JPH01102744A - Af control method for optical head - Google Patents

Abstract

PURPOSE:To prevent reproduced light from being deteriorated by controlling the size of a projecting spot on a recording medium so that the size can be set larger than that at the time of focusing by changing the output ratio of each photoreceiving plane of plural photoreceiving planes differently from an ordinary case when the recording medium in which an incident light quantity to an optical detector is changed ceases. CONSTITUTION:In case where the optical detector split to, for example, plural numbers is constituted of a quartered sensor 13, a switch 19 is provided in the detection circuit of either sensors 13a-13d, for example, 13a. When the recording medium ceases, it is possible to set the size of a projecting spot on the recording medium larger than that at the time of focusing without giving offset on an auto focus control loop by turning OFF the switch 19. In such a way, it is possible to prevent the reproduced light from being deteriorated.

Description

[Detailed Description of the Invention] [P? :1 Field of Application] The present invention is a method for recording information by irradiation with a light beam,
In addition, in recent years, electronic file systems using compact discs and write-once discs, or erasable There is active research and commercialization of optical information recording and reproducing devices 6 such as optical disk systems using magneto-optical materials and phase change materials. As a result, a new optical information recording medium in the form of a card (of a size called otlet size) has appeared.

This card (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
It is characterized by M By Le to L), and its commercialization is expected.

[Problem to be Solved by the Invention 1] The present invention solves the problem of reproduction light deterioration (optical changes such as reflectance of the medium caused by the information market) that occur in optically recordable (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 reflection and transmission.

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 that are particularly durable against temperature and humidity do not satisfy this requirement, as shown by the broken line in FIG. Note that FIG. 5 shows a characteristic curve of the optical recording medium, in which the horizontal axis shows the irradiation energy, and the vertical axis shows the change in reflectance or the degree of hole formation. That is, in a recording medium having the characteristics shown by the broken line, the energy of the irradiated light during information reproduction must be extremely small.

This limitation is due to the fact that the light I that enters the photodetector that detects changes in light intensity becomes very small, and the error signal for auto focusing (hereinafter referred to as FΔF signal), the error signal for auto tracking (hereinafter referred to as AT signal), and the internal information "11" means that it is difficult to detect the signal.

In the case of an optical disc, when fishing on a boat, AF, 8T loop pull-in, information track selection (access), etc. are performed while the information medium, that is, the disc, is rotating. Therefore, the light energy of the part where the medium is effectively irradiated is F
(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.) Therefore, in an optical disk system, more light can be used for irradiating the medium. As a result, the amount of light incident on the photodetector can be adjusted to the required amount. 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. In order to help understand the explanation of this reason, the optical card and the M+fi arrangement Fj of 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. The optical card 20 is provided with a recording area 21, and this area is coated with an optical recording medium by coating, vapor deposition, or the like. Further, the tracking track 22 is preformatted with irregularities or with a reflectance different from that of the surrounding area. Note that other digital format signals (for example, tiger and vine number clock signals, etc.) are provided as necessary. The standard size of an optical card is approximately 85.6++ueX 54mm.

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 μm 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 2'0. 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 0th order, ±1 by the grating 30.
The light beam is split into three beams, passes through a beam splitter 31, changes direction by a prism mirror 32, and is focused onto an optical card 20 onto a spot of several μm by an objective lens 33. The light beam reflected by the optical card 20 passes through the objective lens 33 and the prism mirror 32 again, and the zero reflected light beam, which is separated from the incident light beam by the beam splitter 31, passes through, for example, a 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 T signal can be obtained using the following principle.

As shown in Figure 9, the luminous flux is divided into three parts: 37, 38, 39
is condensed by an objective lens, and at least three spots with a size of several μm are formed between different preformatted tracking tracks 22-1 and 22-2. Tracking track 22-1.22-2
are parallel to each other, so the photodetectors 36b and 36c (
The difference between the electrical signals from (FIG. 8) becomes the T signal. Usually, it is 20% or less compared to the optical appearance of spots 37, 38<*, and spots 39.

Note that a spot 39 where light is focused between the tracking tracks 22 is responsible for recording and reproducing information. Therefore, the information track exists between the tracking tracks.

FIG. 1O 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 track of the card by the drive of a pulse motor 45. The shuttle 41 is driven by a motor 46 and reciprocates in the A=B direction via a belt 47.

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

According to the explanation in 1., the optical card basically moves back and forth,
I can understand recording and playing. The biggest drawback resulting from this reciprocating motion is 1f, which tends to cause vibrations 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 vibrations during reciprocating motion to a practical level, the moving speed must be at most several hundred mm/sec. If the speed is high, the acceleration that occurs during reversal deceleration and acceleration will be large, which will lead to vibration. becomes larger. In contrast, in the case of an optical disk, it is possible to run the disk by 416 kph due to its rotational motion, and the linear velocity is usually on the order of several rr1/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 an optical disk, 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 the W position.

FIG. 11 summarizes and explains the above. In the case of nine cards, when loading card 20,
First, the optical head is waiting at the home position 48, and AF control is first performed at that position.

Next, move the optical head using a pulse motor to the area where the tracking track exists and perform AT control pull-in.The reason why the AF pull-in is not performed in the area where the track exists is because the track information affects the AF signal. In order to perform reliable AF control without giving any error, the optical head is moved to the desired track position i! Move it to 50.

That is, in FIG. 11, the optical head is moved along the dotted line (the -dotted line indicates the beginning of the information section of each track). Thereafter, the optical card is moved back and forth for the first time to record information. That is, during the recording operation of the optical card, the card may be in a stationary state. Therefore, the effects of endogenous degradation become an important issue in optical card systems.

The state at the time of ΔF retraction 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 in a direction perpendicular to the card using a moving means called an actuator. Now, when the lens approaches the card from a far position, the F error signal becomes S-shaped near the surface of the optical card, and then becomes S-shaped near the surface of the recording medium. Point B in FIG. 13 indicates focus on the surface of the card, and point A indicates focus on the surface of the recording medium. AF control is
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 in FIG. 3--dotted chain line, this is done depending on whether the level of the error signal is higher than Vo or not. Usually, 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, so it is possible to distinguish them using the above method. 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 (No. 5) as shown by the dotted line occurs, making it impossible to distinguish between the card surface and the medium surface.
F pull will no longer be possible.

Furthermore, what must be considered for IIG teacher deterioration is:
This is the waiting time from when ΔF and AT are completed to when a track is selected and when an information recording/reproducing command is received.

During the time it takes for this command to arrive, the characteristics of the medium change, the amount of reflected light decreases, and the servo gain decreases.

Ru. For this reason, it becomes vulnerable to external vibrations, etc. ΔF tends to be off. In the example shown in FIG. 8, the optical M ratio of the tracking spot is smaller than that of the Δr7 spot, so during this waiting time, the AF control loop is affected first.

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 is time, and the vertical axis is the change in photoelectricity received by the photodetector. Note that the measurement conditions were that the card was stationary, the spot diameter was φ3 μm, and the light M was 02 m11. Furthermore, it has been experimentally confirmed that this characteristic change changes with the integration of the illumination time even when the light is flickered intermittently, and the line <1t is also observed experimentally.

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%. In particular, the refractive index is 1.8 to 2.0. Absorption coefficient 0.8-1.0
Using polymethine dye, the media film thickness is 800 to 150 mm.
When it is set to 08, the reflectance is 10% to 15%.

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 the rate of decline in reflectance allowed for AF control pull-in is R1/RO
becomes.

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

Means for Solving Problem E] 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-mentioned problem of amphibogenic photodegradation.

The purpose of the above is to provide an AF control method for an optical head that performs auto-focusing (AF) by receiving light from the surface of a recording medium with a photodetector having a light-receiving surface divided into a plurality of parts. When using a recording medium in which the characteristics of the recording medium change when the medium is irradiated with light and the amount of light incident on the photodetector changes: L! When the recording medium is stationary, the size of the irradiation spot on the recording medium-L is made larger than when in focus by operating a means that changes the output ratio of each of the plurality of light receiving surfaces compared to the normal case. This is achieved by a method for controlling ΔFfI11 of an optical head, which is characterized by controlling as follows.

For example, according to one embodiment of the present invention, when the photodetector divided into a plurality of sections Ijq is composed of four-divided sensors 13, the respective sensors 13a, 13i, +3c, 1
For example, any one of 3d.

A switch is provided in the detection circuit of 13a to ensure that the recording medium is static.
1-L, turn off the switch (for example, 13
By setting the output of 'a to zero), the size of the irradiation spot on the recording medium can be made smaller than when focusing, without giving an offset to the AF control loop.

Namely 1. In the embodiment described above, when the optical recording medium is stationary, some sensor outputs of the AF detection sensor are set to zero using a switch, so that the irradiation is performed on the surface of the recording medium without giving an offset signal to the AF servo circuit. The diameter of the light spot can be increased, thereby solving the problem of reproduction deterioration.

[Function] When the diameter of the light spot is set to 2-8, for example, the light energy density becomes 1/4, which greatly solves the problem of reproduction light deterioration.
According to this method, the total photoelectric power applied to the photodetector (Q=t) does not decrease, so the gain of the servo loop does not change.

Now, when the illumination light spot system is φ6 μm and the optical energy density is 174, as shown by the broken line in Fig. 12,
Significant changes were seen.

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

Fig. 1 is a signal processing block diagram of an optical power recording/reproducing apparatus to which the AF control method for an optical head can be applied to the present invention;
The figure shows an example of a flowchart of the control.

In Fig. 1, 1 is an optical card, 2 is a photocoupler for determining whether the optical card is in a predetermined position, and 3 is a pulse generator that receives a signal from the photocoupler 2 and sends a pulse signal to a system controller voice 4. 4 is a system controller that controls the entire optical recording and 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 reflection from the optical card. Receives light and reaches 8F (word, AT
a photodetector for obtaining a signal, 8 a servo circuit that controls the actuator 6 based on the signal from the photodetector 7;
9 is an optical head transport mechanism, lO is a head transport driver,
11 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 having a light receiving surface divided into four parts by the astigmatism method, and an AF differential amplifier which takes the difference between the light receiving surfaces and obtains an autofocus error signal; 15 is an amplifier; ! 6 is a voltage circuit for applying voltage v1 to the amplifier, 7 is a phase compensation circuit, I8 is an actuator driver, and 19 opens or shorts one of the four light-receiving surfaces 13a according to the signal M from the system controller 4. The switch 6 is an actuator.

Next, while referring to the flowchart in FIG.

Operation in the apparatus shown in FIG. 1 and A of the optical head according to the present invention
The FM control method will be explained.

First, an outline of the operation will be explained based on the flowchart in FIG. First, an optical card is loaded into the device and %AF retraction (Step St) in FIG. 2 is performed (Step S2). 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, Δ1
:Turn off the switch 19 in the detection circuit of the river light detector 13a.
Make it F. (Step S3), and then moves to a seek operation (Step 34). At this time, turn on switch 19.
You may then move on to the seek operation (step 83').
). When the optical head reaches the predetermined recording or reproducing position (step S5), the recording or reproducing operation is performed as usual (step S6). Note that when performing the operation in step S3°, the switch 19 is turned off again before proceeding to step S5 (step S4').

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

In Figure 1, the card seal is loaded °1!
is detected by, for example, a photocoupler 2, its output is sent to a pulse generator 3 (binarization circuit), and a pulse signal indicating the end of loading is sent to the system controller 4.

In response to this, the system controller sends a signal to the servo circuit 8 to move the actuator 6 of the optical head 5, and the AF
Perform a pull-in operation. The third diagram shows the outline of the servo circuit.
In the figure, when the switch 19 is ON, the outputs from the respective detection elements (light receiving surfaces) 13a, 13b, 13c, and 13d of the photodetector 13 are the output of 13a, the output of 13d,
The output of 13b and the output of 13c are added and then input to the differential amplifier 13. The output signal (+3a+ +3d) - (13b+ +3c) shown in FIG. 4 (so-called figure 8 curve) is obtained from the differential amplifier 13 at a predetermined amplification factor.

This signal is further amplified by a predetermined amplification factor in the next amplifier 15.

As shown in FIG. 23, the S-curve signal obtained in this way has a potential of 0.0 and 0.00, so as to focus the optical spot on the surface of the recording medium. That is, in FIG. 4, the differential is made so that servo control is possible. However, in order to cancel the offset component of the circuit, uneven sensitivity of the photodetector, etc. 1. Normally ■! is often given a non-zero value.

If the recording medium is static, turn off switch 19.
In order to
) is O. As a result, the objective lens 33 is defocused ΔD from point Δ in FIG.
The light spot on the medium surface F is expanded (blurred) because the servo control is performed at the point F, which has moved by the same amount.

The output from the amplifier 15 is sent to a phase compensation circuit 17. The actuator 6 is processed by the actuator driver circuit 18.
to be applied. When the AF pull-in operation is completed, a switch OFF command signal M is applied from the system controller 4 to the servo circuit 8, and the switch 19 is turned OFF.
, widen the spot.

After that, a command from the system controller 4 is sent to the head' feed driver for track selection, and the optical head 5
If it moves, just move it or press switch 1 once.
9 ONL, , move it in the focused state. The former is a head seek mode in a so-called Oakenloop, and the latter is a seek mode that counts the number of track crossings.

When the track selection is completed, the spot is spread out and remains static, and when recording or reproducing information, the switch 19 is turned on. At the same time, the system controller 4 sends the (IT) signal to the card feed driver to cause it to reciprocate and modulate the semiconductor lasers or emit a constant amount of light to perform recording or reproduction.

With the above operation, it is possible to solve the problem of reproduction light deterioration when the optical spot is in a stationary state after AF pull-in and in a standby state before recording and reproduction.

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

In the embodiment described above, the means for changing the output ratio of each light-receiving surface is made by means (specifically, the switch 19) for zeroing the output from at least one of the plurality of light-receiving surfaces. The object of the present invention can also be achieved by using means for changing the output ratio of the surfaces as means for increasing or decreasing the output from at least one of the plurality of light receiving surfaces. □ FIG. 14 is a diagram schematically showing a servo circuit having such a configuration. In the figure, the recording medium is static! When the power is on, the switch 19' connects it to the X terminal side. Then, the output from the light receiving surface 13a is inputted to the AF differential amplifier 14 via the amplifier or attenuator 70, so the output ratio of each light receiving surface changes, and as a result, the diameter of the spot light on the recording medium is increased. be able to. □Again. Regardless of the embodiment shown in Fig. 14, the output of each light receiving device is set to ΔFF.
It is clear that the present invention is constituted regardless of the method as long as the ratio is changed before inputting power to the dynamic amplifier +4.

Furthermore, in the above embodiments, reproduction light deterioration is described as 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 reproduction light deterioration phenomenon results in an increase in the amount of light. In this case 1
Although it does not have the disadvantage that it becomes difficult to distinguish it from the surface, it does pose 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 optical tape-only reciprocating recording media, and furthermore, reproduction light deterioration also occurs with optical discs. It is also clear that the technical idea of the present invention can be applied even when using a recording material with a high degree of oxidation.

[Effects of the Invention] As explained above, according to the AFF control method for an optical head of the present invention, the method of controlling the AFF of an optical head according to the present invention can be used without using any means such as improving the recording medium, and by using the equipment device of operating the optical head. It is possible to solve the problem of reproduction light deterioration using 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 an AFF control 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 explaining the servo control points when the switch 19 is turned ON and O'FFL. FIG. 5 is a sensitivity characteristic curve of the recording medium. FIG. 6 is a plan view of the optical card. FIG. 7 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. FIG. 11 is a diagram illustrating 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. FIG. 14 is a diagram schematically showing a servo circuit according to another embodiment of the present invention. 1: Optical card, 2: Photo coupler, 3: Pulse generator, 4 system controller, 5: Optical head, 6:
Actuator, 7: Photodetector, 8: Servo circuit, 9:
Optical head feeding mechanism, 10: Head feeding driver, 11
: Optical card feeding mechanism, 12: Card feeding, retry bar,
13: AF destination photodetector 14: Differential amplifier, 15: Amplifier, 16: Switch circuit, 17: Phase compensation circuit, 18:
Actuator driver % 19.19': Defocus switch, 70: Amplifier or attenuator. 2 Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 Irradiation time q 2

Claims (4)

[Claims] (1) Light from the recording medium surface is received by a photodetector with a light receiving surface divided into multiple parts, and auto focusing (AF)
), in the case where a recording medium is used in which the characteristics of the recording medium change due to light irradiation on the recording medium and the amount of light incident on the photodetector changes. When the medium is stationary,
An optical head characterized in that the size of the irradiation spot on the recording medium is controlled to be larger than when it is in focus by operating a means that changes the output ratio of each of the plurality of light receiving surfaces from the normal case. AF control method. (2) The light according to claim 1, wherein the means for changing the output ratio of each light-receiving surface is performed by means for zeroing the output from at least one light-receiving surface of the plurality of light-receiving surfaces. Head AF control method. (3) The means for changing the output ratio of each light-receiving surface is performed by means for increasing or decreasing the output from at least one of the plurality of light-receiving surfaces. AF control method for optical head. (4) 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.