JP2008282450A - Optical information recording/reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording/reproducing apparatus which can easily adjust a correction gain and is adaptable to an automatic adjustment. <P>SOLUTION: The optical information recording/reproducing apparatus comprises: an MPP generating section 23 for generating a main push-pull signal constituted of a main beam; an SPP generating section 24 for generating a sub push-pull signal constituted of a sub beam; and a variable gain amplifier 27 which adjusts an output amplitude of the sub push-pull signal. Furthermore, the apparatus is provided with: a subtractor 26 for generating a tracking error signal from the main push-pull signal and output of the variable gain amplifier; and an amplitude measuring section 25 which detects amplitudes of the main push-pull signal and of the sub push-pull signal. On the basis of the detected main push-pull signal amplitude and sub push-pull signal amplitude, a gain of the variable gain amplifier is adjusted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical information recording / reproducing apparatus for recording or reproducing information on an optical disc, and more particularly to a method for generating a tracking error signal.

  2. Description of the Related Art Conventionally, in an optical disc apparatus such as a CD, a light spot is condensed on an optical disc, and information is recorded or reproduced by causing the light spot to follow a track of the optical disc. Tracking control for causing the light spot to follow the track is performed by returning a signal from the optical disk to the objective lens actuator. A differential push-pull method is known as a method for generating a tracking error signal. This is disclosed in Patent Document 1.

  Next, a method for generating a tracking error signal by the differential push-pull method will be described. FIG. 6 shows a conventional optical pickup. The optical pickup includes a semiconductor laser 71, a grating 72, a beam splitter 73, an objective lens 74, an objective lens actuator 75, a light receiving element 76, and the like.

  The light emitted from the semiconductor laser 71 is separated into a main beam and two side beams by the grating 72, and is condensed on the optical disc 77 through the beam splitter 73 and the objective lens 74.

  The reflected light from the optical disk 77 enters the objective lens 74 and is guided to the light receiving element 76 via the beam splitter 73. Information on the optical disk 77 can be reproduced from the light reception signal of the light receiving element 76. At this time, the objective lens 74 is electromagnetically driven by the objective lens actuator 75 so as to be movable in the focus direction and tracking direction of the optical disc 77.

  The light separated into three beams by the grating 72 is condensed as three light spots LM, LE, and LF on the optical disc through the objective lens 74 as shown in FIG. The light spot LM is a spot by the main beam.

  At that time, a tracking control circuit (not shown) controls the actuator 75 to perform tracking control so that the light spot LM scans the center of the information track as shown in FIG. The light spots LM and LF are shifted from the light spot LM by the main beam by ½ track in the radial direction of the optical disc 77 respectively.

  As shown in FIG. 8, the light receiving element 76 for performing the tracking control is divided into a two-divided light receiving part M arranged at the center, a two-divided light receiving part E arranged at intervals on both sides of the light receiving part M, and the light receiving. It consists of part F.

  Reflected light of light spots LM, LE, and LF shown in FIG. 7 on the optical disc 77 is incident on the light receiving portions M, E, and F of the light receiving element 76, respectively. Light spots LLM, LLE, and LLF shown in FIG. 8 are incident on the light receiving portions M, E, and F by the reflected light of the light spots LM, LE, and LF, respectively.

  As shown in FIG. 8, each of the light receiving portions M, E, and F is divided into two in a direction parallel to the direction of the information track on the optical disc 77, and is divided into regions M1, M2, E1, E2, and F1, F2. ing.

  In this way, a push-pull signal that changes in an alternating manner every time the beam on the optical disk crosses the track is obtained from the difference signal of the light receiving element divided into two in the direction parallel to the track of the optical disk. This is disclosed in Patent Document 2, for example.

  The differential signals obtained by the light receiving portions M, E, and F become the respective push-pull signals. The push-pull signal obtained from the light receiving unit M is referred to as a main push-pull signal MPP, and the push-pull signal obtained from each of the light receiving units E and F is referred to as a sub push-pull signal SPP1 and a sub push-pull signal SPP2.

  Next, a method for generating a tracking error signal using a differential push-pull signal will be described with reference to FIG. As shown in FIG. 9, when generating a tracking error signal, differential amplifiers 78 to 81, adders 82 and 83, and amplifiers 84 and 85 are used. The gains of the amplifiers 84 and 85 are both set to a predetermined value k.

  The main push-pull signal MPP is an output difference between the regions M1 and M2 of the light receiving portion M of the light receiving element 76 and is obtained from the output of the differential amplifier 80. The sub push-pull signal SPP <b> 1 is an output difference between the areas E <b> 1 and E <b> 2 of the light receiving unit E and is obtained from the output of the differential amplifier 78. Similarly, the sub push-pull signal SPP2 is an output difference between the light receiving portions F1 and F2, and is obtained from the output of the differential amplifier 79.

The sub push-pull signals SPP1 and SPP2 are added by the adder 82, then amplified by k times by the amplifier 85, and differentiated from the main push-pull signal MPP by the differential amplifier 81 to generate the tracking error signal TE. Is done. That is, the tracking error signal TE is
TE = MPP-k (SPP1 + SPP2) (1)
It is obtained by.

The output of the adder 82 is input to the amplifier 84 and amplified k times, and then added to the main push-pull MPP by the adder 83 to generate a lens position signal BP corresponding to the amount of movement of the objective lens 74. The That is, the lens position signal BP is
BP = MPP + k (SPP1 + SPP2) (2)
It is obtained by.

  10A shows the main push-pull signal MPP, FIG. 10B shows the addition signal (SPP) of the sub push-pull signals SPP1 and SPP2, FIG. 10C shows the tracking error signal TE, and FIG. 10D shows the lens. The position signal BP is shown.

  In FIG. 10, the horizontal line indicates the reference level of each signal. The vertical line indicates the center position of the track of the optical disc 77, and the intersection with the reference level indicated by the horizontal line corresponds to the target point of tracking control.

  The sub push-pull signal addition signal SPP (SPP1 + SPP2) is 180 degrees out of phase with the main push-pull signal MPP. Further, since the light spot on the light receiving element 76 moves with the movement of the objective lens 74 in the radial direction, the center of the amplitude of each push-pull signal is shifted by an offset amount Δ from the reference level.

  Here, the offset associated with the movement of the objective lens 74 can be removed by optimally selecting the gain value k of the amplifier 85 for the tracking error signal TE according to the equation (1). Then, a tracking error signal that varies in an AC manner for each track of the optical disc 77 with the reference level as the center of amplitude is obtained.

  Further, according to the equation (2), the lens position signal BP is added with the offset of each push-pull signal, and a signal offset from the reference level is obtained. The amount of offset from the reference level in the lens position signal BP is a signal corresponding to the deviation from the center of the objective lens 74.

Here, by the tracking control for controlling the objective lens actuator 75 using the tracking error signal TE, the light spot LM of the main beam can follow the target track of the optical disc 77 as shown in FIG. The lens position signal BP is used for suppressing lens swing.
Japanese Patent Laid-Open No. 7-93764 Japanese Patent Laid-Open No. 2-236827

  In the conventional configuration, the adjustment of the correction gain in the differential push-pull, that is, the adjustment of the gain value k of the amplifier 85 is performed so as to reduce the offset of the tracking error signal TE accompanying the movement of the objective lens 74.

  Therefore, the gain adjustment in the conventional configuration must be performed by forcibly generating the movement of the objective lens 74 at the time of manufacture of the apparatus or at the time of adjustment before shipment. Furthermore, since adjustment takes time, the apparatus automatically adjusts every time an optical disk is inserted into the apparatus by the user, which is not suitable for so-called automatic adjustment.

  It is an object of the present invention to provide an optical information recording / reproducing apparatus that can easily adjust the correction gain and can cope with automatic adjustment.

  The present invention includes means for generating a main push-pull signal by a main beam, means for generating a sub push-pull signal by a sub beam, and means for adjusting the output amplitude of the sub push-pull signal. In addition, there are provided means for generating a tracking error signal from the main push-pull signal and the output of the amplitude adjusting means, means for detecting the amplitude of the main push-pull signal, and means for detecting the amplitude of the sub push-pull signal. Then, the gain of the amplitude adjusting means is adjusted based on the amplitude value detected by the main push-pull amplitude detecting means and the amplitude value detected by the sub push-pull amplitude means.

  According to the present invention, the correction gain in the differential push-pull method can be adjusted easily and in a short time, and automatic adjustment can be supported.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical information recording / reproducing apparatus according to the present invention. FIG. 1 mainly shows a configuration relating to tracking error signal generation according to the present invention. Therefore, a circuit necessary for recording information on the optical disk, a circuit necessary for reproducing information, a circuit for performing focus control, or a circuit or mechanism for rotating the optical disk is omitted.

  The optical disk 21 is irradiated with laser light from the pickup (PU) 22, and the reflected light is detected by the light receiving element 76 in the pickup 22. For example, the pickup 22 has the same configuration as in FIG. 6, and the light receiving element 76 has the same configuration as in FIG.

  As described above, the main push-pull signal MPP and the sub push-pull signal SPP are generated from the output of the light receiving element 76. That is, the MPP generation unit 23 generates a main push-pull signal MPP from the signal of the light receiving element 76, and the SPP generation unit 24 generates a sub push-pull signal SPP (SPP1 + SPP2) from the signal of the light receiving element 76.

  The sub push-pull signal SPP is multiplied by a coefficient k in the variable gain amplifier 27, and is subtracted from the main push-pull signal MPP in the subtractor 26, thereby generating a tracking error signal.

  In addition, a predetermined gain is given to adjust the output amplitude of the tracking error signal output from the subtractor 26 in the DPP generation unit 29. Normally, in tracking control, the tracking error signal is phase compensated by the phase compensation unit 32, and tracking control is performed by driving the objective lens actuator by the driver. When adjusting the tracking error signal, the driver 34 is driven through a speed detection unit 30 and a speed control unit 31 to be described later to adjust the tracking error signal.

  The amplitude measuring unit 25 detects the signal amplitude of the main push-pull signal MPP and the sub push-pull signal SPP. The controller 28 sets the coefficient k of the variable gain amplifier 27 and the gain of the DPP generation unit 29 from the output of the amplitude measurement unit 25. The controller 28 also controls the selector (SEL) 33. The selector 33 switches the outputs of the speed control unit 31 and the phase compensation unit 32.

  FIG. 2 shows a configuration of the amplitude detector 25 that measures the amplitude of the main push-pull signal MPP and the sub push-pull signal SPP. When measuring the amplitude of the main push-pull signal MPP, the HPF 60 cuts the DC component of the main push-pull signal MPP, performs full-wave rectification in the full-wave rectifier circuit 61, and further measures the amplitude through the integrator 62. To do. The DC component of the main push-pull signal MPP is obtained by subtracting the signal before and after the HPF 60 by the subtractor 63 to detect the DC component and measuring the DC component through the integrator 64. The DC component is used for offset adjustment of the main push-pull signal MPP.

  Similarly, the amplitude and DC component of the sub push-pull signal SPP are measured using the HPF 66, the full-wave rectifier circuit 66, the subtractor 68, and the integrators 67 and 69. The DC component is used for offset adjustment of the sub push-pull signal SPP.

  FIG. 3 shows the configuration of the speed detection unit 30 and the speed control unit 31. The tracking error signal is input to the peak voltage detection circuit 40 and the bottom voltage detection circuit 41, and the peak value and the bottom value of the tracking error signal are detected. The center value calculation circuit 42 calculates the center value of the peak value and the bottom value.

  The binarization circuit 43 binarizes the tracking error signal with the center value (zero cross) calculated by the center value calculation circuit 42. The speed detection circuit 44 measures the time from the rise to the fall of the binarized tracking error signal. For example, the track pitch of the DVD is 0.74 μm, and the position of the beam and the track relatively moves by 0.37 μm, which is half the track pitch, from the rise to the fall of the binarized tracking error signal. .

  The speed detection circuit 44 detects the relative speed between the beam and the track from 0.37 μm which is half the track pitch and the time from the rise to the fall of the binarized signal of the tracking error signal. The detected relative speed between the beam and the track is compared with the target speed at the target speed 45, and a drive voltage is output from the subtractor 46 to the driver 34 so that the relative speed between the beam and the track becomes constant.

  FIG. 4 shows the waveforms of the tracking error signal and the track driving signal when adjusting the tracking error signal. The track drive signal is, for example, a signal for driving the objective lens 74 in the tracking direction by applying a drive signal to the objective lens actuator 75 in the pickup shown in FIG. The track drive signal is supplied from the driver 34 to the objective lens actuator in the pickup 22.

  First, in a state where tracking control is not performed, the relative speed between the objective lens and the track is detected by the speed detection circuit 44 in FIG. For example, when the relative speed is 1.5 mm / s or less, the objective lens is driven (track drive start in FIG. 4), and the objective lens is accelerated in the radial direction of the optical disc.

  It is desirable to drive the objective lens in the same direction as the transverse direction of the objective lens and the track by detecting the direction from the phase difference such as the envelope of the tracking error signal and the RF signal. Next, for example, after accelerating the objective lens by about 0.1 ms, speed control is started as shown in FIG. 4 so that the relative speed between the beam and the track is constant. Although not shown in FIG. 1, the RF signal is a reproduction signal reproduced from the optical disc.

  The speed control is performed because the measurement time becomes long when the eccentricity of the optical disk is small, so that the beam surely crosses the track. Further, if the relative speed of the beam and the track is not higher than a certain speed, the amplitude may be attenuated by the HPF 60 and the HPF 65 of the amplitude measuring unit 25 and the measurement error may be increased.

  During the speed control period in which the relative speed between the objective lens and the track is controlled to be constant, the amplitude of the main push-pull signal MPP and the sub push-pull signal SPP is measured by the amplitude measuring unit 25. The measurement time is, for example, the crossing time for 10 tracks under speed control. When the target speed is 3.7 mm / s, the measurement is completed in 2 ms. Therefore, the tracking error signal can be adjusted in a short time.

  Next, the operation for adjusting the tracking error signal will be described using the flowchart shown in FIG. First, in S401, it is determined whether or not the optical disc 21 is loaded. When the optical disk 21 is loaded, the optical disk 21 is rotationally driven by driving a spindle motor (not shown) in S402. Further, the semiconductor laser of the light source in the pickup 22 is turned on, and focus control is started by a focus control circuit (not shown).

  Next, in the state where tracking control is not performed in S403 as described above, the relative speed at which the objective lens crosses the track is monitored and waits until it becomes 1.5 mm / s or less. When the relative speed becomes 1.5 mm / s or less in S403, the process proceeds to S404, and the track driving is started as described above, and the speed control is started.

  At that time, the controller 28 selects the speed control unit 31 side by the selector 33 at the time of starting the track drive, and supplies the track drive signal from the speed control unit 31 to the driver 34 via the selector 33 as shown in FIG. . Thereafter, the speed control unit 31 performs speed control by the method as described above, and performs speed control so that the relative speed between the beam from the pickup 22 and the track is constant.

  During the speed control period, the amplitude measurement unit 25 measures the amplitudes of the main push-pull signal MPP and the sub push-pull signal SPP (S405). After crossing 10 tracks, the speed control of the objective lens is stopped and the track is stopped. The driving in the direction is stopped (S406).

  In step S407, the coefficient k of the variable gain amplifier 27 is calculated based on the amplitude value of the main push-pull signal MPP and the amplitude value of the sub push-pull signal SPP. For example, the coefficient k is calculated so that the amplitude value of the sub push-pull signal SPP multiplied by the coefficient k of the variable gain amplifier 27 is equal to the amplitude value of the main push-pull signal MPP. Set.

  In step S408, a tracking gain for adjusting the tracking error signal output from the subtractor 26 to a predetermined amplitude is calculated. For example, the tracking gain is set in the DPP generator 29 such that the tracking error signal amplitude is 3V. In that case, the main push-pull MPP signal and the sub push-pull SPP signal are 180 degrees out of phase, and when the main push-pull MPP signal amplitude is doubled, the tracking error signal amplitude is known. Accordingly, the amplitude of the tracking error signal is adjusted based on the result measured by the amplitude measuring unit 25. Of course, the tracking error signal amplitude from the subtractor 26 can also be directly measured.

  When the adjustment of the tracking error signal output is completed, tracking control can be performed, and a stable optical disk servo operation can be performed. At this time, when the adjustment of the tracking error signal is completed, the controller 28 selects the output side of the phase compensator 32 by the selector 33 and starts tracking control.

  As described above, the optical information recording / reproducing apparatus according to the present invention condenses the main beam and the sub beam from the light source (semiconductor laser) on the optical disc 21 by the objective lens 74. Then, a tracking error signal is generated from the reflected light from the optical disc 21 of the main beam and the sub beam.

  Further, the present invention adjusts the output amplitude of the sub push-pull signal, the means for generating the main push-pull signal by the main beam (MPP generation unit), the means for generating the sub push-pull signal by the sub beam (SPP generation unit). Means (variable gain amplifier). Further, a means for generating a tracking error signal (subtractor) from the output of the main push-pull signal and the amplitude adjusting means, a means for detecting the amplitude of the main push-pull signal (amplitude measuring unit), and the amplitude of the sub push-pull signal Means for detecting (amplitude measuring section). Then, the gain of the amplitude adjusting means is adjusted based on the amplitude value detected by the main push-pull amplitude detecting means and the amplitude value detected by the sub push-pull amplitude means.

  Furthermore, the present invention adjusts the output amplitude of the tracking error signal after gain adjustment. In addition, the present invention includes means (speed control unit) that drives the objective lens in the radial direction of the optical disk and performs speed control so that the relative speed between the light beam applied to the optical disk and the track is constant. Then, the amplitudes of the main push-pull signal and the sub push-pull signal are detected during speed control, and the gain is adjusted based on the detection result. Furthermore, the present invention adjusts the gain when the optical disc is mounted.

  As described above, the speed of the objective lens is controlled in the radial direction, and the output amplitude of the sub push-pull signal and the tracking error signal are calculated from the amplitude values of the main push-pull signal MPP and the sub push-pull signal SPP measured during the speed control. Adjust the output amplitude. Therefore, the correction gain in the differential push-pull method can be adjusted easily and in a short time, and automatic adjustment can be handled.

1 is a block diagram showing an embodiment of an optical information recording / reproducing apparatus according to the present invention. It is a figure which shows an example of the amplitude measurement part of FIG. It is a figure which shows an example of the speed detection part of FIG. 1, and a speed control part. It is a wave form diagram showing operation at the time of tracking error signal adjustment. It is a flowchart explaining operation | movement of tracking error signal adjustment. It is a figure which shows schematic structure of the optical pick-up of a prior art example. It is a perspective view which shows the light spot formed on an optical disk with the light beam irradiated from the conventional optical pick-up. It is a figure which shows the light receiving element of the conventional optical pick-up. It is a circuit diagram which shows the tracking error signal generator of a prior art example. It is a wave form diagram which shows the main push pull signal, sub push pull signal, tracking error signal, and lens position signal in the conventional tracking error signal generation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Optical disk 22 Pickup 23 MPP production | generation part 24 SPP production | generation part 25 Amplitude measurement part 26 Subtractor 27 Variable gain amplifier 28 Controller 29 DPP production | generation part 30 Speed detection part 31 Speed control part 32 Phase compensation part 33 Selector 34 Driver 40 Peak voltage detection circuit 41 bottom voltage detection circuit 42 center value calculation circuit 43 binarization circuit 44 speed detection circuit 45 target speed setting unit 46 subtractor 60 HPF
61, 66 Full-wave rectifier circuit 62, 64, 67, 69 Integrator 63, 68 Subtractor 60, 65 HPF
71 Semiconductor laser 74 Objective lens 75 Objective lens actuator

Claims (4)

In an optical information recording / reproducing apparatus for condensing a main beam and a sub beam from a light source on an optical disc by an objective lens, and generating a tracking error signal from the reflected light of the main beam and the sub beam from the optical disc,
Means for generating a main push-pull signal by the main beam;
Means for generating a sub push-pull signal by the sub beam;
Means for adjusting an output amplitude of the sub push-pull signal;
Means for generating the tracking error signal from the main push-pull signal and the output of the amplitude adjusting means;
Means for detecting the amplitude of the main push-pull signal;
Means for detecting the amplitude of the sub push-pull signal,
An optical information recording / reproducing apparatus characterized in that the gain of the amplitude adjusting means is adjusted based on the amplitude value detected by the main push-pull amplitude detecting means and the amplitude value detected by the sub push-pull amplitude means. The optical information recording / reproducing apparatus according to claim 1, wherein an output amplitude of the tracking error signal is adjusted after the gain adjustment. Means for driving the objective lens in the radial direction of the optical disk, and controlling the speed so that the relative speed between the light beam irradiating the optical disk and the track is constant, and the main push-pull signal during the speed control; 3. The optical information recording / reproducing apparatus according to claim 1, wherein the amplitude of the sub push-pull signal is detected and the gain is adjusted based on the detection result. 4. The optical information recording / reproducing apparatus according to claim 1, wherein the gain is adjusted when the optical disc is mounted.