JPH03187021A - Optical disk recorder - Google Patents

Abstract

PURPOSE:To prevent the increase of DC offset at the time of recording to prevent the occurrence of off-track by correcting and controlling the servo error based on servo error information except in the part where the offset is increased. CONSTITUTION:A tracking error passes an optical head 12, a tracking error detecting circuit 20, and a sampling and holding circuit 14 and is supplied to a driver 28 through a filter circuit 26 to perform the servo control of tracking of a lens 14 to a disk 12. In this case, the input-side switch of the circuit 24 is opened by a recording pulse passing a delay and pulse width changing circuit 30, and a tracking error signal is not outputted from the circuit 24. Thus, the servo error signal except in the part where the offset due to the recording pulse is increased is used, and the occurrence of off-track due to the increase of the DC offset is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical disc recording device for recording information on a writable optical disc, and is concerned with an optical disc recording device for recording information on a writable optical disc. This was prevented.

[Conventional technology]

BACKGROUND ART Conventionally, there are DRAW (write once) disks and E-DRAW (erasable) disks as writable optical disks. DRAW disks can be written only once, and for example, there are disks in which information pits are formed by burning out a metal recording film using heat generated by laser beam irradiation. E-DRAW disks are rewritable and include, for example, those that utilize magneto-optical recording and those that utilize phase change between a crystalline state and an amorphous state.

In writable optical discs, guide grooves (tracks) called pre-groups are pre-formed during manufacturing, and during recording, these tracks are tracked by tracking control and placed in group areas (guide groove areas) or land areas. Information is recorded by irradiating a recording beam.

There are various methods for detecting tracking errors, such as the push-pull method and the track wobbling method.
In push-pull methods and the like, a DC offset may appear in the tracking error signal. If a DC offset occurs, even if the tracking error signal indicates O, the beam will deviate from the center of the track, and in particularly significant cases, it will cause off-track.

One of the causes of DC offset is that the optical axis of the objective lens of the optical head is tilted with respect to the disk surface due to, for example, radial warping of the disk.

Conventionally, as a method to reduce the DC offset caused by the tilt of the disk, a method called tilt servo detects the tilt of the optical axis of the objective lens and tilts the entire optical head so that it is parallel to the tilt of the disk. There was something I tried to do.

[Problem to be solved by the invention]

According to experiments conducted by the inventors, it was found that the DC offset is larger during recording than during playback. This difference occurs because the optical output of the recording beam is greater than that of the playback beam, or This is thought to be due to the fact that the DC offset occurs differently in response to angular errors due to optical imbalance in the process of forming recording bits.

In this way, the DC offset changes during recording and playback, so for example, as shown in Figure 2, if you are tracing a track and switch from playback mode to record mode, the tracking error signal will have a DC offset. This occurs and the tracking servo works to correct this, resulting in the beam sometimes deviating significantly from the track center.

In particular, depending on the material of the disc recording medium, the difference in DC offset during recording and playback may be very large, and with such optical discs, the moment you switch from playback mode to record mode while tracing a track, There were cases where the vehicle would fall off the track.

In order to prevent the influence of such a difference in DC offset between recording and reproduction, in conventional devices, it was necessary to increase the precision of the tilt servo and minimize the angular error.

However, if the disk has waviness (surface runout) and the degree of radial warping of the disk changes depending on the circumferential position, it is necessary to move the heavy optical head at high speed using a tilt servo to compensate for minute angles. was quite difficult.

Further, such a difference in DC offset between recording and reproduction occurs not only in tracking servo but also in focus servo and the like.

This invention solves the drawbacks in the above conventional techniques, and
It is an object of the present invention to provide an optical disc recording device that prevents DC offset from increasing during recording and prevents track off and the like from occurring.

[Means to solve the problem]

The present invention includes a servo error detection means for detecting a servo error, and a control means for correcting the servo error by driving a servo actuator according to the detected servo error information, and the control means is configured to control the servo error by a recording pulse. The present invention is characterized in that the control is performed based on servo error information detected in areas other than the portion where the servo error offset increases.

[For production]

According to this invention, since control is performed based on servo error information detected in areas other than the portion where the offset of servo error increases due to the recording pulse, it is possible to prevent the offset from increasing during recording.

As a result, the burden on the offset reducing means such as a tilt servo can be reduced, and in some cases, the offset reducing means can be eliminated.

〔Example〕

FIG. 1 shows an embodiment in which the present invention is applied to a tracking servo of a write-once optical disc recording device.

The recording pulse is ALPC (＾uto厘atIc La5e
rPowerControl) After the optical output is stabilized in the circuit 10, it is supplied into the optical head 12 to drive the laser diode. The recording beam output from the laser diode is focused by the objective lens 14 and irradiated onto the recording surface of the optical disk 16, and the recording film is broken to form bits and information is recorded.

At this time, the return light of the recording beam reflected by the optical disk 16 enters the objective lens 14 and is received by the light receiving element in the optical head 12. This received light signal is transmitted to the RF amplifier 1
8 to the signal reproduction processing circuit.

The tracking error detection circuit 20 detects a tracking error from the light reception signal. The frequency band of this tracking error detection circuit 20 needs to be able to sufficiently pass the recording signal frequency band.

The detected tracking error signal is sent to the tracking control means 22, applied to the driver 28 via the sample and hold circuit 24 and the filter 26, and the tracking actuator in the optical head 12 is driven to perform tracking control.

The delay and pulse width changing circuit 30 outputs a signal whose waveform has been shaped so that the recording pulse has the same phase and duration as the bit to be recorded. This is because the start of bit formation is somewhat delayed relative to the rising edge of the recording pulse (because it takes some time to reach the temperature that thermally destroys the recording film), and the end of bit formation is delayed relative to the falling edge of the recording pulse. Since it has the property of being somewhat delayed (due to excess bits being formed due to heat accumulation on the disk), it forms a signal that matches the timing at which bits are actually formed.

While the pulse signal is being outputted from the delay and pulse width changing circuit 30 (that is, while bits are actually being formed), the sample and hold circuit 24 collects a tracking error signal due to the previous bottom level (beam level at which no bits are formed). Hold and output. Filter 26
This is to smooth out the step difference that occurs in the tracking error signal at the hold release timing. Note that in the reproduction mode, the sample hold circuit 24 outputs the tracking error signal as it is.

The operation of the apparatus shown in FIG. 1 is shown in FIG. Figure 3 a-
e indicates the waveform of the portion indicated by the same symbol in FIG. The recording beam is modulated by a recording pulse a and irradiated onto the disk recording surface. Since the bit C formed at this time is delayed with respect to the recording pulse a, the level of the output (b) of the returned light received RF multiplied signal RF amplifier 18 is large (
(because the beam at the recording level is reflected at the part where no bits are formed), and becomes smaller at the falling part (because the beam at the bottom level is reflected at the part where bits are formed).

The hold signal d becomes high level in accordance with the period in which bits are actually formed, and the immediately preceding tracking error signal e during that period is held and output. If the optical axis is tilted with respect to the disk surface, the DC offset will normally increase during this hold period, so if the tracking error signal e is output as is without being held during this period, the average level of the DC offset will increase. becomes large, and tracking servo is applied to correct this, resulting in a large deviation of the beam from the center of the track. On the other hand, by holding as described above, an increase in DC offset is prevented, and an increase in beam deviation from the track center is prevented, so it is possible to prevent off-track etc. at the moment when switching from playback mode to record mode. can do.

Figure 4 shows the relationship between the tilt of the optical axis with respect to the disk surface during recording and the amount of tracking error offset.In the case of conventional devices, if the optical axis is tilted even slightly, the offset becomes very large. It can be seen that in the device shown in the figure, the increase in offset is suppressed (almost the same as during playback).

Therefore, the burden on offset reduction means such as a tilt servo is reduced accordingly, and in some cases, it is possible to eliminate the tilt servo.

Furthermore, since signals from the recording process are not mixed into the tracking servo as a disturbance, the quality of the servo current is improved and servo followability is improved. Note that since the holding time is short, it does not adversely affect the tracking servo.

Tracking error detection circuit 20 in the device shown in FIG.
A specific example of the sample and hold circuit 24 is shown in FIG. A photodetector 32 provided within the optical head 12 is composed of a four-division PIN photodiode, and detects the return light reflected by the disk. The detection signals of each divided portion are combined from those on the same side with respect to the track, and output via analog switches SWI and SW2, capacitors C1 and C2, and buffer amplifiers 34 and 36.
is subtracted to detect tracking error.

The analog switches SWI and SW2 are connected to contact a while the output pulse of the delay and waveform shaping circuit 30 is at a low level (that is, in the blank section in which no bit is formed), and output the detection signal as it is, changing every moment. A tracking error signal is output. Further, while the output pulse of the delay and waveform shaping circuit 30 is at a high level (that is, the section where a bit is formed), it is connected to the contact point S. As a result, the immediately preceding signal is held in the capacitors CI and C2, and a tracking error signal held at a constant value is output.

[Example of change]

In the above embodiment, sample and hold control is performed by delaying and waveform shaping the recording pulse to match the bit formation timing, but even if sample and hold control is performed directly using the recording pulse, The desired effect can be obtained. Further, the hold period can be increased or decreased to some extent with respect to the bit formation period or the beam irradiation period.

In addition, as a recording beam irradiation method, by dividing the recording pulse into multiple pulses within the time to form one bit and irradiating them, heat accumulation on the disk is prevented and the leading edge of the bit and the rear Precisely define the position of the edge,
There is a method that aims to reduce the jitter of the reproduced signal and improve the S/N (see Japanese Patent Application No. 61-307372), but when using this method, the hold period is It is also possible to divide the bit, but there is no problem if the bit is held continuously during the period of forming one bit without being divided.

Further, in the embodiment described above, the immediately preceding tracking error signal is held while a bit is being formed, but 0 may be output instead of being held. In this case, the tracking servo is controlled by the average value of the tracking error when forming the blank part, but E F
M (Eight t.

When recording is performed using Fourteen Modulation) modulation, the average ratio of the length of the blank part to the bit part is approximately 1:1, so even if you take only the average value of the tracking error when forming the blank part, it is almost impossible to estimate the actual tracking error. A value corresponding to the tracking error can be obtained.

In addition, in this case, for example, the capacitors C1 and C2 and the buffer amplifier 34.3 in FIG.
6 becomes unnecessary.

Further, in the above embodiment, the push-pull method was used as the tracking error detection method, but it can be applied to various methods in which the DC offset of the servo signal becomes large during recording, such as the three-beam method or the phase difference method. However, it is effective.

Furthermore, the present invention can be applied not only to tracking servo but also to other controls in which the DC offset of the servo signal becomes large during recording, and is also effective when applied to focus servo, for example.

Further, the present invention is not limited to a recording-only device, but can also be applied to a recording/reproducing device.

〔Effect of the invention〕

As explained above, according to the present invention, control is performed based on servo error information detected in areas other than the portion where the offset of the servo error increases due to the recording pulse, so that the offset increases during recording. It can be prevented.

As a result, the burden on the offset reducing means such as a tilt servo can be reduced, and in some cases, the offset reducing means can be eliminated.

Furthermore, since signals from the recording process are not mixed into the tracking servo as a disturbance, the quality of the servo current is improved and servo followability is improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is an operational waveform diagram of the device of FIG. 1. FIG. 3 is a waveform diagram showing a state in which the tracking error DC offset increases due to switching to the recording mode. FIG. 4 is a characteristic diagram showing the relationship between the inclination of the optical axis with respect to the disk surface and the amount of tracking error offset. FIG. 5 is a circuit diagram showing a specific example of the tracking error detection circuit 20 and sample hold circuit 24 in the apparatus shown in FIG. 12... Optical head, 16... Optical disk, 20...
- Tracking error detection circuit (servo error detection means), 22...Tracking control means (control means), 2
4...Sample hold circuit.

Claims (1)

[Scope of Claims] Servo error detection means for detecting a servo error, and control means for correcting the servo error by driving a servo actuator according to the detected servo error information, the control means for recording An optical disc recording apparatus characterized in that the control is performed based on servo error information detected in a region other than a portion where a servo error offset increases due to a pulse.