WO2013035470A1

WO2013035470A1 - Tracking control method and tracking control device

Info

Publication number: WO2013035470A1
Application number: PCT/JP2012/069953
Authority: WO
Inventors: 佑介金武; 俊哉的崎; 伸夫竹下
Original assignee: 三菱電機株式会社
Priority date: 2011-09-08
Filing date: 2012-08-06
Publication date: 2013-03-14
Also published as: JP2014225306A

Abstract

The invention rapidly inhibits lens offset during tracking lock-in. A tracking control method for an optical pickup that shines a laser beam on an information-recording surface of an optical disk while using an objective lens to condense said laser beam, receives reflected light, and converts said reflected light to an electrical signal comprises: a step (S1) that acquires a track zero-crossing signal obtained by binarizing a tracking error signal generated from the abovementioned electrical signal; a step (S5) that evaluates whether an edge of the track zero-crossing signal changed when the objective lens passed a mark on a track of the optical disk; a step (S6) that starts tracking lock-in in the timing at which the edge changes; a step (S8) that sets a thread movement direction on the basis of the edge of the track zero-crossing signal that exists when tracking lock-in starts; and a step (S10) that moves a thread by only a given amount in the set movement direction.

Description

Tracking control method and tracking control apparatus

The present invention relates to a tracking control method and a tracking control apparatus for performing tracking pull-in to an optical disc.

There are optical disk devices compatible with optical disks such as BD (Bru-ray Disk), DVD (Digital Versatile Disk), and CD (Compact Disk). In order to read information from such an optical disk, it is necessary to cause the objective lens to follow surface vibration (focus direction fluctuation) and eccentricity (track direction fluctuation) that occur during rotation of the optical disk. The components of surface runout and eccentricity are sinusoidal waves with the time taken for one round of the optical disk as a cycle and the amount of surface runout and the amount of eccentricity as amplitudes, respectively. Here, tracking control for causing the objective lens to follow the eccentricity of the optical disk will be described.

Usually, tracking pull-in is performed after the period in which the objective lens crosses the track of the optical disk (hereinafter referred to as the track crossing period) becomes larger than a predetermined value. The “predetermined value” is set to a value that is equal to or greater than the limit value of the track crossing period that allows tracking pull-in. Since the speed at which the objective lens crosses the track of the optical disk (hereinafter referred to as the track crossing speed) is proportional to the reciprocal of the track crossing period, the tracking pull-in is performed after the track crossing speed becomes smaller than the limit value of the track crossing speed. Is done. Although the limit value of the track crossing speed varies depending on the configuration of the optical disc device and the type of the optical disc (BD / DVD / CD, or read-only type / write-once type / rewritable type), since it is almost zero, tracking pull-in is performed. This is the case when the track crossing speed becomes almost zero. In this case, since the absolute value of the eccentric component of the optical disk is substantially maximized, the reference position of the objective lens that follows the eccentricity of the optical disk changes after tracking. Thereby, an offset (hereinafter referred to as a lens offset) from the neutral position of the objective lens (the center position of the optical pickup) occurs. The lens offset amount is obtained by subtracting the eccentric component of the optical disc when tracking pull-in is performed by the center value of the eccentric component of the optical disc. Therefore, if the amount of eccentricity of the optical disk is large, the amount of lens offset increases.

When the lens offset is large, the objective lens is caused to follow the eccentricity of the optical disk in the state where the offset is generated, which may exceed the movable range of the objective lens in the track direction, and may cause damage to the objective lens.

Patent Documents 1 to 3 describe configurations for suppressing lens offset.

In Patent Document 1, the lens shift amount is measured before tracing the lens of the optical pickup to the recording start address. If the lens shift amount exceeds a predetermined threshold, tracing to the recording start address of the lens is performed. There is a description of a configuration in which the lens seek is repeated without performing the steps, and the lens is traced to the recording start address after the lens shift amount falls within a predetermined threshold.

In Patent Document 2, in a disk drive device in which a thread motor is feedforward controlled with a thread drive voltage to stop the optical pickup by moving the optical pickup onto a track in the radial direction of the disk, the optical pickup is stopped based on the previous thread drive voltage. A configuration is described in which the amount of swing in the track direction of the actuator (objective lens driving device) at the position is detected, and the setting value of the sled driving voltage at the next movement of the optical pickup is corrected based on the detection result.

In Patent Document 3, an offset representative value is calculated based on values of a plurality of tracking drive signals for one round of an optical disk, and a thread position of an optical pickup is calculated based on a comparison result between the offset representative value and the offset center value. A configuration for adjusting the is described.

JP 2007-087545 A Japanese Patent Laid-Open No. 2007-066358 JP 2002-208154 A

In optical disk devices, there is a desire to quickly suppress lens offset during tracking pull-in. For example, when the technique described in Patent Document 3 is used, the sled is moved after waiting for a time corresponding to one round of the optical disk after tracking pull-in, and the lens offset cannot be suppressed immediately, and the optical disk There is a possibility that the movable range of the objective lens in the track direction may be exceeded during one round.

Therefore, an object of the present invention is to provide a tracking control method and a tracking control device that can quickly suppress a lens offset at the time of tracking pull-in.

The tracking control method according to the present invention includes:
A method for tracking control of an optical pickup that condenses and irradiates an information recording surface of an optical disc with a laser beam by an objective lens, receives reflected light from the information recording surface of the optical disc and converts it into an electrical signal,
A track zero-cross signal acquisition step of acquiring a track zero-cross signal obtained by binarizing a tracking error signal generated from the electrical signal with a predetermined threshold;
A determination step of determining whether an edge of the track zero-cross signal has changed when the objective lens passes a mark on a track of the optical disc when the track is off;
Based on the determination result of the determination step, a tracking pull-in step for starting tracking pull-in at a timing when the edge changes;
A moving direction determining step for determining a moving direction of a sled that moves the optical pickup based on an edge of the track zero-cross signal at the start of the tracking pull-in;
A sled moving step of moving the sled by a predetermined amount of movement in the determined moving direction simultaneously with the tracking pull-in;
It is characterized by having.

The tracking control device according to the present invention is
A tracking control device for an optical pickup that condenses and irradiates an information recording surface of an optical disc with a laser beam by an objective lens, receives reflected light from the information recording surface of the optical disc and converts it into an electrical signal,
Track zero cross signal acquisition means for acquiring a track zero cross signal obtained by binarizing a tracking error signal generated from the electrical signal with a predetermined threshold;
Determining means for determining whether an edge of the track zero cross signal has changed when the objective lens passes a mark on a track of the optical disc at the time of track off;
Tracking pull-in means for starting tracking pull-in at the timing when the edge changes based on the determination result of the determination means;
A moving direction determining means for determining a moving direction of a sled that moves the optical pickup based on an edge of the track zero-cross signal at the start of the tracking pull-in;
A sled moving means for moving the sled by a predetermined moving amount in the determined moving direction simultaneously with the tracking pull-in;
It is characterized by having.

According to the present invention, it is possible to provide a tracking control method and a tracking control device that can quickly suppress lens offset at the time of tracking pull-in.

It is a figure which shows schematically the structure of the optical disk apparatus containing the tracking control apparatus which concerns on embodiment of this invention. (A)-(d) is a figure which shows the process until tracking drawing is performed from a track-off state when a thread | sled is not moved, (a) is a tracking error signal waveform, (b) is a lens error signal. Waveform, (c) shows the relative position of the objective lens viewed from the optical disc, and (d) shows the track crossing speed. (A)-(e) is a figure which shows the process until the thread control after tracking pull-in is performed from the track-off state at the time of using the technique of patent document 3, (a) is a tracking error. (B) is a lens error signal waveform, (c) is a relative position of the objective lens viewed from the optical disk, (d) is a track crossing speed, and (e) is a thread control waveform. (A) to (e) and (b ′) to (e ′) are diagrams showing a track-off state, (a) is an eccentric component of the optical disc, (b) is a tracking error signal waveform, and (c). Is a track zero cross signal waveform, (d) is a top envelope signal waveform, (e) is a mirror signal waveform, (b ′) is a partially enlarged view of a tracking error signal waveform, and (c ′) is a partially enlarged view of a track zero cross signal waveform. , (D ′) is a partially enlarged view of the top envelope signal waveform, and (e ′) is a partially enlarged view of the mirror signal waveform. (A) to (e) are diagrams showing the process from the track-off state until the tracking pull-in and thread control are performed, in which (a) is a tracking error signal waveform, and (b) is a lens error. (C) shows the relative position of the objective lens viewed from the optical disc, (d) shows the track crossing speed, and (e) shows the thread control waveform. It is a flowchart which shows an example of the tracking control by the tracking control apparatus which concerns on embodiment of this invention. It is a flowchart which shows another example of the tracking control by the tracking control apparatus which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram schematically showing the configuration of an optical disc apparatus 10 including a tracking control apparatus according to an embodiment of the present invention (that is, an apparatus capable of performing the tracking control method according to the embodiment of the present invention). It is. The optical disc device 10 is a device that performs at least one of recording and reproduction of information with respect to the optical disc 40. The optical disc 40 is, for example, a BD, a DVD, or a CD, and may include those classified into a read-only type, a write-once type, and a rewritable type, respectively.

As shown in FIG. 1, the optical disc apparatus 10 includes an optical pickup 11, a spindle motor 12, a laser control unit 13, a spindle control unit 14, a tracking error generation unit 15, a track zero cross signal generation unit 16, a reproduction signal generation unit 17, It has a top envelope signal generation unit 19, a mirror signal generation unit 20, an objective lens control unit 21, a thread control unit 22, a central control unit 30, and a storage unit 31.

The storage unit 31 in the central control unit 30 stores the laser power value of the optical pickup 11, and the rotation speed and rotation method of the spindle motor 12. The laser power value of the optical pickup 11 and the rotation speed and rotation method of the spindle motor 12 differ depending on the type of the BD / DVD / CD or read-only / write-once / rewritable optical disc. The data is input to the control unit 13 and the spindle control unit 14. The rotation method of the spindle motor 12 is divided into a constant angular velocity CAV (Constant Angular Velocity) and a constant linear velocity CLV (Constant Linear Velocity). The laser control unit 13 controls the optical pickup 11 to irradiate and irradiate the information recording surface of the optical disc 40 with the laser light by the objective lens 11 a in the optical pickup 11. Further, the spindle control unit 14 controls the spindle motor 12 to rotate the optical disc 40.

Reflected light from the information recording surface of the optical disc 40 is input to the light receiving element 11 b in the optical pickup 11. The light receiving element 11b converts the received optical signal into an electrical signal and outputs it. The converted electrical signal is input to the tracking error generation unit 15. The tracking error generator 15 generates a tracking error signal detected when the objective lens 11 a in the optical pickup 11 crosses the track of the optical disc 40. As a method for generating a tracking error signal by the tracking error generator 15, a known method such as a push-pull method, a DPP (Differential Push-Pull) method, a DPD (Differential Phase Detection) method, or the like can be used.

The tracking error signal generated by the tracking error generator 15 is input to the track zero cross signal generator 16. The track zero cross signal generator 16 generates a track zero cross signal by binarizing the tracking error signal with a predetermined threshold. Therefore, the track zero cross signal takes a binary value of 0 or 1. The method for generating the track zero cross signal is not limited to this.

The track zero cross signal is input to the central control unit 30. The central control unit 30 refers to the track zero cross signal when performing tracking pull-in to the optical disc. Details of this will be described later.

The reproduction signal generation unit 17 generates a reproduction signal based on the electrical signal output from the light receiving element 11b in the optical pickup 11. The generated reproduction signal is input to the top envelope signal generation unit 19 and the mirror signal generation unit 20.

The top envelope signal generation unit 19 generates a top envelope signal of the reproduction signal.

The mirror signal generator 20 generates a mirror signal from the reproduction signal. Specifically, the mirror signal generation unit 20 generates a bottom envelope signal of the reproduction signal, and generates a mirror signal obtained by binarizing the bottom envelope signal with a predetermined threshold. Therefore, the mirror signal takes a binary value of 0 or 1. The optical disk 40 has an infinite number of spiral tracks, and each track has two irregular shapes. Usually, a mark (a recording mark when the optical disc is a write-once type / rewritable type and an information pit when the optical disc is a read-only type) is formed in the concave portion. That is, a mark exists in the concave portion of the track, and no mark exists in the convex portion of the track. The optical disc 40 has a configuration in which such irregularities are alternately arranged in the radial direction of the optical disc. The tracking pull-in is performed in the concave portion where the mark exists, and the objective lens 11a follows the concave portion thereafter. However, at the time of track-off before tracking pull-in (also referred to as tracking-off), only the optical disk is decentered with the objective lens 11a stopped (the track moves in the radial direction of the optical disk due to the decentering of the optical disk). The objective lens 11a apparently crosses the track of the optical disk. Therefore, when the track is off, the objective lens 11a passes through both the concave and convex portions of the track, so that the reproduction signal has a wavy waveform corresponding to the concave and convex portions. That is, the amplitude of the reproduction signal increases in the concave portion where the mark exists, and the amplitude of the reproduction signal decreases in the convex portion where the mark does not exist. As described above, since the mirror signal is a signal obtained by binarizing the bottom envelope signal of the reproduction signal, when the mirror signal is 0, the objective lens 11a passes through the concave portion where the mark exists, and the mirror signal is 1 In this case, the objective lens 11a passes through a convex portion where no mark exists. The method for generating the mirror signal is not limited to the above.

The objective lens control unit 21 controls the objective lens 11a and causes the objective lens 11a to follow the eccentricity of the optical disc when tracking is pulled. Specifically, the objective lens control unit 21 controls an objective lens actuator (not shown) in the optical pickup 11 so as to be in the radial direction (track direction) of the optical disc and in the direction perpendicular to the information recording surface of the optical disc (focus direction). The objective lens 11a is driven.

The thread control unit 22 controls a thread (not shown) that moves the optical pickup 11, and moves the optical pickup 11 to a desired radial position. Specifically, the sled control unit 22 controls a sled driving device (for example, a sled motor) (not shown) to move the sled mounted with the optical pickup 11 in the radial direction of the optical disc.

In FIG. 1, the central control unit 30 includes a track zero cross signal acquisition unit 32, an eccentricity measurement unit 33, a determination unit 34, a tracking pull-in unit 35, a movement direction determination unit 36, a movement amount determination unit 37, and a sled movement unit 38. including. The function of each part of the central control unit 30 will be apparent from the following description.

In the example of FIG. 1, the tracking control device according to the embodiment of the present invention is realized by the central control unit 30. However, the configuration of the tracking control device is not limited to the configuration of FIG.

FIG. 2 shows a tracking error signal waveform (FIG. 2A), a lens error signal waveform (FIG. 2B), an optical disc in the process from the track-off state to the tracking pull-in when the sled is not moved. It is a figure which shows the relative position (the figure (c)) and the track crossing speed (the figure (d)) of the objective lens seen from FIG. The lens error signal is obtained by converting the position of the objective lens based on the neutral position into an electric signal. The relative position of the objective lens viewed from the optical disk is the relative position of the objective lens with respect to a specific track of the optical disk in the radial direction of the optical disk. The track crossing speed is obtained by differentiating the relative position of the objective lens as viewed from the optical disc with respect to time. The center value of the dotted line in FIGS. 9A and 9B indicates the reference voltage, the center value of the dotted line in FIG. 10C indicates the center value of the eccentric component of the optical disk, and the dotted line in FIG. The center value indicates zero.

The limit value of the track crossing speed at which tracking pull-in is possible is determined by the configuration of the optical disk device and the type of the optical disk, but is mostly close to zero, and tracking pull-in is performed near the shaded portion in the figure. This shaded portion is a portion where the tracking error signal waveform is sparse (FIG. (A)), the portion where the absolute value of the eccentric component of the optical disk is maximum ((c)), and crossing the track. This is the location where the speed is zero ((d) in the figure). As shown in FIG. 6C, since tracking pull-in is performed near the maximum absolute value of the eccentricity component of the optical disc, the reference position of the objective lens that follows the eccentricity of the optical disc changes after the tracking pull-in. As a result, a lens offset occurs as shown in FIG. When a lens offset occurs, the objective lens is made to follow the eccentricity of the optical disc in the state where the offset occurs, so that the movable range in the track direction of the objective lens can be exceeded at the location surrounded by the solid circle in FIG. And may cause damage to the objective lens. In FIG. 2, an arrow A1 indicates tracking pull-in, and an arrow B1 indicates occurrence of a lens offset.

In order to suppress the lens offset after the tracking pull-in, a method of moving the sled after the tracking pull-in using the technique described in Patent Document 3 can be considered. By moving the sled, for example, the objective lens is arranged at the neutral position of the objective lens (the center position of the optical pickup). Hereinafter, this method will be described with reference to FIG.

FIG. 3 shows a tracking error signal waveform (FIG. 3A) and a lens error signal in the process from the track-off state until the thread control after the tracking pull-in is performed when the technique described in Patent Document 3 is used. Waveform (FIG. (B)), relative position of objective lens viewed from optical disc (FIG. (C)), track crossing speed (FIG. (D)), and thread control waveform (FIG. (E)) are shown. FIG. Specifically, the thread control waveform is a waveform of a signal for controlling movement of the thread, and is, for example, a waveform of a thread control signal supplied from the central control unit 30 to the thread control unit 22. The center value of the dotted line in FIGS. 3A, 3B, and 3E indicates the reference voltage, the center value of the dotted line in FIG. 3C indicates the center value of the eccentric component of the optical disc, and FIG. The center value of the dotted line in) indicates zero.

In the thread control shown in FIG. 3, the thread is moved after waiting for the optical disk to make one round after the tracking pull-in. The reason for waiting for the optical disk to make one round is to determine whether the lens offset has occurred in the inner circumference side or the outer circumference side during one round and to measure the lens offset amount. . When the time for one round of the optical disk has elapsed after the tracking pull-in is completed, the sled is moved as shown in FIG. The direction of movement of the sled is the direction in which lens offset occurs, and the amount of movement of the sled corresponds to the amount of lens offset. As shown in FIG. 3B, the lens offset is suppressed by moving the sled. However, in order to wait for the optical disk to make one revolution after the tracking pull-in is completed, the lens offset is generated during this period. Therefore, there is a possibility that the movable range in the track direction of the objective lens may be exceeded at the location surrounded by the round solid line in FIG. In FIG. 3, arrow A2 indicates tracking pull-in, arrow B2 indicates the occurrence of lens offset, arrow C2 indicates the start of movement of the sled, arrow D2 indicates suppression of lens offset, and arrow T2 indicates the period of one round of the optical disc. .

FIG. 4 shows the eccentric component of the optical disc (FIG. 4A), tracking error signal waveform (FIG. 4B), track zero cross signal waveform (FIG. 4C), and top envelope signal waveform in the track-off state. (Drawing (d)) and a figure which shows a mirror signal waveform (figure (e)). The center value of the dotted line in FIG. 7B indicates the reference voltage, and the center value of the dotted line in FIGS. 9A and 9C indicates zero. 4 (b ′) to (e ′) are enlarged views of parts of FIGS. 4 (b) to (e), and are enlarged at two locations. Specifically, the rectangular areas X1 and X2 in FIG. 4 are obtained by enlarging the rectangular areas Y1 and Y2 in FIG. 4, respectively. The tracking error signal is generated by the tracking error generation unit 15, the track zero cross signal is generated by the track zero cross signal generation unit 16, the top envelope signal is generated by the top envelope signal generation unit 19, and the mirror signal is generated by the mirror signal. Generated by the unit 20. Since the objective lens is stopped when the track is off, each waveform shown in FIG. 4 is a waveform depending on the eccentric component of the optical disk. In FIG. 4, the track zero cross signal is a signal obtained by binarizing the tracking error signal with a center value (reference voltage). When the top envelope signal is positive, the mirror signal is 0, and when the top envelope signal is negative, the mirror signal is 1. In FIG. 4, an arrow T3 represents a period of one round of the optical disc.

In the two enlarged waveforms shown in FIGS. 4 (b ′) to (e ′), the portion where the absolute value of the eccentric component of the optical disk is maximized is indicated by a shaded square, and when the objective lens passes the mark ( The edge portion of the track zero cross signal when the top envelope signal is positive and the mirror signal is 0 is indicated by a circle. Here, a circle without shading represents a rising edge, and a shaded circle represents a falling edge. In the example on the left side of the enlarged view, the edge of the track zero-cross signal indicated by a circle changes from a rising state to a falling state with a square shaded portion as a boundary. In FIG. Wraps from bottom to top. Further, in the example on the right side of the enlarged view, the edge of the track zero cross signal indicated by a circle changes from a falling state to a rising state with a square shaded portion as a boundary. In FIG. The eccentricity is folded back from above. In other words, the edge of the track zero cross signal when the objective lens passes the mark changes at the turn-back timing of the eccentricity of the optical disk. The relationship between the edge of the track zero-cross signal when the objective lens passes the mark and the eccentric direction of the optical disk (the direction of the track displacement in the track direction due to the eccentricity of the optical disk) is unique depending on the configuration of the optical disk device and the type of optical disk. Therefore, the decentering direction of the optical disk can be found at the edge change point of the track zero cross signal when the objective lens passes the mark. However, the relationship between the edge of the track zero cross signal when the objective lens passes the mark and the eccentric direction of the optical disc needs to be obtained in advance for each type of optical disc.

In this embodiment, the tracking pull-in is performed at the timing when the edge of the track zero cross signal changes when the objective lens passes the mark. Then, the thread is moved simultaneously with the tracking pull-in. Here, “simultaneously” includes not only the case where the tracking pull-in and the movement of the thread are performed completely simultaneously, but also the case where both are performed substantially simultaneously. For example, it is sufficient that the problems described in the technique disclosed in Patent Document 3 are solved at the same time, and in one example, the thread is moved immediately after the tracking pull-in. As shown above, the eccentric direction of the optical disc can be determined by how the edge of the track zero cross signal changes when the objective lens passes the mark. Move it. In addition, the absolute value of the eccentric component of the optical disc becomes the maximum at the edge change point of the track zero cross signal when the objective lens passes the mark. Simultaneously with the drawing, the sled may be moved by the amount of eccentricity of the optical disk. The amount of eccentricity corresponds to Dh in FIG. 4A, that is, the amplitude value on one side of the eccentric component of the optical disk. In the example of FIG. 3, the sled is moved after waiting for the optical disk to make one round after the tracking pull-in, whereas in this embodiment, the sled is moved simultaneously with the tracking pull-in.

FIG. 5 shows a tracking error signal waveform (FIG. 5A) and a lens error signal waveform (FIG. 5B) in the process from the track-off state to the tracking pull-in and thread control in the present embodiment. FIG. 5 is a diagram showing a relative position of the objective lens as viewed from the optical disc (FIG. 3C), a track crossing speed (FIG. 4D), and a thread control waveform (FIG. 3E). The center value of the dotted line in FIGS. 5A, 5B, and 5E indicates the reference voltage, the center value of the dotted line in FIG. 5C indicates the center value of the eccentric component of the optical disc, and FIG. The center value of the dotted line in) indicates zero.

As shown in FIG. 5E, in this embodiment, since the thread is moved simultaneously with the tracking pull-in, no lens offset occurs after the tracking pull-in as shown in FIG. 5B. The thread control waveform for moving the thread is not limited to that shown in FIG. In FIG. 5, an arrow A4 indicates tracking pull-in, and an arrow C4 indicates the start of sled movement.

Next, the operation (tracking control method) of the tracking control apparatus according to the embodiment of the present invention will be described in detail with reference to FIGS.

FIG. 6 is a flowchart showing an example of tracking control by the tracking control apparatus according to the embodiment of the present invention.

When the tracking control is started (for example, when a program stored in the central control unit 30 starts executing the tracking control), the central control unit 30 acquires a track zero cross signal (step S1). Specifically, the track zero cross signal generation unit 16 generates a tracking error signal based on the electrical signal from the optical pickup 11, binarizes the tracking error signal to generate a track zero cross signal, and the central control unit 30. Obtains a track zero-cross signal from the track zero-cross signal generator 16.

Next, the central control unit 30 measures the eccentricity of the optical disk using the track zero cross signal (step S2). Specifically, the central control unit 30 measures the number of the objective lenses 11a traversing the track of the optical disc (hereinafter referred to as the track traversing number) while the optical disc makes one round in the track-off state. The number of track crossings can be obtained by counting one cycle of the track zero cross signal as one and continuing counting until the optical disk makes one round. The central control unit 30 calculates the amount of eccentricity from the measured number of track crossings. However, the eccentricity referred to here corresponds to Dh in FIG. 4A, and is 2 × Dh = tp × CT / 2, where CT is the number of track crossings and tp is the track pitch of the optical disk. The calculated eccentricity of the optical disk is stored in the storage unit 31.

Next, the central control unit 30 determines whether a tracking pull-in command has been issued (step S3). If a tracking pull-in command is issued (step S3: YES), the process proceeds to the next step S4. If the tracking pull-in command is not issued (step S3: NO), the determination is continued.

In step S4, the central control unit 30 monitors the track zero cross signal when the objective lens 11a passes the mark based on the top envelope signal or the mirror signal. That is, it is checked in real time whether the edge of the track zero cross signal when the objective lens 11a passes the mark rises or falls. The monitoring result in step S4 is stored in the storage unit 31 in real time.

Next, the central control unit 30 determines whether or not the edge of the track zero cross signal when the objective lens 11a passes the mark has changed (step S5). Specifically, it is determined whether the edge has changed from rising to falling or falling to rising. If the edge changes (step S5: YES), the central control unit 30 performs tracking pull-in at the edge change timing (step S6). If the edge does not change (step S5: NO), the track zero cross signal is continuously monitored until it changes.

Next, the central control unit 30 determines whether the tracking pull-in is successful (step S7). If it succeeds (step S7: YES), the process proceeds to the next step S8. If it fails (step S7: NO), the process returns to step S4 and the track zero cross signal is monitored again.

In step S8, the central control unit 30 determines the moving direction of the sled based on the edge of the track zero cross signal at the start of tracking pull-in. Specifically, in step S5, the central control unit 30 determines how the edge of the track zero cross signal at the time of on-track has changed (whether the edge has changed from rising to falling, or has changed from falling to rising). ) To determine the moving direction of the sled. More specifically, the central control unit 30 is based on the relationship between the edge of the track zero-cross signal when the objective lens passes the mark and the eccentric direction of the optical disc, which is obtained in advance for each type of optical disc. The moving direction of the sled is determined from the type of the optical disk to be tracked and the change in edge at the time of tracking pull-in. The above relationship is stored in the storage unit 31, for example.

Next, the central control unit 30 determines the moving amount of the thread based on the eccentricity measured in step S2 (step S9). For example, the central control unit 30 determines the eccentric amount Dh measured in step S2 as the movement amount of the thread.

Next, the central control unit 30 controls the thread control unit 22 to move the thread by the movement amount determined in step S9 in the movement direction determined in step S8 (step S10).

In step S10, when the movement of the thread is completed, the central control unit 30 ends the tracking control. After the end of tracking control in this embodiment, the thread control method is not limited.

In step S10, if the sled is moved by the amount of eccentricity of the optical disk immediately after the tracking pull-in, the sled may move more than the set sled movement due to the influence of sled vibration or the like. As a countermeasure, there is a limit on the amount of thread movement. Specifically, the central control unit 30 limits the movement amount of the thread to a predetermined amount (upper limit value) or less in step S10. However, the predetermined amount may be arbitrary and may not be limited.

Note that the steps S1, S2, S5, S6, S8, S9, and S10 in FIG. 6 include, for example, the track zero cross signal acquisition unit 32, the eccentricity measurement unit 33, the determination unit 34, and the tracking pull-in unit 35 in FIG. This is executed by the movement direction determination unit 36, the movement amount determination unit 37, and the sled movement unit 38.

FIG. 7 is a flowchart showing another example of tracking control by the tracking control apparatus according to the embodiment of the present invention. The flowchart of FIG. 7 is obtained by adding step S11 to the flowchart of FIG.
Steps S1 to S10 in FIG. 7 are the same as steps S1 to S10 in FIG.

In FIG. 7, before determining whether the edge of the track zero cross signal changes in step S5, the central control unit 30 measures the track crossing period and determines whether the track crossing period is equal to or greater than a predetermined value ( Step S11). In this case, the central control unit 30 measures the track crossing period in real time. The track crossing period corresponds to the period of the track zero cross signal, and the period measurement is performed using the track zero cross signal. The measurement result of the track crossing period is an index for determining the timing of tracking pull-in. The reason for introducing the step S11 is that the track zero cross signal may not be accurately generated due to the f characteristic (frequency characteristics) in the portion where the tracking error signal waveform is dense in FIG. This is because the edge of the track zero cross signal when the objective lens passes the mark may change at a location where the tracking error waveform is dense. In order to prevent the start of tracking pull-in due to this edge change, the process proceeds to step S5 after the track crossing period has increased to some extent.

As described above, according to the tracking control device and the tracking control method according to the embodiment, since the thread is moved simultaneously with the tracking pull-in to the optical disc 40, the lens offset can be suppressed quickly. Thereby, for example, it can be avoided that the objective lens exceeds the movable range, and a stable servo operation can be realized.

The tracking control device and the tracking control method according to the embodiment described above may be realized only by hardware resources such as an electronic circuit, or may be realized by cooperation of hardware resources and software. When realized by the cooperation of hardware resources and software, the tracking control device and the tracking control method are realized by, for example, a computer program being executed by a computer, and more specifically, ROM (Read Only Memory). This is realized by reading a computer program recorded on a recording medium such as a main storage device and executing it by a central processing unit (CPU). The computer program may be provided by being recorded on a computer-readable recording medium such as an optical disk, or may be provided via a communication line such as the Internet.

It should be noted that the present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist of the present invention.

For example, in the above-described embodiment, the configuration including the top envelope signal generation unit 19 and the mirror signal generation unit 20 is illustrated, but a configuration including only one of them may be used. In the configuration having the top envelope signal generation unit 19 and the mirror signal generation unit 20, the tracking control apparatus may selectively use the top envelope signal and the mirror signal according to the type of the optical disc. For example, some optical discs do not detect a mirror signal. In this case, tracking control is performed based on the top envelope signal. In the above embodiment, the timing at which the objective lens passes the mark is detected by the top envelope signal or the mirror signal. However, the present invention is not limited to these signals, and any other signal may be used as long as it is a signal for detecting the mark. May be detected. A signal for detecting the mark can be generated by reflected light from the information recording surface of the optical disc.

In the above-described embodiment, the configuration in which the amount of movement of the thread is determined based on the measured amount of eccentricity is exemplified. However, the amount of movement of the thread may be determined by other methods, for example, set in advance. It may be a fixed value.

10 optical disk device, 11 optical pickup, 11a objective lens, 11b light receiving element, 12 spindle motor, 13 laser control unit, 14 spindle control unit, 15 tracking error generation unit, 16 track zero cross signal generation unit, 17 reproduction signal generation unit, 19 Top envelope signal generation unit, 20 mirror signal generation unit, 21 objective lens control unit, 22 thread control unit, 30 central control unit, 31 storage unit, 32 track zero cross signal acquisition unit, 33 eccentricity measurement unit, 34 determination unit, 35 tracking pull-in unit, 36 moving direction determining unit, 37 moving amount determining unit, 38 thread moving unit, 40 optical disk.

Claims

A method for tracking control of an optical pickup that condenses and irradiates an information recording surface of an optical disc with a laser beam by an objective lens, receives reflected light from the information recording surface of the optical disc and converts it into an electrical signal,
A track zero-cross signal acquisition step of acquiring a track zero-cross signal obtained by binarizing a tracking error signal generated from the electrical signal with a predetermined threshold;
A determination step of determining whether an edge of the track zero-cross signal has changed when the objective lens passes a mark on a track of the optical disc when the track is off;
Based on the determination result of the determination step, a tracking pull-in step for starting tracking pull-in at a timing when the edge changes;
A moving direction determining step for determining a moving direction of a sled that moves the optical pickup based on an edge of the track zero-cross signal at the start of the tracking pull-in;
A sled moving step of moving the sled by a predetermined amount of movement in the determined moving direction simultaneously with the tracking pull-in;
A tracking control method comprising:
An eccentricity measuring step for measuring the eccentricity of the optical disc using the track zero-cross signal when the track is off;
A moving amount determining step for determining a moving amount of the thread based on the measured eccentricity amount;
Further comprising
The tracking control method according to claim 1, wherein in the sled moving step, the sled is moved by the determined moving amount.
3. The tracking control method according to claim 2, wherein in the movement amount determination step, the movement amount of the thread is limited to a predetermined amount or less.
4. The track crossing period is measured based on the track zero cross signal, and the determination step is executed when the track crossing period becomes a predetermined value or more. The tracking control method according to the item.
The moving direction determining step determines the moving direction of the sled based on the relationship between the edge of the track zero cross signal and the eccentric direction of the optical disk, which is obtained in advance for each type of optical disk. Item 5. The tracking control method according to any one of Items 1 to 4.
A tracking control device for an optical pickup that condenses and irradiates an information recording surface of an optical disc with a laser beam by an objective lens, receives reflected light from the information recording surface of the optical disc and converts it into an electrical signal,
Track zero cross signal acquisition means for acquiring a track zero cross signal obtained by binarizing a tracking error signal generated from the electrical signal with a predetermined threshold;
Determining means for determining whether an edge of the track zero cross signal has changed when the objective lens passes a mark on a track of the optical disc at the time of track off;
Tracking pull-in means for starting tracking pull-in at the timing when the edge changes based on the determination result of the determination means;
A moving direction determining means for determining a moving direction of a sled that moves the optical pickup based on an edge of the track zero-cross signal at the start of the tracking pull-in;
A sled moving means for moving the sled by a predetermined moving amount in the determined moving direction simultaneously with the tracking pull-in;
A tracking control device comprising:
Eccentricity measuring means for measuring the eccentricity of the optical disc using the track zero cross signal when the track is off,
A moving amount determining means for determining a moving amount of the thread based on the measured eccentricity amount;
Further comprising
The tracking control apparatus according to claim 6, wherein the sled moving unit moves the sled by the determined amount of movement.
The tracking control device according to claim 7, wherein the movement amount determination means limits the movement amount of the thread to a predetermined amount or less.
9. The track crossing period is measured based on the track zero cross signal, and the determination by the determination unit is executed when the track crossing period exceeds a predetermined value. The tracking control device according to claim 1.
The moving direction determining means determines the moving direction of the sled based on the relationship between the edge of the track zero cross signal and the eccentric direction of the optical disk, which is obtained in advance for each type of optical disk. Item 10. The tracking control device according to any one of Items 6 to 9.