JPH0485732A - Tracking controller for optical recording and reproducing device and method thereof - Google Patents

Abstract

PURPOSE:To improve the tracking control reliability by correcting the offset value of a tracking error signal in a record mode only. CONSTITUTION:The light emitted from a semiconductor laser is divided and projected on a DRAW type optical disk. The preceding side spot light SP1 and the following side spot light SP3 are used for the tracking control. Then the SP1 and the SP3 are projected on an unrecorded area and a recorded area respectively. Both areas have different reflection factors and therefore the reflected light beams of the SP1 and SP3 include the components based on the different reflection factors. A monitoring photodiode receives a part of the light beams emitted from the semiconductor laser and monitors this emitting light quantity. Furthermore the peak value of the light emitted from the semiconductor laser is always kept at a fixed level owing to the presence of an automatic power control circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tracking control device in an optical recording/reproducing device applied to a write-once optical disc or the like on which additional information can be recorded.

BACKGROUND OF THE INVENTION A push-pull method is generally used to detect the amount of tracking deviation for tracking control of a write-once optical disc. The push-pull method is also called the far-field method, in which the diffraction pattern of the track is detected by a two-split light-receiving element placed in the far-field region.

Problems to be Solved by the Invention However, the push-pull method has the disadvantage that offset occurs due to the radial inclination of the optical disk. Furthermore, a mechanism in which only the objective lens is driven for tracking has the disadvantage that an offset occurs when the center of the objective lens shifts in the radial direction when an eccentric optical disk is tracked or accessed.

Therefore, in consideration of the stability of the reproducing system, it can be said that the three-spot method, which does not have such drawbacks, is desirable.

In the three-spot method, the light emitted from one light emitting element is divided into three light beams: a central spot light, a leading side spot light, and a trailing side spot light, and is projected onto an optical disk. A tracking error signal representing the amount of tracking deviation is generated by taking the difference between the light reception signal of the reflected light from the optical disk of the preceding side spot light and the light reception signal of the reflected light of the subsequent side spot light.

However, when recording information on a write-once optical disc, the leading side spot light is projected onto an unrecorded area of the optical disc, and the trailing side spot light is projected onto a recorded area. Since the reflectance is different between the unrecorded area and the recorded area of the optical disc, the tracking error signal includes a component (offset) based on this difference in reflectance, making it impossible to accurately detect the amount of track misalignment.

The present invention overcomes the above-mentioned problems in the three-spot method and makes it possible to apply the three-spot method, which is superior to the push-pull method, to write-once optical discs.

Means for Solving the Problems The tracking control device according to the present invention divides the light emitted from one light emitting element into three lights: a central spot light, a leading side spot light, and a trailing sight spot light, and projects them onto an optical disk. In an optical recording and reproducing apparatus that records information on an optical disk (for example, a write-once optical disk) having different characteristics in terms of the amount of reflected light of the leading side spot light and the following side spot light while performing tracking control using the spot method, the above-mentioned method is used. In a means for monitoring the intensity of light emitted from a light emitting element, and in a tracking error signal represented by a difference in received light signals of reflected light of the preceding spot light and the following spot light. The present invention is characterized by comprising means for correcting the amount of offset caused by the characteristics of the optical disc in accordance with the intensity of the emitted light obtained from the monitor means.

The tracking control method according to the present invention performs tracking control using a three-spot method in which the light emitted from one light emitting element is divided into three lights: a central spot light, a leading side spot light, and a trailing side spot light and projected onto an optical disk. However, in an optical recording/reproducing apparatus that records information on an optical disk having different characteristics in terms of the amount of reflected light of the leading side spot light and the following side spot light, the emitted light intensity of the light emitting element is monitored.

In the tracking error signal represented by the difference between the received light signals of the reflected lights of the leading spot light and the trailing spot light. The present invention is characterized in that the amount of offset caused by the characteristics of the optical disc is corrected in accordance with the intensity of the emitted light obtained by the monitor.

The offset amount caused by the characteristics of the optical disk in the tracking error signal can be corrected by adding or subtracting a signal (voltage or current) corresponding to the offset amount to the tracking error signal so as to cancel this offset amount. It will be realized.

This invention is of course applicable to devices having both recording and reproducing functions. In such a recording/reproducing apparatus, in the recording mode, the light emitting element is pulse-driven in accordance with the information to be recorded.

In the reproduction mode, the light emitting element is continuously driven so that the intensity of the projected light is weaker than in the recording mode.

Therefore, the optical recording/reproducing apparatus includes means for determining whether the mode is recording mode or reproduction mode based on the output signal of the monitoring means, and means for operating the correcting means only when it is determined that the mode is recording mode. It is preferable to provide

Function: The intensity of light emitted from the light emitting element is detected. A signal corresponding to the offset amount is added to the tracking error signal so that the offset amount caused by the characteristics of the optical disk included in the tracking error signal cancels the offset amount according to the detected output light intensity. Or corrected by subtraction.

In a device having a recording mode and a reproduction mode, the recording mode is detected by utilizing the fact that the emitted light intensity of the light emitting element is different in the recording mode and the reproduction mode. Then, the offset amount in the tracking error signal is corrected only in the recording mode.

Embodiment FIG. 1 shows an embodiment of the present invention, in which a portion particularly related to tracking control of a magneto-optical disk recording/reproducing apparatus having a recording mode and a reproduction mode is extracted. It is a block diagram.

A three-beam method is used to generate a tracking error signal for tracking control. The light emitted from the semiconductor laser 12, which generates projection light for recording or reproduction, is divided into three parts and projected onto a write-once optical disc as shown in FIG. The central spot light SP2 is for recording or reproducing and focusing control.
The preceding side spot light SPI and the following side spot light SP3 are for tracking control.

When recording information on a write-once optical disc,
Naturally, the preceding side spot light SPI is projected onto the unrecorded area, and the subsequent side spot light SP3 is projected onto the recorded area. The unrecorded area and the recorded area have different reflectances, and the reflected light of the preceding site spot SPJ and the reflected light of the subsequent side spot light SP3 include the above-mentioned component in addition to the component representing the deviation from the track. This includes components based on differences in reflectance.

The photodetector 30 includes a four-divided photodiode 32. which receives reflected light from the central spot SP2. and both side spot light SPI, SF
photodiodes 3 each receiving reflected light from 3;
1. , 32 are included. 4-split photodiode 3
A focusing error signal for controlling focusing in the recording and reproducing modes is generated from the light reception signal No. 2, and a focusing error signal for controlling the focusing in the reproducing mode is also used as a reading signal for recorded information in the reproducing mode.

The light reception signals of the photodiodes 31 and 33 are applied to a differential amplifier circuit 34, and a tracking error signal representing the difference between these light reception signals is obtained. This tracking error signal is amplified by a gain control circuit 35 and then applied to an adder circuit 3B.

As mentioned above, in the recording mode, the reflected light of the two side spot lights SPI and SF3 contains a component based on the difference in reflectance between the unrecorded area and the recorded area, so the tracking error signal and gain control circuit 3
The output signal No. 5 includes an offset amount based on this difference in reflectance. This offset amount is determined by the differential amplifier circuit 34
It takes a positive or negative value depending on whether the positive or negative input is the light reception signal of the photodiode 31 or 33. In this embodiment, it is assumed that it takes a negative value.

Only in the recording mode, a voltage signal representing a value corresponding to the offset amount is input from the power determination circuit 20 (to be described later) to the addition circuit 36. In this adder circuit 36, the voltage signal output from the power determination circuit 20 is added to the output (tracking error signal) of the gain control circuit 35, thereby making a difference in the amount of reflected light between the four side spot lights SPI and SF3. The offset amount based on is canceled. The output signal of this adder circuit 36 is given to a tracking drive circuit 38 via a phase compensation circuit 37, and this circuit 38 drives a tracking actuator 39.
is driven, and appropriate tracking control is performed.

In the reproduction mode, since no signal is supplied from the power determination circuit 20, the output signal of the gain control circuit 35 passes through the adder circuit 36 and is applied to the phase compensation circuit 37, and the tracking actuator 39 performs the tracking actuator 39.
It will be controlled by the error signal itself.

In the recording mode, the semiconductor laser 12 is driven based on a recording signal representing information to be recorded.

In the regeneration mode, it is continuously driven by a constant DC current.

In the recording mode, two recording signals are input to the pulse current drive circuit 10. The output current of this pulse current drive circuit 10 is inputted to a semiconductor laser 12 after being added with a bias current in an adder circuit 11 .

The semiconductor laser 12 is pulse-driven by the output current of the adder circuit 11, and three spots of laser light are projected onto the optical disk as described above.

The monitoring photodiode 13 receives a portion of the light emitted from the semiconductor laser 12 and monitors the amount of the emitted light. The output signal of the monitor photodiode 13 is input to the 1-V conversion amplifier circuit 14, converted into a voltage value, and then applied to the negative input terminal of the differential amplifier circuit 16. Differential amplifier circuit 16
A reference voltage from a reference voltage generation circuit 15 is applied to the positive input terminal of the reference voltage generating circuit 15 . The voltage amplified by the differential amplifier circuit 16 is converted into a bias current by a bias current drive circuit 17 and applied to the adder circuit 11 . Monitor photodiode 13, IV conversion amplifier circuit 14. Reference voltage generation circuit 15, differential amplifier circuit 16. Bias current drive circuit 17
and adder circuit 1] constitute an automatic power control circuit. As a result, the peak value of the light emitted from the semiconductor laser 12 is controlled to always be maintained at a constant value.

In the reproduction mode, the semiconductor laser 12 is continuously driven by a direct current having a value much lower than the peak value of the pulsed current in the recording mode. The above-mentioned automatic power control circuit also operates in the reproduction mode, and the intensity of the light emitted from the semiconductor laser 12 is maintained constant.

The output voltage of the above-mentioned IV conversion amplifier circuit 14 is also given to the power determination circuit 20. The power determination circuit 20 determines whether the mode is 1 recording mode or reproduction mode by determining the intensity of light emitted from the semiconductor laser 12 based on the output signal of the monitor photodiode 13.

In the recording mode, the monitor photodiode 13
An offset voltage signal is output based on the output signal of.

As described above, the intensity of the light emitted from the semiconductor laser 12 in the recording mode is much greater than the intensity of the light emitted in the reproduction mode, so that mode discrimination is possible. - In the recording mode, the offset voltage signal output from the power determination circuit 20 is applied to the adder circuit 36, and offset correction is performed as described above.

Instead of connecting the power determination circuit 20, the CPU determines whether the mode is recording mode or reproduction mode, and when it is determined that the mode is recording mode, an offset voltage is created by the CPU based on the output signal of the monitor photodiode 13, It may also be provided to the adder circuit 3B.

FIG. 2 is a circuit diagram showing a specific configuration of the power determination circuit 20 and the addition circuit 36.

The power determination circuit 20 includes an operational amplifier 21. which acts as an adder and a comparator. Operational amplifier 22, which acts as a buffer inverting amplifier. It is composed of resistors R1, R2, etc., diodes, etc. The output voltage of the I-■ conversion amplifier circuit 14 and a predetermined reference voltage (negative voltage) are added (actually subtracted because the voltage V is negative) through the resistor R2 and applied to the negative input terminal of the amplifier 21. It will be done.

A positive input terminal of amplifier 21 is grounded. Reference voltage■
is a threshold value for determining whether the mode is recording mode or playback mode. When the a voltage of the IV conversion amplifier circuit 14 is higher than the reference voltage V (only in recording mode), an output is generated from the amplifier 21, and this output is applied to the output of the 1-V conversion amplifier circuit 14 as a voltage ), the amplifier 22
The voltage is inverted and applied to the adder circuit 36 as an offset voltage.

The addition circuit 36 is composed of an operational amplifier 36a with a feedback loop and an input resistor for addition. Voltage output from gain control circuit 35 and determination circuit 20
The voltages outputted from the amplifier 3[ia] are added together via each input resistor, and input to the amplifier 3 [ia]. As described above, the addition output of the amplifier 36a is provided to the phase compensation circuit 37.

FIG. 3 shows a modification of the power determination circuit 20. In FIG. The power determination circuit 20 includes a comparator 23. Variable resistor 24
and other resistances.

The positive input terminal of the comparator 23 is the I-V conversion amplifier circuit 1
4, and the negative input terminal is connected to a predetermined reference voltage (
Here, it is connected to a voltage source that generates a positive voltage.

Further, the output terminal of the comparator 23 is connected to the adder circuit 3 via a variable resistor 24 (which becomes the input resistance of the operational amplifier 38a).
6 is connected.

Only when the output voltage of the 1-V conversion amplifier circuit 14 is equal to or higher than the reference voltage V, an output is generated from the comparator 23 and is applied to the adder circuit 36 as an offset voltage. This offset voltage can be adjusted using a variable resistor 24.

Effects of the Invention As described in detail above, according to the present invention, the intensity of the light emitted from the light emitting element is detected. A signal corresponding to the offset amount is added to the tracking error signal so that the offset amount caused by the characteristics of the optical disk included in the tracking error signal cancels the offset amount according to the detected output light intensity. Or corrected by subtraction.

In a device having a recording mode and a reproduction mode, the recording mode is detected by utilizing the fact that the emitted light intensity of the light emitting element is different in the recording mode and the reproduction mode. Then, only in the recording mode, the offset amount in the tracking error signal is corrected.

In this way, tracking in the 3-spot method
It becomes possible to apply the three-spot method to tracking control of an optical disc having characteristics such as a write-once optical disc that causes an offset in an error signal, and to perform accurate tracking control. Therefore, there is no need to employ the push-pull method, which has various inherent problems, and the reliability of tracking control is improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a portion related to tracking control of a magneto-optical disk recording/reproducing apparatus. FIGS. 2 and 3 are circuit diagrams showing details of a power determination circuit and an addition circuit. FIG. 4 shows the relationship between the tracks of the write-once optical disc, the recording bits, and the three projected light spots. 12...Semiconductor laser 13...Monitoring photodiode. 20...Power judgment circuit. 30...Photodetector. 86...Addition circuit. 38...Tracking drive circuit 39...l.Racking actuator SP1...
- Leading side spot light. SF3... Trailing side spot light. Below

Claims (4)

[Claims] (1) The light emitted from the light emitting element is divided into three beams: a central spot, a leading side spot, and a trailing side spot, and is projected onto the optical disk. Tracking is controlled using the 3-spot method. In an optical recording/reproducing device for recording information on an optical disk having characteristics in which the amounts of reflected light of a spot light and a trailing side spot light are different, a means for monitoring the intensity of light emitted from the light emitting element, and a means for monitoring the intensity of the light emitted from the light emitting element, and a means for monitoring the intensity of the light emitted from the light emitting element, Optical recording, comprising means for correcting an offset amount caused by the characteristics of the optical disc in a tracking error signal represented by a difference between received signals of reflected light, in accordance with the intensity of emitted light obtained from the monitoring means. A tracking control device in a playback device. (2) Has a recording and playback function that pulse-drives the light-emitting element in accordance with the information to be recorded in the recording mode, and continuously drives the light-emitting element in the playback mode so that the emitted light intensity is weaker than in the recording mode. Claim (1) further comprising: means for determining whether the recording mode is set based on the output signal of the monitor means; and means for operating the correction means only when it is determined that the recording mode is set. A tracking control device in the optical recording/reproducing device described above. (3) While performing tracking control using the 3-spot method in which the light emitted from the light emitting element is divided into three beams: a central spot, a leading side spot, and a trailing side spot and projected onto the optical disk, In an optical recording/reproducing device that records information on an optical disk in which the reflected light intensity of a spot light and a trailing side spot light are different, the output light intensity of the light emitting element is monitored, and the reflected light intensity of the leading spot light and trailing spot light is A tracking control method in an optical recording and reproducing device, in which an offset amount caused by the characteristics of the optical disk in a tracking error signal represented by a difference between received signals of reflected light is corrected according to an intensity of emitted light obtained by the monitor. (4) Has a recording and playback function that pulse-drives the light-emitting element in accordance with the information to be recorded in the recording mode, and continuously drives the light-emitting element in the playback mode so that the emitted light intensity is weaker than in the recording mode. According to claim (3), the device determines that the mode is a recording mode based on the intensity of the emitted light obtained by the monitor, and corrects the offset amount only when it is determined that the mode is the recording mode. A tracking control method in an optical recording/reproducing device.