for an optical head according to claim 1, wherein the change in the amount of light is caused by a light spot that is irradiated onto a recording medium after the AF control loop is pulled in.