JP4978678B2 - Optical drive device - Google Patents

Description

  The present invention relates to an optical drive device, and more particularly to an optical drive device that performs tilt servo.

  It is known that the quality of RF signals and DPD signals (tracking error signals generated by the phase difference detection method (DPD method)) deteriorates when the optical disc is tilted during reproduction or writing of the optical disc. ing. Regarding the RF signal, when the tilt occurs, the aberration is generated in the light transmission layer up to the surface of the recording layer. The magnitude of this aberration is proportional to the thickness of the light transmission layer. On the other hand, with respect to the DPD signal, an offset due to the occurrence of tilt is the reason for quality degradation. It should be noted that with respect to the DPP signal (tracking error signal generated by the differential push-pull method (DPP method)) and the focus error signal generated by the astigmatism method, the influence of tilt is basically canceled in the calculation process. No quality degradation will occur. However, the tilt effect may remain to some extent.

  As a technique for suppressing signal deterioration due to tilt, there is a technique called tilt servo. In this technique, detection of the tilt angle and control of the incident angle of the light beam to the optical disc according to the detected tilt angle are performed.

  Patent Document 1 discloses an example of tilt servo. The tilt servo disclosed in Patent Document 1 will be briefly described below.

  First, FIG. 16 shows an example of a DPD signal and an MPP (main push-pull) signal when no tilt occurs. The horizontal axis in the figure corresponds to the optical disk radial direction. In the lower part of the figure, a plan view of the recording layer is shown for reference. As shown in the figure, in this example, lands L and grooves G are provided in the recording layer, and a row of codes (recording marks) M is formed on the lands L. As shown in FIG. 16, in a state where the irradiation position of the light beam is at the center of the land L (hereinafter, this state is referred to as “track center state”), both the DPD signal and the MPP signal are zero.

  FIG. 17 is a diagram in which an example of a DPD signal and an MPP signal when tilt is added to FIG. The signal DPDt and the signal MPPt shown in the figure are examples of the DPD signal and the MPP signal when a tilt occurs, respectively. FIG. 18A is an enlarged view of region A in FIG.

  As shown in FIGS. 17 and 18A, when a tilt occurs, an offset occurs in each signal. Since the magnitude of the deviation differs between the DPD signal and the MPP signal, the difference signal S = MPP-DPD between the DPD signal and the MPP signal takes a value other than zero in the track center state. Conversely, if tilt servo is performed so that the difference signal S = 0 in the track center state, the tilt angle can be made zero.

  The technique disclosed in Patent Document 1 utilizes the above characteristic of the difference signal S = MPP-DPD, and performs tilt servo so that the difference signal S = 0 when tracking servo is applied. . Thereby, since the tilt angle can be made zero, the quality deterioration of the RF signal and the DPD signal is suppressed.

JP 2001-307359 A

  However, the technique disclosed in Patent Document 1 is based on the premise that the “on-track state” (the state where tracking servo is applied) and the “track center state” are the same. Actually, since the irradiation position of the light beam swings, the irradiation position of the light beam is not always at the center of the land L even in the on-track state. This causes a deterioration in the accuracy of the tilt servo.

  FIG. 18B is an explanatory diagram of this deterioration in accuracy. For example, when the irradiation position of the light beam is at the position B, the values of the DPD signal and the MPP signal are different from each other even when there is no tilt. For this reason, the tilt angle does not become zero even if the tilt servo is performed so that the difference signal S = 0. That is, the accuracy of the tilt servo deteriorates due to the swing of the light beam irradiation position.

  Accordingly, one of the objects of the present invention is to provide an optical drive device that can reduce the influence of the fluctuation of the light beam irradiation position in the on-track state on the tilt servo.

  An optical drive device according to the present invention for achieving the above object includes an optical system for irradiating a recording layer of an optical disc with a light beam, a photodetector for receiving reflected light from the recording layer of the light beam, Based on the amount of light received by the photodetector, signal generation means for generating a DPD signal and an MPP signal, and at least when the irradiation position of the light beam is near the track center, the slopes of the DPD signal and the MPP signal are equal to each other Amplifying means for amplifying at least one of the DPD signal or the MPP signal, and control for generating a control signal based on the difference between the DPD signal and the MPP signal after amplification processing by the amplifying means Signal generating means and tilt servo means for controlling the incident angle of the light beam to the optical disk based on the control signal. And wherein the door.

  According to the present invention, since the slopes of the DPD signal and the MPP signal are equal to each other, even if the light beam irradiation position fluctuates in the on-track state, the values of the DPD signal and the MPP signal in the state of no tilt are equal to each other. Can be kept in a state. Therefore, it is possible to reduce the influence of the fluctuation of the light beam irradiation position in the on-track state on the tilt servo.

  In the optical drive device, the amplifying unit is configured to output either the DPD signal or the MPP signal so that an amplitude ratio between the MPP signal and the DPD signal is equal to a ratio of a distance between local maximum values sandwiching a track center. It is possible to amplify at least one, and when the irradiation position of the light beam is at a given position between the track center and the track end, the values of the DPD signal and the MPP signal are equal to each other. At least one of the DPD signal and the MPP signal may be amplified. According to the former, when there are land grooves in the recording layer, the values of the DPD signal and the MPP signal in a state where there is no tilt can be kept equal to each other. According to the latter, even if there is no land groove in the recording layer, the values of the DPD signal and the MPP signal in a state where there is no tilt can be kept equal to each other. In addition, the amplification factor can be determined appropriately.

  In the optical drive device, the optical system includes an objective lens for condensing the light beam on the recording layer, and an actuator for controlling the position of the objective lens according to a given control voltage, The control signal generation means may remove a fluctuation component due to lens shift of the objective lens from a difference between the DPD signal and the MPP signal based on the control voltage. According to this, the influence of the lens shift on the tilt servo can be reduced.

  The optical drive apparatus further includes a determination unit that determines that the irradiation position of the light beam is an unrecorded area, and the control signal generation unit amplifies the control voltage according to a determination result of the determination unit. A fluctuation component due to lens shift of the objective lens is removed from the difference between the DPD signal and the MPP signal by subtracting the amplified control voltage from the difference between the DPD signal and the MPP signal. It is good. According to this, the influence of the lens shift on the tilt servo can be reduced even in an unrecorded area.

  The optical drive device according to one aspect of the present invention is controlled to have the same optical axis at least in the vicinity of the recording surface with respect to the recording surface of the optical disc having at least a recording layer having a code and a servo dedicated layer. An optical system that irradiates the first and second light beams so as to focus on the recording layer and the servo-dedicated layer, respectively, and a first light that receives reflected light from the recording surface of the first light beam. A detector, a second photodetector for receiving reflected light from the recording surface of the second light beam, and a first DPD signal and a first light based on the amount of light received by the first photodetector. A signal generating means for generating a second DPD signal and a second MPP signal based on the amount of light received by the second photodetector, the first DPD signal, and the second DPD signal A DPD signal of A tracking error signal generating means for generating a tracking error signal using any one of the MPP signals of 2; a tracking servo means for controlling the optical system based on the tracking error signal; and the first at least near the track center. At least one of the first DPD signal or the first MPP signal is amplified so that the slope of the DPD signal is equal to the slope of the first MPP signal, and at least near the center of the track, the second The tracking error further includes amplification means for amplifying at least one of the second DPD signal and the second MPP signal so that the slope of the DPD signal of the second MPP signal is equal to the slope of the second MPP signal. Signal generation means uses the first DPD signal to generate the tracking error signal. When generating, a control signal is generated based on a difference between the first DPD signal and the first MPP signal, and the tracking error signal generation means is configured to generate the second DPD signal or the second MPP. Control signal generating means for generating a control signal based on a difference between the second DPD signal and the second MPP signal when the tracking error signal is generated using a signal; and the control signal And tilt servo means for controlling an incident angle of the light beam to the optical disc based on the above. According to this, even in an optical disk using a servo-dedicated layer, it is possible to reduce the influence of the fluctuation of the light beam irradiation position in the on-track state on the tilt servo.

  Further, an optical drive device according to another aspect of the present invention has the same optical axis at least in the vicinity of the recording surface with respect to the recording surface of an optical disc having at least a recording layer having a sign and a servo dedicated layer. An optical system that irradiates two controlled light beams so as to be focused on the recording layer and the servo-dedicated layer, respectively, and light that receives reflected light from the recording surface of the light beam that is focused on the servo-dedicated layer A detector, signal generating means for generating a DPD signal and an MPP signal based on the amount of light received by the photodetector, and the slope of the DPD signal and the slope of the MPP signal at least near the track center. Amplifying means for amplifying at least one of the DPD signal and the MPP signal, and a control based on the difference between the DPD signal and the MPP signal. Control signal generating means for generating a control signal, and the optical disc based on the control signal generated based on the difference between the DPD signal and the MPP signal both during reproduction and writing to the optical disc. And tilt servo means for controlling the angle of incidence of the light beam on.

  According to the present invention, it is possible to reduce the influence of the fluctuation of the light beam irradiation position in the on-track state on the tilt servo.

1 is a schematic diagram of an optical drive device according to a first embodiment of the present invention. (A) is a top view of one recording layer of the optical disk by the 1st Embodiment of this invention. (B) is the sectional view on the A-A 'line of (a). It is explanatory drawing of the astigmatism provided by a sensor lens. It is a top view of the photodetector by the 1st Embodiment of this invention. It is a figure which shows the functional block of the process part by the 1st Embodiment of this invention. It is explanatory drawing of the process which the determination part by the 1st Embodiment of this invention produces | generates the recording non-recording determination signal NR. It is a figure which shows the example of MPP signal MPP and DPD signal DPD which are produced | generated by the signal production | generation part 74 by the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the timing which acquires the value of MPP signal MPP and DPD signal DPD. It is explanatory drawing of the process of the amplifier by the 1st Embodiment of this invention. It is a schematic diagram of the optical drive device by the 2nd Embodiment of this invention. (A) is a top view of the recording surface of the optical disk by the 2nd Embodiment of this invention. FIG. 4B is a sectional view taken along line B-B ′ in FIG. It is a top view of the 1st photodetector by the 2nd Embodiment of this invention. It is a top view of the 2nd photodetector by the 2nd Embodiment of this invention. It is a figure which shows the functional block of the process part by the 2nd Embodiment of this invention. Is a diagram showing an example of a MPP signal MPP _R according to a second embodiment of the present invention. It is a figure which shows the example of the DPD signal and MPP signal when the tilt has not generate | occur | produced. FIG. 16 is a diagram in which examples of the DPD signal and the MPP signal when the tilt is generated are added. (A) is the enlarged view of the area | region A shown in FIG. (B) is an explanatory view of the deterioration of tilt servo accuracy due to the swinging of the irradiation position of the light beam.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram of an optical drive device 1 according to a first embodiment of the present invention.

  The optical drive device 1 performs reproduction and recording of the optical disk 11. Various optical recording media such as CD, DVD, and BD can be used as the optical disc 11. In this embodiment, a disc-shaped optical disc having a recording surface multilayered by a multilayer film is used. In addition, the optical disc includes a reproduction-only type (DVD-ROM, BD-ROM, etc.), a write-once type (DVD-R, DVD + R, BD-R, etc.), and a rewritable type (DVD-RAM, DVD-RW, DVD + RW, etc.). There are several types classified by recording methods, such as BD-RE, etc., but the present invention is applicable to any type of optical disc.

  FIG. 2A is a plan view of one recording layer of the optical disc 11. FIG. 2B shows a cross-sectional view of this recording layer taken along the line A-A ′ of FIG.

  As shown in FIG. 2, the recording layer is periodically provided with grooves, and the convex portion of the groove is called a land L and the concave portion is called a groove G. However, the convex portion and the concave portion of the groove are relative, and which of the convex portion and the concave portion is referred to as the land L depends on which of the front surface and the rear surface of the optical disk 11 is on the bottom. In FIG. 2, the land L and the groove G are drawn in a straight line, but in actuality, they slightly meander (wobble) in the radial direction.

  In the example of FIG. 2, the land L is an information writing line, and a code (pit or recording mark) M for storing information is provided in the land L. In FIG. 2, the horizontal width of the symbol M is drawn so as to be considerably smaller than the width of the land. This is because priority is given to the visibility of the drawing, and the actual horizontal width of the symbol M is larger than the width of the land. It is a little small. The code M is recorded or erased by irradiation with a light beam. The unrecorded area of the recording layer of the optical disc 11 is an area where the code M is not recorded. On the other hand, the recording area is an area where the code M is recorded. The information writing line may be provided in the groove G, or may be provided in both the land L and the groove G.

  Returning to FIG. As shown in FIG. 1, the optical drive device 1 includes a laser light source 2, an optical system 3, a photodetector 6, and a processing unit 7. Among these, the laser light source 2, the optical system 3, and the photodetector 6 constitute an optical pickup.

  The optical system 3 includes a diffraction grating 21, a beam splitter 22, a collimator lens 23, a quarter wavelength plate 24, a sensor lens (cylindrical lens) 25, an objective lens 4, and an actuator 5. The optical system 3 functions as an outward optical system that guides the light beam emitted from the laser light source 2 to the optical disc 11, and also functions as a return optical system that guides the return beam from the optical disc 11 to the photodetector 6.

  First, in the forward optical system, the diffraction grating 21 decomposes the light beam emitted from the laser light source 2 into three beams (0th-order diffracted light and ± 1st-order diffracted light) and enters the beam splitter 22 as P-polarized light. The beam splitter 22 reflects the incident P-polarized light and bends its path in the direction of the optical disk 11. The collimator lens 23 converts the light beam incident from the beam splitter 22 into parallel light. The quarter wavelength plate 24 converts the light beam that has passed through the collimator lens 23 into circularly polarized light. The light beam that has passed through the quarter-wave plate 24 enters the objective lens 4.

  The objective lens 4 condenses the light beam incident from the quarter-wave plate 24 (a light beam in a parallel light state) on the optical disk 11 and parallelizes the return light beam reflected from the recording surface of the optical disk 11. Return to. This return light beam is diffracted by the land group of the recording surface, and is decomposed into 0th order diffracted light and ± 1st order diffracted light. The 0th order diffracted light and the ± 1st order diffracted light are different from the 0th order diffracted light and ± 1st order diffracted light generated by the diffraction grating 21 and are confusing. The −1st order diffracted light is referred to as a main beam MB, a sub beam SB1, and a sub beam SB2, respectively. In the case of the 0th order diffracted light and the ± 1st order diffracted light, the diffracted light generated by the diffraction on the land group of the recording surface is indicated. The main beam MB, sub beam SB1, and sub beam SB2 each independently generate reflected light.

  The actuator 5 controls the position and orientation of the objective lens 4 according to a control signal (control voltage) input from the processing unit 7. The actuator 5 has a three-axis configuration, and in addition to linearly moving the objective lens 4 in a direction perpendicular to the recording surface of the optical disk 11 (focus servo) and a horizontal direction (tracking servo), the recording surface of the optical disk 11 (especially radial) (Tilt servo) is also provided. When the objective lens 4 rotates with respect to the recording surface of the optical disk 11, the incident angle of the light beam on the optical disk 11 changes.

  In the return path optical system, a light beam that has passed through the objective lens 4 and has become S-polarized light by reciprocating the quarter-wave plate 24 is incident on the collimator lens 23. The light beam that has passed through the collimator lens 23 is incident on the beam splitter 22 while being condensed. The beam splitter 22 transmits the incident light beam and makes it incident on the sensor lens 25 (cylindrical lens). The sensor lens 25 gives astigmatism to the light beam incident from the beam splitter 22. The light beam provided with astigmatism enters the photodetector 6.

  FIG. 3 is an explanatory diagram of astigmatism imparted by the sensor lens 25. As shown in the figure, the sensor lens 25 has a lens effect only in one direction (MY axis direction = subordinate direction). Therefore, the focal position of the optical system constituted by the collimator lens 23 (FIG. 1) and the sensor lens 25 differs between the MY axis direction and the MX axis direction (bus line direction) which is a direction perpendicular to the MY axis direction. (MY axis focus and MX axis focus shown in FIG. 3). A point where the lengths of the light beams in the MY axis direction and the MX axis direction are equal is referred to as a focal point.

  In the optical drive device 1, the objective lens 4 is arranged so that the joint point of the light beam (signal light) reflected by the layer to be focused (access target layer) is positioned on the photodetector 6. Position control is performed (focus servo). In other words, the joint point of the light beam (stray light) reflected by a layer other than the access target layer is not located on the photodetector 6, and the spot (stray light spot) that stray light forms on the photodetector 6 is As compared with a spot (signal light spot) formed on the photodetector 6 by the signal light, the signal light has a shape spreading in at least one of the MY axis direction and the MX axis direction.

  Returning to FIG. The photodetector 6 is installed on a plane that intersects the optical path of the return light beam emitted from the optical system 3. The photodetector 6 includes three light receiving surfaces, and each light receiving surface is divided into a plurality of light receiving regions. In the optical drive device 1, these light receiving areas are used in appropriate combinations, so that a main push-pull (MPP) signal MPP, a sub push-pull (SPP) signal SPP, a DPD signal DPD, a tracking error signal TE, a focus error signal FE, Various signals such as full addition signals (pull-in signal PI, RF signal RF) can be generated. The specific contents will be described later.

  As an example, the processing unit 7 is configured by a DSP (Digital Signal Processor) having an A / D conversion function that converts analog signals for multiple channels into digital data, and receives an output signal of the photodetector 6. MPP signal MPP, SPP signal SPP, DPD signal DPD, tracking error signal TE, focus error signal FE, and full addition signal (pull-in signal PI, RF signal RF) are generated. Details of the processing of the processing unit 7 will also be described later.

  The CPU 8 is a processing device built in a computer, a DVD recorder, or the like, and instructs the processing unit 7 to perform either reproduction or writing and specifies an access position on the optical disc 11 via an interface (not shown). An instruction signal is transmitted. The processing unit 7 that has received this instruction signal controls the objective lens 4 and moves it parallel to the surface of the optical disk 11 (this movement is referred to as “lens shift”) to realize an on-track state (tracking servo). . In the on-track state, the CPU 8 acquires the RF signal RF generated by the processing unit 7 as a data signal.

  From here, the detail of the structure of the photodetector 6 and the detail of the process of the process part 7 are demonstrated.

  FIG. 4 is a top view of the photodetector 6 according to the present embodiment. The figure also shows an example of spots formed by signal light on the light receiving surface. The X and Y directions shown in the figure correspond to the optical disc tangential direction and the optical disc radial direction, respectively.

  As shown in FIG. 4, the photodetector 6 includes three light receiving surfaces 61 to 63 each having a square shape. Among these, the light receiving surface 61 is divided into four squares (light receiving regions 61A to 61D) having the same area. The light receiving surfaces 62 and 63 are divided into two upper and lower areas with the same area (light receiving regions 62A and 62B and light receiving regions 63A and 63B). The light receiving surfaces 61 to 63 are arranged at positions where the main beam MB, the sub beam SB1, and the sub beam SB2 can be received.

The photodetector 6 that has received the light beam outputs a signal having an amplitude of a value (light reception amount) obtained by dividing the intensity of the light beam by the area of the light receiving surface for each light receiving region. Hereinafter, an output signal corresponding to the light receiving region _X is represented as I _X.

  FIG. 5 is a diagram illustrating functional blocks of the processing unit 7. As shown in the figure, the processing unit 7 includes a focus error signal generation unit 70, a focus servo unit 71, a full addition signal generation unit 72, a determination unit 73 (determination unit), a signal generation unit 74 (signal generation unit), tracking. An error signal generation unit 75, a tracking servo unit 76, an amplification unit 77 (amplification unit), a control signal generation unit 78 (control signal generation unit), and a tilt servo unit 79 (tilt servo unit) are included.

  The focus error signal generation unit 70 generates a focus error signal FE based on the amount of light received by each of the light receiving regions 61A to 61D constituting the light receiving surface 61 for receiving the main beam MB. Specifically, the calculation of the following equation (1) is performed to generate the focus error signal FE.

  The focus servo unit 71 generates a control signal for controlling the position of the objective lens 4 in a direction perpendicular to the recording surface of the optical disc 11 so that the value of the focus error signal FE becomes zero. This control signal is output to the actuator 5, and the actuator 5 controls the position of the objective lens 4 in a direction perpendicular to the recording surface of the optical disk 11. By this control, the light beam can be focused on the recording layer.

  The full addition signal generation unit 72 generates the RF signal RF and the pull-in signal PI based on the received light amounts of the light receiving regions 61A to 61D that constitute the light receiving surface 61 for receiving the main beam MB. Specifically, these signals are generated by performing the calculation of the following equation (2). As is clear from Equation (2), the RF signal RF and the pull-in signal PI are the same signal. However, the pull-in signal PI is normally output in a band-limited state by passing through a low-pass filter. The band is limited in order to remove fluctuations and noise according to the presence or absence of the code M.

  The pull-in signal PI is a signal used for layer recognition in the focus servo unit 71. That is, the pull-in signal PI has a property that when the focal position of the light beam moves between the layers, the pull-in signal PI becomes maximum when the surface of the recording layer is in focus. Therefore, the focus servo unit 71 compares the value of the pull-in signal PI with a predetermined threshold value and detects a portion that is higher than the threshold value, so that the focal position of the light beam is near the recording layer. Detect that it matches.

  The RF signal RF is input to the CPU 8 as a data signal. The CPU 8 acquires information written on the optical disc 11 based on the RF signal RF.

  The determination unit 73 uses the RF signal RF to determine whether the irradiation position of the light beam is a recording area or an unrecorded area, and a recording / unrecording determination signal NR indicating the result is used as a control signal generation unit 78. Output to.

  FIG. 6 is an explanatory diagram of processing for generating the recording / unrecording determination signal NR. As shown in the figure, the RF signal RF is a signal that vibrates vigorously in a short period in the recording area and does not change in the unrecorded area. Since the vibration of the RF signal RF corresponds to the change in reflectance due to the symbol M, the vibration of the RF signal RF does not occur in the unrecorded area. In the RF signal RF, as shown in the top diagram of FIG. 6, an offset that changes due to non-uniformity of the reflectance of the recording layer or confocal crosstalk appears, and the bottom value deviates from Vref. Here, when there is no offset, the bottom value is assumed to be Vref. In addition, the amplitude of the RF signal RF can also vary due to non-uniform reflectance of the recording layer and confocal crosstalk. Therefore, the determination unit 73 first performs bottom clamp processing for aligning the lower values of the RF signal RF to obtain a clamp signal RFC shown in FIG.

  When the clamp signal RFC is obtained, the determination unit 73 then obtains a top envelope signal ENV that envelops the maximum value of the clamp signal RFC with a predetermined droop plate. The slice signal SS is obtained by slicing the top envelope signal ENV with a predetermined slice level SL stored in advance. Note that the slice level SL is preferably set to a value approximately between the maximum value and the minimum value of the clamp signal RFC.

  Finally, the determination unit 73 generates a recording / non-recording determination signal NR based on the slice signal SS. Specifically, the recording / unrecording determination signal NR is set to high when the high level of the slice signal SS continues for a predetermined time D or more, and the recording / non-recording determination signal NR is set when the slice signal SS continues to be low for the predetermined time D or longer. Is set to low to generate a recording / unrecording determination signal NR. The reason why the rising and falling delay processes are performed in this way is to prevent the RF signal RF from being greatly influenced by noise and thus preventing erroneous determination of an unrecorded area or a recording area due to noise. It is. When the recording / unrecording determination signal NR generated in this way is low, it indicates that the irradiation position of the light beam has entered the recording area in the access target layer, and when it is high, the irradiation position of the light beam is the access target layer. This signal indicates that an unrecorded area has been entered.

  Returning to FIG. The signal generation unit 74 generates an MPP signal MPP, an SPP signal SPP, and a DPD signal DPD based on the amount of light received by the photodetector 6. Specifically, each signal is generated according to the following equations (3) to (5). P (X, Y) is a function indicating the phase difference between the signal X and the signal Y.

FIG. 7 is a diagram illustrating an example of the MPP signal MPP and the DPD signal DPD generated by the signal generation unit 74. The horizontal axis in the figure corresponds to the optical disk radial direction. In the lower part of the figure, a plan view of the recording layer is shown for reference. Line C _R shown in the figure is a line segment indicating a track center of the recording layer.

As shown in FIG. 7, the MPP signal MPP is a signal that takes a local maximum value (local minimum value) near the boundary between the land L and the groove G. On the other hand, the DPD signal DPD is a signal having a maximum value (minimum value) in the vicinity of the center of the land L and the groove G where the row of the code M is not formed. Thus, placing a, and b as shown the distance between maxima across the track center C _R, respectively, these ratios a: b is approximately 1: 2. Further, the amplitude s of the MPP signal MPP and the amplitude t of the DPD signal DPD are made substantially equal to each other.

  Returning to FIG. The tracking error signal generation unit 75 uses each signal generated by the signal generation unit 74 and generates a tracking error signal TE by either one of the DPP method and the DPD method. Specifically, when the DPP method is employed, a differential push-pull signal (DPP) signal DPP is generated by the following equation (6) using the MPP signal MPP and the SPP signal SPP, and the tracking error signal TE Output as. However, k is a positive constant, and a lens shift offset (offset caused by the lens shift described above) and a tilt offset (offset caused by tilting the optical disc) generated in the MPP signal MPP and the SPP signal SPP, respectively. It is decided to cancel. Normally, the k value is an intensity ratio between the MPP signal MPP and the SPP signal SPP (light intensity ratio between the main signal light and the sub signal light). When the DPD method is employed, the tracking error signal generation unit 75 outputs the DPD signal DPD generated by Expression (5) as it is as the tracking error signal TE.

  At the time of writing, it is preferable that the tracking error signal generator 75 employs the DPP method. This is because the tracking servo must be performed in a state where the recording layer has no code, so that the DPD method cannot be used. On the other hand, at the time of reproduction, the tracking error signal generation unit 75 may use only the DPP method, or may switch between the DPP method and the DPD method based on the above-described recording / unrecording determination signal NR. That is, the DPP method may be used in an unrecorded area where the DPD method cannot be used because there is no code, and the DPD method may be used in a recording area with a code.

The tracking servo unit 76 generates a control signal for controlling the position of the objective lens 4 in a direction parallel to the recording surface of the optical disc 11 so that the value of the tracking error signal TE becomes zero. This control signal is output to the actuator 5, which controls the position of the objective lens 4 in a direction horizontal to the recording surface of the optical disk 11. This control has made it possible to focus the light beam onto the track center C _R. However, the irradiation position of the light beam to swing, is that the irradiation position of the even light beam a on-track state is not always entirely located on the track center C _R, are as described above.

Amplifying section 77, at least so that the irradiation position of the light beam the inclination of the DPD signal DPD and MPP signal MPP are equal to each other when in the vicinity of the track center _{C R,} amplifying at least one of the DPD signal DPD or MPP signal MPP To do.

FIG. 9 is an explanatory diagram of processing of the amplification unit 77. The MPP signal MPP shown in FIG. 9 amplifies the MPP signal MPP shown in FIG. 7 by (a / b) × (t / s) times and sets the amplitude to s ′ = (a / b) × t. Is. In the example of FIG. 7, since a: b is approximately 1: 2, s′≈ (1/2) × t. The DPD signal DPD shown in FIG. 9 is the same as the DPD signal DPD shown in FIG. As is apparent from the drawing, by which to amplify the MPP signal MPP, when the irradiation point of the optical beam from the track center _{C R} in the range of distance x (2x = width of the land L), the MPP signal MPP and the DPD signal The slope of DPD is equal. As described above, the processing of the amplification unit 77 makes it possible to make the slopes of the DPD signal DPD and the MPP signal MPP equal to each other.

  The amplification unit 77 may use an amplification factor stored in advance when performing the amplification, or may adaptively determine the amplification factor by feedback processing. Hereinafter, determination of the amplification factor by feedback processing will be described in detail.

First, the amplifying unit 77 starts to amplify the MPP signal MPP with a predetermined relatively small amplification factor. Then, the track jump is executed in the amplification state, and when the value of the MPP signal MPP is a given value between 0 and the maximum value, that is, the irradiation position of the light beam is between the track center _CR and the track end. When it is at a given position in between (a specific position in the region y shown in FIG. 7), the values of the MPP signal MPP and the DPD signal DPD are acquired. Then, the amplification factor is adjusted so that they are equal. The amplifying unit 77 stores the finally obtained amplification factor and uses it for subsequent amplification processing of the MPP signal MPP.

FIG. 8 is an explanatory diagram for explaining timings for acquiring values of the MPP signal MPP and the DPD signal DPD. Here, it is assumed that the midpoint (reference value) of the MPP signal MPP is the voltage value Vref. First, the amplifying unit 77 slices the MPP signal MPP with a predetermined voltage value Vref stored in advance, so that it becomes high when the MPP signal MPP has a zero-cross signal TZC (the value of the MPP signal MPP is equal to or higher than the voltage value Vref). , A signal that goes low when the voltage value is less than Vref). Next, amplification processing is performed at the rising timing of the delay signal of the zero cross signal TZC. For example, the delay signals TZC_delay1 and TZC_delay2 are generated by delaying the zero-cross signal TZC according to two types of delay times d1, d2 (d1 <d2). Then, an S / H signal rising at the rising edge of the delay signal TZC_delay1 and falling at the rising edge of the delay signal TZC_delay2 is generated, and when the S / H signal is high, the values of the MPP signal MPP and the DPD signal DPD are acquired. The delay times d1 and d2 are determined when the amplification unit 77 is at a given position between the track center _CR and the track end (a specific position in the region y shown in FIG. 7). ) Is appropriately determined in advance in consideration of the rotational speed of the optical disc so that the values of the MPP signal MPP and the DPD signal DPD are obtained.

  Here, it is preferable that the offsets generated in the MPP signal MPP and the DPD signal DPD are canceled so as to be zero. Since the DPP signal DPP cancels the offset due to the effects of lens shift and tilt, the DPP signal DPP and the DPD signal DPD are used to adjust the amplification factor so that they are equal. A signal obtained by multiplying the amplitude ratio between the signal DPP and the MPP signal MPP (usually, twice because the amplitude of the signal MPP and the signal kSPP is equal) may be used.

  Returning to FIG. The control signal generator 78 generates a tilt servo control signal Vtc based on the difference between the DPD signal DPD and the MPP signal MPP after the amplification processing by the amplifier 77. Specifically, the control signal Vtc is generated by the following equation (7). However, Vrc is a function of the control voltage of the actuator 5 and particularly indicates a control voltage component generated by a control signal for controlling in a direction parallel to the recording surface of the optical disc 11. β is a positive constant, and is determined so that lens shift offsets generated in the MPP signal MPP and the DPD signal DPD are removed (a specific method for determining the value of β will be described later).

  Hereinafter, the principle of Expression (7) will be described in detail. The following description will be made on the assumption that the tracking servo section 76 performs tracking servo using the DPP method. Further, it is assumed that the irradiation position of the light beam is a recording area.

  First, the value of the MPP signal MPP is obtained. Now, let it be assumed that the focal position of the light beam is deviated in the radial direction of the optical disk by a minute distance Δx from the track center. In this case, the signal MPP and the signal kSPP (a signal obtained by amplifying the SPP signal SPP by k times) are expressed by the following equations (8) and (9), respectively. Here, Vr1 and Vt1 are a lens shift offset and a tilt offset that appear in the signal MPP and the signal kSPP, respectively. The reason why these values are the same between the signal MPP and the signal kSPP is that the constant k is determined so that the amplitude of the signal MPP and the amplitude of the signal kSPP are the same. V0m and V0s are stray light components included in the signal MPP and the signal kSPP, respectively. Further, (1/2) × γ is a signal component generated because the focal position of the light beam is deviated from the track center by a minute distance Δx in the optical disc radial direction.

  When Expression (8) and Expression (9) are applied to Expression (6), the following Expression (10) is obtained.

  In the tracking servo by the DPP method, the position of the objective lens 4 is controlled so that the value of the DPP signal DPP becomes 0. Therefore, when the right side of Expression (10) is set to 0, γ = −V0m + V0s. However, since the irradiation position of the light beam actually fluctuates as described above, the value of the DPP signal DPP slightly fluctuates around zero. When this vibration component is Δdpp, the actual value of γ is as shown in Expression (11).

  By applying Expression (11) to Expression (8), the value of the MPP signal MPP during execution of tracking servo by the DPP method is obtained as shown in Expression (12).

  When the right side of equation (10) is set to 0, the value of γ is not 0 means that the above-described minute distance Δx is not 0. That is, while tracking servo is performed using the DPP method, the DPP signal DPP vibrates in the range of Δdpp, but the center of the vibration does not become the track center. This affects the value of the DPD signal DPD.

  Next, the value of the DPD signal DPD is obtained. During tracking servo execution by the DPP method, the DPD signal DPD should also be zero in principle. However, since a tilt offset, a lens shift offset, and a stray light offset occur in the DPD signal DPD, these offset components appear in the DPD signal DPD during tracking servo execution by the DPP method.

  In addition, since the above-mentioned minute distance Δx does not become 0 during execution of tracking servo by the DPP method and vibration corresponding to Δdpp appears in the DPD signal DPD, (α / 2) × γ = in the DPD signal DPD. An offset of (α / 2) × (Δdpp−V0m + V0s) occurs. Where α is the ratio of the slope of the DPD signal DPD near the track center to the slope of the MPP signal MPP near the track center. In the present embodiment, α = 1 by the processing of the amplification unit 77.

  Eventually, the DPD signal DPD is expressed by the following equation (13). However, Vr2, Vt2, and V1 are a lens shift offset, a tilt offset, and a stray light component, respectively.

  By applying the equations (12) and (13) to the equation (7), the control signal Vtc is obtained as the following equation (14).

  When α = 1 is substituted, the equation (14) is transformed into the following equation (15).

  The parentheses on the right side of Equation (15) can be removed by appropriately determining the value of β in advance. As can be seen from the equation (15), by setting α = 1, the influence of the stray light component V0s corresponding to the sub-beam is canceled. Usually, since the influence of stray light appears dominantly in the sub-beam, it can be said that Expression (15) has almost no influence of stray light. That is, since the stray light components V0m and V1 corresponding to the main beam MB can be normally ignored, the control signal Vtc is expressed as the following equation (16).

  If the “on-track state” and the “track center state” are the same, it is possible to eliminate the influence of the tilt of the optical disc by performing tilt servo so that the value of Equation (16) becomes zero. become. This is because the magnitude of the tilt offset differs between the phase difference signal DPP and the MPP signal MPP.

  Actually, as described many times, the light beam irradiation position fluctuates even in the on-track state. However, in this embodiment, as shown in FIG. 9, the slopes of the DPD signal DPD and the MPP signal MPP are equal to each other in the vicinity of the track center. For this reason, even if the light beam irradiation position is slightly deviated from the track center, since Δdpp is canceled by setting α = 1, the tilt offsets of the phase difference signal DPP and the MPP signal MPP are equal to each other. When and when the tilt offset becomes 0, there is an equal relationship. Therefore, by performing the tilt servo so that the value of Expression (16) becomes 0, it is possible to eliminate the influence of the tilt of the optical disk regardless of the fluctuation of the light beam irradiation position.

  Note that the control signal Vtc may be generated using the following equation (17) instead of the equation (7).

  When the control signal Vtc is generated using the equation (17), if α = 1 as described above, the control signal Vtc can be written as the following equation (18). In this case, Δdpp is canceled, but the stray light component V0s of the sub beam remains without being canceled. It is possible to set α = −1. In this case, however, the stray light component V0s is canceled, while V0m and Δdpp remain.

  Next, a method for determining β will be described. In the case where the irradiation position of the light beam is in the recording area, β is determined so as to satisfy βVrc = Vr1−Vr2, as is clear from the equation (15). On the other hand, when the irradiation position of the light beam is in an unrecorded area, the value of the DPD signal DPD is always 0, so the value of β needs to be changed. This will be described in detail below.

  When the irradiation position of the light beam is in an unrecorded area, since the value of the DPD signal DPD is 0, Expression (14) can be rewritten as the following Expression (19).

  As understood from the equation (19), in order to remove the lens shift offset component from the control signal Vtc, it is only necessary to determine β so that βVrc = Vr1.

  Specifically, the value Vtc0 of Vtc when Vrc = 0 is obtained. Next, β may be determined so that Vtc−Vtc0 = 0 at a predetermined value of Vrc. In order to reduce the influence of stray light, it is better not to increase the value of a certain predetermined Vrc too much.

  The control signal generator 78 stores two values of β corresponding to the recording area and the unrecorded area, respectively. When the determination result of the determination unit 73 (recorded / unrecorded determination signal NR) indicates that the irradiation position of the light beam is a recording area, β corresponding to the recording area indicates that it is an unrecorded area. If it is, β corresponding to the unrecorded area is selected, and Vrc is amplified by the selected β. Thereafter, the lens shift offset component can be removed from the difference between the DPD signal DPD and the MPP signal MPP by substituting the amplified Vrc (= βVrc) into the equation (7). At this time, when the recording / unrecording determination signal NR shown in FIG. 6 indicates that the irradiation position of the light beam is in the unrecorded area, the DPD signal DPD may be turned off.

  As described above, the control signal Vtc may be generated using the equation (17) instead of the equation (7). However, when β is determined, the equation (17) is used. However, it is preferable to use the MPP signal MPP that is less affected by stray light.

  In the control signal Vtc of Expression (17), the stray light component V0s and the vibration component Δdpp corresponding to the sub beams SB1 and SB2 remain. However, when the irradiation position of the light beam is in an unrecorded area, precise tilt servo is not required in the first place. Therefore, tilt servo may be performed using the control signal Vtc of Expression (17).

  The tilt servo unit 79 (FIG. 5) controls the incident angle of the light beam to the optical disc 11 based on the control signal Vtc generated by the control signal generation unit 78. Specifically, the objective lens 4 is rotated in the radial direction so that the value of the control signal Vtc shown in Expression (7) becomes zero. Note that the optical system 3 may be rotated in the radial direction instead of the rotation of the objective lens 4, or the tilt of the optical disk 11 may be directly controlled.

  As described above, according to the optical drive device 1 according to the present embodiment, since the slopes of the DPD signal DPD and the MPP signal MPP are equal to each other, even if the light beam irradiation position fluctuates in the on-track state, the tilt The values of the DPD signal DPD and the MPP signal MPP in a state where there is no signal can be kept equal to each other. Therefore, it is possible to reduce the influence of the fluctuation of the light beam irradiation position in the on-track state on the tilt servo.

  In the first embodiment, when the principle of Expression (7) is described, it is assumed that the tracking servo unit 76 performs tracking servo using the DPP method. The same applies when tracking servo is performed using the DPD method, but will be described in detail below.

  When tracking servo is performed using the DPD method, the DPD signal DPD is expressed by the following equation (20). However, Δdpd is a vibration component of the DPD signal DPD due to fluctuation of the irradiation position of the light beam.

  The value of the MPP signal MPP is obtained. Now, let it be assumed that the focal position of the light beam is deviated in the radial direction of the optical disk by a minute distance Δx from the track center. When tracking servo is not applied, the DPD signal DPD is expressed by the following equation (21). However, Vr2, Vt2, and V1 are a lens shift offset, a tilt offset, and a stray light component, respectively. Further, δ is a signal component generated because the focal position of the light beam is shifted from the track center by a minute distance Δx in the radial direction of the optical disc.

  From Expression (20) and Expression (21), δ is expressed by the following Expression (22).

  During tracking servo execution by the DPD method, the above-mentioned minute distance Δx does not become zero, and the MPP signal MPP also exhibits a vibration corresponding to the above-mentioned Δdpd. = (Δdpd−Vr2−Vt2−V1) / α offset occurs. Therefore, the MPP signal MPP can be expressed by the following equation (23) in the same manner as the equation (8).

  By applying the equations (20) and (23) to the equation (7), the control signal Vtc is obtained as the following equation (24).

  When α = 1 is substituted, the equation (24) is transformed into the following equation (25).

  The parentheses on the right side of the equation (25) can be removed by appropriately determining the value of β in advance. Further, since the stray light components V0m and V1 corresponding to the main beam MB can be normally ignored, the control signal Vtc is eventually expressed as the following equation (26).

  Expression (26) is the same as Expression (16). That is, when tracking servo is performed using the DPD method, the control signal Vtc can be obtained and tilt servo can be performed in the same manner as when tracking servo is performed using the DPP method. Further, even if the light beam irradiation position fluctuates, Δdpd is canceled out. Therefore, it is possible to eliminate the influence of the tilt of the optical disc by performing the tilt servo so that the value of Expression (24) becomes zero. ing.

  FIG. 10 is a schematic diagram of an optical drive device 1 according to the second embodiment of the present invention.

  In the present embodiment, a disc-shaped optical disc in which a recording layer 12 and a servo dedicated layer 13 are provided on the recording surface and the recording layer 12 is multilayered by a multilayer film is used as the optical disc 11.

  FIG. 11A is a plan view of the recording surface of the optical disc 11. FIG. 11B shows a cross-sectional view taken along line B-B ′ of FIG.

  As shown in FIG. 11, a plurality of recording layers 12 and one servo dedicated layer 13 are provided on the recording surface of the optical disc 11. The servo-dedicated layer 13 is periodically provided with grooves, and the convex portion of the groove is called a land L and the concave portion is called a groove G. However, the convex portion and the concave portion of the groove are relative, and which of the convex portion and the concave portion is referred to as the land L depends on which of the front surface and the rear surface of the optical disk 11 is on the bottom. In FIG. 11, the land L and the groove G are drawn in a straight line, but in reality, they slightly meander (wobble) in the radial direction.

  In the example of FIG. 11, the land L is an information writing line, and each recording layer 12 is provided with a code (pit or recording mark) M for storing information at a position corresponding to the land L. In FIG. 11, the horizontal width of the symbol M is drawn so as to be considerably smaller than the width of the land. This is because priority is given to the visibility of the drawing, and the actual horizontal width of the symbol M is larger than the width of the land. It is a little small. The code M is recorded or erased by irradiation with a light beam. The unrecorded area of each recording layer 12 is an area where the code M is not recorded. On the other hand, the recording area is an area where the code M is recorded. Note that the information writing line may be provided at a position corresponding to the groove G, or may be provided at a position corresponding to each of the land L and the groove G.

As shown in FIG. 11, the symbol M is also provided in the land L of the servo dedicated layer 13. The symbol M is not a code for storing information, which is for generating a DPD signal DPD _S to be described later, are previously provided on the entire surface. Similarly, the symbol M may be provided at a position corresponding to the groove G, or may be provided at a position corresponding to each of the land L and the groove G.

  Returning to FIG. As shown in FIG. 10, the optical drive device 1 includes laser light sources 2-1, 2-2, an optical system 3, a photodetector 6-1 (first photodetector), and a photodetector 6-2 (first detector). 2 photodetectors) and a processing unit 7. Among these, the laser light source 2, the optical system 3, and the photodetector 6 constitute an optical pickup.

  The optical system 3 includes a polarization beam splitter 41, a collimator lens 42, a dichroic prism 43, a quarter wavelength plate 44, a sensor lens (cylindrical lens) 46, a diffraction grating 47, a beam splitter 48, a collimator lens 49, and a sensor lens (cylindrical lens). ) 51, the objective lens 4, and the actuator 5. The optical system 3 functions as an outward optical system that guides the light beams emitted from the laser light sources 2-1 and 2-2 to the optical disc 11, and sends the return beam from the optical disc 11 to the photodetectors 6-1 and 6-2. It also functions as a return optical system that leads to

  First, in the forward optical system of the light beam emitted from the laser light source 2-1 (first light beam; hereinafter referred to as the recording layer light beam), the recording layer light beam first enters the polarization beam splitter 41. . The polarization beam splitter 41 allows the incident recording layer light beam to pass therethrough and enter the collimator lens 42. The collimator lens 42 converts the recording layer light beam into parallel light and makes it incident on the dichroic prism 43. The dichroic prism 43 reflects the incident parallel light in the direction of the optical disk 11 and makes it incident on the quarter-wave plate 44. The quarter-wave plate 44 makes incident parallel light circularly polarized and enters the objective lens 4.

  On the other hand, in the forward optical system of the light beam emitted from the laser light source 2-2 (second light beam; hereinafter referred to as a servo dedicated layer light beam), the diffraction grating 47 first generates the servo dedicated layer light beam 3. The beam is decomposed into beams (0th order diffracted light and ± 1st order diffracted light) and is incident on the beam splitter 48. The beam splitter 48 passes the incident servo dedicated layer light beam and makes it incident on the collimator lens 49. The collimator lens 49 converts the incident servo dedicated layer light beam into parallel light and makes it incident on the dichroic prism 43. The dichroic prism 43 passes the incident parallel light and makes it incident on the quarter wavelength plate 44. The quarter-wave plate 44 makes incident parallel light circularly polarized and enters the objective lens 4. Here, in the servo dedicated layer, the diffraction grating 47 may not be provided when only the DPD method is performed.

  The optical system 3 is configured so that the optical axes of two types of light beams (parallel light beams) incident on the objective lens 4 coincide. The objective lens 4 condenses these two types of light beams having the same optical axis on the optical disc 11 and returns the return light beam reflected by the recording surface of the optical disc 11 to parallel light.

  Here, the collimator lens 49 is configured to be driven in a focus direction (a direction perpendicular to the recording surface). The objective lens 4 can be driven in three directions: a focus direction, a direction parallel to the recording surface of the optical disc 11, and a direction rotating with respect to the recording surface of the optical disc 11. Control of the position and orientation of the objective lens 4 is performed by the actuator 5 as in the first embodiment. The optical drive device 1 controls the positions of the collimator lens 49 and the objective lens 4 in order to focus the servo-dedicated layer light beam on the servo-dedicated layer and to focus the recording layer light beam on the access target layer. (Focus servo).

  The return light beam of the servo dedicated layer light beam is diffracted by the land group of the servo dedicated layer 13 and decomposed into the main beam MB, the sub beam SB1, and the sub beam SB2.

  In the return path optical system for the recording layer light beam, the recording layer light beam that has passed through the objective lens 4 is incident on the dichroic prism 43 via the quarter-wave plate 44, bent by the dichroic prism 43, and collimator lens 42. Is incident on. The light beam that has passed through the collimator lens 42 is reflected by the polarization beam splitter 41 while condensing, and enters the sensor lens 46 (cylindrical lens). The sensor lens 46 gives astigmatism to the incident recording layer light beam. The recording layer light beam to which astigmatism is applied is incident on the photodetector 6-1.

  In the return optical system for the servo-dedicated layer light beam, the servo-dedicated layer light beam that has passed through the objective lens 4 enters the collimator lens 49 via the quarter-wave plate 44 and the dichroic prism 43. The light beam that has passed through the collimator lens 49 is reflected by the beam splitter 48 while condensing, and enters the sensor lens 51 (cylindrical lens). Similar to the sensor lens 46, the sensor lens 51 imparts astigmatism to the incident servo dedicated layer light beam. The servo dedicated layer light beam provided with astigmatism is incident on the photodetector 6-2.

The photodetector 6-1 is installed on a plane that intersects the optical path of the return light beam of the recording layer light beam emitted from the optical system 3. On the other hand, the photodetector 6-2 is installed on a plane that intersects the optical path of the return light beam of the servo-dedicated layer light beam emitted from the optical system 3. The light detector 6-1 includes one light receiving surface, and the light detector 6-2 includes three light receiving surfaces, and each light receiving surface is divided into a plurality of light receiving regions. In the optical drive device 1, these light receiving areas are used in appropriate combinations, so that the recording layer MPP signal MPP _R , the servo dedicated layer MPP signal MPP _S , the servo dedicated layer SPP signal SPP _S , and the recording layer DPD signal DPD are used. _R , servo dedicated layer DPD signal DPD _S , tracking error signal TE, recording layer focus error signal FE _R , servo dedicated layer focus error signal FE _S , full addition signal (recording layer pull-in signal PI _R , servo dedicated layer It is possible to generate various signals such as the pull-in signal PI _S for use and the RF signal RF). The specific contents will be described later.

As an example, the processing unit 7 is configured by a DSP (Digital Signal Processor) having an A / D conversion function that converts analog signals for multiple channels into digital data, and includes optical detectors 6-1 and 6-2. Upon receiving the output signal, MPP signals MPP _R , MPP _S , SPP signal SPP _S , DPD signals DPD _R , DPD _S , tracking error signal TE, focus error signals FE _R , FE _S , full addition signals (pull-in signals PI _R , PI _S and RF signal RF) are generated. Details of the processing of the processing unit 7 will also be described later.

  The CPU 8 is a processing device incorporated in a computer, a DVD recorder, or the like, and transmits an instruction signal for specifying an access position on the optical disc 11 to the processing unit 7 via an interface (not shown). Receiving this instruction signal, the processing unit 7 controls the objective lens 4 and moves it parallel to the surface of the optical disk 11 to realize an on-track state (tracking servo). In the on-track state, the CPU 8 acquires the RF signal RF generated by the processing unit 7 as a data signal.

  From here, the detail of the structure of the photodetector 6 and the detail of the process of the process part 7 are demonstrated.

  FIG. 12 is a top view of the photodetector 6-1 according to the present embodiment. FIG. 13 is a top view of the photodetector 6-2 according to the present embodiment. 12 and 13 also show examples of spots formed on the light receiving surface by the signal light. The X and Y directions shown in FIGS. 12 and 13 correspond to the optical disc tangential direction and the optical disc radial direction, respectively.

  As shown in FIG. 11, the photodetector 6-1 includes a square light receiving surface 61. The light receiving surface 61 is divided into four squares (light receiving regions 61A to 61D) having the same area, and is arranged at a position where the return light beam of the recording layer light beam can be received.

  As shown in FIG. 13, the photodetector 6-2 includes three light receiving surfaces 62 to 64 each having a square shape. Among these, the light receiving surface 62 is divided into four squares (light receiving regions 62A to 62D) having the same area. The light receiving surfaces 63 and 64 are divided into two upper and lower areas with the same area (light receiving regions 63A and 63B and light receiving regions 64A and 64B). The light receiving surfaces 62 to 64 are respectively arranged at positions where the main beam MB, the sub beam SB1, and the sub beam SB2 can be received.

The photodetectors 6-1 and 6-2 that receive the light beam output a signal having an amplitude of a value (amount of received light) obtained by dividing the intensity of the light beam by the area of the light receiving surface for each light receiving region. The output signal corresponding to the light receiving region X is expressed as I _X as in the first embodiment.

  FIG. 14 is a diagram illustrating functional blocks of the processing unit 7. As shown in the figure, the processing unit 7 includes a focus error signal generation unit 70, a focus servo unit 71, a full addition signal generation unit 72, a determination unit 73 (determination unit), a signal generation unit 74 (signal generation unit), tracking. Error signal generation unit 75 (tracking error signal generation unit), tracking servo unit 76 (tracking servo unit), amplification unit 77 (amplification unit), control signal generation unit 78 (control signal generation unit), tilt servo unit 79 (tilt servo) Means).

Focus error signal generating unit 70 generates the focus error signal FE _R recording layer based on the received light amount of the light receiving regions 61A~61D constituting the light receiving surface 61 for receiving the light beam recording layer, servo generating a focus error signal FE _S servo layer based on the received light amount of the light receiving regions 62A~62D constituting the light receiving surface 62 for receiving the main beam MB of dedicated layer for light beam. Specifically, by calculating the following equation (27) and (28), to generate these focus error signal _FE R, FE _S.

Focus servo unit 71 controls the position of the collimator lens 49 and the objective lens 4 to the recording surface perpendicular direction of the optical disc 11, that the value of each focus error signal FE _R, FE _S is made to be 0 Then, the recording layer light beam is focused on the recording layer, and the servo dedicated layer light beam is focused on the dedicated servo layer (focus servo).

Total sum signal generator 72, based on the received light amount of the light receiving regions 61A~61D constituting the light receiving surface 61 for receiving the light beam recording layer, generating a pull-in signal PI _R for RF signal RF and the recording layer To do. Further, based on the received light amount of the light receiving regions 62A~62D constituting the light receiving surface 62 for receiving the servo-only layer for light beam, and generates a pull-in signal PI _S servo-only layer. Specifically, the following equations (29) and (30) are calculated to generate these signals. As is clear from Equation (27), the RF signal RF and the pull-in signal PI are the same signal. However, the pull-in signal PI _R and pull-in signal PI _S servo dedicated layer for the recording layer is usually band-limited is output in a state of being made by passing the low-pass filter. The band is limited in order to remove fluctuations and noise according to the presence or absence of the code M.

Pull-in signal PI _R and pull-in signal PI _S servo dedicated layer for the recording layer is a signal used for the layer recognized in the focus servo unit 71. That is, these pull-in signals have the property that when the focal position of the light beam moves between the layers, it becomes maximum when the layer surface is in focus. Therefore, the focus servo unit 71 compares the value of the pull-in signal with a predetermined threshold value, and detects a portion that is higher than the threshold value, so that the focal position of the light beam is dedicated to the recording layer or the servo. Detect that it is close to the layer.

  The RF signal RF is input to the CPU 8 as a data signal. The CPU 8 acquires information written on the optical disc 11 based on the RF signal RF.

  The determination unit 73 uses the RF signal RF to determine whether the irradiation position of the light beam is a recording area or an unrecorded area, and a recording / unrecording determination signal NR indicating the result is used as a control signal generation unit 78. Output to. A specific method for generating the recording / non-recording determination signal NR is the same as that described with reference to FIG. 6 in the first embodiment, and a description thereof will be omitted.

The signal generator 74 generates MPP signals MPP _R , MPP _S , SPP signal SPP _S , and DPD signals DPD _R , DPD _S based on the amount of light received by the photodetectors 6-1, 6-2. Specifically, each signal is generated according to the following equations (31) to (35).

As shown in FIG. 11, the recording layer 12 is not provided with land grooves. However, since the edge of the symbol M acts like the edge of the land-groove, it is possible to obtain significant MPP signal MPP _R. Figure 15 is a diagram depicting an example of in the same manner as in FIG. 7, thus obtained MPP signal MPP _R. As shown in the figure, MPP signal MPP _R when the focus position of the light beam is at the edge of the code M, takes a maximum value.

The tracking error signal generation unit 75 uses each signal generated by the signal generation unit 74 and generates a tracking error signal TE by either one of the DPP method and the DPD method. Specifically, when the DPP method is employed, the DPP signal DPP _S is generated by the following equation (36) using the MPP signal MPP _S and the SPP signal SPP _S, and is output as the tracking error signal TE. However, k is a positive constant, and is determined so as to cancel the lens shift offset and the tilt offset generated in the MPP signal MPP _S and the SPP signal SPP _S, respectively. Normally, the k value is an intensity ratio between the MPP signal MPP _S and the SPP signal SPP _S (light intensity ratio between the main signal light and the sub signal light). When the DPD method is adopted, the tracking error signal generation unit 75 directly uses one of the DPD signals DPD _R and DPD _S generated by the equations (32) and (35) as the tracking error signal TE. Output.

At the time of writing, it is preferable that the tracking error signal generation unit 75 outputs one of the DPP signal DPP _S and the DPD signal DPD _S as the tracking error signal TE. This is because the DPD method in the recording layer cannot be used when there is no code in the recording layer. On the other hand, at the time of reproduction, the tracking error signal generator 75 outputs switching the DPD signal DPD _R and DPP signal DPP _S (or DPD signal DPD _S) on the basis of not recording determination signal NR received as input from deciding section 73 It is preferable. In other words, the DPP method (or DPD method) in the servo dedicated layer is used in the unrecorded area where the DPD method in the recording layer cannot be used because there is no code, and the DPD method in the recording layer is used in the recording area with the code. Is preferred. Thus, by performing tracking servo using the recording layer as much as possible, it becomes possible to improve the accuracy of tracking servo. However, of course, at the time of reproduction, the tracking error signal generator 75 may output only the DPP signal DPP _S (or DPD signal DPD _S ) as the tracking error signal TE.

  The tracking servo unit 76 generates a control signal for controlling the position of the objective lens 4 in a direction parallel to the recording surface of the optical disc 11 so that the value of the tracking error signal TE becomes zero. Since the details are the same as those described in the first embodiment, the description thereof is omitted.

Amplification unit 77, so that the inclination of the DPD signal DPD _S and MPP signal MPP _S when the irradiation position of at least the light beam is in the vicinity of the track center _{C R} are equal to each other, one of the DPD signal DPD _S or MPP signal MPP _S At least one is amplified. At least the irradiation position of the light beam so that the slope of the DPD signal DPD _R and MPP signal MPP _R when in the vicinity of the track center _{C R} are equal to each other, at least one of the DPD signal DPD _R or MPP signal MPP _R Amplify. The specific amplification process and the method for determining the amplification factor are the same as those described in the first embodiment, and thus description thereof is omitted.

Control signal generating section 78, (when the focal position of the light beam is on the recording area during playback) when the tracking error signal generator 75 is generating a tracking error signal TE using the DPD signal DPD _R, DPD generating a control signal Vtc based on the difference signal DPD _R and MPP signal MPP _R. Specifically, the control signal Vtc is generated by the following equation (37). On the other hand, when the tracking error signal generator 75 generates the tracking error signal TE using the DPP signal DPP _S or DPD signal DPD _S (the focal position of the light beam is in the unrecorded area during writing or reproduction). The control signal Vtc is generated based on the difference between the DPD signal DPD _S and the MPP signal MPP _S. Specifically, the control signal Vtc is generated by the following equation (38). However, when the focal position of the light beam is in an unrecorded area during reproduction, the control signal Vtc may be generated by Expression (37). In this case, better to not select to clear the DPD signal DPD _R is more reliable. Note that β in the equations (37) and (38) is determined by a method similar to the method described in the first embodiment.

Table 1 summarizes typical examples of the relationship between the writing and reproduction and the tracking error signal TE and the control signal Vtc. However, the relationship between writing and reproduction and each signal is not limited to the example described in Table 1. For example, during reproduction, as described above, the DPP signal DPP _S or the DPD signal DPD _S may be used as the tracking error signal TE regardless of whether or not the focal position of the light beam is in the recording area. In other words, tilt servo may be performed using only the servo dedicated layer during writing and during reproduction. In that case, you may use Formula (38).

  The tilt servo unit 79 controls the incident angle of the light beam on the optical disc 11 based on the control signal Vtc generated by the control signal generation unit 78. Specifically, the objective lens 4 is rotated in the radial direction so that the value of the control signal Vtc shown in the equations (37) and (38) becomes zero. Note that the optical system 3 may be rotated in the radial direction instead of the rotation of the objective lens 4, or the tilt of the optical disk 11 may be directly controlled.

  By performing tilt servo so that the value of the control signal Vtc shown in Expression (37) and Expression (38) becomes 0, even if the light beam irradiation position fluctuates in the on-track state, there is no tilt. The principle that the values of the DPD signal DPD and the MPP signal MPP can be kept equal to each other is as described in the first embodiment. Therefore, also by the optical drive device 1 according to the present embodiment, it is possible to reduce the influence of the swing of the light beam irradiation position in the on-track state on the tilt servo.

In the second embodiment, the description has been made on the assumption that both the land groove and the symbol M are provided in the servo dedicated layer. However, even if only one of them is provided. A similar process is possible. In other words, if first only land-groove is provided in the servo-only layer, so becomes a DPD signal DPD _S is always 0, as described with reference to equation (19) in the first embodiment, the DPD signal even if the DPD _S becomes zero at all times, the tilt servo is possible. If only code M is provided in the servo-only layer, so similar MPP signal MPP _S and MPP signal MPP _R described with reference to obtain 15, both land-groove and the code M is provided As in the case of the above, the influence of the fluctuation of the light beam irradiation position in the on-track state on the tilt servo can be reduced.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to such embodiment at all, and this invention can be implemented in various aspects in the range which does not deviate from the summary. Of course.

DESCRIPTION OF SYMBOLS 1 Optical drive apparatus 2 Laser light source 3 Optical system 4 Objective lens 5 Actuator 6 Photodetector 7 Processing part 11 Optical disk 12 Recording layer 13 Servo exclusive layers 21 and 47 Diffraction gratings 22 and 49 Beam splitters 23, 41, 45, 48, and 50 Collimator lenses 24, 44 1/4 wavelength plates 25, 46, 51 Sensor lens 42 Polarizing beam splitter 43 Dichroic prisms 61-64 Light receiving surface 70 Focus error signal generation unit 71 Focus servo unit 72 Full addition signal generation unit 73 Determination unit 74 Signal Generation unit 75 Tracking error signal generation unit 76 Tracking servo unit 77 Amplification unit 78 Control signal generation unit 79 Tilt servo unit

Claims (7)

An optical system for irradiating a recording layer of an optical disc with a light beam;
A photodetector for receiving reflected light from the recording layer of the light beam;
Signal generating means for generating a DPD signal and an MPP signal based on the amount of light received by the photodetector;
Amplifying means for amplifying at least one of the DPD signal and the MPP signal so that the slopes of the DPD signal and the MPP signal are equal to each other at least when the irradiation position of the light beam is near the track center;
Control signal generating means for generating a control signal based on the difference between the DPD signal and the MPP signal after amplification processing by the amplification means;
An optical drive device comprising: tilt servo means for controlling an incident angle of the light beam to the optical disk based on the control signal.   The amplifying unit amplifies at least one of the DPD signal and the MPP signal so that an amplitude ratio of the MPP signal and the DPD signal is equal to a ratio of a distance between local maximum values sandwiching a track center. The optical drive device according to claim 1.   The amplifying unit is configured to cause the DPD signal or the MPP signal to be equal to each other when the irradiation position of the light beam is at a given position between the track center and the track end. 3. The optical drive device according to claim 1, wherein at least one of the two is amplified. The optical system is
An objective lens for condensing the light beam on the recording layer;
An actuator for controlling the position of the objective lens according to a given control voltage;
4. The control signal generation unit removes a fluctuation component due to lens shift of the objective lens from a difference between the DPD signal and the MPP signal based on the control voltage. 5. The optical drive device according to Item. A determination means for determining that the irradiation position of the light beam is an unrecorded area;
The control signal generation means amplifies the control voltage at an amplification factor according to the determination result of the determination means, and subtracts the amplified control voltage from the difference between the DPD signal and the MPP signal, 5. The optical drive device according to claim 4, wherein a fluctuation component due to lens shift of the objective lens is removed from a difference between the DPD signal and the MPP signal. First and second light beams, which are controlled to have the same optical axis at least in the vicinity of the recording surface, are recorded on the recording surface of an optical disc having at least a recording layer having a sign and a servo dedicated layer, respectively. An optical system for irradiating in focus on the layer and the servo dedicated layer;
A first photodetector for receiving reflected light from the recording surface of the first light beam;
A second photodetector for receiving reflected light from the recording surface of the second light beam;
The first DPD signal and the first MPP signal are generated based on the received light amount of the first photodetector, and the second DPD signal and the second MPD signal are generated based on the received light amount of the second photodetector. Signal generating means for generating the MPP signal of
Tracking error signal generating means for generating a tracking error signal using any one of the first DPD signal, the second DPD signal, and the second MPP signal;
Tracking servo means for controlling the optical system based on the tracking error signal;
At least one of the first DPD signal and the first MPP signal is amplified so that the slope of the first DPD signal is equal to the slope of the first MPP signal at least near the track center. And amplifying at least one of the second DPD signal and the second MPP signal so that the slope of the second DPD signal is equal to the slope of the second MPP signal at least near the center of the track. Amplifying means;
When the tracking error signal generating means generates the tracking error signal using the first DPD signal, a control signal is generated based on a difference between the first DPD signal and the first MPP signal. When the tracking error signal generating means generates the tracking error signal using the second DPD signal or the second MPP signal, the second DPD signal and the second MPP signal Control signal generating means for generating a control signal based on the difference;
An optical drive device comprising: tilt servo means for controlling an incident angle of the light beam to the optical disk based on the control signal. Two optical beams controlled to have the same optical axis at least in the vicinity of the recording surface are applied to the recording surface of the optical disc having at least a recording layer and a servo dedicated layer, respectively. An optical system for irradiating the layer in focus;
A photodetector for receiving reflected light from the recording surface of the light beam focused on the servo dedicated layer;
Signal generating means for generating a DPD signal and an MPP signal based on the amount of light received by the photodetector;
Amplifying means for amplifying at least one of the DPD signal and the MPP signal so that the slope of the DPD signal and the slope of the MPP signal are equal at least near the center of the track;
Control signal generating means for generating a control signal based on a difference between the DPD signal and the MPP signal;
Tilt servo for controlling the incident angle of the light beam to the optical disk based on the control signal generated based on the difference between the DPD signal and the MPP signal both during reproduction of the optical disk and during writing to the optical disk And an optical drive device.

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