JP2011040143A - Optical drive device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical drive device that needs no complex countermeasures against stray light during tracking servo of a multilayer disk having a land and a groove. <P>SOLUTION: The optical drive device reproduces a multilayer disk having a land and a groove, and includes an optical system that irradiates the recording surface of the multilayer disk with an optical beam, a photodetector that receives reflected light from the recording surface of the optical beam, a tracking-error-signal generating part 61-1 that generates a tracking error signal TE<SB>DPD</SB>based on the received light amount of the photodetector by using a DPD method, and a tracking servo part 62 that controls the optical system so that a focus of the optical beam matches the center of a code string formed in the land or the groove based on the tracking error signal TE<SB>DPD</SB>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  As a specific method of optical disk tracking servo, a differential push-pull method (DPP method) and a phase difference detection method (DPD method) are known. The DPP method uses diffraction at a step between a land and a groove provided on the surface of an optical disk, and can focus a light beam on the center of the land or groove. On the other hand, the DPD method uses diffraction by a code (pit or recording mark) recorded in a recording layer, and the light beam can be focused at the center of the code string.

  In the DPP method, an offset due to the lens shift of the objective lens is generated. In order to cancel this, a three-beam method is used in which the light beam is divided into zero-order diffracted light and ± first-order diffracted light. On the other hand, in the DPD method, since the control is performed by detecting the phase difference, the offset due to the lens shift of the objective lens hardly causes a problem, and the one-beam method is used.

  When a ROM or recorded recording optical disk is reproduced, since a code is already recorded in the recording layer, tracking servo by the DPD method can be performed at least in the recording area (for example, Patent Document 1, Patent Document 1). 2). However, since the DPD method cannot be used in an unrecorded area and the irradiation position of the light beam may straddle the unrecorded area even during reproduction, the DPP method has conventionally been used when reproducing an optical disc having a land groove. Used.

JP 2005-293637 A JP 2002-74687 A

  However, the DPP method has a problem that it is strongly influenced by stray light (reflected light other than on the recording surface. If the optical disk is a multilayer disk, it includes reflected light other than the access target layer). This is because ± first-order diffracted light with relatively weak signal light intensity is used. On the other hand, since the DPD method that does not use ± first-order diffracted light is not easily affected by stray light, it is preferable to use the DPD method as much as possible. Therefore, in principle, it is desired to use the DPD method and switch to the DPP method when the irradiation position of the light beam reaches an unrecorded area.

  Patent Documents 1 and 2 describe a technique that uses the DPD method in a recording area and uses the DPP method in an unrecorded area.

  However, the techniques described in Patent Documents 1 and 2 are techniques for using the DPP method at the time of a track jump across an unrecorded area. By performing tracking servo by the DPD method, an on-track state (tracking) When the reproduction is performed while maintaining the servo-on state and being controlled to be in the center of the track), even if the irradiation position of the light beam reaches the unrecorded area, the DPD method is not switched. The tracking error signal generation by is continued. For this reason, the on-track state may not be maintained. This will be described in detail below.

  The technique disclosed in paragraph [0023] of Patent Document 1 switches between the DPD method and the DPP method depending on the amplitude at the time of track jump. Therefore, the switching between the DPD method and the DPP method can be performed only at the time of track jump, and basically the DPD method and the DPP method cannot be switched in an on-track state where no amplitude is generated in the tracking error signal.

  The technique disclosed in the paragraph [0045] of FIG. 5 and Patent Document 2 shows that edit information (information stored in response to data recording or deletion) recorded in a specific area of the optical disc when performing a track jump. It is determined whether or not the unrecorded area is crossed by reference, and the DPD method and the DPP method are switched according to the result. There is no description about switching between the DPD method and the DPP method in the on-track state.

  Accordingly, one of the objects of the present invention is to perform DPP when the irradiation position of the light beam reaches an unrecorded area during reproduction while maintaining the on-track state by performing tracking servo by the DPD method. It is an object of the present invention to provide an optical drive device that can be switched to tracking servo according to the method.

  Further, when the optical disk is a multilayer disk, the stray light includes reflected light from layers other than the access target layer, so that the stray light intensity is particularly strong compared to the case of a single-layer disk, and DPP using ± first-order diffracted light. The law requires complex stray light countermeasures.

  Accordingly, another object of the present invention is to provide an optical drive device that does not require a complicated countermeasure against stray light in the tracking servo of a multi-layer disc having land grooves.

  In order to achieve the above object, an optical drive device according to the present invention is an optical drive device for reproducing an optical disk having land grooves, an optical system for irradiating a recording surface of the optical disk with a light beam, and the light beam. A photodetector that receives the reflected light from the recording surface, a first tracking error signal generation unit that generates a first tracking error signal using the DPD method based on the amount of light received by the photodetector; One of the second tracking error signal generating means and a second tracking error signal generating means for generating a second tracking error signal using the DPP method based on the amount of light received by the photodetector. Tracking servo means for controlling the optical system based on the above, and determination means for determining that the irradiation position of the light beam is an unrecorded area, Racking servo means in response to the determination result of said determining means running control based on the first tracking error signal, and switches the control based on the second tracking error signal.

  According to the present invention, when reproduction is performed while maintaining the on-track state by performing tracking servo by the DPD method, the tracking servo by the DPP method is performed when the irradiation position of the light beam reaches an unrecorded area. It becomes possible to switch.

  In the optical drive device, the determination unit determines that the irradiation position of the light beam is an unrecorded area depending on whether or not the second tracking error signal has changed beyond a first predetermined range. It is good to do. According to this, it can be appropriately determined that the irradiation position of the light beam has reached the unrecorded area.

  Further, in this optical drive device, the tracking servo means may determine that the irradiation position of the light beam is an unrecorded area by the determination means during execution of control based on the first tracking error signal. The control is switched to the control based on the second tracking error signal, and the second tracking error signal is within the second predetermined range narrower than the first predetermined range during the control based on the second tracking error signal. The control may be switched to the control based on the first tracking error signal depending on whether or not it has entered. Further, the apparatus further includes an RF signal generation unit that generates an RF signal based on the amount of light received by the photodetector, and the determination unit determines that the irradiation position of the light beam is a recording area according to the RF signal. The tracking servo means, when executing the control based on the first tracking error signal, the second tracking when the irradiation position of the light beam is determined to be an unrecorded area by the determination means. The control is switched to the control based on the error signal, and the first tracking is performed when the determination unit determines that the irradiation position of the light beam is the recording area during the control based on the second tracking error signal. It may be switched to control based on the error signal. According to these, the tracking servo means can stably switch control even in an unrecorded area.

  The optical drive device may further include RF signal generation means for generating an RF signal based on the amount of light received by the photodetector, and the determination means may determine an irradiation position of the light beam according to the RF signal. It may be determined that the area is an unrecorded area. This also makes it possible to appropriately determine that the light beam irradiation position has reached the unrecorded area.

  Further, in this optical drive device, the determination means determines whether the irradiation position of the light beam is an unrecorded area or a recording area in accordance with the RF signal, and the tracking servo means When the determination means determines that the irradiation position of the light beam is an unrecorded area during execution of the control based on the tracking error signal of 1, the control is switched to the control based on the second tracking error signal, and When the control unit based on the second tracking error signal determines that the light beam irradiation position is a recording area during the control, the control may be switched to the control based on the first tracking error signal. Good.

  An optical drive apparatus according to another aspect of the present invention is an optical drive apparatus for reproducing a multilayer disk having land grooves, an optical system for irradiating a recording surface of the multilayer disk with the light beam, and the light beam A photodetector that receives reflected light from the recording surface, tracking error signal generation means that generates a tracking error signal using the DPD method based on the amount of light received by the photodetector, and based on the tracking error signal Tracking servo means for controlling the optical system.

  According to the present invention, since the DPD method is used instead of the DPP method in the tracking servo of the multi-layer disk having land grooves, a complicated countermeasure against stray light becomes unnecessary.

  According to the present invention, when reproduction is performed while maintaining the on-track state by performing tracking servo by the DPD method, the tracking servo by the DPP method is performed when the irradiation position of the light beam reaches an unrecorded area. It becomes possible to switch.

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 the sensor lens by the 1st Embodiment of this invention. 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. FIG. 6 is a diagram showing temporal changes in tracking error signals TE _DPD and TE _DPP when performing reproduction while maintaining the vicinity of the track center in the optical drive device according to the first embodiment of the present invention. It is a figure which shows the internal circuit of the determination part by the 1st Embodiment of this invention. In the optical drive device according to the first embodiment of the present invention, the time change of the output signal _VOUT of the determination unit when performing reproduction while maintaining the vicinity of the track center is described side by side with the time change of the tracking error signal TE _DPP. It is a thing. In the optical drive device according to the modification of the first embodiment of the present invention, the time change of the output signal _VOUT of the determination unit when performing reproduction while maintaining the vicinity of the track center is the time change of the tracking error signal TE _DPP . Are listed side by side. It is a figure which shows the functional block of the process part of the optical drive apparatus by the 2nd Embodiment of this invention. It is a figure which shows the time change of the various signals which the determination part by the 2nd Embodiment of this invention utilizes when reproducing | regenerating while maintaining track center vicinity. In the optical drive device according to the modification of the embodiment of the present invention, the time change of the output signal _VOUT of the determination unit when performing reproduction while maintaining the vicinity of the track center is described side by side with the time change of the tracking error signal TE _DPP. It is a thing.

  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 according to the recording method, such as BD-RE.) In this embodiment, a write-once type or a rewritable type is used.

  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 width of the code 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 width of the code M is the land width. A little smaller than the width. 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 5, and a processing unit 6. Of these, the laser light source 2, the optical system 3, and the photodetector 5 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, and an objective lens 4. 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 disk 11, and also functions as a backward optical system that guides the return beam from the optical disk 11 to the photodetector 5.

  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.

  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 5.

  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 5. 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 5, and the spot (stray light spot) that stray light forms on the photodetector 5 is As compared with a spot (signal light spot) formed on the photodetector 5 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 5 is installed on a plane that intersects the optical path of the return light beam emitted from the optical system 3. The photodetector 5 includes three light receiving surfaces, and each light receiving surface is divided into a plurality of light receiving regions. The optical drive device 1 generates various signals such as a focus error signal FE, a full addition signal (a pull-in signal PI, an RF signal RF), a tracking error signal TE _DPD , and TE _DPP by appropriately combining these light receiving areas. It is possible to do. The specific contents will be described later.

The processing unit 6 is configured by a DSP (Digital Signal Processor) having an A / D conversion function that converts analog signals for multiple channels into digital data as an example, and receives an output signal from the photodetector 5, A focus error signal FE, a full addition signal (pull-in signal PI, RF signal RF), and tracking error signals TE _DPD and TE _DPP are generated. Details of the processing of the processing unit 6 will also be described later.

  The CPU 7 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 6 via an interface (not shown). Receiving this instruction signal, the processing unit 6 controls the objective lens 4 and moves it parallel to the surface of the optical disk 11 (this movement is called “lens shift”) to realize an on-track state (tracking servo). . In the on-track state, the CPU 7 acquires the RF signal generated by the processing unit 6 as a data signal.

  From here, the detail of the structure of the photodetector 5 and the detail of the process of the process part 6 are demonstrated.

  FIG. 4 is a top view of the photodetector 5 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 5 includes three light receiving surfaces 51 to 53 each having a square shape. Among these, the light receiving surface 51 is divided into four squares (light receiving regions 51A to 51D) having the same area. The light receiving surfaces 52 and 53 are divided into two upper and lower areas with the same area (light receiving regions 52A and 52B and light receiving regions 53A and 53B). The light receiving surfaces 51 to 53 are arranged at positions where the main beam MB, the sub beam SB1, and the sub beam SB2 can be received.

The photodetector 5 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 6. As shown in the figure, the processing unit 6 includes a tracking error signal generation unit 61-1 (first tracking error signal generation unit), a tracking error signal generation unit 61-2 (second tracking error signal generation unit), and a tracking. A servo unit 62 (tracking servo unit), a determination unit 63 (determination unit), a full addition signal generation unit 64 (RF signal generation unit), a focus error signal generation unit 65, and a focus servo unit 66 are provided.

The tracking error signal generation unit 61-1 generates a tracking error signal TE _DPD (first tracking error signal) using the DPD method based on the output signal of the photodetector 5. Hereinafter, a method for generating the tracking error signal TE _DPD will be described in detail.

In generating the tracking error signal TE _DPD , the tracking error signal generation unit 61-1 uses two phase difference signals S1p = P (I _51A , I _51B ) and S2p = P (I _51C ) from the output signal of the photodetector 5. , I _51D ). P (X, Y) is a function indicating the phase difference between the signal X and the signal Y. Then, the phase difference signals S1p and S2p are added and output as a tracking error signal TE _DPD .

The phase difference indicated by the phase difference signals S1p and S2p is 0 when the light beam is diffracted by the code M and the incident light is incident on the recording surface when the focal position of the incident light on the recording surface is at the center of the track. The focal position of the light increases as it moves away from the track center. Therefore, the on-track state can be realized by controlling the objective lens 4 so that the sum of the phase differences indicated by the tracking error signal TE _DPD becomes zero.

  However, the phase difference indicated by the phase difference signals S1p and S2p becomes 0 not only when the on-track state is applied but also when the light beam is irradiated on the area without the code M (unrecorded area). Therefore, an on-track state cannot be realized in the unrecorded area by the DPD method.

The tracking error signal generation unit 61-2 generates a tracking error signal TE _DPP (second tracking error signal) using the DPP method based on the output signal of the photodetector 5. Hereinafter, a method for generating the tracking error signal TE _DPP will be described in detail.

In the generation of the tracking error signal TE _DPP , the tracking error signal generation unit 61-2 calculates the differential push-pull signal DPP by the following equation (1). Then, this differential push-pull signal DPP is output as a tracking error signal TE _DPP . However, MPP and SPP are a main push-pull signal and a sub push-pull signal, respectively, and are represented by equations (2) and (3), respectively. Further, k is a positive constant and is determined so as to cancel out the lens shift offset (offset caused by the above-described lens shift) generated in each of the main push-pull signal MPP and the sub push-pull signal SPP.

  As shown in FIG. 4, each beam MB, SB1, SB2 has push-pull regions P1 and P2. These are regions where the above-described 0th-order diffracted light and ± 1st-order diffracted light interfere with each other. As shown in FIG. 4, the main beam MB and the sub-beams SB1 and SB2 have the push-pull region P1 and the push-pull region P2. The positional relationship is reversed.

The relative intensities of the push-pull areas P1 and P2 change as the focal position of the incident light on the recording surface moves in the radial direction of the optical disc (that is, moves in the direction crossing the track). When the focal position of the incident light on the recording surface is at the center of the track, the intensities of the push-pull areas P1 and P2 are equal. Therefore, the value of the main push-pull signal MPP is 0 when the focal position of the incident light on the recording surface is at the center of the track, and other than 0 otherwise. The same applies to the sub push-pull signal SPP. However, as described above, since the positional relationship between the push-pull region P1 and the push-pull region P2 is reversed between the main beam MB and the sub beams SB1 and SB2, the main push-pull signal MPP and the sub push-pull signal SPP are The phase is 180 ° different and the sign is reversed. For this reason, the value of the differential push-pull signal DPP represented by the equation (1) is also 0 when the focal position of the incident light on the recording surface is at the center of the track, and other than 0 otherwise. Thus, the on-track state can be realized by controlling the objective lens 4 so that the tracking error signal TE _DPP becomes zero.

The tracking servo unit 62 controls the optical system 3 (more specifically, the objective lens 4) based on one of the tracking error signals TE _DPD and TE _DPP (tracking servo). Hereinafter, a mode for controlling the optical system 3 based on the tracking error signal TE _DPD is referred to as a DPD mode, and a mode for controlling the optical system 3 based on the tracking error signal TE _DPP is referred to as a DPP mode.

  When the above-described instruction signal is input from the CPU 7, the tracking servo unit 62 first starts tracking servo in the DPD mode to realize an on-track state. When the determination unit 63 notifies the determination result that the irradiation position of the light beam is an unrecorded area during tracking servo in the DPD mode, the tracking servo is performed by switching to the DPP mode. On the other hand, when the determination result that the irradiation position of the light beam is the recording area is notified from the determination unit 63 during the tracking servo in the DPP mode, the tracking servo is performed by switching to the DPD mode. These switching processes will be described in more detail later together with the description of the determination unit 63.

The determination unit 63 determines whether the irradiation position (focal position) of the light beam is in an unrecorded area or a recorded area in the access target layer. Specifically, the tracking error signal TE _DPP generated by the tracking error signal generation unit 61-2 is monitored, and the above determination is made according to whether or not it has changed beyond a predetermined range. Details will be described below.

FIG. 6 is a diagram illustrating temporal changes in tracking error signals TE _DPD and TE _DPP when reproduction is performed while maintaining the vicinity of the track center. A solid line of the tracking error signal TE _DPP indicates a case where the mode is switched according to the present embodiment, and a dotted line indicates a case where the switching to the DPP mode according to the present embodiment is not performed.

When the focal position is in the recording area and the focal position is at the track center, the value of the tracking error signal TE _DPD becomes zero. On the other hand, when the focal position is slightly deviated from the track center, the value of the tracking error signal TE _DPD is other than zero. Therefore, the tracking servo section 62 controls the objective lens 4 so that the value of the tracking error signal TE _DPD becomes 0, so that the on-track state is appropriately realized. Thereby, as shown in FIG. 6, the value of the tracking error signal TE _DPP is also maintained at 0.

On the other hand, when the focal position is in the unrecorded area, there is no code M at the irradiation position of the light beam, so that the value of the tracking error signal TE _DPD remains 0 even if the focal position deviates from the track. Therefore, when the tracking servo unit 62 performs control based on the tracking error signal TE _DPD , the light beam irradiation position gradually shifts from the track. Along with this deviation, the value of the tracking error signal TE _DPP gradually moves away from 0 as shown in FIG. 6, and finally the same vibration as that at the time of track jump is performed unless mode switching is performed according to the present embodiment. Will repeat.

The determination unit 63 determines whether the irradiation position of the light beam is in an unrecorded area or a recorded area in the access target layer by detecting such a change in the value of the tracking error signal TE _DPP . That is, the determination unit 63 stores predetermined threshold values Δ1, Δ2 (0 ≦ Δ2 <Δ1) in advance, and the tracking error signal TE _DPP is being executed while the tracking servo unit 62 is executing control based on the tracking error signal TE _DPD. When the value of γ exceeds the range of −Δ1 to Δ1, it is determined that the irradiation position of the light beam has entered an unrecorded area in the access target layer (the determination unit 63 only determines so, and the unrecorded area There is no 100% guarantee that you are in the area.) On the other hand, when it falls within the range of -Δ2 to Δ2, it is determined that the irradiation position of the light beam has entered the recording area in the access target layer (the determination unit 63 only determines so, There is no 100% guarantee that you are in the area.)

  The determination unit 63 notifies the tracking servo unit 62 of the result of the above determination. When the tracking servo unit 62 is notified of the determination result that the irradiation position of the light beam has entered an unrecorded area in the access target layer, the tracking servo unit 62 stops the tracking servo in the DPD mode and switches to the tracking servo in the DPP mode. . On the other hand, when the determination result that the irradiation position of the light beam has entered the recording area in the access target layer is notified, the tracking servo in the DPP mode is stopped and the tracking servo in the DPD mode is switched.

FIG. 7 is a diagram specifically illustrating an internal circuit of the determination unit 63. As shown in the figure, the determination unit 63 includes comparators 70 and 71 and an output signal generation unit 72. Each of the comparators 70 and 71 has two input terminals, to which the tracking error signal TE _DPP and the reference potential V _ref are input. The reference potential V _ref is the potential of the tracking error signal TE _DPP when the value of the tracking error signal TE _DPP the focal point of the light beam is at the track center is 0, optionally in consideration of the operating point of the circuit It is decided. That is, the tracking error signal TE _DPP is a value including the reference potential Vref. The output signal generator 72 receives the output signals V ₁ and V ₂ from the comparators 70 and 71 and generates an output signal _VOUT .

FIG. 8 shows the time changes of the signals V ₁ , V ₂ , and V _OUT when performing reproduction while maintaining the vicinity of the center of the track side by side with the time changes of the tracking error signal TE _DPP . Note that the time scale in FIG. 8 is shorter than that in FIG. As understood from FIG. 8, the comparator 70, the value of signal V ₁ and the row when the value of the tracking error signal TE _DPP is within the range of -Deruta1～deruta1, the signal V ₁ otherwise Set the value to high. On the other hand, the comparator 71 sets the value of the signal V ₂ to low when the value of the tracking error signal TE _DPP is within the range of −Δ2 to Δ2, and sets the value of the signal V ₂ to high otherwise. The output signal generator 72, a high signal _{V OUT} at the rising edge of the signal _{V 1,} and a low signal _{V OUT} at the falling edge of the signal _{V 2.} The determination unit 63 notifies the tracking servo unit 62 of this signal _VOUT as a determination result of whether the light beam irradiation position is in an unrecorded area or a recorded area in the access target layer.

The tracking servo unit 62 performs mode switching according to the output signal _VOUT . That is, when _VOUT is low, the DPD mode is selected, and when _VOUT is high, the DPP mode is selected. As a result, the tracking error signal TE _DPP changes as shown in FIG.

It should be noted here that when the irradiation position of the light beam is in an unrecorded area, the output signal _VOUT becomes a signal that vibrates violently as shown in FIG. Due to this vibration, if the tracking servo unit 62 is sensitive to the output signal _VOUT and performs mode switching, mode switching frequently occurs in an unrecorded area, and the tracking servo may become unstable. is there. Therefore, when switching from the DPP mode to the DPD mode, it is preferable to perform processing with a certain delay. Specifically, the tracking servo unit 62 may delay the process, or the determination unit 63 may delay the output timing of the determination result.

FIG. 9 shows a specific example of the delay process. FIG. 9 shows the time changes of the signals V ₁ , V ₂ , and V _OUT during reproduction while maintaining the vicinity of the track center in the same manner as FIG. 8 along with the time change of the tracking error signal TE _DPP. there is, in this example, the timing at which the output signal V _OUT by the output signal generation unit 72 of the determination unit 63 is low, rather than immediately after the falling edge of the signal V _2, a predetermined delay time from the fall of the signal V ₂ It is assumed that d has elapsed. For example, the delay time d is a time for the tracking error signal TE _DPP to return to zero. According to this example, as shown in FIG. 9, since the value of the tracking error signal TE _DPP can return to near zero, the oscillation period of the output signal _VOUT is long. Accordingly, since the frequency of switching between the DPD mode and the DPP mode can be reduced, tracking servo can be performed relatively stably.

  As described above, according to the optical drive device 1 according to the present embodiment, when the reproduction is performed while maintaining the on-track state by performing the tracking servo by the DPD method, the irradiation position of the light beam is not recorded. When reaching the area, it is possible to switch to the tracking servo by the DPP method.

  Returning to FIG. The full addition signal generation unit 64 generates the RF signal RF and the pull-in signal PI based on the received light amounts of the light receiving regions 51A to 51D constituting the light receiving surface 51 for receiving the main beam MB. Specifically, these signals are generated by performing the calculation of the following equation (4). As is clear from Equation (4), 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 66. 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 66 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 7 as a data signal. The CPU 7 acquires information written on the optical disc 11 based on the RF signal RF.

The focus error signal generation unit 65 generates a focus error signal FE based on the amount of light received by each of the light receiving regions 51A to 51D constituting the light receiving surface 51 for receiving the main beam MB. Specifically, the calculation of the following equation (5) is performed to generate the focus error signal FE.

  The focus servo unit 66 controls 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 0, so that the focus of the light beam is applied to the recording layer. Align (focus servo).

  FIG. 10 is a diagram showing functional blocks of the processing unit 6 of the optical drive device 1 according to the second embodiment of the present invention. The optical drive device 1 according to the present embodiment is the same as the optical drive device 1 according to the first embodiment, except that the processing of the determination unit 63 is partially different. Below, it demonstrates paying attention only to the process of the determination part 63. FIG.

As shown in FIG. 10, the RF signal RF is input to the determination unit 63 according to the present embodiment instead of the tracking error signal TE _DPP . The determination unit 63 detects whether the irradiation position of the light beam is in an unrecorded area or a recorded area in the access target layer according to the RF signal RF. Details will be described below.

  FIG. 11 is a diagram showing temporal changes of various signals used by the determination unit 63 when reproduction is performed while maintaining the vicinity of the track center.

  First, as shown in FIG. 11, the RF signal RF is a signal that vibrates violently in a short period in the recording area. Since this vibration corresponds to a change in reflectance due to the symbol M, the RF signal RF does not vibrate in the unrecorded area. Although an example is shown in FIG. 11, an offset that changes due to non-uniform reflectance of the recording layer or confocal crosstalk appears in the RF signal RF. Further, 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 63 first performs bottom clamp processing for aligning the lower values of the RF signal RF to obtain the clamp signal RFC shown in FIG.

  When the clamp signal RFC is obtained, the determination unit 63 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 63 generates an unrecorded area detection signal NR based on the slice signal SS. Specifically, the unrecorded area detection signal NR is set high when the high of the slice signal SS continues for a predetermined time D or longer, and the unrecorded area detection signal NR when the slice signal SS remains low for the predetermined time D or longer. Is set to low to generate an unrecorded area detection 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.

  The unrecorded area detection signal NR indicates that the irradiation position of the light beam has entered the recording area in the access target layer when it is low, and the irradiation position of the light beam is not detected in the access target layer when it is high. This signal indicates that the recording area has been entered. The determination unit 63 notifies the tracking servo unit 62 of the unrecorded area detection signal NR as a determination result of whether the irradiation position of the light beam is in an unrecorded area or a recorded area in the access target layer. The tracking servo unit 62 switches modes according to the input unrecorded area detection signal NR. That is, the tracking servo section 62 enters the DPD mode when the unrecorded area detection signal NR is low, and enters the DPP mode when it is high. FIG. 11 shows an example of generating the unrecorded area detection signal NR by processing the RF signal RF.

  As described above, even when the optical drive device 1 according to the present embodiment performs reproduction while maintaining the on-track state by performing tracking servo by the DPD method, the irradiation position of the light beam is an unrecorded area. When it reaches the point, it becomes possible to switch to the tracking servo by the DPP method.

  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.

For example, the determination unit 63 generates both of the output signals V ₁ and non-recorded area detection signal NR, determination and notification of radiation that position has entered the recording region of the optical beam based on the non-recorded area detection signal NR performed, the determination and notification of the irradiation position is entered in the unrecorded area of the light beam may be performed on the basis of the output signal V _1. As described above, the output signal V _OUT generated using the signals V ₁ and V ₂ vibrates violently when the irradiation position of the light beam is in an unrecorded area. Therefore, it has been described that it is preferable to perform processing with a certain delay when switching from the DPP mode to the DPD mode. However, this delay is caused by the unrecorded area detection signal NR in the output signal V _1. It can also be realized by combining. That is, the determination unit 63 determines and notifies that the light beam irradiation position has entered the recording area based on the unrecorded area detection signal NR, and determines that the light beam irradiation position has entered the unrecorded area. and it may be the be performed on the basis of the output signal V ₁ the notification. By doing so, the tracking servo section 62 can stably switch modes even in an unrecorded area.

FIG. 12 assumes that the determination unit 63 performs the above processing, and similarly to FIGS. 8 and 9, the signals V ₁ , NR, and V _OUT when performing reproduction while maintaining the vicinity of the track center are shown. The time change is described side by side with the time change of the tracking error signal TE _DPP . According to this example, as shown in FIG. 12, the value of the output signal _VOUT becomes high while the focal position of the light beam enters the unrecorded area and once becomes high, and then remains within the unrecorded area. Maintained in a state. Accordingly, since the frequency of switching between the DPD mode and the DPP mode can be greatly reduced, tracking servo can be performed more stably.

The configuration of the photodetector 5 and the calculation formula (1) of the differential push-pull signal DPP by the processing unit 6 shown in the above embodiment are the most basic. Actually, particularly when the optical disk 11 is a multilayer disk, a light receiving area for receiving stray light is provided on the light receiving surface of the photodetector 5 as a countermeasure against stray light, and the differential is based on the amount of light received in the light receiving area. The push-pull signal DPP may be calculated. By doing so, an offset generated in the tracking error signal TE _DPP due to stray light can be reduced.

When only a multilayer disk having a land group is used as the optical disk 11, the tracking servo unit 62 may always control the optical system 3 based on the tracking error signal TE _DPD in the recording area. In this way, since the DPD method is used instead of the DPP method in the tracking servo of the multi-layer disk having land grooves, a complicated countermeasure against stray light becomes unnecessary.

DESCRIPTION OF SYMBOLS 1 Optical drive device 2 Laser light source 3 Optical system 4 Objective lens 5 Photodetector 6 Processing part 11 Optical disk 21 Diffraction grating 22 Beam splitter 23 Collimator lens 24 1/4 wavelength plate 25 Sensor lens 51-53 Light-receiving surface 51A-51D, 52A , 52B, 53A, 53B Light receiving area 61-1 and 61-2 Tracking error signal generator 62 Tracking servo unit 63 Determination unit 64 Fully added signal generator 65 Focus error signal generator 66 Focus servo unit 70, 71 Comparator 72 Output signal Generator

Claims (5)

An optical drive device for reproducing a multi-layer disc having land grooves,
An optical system for irradiating the recording surface of the multilayer disc with a light beam;
A photodetector for receiving reflected light from the recording surface of the light beam;
First tracking error signal generating means for generating a first tracking error signal using the DPD method based on the amount of light received by the photodetector;
Tracking servo means for controlling the optical system so that the light beam is focused on the center of a code string formed in the land or the groove based on the first tracking error signal. Optical drive device to do. Second tracking error signal generation means for generating a second tracking error signal using the DPP method based on the amount of light received by the photodetector;
Determination means for determining that the irradiation position of the light beam is an unrecorded area,
The tracking servo means controls the optical system based on one of the first and second tracking error signals;
The tracking servo means switches to control based on the second tracking error signal according to a determination result of the determination means that is executing control based on the first tracking error signal. Item 4. The optical drive device according to Item 1. The determination means determines whether the irradiation position of the light beam is an unrecorded area or a recording area,
The tracking servo means detects the second tracking error signal when the determination means determines that the irradiation position of the light beam is an unrecorded area during execution of control based on the first tracking error signal. When the control unit determines that the irradiation position of the light beam is a recording area while executing the control based on the second tracking error signal, the first tracking error signal is switched to the control based on the second tracking error signal. The optical drive device according to claim 2, wherein the control is switched to control based on the above. RF signal generation means for generating an RF signal based on the amount of light received by the photodetector is further provided,
The optical drive apparatus according to claim 2, wherein the determination unit determines that the irradiation position of the light beam is an unrecorded area according to the RF signal. The determination means determines whether the irradiation position of the light beam is an unrecorded area or a recorded area according to the RF signal,
The tracking servo means detects the second tracking error signal when the determination means determines that the irradiation position of the light beam is an unrecorded area during execution of control based on the first tracking error signal. When the control unit determines that the irradiation position of the light beam is a recording area while executing the control based on the second tracking error signal, the first tracking error signal is switched to the control based on the second tracking error signal. The optical drive device according to claim 4, wherein the control is switched to control based on the above.

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