JP2007328874A - Optical disk drive and tracking control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve quality of a tracking error signal DPP. <P>SOLUTION: In an optical disk drive 10 for generating an offset signal OFS indicating offset from a detection signal in accordance with light receiving quantity of a sub-reflected light spot Qs by a sub-beam SB for tracking control, a tracking control part 12A eliminates a frequency component being the prescribed cut off frequency of the number of rotation of disk or more from the offset signal OFS generated consequently by performing a LPF process for a side push-pull signal SPP generated from the detection signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus and a tracking control method, and is suitable for application to an optical disc apparatus that requires high-precision tracking control, for example.

  2. Description of the Related Art Conventionally, an optical disc apparatus detects a deviation of an irradiation position of a light beam with respect to a desired track in a signal recording layer of an optical disc (hereinafter referred to as an irradiation deviation) as a tracking error signal.

  In general, this tracking error signal is obtained by dividing light into two regions by using a phenomenon that light and dark are produced in a reflected light beam that is reflected by an optical disk according to an irradiation deviation from the track of the light beam. The reflected light beam is received by the detector, and a tracking error signal is generated from the light amount difference between the two areas, and is generated by a so-called push-pull method.

  In the optical disc apparatus, in order to accurately irradiate the desired beam with the light beam, the objective lens is moved so as to reduce the irradiation deviation based on the tracking error signal to control the irradiation position of the light beam. At this time, if the received light beam deviates from the center of the photodetector due to a lens shift or the like in which the positional relationship between the photodetector that receives the light beam and the objective lens is shifted, the generated tracking error signal is In fact, a so-called offset occurs in which the signal level changes even though there is no irradiation deviation.

Therefore, in the optical disc apparatus, the light beam is split into a main beam and a sub beam, an offset signal indicating only an offset is generated from the sub beam, and the offset signal is subtracted from a main push-pull signal indicating both irradiation deviation and offset. Thus, there is a configuration in which an offset component is canceled from the main push-pull signal and a tracking error signal representing only an irradiation deviation is generated (for example, see Patent Document 1).
JP 2005-122869 A

  By the way, in the optical disk apparatus having such a configuration, in order to increase the utilization efficiency of the main beam used for recording and reproduction of the optical disk, the light amount of the sub beam is made smaller than that of the main beam, and the side push-pull signal acquired from the sub beam is An offset signal is generated by amplifying and matching the signal level with the offset component of the main push-pull signal acquired from the main beam.

  For this reason, the offset signal generated from the sub beam greatly amplifies noise components due to scratches on the optical disk and stray light. As a result, when the offset signal is subtracted from the main push-pull signal, not only the offset component but also the noise component is subtracted, resulting in a problem that the quality of the tracking error signal is lowered.

  The present invention has been made in consideration of the above points, and intends to propose an optical disc apparatus and a tracking control method for improving the quality of a tracking error signal.

  In order to solve such a problem, in the present invention, a light beam emitted from a light source is split into a main beam for reading recorded information in a signal recording layer of a rotated optical disc and a sub beam for tracking control, and the main beam And the sub beam is condensed and irradiated to the track of the signal recording layer of the optical disc, the main beam and the sub beam reflected by the optical disc are received, and a detection signal corresponding to the amount of received light is generated. An offset including an offset component that generates a main push-pull signal based on the corresponding detection signal, and that indicates that the main beam and the sub beam have deviated from the center of the light detection unit based on the detection signal corresponding to the received light amount of the received sub beam. Generate signal and offset signal from main push-pull signal By subtracting, a tracking error signal is generated, and the objective lens is driven in the tracking direction based on the tracking error signal, so that a component having a predetermined cutoff frequency higher than the rotation speed of the optical disk is removed from the offset signal. .

  As a result, it is possible to remove the noise component from the offset signal that is generated from the detection signal corresponding to the sub-beam having a small amount of light and greatly affects the noise component, and to improve the quality of the offset signal.

  According to the present invention, the noise component is removed from the offset signal that is generated from the detection signal corresponding to the sub-beam having a small amount of light and the influence of the noise component greatly appears, and the quality of the offset signal used for generating the tracking error signal is improved. Thus, an optical disc apparatus and a tracking control method that improve the quality of the tracking error signal can be realized.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Overall Configuration of Optical Disc Device In FIG. 1, reference numeral 10 denotes an optical disc device as a whole, which includes a CPU (Central Processing Unit), a ROM (Read Only Memory) storing a cutoff frequency and various programs, and the CPU. A control unit 12 including a RAM (Random Access Memory) as a work memory controls each unit of the optical disc apparatus 10.

  That is, the control unit 12 rotates the spindle motor 14 via the servo circuit 13 and rotationally drives the optical disk 100 placed on a turntable (not shown) by a CLV (Constant Linear Velocity) method. Further, the control unit 12 rotates the feed motor 15 via the servo circuit 13 and moves the optical pickup 20 along the guide shaft 17 in the radial direction of the optical disc 100. Further, the control unit 12 controls the optical pickup 20 to execute reading and writing of data with respect to the optical disc 100.

  As shown in FIG. 2, the laser diode 21 of the optical pickup 20 emits laser light in accordance with the drive current supplied from the control unit 12 (FIG. 1), and enters the diffraction element 22 as a light beam 40.

  The diffraction element 22 splits the light beam 40 into a main beam MB that is a zero-order light beam and four sub-beams SB that are ± first-order light beams, and enters the beam splitter 24. Note that in order to increase the light use efficiency of the main beam MB for reading the recording information of the signal recording layer, the light amount of the sub beam SB is made smaller than that of the main beam MB.

  The beam splitter 24 reflects the incident light beam 40 composed of the main beam MB and the sub beam SB, changes its direction by 90 °, and enters the collimator lens 25. The collimator lens 25 converts the light beam 40 incident as diverging light into parallel light, changes its direction by 90 ° by the rising mirror 26, and makes it incident on the objective lens 30 via the λ / 4 wavelength plate 27. The objective lens 30 condenses the light beam 40 and irradiates the optical disc 100 with it.

  As a result, as shown in FIG. 3, the main spot Pm by the main beam MB and the four sub-spots Ps by the four sub-beams SB are irradiated as light beams 40 onto desired tracks in the signal recording layer of the optical disc 100. Here, the track TR is composed of a groove G and a land L, and the objective lens 30 irradiates the main spot Pm to the center of the track TR which is the center of the groove G, and each sub spot Ps from the center of the track TR. Irradiate to a position shifted by 1/4 track.

  The objective lens 30 (FIG. 2) receives a reflected light beam 50 formed by reflecting the light beam 40 by the optical disc 100, and passes through the λ / 4 wavelength plate 27, the upright mirror 26, and the collimator lens 25, and thereby a beam splitter. 24 is incident. The beam splitter 24 transmits the reflected light beam 50 and enters the photodetector 60 through the multi lens 33 that corrects aberration.

  Here, as shown in FIG. 4, the photodetector 60 includes a main spot detector 61 and two sub-spot detectors 62 and 63. The main spot detector 61 has four detection areas 61 </ b> A to 61 </ b> D, and receives the main reflected spot Qm by the main beam MB as a reflected light beam 50.

  On the other hand, the sub-spot detectors 62 and 63 have detection areas 62A and 62B and detection areas 63A and 63B, respectively, and receive the sub-reflection spot Qs by the sub-beam SB as the reflected light beam 50 by the sub-spots 62 and 63, respectively. To do. The photodetector 60 photoelectrically converts the reflected light beam 50 to generate a detection signal, and supplies the detection signal to the control unit 12 (FIG. 1).

  Incidentally, since the optical disc apparatus 10 generates a focus error signal using the astigmatism method, the light intensity distribution of each reflected light spot Q apparently rotates 90 degrees. Therefore, the alignment direction of the sub-spot Ps with respect to the main spot Pm (FIG. 3) is the vertical direction, whereas the dividing line Cp when calculating the tracking error signal in FIG. 4 is the horizontal direction.

  The control unit 12 (FIG. 1) generates a reproduction RF signal, a focus error signal, and a tracking error signal DPP from this detection signal, and sends them to the servo circuit 13. The servo circuit 13 generates a drive control signal based on the focus error signal and the tracking error signal DPP supplied from the control unit 12, and controls the biaxial actuator 36 (FIG. 2), so that the light beam 40 is transmitted to the optical disc 100. The objective lens 30 is driven in the focus direction and the tracking direction so as to accurately irradiate the desired track at.

(2) Generation of Tracking Error Signal Next, generation of the tracking error signal will be described.

  When the detection signal is supplied from the photodetector 60 of the optical pickup 20, the control unit 12 (FIG. 1) in the optical disc apparatus 10 generates a tracking error signal from the detection signal by the tracking control unit 12A.

  Specifically, as shown in FIG. 5, the tracking control unit 12A supplies the main detection signal MD supplied from the main spot detector 61 (FIG. 4) to the MPP generation unit 71, while the sub spot detector 62 and The sub detection signal SD supplied from 63 is supplied to the SPP generator 72.

  The MPP generation unit 71 subtracts the main detection signals MDc and MDd representing the light reception amounts of the detection regions 61C and 61D from the main detection signals MDa and MDb representing the light reception amounts of the detection regions 61A and 61B (FIG. 4) according to the following equation. As a result, the main push-pull signal MPP that is the light amount difference across the dividing line Cp in the main spot detector 61 is calculated.

  MPP = (MDa + MDb) − (MDc + MDd) (1)

  Thereby, the MPP generation unit 71 can obtain the main push-pull signal MPP in which one cycle is a sine wave corresponding to the track pitch of the optical disc 100 as shown in FIG. That is, the main push-pull signal MPP represents a deviation of the main spot Pm from the center position of the track TR (hereinafter referred to as an irradiation deviation).

  Further, the center of the reflected light spot Qm is the center of the main spot detector 61 due to the fact that only the objective lens 30 moves in the tracking direction (hereinafter referred to as lens shift). If so, a so-called offset is generated in which the signal level of the main push-pull signal MPP changes despite the fact that no irradiation deviation has occurred. Then, the MPP generation unit 71 (FIG. 5) sends the main push-pull signal MPP including the irradiation deviation component and the offset component to the DPP generation unit 75.

  On the other hand, the SPP generation unit 72 (FIG. 5), from the sub detection signals SD62a and SD63a representing the light reception amounts of the detection regions 62A and 63A (FIG. 4), sub detection signals representing the light reception amounts of the detection regions 62B and 63B, according to the following equation. By subtracting SD62b and SD63b, respectively, the light amount difference across the dividing line Cp in the sub spot detectors 62 and 63 is calculated, and the sum of the light amount differences is calculated as the side push-pull signal SPP.

  SPP = (SD62a-SD62b) + (SD63a-SD63b) (2)

  Here, as described above with reference to FIG. 3, the two sub-spots Ps adjacent in the tracking direction are each irradiated to a position separated by a half track, so the phase between the two adjacent sub-spots Ps is 180 ° off. For this reason, by calculating the light amount difference in each detection area of the sub spot detectors 62 and 63, the irradiation deviation component generated in each sub reflection spot Qs is canceled, and the above-described offset component remains in each light amount difference. It is.

  For this reason, the side push-pull signal SPP calculated according to the equation (2) mainly represents an offset. Then, the SPP generation unit 72 sends the side push-pull signal SPP to an LPF (Low Pass Filter) processing unit 73.

  The LPF processing unit 73 removes high-frequency components from the side push-pull signal SPP by LPF processing, which will be described later, and sends the side push-pull signal SPP subjected to LPF processing to the coefficient multiplication unit 74.

  The coefficient multiplication unit 74 multiplies the LPF-processed side push-pull signal SPP by a predetermined coefficient K corresponding to the light amount ratio of the main reflected light spot Qm and the sub-reflected light spot Qs according to the following formula, and performs the LPF process. The offset signal OFS is calculated by matching the signal level of the side push-pull signal SPP to the same level as the offset component included in the main push-pull signal MPP.

  OFS = K × SPP (3)

  As a result, the coefficient multiplication unit 74 can generate the offset signal OFS that does not include the irradiation deviation component and includes the offset component at the same level as the main push-pull signal MPP as shown in FIG. 6B. Then, the coefficient multiplier 75 sends this offset signal OFS to the DPP generator 75.

  When the DPP generation unit 75 calculates the tracking error signal DPP by subtracting the offset signal OFS from the main push-pull signal MPP according to the following equation to cancel the offset, the tracking error signal DPP is converted into the servo circuit 13 (FIG. 2). It is made to supply to.

  DPP = MPP-OFS (4)

  Up to this point, for convenience of explanation, when the irradiation position of the light beam 40 is moved in the radial direction (tracking direction) of the optical disc 100 as the tracking error signal DPP, the spot P (Pm and Ps) by the light beam 40 with respect to the track TR. The tracking error signal DPP calculated as a sine wave according to the irradiation deviation of) has been described. Next, the tracking error signal DPP actually generated when the optical disc 100 is rotated and a desired track TR is irradiated with a spot by the light beam 40 will be described.

(3) Noise component and offset component in tracking error signal (3-1) Noise component As described above, the tracking error signal DPP is obtained by subtracting the offset signal OFS from the main push-pull signal MPP as shown in equation (4). Is calculated by Here, the light quantity of the sub beam SB that is the basis of the offset signal OFS is smaller than that of the main beam MB, and therefore, the signal level of the side push-pull signal SPP is smaller than that of the main push-pull signal MPP. For this reason, it is necessary to amplify the side push-pull signal SPP as in equation (3) so that the signal level of the offset signal OFS matches the same level as the offset component of the main push-pull signal MPP.

  However, the side push-pull signal SPP includes not only an offset component but also a noise component having a high frequency caused by stray light, a scratch on the optical disc 100, and the like. Not only the components but also the noise components are simultaneously amplified, and the quality of the offset signal OFS is degraded.

  For example, when the optical disc 100 is rotated with the objective lens 30 fixed, that is, when the optical disc 100 is rotated with the tracking servo turned OFF, the track TR is formed in a spiral shape, and therefore the track TR with respect to the objective lens 30 is formed. Position gradually shifts according to the rotation of the optical disk 100, and an irradiation shift occurs with one rotation of the optical disk 100 as one cycle. As a result, as shown in FIG. 7A, a periodic pattern representing an irradiation deviation is formed in the generated main push-pull signal MPP.

  However, when the side push-pull signal SPP is amplified as it is in the tracking servo OFF state to generate the offset signal OFS so as not to cause a periodic offset due to lens shift, the offset in the side push-pull signal SPP is generated. Not only the components but also the above-mentioned high-frequency noise components are simultaneously amplified, and as shown in FIG. 7B, no periodic offset is generated, so that a large amplitude is generated in the offset signal OFS that should be substantially linear. .

  Therefore, in the present embodiment, an LPF process, which will be described later, is performed on the side push-pull signal SPP to remove a high-frequency noise component.

  However, as will be described in detail later, the optical disc apparatus 10 may periodically shift the objective lens 30 to cause a periodic offset in the side push-pull signal SPP. If this periodic offset component is removed from the side push-pull signal SPP, the offset component cannot be offset from the main push-pull signal MPP even if the offset signal OFS based on the side push-pull signal SPP is subtracted.

  Therefore, in the present embodiment, although the noise component is removed from the side push-pull signal SPP by the LPF process, this periodic offset component is left. Next, this periodic offset will be described.

(3-2) Offset Component Generally, it is known that the track center Ct, which is the center of the track TR, is slightly decentered from the rotation center Cr of the optical disc 100. Thereby, a periodic offset occurs in the side push-pull signal SPP.

  That is, as shown in FIG. 8A, when the track center Ct is located closer to the rotation center Cr when viewed from the objective lens 30, the track TR is biased to the outside of the objective lens 30. At this time, the tracking control unit 12A shifts the objective lens 30 outward to adjust the light beam 40 to the track irradiation position, so that the side push-pull signal SPP is negative with respect to the reference voltage as shown in FIG. An offset occurs.

  On the other hand, as shown in FIG. 8B, when the track center Ct and the rotation center Cr are at the same distance as viewed from the objective lens 30 and the two centers are aligned at right angles to the tracking direction, the track TR comes to the center position of the objective lens 30. At this time, since the tracking control unit 12A aligns the objective lens 30 with the center of the optical path, the offset of the side push-pull signal SPP becomes almost zero as shown in FIG.

  On the other hand, as shown in FIG. 10A, when the track center Ct is at a position separated from the rotation center Cr as viewed from the objective lens 30, the track TR is biased toward the inner peripheral side with respect to the objective lens 30. To do. At this time, the tracking control unit 12A shifts the objective lens 30 inward to adjust the light beam 40 to the track irradiation position, so that the side push-pull signal SPP is positive with respect to the reference voltage as shown in FIG. An offset occurs.

  Further, as shown in FIG. 10B, when the track center Ct and the rotation center Cr are at the same distance as viewed from the objective lens 30 and are arranged at right angles to the tracking direction, the track TR is again the objective lens. Come to the center of 30. At this time, since the tracking control unit 12A aligns the objective lens 30 with the center of the optical path, the offset of the side push-pull signal SPP becomes almost zero as shown in FIG.

  Therefore, an offset with one rotation (360 °) of the optical disc 100 (track TR) as one cycle is generated according to the eccentricity of the track TR. Since the eccentric amount of the track TR in each optical disc 100 is constant on the inner and outer peripheral sides of the optical disc 100, the side push-pull signal SPP periodically varies with substantially the same amplitude according to the rotation of the optical disc 100. An offset component appears. That is, the offset due to the eccentricity of the optical disc 100 (the eccentricity of the track TR) occurs at a cycle of one rotation of the optical disc 100.

  Here, other causes for the occurrence of an offset in the side push-pull signal SPP include various factors such as a shift of the moving axis of the objective lens 30 from the radius of the optical disc 100 and a fluctuation of inertia of the objective lens 30 when the seek movement is stopped. However, in many cases, these offset components are generated not as periodic, but as direct current components, or appear as frequencies lower than the disk rotation speed. On the other hand, as described above, noise components due to stray light or scratches on the optical disc 100 generally appear in the side push-pull signal SPP as components higher than the disc rotation speed.

  Therefore, in the present embodiment, once the frequency component equal to or higher than a predetermined threshold value higher than the disc rotation speed is removed, the noise component is removed from the side push-pull signal SPP by the LPF process, and once per rotation of the optical disc 100. The periodic offset component generated in the period is surely left.

(4) LPF processing Next, the LPF processing will be described.

  Specifically, the cut-off frequency of the LPF processing unit 73 of the tracking control unit 12 </ b> A is set to be larger than the disc rotation speed of the optical disc 100. Here, since the optical disc apparatus 100 rotates the optical disc 100 by the CLV method, a plurality of cut-off frequencies corresponding to the number of disc revolutions are set.

  For example, as shown in FIG. 11, the LPF processing unit 73 is set with three stages of cut-off frequencies as cut-off frequencies. In this case, for the disk rotation speed less than 7200 [rpm], 130 Hz which is 10 [Hz] higher than 120 [Hz] corresponding to 7200 [rpm] is set as the first cutoff frequency. On the other hand, for a disk rotational speed of 7200 [rpm] or more and less than 9600 [rpm], the second cutoff frequency is 170 [Hz], which is 10 [Hz] larger than 160 [Hz] corresponding to 9600 [rpm]. ] Is set. On the other hand, for the disc rotation speed of 12000 [rpm] or more, 210 [Hz] which is 10 [Hz] larger than 200 [Hz] corresponding to 12000 [rpm] is set as the third cutoff frequency.

  Then, the LPF processing unit 73 selects a cut-off frequency corresponding to the disc rotation speed information of the optical disc 100 supplied from the control unit 12, and removes a frequency component equal to or higher than the cut-off frequency from the side push-pull signal SPP.

  As a result, the LPF processing unit 73 can remove a periodic offset component that occurs once per rotation of the optical disc 100 while removing a noise component from the side push-pull signal SPP.

  At this time, the LPF processing unit 73 selects the cut-off frequency according to the number of rotations of the disc, and therefore can almost eliminate noise components having a frequency higher than the offset component due to the eccentricity of the optical disc 100. A noise component can be effectively removed from the side push-pull signal SPP.

  Thus, by LPF processing using the cutoff frequency set to be equal to or higher than the disk rotation speed, for example, the offset signal from the same side push-pull signal SPP used in FIG. 7B (in the case of tracking servo OFF) is used. When the OFS is generated, a good offset signal OFS representing a substantially straight line can be obtained as shown in FIG.

  As a result, as shown in FIG. 12, even when an offset due to the eccentricity of the optical disc 100 appears periodically, it is possible to obtain a high-quality offset signal OFS with less noise components while leaving the offset components. it can. In FIG. 12, the offset signal OFS is preliminarily multiplied by minus so that the phase of the offset signal OFS is opposite to that of the main push-pull signal MPP. In this case, by adding the offset signal OFS to the main push-pull signal MPP, it is possible to generate a tracking error signal DPP that represents an irradiation deviation by canceling the offset component.

(5) Operation and Effect In the above configuration, the reflected light beam is detected from the detection signal corresponding to the received light amount of the sub reflected light spot Qs by the sub beam SB for tracking control out of the reflected light beam 50 reflected by the optical disc 100. In the optical disc apparatus 10 that generates the offset signal OFS that includes an offset component indicating that 50 is shifted from the center of the photodetector 60, the tracking control unit 12A performs the side push-pull signal SPP generated from the detection signal. By executing the LPF process, a frequency component equal to or higher than a predetermined cutoff frequency higher than the disk rotation speed is removed from the resulting offset signal OFS.

  Here, as in the conventional so-called differential push-pull method, in the method of generating a side push-pull signal that represents both offset and irradiation deviation from the sub-beam SB, if the side push-pull signal SPP is subjected to LPF processing, a tracking error is generated. Since the high-frequency irradiation shift component necessary for generating the signal DPP is also removed, and the tracking error signal DPP with high accuracy cannot be generated, the LPF processing cannot be executed.

  On the other hand, in the above-described embodiment, a high frequency is obtained in advance by a so-called five-spot differential push-pull method that splits the light beam 40 into a total of five light beams including the main beam MB and the four sub beams SB. Since the side push-pull signal SPP representing only the offset is generated by canceling the irradiation deviation component, the irradiation deviation component of the side push-pull signal SPP is not required for generating the tracking error signal DPP. Furthermore, the high frequency offset component caused by the lens shift corresponding to the irradiation deviation in the side push-pull signal SPP has a very small signal change compared to the offset component caused by the eccentricity of the optical disc 100, and is eliminated. However, it hardly causes any trouble. In addition, the offset component that appears greatly in the side push-pull signal SPP often occurs at a frequency lower than the offset component that appears in substantially the same period as the disk rotation speed, and at a frequency equal to or higher than the disk rotation speed, noise is greater than the offset component. The influence of the component becomes large.

  In the present invention, paying attention to the above, a frequency component having a frequency equal to or higher than the cut-off frequency equal to or higher than the disk rotation speed is removed from the side push-pull signal SPP.

  Thus, the tracking control unit 12A can effectively remove the noise component from the offset signal OFS generated based on the side push-pull signal SPP, while reducing the offset component that is simultaneously removed as much as possible. The quality of the signal OFS can be improved.

  Further, since a so-called peaky noise component showing a steep change can be surely removed from the offset signal OFS, it is possible to prevent a sudden change in the drive voltage of the biaxial actuator 36, and the optical disc apparatus 10 at the time of tracking servo can be prevented. The operation can be stabilized.

  In the CLV optical disc apparatus 10 that changes the rotational speed of the optical disc 100 according to the position of the track irradiated with the light beam 40 on the optical disc 100, the tracking control unit 12A sets the cutoff frequency according to the disc rotational speed. Since the change is made, it is possible to more effectively remove the frequency component having a high ratio of the noise component equal to or higher than the disk rotation speed.

  Further, in the tracking control unit 12A, three cutoff frequencies are set according to the rotation speed of the optical disc 100, and one cutoff frequency is selected from the three cutoff frequencies according to the disk rotation number supplied from the control unit 12. Is selected, and the frequency component that is equal to or higher than the cutoff frequency is removed from the side push-pull signal SPP, so that the LPF process can be executed with a simple configuration.

  Further, the optical disk apparatus 10 generates the offset signal OFS by generating the offset signal OFS by multiplying the side push-pull signal SPP by a predetermined coefficient K, since the light amount of the sub beam SB is smaller than the light amount of the main beam MB. Is set to the same level as the offset component of the main push-pull signal MPP generated from the main beam MB.

  Since the tracking control unit 12A removes the noise component from the side push-pull signal SPP by LPF processing, it can prevent the noise component from being amplified in the offset signal OFS.

  According to the above configuration, in the optical disc apparatus 10 that generates the offset signal OFS representing the offset due to the lens shift from the sub beam SB, the side push-pull signal SPP generated from the sub beam SB has a cutoff frequency higher than the disc rotation speed. By removing the frequency component, the noise component is removed from the offset signal OFS, which is generated from the detection signal corresponding to the sub beam SB with a small amount of light, so that the influence of the noise component appears greatly, and the tracking error signal is generated. The quality of the offset signal OFS used can be improved, and thus the optical disc apparatus and the tracking control method for improving the quality of the tracking error signal DPP can be realized.

(6) Other Embodiments In the above-described embodiment, the tracking control unit 12A has described the case where three cutoff frequencies are set according to the number of disk rotations. The number of cut-off frequencies is not limited to this, and there is no limit. Further, the cut-off frequency may be constantly changed so as to follow the disc rotation speed. For example, by setting the disc rotation speed +10 [Hz] as the cut-off frequency, the noise component is more effectively removed. be able to.

  Further, in the above-described embodiment, the case where the CLV method in which the disk rotation speed changes according to the track irradiation position on the optical disk 100 has been described, but the present invention is not limited to this, and the disk rotation speed is always set. The same effect can be obtained even when applied to a constant CAV (Constant Angular Velocity) method or a method in which the disk rotation speed changes partially.

  Furthermore, in the above-described embodiment, the optical disk apparatus 10 has been described with respect to the case where the light beam 40 is divided into the main beam MB and the four sub-beams SB, which is a so-called 5-spot differential push-pull method. The present invention is not limited to this, and the same effect can be obtained for any type of optical disc apparatus as long as the system generates an offset signal mainly representing an offset from the sub-beam SB.

  Furthermore, in the above-described embodiment, the tracking control unit 12A has described the case where the LPF process is performed before the side push-pull signal SPP is multiplied by the coefficient K. However, the present invention is not limited to this. After the side push-pull signal SPP is multiplied by the coefficient K, LPF processing may be executed, and this may be used as the offset signal OFS. Even in this case, the same effects as those of the above-described embodiment can be obtained.

  Furthermore, in the above-described embodiment, the spindle motor 14 as the disk rotating unit, the diffraction element 22 as the separation unit, the objective lens 30 as the objective lens, the photodetector 60 as the light detection unit, and the main push An MPP generation unit 71 as a pull signal generation unit, an SPP generation unit 72 as an offset signal generation unit, an LPF processing unit 73 and a coefficient multiplication unit 74, and a DPP generation unit 75 as a tracking signal generation unit serve as an optical disc apparatus. Although the case where the optical disk device 10 is configured has been described, the present invention is not limited to this, and a disk rotating unit, a spectroscopic unit, an objective lens, a main push-pull signal generation unit, and other various configurations, The optical disc apparatus of the present invention is configured by the offset signal generation unit and the tracking signal generation unit. It may be.

  The optical disk device and the tracking control method of the present invention can be used for an optical disk device mounted on various electronic devices, for example.

1 is a schematic diagram illustrating an overall configuration of an optical disc device. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram which shows the main spot and subspot with which a track | truck is irradiated. It is a basic diagram with which it uses for description of light reception of a reflected light spot. It is a basic diagram which shows the structure of a tracking control part. It is an approximate line figure used for explanation of generation of a tracking error signal. It is a basic diagram with which it uses for description of the noise removal by LPF process. It is a basic diagram with which it uses for description of the positional relationship (1) of eccentricity and an objective lens. It is a basic diagram with which it uses for description of generation | occurrence | production of a periodic offset. It is a basic diagram with which it uses for description of the positional relationship (2) of eccentricity and an objective lens. It is a basic diagram with which it uses for description of the cut-off frequency in LPF processing. It is an approximate line figure showing each signal after LPF processing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical disk apparatus, 12 ... Control part, 12A ... Tracking control part, 13 ... Servo circuit, 14 ... Spindle motor, 17 ... Guide shaft, 20 ... Optical pick-up, 21 ... Laser diode, 22 ...... Diffraction element, 30 ... Objective lens, 36 ... Biaxial actuator, 40 ... Light beam, 50 ... Reflected light beam, 60 ... Photo detector, 71 ... MPP generator, 72 ... SPP generation , 73... LPF processing unit, 74... Coefficient multiplication unit, 75... DPP generation unit, MB ... main beam, SB ... sub-beam, MPP ... main push-pull signal, OFS ... offset signal, DPP ... ... tracking error signal, SPP ... side push-pull signal.

Claims (5)

A disk rotating unit for rotating the optical disk;
A spectroscopic unit that splits a light beam emitted from a light source into a main beam for reading recorded information in a signal recording layer of the optical disc and a sub beam for tracking control;
An objective lens for condensing the main beam and the sub beam and irradiating the track of the signal recording layer;
A light detection unit that receives the main beam and the sub beam reflected by the optical disc and generates a detection signal corresponding to the amount of received light;
A main push-pull signal generator that generates a main push-pull signal based on the detection signal corresponding to the amount of light received by the received main beam;
An offset signal generation unit that generates an offset signal including an offset component indicating that the main beam and the sub beam are deviated from the center of the light detection unit based on the detection signal corresponding to the received light amount of the sub beam received;
A tracking signal generation unit that generates a tracking error signal by subtracting the offset signal from the main push-pull signal;
A drive unit for driving the objective lens in the tracking direction based on the tracking error signal,
The offset signal generator is
A component having a predetermined cutoff frequency or higher higher than the rotational speed of the optical disc is removed from the offset signal. The rotating part is
Changing the number of revolutions of the optical disc in accordance with the position of the track with which the light beam is irradiated relative to the optical disc,
The offset signal generator is
The optical disc apparatus according to claim 1, wherein the cut-off frequency is changed in accordance with a change in the rotational speed of the optical disc. The offset signal generator is
The optical disc apparatus according to claim 1, wherein the cut-off frequency is changed stepwise in accordance with a change in the rotation speed of the optical disc. The light quantity of the sub beam is small compared to the main beam,
The offset signal generator is
2. The optical disc apparatus according to claim 1, wherein a signal level of the offset signal is set to be substantially equal to an offset component of the main push-pull signal in accordance with a light amount of the sub beam. The optical beam emitted from the light source is split into a main beam for reading recorded information in the signal recording layer of the rotated optical disc and a sub beam for tracking control, and the main beam and the sub beam are condensed to collect the optical disc. Irradiating the track of the signal recording layer in
A light detection step of receiving the main beam and the sub beam reflected by the optical disc and generating a detection signal corresponding to the amount of received light;
A main push-pull signal generating step for generating a main push-pull signal based on the detection signal according to the received light amount of the received main beam;
An offset signal generation step for generating an offset signal including an offset component indicating that the main beam and the sub beam are deviated from the center of the light detection unit based on the detection signal corresponding to the received light amount of the sub beam received;
A tracking signal generation step for generating a tracking error signal by subtracting the offset signal from the main push-pull signal;
A driving step for driving the objective lens in the tracking direction based on the tracking error signal;
In the offset signal generation step,
A tracking control method, wherein a component having a predetermined cutoff frequency or higher than the rotational speed of the optical disc is removed from the offset signal.

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