JP4300906B2 - Optical disk servo offset correction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a servo offset correction method suitably used for an electric / electronic device having a servo control function, and more particularly to a servo offset correction method for an optical disc apparatus.
[0002]
[Prior art]
In general, servo (automatic control) is a control method in which negative feedback is performed so that an error signal representing a difference between a control target amount and a target value is zero in order to keep the control target amount at a target value. However, in actual servo control, an error signal is offset by a change in the environment of the circuit and detection system (change in power supply voltage, temperature, etc.), so the control target is controlled to a target value to which an unintended offset is added. .
[0003]
As a conventional technique for solving the above problem, a means for detecting the environmental change is prepared separately. When the specified environmental change is exceeded, the servo control is temporarily suspended (servo loop is opened), and the error signal A method for statically correcting the offset is known.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-208247
[Problems to be solved by the invention]
However, in the above-described conventional offset correction method, it is necessary to interrupt servo control. Therefore, in a servo offset correction method (for example, tracking servo during recording in an optical disk drive device) that requires continuous servo application. Trouble occurs.
[0006]
In the present invention, by calculating the offset change amount of the servo error signal with reference to the inflection point of the servo error signal, the dynamic offset correction is performed without interrupting the servo control (with the servo loop closed). An object of the present invention is to provide a servo offset correction method. It is another object of the present invention to apply the offset correction method to an optical disk drive device, and in particular to prevent a tracking servo from shifting during recording.
[0007]
[Means for Solving the Problems]
Accordingly, the present invention has been made to solve the above-described problem. Light is emitted from a light source to an optical disc, and tracking control of a beam spot on the optical disc is performed in a radial direction of the optical disc from a first position currently being tracked. The gain of the first tracking error signal is measured at a second position shifted by a predetermined amount toward the inner peripheral side of the optical disc on one side , and a predetermined amount is applied to the outer peripheral side of the optical disc in the other direction in the radial direction of the optical disc. The gain of the second tracking error signal is measured at the shifted third position, the gain of the first tracking error signal is compared with the gain of the second tracking error signal, and the gain of the first tracking error signal is If larger, bi on the inner peripheral side of the first of said optical disc is the second position side of a position Correcting the position of the beam spot, wherein when the gain of the second tracking error signal is large, correct the position of the beam spot on the outer peripheral side of the first of said optical disk is the third position side than the position This is a method for correcting the servo offset of an optical disc.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, light is emitted from the light source to the optical disc, and the tracking control of the beam spot on the optical disc is one side in the radial direction of the optical disc from the first position where tracking is currently being performed. The gain of the first tracking error signal is measured at a second position shifted by a predetermined amount toward the inner peripheral side of the optical disc, and a third shifted by a predetermined amount toward the outer peripheral side of the optical disc, which is the other direction in the radial direction of the optical disc . When the gain of the second tracking error signal is measured, the gain of the first tracking error signal is compared with the gain of the second tracking error signal. , complement the position of the beam spot on the inner peripheral side of the first of said optical disc is the second position side of a position And, when the gain of the second tracking error signal is large, and correcting the position of the beam spot on the outer peripheral side of the first of said optical disk is the third position side than the position A servo offset correction method for an optical disk, which has an effect of dynamically performing offset correction without interrupting servo control. Furthermore, a write error during recording can be prevented and recording characteristics can be improved.
[0014]
(Embodiment 1)
FIG. 1 is a schematic block diagram showing the configuration of the optical disk drive apparatus of the present invention. In FIG. 1, reference numeral 1 denotes an optical disc capable of recording information or data by light, and has at least a substrate, a recording layer provided on a part or the entire surface of the substrate, and a protective material provided on the recording layer. is doing. As the optical disc 1, for example, an optical disc capable of recording information such as a DVD-R disc, a DVD-RW disc, a DVD-RAM disc, a CD-R disc, and a CD-RW disc is preferably used.
[0015]
The optical disc 1 is provided with a spiral groove (not shown) between the inner periphery and the outer periphery, and this groove becomes a track. Data is recorded on this track in units of error correction units, for example, in the form of pits. Further, the outer portion of the track has a meandering shape called a wobble with a constant length period, and is extracted as a clock signal for rotation control, for example. In addition, information and address information of various optical disc manufacturers called LPP are embedded in land portions (protruding portions) between a pair of adjacent tracks, and LPP is also used as a reference signal during recording. .
[0016]
This optical disk 1 is mounted on a spindle motor 4 and is driven to rotate. During recording, CLV rotation control with a constant linear velocity is performed based on a wobble signal period that is a meandering component read by the optical pick 2. At the time of reproduction, rotation control is performed at a constant angular velocity based on CLV control or an FG signal (rotation information from the encoder of the spindle motor 4) which is rotation cycle information of the spindle motor 4. The optical pick 2 is equipped with a light emission source (not shown), and for example, a laser diode is preferably used as the light emission source. The light emitted from the light source is transmitted or reflected by various optical components, and finally the light spot collected by the objective lens 3 is irradiated onto the optical disc 1. Further, the light reflected by the optical disc 1 is transmitted or reflected through various optical components via the objective lens 3, enters a light receiving means (not shown) mounted on the optical pick 2, and enters the light receiving means. The light is converted into an electric signal by a photo detector or the like, and the electric signal is demodulated into data usable by servo control or a computer.
[0017]
The optical pick 2 is attached to a device that is movably attached to a feed mechanism (not shown) so as to be movable between the inner periphery and the outer periphery of the optical disc 1. The objective lens 3 is supported by an actuator (not shown) and can be moved by driving in the tracking and focusing directions.
[0018]
Based on the focus and tracking error signals, the optical spot is controlled by a control means to be described later so that the light spot accurately follows the track with respect to the surface shake and eccentricity component of the optical disk 1.
[0019]
For recording data on the optical disk 1, the optical disk controller 11 receives a recording command and received data corresponding to information to be recorded on the optical disk 1 from the host via the interface 13. The optical disk controller 11 performs 8-16 conversion on the received data and modulates the data to be recorded. Then, the laser driver 5 is driven in accordance with the recording data string to supply current to a light emitting source which is a laser diode mounted on the optical pick 2, and the light emitting source emits pulses by the driving current. The optical disk 1 is irradiated with light through the objective lens 3 through optical components, and data is recorded on the track of the optical disk 1 in the form of pits, for example.
[0020]
On the other hand, data reproduction processing is performed as follows. The light source of the optical pick 2 emits light, and the optical disk 1 is irradiated with light through various optical components and through the objective lens 3. At this time, as a matter of course, the objective lens 3 is irradiated with light that is weaker than the light intensity during recording. Reflected light from the optical disc 1 passes through the objective lens 3 and is taken into the optical pick 2 and enters a light receiving means provided in the optical pick 2 through various optical components. The light incident on the light receiving means is guided to a photodetector which is built in the light receiving means and divided into a plurality of parts. The photodetector divided into a plurality outputs an electrical signal corresponding to the intensity of light and the area to be irradiated. The electric signal is amplified by the head amplifier circuit 6 and current-voltage conversion of the electric signal is performed. The converted electric signal is passed through an RF analog reproduction circuit 9 having an AGC, a filter, an equalizer correction circuit, and the like. After that, the electric signal is transmitted to the optical disc controller 11. Then, the electric signal is binarized in the optical disk controller 11 and converted into a predetermined data string, and the data string is converted into transmission data through decoding means having an 8-16 demodulating circuit and an error correcting circuit, and the transmission is performed. Data is transmitted to the host via the interface 13.
[0021]
Next, servo control using a focus error signal and a tracking error signal will be described.
[0022]
The light source of the optical pick 2 emits light, and the optical disk 1 is irradiated with light through various optical components and through the objective lens 3. Reflected light from the optical disc 1 passes through the objective lens 3 and is taken into the optical pick 2 and enters a light receiving means provided in the optical pick 2 through various optical components. The light incident on the light receiving means is guided to a photodetector which is built in the light receiving means and divided into a plurality of parts. The photodetector divided into a plurality outputs an electrical signal corresponding to the intensity of light and the area to be irradiated. The electric signal is amplified by the head amplifier circuit 6, current-voltage conversion of the electric signal is performed, and further, the offset of the circuit is applied to the electric signal subjected to voltage conversion. The signal is sent to the D conversion circuit 8, the electric signal is sampled by the A / D conversion circuit 8, converted into a digital signal, and sent to the DSP 15. The DSP 15 performs arithmetic processing for generating a tracking error signal and a focus error signal based on these digital signals. The tracking or focus error signal is subjected to predetermined processing by a filter and phase compensation processing means provided in the DSP 15 to be converted into a PWM signal having a different pulse width, and the PWM signal as the drive signal is converted into the DSP 15. Is sent to the actuator drive circuit 7 to drive at least the objective lens 3 in the tracking and focusing directions, and servo control is performed so that each error signal becomes substantially zero. In the present embodiment, a push-pull method is used as a tracking error signal generation unit.
[0023]
In the wobble / LPP reproduction circuit 10, the wobble signal and the LPP pulse signal are extracted by the electric signal sent from the head amplifier circuit 6. The LPP pulse signal output from the wobble / LPP reproduction circuit 10 is sent to the optical disc controller 11, and the optical disc controller 11 demodulates the LPP pulse signal and converts it into LPP data. The LPP data is sent to the microcomputer 12, Identify the optimum parameters for recording, disc manufacturer, and disc type. Then, in order to perform recording with higher accuracy, the microcomputer 12 reads parameters related to recording corresponding to the disk information from the memory 14 and records data.
[0024]
The dynamic tracking offset correction method that is the gist of the present invention will be described below with reference to FIGS.
[0025]
First, the nature of the tracking error signal in the optical disc apparatus will be described. FIG. 2 shows a track groove of an optical disk and a corresponding tracking error signal. The recording optical disc 1 is physically grooved in advance as a track position index, and the tracking signal is generated by utilizing the interference of the laser beam by this groove (push-pull method). The reflected light from the optical disk 1 is converted into an electric signal by the light receiving means, amplified and calculated by the head amplifier circuit 6 or the DSP 15, and becomes a tracking error signal. As shown by the solid line waveform 201, the zero-cross position of the tracking error signal is the center of the land or groove. That is, the zero cross position P1 shown in FIG. 2 indicates the center of the groove, and the zero cross position P2 indicates the center of the land. Accordingly, the laser spot can be made to follow the center of the track by applying servo so that the tracking error signal becomes zero.
[0026]
If the tracking error signal has an offset due to the heat of the light source or the fluctuation of the power supply voltage of the circuit as shown by the dotted line waveform 202 shown in FIG. 2, the zero cross position (position where the tracking error signal is 0) shifts from the track center. An off-track state is entered (the spot position is shifted from the track center). Specifically, referring to FIG. 2, the zero-cross position of the solid line waveform 201 where no offset occurs coincides with the groove center as shown by the solid line L1, but the zero-cross position of the dotted line waveform 202 where the offset occurs due to various circumstances. Does not coincide with the groove center as indicated by the dotted line L2.
[0027]
As described above, when an offset is added to the tracking error signal due to various circumstances, the data reading performance is deteriorated at the time of data reproduction, the recording quality is deteriorated at the time of data recording, and the write error due to the track deviation occurs at the worst.
[0028]
During data reproduction, even if off-tracking occurs and data reading becomes difficult, the servo loop is opened (that is, servo control is not performed), and offset correction is performed so that the DC level of the tracking error signal becomes zero. Retry processing is possible (hereinafter abbreviated as static offset correction). However, if a plurality of static offset corrections are performed, the data transfer rate decreases, and it becomes difficult to maintain a prescribed reproduction rate. On the other hand, at the time of data recording, it is necessary to continuously record data from the viewpoint of data continuity, recording quality uniformity, etc., and the servo loop cannot be opened until a predetermined amount of data recording is completed (DVD The servo control cannot be turned off for about 1 hour in full-surface recording at -R standard speed), and the above-described static offset correction cannot be executed.
[0029]
It should be noted that the tracking error signal is sinusoidal (in the case of push-pull) as shown in FIG. The inflection point of the sine wave is the zero cross position (for example, P1 and P2 shown in FIG. 2). Therefore, the tracking servo gain becomes maximum when the tracking servo is applied to the track center (zero cross position). That is, in the case where the servo is applied in the state of the solid line waveform 201 in FIG. 2 and the case where the servo is applied in the state of the dotted line waveform 202, the servo is applied when the servo is applied in the state of the solid line waveform 201. Gain increases. Therefore, the spot position is offset by a predetermined amount to the inner or outer peripheral side of the optical disc 1, and a servo signal is measured by adding a disturbance signal at the offset position, and this time, a predetermined amount is offset to the opposite side. By measuring the servo gain and correcting the offset of the tracking error signal in the direction in which the servo gain is large (inner side or outer side), information can be recorded or reproduced at the center side of the track.
[0030]
As apparent from the above, it is possible to keep the laser spot at the center of the track by correcting the offset of the tracking error signal so as to maximize the servo gain. What is important is that the servo gain measurement can be performed with the servo loop closed. That is, the greatest feature of the present invention is that offset correction can be performed with the servo loop closed, and dynamic offset correction can be realized even in a situation where the servo cannot be turned off, such as during recording. .
[0031]
Next, a specific configuration of the servo block will be described. In FIG. 3, reference numeral 301 denotes an error signal detector that detects an error between the set control target value and the control target amount. Reference numeral 302 denotes an offset adder that adds an arbitrarily settable offset to the error signal output from the error signal detector 301. A disturbance injection unit 303 adds a disturbance, that is, a periodic signal (in general, a single frequency sine wave is preferable) to the servo signal. The servo gain can be calculated from the disturbance signal level before and after the disturbance addition by the disturbance injection unit 303. The disturbance injection unit 303 may be inserted anywhere in the servo loop. Reference numeral 304 collectively represents transfer functions, and expresses all transfer functions including a detection system, a drive system, and phase compensation. Among them, the error signal detection unit 301 and the transfer function 304 are provided in all servo systems, and feedback is applied so that the control target amount follows the target value if the gain of the transfer function 304 is sufficiently large. In the case of the present embodiment, the offset addition unit 302 and the disturbance injection unit 303 are stored in the DSP 15, but may be provided by other means.
[0032]
Hereinafter, a specific algorithm of the offset correction method will be described with reference to FIG. 3 described above, the flowchart of FIG. 4, and the transition graph of the offset addition amount of FIG. 5.
[0033]
First, the offset is changed in the plus direction from the current position using the offset adding unit 302. The offset amount may be about 1/16 to 1/7 (preferably about 1/10) of the tracking error amplitude. At this time, the laser spot is slightly deviated from the track center. However, the off-track amount in the above range does not affect the recording and reproducing performance. In this state, a servo signal is measured by injecting a sinusoidal disturbance signal of several kHz (0.8 kHz to 7 kHz) from the disturbance injection unit 303. The gain measurement takes about one turn of the disk, but if the disturbance amplitude is made sufficiently small, the influence on the recording / reproducing performance can be ignored (401, 501). Next, the offset is changed in the minus direction, and the servo gain is measured in the same manner as 401 (402, 502). Here, the servo gains obtained at 401 and 402 are compared (403). If the gain obtained by changing the offset to the plus side is larger, the offset correction amount is set to the plus side. Let it be the side. This offset correction amount is preferably suppressed to about 1/160 to 1/70 of the tracking error amplitude in order to round off the gain measurement variation due to the disk groove shape or the like (404, 405). Finally, the offset correction amount calculated by the offset adding unit 302 is added (406). In the next offset correction, the offset amount 406 is used as a reference. It is sufficient that the offset correction is performed every several seconds (0.1 to 600 seconds: more preferably 0.8 to 1.3 seconds). As is obvious, the order of the offset plus direction (401) and minus direction (402) may be reversed.
[0034]
By repeating the above operation periodically or at random timing, the laser spot always traces the track center. Note that, during recording of an overwritable medium such as a DVD-RW, if the above gain measurement is always performed on the same track, the measurement error tends to increase. Therefore, it is desirable to perform offset correction at random intervals. As a random number generation method, for example, a method in which several bits of a time counter value in a microcomputer are extracted and squared is known.
[0035]
Since this offset correction method is performed with the servo loop closed, it can be operated at all times regardless of whether recording or reproduction is in progress.
[0036]
(Embodiment 2)
The servo error signal dynamic offset correction method according to the present invention can be applied not only to an optical disc apparatus but also to all servo apparatuses. However, the servo error signal to be used must have at least one inflection point (the above-mentioned tracking error signal has an inflection point at the zero cross point).
[0037]
Hereinafter, a specific method of applying the offset correction method of the present invention to general servo control will be described.
[0038]
An error signal curve having an inflection point is shown in FIG. 601 is an error amount-error signal curve with an error signal offset of 0, 602 is an error amount-error signal curve with an error signal offset of Δx, 603 is a servo gain-error signal curve with an error signal offset of 0, and 604 is an error signal offset. Represents a servo gain-error signal curve of Δx. The inflection points of the error amount-error signal curves 601 and 602 and the maximum (or minimum) of the servo gain-error signal curves 603 and 604 coincide with each other. As described above, since the feedback is applied so that the error signal becomes 0 when the servo loop is closed, the servo with the error amount 0 is applied when the error signal offset is 0, and the error amount y2 is applied when the error signal offset Δx.
[0039]
Next, a specific offset correction method will be described with reference to FIG. 3 and FIG. First, static offset correction of the error signal is performed so that the error signal offset becomes 0 when the error amount is 0 in the servo-off state (state of the error amount-error signal curve 601). If the servo is off, offset correction can be easily performed. Subsequently, the offset of the offset adding unit 302 is changed, the error amount-error signal curve 601 is measured, and the inflection point offset x0 is detected. From here, the servo is turned on and servo control is started. When the servo is turned on, the servo gain-error signal curve 604 is measured by the disturbance injection unit 303 while the offset is changed stepwise by the offset addition unit 302, and the error amount-error signal is determined from the maximum (or minimum) of the obtained servo gain. An inflection point offset x1 of the curve 602 is detected. Since the offset change amount can be obtained from x1−x0 = Δx, offset correction is performed so as to make this 0. It is not necessary to perform the offset correction as long as the amount of change in the offset is acceptable.
[0040]
【The invention's effect】
As described above, according to the present invention, the present invention obtains an inflection point of a servo error signal using the fact that the servo gain becomes maximum or minimum at the inflection point, and the servo is based on the obtained inflection point. Control for calculating the offset change amount of the error signal is added. According to the present invention, it is possible to perform dynamic offset correction without interrupting servo control (with the servo loop closed).
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical disk apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram showing a track groove and a tracking error signal corresponding to the first embodiment of the present invention. FIG. 4 is a block diagram showing a servo unit according to the first embodiment. FIG. 4 is a flowchart of an offset correction method according to the first embodiment of the invention. FIG. 5 is a graph showing a transition of the offset addition amount according to the first embodiment. The figure which shows the error signal curve with the inflection point of Embodiment 2 of this invention
DESCRIPTION OF SYMBOLS 1 Optical disk 2 Optical pick 3 Objective lens 4 Spindle motor 5 Laser driver 6 Head amplifier circuit 7 Actuator drive circuit 8 A / D conversion circuit 9 RF system analog reproduction circuit 10 Wobble / LPP reproduction circuit 11 Optical disk controller 12 Microcomputer 13 Interface 14 Memory 15 DSP
201 Solid line waveform 202 Dotted line waveform 301 Error signal detection unit 302 Offset addition unit 303 Disturbance injection unit 304 Transfer function 601 Error amount-error signal curve 602 Error amount-error signal curve 603 Servo gain-error signal curve 604 Servo gain-error signal curve

Claims (1)

Light is emitted from the light source to the optical disc,
The first tracking error at a second position in which the tracking control of the beam spot on the optical disk is shifted by a predetermined amount from the first position currently being tracked to the inner peripheral side of the optical disk, which is one side in the radial direction of the optical disk. Measure the gain of the signal,
Measuring the gain of the second tracking error signal at a third position shifted by a predetermined amount toward the outer peripheral side of the optical disc, which is the other direction in the radial direction of the optical disc ;
Comparing the gain of the first tracking error signal and the gain of the second tracking error signal;
When the gain of the first tracking error signal is large, the position of the beam spot is corrected on the inner peripheral side of the optical disc, which is the second position side than the first position,
When the gain of the second tracking error signal is large, the position of the beam spot is corrected to the outer peripheral side of the optical disk, which is the third position side than the first position. Servo offset correction method.

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