JP2012221523A - Tracking-control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tracking-control method suitable for an optical pickup device for reading a signal recorded on an optical disk.SOLUTION: A push-pull signal generation circuit 5 for generating a tracking error signal for use in a push-pull system from a signal by a quadripartite sensor 1 and a differential signal generation circuit 9 for generating a tracking error signal for use in a differential signal detection system, the signal obtained by the quadripartite sensor, are disposed to switch from a tracking error signal obtained from the push-pull signal generation circuit 5, switching to a state of performing tracking control using a tracking error signal obtained from the differential signal generation circuit 9 if a laser spot moves to a signal-recorded track direction when the laser spot is reading a signal recorded on a signal track having the signal-recorded track on only one side.

Description

  The present invention relates to a tracking control method for an optical pickup device in which a signal recorded on an optical disk is read by a laser beam.

  2. Description of the Related Art Optical disk apparatuses that can perform a signal read operation by irradiating a signal recording layer of an optical disk with laser light emitted from an optical pickup apparatus have become widespread.

  Reading operation of the signal recorded on the signal recording layer by the optical pickup device is performed by irradiating the signal recording layer with the laser light emitted from the laser diode, and detecting the change of the laser light reflected from the signal recording layer with a photodetector. Is done by detecting by.

  In order to read out the signal recorded on the signal recording layer by the laser beam, it is necessary to accurately perform the tracking control operation for causing the laser beam to follow the signal track spirally provided on the signal recording layer. .

  There are various types of such tracking control methods. In addition to the push-pull method and the phase difference method using the main beam, two sub-beam light-receiving units that are irradiated with the two sub-beams and the main beam that is irradiated with the main beam. A tracking control method called a differential push-pull method is generally employed in which a photodetector incorporating a light receiving portion is provided and a tracking error signal is generated by a signal obtained from the photodetector.

In addition, a tracking control method that selectively uses a tracking control method based on a differential push-pull method and a phase difference detection method in accordance with an optical disk has been proposed for optical disk devices. (See Patent Document 1)
Recently, a four-layer type optical disc having a plurality of signal recording layers, for example, four layers, instead of a single layer, has been commercialized, and an optical disc having such a plurality of signal recording layers has been commercialized. An optical pickup device that can read out signals recorded in each signal recording layer has also been commercialized.

JP 2008-84415 A

  The tracking control by the differential push-pull method generates a tracking error signal using signals obtained from a sub-beam light-receiving unit that receives two sub-beams and a main-beam light-receiving unit that receives a main beam. There is an advantage that it is possible to solve the offset problem that occurs in the push-pull method in which the tracking control operation is performed using the signal obtained only from the light receiving section for use.

  However, such a differential push-pull method requires a diffraction grating that separates the laser beam into a main beam and a sub beam, so that there is a problem that the optical configuration is complicated as well as being expensive.

  In addition, when performing the reproduction operation of the signal recorded on the optical disc provided with the plurality of signal recording layers described above, the reflected light reflected from the signal recording layer different from the signal recording layer performing the signal reproduction operation. That is, there is a problem that stray light is applied to the sub-beam light-receiving unit and adversely affects the sub-beam detection operation.

  As a method for solving such a problem caused by stray light, many techniques such as making the shape of the sub-beam light-receiving part an octagon have been proposed, but there is a problem that it is expensive and requires accuracy.

  In order to solve such a problem, it is conceivable to employ a push-pull type tracking control method using only the main beam. However, such a tracking control method has a problem that an offset is generated, and in particular, a write-once type optical disc. When the signal recorded on the track between the track where the signal is recorded and the track where the signal is not recorded is read out, the direction of the track in which the laser beam is recorded If it is shifted to, a large offset occurs in the tracking error signal which is a push-pull signal, and there is a problem that the tracking control operation cannot be performed accurately.

  The present invention seeks to provide a tracking control method capable of solving such a problem.

  The present invention provides a push-pull signal generation circuit that generates a tracking error signal used in a push-pull method from a four-divided sensor that receives return light reflected from a signal recording layer provided on an optical disc, and the four-divided sensor A phase difference signal generation circuit for generating a tracking error signal used in the phase difference detection method obtained from the above is provided, and a signal recorded on a signal track having a track on which only one laser spot is recorded is read out. When the laser spot moves in the direction of the recorded track, the tracking error signal obtained from the push-pull signal generation circuit is switched to a state in which the tracking control operation is performed using the tracking error signal obtained from the phase difference signal generation circuit. It is characterized by That.

  Further, the present invention is characterized in that the tracking error signal is switched by detecting a change in the push-pull signal output from the push-pull signal generation circuit.

  The present invention is characterized in that the tracking error signal is switched by detecting the offset of the push-pull signal output from the push-pull signal generation circuit.

  Furthermore, the present invention is characterized in that the tracking error signal is switched by detecting the amplitude change of the push-pull signal output from the push-pull signal generation circuit.

  According to the tracking control method of the present invention, the push-pull is performed when the laser spot moves in the direction of the signal recorded track when the signal recorded on the signal track having the signal recorded track on only one laser spot is being read. The tracking error signal obtained from the signal generation circuit is switched to the state in which the tracking control operation is performed using the tracking error signal obtained from the phase difference signal generation circuit, that is, the tracking control operation by the phase difference detection method is performed. Therefore, even if the push-pull signal is affected by the offset, an accurate tracking control operation can be performed.

It is a block diagram for demonstrating the tracking control method of this invention. It is a figure for demonstrating the relationship between the signal track for demonstrating the tracking control method of this invention, and a laser spot. It is a figure for demonstrating the tracking control method of this invention.

  Provided is a tracking control method for an optical pickup apparatus that eliminates the need for a diffraction grating that generates one main beam and two sub beams from laser light emitted from a laser diode.

  FIG. 1 shows an embodiment for explaining the tracking control method of the present invention. In the figure, reference numeral 1 denotes a four-divided sensor incorporated in a photodetector to which return light reflected from a signal recording layer of an optical disc is irradiated. As is well known, four light receiving portions A, B, C, D It is composed of.

  In such a configuration, the laser spot S of the return light is irradiated and generated on the quadrant sensor 1 as shown in the figure, but when the laser spot is displaced in the radial direction on the optical disc, the laser spot S on the quadrant sensor 1 is an arrow. It is provided to move in the A direction.

  Reference numeral 2 denotes a first addition circuit for adding signals obtained from the light receiving part A and the light receiving part D constituting the quadrant sensor 1, and 3 denotes a signal obtained from the light receiving part B and the light receiving part C constituting the quadrant sensor 1. 2 is a subtracting circuit for subtracting the signal obtained from the second adding circuit 3 from the signal obtained from the first adding circuit 2, and a push-pull tracking control method is applied to its output terminal. The push-pull signal to be used is output. In other words, the first adder circuit 2, the second adder circuit 3, and the subtractor circuit 4 constitute a push-pull signal generation circuit 5 that generates the push-pull signal.

  Reference numeral 6 denotes a third adding circuit for adding signals obtained from the light receiving parts A and C constituting the quadrant sensor 1, and 7 denotes a signal obtained from the light receiving parts B and D constituting the quadrant sensor 1. 4 is a phase difference detection circuit for detecting the phase difference between the signal obtained from the third addition circuit 6 and the signal obtained from the fourth addition circuit 7, and a phase difference detection is provided at its output terminal. A phase difference signal used in the tracking control method is output. That is, the third addition circuit 6, the fourth addition circuit 7, and the phase difference detection circuit 8 are configured to constitute a phase difference signal generation circuit 9 that generates the phase difference signal.

  Reference numeral 10 denotes an offset amount detection circuit for detecting an offset amount of a tracking error signal which is an output signal of the subtracting circuit 4, that is, a push-pull signal output from the push-pull signal generating circuit 5. A level detection signal is output when the predetermined level is reached.

  A tracking signal selection circuit 11 outputs a selection signal when a level detection signal output from the offset amount detection circuit 10 is input. Reference numeral 12 denotes an output signal of the subtraction circuit 4, that is, a tracking error signal that is an output signal of the push-pull signal generation circuit 5, and an output signal of the phase difference detection circuit 8, that is, a tracking error that is an output signal of the phase difference signal generation circuit 9. A selection switch to which a signal is input, and an error signal output as a tracking control signal to the output terminal 12a is selected from the push-pull signal and the phase difference signal by the selection signal output from the tracking signal selection circuit 11 and output. Is configured to do.

  Reference numeral 13 denotes a tracking control circuit in which a signal output to the output terminal 12a of the selection switch 12, that is, a tracking error signal that is a push-pull signal or a tracking error signal that is a phase difference signal is input as a tracking error signal. 14 is configured to supply a tracking drive signal.

  In such a configuration, the tracking control operation by the tracking error signal output from the push-pull signal generation circuit 5, that is, the tracking control operation by the push-pull method and the tracking control operation by the tracking error signal output from the phase difference signal generation circuit 9, That is, since the tracking control operation by the phase difference detection method is well known, its description is omitted.

  As described above, the circuit for tracking control according to the present invention is configured. Next, the relationship between the signal track of the optical disc and the laser spot and the relationship between the level of the push-pull signal and the amount of off-track are shown. 2 and FIG. In FIG. 2, a figure □ shows a state where signal recording called a pit is performed.

  FIG. 2A shows a state where the laser spot L is performing a read operation of a signal recorded on the track on which the pits P1, P2 and P3 are formed on the optical disk. Only one of them has a track on which a signal is recorded, such as the pits P11, P12, P13, P14, and P15 (here, a track on the inner circumference side of the optical disk).

  FIG. 3 shows the relationship between the amplitude of the push-pull signal output from the push-pull signal generation circuit 5 and the shift amount of the laser spot L with respect to the track. A characteristic T1 indicated by a solid line is irradiated with the laser spot L. The amplitude change is shown when there are tracks on which signals are recorded or tracks on which no signals are recorded on both sides of the track. As is clear from the characteristic T1, the level of the push-pull signal is point-symmetric on the inner peripheral side and the outer peripheral side. Therefore, the tracking control operation by the push-pull method can be accurately performed using such a push-pull signal.

  FIG. 2B shows a state where the laser spot L is shifted from the state shown in FIG. 2A to the track side adjacent to the inner peripheral side. When the laser spot L shifts to the inner peripheral side, the amplitude of the push-pull signal changes as shown by the characteristic T2 indicated by the broken line in FIG. 3 due to the influence of the pits P12 and P13 recorded on the signal track adjacent to the inner peripheral side. To do.

  As can be seen by comparing the characteristics indicated by T1 in FIG. 3 with the characteristics indicated by T2, the offset amount with respect to T1 increases due to the influence of the pits recorded on the track adjacent to the inner periphery when the track deviation amount increases. .

  In the present invention, the tracking error signal used for the tracking control operation is selected by detecting the magnitude of the offset amount. That is, the offset amount is detected by the offset amount detection circuit 10, and when the offset amount reaches a set value, a control signal for switching the tracking error signal is output from the tracking signal selection circuit 11 to the selection switch 12. It is configured.

  That is, in the present invention, the phase difference signal generation circuit when the offset value of the push-pull signal becomes a set value from the state in which the tracking error signal output from the push-pull signal generation circuit 5 is output to the output terminal 12a of the selection switch 12. 9 is configured to output a tracking error signal output from the output terminal 12a.

  When the tracking error signal selection switching operation described above is performed, the tracking control operation by the tracking control circuit 13 is switched from the push-pull tracking control method to the phase difference signal detection tracking control method. In other words, when both tracks adjacent to the track where the laser spot tracking control operation is performed are in the same state, that is, the track where the signal is recorded or the track where the signal is not recorded, no offset is generated and the push is performed. The tracking control operation by the pull method is performed, and the tracking control operation by the phase difference signal detection method is performed on the signal track having the signal unrecorded track and the signal recording track on both sides.

  In this way, the tracking control method is switched from the push-pull method to the phase difference detection method at the boundary between the signal non-recorded track and the signal recording track. The control signal is configured to be inverted. That is, when the tracks on both sides adjacent to the track on which tracking control is performed are in the same state, the tracking control method is returned from the phase difference signal detection method to the push-pull method. This is because the push-pull method is more advantageous when performing the tracking control operation not only in the signal non-recording area but also in the signal recording area.

  In this embodiment, the tracking control method is switched from the push-pull method to the phase difference detection method by detecting the offset amount of the push-pull signal, but by detecting the change in the amplitude of the push-pull signal. The tracking control method can be switched.

  The present invention is effective for an optical pickup device that performs an operation of reading a signal recorded on an optical disc in which a plurality of signal recording layers are provided close to each other, such as an optical disc of Blu-ray standard. The present invention can also be implemented in an optical pickup device that performs an operation of reading a signal recorded on the optical disc.

DESCRIPTION OF SYMBOLS 1 4 divided sensor 5 Push-pull signal generation circuit 8 Phase difference detection circuit 9 Phase difference signal generation circuit 10 Offset amount detection circuit 11 Tracking signal selection circuit 12 Selection switch 13 Tracking control circuit

Claims (4)

A tracking control method for an optical pickup device including a four-divided sensor for receiving return light reflected from a signal recording layer provided on an optical disc, and a tracking error signal used in a push-pull method from the four-divided sensor. A push-pull signal generation circuit to be generated and a phase difference signal generation circuit for generating a tracking error signal used for the phase difference detection method obtained from the four-divided sensor are provided, and a signal having a track on which only one laser spot is recorded. Tracking error obtained from the phase difference signal generation circuit from the tracking error signal obtained from the push-pull signal generation circuit when the laser spot moves in the direction of the track where the signal has been recorded during the readout operation of the signal recorded on the track Trackin using signal Tracking control method being characterized in that the switched on state of performing the control operation. 2. The tracking control method according to claim 1, wherein the tracking error signal is switched by detecting a change in the push-pull signal output from the push-pull signal generation circuit. 3. The tracking control method according to claim 2, wherein the tracking error signal is switched by detecting an offset amount of the push-pull signal output from the push-pull signal generation circuit. The tracking control method according to claim 2, wherein the tracking error signal is switched by detecting a change in amplitude of the push-pull signal output from the push-pull signal generation circuit.

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