JP2012009103A - Light recording medium driving device and focus-on method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the focus-one operation.SOLUTION: In the case in which a recording layer (L1 or L2) other than the nearest recording layer (L0) and the furthest recording layer (L3) seen from the side at which laser light enters at an light recording medium is considered as a target layer and the focus-on operation is performed, a spherical aberration correction part performs spherical aberration correction using a predetermined position between the target layer (for example, L1) and the passing layer (for example, L0) as a spherical aberration correction position. Then, a focus control part performs signal amplitude correction to focus error signals corresponding to the difference of position between the spherical aberration correction position and the optimal spherical aberration correction position on the target layer, thereby performing focus-on control.

Description

  The present invention relates to an optical recording medium driving apparatus that performs recording or reproduction on an optical recording medium on which a signal is recorded and reproduced by light irradiation, and a focus when a predetermined recording layer formed on the optical recording medium is focused on. On the on method.

JP 2008-123666 A

  As a technique for recording and reproducing digital data, for example, optical disc recording media (including magneto-optical discs) such as CD (Compact Disc), DVD (Digital Versatile Disc), Blu-ray Disc (registered trademark), etc. There is a data recording technique that uses the recording medium as a recording medium. An optical disk recording medium (also simply referred to as an optical disk) is a generic term for recording media in which a laser beam is irradiated onto a disk on which a signal is recorded by pits or marks, and a signal is read by a change in reflected light.

In such an optical disc recording medium, the recording layer is made multilayer for the purpose of increasing the recording capacity. Even in the present situation, for example, a disc having two recording layers is widely used for DVDs and the like.
When the recording layers are multi-layered, each of the recording layers is selectively focused on to read signals from each recording layer.

By the way, in the Blu-ray disc and the next generation optical disc, those having three or more recording layers have been developed.
Consider focus-on for an optical disc having three or more layers. For example, an optical disk having recording layers L0, L1, L2, and L3 is assumed as a four-layer disk. Then, it is assumed that the recording layers L0, L1, L2, and L3 are provided in order from the back to the front as seen from the laser light incident surface side.

In this case, consider a case where the focus is turned on with the second recording layer L1 from the back as the target layer. For example, in this case, for example, an S-shaped curve of a focus error signal is observed while moving the objective lens of the optical recording medium driving device away from a position close to the disk surface, and focus-on control is performed at an appropriate timing.
At this time, the focus position of the laser beam reaches the vicinity of the recording layer L1 that has passed through the recording layer L0 as the objective lens moves. An S-shaped curve of the focus error signal is observed near each of the recording layers L0 and L1. Therefore, if the focus-on control is performed at the timing when the second S-shaped curve is observed during the focus movement period, the target recording layer L1 can be focused on.

By the way, in the case of a high density disc such as a Blu-ray disc, it is known that spherical aberration occurs due to a difference in the thickness of the cover layer as viewed from the recording layer. In particular, in an optical disc having a multi-layered recording layer, the thickness of the cover layer (distance from the recording layer to the laser incident surface) differs in each layer, so that it is essential to perform spherical aberration correction.
When spherical aberration correction is essential, some spherical aberration correction value must be set even when the focus is on.
Conventionally, when focus is on, a spherical aberration correction value is set in accordance with a target layer to be focused on.

However, if the spherical aberration correction value is set to a value that matches the target layer, the S-shape of the focus error signal for other recording layers may not be detected properly.
An example is shown in FIG. FIG. 5 shows a focus error signal waveform when the objective lens is moved. Dashed lines th1 and th2 are focus-on possible amplitudes and S-shaped detectable thresholds. A thick line SA indicates a spherical aberration setting position.
As shown on the left of FIG. 5A, when the spherical aberration setting position SA is adjusted to the target layer in order to improve the signal state of the target layer (L1), the focus error signal balance of the passing layer (L0) is lost and the amplitude is reduced. Is greatly attenuated, making it difficult to detect the passing layer (L0). Further, as shown on the right side of FIG. 5A, when the spherical aberration setting position SA is matched with the passing layer (L0), the same signal deterioration occurs in the target layer (L1), and it becomes difficult to focus on.
Further, for example, as shown in FIG. 5B, even if the spherical aberration setting position SA is set from the position of each recording layer on the standard so that the balance of the focus error signal in the target layer (L1) is optimal, the actual setting is not possible. However, optimization is difficult due to a film thickness error (recording layer distance error or recording layer position error), resulting in a balance shift. The passing layer (L0) is difficult to detect the recording layer due to signal deterioration.
In particular, due to the variation in film thickness, the recording layer position is actually shifted by several μm in both the passing layer and the target layer. In the state where the actual film thickness is not known, even if the optimum spherical aberration position is set from the position of each recording layer on the standard, it tends to be in a state of causing a balance shift or amplitude change.

  Patent Document 1 describes that a spherical aberration position is set at a position shifted by a predetermined amount from the intermediate position of each recording layer to eliminate the balance error of the focus error signal in both recording layers. However, in practice, in a multilayer disc having three or more layers, it is difficult to always set an appropriate spherical aberration position due to a narrow layer interval and a film thickness error, and a balance error of the focus error signal is likely to occur.

  An object of the present invention is to realize a stable focus-on operation in view of the problem that the focus error signal waveform is distorted and control becomes difficult at the time of focus-on in a multi-layer disc having three or more layers.

  The optical recording medium driving apparatus of the present invention performs at least laser beam irradiation and reflected light detection on an optical recording medium having three or more recording layers, at least for signal readout, for the optical recording medium. An optical head having a focusing mechanism and a spherical aberration correcting mechanism, and the focusing mechanism is driven based on a focus error signal generated from reflected light information obtained by the optical head, and the recording layer of the optical recording medium A focus control unit that performs focus-on control on the lens, a spherical aberration correction unit that performs spherical aberration correction by driving the spherical aberration correction mechanism based on the spherical aberration correction value, and a control unit. The control unit uses the recording layer excluding the recording layer closest to and the farthest recording layer from the laser beam incident side of the optical recording medium as a target layer, and focuses on the closest recording layer or the farthest recording layer. When focus-on control to the target layer is performed as a passing layer at the focal position of the process, the spherical aberration correction unit performs spherical aberration correction using the predetermined position between the target layer and the passing layer as a spherical aberration correction position. And executing a signal amplitude correction on the focus error signal in accordance with a positional difference between the spherical aberration correction position and the optimum spherical aberration correction position for the target layer. Execute on control.

In addition, after the completion of the focus-on control, the control unit causes the spherical aberration correction unit to perform spherical aberration correction to the optimal spherical aberration correction position for the target layer as a transition process to steady focus servo, and Control to end signal amplitude correction applied to the focus error signal is performed.
Further, the control unit further causes the focus control unit to change the focus loop gain to a focus-on gain and then execute the focus-on control, and the steady focus after the focus-on control is completed. As a shift process to the servo, control to return the focus loop gain to the normal gain is performed.
Further, the control unit performs control to set the AGC response to the focus error signal as a high-speed response setting during the execution period of the transition process to the steady focus servo.
When the control unit performs focus-on control using the nearest recording layer or the farthest recording layer as a target layer, the spherical aberration to the spherical aberration correction position for the target layer is sent to the spherical aberration correction unit. With the correction being executed, the focus control unit is caused to execute the focus on control.
In addition, the predetermined position between the target layer and the passing layer that is instructed to the spherical aberration correction unit as the spherical aberration correction position is determined by the standard of the optical recording medium or the past spherical aberration correction. Between the optimal spherical aberration correction position and the optimal spherical aberration correction position for the passing layer, and a position where an equivalent focus error signal can be obtained in the target layer and the passing layer.
Further, as a gain to be given to the focus error signal for the signal amplitude correction, a memory for storing a gain table indicating a gain corresponding to a positional difference between the spherical aberration correction position and the optimum spherical aberration correction position for the target layer And a control unit that controls the signal amplitude correction using the gain table.

  In the focus-on method of the present invention, the recording layer excluding the recording layer closest to the laser beam incident side and the recording layer farthest from the laser light incidence side in the optical recording medium is used as a target layer, and the closest recording layer or the farthest recording layer is recorded. When performing focus-on control on the target layer using the layer as the pass layer at the focus position in the focus-on process, the spherical aberration correction unit sets the predetermined position between the target layer and the pass layer to the spherical aberration correction position. Then, a spherical aberration correction is performed, and a signal amplitude correction corresponding to a positional difference between the spherical aberration correction position and the spherical aberration correction position for the target layer is performed for the focus error signal, and then the focus control unit The focus on control is executed.

In the present invention, there are n (n ≧ n) as an optical recording medium having three or more recording layers, that is, from the recording layer L0 closest to the laser beam incident side to the recording layer L (n−1) farthest from the laser beam incident side. In the case of having the recording layer 3), the present embodiment is characterized in the case of focus-on control to recording layers other than the recording layers L0 and L (n-1).
For example, the focus-on control is performed on the recording layer L1 in a three-layer disc having recording layers L0, L1, and L2 in order.
For example, this is a case where focus-on control is performed on the recording layer L1 or L2 in a four-layer disc having the recording layers L0, L1, L2, and L3.
For example, when focus-on control is performed on the recording layer L1 of a four-layer disc, a predetermined position between the target layer (L1) and the passing layer (L0) (a position where an equivalent focus error signal amplitude is obtained in the target layer and the passing layer) ) Is used to execute spherical aberration correction. Further, with respect to the focus error signal, signal amplitude correction corresponding to the position difference between the spherical aberration correction position and the optimal spherical aberration correction position for the target layer (L1) is executed. After that, the objective lens is moved to detect the S-shaped curve, and focus-on control for turning on the focus is executed.
This operation assumes that even if a spherical aberration position is set at a predetermined position between the target layer and the passing layer, the balance error and amplitude attenuation of the focus error signal cannot be completely prevented, and the signal attenuation amount is estimated. Based on the idea of correcting the focus error signal in a possible state.

  According to the present invention, the focus-on operation to each recording layer of an optical recording medium having three or more layers is stabilized. In particular, stable focus-on control can be performed with respect to the focus-on to the central recording layer that reaches via the passing layer.

1 is a block diagram of a disk drive device according to an embodiment of the present invention. It is explanatory drawing of the 4 layer disc used in embodiment. It is explanatory drawing of the spherical aberration correction mechanism of embodiment. It is a block diagram of a focus servo circuit of an embodiment. It is explanatory drawing of the S-shaped waveform at the time of embodiment and the conventional focus on operation | movement. It is explanatory drawing of the focus on operation | movement to the recording layers L1 and L2 of embodiment. It is a flowchart of focus on control of an embodiment. It is a flowchart of the regular servo transfer process of an embodiment. It is explanatory drawing of the gain table of embodiment. It is explanatory drawing of the gain table of embodiment.

Hereinafter, as an embodiment of the optical recording medium driving apparatus of the present invention, a disk drive apparatus that performs recording / reproduction corresponding to a multilayer optical disk will be described and described in the following order.
<1. Configuration of disk drive device>
<2. Focus on operation>
<3. Regular servo transfer processing>

<1. Configuration of disk drive device>

FIG. 1 is a block diagram showing an internal configuration of a disk drive device as an embodiment of the present invention.
This disk drive device is configured to be compatible with each of CD, DVD, and BD (Blu-ray Disc) as an optical disk D shown in the figure. As a result, the optical pickup 1 is a so-called three-wavelength monocular pickup configured to irradiate laser beams having different wavelengths λ = 780 nm, 650 nm, and 405 nm using a common objective lens. It has been adopted.

Further, this disk drive device is configured to be compatible with a multilayer disk having multiple recording layers.
As an example, FIG. 2 shows a cross-sectional structure of an optical disc D as a four-layer BD having four recording layers.
In the case of a four-layer BD, recording layers L0 to L3 are provided in order. Hereinafter, the recording layer L (x) is also referred to as “L (x) layer”.
As shown in the figure, the layers are formed in the order of cover layer → L3 layer → L2 layer → L1 layer → L0 layer → substrate from the side where the laser beam enters. That is, the L0 layer is the recording layer farthest from the laser beam incident side, and the L3 layer is the closest recording layer.
The L0 layer is formed at a position of about 100 μm from the surface of the cover layer. Therefore, the L0 layer to the L3 layer are laminated in the range of 100 μm. The interval between the recording layers is manufactured to a predetermined value within a range of about 10 to 25 μm. The layer spacing between L0 and L1, between L1 and L2, and between L2 and L3 is not necessarily defined as a constant spacing.

  The disc drive apparatus shown in FIG. 1 is configured to be able to selectively focus on the L0 to L3 layers formed on the optical disc D in this way, so that information can be recorded on each recording layer. Information can be read out.

In FIG. 1, an optical disk D is loaded on a turntable (not shown) when loaded in a disk drive device, and is rotated at a constant linear velocity (CLV) by a spindle motor 2 during a recording / reproducing operation. In some cases, it is rotationally driven at a constant angular velocity (CAV).
During reproduction, information recorded as pits or marks on a track on the optical disk D is read out by the optical pickup (optical head unit) 1.
In the optical disk D, for example, physical information on the disk is recorded as embossed pits or wobbling grooves as reproduction-only management information, and the information is also read out by the optical pickup 1. Further, ADIP information embedded as wobbling of the groove track is recorded on the recordable optical disc D, but the optical pickup 1 can also read the ADIP information.

  In the optical pickup 1, a laser diode serving as a laser light source, a photodetector for detecting reflected light, an objective lens serving as an output end of the laser light, a laser beam is irradiated onto the disk recording surface via the objective lens, and An optical system or the like for guiding the reflected light to the photodetector is formed. In this case, two laser diodes are provided: a laser diode that outputs CD and DVD laser light with wavelengths of 780 nm and 650 nm, and a laser diode that outputs laser light with a wavelength of 405 nm corresponding to the BD system. As a three-wavelength monocular system, laser light of each wavelength output from these two laser diodes is irradiated to the optical disc D through a common objective lens.

In the optical pickup 1, the objective lens is held so as to be movable in the tracking direction and the focus direction by a biaxial mechanism.
The entire optical pickup 1 can be moved in the radial direction of the disk by a thread mechanism 3.
The laser diode in the optical pickup 1 is driven to emit laser light by a drive signal (drive current) from the laser driver 9.

In the present embodiment, since the optical disk D also supports BD, the optical pickup 1 is provided with a spherical aberration correction mechanism for correcting spherical aberration. This spherical aberration correction mechanism is driven by an SA (spherical aberration) correction driver 14 in the drawing, thereby correcting the spherical aberration.
The configuration within the optical pickup 1 including the spherical aberration correction mechanism will be described later.

Reflected light information from the optical disk D is detected by the above-described photodetector, and is supplied to the matrix circuit 4 as an electric signal corresponding to the amount of received light.
The matrix circuit 4 includes a current-voltage conversion circuit, a matrix calculation / amplification circuit, and the like corresponding to output currents from a plurality of light receiving elements as photodetectors, and generates necessary signals by matrix calculation processing.
For example, an RF signal (reproduction data signal) corresponding to reproduction data, a focus error signal FE for servo control, a tracking error signal TE, a pull-in signal (light amount sum signal) PI, and the like are generated. Further, a push-pull signal PP is generated as a signal related to groove wobbling, that is, a signal for detecting wobbling.

  The reproduction data signal (RF signal) output from the matrix circuit 4 is sent to the data signal processing unit 5, the focus error signal FE, the tracking error signal TE, and the pull-in signal PI are sent to the servo circuit 11, and the push-pull signal PP is the wobble signal processing circuit. 6 respectively.

  Further, the RF signal is supplied to the data signal processing unit 5, and the information of the amplitude value is supplied to the system controller 10 via the A / D converter 15 which is branched and illustrated. Information on the RF signal amplitude value supplied to the system controller 10 is used as an evaluation index (evaluation value) of the reproduction signal quality in the automatic adjustment processing of a spherical aberration correction value described later.

When the optical disc D is a recordable disc, management information such as physical information of the disc, ADIP information, and the like are recorded on the optical disc D by a wobbling groove.
The wobble signal processing circuit 6 detects information recorded by the wobbling groove of the optical disc D from the push-pull signal PP from the matrix circuit 4 and supplies it to the system controller 10.

The data signal processing unit 5 performs binarization processing of the RF signal.
For example, the data signal processing unit 5 performs A / D conversion processing of RF signals, reproduction clock generation processing by PLL, PR (Partial Response) equalization processing, Viterbi decoding (maximum likelihood decoding), etc., and partial response maximum likelihood decoding processing A binary data string is obtained by (PRML detection method: Partial Response Maximum Likelihood detection method).
Then, the data signal processing unit 5 supplies a binary data string as information read from the optical disc D to the subsequent encoding / decoding unit 7.

  The encode / decode unit 7 performs demodulation of reproduction data during reproduction and modulation processing of recording data during recording. That is, data demodulation, deinterleaving, ECC decoding, address decoding, etc. are performed during reproduction, and ECC encoding, interleaving, data modulation, etc. are performed during recording.

At the time of reproduction, the binary data string decoded by the data signal processing unit 5 is supplied to the encoding / decoding unit 7. The encoding / decoding unit 7 performs demodulation processing on the input binary data string, and obtains reproduction data from the optical disc D.
For example, the reproduction data from the optical disc D is obtained by performing demodulation processing on data recorded on the optical disc D subjected to run-length limited code modulation and ECC decoding processing as error correction.
The data decoded to the reproduction data by the encoding / decoding unit 7 is transferred to the host interface 8 and transferred to the host device 100 based on an instruction from the system controller 10. The host device 100 is, for example, a computer device or an AV (Audio-Visual) system device.

At the time of recording, recording data is transferred from the host device 100, and the recording data is supplied to the encoding / decoding unit 7 via the host interface 8.
In this case, the encoding / decoding unit 7 performs error correction code addition (ECC encoding), interleaving, sub-code addition, and the like as recording data encoding processing. Further, the run-length limited code modulation is performed on the data subjected to these processes.

The recording data processed by the encoding / decoding section 7 is subjected to a recording compensation process in the write strategy section 16 as a recording compensation process for fine adjustment of optimum recording power and pulse waveform of recording layer characteristics, laser beam spot shape, recording linear velocity, etc. The laser driving pulse in a state where adjustment or the like is performed is supplied to the laser driver 9.
Then, the laser driver 9 applies the laser driving pulse subjected to the recording compensation process to the laser diode in the optical pickup 1 to execute the laser emission driving. As a result, a mark corresponding to the recording data is formed on the optical disc D.

The laser driver 9 includes a so-called APC circuit (Auto Power Control), and the laser output depends on the temperature or the like while monitoring the laser output power by the output of the laser power monitoring detector provided in the optical pickup 1. Control to be constant.
The target value of the laser output at the time of recording and reproduction is given from the system controller 10, and control is performed so that the laser output level becomes the target value at the time of recording and reproduction.

The servo circuit 11 generates various servo drive signals for focus, tracking, and thread from the focus error signal FE and tracking error signal TE from the matrix circuit 4, and executes the servo operation.
That is, the focus drive signal FD and the tracking drive signal TD are generated according to the focus error signal FE and the tracking error signal TE, and the focus coil and tracking coil of the biaxial mechanism in the optical pickup 1 are driven. As a result, a tracking servo loop and a focus servo loop are formed by the optical pickup 1, the matrix circuit 4, the servo circuit 11, and the biaxial mechanism.
The servo circuit 11 executes a track jump operation by turning off the tracking servo loop and outputting a jump drive signal in response to a track jump command from the system controller 10.

  The servo circuit 11 generates a thread drive signal SD based on a thread error signal obtained as a low frequency component of the tracking error signal TE, an access execution control from the system controller 10, and the like, thereby driving the thread mechanism 3. . Although not shown, the sled mechanism 3 has a mechanism including a main shaft that holds the optical pickup 1, a sled motor, a transmission gear, and the like. The sled mechanism 3 drives the sled motor according to a sled drive signal. The slide movement is performed.

The servo circuit 11 performs focus-on control for focusing on the recording layer formed on the optical disc D based on the focus error signal FE and the pull-in signal PI from the matrix circuit 4.
The servo circuit 11 also performs focus jump control based on the focus error signal FE and the pull-in signal PI, particularly as focus control corresponding to the optical disk D as a multilayer disk.

  The servo circuit 11 is configured to be able to set a spherical aberration correction value for the SA correction driver 14. That is, the servo circuit 11 can set a spherical aberration correction value based on an instruction from the system controller 10 for the SA correction driver 14. The SA correction driver 14 drives the spherical aberration correction mechanism in the optical pickup 1 with a drive signal Sd corresponding to the set spherical aberration correction value.

The spindle servo circuit 12 performs control to rotate the spindle motor 2 at CLV.
The spindle servo circuit 12 obtains the reproduction clock generated by the data signal processing unit 5 as the current rotation speed information of the spindle motor 2, and compares it with predetermined CLV reference speed information to generate a spindle error signal. To do.
If the optical disc D is a recordable disc, the clock generated by the PLL processing for the wobble signal can be obtained as the current rotational speed information of the spindle motor 2, and this is used as predetermined CLV reference speed information. A spindle error signal can also be generated by comparing with.
The spindle servo circuit 12 outputs a spindle drive signal generated according to the spindle error signal, and causes the spindle driver 13 to execute CLV rotation of the spindle motor 2.
The spindle servo circuit 12 generates a spindle drive signal in response to a spindle kick / brake control signal from the system controller 10 and executes operations such as starting, stopping, acceleration, and deceleration of the spindle motor 2.

Various operations of the servo system and the reproduction system as described above are controlled by a system controller 10 formed by a microcomputer.
The system controller 10 executes various processes in accordance with commands from the host device 100 given via the host interface 8.
For example, when a write command (write command) is issued from the host device 100, the system controller 10 first moves the optical pickup 1 to an address to be written. Then, the encoding / decoding unit 7 causes the encoding process to be performed on the user data (for example, video data, audio data, computer use data, etc.) transferred from the host device 100 as described above. Then, recording on the optical disc D is performed by the laser driver 9 performing laser emission driving in accordance with the encoded data as described above.
Further, for example, when a read command for requesting transfer of certain data recorded on the optical disc D is supplied from the host device 100, the system controller 10 first performs seek operation control with the instructed address as a target. That is, a command is issued to the servo circuit 11 and the access operation of the optical pickup 1 targeting the address specified by the seek command is executed.
Thereafter, operation control necessary for transferring the data in the designated data section to the host device 100 is performed. In other words, the signal read from the optical disc D (reproduction data signal) is subjected to reproduction processing in the data signal processing unit 5 and the encoding / decoding unit 7 to transfer the requested data.

Further, the system controller 10 performs automatic adjustment processing for the spherical aberration correction value during recording and reproduction, which will be described later.
Further, a processing operation for realizing a focus-on operation as the present embodiment described later is also performed, which will be described later.

The memory unit 17 stores parameters, constants, and the like used by the system controller 10 for various processes. For example, it is composed of a nonvolatile memory.
For example, the memory unit 17 is used as an area for storing a gain table used at the time of a focus-on process described later. Further, it may be used for storing a spherical aberration correction value when spherical aberration correction is performed at an optimum position with respect to the recording layer.

In the example of FIG. 1, the disk drive device connected to the host device 100 has been described. However, as an example of the disk drive device, there may be a form that is not connected to other devices. In this case, an operation unit and a display unit are provided, and the configuration of the data input / output interface part is different from that in FIG. That is, it is only necessary that recording and reproduction are performed in accordance with a user operation and a terminal portion for inputting / outputting various data is formed.
Of course, various other examples of the configuration of the disk drive device are conceivable. For example, there may be a form of a read-only device having no recording function.

FIG. 3 shows an example of a spherical aberration correction mechanism provided in the optical pickup 1 shown in FIG. FIG. 3 mainly shows the configuration of the optical system in the optical pickup 1.
In FIG. 3, laser light output from a semiconductor laser (laser diode) 81 is converted into parallel light by a collimator lens 82, passes through a beam splitter 83, a movable lens 87 as a spherical aberration correction lens group, and a fixed lens 88. The optical disk D is irradiated from the objective lens 84. The spherical aberration correction lens groups 87 and 88 are called expanders. Since the spherical aberration correction is performed by driving the movable lens 87, the movable lens 87 is hereinafter also referred to as a spherical aberration correction lens 87.

  Reflected light from the optical disk D passes through the objective lens 84, the fixed lens 88, and the movable lens 87, is reflected by the beam splitter 83, and enters the detector 86 through the collimator lens (condensing lens 85).

In such an optical system, the objective lens 84 is supported by the biaxial mechanism 91 so as to be movable in the focus direction and the tracking direction, and focus servo and tracking servo operations are performed.
The spherical aberration correction lens 87 has a function of defocusing the wavefront of the laser light. That is, the spherical aberration correction lens 87 can be moved in the J direction, which is the optical axis direction, by an actuator 90 to which a drive signal Sd is supplied as shown in the figure, and the object point of the objective lens 84 is adjusted by this movement. To do.
That is, the spherical aberration correction can be executed by performing the control for causing the actuator 90 to move back and forth based on the drive signal Sd.

In FIG. 3, the configuration corresponding to the case where spherical aberration correction is performed by a so-called expander is illustrated, but a configuration in which spherical aberration correction is performed using a liquid crystal panel can also be adopted.
That is, in the liquid crystal panel inserted in the optical path from the semiconductor laser 81 to the objective lens 84, the diameter of the laser beam is varied to variably adjust the boundary between the laser beam transmitting region and the shielding region, thereby correcting spherical aberration. Is to do.
In this case, the liquid crystal driver that drives the liquid crystal panel is controlled to change the transmission region.

  Further, as the spherical aberration correction mechanism, the movable lens 87 and the fixed lens 88 are omitted in addition to the configuration in which the movable lens 87 and the fixed lens 88 are provided to drive the movable lens 87 as shown in FIG. Alternatively, this can be realized by a configuration in which the collimator lens 82 is driven in the J direction. In that case, an actuator 90 may be provided for the collimator lens 82, and a drive signal Sd may be supplied to the actuator 90 to execute drive control of the collimator lens 82 in the J direction.

FIG. 4 shows an internal configuration of the servo circuit 11 shown in FIG. In FIG. 4, only the focus control system portion in the servo circuit 11 is extracted and shown.
In FIG. 4, the focus error signal FE from the matrix circuit 4 shown in FIG. 1 is adjusted in amplitude level by an AGC (Automatic Gain Control) circuit 20 in the servo circuit 11. In this example, responsiveness variable control of the AGC circuit 20 is enabled by the control signal CNT from the system controller 10.
The focus error signal FE having the amplitude level adjusted by the AGC circuit 20 is converted into digital data by the A / D converter 21 and input to the focus servo calculation unit 22.
The focus servo calculation unit 22 performs filtering for phase compensation etc. on the focus error signal FE inputted as digital data, amplitude adjustment by adding gain to the focus error signal FE, focus bias addition, loop gain processing, etc. The focus servo signal is generated by performing various predetermined calculations. The gain focus bias value, servo loop gain, and the like are variably set by a control signal CNT from the system controller 10.

The focus servo signal output from the focus servo calculation unit 22 is supplied to a terminal t2 in the illustrated switch SW.
The switch SW is configured to be able to selectively select the terminal t2, the terminal t3, and the terminal t4 with respect to the terminal t1 according to the control signal CNT. A fixed voltage 23 is supplied to the terminal t3, and a Hold voltage 24 is supplied to the terminal t4.
A D / A converter 25 is connected to the terminal t1, and the output of the D / A converter 25 is output as a focus drive signal FD via the focus driver 26 as shown in the figure.

In the servo circuit 11, the switch SW terminal switching control is performed to perform focus on control and focus jump control.
As for the focus-on control, first, the terminal t3 is selected by the switch SW and the fixed voltage 23 is output, so that the objective lens 84 is driven in the direction approaching the optical disc D or the direction away from the optical disc D by the biaxial mechanism 91. be able to. Then, a condition determination based on a predetermined threshold is performed for the focus error signal FE at that time, and as a result, switching to the terminal t2 is performed at a timing when the focus should be turned on, and the focus servo is pulled. Thereby, focus-on control to the target layer is performed.

Further, at the time of focus jump, first, switching to the terminal t3, applying the fixed voltage 23 as the kick voltage, switching to the terminal t4, and applying the Hold voltage 24, the objective lens 84 is moved to the jump destination. Move to the recording layer side. Note that the Hold voltage 24 is calculated from a value corresponding to the Hold position of the objective lens 84 from the difference in recording layer position between CD, DVD, and DB, and a voltage corresponding to the value is output.
After starting the application of the kick voltage, if it is determined that the focus servo pull-in is OK based on the condition determination based on the focus error signal FE and the predetermined threshold, the terminal t3 is selected and a fixed voltage as a brake voltage is selected. 23 is output. Then, by selecting the terminal t2, the focus servo is pulled in the jump-destination recording layer. Thereby, a focus jump operation is performed.

Here, the disk drive device according to the embodiment described so far is configured to support BD as the optical disk D.
As described above, with respect to BD, spherical aberration due to the difference in the thickness of the cover layer is generated as the NA increases, and it is essential to correct the BD. Also in the disk drive device of the present embodiment, in order to perform such spherical aberration correction, the spherical aberration correction mechanism (fixed lens 88, movable lens 87, actuator 90) and SA correction as shown in FIG. A driver 14 is provided.

  The spherical aberration is corrected by setting a spherical aberration correction value to the SA correction driver 14, and for such a spherical aberration correction value, an initial value serving as a reference in each recording layer is set in advance in the disc. It is set for the drive device. That is, the spherical aberration correction value that is optimal at each position of the L0 layer, the L1 layer, the L2 layer, and the L3 layer is set as the initial value of the spherical aberration correction value in each recording layer.

  Ideally, if spherical aberration correction is performed by setting a corresponding initial value for each recording layer, spherical aberration can be corrected appropriately. However, in reality, an error occurs in the thickness of the cover layer (the distance from the recording layer to the laser light incident surface) for each individual optical disk D, and thus the spherical aberration correction value is automatically adjusted for each optical disk D. Has been done.

The automatic adjustment processing of the spherical aberration correction value is performed in response to the first focus-on state for a predetermined recording layer. For example, the evaluation value obtained when the correction value is changed to a different value with respect to the initial value of the spherical aberration correction value set in advance for the recording layer is acquired. Then, the shift value from the initial value when the best evaluation value is obtained is determined as the correction shift value, and the optimum spherical aberration correction position is determined in consideration of the correction shift value.
For example, when the focus servo can be turned on once for the first time focus on the L0 layer, signal readout by the optical pickup 1 is executed while changing the setting of the spherical aberration correction value with reference to the initial value. The RF signal amplitude value obtained at that time is used as an evaluation value, and a shift value from an initial value that makes the value the best (in this case, maximum) is obtained as a correction shift value. The position obtained by adding the correction shift value to the initial value of the spherical aberration correction position for the L0 layer is set as the optimum spherical aberration correction position for the L0 layer actually obtained.

The specific automatic adjustment processing when such a method is adopted is as follows.
In response to the fact that the focus servo can be turned on in the L0 layer, the system controller 10 reads out the initial value for the L0 layer stored in the memory unit 17 and the like, and corrects the spherical aberration by changing the value from the initial value. The values are sequentially instructed to the servo circuit 11 and set in the SA correction driver 14, and the amplitude value of the RF signal obtained by the matrix circuit 4 in the setting state of each spherical aberration correction value is passed through the A / D converter 15. get. As a result, the shift value from the initial value when the RF signal amplitude value is maximized is determined as the correction shift value. The determined correction shift value (or initial spherical value + optimum spherical aberration correction position based on the correction shift value) is stored in the memory unit 17 as an optimal spherical aberration correction value used for recording / reproduction on the L0 layer.
After such an operation is performed on each recording layer, the optimum spherical aberration correction position stored for the recording layer is set in the SA correction driver 14 at the time of signal reading in each recording layer.

  By performing such automatic adjustment processing, the spherical aberration correction value is set to an optimum value based on the actually measured RF signal amplitude value (that is, the evaluation value of the reproduction signal quality). Even when an error occurs in the thickness of the cover layer, recording / reproduction can be performed in the optimum spherical aberration correction state.

Here, the correction shift value is obtained from the spherical aberration correction value when the evaluation value is the best, but if the correction shift value is obtained from at least the spherical aberration correction value at which the evaluation value is better than a predetermined value. Thus, a shift correction value that can correct the thickness error of the cover layer of the optical disc D can be obtained.

<2. Focus on operation>

The focus-on operation of this embodiment will be described.
The disk drive device according to the present embodiment performs spherical aberration correction corresponding to the optical disk D as the multilayer BD. However, even when focus-on is performed, stable focus servo can be pulled in. In other words, the spherical aberration correction value is adjusted to an appropriate value.

For example, in the case of a four-layer disc, when focusing on the inner L1 layer and L2 layer, it is necessary to focus on the target layer by passing through the L0 layer or the L3 layer. Both focus on must be stable.
FIG. 6A schematically shows an example of operation when the focus is on the L1 layer, and FIG. 6B schematically shows an operation example when the focus is on on the L2 layer.
At the time of focusing on the L1 layer, for example, the objective lens 84 is moved to a position closest to the optical disc D and then driven away from the optical disc D. Therefore, as shown by an arrow FS in FIG. 6A, the focus point of the laser light passes through the L0 layer and reaches the vicinity of the L1 layer.
For this reason, as the focus-on operation, if the first recording layer (L0 layer) is detected in the objective lens moving process and then the second recording layer (L1) is detected, the focus servo loop is turned on. Good.

When focusing on the L2 layer, for example, the objective lens 84 is moved to the position farthest from the optical disc D and then driven in a direction approaching the optical disc D. Therefore, as shown by the arrow FS in FIG. 6B, the focus point of the laser light passes through the L3 layer and reaches the vicinity of the L2 layer.
For this reason, as a focus-on operation, if the first recording layer (L3 layer) is detected in the objective lens moving process and then the second recording layer (L2) is detected, the focus servo loop is turned on. Good.

Conventionally, a pull-in signal (light amount sum signal) has been used for recording layer detection during the movement of the objective lens. This is because the amplitude level of the sum signal rises when passing through the recording layer, so that the recording layer can be detected when the amplitude of the pull-in signal exceeds a predetermined value.
On the other hand, in a BD having three or more layers, the recording layer may not be detected with a pull-in signal because the recording layer interval is narrow. Therefore, the focus error signal FE is used for recording layer detection and focus on.

When the focus is on, the spherical aberration correction value is set in accordance with the focus on target layer. For example, when focusing on the L1 layer, the focus-on operation is performed with the initial value of spherical aberration correction for the L1 layer set.
However, if the spherical aberration correction value is set to a value that matches the target layer, the S-shape of the focus error signal for other recording layers cannot be properly detected as described above with reference to FIG. there is a possibility.
Further, as described in FIG. 5B, even if the spherical aberration correction position is set at a position where the balance error of the focus error signal FE can be improved in the target layer, a balance error actually occurs. The attenuation of the focus error signal FE is large, and the detection performance is also deteriorated.
Furthermore, setting the intermediate position between the target layer and the passing layer also cannot prevent a balance shift or amplitude change in a multilayer disc having three or more layers.
Due to the variation in the film thickness allowed by the standard, the pass layer and the target layer actually deviate from each other by several μm, and both layers eventually cause a balance deviation and an amplitude change.
For these reasons, in particular, the focus-on operation with respect to the optical disc D having three or more layers becomes unstable, and its stabilization is required.

In this embodiment, in order to stably perform both the detection of the passing layer and the focus-on in the target layer, it is possible to estimate, instead of trying to prevent the balance error and amplitude attenuation of the focus error signal FE. The idea is to improve stability by making corrections in a stable control state.
Specifically, on the assumption that the focus error signal FE is out of balance and the amplitude is attenuated when the first focus is turned on, including the film thickness error, both the passing layer and the target layer as shown in FIG. A spherical aberration correction position SA is set at a position between two layers where the signal levels at the layers will be equal. Since the optimum spherical aberration correction position SA for each recording layer differs depending on the optical system, the optimum position is derived by simulation or the like.
The balance deviation amount and amplitude attenuation amount of the focus error signal FE can be estimated by the difference between the spherical aberration correction position and the optimal spherical aberration correction position for each recording layer. Thus, focus on control is executed after signal amplitude correction is executed according to the positional difference between the spherical aberration correction position and the optimum spherical aberration correction position for the target layer for the focus error signal.
Only by setting the spherical aberration correction position SA at a position between the pass layer and the target layer as shown in FIG. 5C, the balance error and amplitude change of the focus error signal FE cannot be prevented, but from this state, a predetermined value is obtained. Is applied to the focus error signal FE for amplitude correction, as shown in FIG. 5C, a focus error signal FE that can stably detect the pass layer and the target layer can be obtained.

In FIG. 6A, “dm” indicates a layer interval between the target layer (L1) and the passing layer (L0). This layer interval dm is defined by the cover thickness (thickness from each recording layer to the cover layer surface (laser incident surface)) of the L0 layer and the L1 layer. The cover thickness of the L0 layer is, for example, 100 μm, and the cover thickness of the L1 layer is dL1 in the figure. However, the cover thickness of the L0 layer and the L1 layer varies from one optical disc D to another. For this reason, the layer spacing dm also varies from disk to disk D.
The SA position shown in the figure is a spherical aberration correction position as a position between the passing layer (L0) and the target layer (L1).
The position difference between this SA position and the optimal spherical aberration correction position for the target layer (L1) is shown as “dSA”.
When focusing on the L1 layer in the present embodiment, the spherical aberration correction position is set to the SA position in the figure, and the gain corresponding to the position difference dSA is given to the focus error signal FE, and the arrow FS Perform the search operation shown. Then, a focus-on operation is performed to turn on the focus servo loop at the time of detection of the second S-shape of the focus error signal FE (that is, the time of detection of the L1 layer).

In the figure, the optimum spherical aberration correction position for the target layer (L1) is shown as the position difference dSA with the position of the target layer (L1) coinciding with the target layer (L1). It does not necessarily coincide with the target layer position in the standard. Until the optimum spherical aberration correction position for each recording layer is determined in the above-described spherical aberration correction operation, the optimum spherical aberration correction position for the disk drive device (system controller 10) and each recording layer (L0 to L3) is It is unknown.
Therefore, for example, when the focus is first turned on for the L1 layer, a predetermined position where the signal level in both layers is estimated to be equal between the standard L0 layer position and the L1 layer position is set as the SA position at the time of focus on. The position difference dSA is a difference between the SA position and the standard L1 layer position.
In the recording / reproducing operation after focus-on by the L1 layer, the optimum spherical aberration correction position for the L1 layer is determined by the spherical aberration correction operation described above. Similarly, for the L0 layer, the optimum spherical aberration correction position is determined in the recording / reproducing operation for the L0 layer.
Therefore, when the focus is turned on to the L1 layer after determining the optimum spherical aberration correction position, the signal in both layers is set as an intermediate between the optimum spherical aberration correction position for the L0 layer and the optimum spherical aberration correction position for the L1 layer. A spherical aberration correction position (SA position in the figure) is set at a predetermined position where the level will be equivalent, and the position difference dSA is the difference between the SA position and the optimum spherical aberration correction position of the L1 layer. In this case, the layer interval dm may be considered as the interval between the optimal spherical aberration correction position of the L0 layer and the optimal spherical aberration correction position of the L1 layer, and the intermediate position may be considered as the SA position in the figure.

In FIG. 6B, “dm” indicates a layer interval between the target layer (L2) and the passing layer (L3). This layer interval dm is defined by the cover thicknesses dL2 and dL3 of the L2 layer and the L3 layer. Also in this case, the layer spacing dm varies for each disk D.
The illustrated SA position is a spherical aberration correction position as a certain position between the passing layer (L3) and the target layer (L2). The position difference between this SA position and the optimum spherical aberration correction position for the target layer (L2) is shown as “dSA”.
When focusing on the L2 layer in the present embodiment, the spherical aberration correction position is set to the SA position in the figure, and the gain corresponding to the position difference dSA is given to the focus error signal FE, and the arrow FS Perform the search operation shown. Then, a focus-on operation is performed to turn on the focus servo loop at the time of detection of the second S-character of the focus error signal FE (that is, the time of detection of the L2 layer).

Also in this case, the optimal spherical aberration correction positions for the passing layer (L3) and the target layer (L2) do not necessarily match the positions of the passing layer (L3) and the target layer (L2) on the standard. Thus, for example, when the focus is first turned on for the L2 layer, a predetermined position between the L3 layer position on the standard and the L2 layer position is set as the SA position at the time of focus on, and the positional difference dSA is the L2 on the SA and the standard. The difference from the layer position.
After the optimal spherical aberration correction position for the L2 layer (and L3 layer) is determined, when focusing on the L2 layer, the optimal spherical aberration correction position for the L3 layer and the optimal spherical aberration correction position for the L2 layer A spherical aberration correction position (SA position in the figure) is set at a predetermined position between and the position difference dSA is a difference between the SA position and the optimum spherical aberration correction position of the L2 layer.
In this case, the layer interval dm may be considered as the interval between the optimal spherical aberration correction position of the L3 layer and the optimal spherical aberration correction position of the L2 layer, and the intermediate position may be considered as the SA position in the figure.

An example of focus-on control is shown in FIG. FIG. 7 shows a flowchart of control processing performed by the system controller 10 on the servo circuit 11.
When starting the focus-on control, the system controller 10 first branches the process in step F101 depending on whether the target layer is the L0 layer, the L3 layer, or the L1 layer, the L2 layer. That is, it is determined whether the recording layer is the closest or farthest recording layer (L0, L3) from the laser light incident surface side or the other central recording layer (L1, L2).

In the case of the focus-on operation using the L1 layer or the L2 layer as the target layer, the system controller 10 proceeds to step F103, and the signal level in both layers is equal between the passing layer and the target layer at the spherical aberration correction position. Set it to the position where it will be. That is, the SA position described above with reference to FIGS. 6A and 6B is instructed to the SA correction driver via the servo circuit 11.
In step F104, the system controller 10 performs gain addition control on the focus error signal FE. In this case, the focus servo calculation unit 22 in the servo circuit 11 is instructed with a gain value corresponding to the position difference dSA shown in FIG. 6, and the amplitude level correction of the focus error signal FE is executed.

Here, the system controller 10 can obtain the gain value corresponding to the position difference dSA by a predetermined calculation using the value of dSA.
Alternatively, a gain table as shown in FIG. 8 or FIG. 9 may be stored in the memory unit 17 and the gain value may be instructed using this gain table.

The gain table shown in FIG. 9A is an example of a table that can be applied when the behavior of the amplitude attenuation of the focus error signal FE according to the position difference dSA is the same in the target layer and the pass layer and does not depend on the absolute position. is there.
In this gain table, an appropriate gain value to be given to the focus error signal FE corresponding to the position difference dSA is obtained in advance by simulation and stored. In this case, the SA position shown in FIG. 6 is an intermediate position having an equivalent distance from the optimum spherical aberration correction position for the L0 layer and the optimum spherical aberration correction position for the L1 layer when focusing on the L1 layer. And
For example, when the target layer is the L1 layer, the gain to be given in each case where the positional difference dSA is 6 μm, 7 μm, 8 μm, 9 μm, 10 μm,... (... Gain6, Gain6, Gain7, Gain8 , Gain9, Gain10 ...) are stored. Similarly, when the target layer is the L2 layer, gains (... Gain 26, Gain 27, Gain 28, Gain 29, Gain 30...) To be given according to the value of the position difference dSA are stored.
For example, in the case where the target layer is the L1 layer, and the layer spacing (or the distance between each optimum spherical aberration correction position in the target layer and the passing layer) dm = 16 μm, the optimum spherical aberration between the intermediate position and the target layer The distance from the correction position, that is, the positional difference dSA = 8 μm.
In this case, “Gain 8” is selected from the gain table as indicated by the hatched portion in FIG.

The gain table shown in FIG. 10A is an appropriate table example when the amplitude attenuation behavior of the focus error signal FE differs depending on the absolute position of the target layer and the passing layer and the positional difference dSA with respect to each.
Based on the target layer position (the cover thickness of the target layer), the SA position where the amplitude of the focus error signal FE is equal is obtained by simulation according to the interlayer distance (layer spacing dm) from the passing layer.
For example, it is assumed that the cover thickness of the L0 layer is 100 μm, and the distance between the L0 layer and the L1 layer (or the distance between the optimum spherical aberration correction positions in the target layer and the passing layer) dm is about 10 to 20 μm. At this time, the position of the L1 layer serving as the target layer is about 85 μm from the cover layer surface. For this reason, for example, the table is formed in steps of 1 μm around 85 μm as the target layer position. Further, the table is formed in steps of 1 μm as the interlayer distance. Note that the increment of 1 μm is merely an example.
Then, a gain value to be given to the focus error signal FE is obtained by a simulation in advance using a combination of the target layer position and the interlayer distance, and is set in the gain table.

  For example, if the interlayer distance is dm = 14 μm and the position of the target layer (L1) is 85 μm, the position of “90 μm” is selected as the SA position as shown by hatching in FIG. “GainBC” is selected as the gain to be given to the focus error signal FE.

For example, by using such a gain table, the system controller 10 can determine the gain value instructed to the focus servo calculation unit 22 in step F104.
In the examples of the gain tables in FIGS. 9 and 10, the target layer position, the interlayer distance, etc., when the current disk D is not known, use values etc. referring to the standard values, and the above spherical aberration correcting operation. After this is found, a more appropriate gain value can be derived by using the actual value.

When the processing of steps F103 and F104 in FIG. 7 is completed, the system controller 10 next changes the focus loop gain to the setting for focus on in step F105. That is, the system controller 10 instructs the focus servo calculation unit 22 to increase the loop gain. This enhances the servo response when the focus is on, and makes it easier to pull the servo to the in-focus position.
In step F106, the system controller 10 performs focus on operation control.
That is, the servo circuit 11 starts a focus-on operation. As described with reference to FIGS. 6A and 6B, the servo circuit 11 has an objective lens in the direction away from the near position (for the L1 layer target) or the direction closer to the far position (for the L2 layer target). Start moving. Then, the focus error signal FE is monitored in the process of moving the objective lens, and the target layer (L1 or L2) is detected. At the timing when the target layer is detected, the focus servo loop is turned on, the servo pull-in is executed, and the focus is turned on.
Thus, the processing up to the focus-on when the L1 layer or the L2 layer is the target layer is completed.

On the other hand, when the L0 layer or the L3 layer is the target layer, the system controller 10 proceeds from step F101 to F102. Then, the spherical aberration correction position is set to the optimum spherical aberration correction position for the target layer. That is, the best focus error signal FE is obtained in the target layer. Then, the same control as described above is performed in steps F105 and F106.
That is, in this case, in the focus-on operation, the servo circuit 11 starts moving the objective lens in a direction away from the close position (when the target is the L0 layer) or a direction close to the far position (when the target is the L3 layer). Then, the focus error signal FE is monitored in the process of moving the objective lens, and the target layer is detected. In this case, the first S-shaped curve may be observed. Since the spherical aberration correction position is the optimum spherical aberration correction position corresponding to the L0 layer or the L3 layer, which is the target layer, a good S-curve is observed in the target layer. Accordingly, the focus on operation is stably executed.

According to such a focus-on control of the present embodiment, the focus-on operation for any of the L0 layer, the L1 layer, the L2 layer, and the L3 layer can be stably executed.
In particular, when the L1 layer and the L2 layer are the target layers, the focus error signal amplitudes in the two recording layers can be made equal by setting the SA position at an intermediate position between the passing layer and the target layer. Then, a gain corresponding to the positional difference dSA between the set SA position and the optimum spherical aberration correction position for the target layer is given to the focus error signal FE, so that stable detection and focus-on control for the passing layer and the target layer are performed. Will be able to. This realizes a stable focus-on operation.

  As described above, when the focus is turned on when the optimum spherical aberration correction position of each actual recording layer is unknown, each recording layer position on the standard is used as the optimum spherical aberration correction position and the SA position or position is determined. What is necessary is just to obtain | require difference dSA. After the identification, the actual optimum spherical aberration correction position is used. Thereby, a focus-on operation that is stable to some extent can be performed even before the identification, and the focus-on stability after the identification can be further improved.

In addition, the threshold shown in FIG. 5 is used to determine the pass layer and the target layer by making appropriate the gain to be applied to correct the attenuation of the focus error signal FE when the focus is turned on to the L1 layer and the L2 layer. Th1 and th2 can be used in common with the focus-on to the L0 layer and the L3 layer so that there is no problem. That is, it is not necessary to change the thresholds th1 and th2 when the L1 layer and L2 layer targets are set.

<3. Regular servo transfer processing>

The processing up to the focus on has been described above. Here, the processing up to shifting to the steady servo immediately after the focus is turned on will be described.

FIG. 8 shows the processing of the system controller 10 immediately after the focus is turned on.
In step F111, the system controller 10 determines the sequence of the steady servo transfer process depending on whether the target layer is the L1 layer, the L2 layer, the L0 layer, or the L3 layer.

When the target layer is the L1 layer or the L2 layer, the system controller 10 executes the processes of steps F114 to F118.
First, in step F114, the system controller 10 controls the AGC circuit 20 in the servo circuit 11 to turn on the AGC operation with the high-speed response setting.
In step F115, the system controller 10 controls the focus servo calculation unit 22 to gradually return the gain given to the focus error signal FE to the normal setting.
Further, in step F116, the focus servo calculation unit 22 is instructed to return the focus loop gain to the normal setting.
In step F117, the system controller 10 controls the SA correction driver 14 via the servo circuit 11 to set the spherical aberration correction position to be the optimum spherical aberration correction position for the target layer.
Finally, in step F118, the AGC circuit 20 is controlled to return to the normal response setting.

The meaning of the processing in steps F114 to F118 is as follows.
When the focus-on operation is performed with the L1 layer or the L2 layer as the target layer, as described with reference to FIG. 7, the spherical aberration correction position is set to the intermediate position, and a correction gain is given to the focus error signal FE. Furthermore, the servo loop gain is increased to improve the pull-in response.
For this reason, it is necessary to return these to normal settings as a process of shifting to the steady servo.

First, Step F115 is performed for the purpose of ending the amplitude correction applied to the focus error signal FE and returning to the normal setting.
As described above, the gain given in step F104 in FIG. 7 obtains a sufficient signal amplitude of the focus error signal FE in the pass layer and the target layer when the intermediate position between the pass layer and the target layer is set as the spherical aberration correction position. Is the gain to give. In this case, since the spherical aberration correction position is far from the optimum spherical aberration correction positions of the pass layer and the target layer, the gain given to the focus error signal FE is relatively large. Although this is returned to the normal state, returning to the original gain at a stroke may make the servo state unstable. In some cases, the focus is lost, and the focus-on operation must be performed again.
Therefore, it is preferable to gradually reduce the gain applied to the focus error signal FE.
Further, in order to stabilize the amplitude level of the focus error signal FE in the process of decreasing the gain, the follow-up speed (AGC time constant) in the AGC circuit 20 is set to be higher than normal. This can shorten an unstable transient state when changing the gain setting. For this reason, a high-speed response setting is performed for the AGC circuit 20 in step F114. In step F118, the response setting of the AGC circuit 20 is returned to the normal state.

In step F116, the focus loop gain is returned to the normal setting. This is a process corresponding to the fact that the loop gain was increased when the focus was turned on.
In step F117, spherical aberration correction is performed at the optimum spherical aberration correction position for the target layer that is currently focused on, so that a spherical aberration correction state suitable for servo operation and recording / reproducing operation after focus on is achieved. is there.

As described above, as a process for shifting to the steady servo, normalization of the gain of the focus error signal FE, optimization of spherical aberration correction, normalization of the servo loop gain are performed, and accompanying this, temporary AGC response setting is performed. Speed up.
The order of normalization of the gain of the focus error signal FE, optimization of spherical aberration correction, and normalization of the servo loop gain is not particularly limited to the order of FIG. 8, but may be performed in an order that considers servo stability as much as possible. Good.
In that sense, as shown in FIG. 8, in order to shorten the time when the signal state is not optimal as much as possible, the gain of the focus error signal FE is first normalized, and then the servo loop gain is normalized. Then, it is preferable to optimize the spherical aberration correction that requires a relatively long time in a state where the focus servo system is stabilized. It is preferable to set the AGC circuit 20 to a high-speed response in order to stabilize the amplitude of the focus error signal FE during these three processing periods.

Next, the case where the target layer for the focus-on operation is the L0 layer or the L3 layer will be described. In this case, the gain control for the focus error signal FE is not particularly performed during the focus-on operation of FIG. Furthermore, the spherical aberration correction position is the optimum spherical aberration correction position for the target layer. Therefore, it is not necessary to normalize the gain of the focus error signal FE and optimize the spherical aberration correction position immediately after the focus is turned on.
Therefore, in this case, the system controller 10 turns on the AGC circuit 20 with normal response setting in step F112. In step F113, the focus servo calculation unit 22 is instructed to return the servo loop gain to the normal state.
This completes the transition process to the steady servo.

  In the present embodiment, the transition process to the steady servo is performed as described above, so that even after the focus-on operation as shown in FIG. 7 is executed (particularly after the focus-on operation with respect to the L1 layer or the L2 layer), it is stable. To shift to the steady servo state.

Although the embodiments have been described above, various modifications can be considered for the configuration example and the processing example of the optical recording medium driving device of the present invention.
In the embodiments, an example has been described in which the recording apparatus of the present invention is realized by a disk drive apparatus compatible with a Blu-ray optical disk. However, the present invention can also be applied to recording apparatuses for other optical recording media.
For example, it can be applied as an optical recording medium driving device corresponding to a next generation optical disc having three or more recording layers.
The present invention can also be applied to an optical recording medium driving apparatus that records and reproduces information by irradiating a laser on another type of optical recording medium such as an optical card instead of a disk medium.

  1 optical pickup, 2 spindle motor, 3 thread mechanism, 4 matrix circuit, 5 data signal processing unit, 6 wobble signal processing circuit, 7 encoding / decoding unit, 8 host interface, 9 laser driver, 10 system controller, 11 servo circuit, 12 spindle servo circuit, 13 spindle driver, 14 SA correction driver, 15 A / D converter, 20 AGC circuit, 22 focus servo calculation unit, SW switch, 26 focus driver, 84 objective lens, 87 spherical aberration correction lens, 91 2 Shaft mechanism, 100 host equipment,

Claims (8)

The optical recording medium having three or more recording layers performs at least laser beam irradiation and reflected light detection for signal reading for signal reading, and has at least a laser beam focusing mechanism and a spherical aberration correction mechanism. An optical head,
A focus control unit that drives the focus mechanism based on a focus error signal generated from reflected light information obtained by the optical head unit, and performs focus-on control on the recording layer of the optical recording medium;
A spherical aberration correction unit that performs spherical aberration correction by driving the spherical aberration correction mechanism based on a spherical aberration correction value;
In the optical recording medium, the recording layer excluding the recording layer closest to the laser light incident side and the recording layer farthest from the target is the target layer, and the closest recording layer or the farthest recording layer is a focal position in the focus-on process. When the focus on control to the target layer is performed as the pass layer of the lens, the spherical aberration correction unit is caused to execute the spherical aberration correction using the predetermined position between the target layer and the pass layer as the spherical aberration correction position. For the focus error signal, after performing signal amplitude correction according to the positional difference between the spherical aberration correction position and the optimal spherical aberration correction position for the target layer, the focus control unit performs the focus on control. A control unit,
An optical recording medium driving device comprising:   After the focus-on control is completed, the control unit causes the spherical aberration correction unit to perform spherical aberration correction to the optimum spherical aberration correction position for the target layer as a transition process to steady focus servo, and further, the focus The optical recording medium driving device according to claim 1, wherein control is performed to end signal amplitude correction applied to the error signal.   The control unit further causes the focus control unit to change the focus loop gain to a focus-on gain and then execute the focus-on control, and the steady-state focus servo after completion of the focus-on control. The optical recording medium driving device according to claim 2, wherein, as the shift process, control for returning the focus loop gain to the normal gain is performed.   4. The optical recording medium driving device according to claim 3, wherein the control unit performs control to set an AGC response to a focus error signal as a high-speed response setting during an execution period of the transition process to the steady focus servo.   When the control unit performs focus-on control using the nearest recording layer or the farthest recording layer as a target layer, the spherical aberration correction unit corrects spherical aberration to the optimum spherical aberration correction position for the target layer. The optical recording medium driving device according to claim 1, wherein the focus control unit is configured to execute the focus-on control in a state in which the focus control unit is executed.   The predetermined position between the target layer and the passing layer, which is instructed to the spherical aberration correction unit as the spherical aberration correction position, is determined by the optical recording medium standard or the past spherical aberration correction, and is optimal for the target layer. 2. The optical recording according to claim 1, wherein the optical recording is a position between a spherical aberration correction position and an optimum spherical aberration correction position for the passing layer, and an equivalent focus error signal is obtained in the target layer and the passing layer. Medium drive device. As a gain to be given to the focus error signal for the signal amplitude correction, a memory unit that stores a gain table indicating a gain according to a positional difference between the spherical aberration correction position and the optimal spherical aberration correction position for the target layer Further comprising
The optical recording medium driving device according to claim 1, wherein the control unit controls the signal amplitude correction using the gain table. The optical recording medium having three or more recording layers performs at least laser beam irradiation and reflected light detection for signal reading for signal reading, and has at least a laser beam focusing mechanism and a spherical aberration correction mechanism. An optical head,
A focus control unit that drives the focus mechanism based on a focus error signal generated from reflected light information obtained by the optical head unit, and performs focus-on control on the recording layer of the optical recording medium;
A spherical aberration correction unit that performs spherical aberration correction by driving the spherical aberration correction mechanism based on a spherical aberration correction value;
A focus-on method for an optical recording medium driving device comprising:
In the optical recording medium, the recording layer excluding the recording layer closest to the laser light incident side and the recording layer farthest from the target is the target layer, and the closest recording layer or the farthest recording layer is a focal position in the focus-on process. When the focus on control to the target layer is performed as the passing layer, the spherical aberration correction unit performs spherical aberration correction with a predetermined position between the target layer and the passing layer as a spherical aberration correction position. Further, the focus error signal is corrected according to the positional difference between the spherical aberration correction position and the optimum spherical aberration correction position for the target layer for the focus error signal, and then the focus on control is executed by the focus control unit. Focus on method.

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