JP2012212491A - Tracking control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tracking control method which is suitable for an optical pickup device performing a reading operation of a signal recorded in an optical disk.SOLUTION: The tracking control method includes: a push-pull signal generation circuit 5 for generating a tracking error signal used in a push-pull system from a four-division sensor 1; and a phase difference signal generation circuit 9 for generating a tracking error signal used in a phase difference detection system obtained from the four-division sensor 1, and includes switching a state where a tracking control operation is performed by using from the tracking error signal obtained from the push-pull signal generation circuit 5 to the tracking error signal obtained from the phase difference signal generation circuit 9, when a laser spot has moved from a signal unrecorded region to a signal recorded region on the same track.

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. As described above, there is a problem that the push-pull signal changes greatly at the boundary between the signal recording area where the signal is recorded and the signal unrecorded area where the signal is not recorded, so 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 push-pull signal generation circuit when a laser spot moves from a signal non-recording area to a signal recording area on the same track The tracking error signal obtained from the above 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.

  Further, the present invention is characterized in that the selection switching operation of the tracking error signal is performed using the level change of the sum signal obtained by adding the signals obtained from the four light receiving parts constituting the four-divided sensor. It is.

  According to the tracking control method of the present invention, the 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 from the signal unrecorded area to the signal recording area on the same track. Since the signal is used to switch to the state where the tracking control operation is performed, that is, the state is switched to the state where the tracking control operation based on the phase difference detection method is performed, even if the push-pull signal is affected by the offset, it is accurate. Tracking control operation can be performed.

  Further, in the present invention, the selection switching operation of the tracking error signal is performed using the level change of the sum signal obtained by adding the signals obtained from the four light receiving units constituting the four-divided sensor. And the boundary of the signal recording area can be reliably detected. Therefore, according to the tracking control method of the present invention, it is possible to accurately perform the tracking control operation in the write-once type optical disc in which the signal recording area and the signal non-recording area are on the same signal track.

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 a fifth adder circuit for adding signals obtained from the first adder circuit 2 and the second adder circuit 3, and all of the light receiving parts A, B, C constituting the four-divided sensor 1 are provided at output terminals thereof. , D is obtained by adding signals obtained from D, that is, a sum signal is output. Reference numeral 11 denotes a signal level detection circuit to which the sum signal output from the fifth addition circuit 10 is input, and is configured to output a signal level detection signal when the level of the input signal decreases below a predetermined level. Yes.

  A tracking signal selection circuit 12 outputs a selection signal when the signal level detection signal output from the signal level detection circuit 11 is input. Reference numeral 13 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 13a is selected from the push-pull signal and the phase difference signal according to the selection signal output from the tracking signal selection circuit 12 and output. Is configured to do.

  Reference numeral 14 denotes a tracking control circuit in which a signal output to the output terminal 13a of the selection switch 13, that is, a tracking error signal which is a push-pull signal or a tracking error signal which is a phase difference signal is input as a tracking error signal. 15 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 tracking control circuit according to the present invention is configured. Next, the relationship between the signal track of the optical disk and the laser spot will be described with reference to FIG. In the figure, a figure □ shows a state where signal recording called a pit is performed.

  FIG. 2A shows a state in which the laser spot L is in a signal non-recorded area where no signal is recorded on the optical disk. From this state, the laser spot L is positioned as the optical disk rotates. The pits P1, P2 and P3 on the current track move in the arrow B direction.

  FIG. 2B shows a state in which the laser spot L has moved from the signal non-recording area to the signal recording area due to the movement of the pits P1, P2 and P3 in the direction of arrow B.

  As the optical disk rotates, the position of the laser spot L moves from the position shown in FIGS. 3A to 3B, and the light receiving parts A, B, C, and 4 constituting the 4-split sensor 1 accompanying such movement. The level change of the sum signal obtained from D will be described with reference to FIG.

  FIG. 3 is a characteristic diagram showing the relationship between the spot position in the tangential direction, that is, the direction in which the signal recording pits on the track formed on the optical disc continue and the level of the sum signal. In the figure, S1 indicated by a solid line indicates the level of the sum signal in the signal non-recorded area, and S2 indicated by a broken line is obtained when the laser spot L moves on the pit formed in the signal recording area. This shows the level change of the sum signal. As is apparent from the figure, when the laser spot L moves on the pit, the level of the sum signal decreases.

  In the present invention, a tracking error signal to be used for the tracking control operation is selected by detecting such a decrease in level of the sum signal. That is, the level of the sum signal is detected by the signal level detection circuit 11, and the control signal for switching the tracking error signal is output from the tracking signal selection circuit 12 to the selection switch 13 when the signal level decreases. Has been.

  That is, in the present invention, the phase difference signal generation circuit 9 outputs the tracking error signal output from the push-pull signal generation circuit 5 when the level of the sum signal decreases from the state in which the tracking error signal is output to the output terminal 13a of the selection switch 13. The tracking error signal is output to the output terminal 13a.

  When the tracking error signal selection switching operation described above is performed, the tracking control operation by the tracking control circuit 14 is switched from the push-pull tracking control method to the phase difference signal detection tracking control method. That is, the tracking control operation by the push-pull method is performed in the signal non-recording area, and the tracking control operation by the phase difference signal detection method is performed at the boundary between the signal non-recording area and the signal recording area.

  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-recording area and the signal recording area. The control signal is configured to be inverted. In other words, the tracking control method is returned from the phase difference signal detection method to the push-pull method when passing through the boundary portion. 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.

  When the signal level detection circuit 11 passes through the boundary between the signal non-recording area and the signal recording area, the laser spot is located in the signal recording area, so that the level of the sum signal changes up and down as the optical disk rotates. However, since this state is not the boundary between the signal unrecorded area and the signal recorded area, the tracking signal selection circuit 12 does not output a control signal for switching the tracking error signal from the push-pull method to the phase difference signal detection method. It is configured.

  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 division | segmentation sensor 5 Push pull signal generation circuit 8 Phase difference detection circuit 9 Phase difference signal generation circuit 11 Signal level detection circuit 12 Tracking signal selection circuit 13 Selection switch 14 Tracking control circuit

Claims (2)

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 for generating and a phase difference signal generation circuit for generating a tracking error signal used in the phase difference detection method obtained from the four-divided sensor are provided, and a laser spot is an unrecorded area on the same track. The tracking error signal obtained from the push-pull signal generation circuit when moving from the signal to the signal recording area 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. Tracking control method. 2. The tracking control method according to claim 1, wherein the tracking error signal is switched by using a level change of a sum signal obtained by adding signals obtained from four light receiving units constituting a four-divided sensor. .

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