JP4264653B2 - Optical disc apparatus, focus bias, and spherical aberration correction value adjustment method - Google Patents

Description

  The present invention relates to an optical disc apparatus capable of reproducing at least a signal for an optical disc recording medium, and a focus bias and spherical aberration correction value adjusting method.

JP 2002-352449 A JP-A-10-269611 JP 2000-285484 A JP-A-9-251645 JP2000-11388

  As a technique for recording / reproducing digital data, optical disks (including magneto-optical disks) such as CD (Compact Disk), MD (Mini-Disk), and DVD (Digital Versatile Disk) are used as recording media. There is data recording technology. An optical disk is a general term for recording media that read a signal by irradiating a laser beam to a disk in which a metal thin plate is protected with plastic, and changing the reflected light.

The optical disc includes, for example, a read-only type as known as CD, CD-ROM, DVD-ROM, MD, CD-R, CD-RW, DVD-R, DVD-RW, DVD + RW, DVD -There is a type in which user data can be recorded as known in RAM and the like. In the recordable type, data can be recorded by utilizing a magneto-optical recording method, a phase change recording method, a dye film change recording method, or the like. The dye film change recording method is also called a write-once recording method, and can be recorded only once and cannot be rewritten. On the other hand, the magneto-optical recording method and the phase change recording method can rewrite data, and are used for various purposes including recording of various content data such as music, video, games, application programs and the like.
In recent years, a high-density optical disk called a Blu-ray Disc has been developed, and the capacity has been significantly increased.

For a high-density disc such as a Blu-ray disc, in a disc structure having a cover layer of about 0.1 mm in the disc thickness direction, a laser having a wavelength of 405 nm (so-called blue laser) and an objective lens having an NA (Numerical Aperture) of 0.85 The phase change mark (phase change mark) is recorded and reproduced under the condition of the combination of
As a storage capacity, about 23.3 GB (gigabytes) can be secured on a direct 12 cm disk.
Further, when the recording layer has a two-layer structure, for example, a capacity of about 46.6 GB, which is about twice the above, can be obtained.

As already known, in an optical disc apparatus that performs recording / reproduction on an optical disc, a focus servo operation for controlling the focal position of a laser beam on a disc recording surface, or a track on a track (pit train or groove (groove) by a laser beam) Tracking servo operation is performed to control to trace).
Regarding the focus servo, it is known that it is necessary for an appropriate servo operation to apply an appropriate focus bias to the focus loop.

  In particular, in the case of a high-density disk, it is necessary to correct spherical aberration in order to cope with a cover layer thickness error or a multilayered recording layer. For example, an expander or a liquid crystal element is used in an optical pickup. A device having a spherical aberration correction mechanism has been developed, and is disclosed in, for example, Patent Documents 1 and 2 above.

In particular, in a writable optical disc apparatus (recording / reproducing apparatus) having a high NA lens such as the above-mentioned Blu-ray disc, since the margin of focus bias / spherical aberration is narrow, automatic adjustment of the focus bias and spherical aberration is essential. The
As a technique for adjusting the focus bias, for example, Patent Document 3 is known.
Also, for example, Japanese Patent Application Laid-Open No. 2004-133620 is known as a method for adjusting spherical aberration.
Further, a method for simultaneously adjusting the focus bias / spherical aberration is disclosed in Patent Document 5.

As shown in these Patent Documents 3 to 5, in the conventional method, the signal is read while successively changing the focus bias and the spherical aberration correction value, and the amplitude level of the RF signal obtained thereby is maximized. A combination of the focus bias and the spherical aberration correction value is determined.
The focus bias and the spherical aberration correction value thus detected are set, and signal recording / reproduction is performed.

  According to such a method, it is possible to perform optimum focus bias setting and spherical aberration correction based on the actually measured RF signal. For example, when the focus error signal is offset due to a change over time or the like, Even when spherical aberration occurs due to the cover thickness being different for each object, it is possible to suppress deterioration in signal recording / reproduction quality.

  However, in the conventional focus bias adjustment and spherical aberration correction methods, particularly with regard to the focus bias, the optimum focus bias is that the amplitude level of the RF signal is maximized when astigmatism occurs in the optical system. The problem is that this is not a condition for obtaining.

This will be described with reference to FIG.
In FIG. 7, the horizontal axis represents the amount of astigmatism, and the vertical axis represents the focus bias value.
The white square in the figure indicates the focus bias value at which the RF signal amplitude is maximum when a certain amount of astigmatism, and the black circle indicates the push-pull signal amplitude when the amount is astigmatism. The maximum focus bias value is shown.

  Here, in obtaining the optimum value as the focus bias, a method based on the push-pull signal amplitude as well as the RF signal amplitude as described above is conventionally known. That is, the focus bias value when the push-pull signal amplitude is maximum is the optimum focus bias value.

Based on this, let us consider the characteristics shown in the figure.
First, at point A in the figure, the astigmatism amount is zero. In this case, as shown in the drawing, the focus bias value at which the RF signal amplitude becomes maximum and the focus bias value at which the push-pull signal amplitude becomes maximum coincide with each other at the focus bias value FB0.
That is, from this, when there is no astigmatism in the optical system, the amplitude levels of both the RF signal and the push-pull signal can be maximized by setting the value of the focus bias FB0. In other words, the focus bias FB0 satisfies the two conditions of being an optimum value at the same time, and thus can be said to be an optimum focus bias.
Then, in order to obtain the focus bias FB0 as such an optimum value, as understood from the above description, any one of the conditions for maximizing the RF signal amplitude or the conditions for maximizing the push-pull signal amplitude is used. Therefore, when there is no astigmatism, an optimum focus bias can be obtained by setting conditions that maximize the RF signal amplitude as in the prior art.

However, astigmatism occurs, the focus bias value at which the RF signal amplitude is maximum differs from the focus bias value at which the push-pull signal amplitude is maximum at the point B shown in the figure. I understand.
That is, when the amount of astigmatism at point B is reached, the focus bias value that maximizes the RF signal amplitude is FB1 in the figure. On the other hand, the focus bias value that maximizes the push-pull signal amplitude is FB2 shown in the figure.
Therefore, when astigmatism occurs in the optical system, the push-pull signal amplitude is not maximized even if the focus bias that maximizes the RF signal amplitude is set, and the push-pull signal amplitude is maximized. Even if the focus bias is set, the RF signal amplitude does not become the maximum.
Therefore, it can be seen that when the optical system has astigmatism, the focus bias obtained on the basis of either the RF signal amplitude or the push-pull signal amplitude is highly likely not to be the optimum focus bias.

  From the above, by setting a focus bias that maximizes the RF signal amplitude as in the prior art, there is a possibility that an optimum focus state cannot be obtained when astigmatism occurs. There is a possibility that the reproduction quality may deteriorate.

In view of the above-described problems, the present invention has an object to enable accurate focus bias adjustment and spherical aberration correction value adjustment even when astigmatism occurs in an optical system. And
Therefore, in the present invention, the optical disk apparatus is configured as follows.
That is, first, a rotation driving means for rotating the optical disk recording medium, and at least for reading data, performing laser irradiation and reflected light detection on the optical disk recording medium, a laser beam focus servo mechanism, tracking servo mechanism, And head means having a spherical aberration correction mechanism.
Further, an RF signal generating means for generating an RF signal from a signal based on the reflected light obtained by the head means, and a push-pull signal generating means for generating a push-pull signal from the signal based on the reflected light obtained by the head means. Prepare.
Further, the focus servo means for driving the focus servo mechanism based on the focus error signal generated as a signal based on the reflected light obtained by the head means to execute the focus servo, and the reflected light obtained by the head means Tracking servo means for driving the tracking servo mechanism on the basis of a tracking error signal generated as a signal based thereon and executing tracking servo.
A spherical aberration correction unit configured to drive the spherical aberration correction mechanism based on the spherical aberration correction value to execute the spherical aberration correction; and a focus bias unit configured to add a focus bias to the focus loop including the focus servo unit. .
In addition, control means for executing the following processes is provided.
That is, it was obtained by the RF signal generation unit based on the result of data reproduction while changing both the focus bias set in the focus bias unit and the spherical aberration correction value set in the spherical aberration correction unit. A first indexing process is performed for determining a set of a focus bias and a spherical aberration correction value that maximizes the amplitude value of the RF signal.
Further, in a state where the spherical aberration correction value determined by the first indexing process is set in the spherical aberration correction means, at least the tracking servo by the tracking servo means is turned off, and the focus set in the focus bias means When the optical disk recording medium is rotationally driven by the rotational drive means while changing the bias stepwise, the focus bias at which the amplitude value of the push-pull signal obtained by the push-pull signal generation means is maximized is determined. The second indexing process is executed.
Further, by performing a required calculation process based on the focus bias determined by the first indexing process and the focus bias determined by the second indexing process, an optimum focus bias value is obtained. A calculation process to be calculated, a focus bias based on the value calculated by the calculation process, and the spherical aberration correction value calculated by the first indexing process are set in the focus bias unit and the spherical aberration correction unit. In this way, a setting control process for performing control is executed.

In the present invention, the focus bias and spherical aberration correction value adjustment method is as follows.
That is, at least a signal can be reproduced from the optical disc recording medium, and the focus bias and spherical aberration correction value adjustment method in the optical disc apparatus in which the focus bias and the spherical aberration correction value can be variably set. A first indexing procedure for determining a set of the focus bias and the spherical aberration correction value that maximizes the amplitude value of the RF signal based on the result of data reproduction while changing both values is provided.
In addition, when the spherical aberration correction value determined by the first indexing procedure is set, at least the tracking servo is turned off and the optical disk recording medium is rotated while the focus bias is changed stepwise. A second indexing procedure for determining the focus bias at which the amplitude value of the obtained push-pull signal is maximized is provided.
Further, by performing a required calculation process based on the focus bias determined by the first indexing procedure and the focus bias determined by the second indexing procedure, an optimum focus bias value is obtained. A calculation procedure for calculating, and a setting control procedure for performing control so as to set the focus bias based on the value calculated by the calculation procedure and the spherical aberration correction value calculated by the first indexing procedure It is.

According to the present invention, first, the focus bias and the spherical aberration correction value that maximizes the RF signal amplitude are determined. Then, after the spherical aberration correction value determined at this time is set, at least the tracking servo is turned off and the push-pull signal in the state where the optical disk recording medium is driven to rotate (hereinafter referred to as the push-pull signal in the traverse state). The focus bias that maximizes the amplitude is also determined. Based on the two focus biases thus determined, an optimum focus bias value is calculated.
That is, the focus bias calculated based on the focus bias that maximizes the RF signal amplitude and the focus bias that maximizes the push-pull signal amplitude in the traverse state is set as the optimum focus bias. is there.
Thus, by setting the focus bias based on both the RF signal amplitude and the push-pull signal amplitude, a more appropriate focus state can be obtained even when astigmatism occurs.

As described above, according to the present invention, it is possible to obtain a more appropriate focus state even when astigmatism occurs. Therefore, it is possible to suppress the deterioration in signal recording / reproduction quality accompanying such astigmatism. Can do.
If the reduction in signal recording / reproduction quality due to astigmatism can be suppressed in this way, the tolerance for astigmatism can be increased correspondingly, thereby increasing the product yield. The cost of the product can be reduced.

Hereinafter, the best mode for carrying out the invention (hereinafter referred to as an embodiment) will be described.
FIG. 1 shows a configuration of an optical disc apparatus according to the embodiment.
First, it is assumed that the disc 1 is an optical disc (writeable disc) that records data by a phase change method, for example. Further, a wobbling (meandering) groove is formed on the disk, and this groove is used as a recording track. Depending on the wobbling of the groove, address information or the like is embedded as so-called ADIP information.
Note that a read-only disc on which data is recorded by embossed pits may be loaded as the disc 1.

Such a disk 1 is loaded on a turntable (not shown) and is rotationally driven by a spindle motor 52 at a constant linear velocity (CLV) during a recording / reproducing operation.
Then, ADIP information embedded as wobbling of the groove track on the disk 1 is read by the optical pickup (optical head) 51.
At the time of recording, the user data is recorded on the track as a phase change mark by the optical pickup 51, and at the time of reproduction, the phase change mark recorded by the optical pickup is read out.

In the pickup 51, a laser diode serving as a laser light source, a photodetector for detecting reflected light, an objective lens serving as an output end of the laser light, and a laser recording light are irradiated onto the disk recording surface via the objective lens. An optical system (described later) for guiding the reflected light to the photodetector is formed.
The laser diode outputs a so-called blue laser having a wavelength of 405 nm, for example. The NA by the optical system is 0.85.

In the pickup 51, the objective lens is held so as to be movable in the tracking direction and the focus direction by a biaxial mechanism.
The entire pickup 51 can be moved in the radial direction of the disk by a thread mechanism 53.
The laser diode in the pickup 51 is driven to emit laser light by a drive signal (drive current) from the laser driver 63.

  As will be described later, the pickup 51 is provided with a mechanism for correcting the spherical aberration of the laser light, and the spherical aberration is corrected by the control of the system controller 60 and the servo circuit 62.

Reflected light information from the disk 1 is detected by a photo detector, converted into an electric signal corresponding to the amount of received light, and supplied to the matrix circuit 54.
The matrix circuit 54 includes a current-voltage conversion circuit, a matrix calculation / amplification circuit, and the like corresponding to output currents from a plurality of light receiving elements as photodetectors, and generates necessary signals by matrix calculation processing.
For example, a high-frequency signal (also referred to as a reproduction data signal or an RF signal) corresponding to reproduction data, a focus error signal for servo control, a tracking error signal, and the like are generated.
Further, a push-pull signal is generated as a signal related to groove wobbling, that is, a signal for detecting wobbling.

A reproduction data signal output from the matrix circuit 54 is supplied to a reader / writer (RW) circuit 55, a focus error signal and a tracking error signal are supplied to a servo circuit 61, and a push-pull signal is supplied to a wobble circuit 58.
In particular, in the case of the embodiment, the push-pull signal is also supplied to the system controller 60 described later.

The reader / writer circuit 55 performs binarization processing on the reproduction data signal, reproduction clock generation processing by PLL, etc., reproduces the data read out as the phase change mark, and supplies it to the modulation / demodulation circuit 56.
The modem circuit 56 includes a functional part as a decoder at the time of reproduction and a functional part as an encoder at the time of recording.
At the time of reproduction, as a decoding process, a run-length limited code is demodulated based on the reproduction clock.
The ECC encoder / decoder 57 performs ECC encoding processing for adding an error correction code during recording, and ECC decoding processing for performing error correction during reproduction.
At the time of reproduction, the data demodulated by the modulation / demodulation circuit 56 is taken into an internal memory, and error detection / correction processing and deinterleaving processing are performed to obtain reproduction data.
The data decoded to the reproduction data by the ECC encoder / decoder 57 is read out and transferred to an AV (Audio-Visual) system 120 based on an instruction from the system controller 60.

The push-pull signal output from the matrix circuit 54 as a signal related to groove wobbling is processed in the wobble circuit 58. The push-pull signal as ADIP information is demodulated into a data stream constituting an ADIP address in the wobble circuit 58 and supplied to the address decoder 59.
The address decoder 59 decodes the supplied data, obtains an address value, and supplies it to the system controller 60.
The address decoder 9 generates a clock by PLL processing using the wobble signal supplied from the wobble circuit 8, and supplies it to each unit as an encode clock at the time of recording, for example.

At the time of recording, recording data is transferred from the AV system 120. The recording data is sent to a memory in the ECC encoder / decoder 57 and buffered.
In this case, the ECC encoder / decoder 57 performs error correction code addition, interleaving, subcode addition, and the like as encoding processing of the buffered recording data.
The ECC-encoded data is subjected to RLL (1-7) PP modulation in the modulation / demodulation circuit 56 and supplied to the reader / writer circuit 55.
As described above, the clock generated from the wobble signal is used as the reference clock for the encoding process during recording.

The recording data generated by the encoding process is subjected to a recording compensation process by the reader / writer circuit 55, and fine adjustment of the optimum recording power and adjustment of the laser drive pulse waveform with respect to the recording layer characteristics, laser beam spot shape, recording linear velocity, etc. Etc. are sent to the laser driver 63 as a laser drive pulse.
The laser driver 63 applies the supplied laser drive pulse to the laser diode in the pickup 51 to perform laser emission driving. As a result, pits (phase change marks) corresponding to the recording data are formed on the disc 1.

The laser driver 63 includes a so-called APC circuit (Auto Power Control), and the laser output is monitored regardless of the temperature or the like while monitoring the laser output power by the output of the laser power monitoring detector provided in the pickup 51. Control to be constant.
The target value (recording laser power / reproducing laser power) of the laser output at the time of recording and reproduction is given from the system controller 60, and the laser output level is controlled to be the target value at the time of recording and reproduction.

The servo circuit 61 generates various servo drive signals for focus, tracking, and thread from the focus error signal and tracking error signal from the matrix circuit 54, and executes the servo operation.
That is, a focus drive signal and a tracking drive signal are generated according to the focus error signal and tracking error signal, and the focus coil and tracking coil of the biaxial mechanism in the pickup 51 are driven. Thus, a pickup 51, a matrix circuit 54, a servo circuit 61, a tracking servo loop and a focus servo loop by a biaxial mechanism are formed.

  The servo circuit 61 turns off the tracking servo loop and outputs a jump drive signal in response to a track jump command from the system controller 60, thereby executing a track jump operation.

  The servo circuit 61 generates a thread drive signal based on a thread error signal obtained as a low frequency component of the tracking error signal, access execution control from the system controller 60, and the like, and drives the thread mechanism 53. Although not shown, the sled mechanism 53 has a mechanism including a main shaft that holds the pickup 51, a sled motor, a transmission gear, and the like, and by driving the sled motor according to a sled drive signal, a required slide of the pick-up 51 is obtained. Movement is performed.

The spindle servo circuit 62 performs control to rotate the spindle motor 2 at CLV.
The spindle servo circuit 62 obtains the clock generated by the PLL processing for the wobble signal as the current rotational speed information of the spindle motor 52 and compares it with predetermined CLV reference speed information to generate a spindle error signal. .
At the time of data reproduction, the reproduction clock (clock serving as a reference for decoding processing) generated by the PLL in the reader / writer circuit 55 becomes the current rotational speed information of the spindle motor 52, and this is used as a predetermined CLV. A spindle error signal can also be generated by comparing with the reference speed information.
The spindle servo circuit 62 outputs a spindle drive signal generated according to the spindle error signal, and causes the spindle motor 62 to perform CLV rotation.
The spindle servo circuit 62 generates a spindle drive signal in response to a spindle kick / brake control signal from the system controller 60, and executes operations such as starting, stopping, acceleration, and deceleration of the spindle motor 2.

Various operations of the servo system and the recording / reproducing system as described above are controlled by a system controller 60 formed by a microcomputer.
The system controller 60 executes various processes according to commands from the AV system 120.

  For example, when a write command (write command) is issued from the AV system 120, the system controller 60 first moves the pickup 51 to the address to be written. Then, the ECC encoder / decoder 57 and the modulation / demodulation circuit 56 execute the encoding process as described above on the data transferred from the AV system 120 (for example, video data of various systems such as MPEG2 or audio data). Then, recording is executed by supplying the laser drive pulse from the reader / writer circuit 55 to the laser driver 63 as described above.

For example, when a read command for transferring certain data (such as MPEG2 video data) recorded on the disc 1 is supplied from the AV system 120, seek operation control is first performed for the instructed address. . That is, a command is issued to the servo circuit 61 to cause the pickup 51 to access the address specified by the seek command.
Thereafter, operation control necessary for transferring the data in the designated data section to the AV system 120 is performed. That is, data reading from the disk 1 is performed, decoding / buffering and the like in the reader / writer circuit 55, the modem circuit 56, and the ECC encoder / decoder 57 are executed, and the requested data is transferred.

  When recording / reproducing data using these phase change marks, the system controller 60 uses the ADIP addresses detected by the wobble circuit 58 and the address decoder 59 to control access and recording / reproducing operations.

In the example of FIG. 1, the optical disk apparatus connected to the AV system 120 is used. However, the optical disk apparatus of the present invention may be connected to, for example, a personal computer.
Furthermore, there may be a form that is not connected to other devices. In this case, an operation unit and a display unit are provided, and the configuration of the interface part for data input / output is different from that in FIG. That is, it is only necessary that recording and reproduction are performed in accordance with a user operation and a terminal unit for inputting / outputting various data is formed.
Of course, there are various other configuration examples. For example, an example of a reproduction-only device can be considered.

Next, FIG. 2 shows an example of a spherical aberration correction mechanism provided in the pickup 51 shown in FIG.
In FIG. 2, the configuration of the optical system in the pickup 51 is shown.
In FIG. 2, laser light output from a semiconductor laser (laser diode) 81 is converted into parallel light by a collimator lens 82, transmitted through a beam splitter 83, a movable lens 87 as a spherical aberration correction lens group, and a fixed lens 88. , And the disc 1 is irradiated from the objective lens 84. The spherical aberration correction lens groups 87 and 88 are called expanders. Since spherical aberration correction is performed by driving the movable lens 87, hereinafter, it may be expressed in particular as an expander 87.

  The reflected light from the disk 1 passes through the objective lens 84, the fixed lens 88, and the movable lens 87, is reflected by the beam splitter 83, and enters the detector 86 through the collimator lens (condensing lens 85).

In such an optical system, the objective lens 84 is supported by the biaxial mechanism 91 so as to be movable in the focus direction and the tracking direction, and focus servo and tracking servo operations are performed.
The spherical aberration correction lenses 87 and 88 have a function of defocusing the wavefront of the laser light. That is, the movable lens 87 can be moved in the J direction, which is the optical axis direction, by the actuator 90, and the object point of the objective lens 84 is adjusted by this movement.
In other words, the spherical aberration correction can be executed by performing the control for causing the actuator 90 to move back and forth.

In FIG. 2, the configuration corresponding to the case where spherical aberration correction is performed by a so-called expander is illustrated, but a configuration in which spherical aberration correction is performed using a liquid crystal panel can also be employed.
That is, in the liquid crystal panel inserted in the optical path from the semiconductor laser 81 to the objective lens 84, the diameter of the laser beam is varied to variably adjust the boundary between the laser beam transmitting region and the shielding region, thereby correcting spherical aberration. Is to do.
In this case, the liquid crystal driver that drives the liquid crystal panel is controlled to change the transmission region.

3 shows the internal configuration of the servo circuit 61 shown in FIG.
In FIG. 3, the focus error signal FE and the tracking error signal TE from the matrix circuit 54 shown in FIG. 1 are converted into digital data by the A / D converters 11 and 21, respectively, and input to the DSP 10 in the servo circuit 61. Is done.
The DSP 10 has functions as a focus servo calculation unit 12 and a tracking servo calculation unit 22.

The focus error signal FE from the A / D converter 11 is input to the focus servo calculation unit 12 via the adder 15.
The focus servo calculation unit 12 generates and outputs a focus servo signal by performing predetermined calculations such as filtering for phase compensation and loop gain processing on the focus error signal FE input as digital data. . The focus servo signal is converted into an analog signal by the D / A converter 13 (including PWM and PDM) and then input to the focus driver 14 to drive the focus actuator. That is, a current is applied to the focus coil of the biaxial mechanism 91 that holds the objective lens 84 in the optical pickup 51, and the focus servo operation is executed.

  The tracking servo calculation unit 22 performs predetermined calculations such as filtering for phase compensation and loop gain processing on the tracking error signal TE input as digital data, and generates and outputs a tracking servo signal. . The tracking servo signal is converted into an analog signal by the D / A converter 23 (including PWM and PDM), and then input to the tracking driver 24 to drive the tracking actuator. That is, a current is applied to the tracking coil of the biaxial mechanism 91 that holds the objective lens 84 in the optical pickup 51 to execute a tracking servo operation.

The DSP 10 is provided with functional parts for focus bias addition, spherical aberration correction value setting, and adjustment of the focus bias and spherical aberration correction value.
The adder 15 adds a focus bias to the focus error signal FE. The focus bias value to be added is set in the focus bias setting unit 16. The focus bias setting unit 16 outputs a focus bias value set in an adjustment process described later, whereby an appropriate focus bias is added to the focus servo loop.

The spherical aberration correction value setting unit 20 sets a spherical aberration correction value by a spherical aberration correction mechanism. The set spherical aberration correction value is converted into an analog signal by the D / A converter 25 and supplied to the spherical aberration correction driver 26.
For example, in the case of a spherical aberration correction mechanism as shown in FIG. 2, the spherical aberration correction driver 26 is a circuit that supplies a drive signal Sd to an actuator 90 that moves the expander 87. Alternatively, in the case of a spherical aberration correction mechanism using a liquid crystal panel, the circuit supplies a signal Sd for instructing the liquid crystal driver to apply a voltage to a required cell of the liquid crystal panel.
Accordingly, the spherical aberration correction driver 26 is configured to drive the spherical aberration correction mechanism in the pickup 51 based on the spherical aberration correction value supplied from the spherical aberration correction value setting unit 20.

The nonvolatile memory 18 stores an initial value as a focus bias value and a spherical aberration correction value, and further, an adjustment value obtained by adjusting a focus bias / spherical aberration correction value described later, that is, an optimum focus bias value and The spherical aberration correction value is stored.
The setting unit 17 sets the setting value in the focus bias setting unit 16 and the setting value in the spherical aberration correction value setting unit 20. For example, the setting value is set to a value stored in the nonvolatile memory 18 or each setting value is changed according to an instruction from the system controller 60.

  As described above, the operation related to the adjustment of the focus servo / spherical aberration correction value formed by the DSP 10 and the focus servo calculation unit 22 and the tracking servo calculation unit 22 is controlled by the system controller 60.

Here, in the embodiment, the focus bias and the spherical aberration correction value are adjusted to optimum values by the configuration of the optical disc apparatus described so far.
However, as described above, when trying to adjust the focus bias to the optimum value, for example, astigmatism occurs in the optical system only on the condition that the RF signal amplitude is maximized as in the prior art. In such a case, there is a possibility that an appropriate focus bias cannot be obtained.
That is, as described with reference to FIG. 7, when astigmatism occurs, the focus bias value that maximizes the RF signal amplitude and the focus bias value that maximizes the push-pull signal amplitude are obtained. Even if a focus bias that maximizes the RF signal amplitude is set, the push-pull signal amplitude does not become maximum, and even if a focus bias that maximizes the push-pull signal amplitude is set, the RF signal amplitude does not It will not be the maximum.
In this case, the push-pull signal amplitude is also a reference for determining whether or not an optimum value is obtained as the focus bias value, similarly to the RF signal amplitude. Therefore, as described above, the focus bias that maximizes the RF signal amplitude and the focus bias that maximizes the push-pull signal amplitude differ from each other. If the optical system has astigmatism, the RF signal amplitude and the push-pull It is highly possible that the focus bias obtained based on any one of the signal amplitudes is not the optimum focus bias.

Therefore, in the embodiment, the focus bias and the spherical aberration correction value are adjusted as shown in FIG.
In FIG. 4, in FIG. 4A, the vertical axis represents the focus bias and the horizontal axis represents the spherical aberration correction value, the contour of the RF signal amplitude is shown by the contour line. In FIG. The characteristics of the push-pull signal amplitude in the traverse state when the horizontal axis represents the axis and spherical aberration correction values are indicated by contour lines.

In the contour lines shown in these figures, it is shown that the smaller the value of the number given in the figures, the higher the amplitude level is obtained.
That is, as the RF signal amplitude characteristic shown in FIG. 4 (a), a characteristic in which the base spreads from the center to an approximately concentric circle of an ellipse is obtained.
Further, as the push-pull signal amplitude characteristic shown in FIG. 4B, the band-like area near the diagonal line is the highest level area as shown in the figure, and the skirt spreads from this area to both sides. It will be obtained.

In the embodiment, first, for the RF signal amplitude having the characteristics as shown in FIG. 4A, an operation for determining a set of a focus bias and a spherical aberration correction value that maximizes the RF signal amplitude is performed.
As the technique, the amplitude level of the RF signal obtained at each stage is detected while changing the focus bias value indicated by Y and the spherical aberration correction value indicated by X in FIG. . Then, a set of the focus bias and the spherical aberration correction value in which the detected RF signal amplitude is maximized is determined.

Specifically, first, in the optical disc apparatus, for example, the setting values of five stages for each of the focus bias value and the spherical aberration correction value are stored in the nonvolatile memory 18 shown in FIG.
Then, under the setting of the first stage value of the focus bias stored in this manner, the spherical aberration correction value is changed in five stages, and the amplitude level of the RF signal obtained in each stage is detected. Further, information on each of these RF signal amplitude levels is stored in association with the focus bias value and spherical aberration correction value set at that time.
By performing this operation in the same manner for the remaining four levels of the focus bias, a total of 25 types of amplitude levels of the RF signal are detected by changing the focus bias value and the spherical aberration correction value by five levels, respectively. Are stored in association with each value set in.

Then, based on the information stored by the above operation, a set of a focus bias value and a spherical aberration correction value when the highest RF signal amplitude is obtained is determined.
Hereinafter, the focus bias value calculated in this way is referred to as a focus bias value FBa. Similarly, the spherical aberration correction value is referred to as a spherical aberration correction value SAa.
FIG. 4A shows a state when the focus bias value and the spherical aberration correction value indicated by Y and X are the focus bias FBa and the spherical aberration correction value SAa thus determined, respectively. .

When the focus bias value FBa and the spherical aberration correction value SAa that maximize the RF signal amplitude are determined in this way, the focus bias is determined based on the push-pull signal amplitude.
First, in calculating the focus bias here, the spherical aberration correction value SAa calculated as described above is set in the spherical aberration correction value setting unit 20. That is, in this case, the spherical aberration correction value is fixed, and only the focus bias value is changed stepwise.
Also in this case, the setting value of the focus bias is changed, for example, by five steps. Then, the push-pull signal amplitude level in the traverse state obtained at each stage is detected while changing the setting value of the focus bias in this way.

Here, the push-pull signal in the traverse state referred to in the embodiment refers to a push-pull signal obtained in a state where at least the tracking servo is turned off and the disk 1 is rotationally driven.
Therefore, specifically, the above-described operation is as follows. When the setting value of the focus bias is changed stepwise while the tracking servo is turned off and the disk 1 is rotationally driven as described above, That is, the amplitude level of the obtained push-pull signal is detected.
Then, the information of the push-pull signal amplitude level obtained at each stage by such an operation is stored in association with each set value of the focus bias.
Then, the focus bias value at which the push-pull signal amplitude is maximized is determined based on the stored information.
The focus bias value calculated based on the push-pull signal amplitude is hereinafter referred to as a focus bias value FBb.
Also in this case, FIG. 4B shows a state when the focus bias indicated by Y in the figure is the focus bias value FBb.

After performing such an operation, for the spherical aberration correction value, the spherical aberration correction value SAa calculated based on the RF signal amplitude level as described above is used as the spherical aberration correction value at the time of recording / reproducing as it is. It is supposed to be set.
For one focus bias, a value calculated based on the focus bias value FBa and the focus bias FBb is set.
Specifically, the focus bias value FBa and the focus bias FBb are each weighted with a predetermined coefficient, and an average value thereof is calculated. That is,
(Focus bias FBa × coefficient α + focus bias FBb × coefficient β) / 2
Perform the calculation by.
The focus bias value FBc obtained by this calculation is set as the focus bias FBc during recording / reproduction.

In this manner, by setting the focus bias value FBc based on both the focus bias value FBa that maximizes the RF signal amplitude and the focus bias value FBb that maximizes the push-pull signal amplitude, Under conditions where astigmatism occurs, a more appropriate focus state can be obtained than when the focus bias is set based on only one of the RF signal amplitude and the push-pull signal amplitude, for example.
As a result, it is possible to suppress a decrease in recording / reproduction quality when astigmatism occurs.

  In this way, if the reduction in recording / reproduction quality can be suppressed even when astigmatism occurs, the tolerance for astigmatism can be increased, and the product yield can be increased accordingly. In addition, by improving the yield in this way, the cost of the product can be reduced.

In this case, depending on the linear density and track density of the disk 1, a more appropriate focus state can be obtained by setting a focus bias that maximizes the RF signal amplitude, or the push-pull signal amplitude is maximum. It has been found that the condition for optimizing the focus bias is different, for example, a more appropriate focus state can be obtained by setting the focus bias.
Therefore, the weighting ratio between the focus bias FBa and the focus bias FBb should be set differently according to the linear density and track density of the disc 1 (that is, for each media type of the disc 1).
According to the experiment, it has been obtained that a relatively appropriate focus state tends to be obtained when the focus bias FBb that maximizes the push-pull signal amplitude is emphasized. Based on this, in the embodiment, the weighting ratio is set so that at least the value of the coefficient β is equal to or greater than the value of the coefficient α.

Next, processing operations to be executed in order to realize the operation as the embodiment described above will be described with reference to the flowchart of FIG.
The processing operation shown in FIG. 5 is performed by the system controller 60 shown in FIG.
For convenience of explanation, FIG. 5 shows an operation when a rewritable disc that has been recorded as the disc 1 or a read-only disc is loaded.

First, in step S101 shown in the figure, signal reproduction is performed while changing the focus bias value and the spherical aberration correction value, and processing for storing information on the amplitude level of the RF signal obtained thereby is executed. .
As described above, for the nonvolatile memory 18 in the DSP 10 shown in FIG. 3, the focus bias value for adjustment and the spherical aberration correction value are prepared in advance in five stages in this case. Yes.
For these values, first, the setting unit 17 is controlled to cause the focus bias setting unit 16 to set the focus bias value as the first step stored in the nonvolatile memory 18. Then, under the setting of the focus bias, the setting unit 17 is controlled so that each spherical aberration correction value stored in the nonvolatile memory 18 is changed stepwise by the spherical aberration correction value setting unit 20. Execute the signal playback operation while setting. After that, the amplitude level of the RF signal obtained under the setting of each spherical aberration correction value is detected, and information on the amplitude level of these RF signals is obtained from the focus bias value and spherical aberration correction value set at that time. Store it in association.
By performing this operation in the same manner for the remaining four stages of the focus bias value, in this case, the RF signal amplitude obtained by setting the focus bias value × 5 and the spherical aberration correction value × 5 in total 25 ways. Stores level information.

In the subsequent step S102, a set of the focus bias value (FBa) and the spherical aberration correction value (SAa) when the RF signal amplitude becomes maximum is determined from the information stored in step S101.
In step S103, a process for holding the focus bias value FBa determined in this way is executed. For example, information on the focus bias value FBa may be stored in the nonvolatile memory 18 described above.

In step S104, the spherical aberration correction value SAa determined in step S101 is set.
That is, the setting unit 17 is controlled to set the spherical aberration correction value SAa.

In step S105, the amplitude level of the push-pull signal in the traverse state is detected while changing the focus bias value, and processing for storing information on the amplitude level of the push-pull signal is executed.
That is, first, the tracking servo calculation unit 22 is controlled to turn off the tracking servo, and the spindle circuit 62 is further controlled to rotate the disk 1 at a required rotational speed. Then, the setting unit 17 causes the focus bias setting unit 16 to set the first-stage focus bias value stored in the nonvolatile memory 18, and the amplitude level of the push-pull signal supplied from the matrix circuit 54 at this time is set. To detect. At the same time, the information of the push-pull signal amplitude level detected in this way is stored in association with the set focus bias value.
The focus bias setting / storing process operation is similarly performed for the remaining four stages of the focus bias value, and information on the push-pull signal amplitude level in the traverse state at each stage of the focus bias value is thereby obtained. obtain.

In step S106, the value of the focus bias value (FBb) at which the push-pull signal amplitude level is maximized is determined based on the information stored in step S105.
In step S107, a process for holding the calculated focus bias value FBb is executed. The focus bias value FBb may be stored in the nonvolatile memory 18, for example.

In the subsequent step S108, the focus bias value FBa and the focus bias value FBb are weighted by the coefficient α and the coefficient β, respectively, and a process for calculating an average value of these weighted values as the focus bias value FBc is executed.
In other words, as explained earlier,
(FBa · α + FBb · β) / 2
The focus bias value FBc is calculated by performing the above calculation.

Then, in step S109, a process for setting the focus bias value FBc and the spherical aberration correction value SAa as the focus bias value and the spherical aberration correction value at the time of recording and reproduction is executed.
That is, the setting unit 17 executes processing for causing the focus bias setting unit 16 to set the focus bias value FBc and causing the spherical aberration correction value setting unit 20 to set the spherical aberration correction value SAa.
As a result, the recording / reproducing operation for the disc 1 (of course, only the reproducing operation in the case of a reproduction-only disc) can be performed under the setting of the focus bias value FBc and the spherical aberration correction value SAa.

In FIG. 5, the operation has been described by taking the case where the disc 1 is a recorded writable disc or a read-only disc as an example. However, for an unrecorded writable disc, before the above processing, First, a process for performing a test writing operation is added. Then, the amplitude level of the RF signal may be detected for the signal written in this way.
Note that the laser power set when performing such trial writing may be based on a rough set value such as using an initial value stored in advance.

Various timings for executing the series of adjustment processes shown in FIG. 5 can be considered as follows.
First, of course, it is appropriate to execute it when the disc is loaded.
It is also conceivable to execute during playback, before and after seek, or after a predetermined time has elapsed, or according to the trace position (inner and outer periphery) on the disk.
For example, during reproduction, the data read from the disk 1 can be performed at a timing with sufficient margin for buffering.
In addition, the timing immediately before or after the seek is also suitable as the execution timing of the adjustment process.

Also, by adjusting according to the temperature state of the device (change in the focus bias optimum value due to the temperature characteristics of the device and actuator), aging, and the trace position (radius position) on the disk, adjustments corresponding to these circumstances State and can.
Therefore, even during the operation period with respect to the disk 1, the adjustment processing is executed regularly or irregularly, which is appropriate for stabilizing the operation of the apparatus. It is also conceivable that adjustment processing is performed using temperature change detection, reproduction data error rate / jitter deterioration, etc. as triggers.

By the way, as can be understood from the above description, in the embodiment, first, the focus bias value at which the RF signal amplitude is maximized is obtained as in the prior art.
Thus, when obtaining the optimum focus bias based on the RF signal amplitude, a signal with a longer mark length in the RF signal is less affected by astigmatism, and a signal with a shorter mark length is affected by astigmatism. It tends to be easy to receive.
In consideration of this, the focus bias value with which the optimum focus state can be obtained can be obtained with higher accuracy by using only the amplitude of the signal having a relatively long mark length in the RF signal as a reference.

This will be described with reference to FIG.
FIG. 6 shows a signal having a long mark length in the RF signal as a contour line of the RF signal amplitude characteristic when the vertical axis is the focus bias similar to FIG. 4A and the horizontal axis is the spherical aberration correction value. The characteristics when used as a reference are shown.
As shown in FIG. 6, when a signal having a long mark length in the RF signal is used as a reference, a characteristic in which the base spreads from the center to a substantially concentric circle can be obtained. In this case, as the mark length is longer, the contour line shape of such RF signal amplitude characteristics approaches a concentric circle.
On the other hand, when a signal with a short mark length is used as a reference, for example, it becomes an ellipse as shown in FIG. 4A, and the axis of this ellipse tends to have an inclination.

Here, generally, the closer the shape of the contour line is to a concentric circle, the more accurately the optimum focus bias value and spherical aberration correction value can be obtained.
That is, in the case of an ellipse as shown in FIG. 4A and the axis thereof being inclined, the focus bias value at which the RF signal amplitude becomes maximum also changes as the spherical aberration correction setting value changes. However, if it is concentric, the focus bias and the spherical aberration correction value that maximize the RF signal amplitude can be obtained independently regardless of changes in the respective values. This is because the accuracy for obtaining the value is improved.
For this reason, it can be understood that the detection accuracy of the optimum value is improved when the amplitude of the signal having a long mark length in which the contour line shape approaches a concentric circle is used as a reference.

  Based on the above idea, in the embodiment, a signal having a short mark length such as 2T or 3T is not used in determining the optimum value based on the RF signal amplitude. In other words, the optimum value is obtained based only on the amplitude of the signal that is assumed to have a long mark length obtained in the RF signal. Specifically, for example, it is based only on the amplitude of a signal with a mark length of 5T.

In this way, in order to selectively acquire only the amplitude of a signal having a specific mark length in the RF signal, the following method can be employed.
First, information on the zero-crossing interval of the RF signal assumed for a signal having a predetermined mark length from which the amplitude level is acquired is stored in advance. Then, based on the information of the zero cross interval, the signal of the predetermined mark length is detected from the signal of each mark length obtained in the RF signal. In addition, the amplitude level of the signal thus detected may be acquired.
Alternatively, it is possible to improve the accuracy by acquiring a large number of signal amplitude levels with the predetermined mark length and taking the average value thereof.

  By the way, in the embodiment described so far, the adjustment focus bias value and the spherical aberration correction value for obtaining the optimum value are prepared in five stages, but this is only an example. However, the number is not particularly limited.

  In the embodiment, the tracking servo is only turned off to detect the push-pull signal amplitude in the traverse state. However, the tracking voltage is further applied so that the track is more reliably traversed. May be.

  Further, as the spherical aberration correction mechanism, in addition to the beam expander and the liquid crystal element exemplified in the embodiment, a mechanism using another method such as a mechanism using a deforming mirror can be configured.

It is the block diagram shown about the internal structure of the optical disk apparatus as embodiment in this invention. It is the figure illustrated about the structure of the spherical aberration correction mechanism with which the optical disk apparatus of embodiment is provided. It is the block diagram shown about the internal structure of the servo circuit with which the optical disk apparatus of embodiment is provided. FIG. 4 is a characteristic diagram showing contours of an RF signal amplitude characteristic and a push-pull signal amplitude characteristic (during traverse) with respect to a focus bias and a spherical aberration correction value. It is the flowchart shown about the processing operation which should be performed in order to implement | achieve focus bias and spherical aberration correction value adjustment operation | movement as embodiment. FIG. 5 is a characteristic diagram showing contours of amplitude characteristics of a signal having a particularly long mark length as RF signal amplitude characteristics with respect to a focus bias and a spherical aberration correction value. FIG. 5 is a characteristic diagram showing a relationship between a focus bias at which the RF signal amplitude is maximum and a focus bias at which the spherical aberration correction value is maximum, with the astigmatism amount as a reference.

Explanation of symbols

  1 disk, 10 DSP, 11, 21 A / D converter, 12 focus servo calculation unit, 13, 23, 25 D / A converter, 14 focus driver, 15 adder, 16 focus bias setting unit, 17 setting unit, 18 non-volatile memory, 20 spherical aberration correction value setting unit, 22 tracking servo calculation unit, 24 tracking driver, 26 spherical aberration correction driver, 51 pickup, 52 spindle motor, 53 thread mechanism, 54 matrix circuit, 55 reader / writer circuit, 56 modulation / demodulation circuit, 57 ECC encoder / decoder, 58 wobble circuit, 59 address decoder, 60 system controller, 61 servo circuit, 62 spindle servo circuit, 63 laser driver, 87 expander, 120 AV system

Claims (4)

A rotation driving means for rotating the optical disk recording medium;
At least for reading data, the optical disk recording medium is irradiated with laser and reflected light is detected, and the laser beam focus servo mechanism, tracking servo mechanism, and head means having a spherical aberration correction mechanism,
RF signal generating means for generating an RF signal from a signal based on reflected light obtained by the head means;
Push-pull signal generating means for generating a push-pull signal from a signal based on reflected light obtained by the head means;
Focus servo means for driving the focus servo mechanism based on a focus error signal generated as a signal based on reflected light obtained by the head means to execute focus servo;
Tracking servo means for driving the tracking servo mechanism and executing tracking servo based on a tracking error signal generated as a signal based on reflected light obtained by the head means;
Spherical aberration correction means for performing spherical aberration correction by driving the spherical aberration correction mechanism based on the spherical aberration correction value;
A focus bias means for adding a focus bias to a focus loop including the focus servo means, and
The RF signal obtained by the RF signal generation means based on the result of data reproduction while changing both the focus bias set in the focus bias means and the spherical aberration correction value set in the spherical aberration correction means A first indexing process for determining a set of a focus bias and a spherical aberration correction value in which the amplitude value of
With the spherical aberration correction value determined by the first indexing process set in the spherical aberration correction means, at least the tracking servo by the tracking servo means is turned off, and the focus bias set in the focus bias means is set. When the optical disk recording medium is rotationally driven by the rotational driving means while being changed stepwise, a second focus bias is obtained that maximizes the amplitude value of the push-pull signal obtained by the push-pull signal generating means. Indexing process,
The optimum focus bias value is calculated by performing a required calculation process based on the focus bias determined by the first indexing process and the focus bias determined by the second indexing process. Calculation process,
Setting for performing control so as to set the focus bias based on the value calculated by the calculation process and the spherical aberration correction value calculated by the first index process to the focus bias unit and the spherical aberration correction unit. Control processing,
Comprising control means configured to perform
An optical disc device characterized by the above. In the first indexing process in the control means,
One of the focus bias set in the focus bias means and the spherical aberration correction value set in the spherical aberration correction means is changed stepwise, and data reproduction is performed while changing the other stepwise in each step. To be
The optical disk apparatus according to claim 1, wherein In the calculation process in the control means,
The focus bias calculated by the first indexing process and the focus bias determined by the second indexing process are respectively weighted by necessary coefficients, and an average value thereof is calculated.
The optical disc apparatus according to claim 1, wherein: As a method for adjusting a focus bias and a spherical aberration correction value in an optical disc apparatus capable of reproducing at least a signal on an optical disk recording medium and variably setting a focus bias and a spherical aberration correction value,
A first indexing procedure for determining a set of the focus bias and the spherical aberration correction value having the maximum amplitude value of the RF signal based on the result of the data reproduction while changing both the focus bias and the spherical aberration correction value; ,
Obtained when the optical disk recording medium is driven to rotate while at least the tracking servo is turned off and the focus bias is changed stepwise with the spherical aberration correction value determined by the first indexing procedure set. A second indexing procedure for determining the focus bias with the maximum amplitude value of the push-pull signal;
The optimum focus bias value is calculated by performing a required calculation process based on the focus bias determined by the first indexing procedure and the focus bias determined by the second indexing procedure. Calculation procedure,
A setting control procedure for performing control so as to set the focus bias based on the value calculated by the calculation procedure and the spherical aberration correction value calculated by the first indexing procedure;
A method for adjusting a focus bias and a spherical aberration correction value, comprising:

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