JP2007220207A - Optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device permitting to attain high precision tracking servo without strictly limiting allowable eccentricity. <P>SOLUTION: A coarse adjusting servo part 21 detects a tracking error signal envelope obtained on the border of a mirror part (unrecorded area) and a signal part (recorded area) of an optical disk, and after performing firstly coarse tracking servo using the signals as servo signals and memorizing the servo signals by one round, the servo part 21 makes feed forward control according to the memory values. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus for recording data on an optical disc and / or reproducing data recorded on an optical disc, and more particularly to a beam spot formed on a disc by a laser beam (beam) applied to the optical disc from an optical head or a pickup. The present invention relates to an optical disc apparatus that performs tracking servo control for performing on-track control at the center of each track.

  As a conventional optical disk tracking method, a three-spot method, a push-pull method, or the like is known. In either case, a tracking error signal is generated from the return light when the beam traces the pit, and tracking is performed by feedback servo.

  According to this method, since tracking is performed by the feedback servo, the DC gain required for the tracking servo increases when the eccentricity is large. Therefore, the allowable eccentricity is determined by the tracking servo specification. For example, ± 70μm for compact disc (CD), ± 50μm for digital versatile disc (DVD), and ± 25μm for Blu-ray disc (registered trademark). The amount is getting smaller.

  That is, the track interval P becomes narrower due to the increase in capacity, while the DC gain G is finite and the tracking residual error ε becomes smaller due to the servo bandwidth problem (for example, 3 to 5% of the track interval P) Therefore, the allowable eccentricity E is limited. In other words, from ε = E / G, to achieve the desired ε, the allowable eccentricity E must be suppressed.

  Incidentally, a disk recording / reproducing apparatus intended to enable stable writing and erasing in the entire area of the disk is described in Patent Document 1 below. This disk recording / reproducing apparatus has a tracking servo circuit that applies tracking servo to the disk and performs a reading operation and a writing operation for each track. The eccentricity signal of the remaining disk is obtained, the eccentricity signal is stored, and the stored eccentricity signal is aligned with the tracking error signal of the tracking servo circuit during the next writing operation. I try to add it.

Japanese Patent Laid-Open No. 10-275353

  By the way, since the optical disk is required to have removable properties, the amount of eccentricity tends to be large, and there is a limit to strictly limit the allowable amount of eccentricity.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical disc apparatus capable of realizing a highly accurate tracking servo without severely limiting the allowable eccentricity.

  In order to solve the above problems, an optical disk apparatus according to the present invention irradiates laser light from an objective lens onto an optical disk in an optical disk apparatus that records data on an optical disk and / or reproduces data recorded on the optical disk. An optical pickup for detecting the amount of the reflected light, and a beam spot formed on the disk by the laser beam emitted from the optical pickup to the optical disk is on-tracked at the center of each track in the disk radial direction. A tracking servo unit that controls the position via an actuator, and the tracking servo unit detects an envelope of the tracking error signal obtained at the boundary between the mirror unit and the signal unit on the optical disc and servos the signal. First, perform coarse tracking servo as a signal In addition, after storing the servo signal for one round, the coarse adjustment servo unit that performs feedforward control with the memory value, and the fine adjustment that finely adjusts the lens actuator by feedback control after the feedforward control by the coarse adjustment servo unit. And an adjustment servo unit.

  This optical disc apparatus is used for tracking servo control, in addition to the feedback servo by the servo error signal by the signal from the conventional recording area, the feed performed by the tracking error signal obtained at the boundary between the recording part and the non-recording part. Use the forward servo together.

  The optical disk apparatus according to the present invention can trace a beam spot at the center of each track at any radius, improving the reproduction signal quality and obtaining a stable reproduction signal.

  The best mode for carrying out the present invention will be described below with reference to the drawings. This embodiment is an optical disk reproducing apparatus that reproduces data recorded on an optical disk, and in particular, a laser beam emitted from the optical pickup to the optical disk is set to be on-track at the center of each track. This is an optical disk reproducing device characterized by tracking servo control. This tracking servo control can also be applied to an optical disk recording apparatus that records data on an optical disk. Of course, the present invention can also be applied to an optical disc recording / reproducing apparatus.

  FIG. 1 is a configuration diagram of an optical disk reproducing apparatus. In FIG. 1, the optical disk reproducing apparatus drives the spindle motor 12 to rotationally drive the optical disk 18 so that the linear velocity is constant. In this state, the optical pickup 20 is driven to reproduce desired information. First, the optical pickup 20 drives the laser diode 4 based on the drive signal output from the driver, and converts the light beam L1 output from the laser diode 4 into parallel rays by the lens 3. Further, it is guided to the objective lens 1 through the beam splitter 2, and the light beam L 1 is condensed and irradiated onto the disk 8 by the objective lens 1.

  The optical pickup 20 receives the reflected light L2 of the irradiated light beam L1 with the objective lens 1, reflects the reflected light L2 with the beam splitter 2, enters the cylindrical lens 5, and condenses the emitted light on the light receiving element 6. The light receiving element 6 divides the light receiving surface into, for example, two parts in the radial direction of the disk 18 and further divides the light receiving surface into, for example, two parts in a direction perpendicular to the dividing direction, and is obtained from each of the divided light receiving surfaces A to D. The received light signal is supplied to the matrix circuit 7 through the amplifier circuit.

The matrix circuit 7 obtains the addition signals (SA + SC) and (SB + SD) between the light receiving surfaces arranged in the diagonal direction with respect to the light reception signals SA to SD, and the subtraction circuit calculates the difference between the addition signal (SA + SC) and the addition signal (SB + SD). To generate a focus error signal FE. That is, FE = (SA + SC) − (SB + SD) (1)
It becomes. The focus actuator 10 is driven by a focus servo circuit 8 so that the signal level of the focus error signal FE becomes zero, and focus control is performed.

  Further, the matrix circuit 7 generates a tracking position target value (for fine adjustment) under the control of the controller 18 in order to use a tracking error signal TE-1 for fine adjustment, which will be described later, in the tracking servo circuit 9. Supply to circuit 9.

  Further, the matrix circuit 7 generates an eccentricity signal and supplies it to the tracking servo circuit 9 in order to use the tracking error signal TE-2 for coarse adjustment described later in the tracking servo circuit 9.

  Then, a signal (SA + SB + SC + SD) obtained by adding the light reception signals SA to SD of the respective light receiving surfaces divided into four by the matrix circuit 7 is obtained as an RF signal, which is supplied to the signal processing circuit 15 and also to the PLL circuit 14. In the PLL circuit 14, a clock is reproduced from the supplied RF signal, and the reproduced clock is supplied to the spindle servo circuit 13. Based on this reproduction clock, the spindle servo circuit 13 controls the spindle motor 12.

  Further, in the signal processing circuit 15, for example, an EFM (Eight Fourteen Modulation) modulated RF signal is demodulated by a demodulator, and error correction is performed by a CIRC (Cross Interleave Reed Solomon Code) decoder. The data is sent from the interface circuit 16 to, for example, a host computer.

  FIG. 2 shows a schematic configuration of the tracking servo circuit 9. The tracking servo circuit 9 includes a coarse adjustment servo unit 21 that coarsely adjusts tracking and a fine adjustment servo unit 22 that finely adjusts tracking.

  The coarse adjustment servo unit 21 constitutes a feed forward servo. An envelope of the tracking error signal obtained at the boundary between the mirror part (unrecorded area) and the signal part (recording area) of the optical disc is detected, and the coarse tracking servo is first performed using the signal as a servo signal. Is stored for one round, and then feedforward control is performed using the memory value.

  In order to obtain the tracking error signal (coarse servo signal) at the boundary portion by the coarse adjustment servo unit 21, the optical disc apparatus positions the laser spot irradiated on the disc from the optical pickup 20 on the boundary portion. Need to be controlled.

  For this reason, the optical disk apparatus moves the optical pickup 20 in the radial direction of the disk to search for a position where the duty of the servo signal envelope waveform is 50%. That is, the position of the optical pickup 20 is controlled so that a signal waveform shown in FIG. The optical pickup 20 is moved by the sled servo from the inner periphery toward the outer periphery, and an intermittent signal with a duty of 50% is searched.

  Further, if the optical pickup 20 can move up to the inside of the lead-in of the disk, a signal area on the innermost peripheral side and a predetermined boundary position between the mirrors may be used.

  For the type of disk whose outermost peripheral position (diameter position) of the groove area is known, the optical pickup 20 is moved to that position.

  In addition, the boundary portion may differ depending on the type of disk. In that case, the disc is identified, the position of the boundary is grasped, and the optical pickup 20 is moved.

  Disc discrimination is performed by the following configuration and operation. For example, a case where it is determined whether the disc is a CD or a DVD will be described.

  A disk sensor is arranged near the spindle motor 12. The disk sensor is tilted 18 degrees with respect to the vertical line of the disk. The light emitting element is an infrared light emitting diode and the light receiving element is a photodiode. The disk sensor detects the amount of primary light diffracted by the pits of the disk. Since the track pitch is different between DVD (track pitch 0.74 μm) and CD (track pitch 1.6 μm), the optical axis of the primary light is different between DVD and CD. If the disc discrimination sensor is arranged on the optical axis of the primary light on the CD disc, the detected light quantity (current) becomes CD disc> DVD disc. For this reason, it is possible to distinguish between a CD and a DVD. This disc discrimination is performed by causing the sensor to emit light up to three times in a pulse form immediately after disc tray loading → chucking → disc rotation.

The fine adjustment servo unit 22 performs feedback servo using a servo error signal based on a signal from a conventional recording area. For example, the addition signals (SA + SD) and (SB + SC) are obtained for the light receiving surfaces arranged in the radial direction of the disk 18 by the matrix circuit 7, and the difference between the addition signal (SA + SD) and the addition signal (SB + SC) is obtained by the subtraction circuit. Thus, a tracking error signal TE-1 for fine adjustment is generated. That is, TE-1 = (SA + SD)-(SB + SC) (2)
It becomes. The tracking actuator 11 is driven by the tracking servo circuit 9 so that the signal level of the tracking error signal TE-1 for fine adjustment becomes zero level. Thus, tracking control is performed.

  In this way, the tracking servo circuit 9 performs a feed forward servo performed by the tracking error signal obtained at the boundary between the recorded part and the unrecorded part, in addition to the feedback servo by the servo error signal by the signal from the conventional recording area. Combined. Thereby, a highly accurate tracking servo can be realized without strictly limiting the allowable eccentricity.

  Hereinafter, the principle of the coarse adjustment servo performed by the tracking servo circuit 9 will be described. As shown in FIG. 3, the optical disc 18 generally has a signal recording area 23 and a mirror area 24 where no signal is recorded. Although a pit area portion is shown and described as a signal recording area, a groove portion may be used.

  The coarse adjustment servo unit 21 performs coarse adjustment of tracking using the boundary portion between the signal recording area and the mirror area.

  FIG. 4 shows the behavior of the light spot at the boundary. FIG. 4A shows a case where the light spot 25 crosses the pit area 23 and the mirror portion 24. In this case, tracking errors are observed intermittently. That is, the tracking error signal is observed only in the portion where the spot 25 has passed through the pit portion 23. The observation tracking error signal is as shown in FIG. FIG. 5 shows the waveform of the observation tracking error signal.

  FIG. 4B shows a case where a spot 25 passes through the mirror portion 24. In this case, no tracking error signal is observed. The observation tracking error signal is as shown in FIG.

  FIG. 4C shows a case where a spot 25 passes over the pit area portion 23. In this case, the tracking error signal is completely observed. The observation tracking error signal is as shown in FIG.

  When the spot 25 passes through the boundary between the signal recording area 23 and the mirror area 24, there is an eccentricity, so that the repetition of FIG. 4B or FIG. 4C, that is, the state of FIG. Observed across. That is, the tracking error signal at the boundary portion is as shown in FIG.

  When the envelope is detected for the tracking error signal as shown in FIG. 5A, the result is as shown in FIG. Further, FIG. 6B shows the result of applying a low-pass filter to the envelope detection signal. This voltage is V.

  Since α at the pit level and β at the mirror level, e = V−α is calculated, and e is returned as an error signal to the actuator 11 on which the lens is mounted. That is, V = α. That is, the head passes through the pit portion 23 over the entire circumference, and the tracking error signal is observed.

  Since tracking errors are observed over the entire circumference, the head follows the eccentricity to some extent. This completes the coarse tracking servo.

  However, since the tracking error is not zero, it does not follow the pit train completely. Thus, tracking servo (feedback) using a three-spot method, push-pull method, or the like can be performed to completely follow the pit row.

  By the way, if the radius changes, or if the pickup is moved from the boundary portion to the inner signal area 23 in FIG. 3, the feedforward tracking servo voltage described in FIG. 6 does not function. This is because the feed forward tracking servo voltage cannot be obtained because the boundary portion is lost.

  In order to solve this problem, once the feedforward tracking servo voltage is obtained at the boundary, the servo voltage for one rotation may be stored in the memory.

  FIG. 7 shows a tracking servo control procedure of the tracking servo circuit 9. First, in step S1, the coarse adjustment servo unit 21 starts eccentric servo at the boundary portion. The eccentric servo is operated until it can be determined in step S2 that a tracking error has been detected over the entire circumference. When tracking servo is observed over the entire circumference (YES in step S2), the servo voltage is stored in the memory for one revolution (step S3). In order to save in the memory, for example, a value obtained by counting the pulse output from the encoder installed in the spindle motor may be used as the input address, and the eccentric servo value may be saved. The eccentric servo signal obtained by the coarse adjustment servo unit 21 is applied to the lens actuator 11 as feed forward.

  Thereafter, the conventional tracking servo (fine adjustment servo) is performed by the fine adjustment servo unit 22 in step S4 and completed by following the pit train completely. This tracking servo is performed as a feedback servo for the actuator 11.

  FIG. 8 shows a detailed configuration of the tracking servo circuit 9. The coarse adjustment servo unit 21 performs eccentric servo so that the tracking error signal is observed over the entire circumference at the boundary portion. When the eccentricity error is zero, that is, when V = α as described above, the eccentric servo signal for one rotation is stored in the memory 31, and the eccentric signal is added from the adder 37 to the actuator 11 via the servo filter B32. Feed forward. At the same time, the tracking error sensor 35 detects that V = α, the switch 36 is closed, and tracking servo (feedback servo) is performed by the servo filter A 34 of the fine adjustment servo unit 22.

It is a block diagram of an optical disk reproducing device. It is the schematic of a tracking servo circuit. It is a format diagram of a disc. It is a figure which shows the behavior of the light spot in the boundary part of a signal recording area and a mirror area. It is a figure which shows the waveform of an observation tracking error signal. It is a wave form diagram of an envelope detection signal of a tracking error signal, and a low pass filter output signal. It is a flowchart which shows the procedure of the tracking servo control of a tracking servo circuit. It is a detailed block diagram of a tracking servo circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Objective lens, 7 Matrix circuit, 9 Tracking circuit, 11 Tracking actuator (lens actuator), 12 Spindle motor, 21 Coarse adjustment servo part, 22 Fine adjustment servo part

Claims (2)

In an optical disc apparatus for recording data on an optical disc and / or reproducing data recorded on an optical disc,
An optical pickup that irradiates the optical disk with laser light from the objective lens and detects the amount of reflected light; and
A tracking servo unit for controlling the position of the objective lens in the radial direction of the disk via an actuator so that a laser beam irradiated on the optical disk from the optical pickup forms an on-track beam spot formed on the disk at the center of each track; With
The tracking servo section
After detecting the envelope of the tracking error signal obtained at the boundary between the mirror part and the signal part on the optical disk, first performing coarse tracking servo using the signal as a servo signal, and storing the servo signal for one round, A coarse adjustment servo unit that performs feedforward control according to the memory value;
An optical disc apparatus further comprising: a fine adjustment servo unit that finely adjusts the lens actuator by feedback control after the feedforward control by the coarse adjustment servo unit.   The coarse adjustment servo unit searches for a position where the duty of the servo signal envelope waveform is 50% in order to place the light spot at a predetermined position which is a boundary between the signal area and the mirror area of the disk. The optical disc apparatus according to claim 1.

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