JP3995970B2 - Recording / playback device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a recording / reproducing apparatus, a recording / reproducing method, and a recording medium for a recording medium including a plurality of information layers.
[0002]
[Prior art]
As an optical recording medium capable of optically recording or reproducing information, an optical disk, an optical card, and the like are known. An optical recording medium uses a laser beam such as a semiconductor laser as a light source, and records or reproduces information by irradiating a minutely condensed light beam through a lens.
[0003]
In these optical recording media, technical development for further increasing the recording capacity has been actively conducted. Among them, the multilayer recording medium in which information layers are laminated has a feature that the recording capacity can be doubled according to the number of information layers and can be easily combined with other high-density recording technologies. . As a multilayer recording medium, a read-only DVD-ROM disc has already been put into practical use. In the future, the practical application of recordable multilayer recording media in which recordable information layers such as phase change materials, magneto-optical materials, and dye materials are laminated is expected.
[0004]
On the other hand, basic techniques for recording and reproducing information from an optical recording medium include a focus servo for condensing a light beam on the optical recording medium using an objective lens and a tracking servo for following an information track to be recorded. These servo operations are performed based on signals obtained by receiving reflected light from the optical recording medium by a photodetector. A recording medium using a phase change material or a dye material for the information layer records and reproduces a signal by using a change in the amount of reflected light of light irradiated on the information layer thin film. Information is recorded by irradiating with light having a power about 10 times higher than that during reproduction. Therefore, the photodetector that obtains the control signal for servo has an operation in which the objective lens follows the position of the information layer thin film under the condition that the state of the reproduction track is unrecorded or recorded and the operation is reproduction or recording. Even if they are the same, the amplitude of the servo signal changes because the amount of reflected light changes. In order to compensate for the amplitude change of the servo signal, the focus gain is inversely proportional to the value of the sum signal of the focus signal during the focus operation, and similarly the tracking gain is inversely proportional to the value of the tracking sum signal during the tracking operation. Yes.
[0005]
In reproduction of a reproduction-only multilayer recording medium composed of a plurality of information layers, light from not only the target information layer but also an adjacent information layer is incident on a reproduction photodetector, which is a servo signal. It becomes an offset. For this reason, at the time of reproduction, crosstalk from other information layers is predicted in advance, and the servo signal is corrected so as to increase the servo gain relatively compared to the case of a single information layer.
[0006]
[Problems to be solved by the invention]
However, in a multilayer recording medium having a recordable information layer, there is a problem that the optimum servo condition changes depending on the recording state of the adjacent information layer when recording / reproducing on the target information layer. is there.
[0007]
For example, in the case of an optical recording medium having two information layers, there are roughly four states depending on the combination of the unrecorded / recorded state of each information layer. Here, each information layer is in a form in which the reflectance decreases when the recording state is changed from the unrecorded state. The light source side is the first information layer, and the information layer on the far side from the light source is the second information layer. Here, an example of the servo operation to the second information layer at the back will be described. In this case, the focus gain is inversely proportional to the sum of the reflected light from the information layer incident on the focus photodetector as described above between the unrecorded state and the recorded state. The reflected light from the recording medium is added with the reflected light of the second information layer and the reflected light of the first information layer on the light source side, and the focus gain is determined based on the synthesized result. For this reason, even if the state of the target second information layer is the same, the amount of reflected light varies depending on whether the first information layer on the light source side is an unrecorded state or a recorded state. Therefore, the servo gain of the second information layer is learned and determined in advance in an area where both the first and second information layers are unrecorded. Next, when recording is performed on the first information layer and the area where the first and second information layers are both unrecorded and the servo gain is learned is reproduced, the amount of reflected light from the first information layer is reduced. Therefore, the ratio of the reflected light from the second information layer in the reflected light is relatively increased. As a result, the servo gain is not sufficiently corrected by the focus sum signal, and the operation becomes unstable.
[0008]
The above phenomenon is also true for the tracking servo, and there is a problem that the servo operation becomes unstable because the focus gain or tracking gain changes depending on the recording state of the information layer other than the target information layer. .
[0009]
The present invention has been made in order to solve the above-described problem, and can be applied to a target information layer without depending on a recording state of an information layer other than the target information layer among a plurality of information layers included in the recording medium. It is an object of the present invention to provide a recording / reproducing apparatus, a recording / reproducing method, and a recording medium capable of performing a servo operation stably.
[0010]
[Means for Solving the Problems]
The recording / reproducing apparatus of the present invention A recording / reproducing apparatus for a recording medium including a plurality of information layers, wherein a focus error signal is generated from a light beam reflected by the recording medium, and the recording medium is irradiated according to the focus error signal A focus control unit that performs focus control so that a light beam follows the target information layer among the plurality of information layers, and generates a tracking error signal from the light beam reflected by the recording medium, and the tracking error A tracking control unit that performs tracking control so that a light beam applied to the recording medium follows one of a plurality of tracks formed on a target information layer among the plurality of information layers according to a signal And the plurality of tracks include wobble tracks that meander in a predetermined cycle along the track direction. The wobble amplitude detection circuit for detecting the wobble amplitude value of the wobble signal included in the tracking error signal in the closed loop state is compared with the wobble amplitude value and the reference amplitude value, and the focus control is performed according to the comparison result And a gain setting unit for setting the gain of This achieves the above object.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0036]
(First embodiment)
FIG. 1 shows a configuration of a recording / reproducing apparatus 1000 according to an embodiment of the present invention.
[0037]
The recording / reproducing apparatus 1000 includes a motor 2 that rotates a recording medium 1 including a plurality of information layers, an optical pickup 3 that irradiates the recording medium 1 with a light beam, and a control unit that controls the motor 2 and the optical pickup 3. .
[0038]
The recording medium 1 is an optical disc, for example. The motor 2 is, for example, a spindle motor.
[0039]
The optical pickup 3 includes a light source 11 that emits a light beam, an objective lens 12 that converges the light beam emitted from the light source 11, a photodetector 13 that detects the light beam reflected by the recording medium 1, and a voice coil. 15 and the like. By passing a current through the voice coil 15, the optical BIC 3 is configured to be movable in the direction perpendicular to the recording medium 1 or in the radial direction of the recording medium 1.
[0040]
The control unit is configured such that the light modulation system 4 that drives the light source 11 of the optical pickup 3 and the focal point of the light beam emitted from the optical pickup 3 are positioned on the target information layer among the plurality of information layers of the recording medium 1. A control system 5 for controlling the optical pickup 3 and controlling the optical pickup 3 so that the light beam emitted from the optical pickup 3 follows a track formed in the target information layer; A signal reproduction system 6 that reproduces recorded signals, and a system control system 8 that manages the operations of the light modulation system 4, the control system 5, and the signal reproduction system 6 and manages input / output with external devices are included.
[0041]
The system control system 8 controls the operation timing of the light modulation system 4, the control system 5, and the signal reproduction system 6, but the signals for controlling such timing are omitted in FIG. Only the signal is shown.
[0042]
Hereinafter, an operation of the recording / reproducing apparatus 1000 when reproducing a signal recorded on the recording medium 1 will be described.
[0043]
The system control system 8 instructs the rotation control unit 9 to drive the motor 2. The rotation control unit 9 drives the motor 2 so that the recording medium 1 rotates at a constant speed in accordance with an instruction from the system control system 8.
[0044]
The system control system 8 outputs a control signal indicating that the operation mode of the recording / reproducing apparatus 1000 is the reproduction mode to the light modulation system 4. This control signal is supplied to the laser driving unit 10 via the encoder 23. The laser driver 10 controls the current flowing through the light source 11 so that the intensity of the light beam emitted from the optical pickup 3 becomes the reproduction power.
[0045]
The light beam emitted from the light source 11 is converged by an optical system (not shown) of the optical pickup 3 and the objective lens 12. The converged light beam is irradiated onto the recording medium 1 to form a light spot on one of a plurality of information layers included in the recording medium 1. The light beam reflected by the recording medium 1 enters the photodetector 13 via the objective lens 12 and the optical system of the optical pickup 3.
[0046]
The photodetector 13 has a plurality of light receiving surfaces (for example, four light receiving surfaces). The photodetector 13 performs photoelectric conversion. As a result, each of the plurality of light receiving surfaces outputs a signal having a voltage value corresponding to the amount of incident light. Signals output from each of the plurality of light receiving surfaces are amplified by the preamplifier 14.
[0047]
The preamplifier 14 outputs at least five types of signals: focus servo signals F + and F−, tracking servo signals T + and T−, and a signal reproduction high-frequency signal RF.
[0048]
Here, the focus servo signal F + (focus signal F +) indicates a positional deviation in the positive direction between the focal point of the light beam and the target information layer. The focus signal F + is, for example, an output signal from a light receiving surface arranged in a region where the amount of light increases when the focal position of the light beam is displaced toward the objective lens with respect to the target information layer. A focus servo signal F- (focus signal F-) indicates a positional deviation in the negative direction between the focal point of the light beam and the target information layer. The focus signal F− is, for example, an output signal from a light receiving surface arranged in a region where the amount of light increases when the focal position of the light beam is shifted to the opposite side of the objective lens with respect to the target information layer.
[0049]
A tracking servo signal T + (tracking signal T +) indicates a positional deviation in the positive direction between the light spot and the target track. The tracking signal T + is, for example, an output signal from a light receiving surface arranged in a region where the amount of light increases when the light spot is displaced to the outer peripheral side with respect to the target track when the recording medium is a disk shape. . The tracking servo signal T- (tracking signal T-) indicates the positional deviation in the negative direction between the light spot and the target track. For example, when the recording medium is a disk shape, the tracking signal T− is an output signal from a light receiving surface arranged in a region where the light amount increases when the light spot is displaced to the inner circumference side with respect to the target track. It is.
[0050]
The preamplifier 14 functions as a focus signal generation unit that generates a focus signal F + and a focus signal F−. The preamplifier 14 functions as a tracking signal generation unit that generates the tracking signal T + and the tracking signal T−.
[0051]
The focus control unit 16 generates a focus error signal according to the difference between the focus signal F + and the focus signal F−, and the focus of the light beam irradiated on the recording medium 1 and the recording medium 1 according to the focus error signal. Focus control is performed to keep the distance from the target information layer within a predetermined error range among the plurality of information layers. Such focus control is achieved, for example, by moving the objective lens 12 in a direction perpendicular to the recording medium 1 in accordance with a focus error signal.
[0052]
The gain setting unit 7 adjusts the focus control gain so as to compensate for the influence of the light beam reflected by the information layer other than the target information layer among the plurality of information layers of the recording medium 1 according to the focus error signal. Set the servo gain.
[0053]
Thus, by setting the focus control gain (focus servo gain) so as to compensate the influence of the light beam reflected by the information layer other than the target information layer, recording of the information layer other than the target information layer is performed. A stable servo operation can be performed on the target information layer without depending on the state. As a result, it is possible to reduce the occurrence of errors when recording / reproducing is performed on the recording medium 1.
[0054]
The tracking control unit 17 generates a tracking error signal according to the difference between the tracking signal T + and the tracking signal T−, and uses the light spot of the light beam irradiated on the recording medium 1 as a target according to the tracking error signal. Tracking control is performed to follow a target track (guide groove) among a plurality of tracks (guide grooves) formed in the information layer. Such tracking control is achieved, for example, by moving the objective lens 12 in the radial direction of the recording medium 1 in accordance with the tracking error signal.
[0055]
The gain setting unit 7 performs tracking control gain (tracking) so as to compensate for the influence of the light beam reflected by the information layer other than the target information layer among the plurality of information layers of the recording medium 1 according to the tracking error signal. Set the servo gain.
[0056]
As described above, by setting the tracking control gain (tracking servo gain) so as to compensate the influence of the light beam reflected by the information layer other than the target information layer, the recording of the information layer other than the target information layer is performed. A stable servo operation can be performed on the target information layer without depending on the state. As a result, it is possible to reduce the occurrence of errors when recording / reproducing is performed on the recording medium 1.
[0057]
The binarization unit 20 converts the high-frequency signal RF output from the preamplifier 14 into a binarized signal. The decoder 21 demodulates the binarized signal output from the binarizing unit 20 to generate a demodulated signal. The system control system 8 outputs the demodulated signal output from the decoder 21 to the external device as a demodulated signal S02.
[0058]
Based on the binarized signal output from the binarizing unit 20, the layer identifying unit 22 identifies which of the plurality of information layers included in the recording medium 1 is the information layer being reproduced. If the information layer being reproduced is not the target information layer, the layer identification unit 22 instructs the jump circuit 19 to move the focal position of the light beam to the target information layer. The layer identification unit 22 also manages information recorded in each of the plurality of information layers, and demodulates each form, recording / reproduction condition, and the like of the plurality of information layers.
[0059]
FIG. 2A shows an exemplary configuration of the recording medium 1 and an exemplary configuration of an optical system for the recording medium 1.
[0060]
The recording medium 1 includes three information layers 226, 227, 228, two separation layers 230, 231 and two substrates 225, 229. The information layer 226 and the information layer 227 are separated by a certain distance by the separation layer 230, and the information layer 227 and the information layer 228 are separated by a certain distance by the separation layer 231.
[0061]
The recording medium 1 is formed by laminating a substrate 225, an information layer 226, a separation layer 230, an information layer 227, a separation layer 231, an information layer 228, and a substrate 229 in this order from the light beam incident side.
[0062]
Each of the information layers 226, 227, and 228 may be a read-only information layer or a recordable information layer. The read-only information layer includes a surface on which concave / convex pits representing information are formed, and a reflective film formed on the surface. Various systems can be applied as a system for recording a signal on a recordable information layer. For example, a deformation recording method that utilizes the change in the shape of the thin film due to the heat of the light beam, a phase change recording method that utilizes the change in the phase state of the thin film, and a magneto-optical recording method that utilizes the change in the magnetization direction In addition, a recording method that utilizes a change in state by light energy, such as a photochromic material, can be applied.
[0063]
Furthermore, in order to enable recording / reproduction with respect to the information layer 228 located farthest from the light incident side, the information layers 226 and 227 transmit the light beam with respect to the wavelength of the light beam. It is necessary to have properties (permeability).
[0064]
The present invention is particularly effective when at least one of the plurality of information layers is a recordable information layer.
[0065]
In FIG. 2A, an optical path 41 indicated by a solid line indicates an optical path of light incident on the information layer 227 and reflected by the information layer 227 when the focus of the light beam is on the information layer 227. In the example shown in FIG. 2, the light beam is converged on the information layer 227 in a state where the light beam is almost limited to the diffraction limit.
[0066]
In FIG. 2A, the optical path 42 indicated by the alternate long and short dash line 42 indicates the optical path of the light beam reflected by the information layer 226, and the optical path 43 indicated by the broken line 43 indicates the optical path of the light beam reflected by the information layer 228. .
[0067]
As shown in FIG. 2A, the light beam reflected by the information layer 227 is focused again on the photodetector 13 via the objective 12, the detection lens 39 and the cylindrical lens 40.
[0068]
On the other hand, since the light beam reflected by the information layer 226 becomes divergent light after passing through the objective lens 12, it is incident on the photodetector 13 so as to cover the entire plurality of light receiving surfaces of the photodetector 13. The As a result, the light beam reflected by the information layer 226 is incident on the plurality of light receiving surfaces of the photodetector 13 substantially evenly. In addition, the light beam reflected by the information layer 228 becomes convergent light after passing through the objective lens 12, and is focused between the detection lens 39 and the photodetector 13. The light is incident on the photodetector 13 so as to cover the whole. As a result, the light beam reflected by the information layer 228 is substantially uniformly incident on the plurality of light receiving surfaces of the photodetector 13.
[0069]
FIG. 2B shows an exemplary configuration of the photodetector 13 and an exemplary configuration of the preamplifier 14.
[0070]
The photodetector 13 includes light receiving surfaces 13a, 13b, 13c, and 13d that are divided into four.
[0071]
The light beam reflected by the information layer 227 enters the photodetector 13 along the optical path 41. As a result, a light spot is formed on the light receiving surfaces 13a to 13d of the photodetector 13. In FIG. 2B, reference numeral 41 a indicates the shape of the light spot when the focal point of the light beam reflected by the information layer 227 is on the light receiving surfaces 13 a to 13 d of the photodetector 13. The light spot 41a has a circular shape that extends substantially equally to each of the light receiving surfaces 13a to 13d.
[0072]
In FIG. 2B, reference numeral 41 b indicates the shape of the light spot when the focal position of the light beam is slightly shifted toward the objective lens 12 with respect to the information layer 227. The light spot 41b has an elliptical shape extending in a direction connecting the light receiving surface 13b and the light receiving surface 13c. Reference numeral 41 c indicates the shape of the light spot when the focal position of the light beam is slightly shifted to the side opposite to the objective lens 12 with respect to the information layer 227. The light spot 41c has an elliptical shape extending in a direction connecting the light receiving surface 13a and the light receiving surface 13d.
[0073]
In FIG. 2, reference numeral 42 a indicates the shape of the light spot when the light beam reflected by the information layer 226 is incident on the photodetector 13 along the optical path 42. The light spot 42a is a circle that covers all of the light receiving surfaces 13a to 13d. Reference numeral 43 a indicates the shape of the light spot when the light beam reflected by the information layer 228 is incident on the photodetector 13 along the optical path 43. The light spot 43a is a circle that covers all of the light receiving surfaces 13a to 13d.
[0074]
The shapes of the light spot 42 a and the light spot 43 a hardly change with respect to the positional deviation between the focal point of the light beam and the information layer 227. The light beams reflected by the information layers 226 and 228 irradiate the light receiving surfaces 13a to 13d of the photodetector 13 substantially evenly regardless of the positional deviation between the focal point of the light beam and the information layer 227.
[0075]
Each of the light receiving surfaces 13a to 13d of the photodetector 13 outputs a signal having a voltage corresponding to the amount of incident light.
[0076]
Signals output from the light receiving surfaces 13 a and 13 d arranged on the diagonal line of the photodetector 13 are supplied to the addition amplifier 44 in the preamplifier 14. The addition amplifier 44 adds the signal output from the light receiving surface 13a and the signal output from the light receiving surface 13d, and amplifies the addition result to generate the focus signal F +.
[0077]
Signals output from the light receiving surfaces 13 b and 13 c arranged on the diagonal line of the photodetector 13 are supplied to the addition amplifier 45 in the preamplifier 14. The addition amplifier 45 adds the signal output from the light receiving surface 13b and the signal output from the light receiving surface 13c, and amplifies the addition result to generate the focus signal F−.
[0078]
The focus control unit 16 (FIG. 1) generates a focus error signal according to the difference between the focus signal F + and the focus signal F− so that the focus error signal becomes substantially zero (that is, the value of the focus signal F +). The position of the focal point of the light beam with respect to the target information layer 227 is controlled (so that the value of the focus signal F− is substantially equal). Such control is achieved, for example, by controlling the position of the objective lens 12 according to the focus error signal.
[0079]
As described above, while performing focus control on the target information layer 227, the light beams reflected by the information layers 226 and 228 other than the target information layer 227 are substantially reflected on the light receiving surfaces 13a to 13d of the photodetector 13. Since the illumination is performed uniformly, the component of the focus signal F + and the component of the focus signal F− generated based on the light beams reflected by the information layers 226 and 228 are substantially equal. Focus control is performed according to the difference between the focus signal F + and the focus signal F−. Thereby, it is possible to almost eliminate the influence of the light beams reflected by the information layers 226 and 228 other than the target information layer 227 on the focus control.
[0080]
2A and 2B, the case where the focusing method is the astigmatism method has been described as an example, but the present invention is not limited to this. While the focus control for the target information layer is performed according to the difference between the focus signal F + and the focus signal F−, and the focus control for the target information layer is performed, the information layer other than the target information layer is used. As long as the focus signal F + and the focus signal F− are generated so that the component of the focus signal F + and the component of the focus signal F− are substantially equal to the reflected light beam, the present invention is applied to an arbitrary focus method. Can be applied.
[0081]
2A and 2B, the case where the recording medium 1 includes three information layers has been described as an example, but the present invention is not limited to this. The present invention can be applied to a recording medium including an arbitrary number of information layers of two or more. Further, although the case where focus control is performed on the second information layer among the three information layers has been described as an example, the present invention is not limited to this. It goes without saying that the present invention can be applied when focus control is performed on an arbitrary information layer among a plurality of information layers.
[0082]
Further, the same thing as the focus control applies to the tracking control. That is, using a photodetector having a light receiving surface divided into at least two along the track direction, the signals output from the light receiving surface arranged on one side along the track direction are added and the addition result A tracking signal T + is generated by amplifying the signal, a signal output from the light receiving surface arranged on the other side along the track direction is added, and a tracking signal T− is generated by amplifying the addition result, By performing the tracking control according to the difference between the tracking signal T + and the tracking signal T−, it is possible to almost eliminate the influence of the light beam reflected by the information layer other than the target information layer on the tracking control.
[0083]
FIG. 3 shows an example of the configuration of the focus control unit 16 (FIG. 1) and an example of the configuration of the gain setting unit 7 (FIG. 1).
[0084]
The focus control unit 16 receives the focus signal F + and the focus signal F−, generates a focus error signal 31s according to the difference between the focus signal F + and the focus signal F−, and a differential amplifier circuit The focus drive circuit 33 that drives the voice coil 15 of the optical pickup 3 in accordance with the focus error signal output from 31 and the focus servo gain set by the gain setting unit 7, and provides a predetermined current to the focus drive circuit 33 The offset circuit 34 is included.
[0085]
The gain setting unit 7 includes an S-shaped amplitude detection circuit 35, a gain setting circuit 32, and an S-shaped reference value circuit 36.
[0086]
Hereinafter, operations of the focus control unit 16 and the gain setting unit 7 will be described with reference to FIG.
[0087]
The focus drive circuit 33 moves the objective lens 12 in a direction perpendicular to the recording medium 1 by setting the focus control to an open loop and flowing a predetermined current provided from the offset circuit 34 to the voice coil 15.
[0088]
The S-shaped amplitude detection circuit 35 detects the amplitude value of the focus error signal 31s corresponding to the target information layer. The S-shaped reference value circuit 36 outputs a reference amplitude value obtained in advance through experiments. The gain setting circuit 32 determines the reference focus servo gain by comparing the detected amplitude value with the reference amplitude value output from the S-shaped reference value circuit 36. The gain setting circuit 32 outputs a focus servo gain setting signal 7s indicating the reference focus servo gain to the focus driving circuit 33.
[0089]
The focus drive circuit 33 sets the focus control gain (focus servo gain) in accordance with the focus servo gain setting signal 7s, and sets the focus control to a closed loop. As a result, focus control based on the focus servo gain set according to the focus servo gain setting signal 7s is started.
[0090]
The control for setting the focus control to the closed loop / open loop is achieved, for example, by providing a switch in the middle of the focus control feedback loop and switching the switch ON / OFF by the focus drive circuit 33.
[0091]
The gain setting unit 7 preferably further includes a summing amplifier circuit 37. The summing amplifier circuit 37 receives the focus signal F + and the focus signal F−, and generates a focus sum signal corresponding to the sum of the focus signal F + and the focus signal F−. In this case, the gain setting circuit 32 finely adjusts the focus servo gain based on the focus sum signal output from the addition amplification circuit 37 in addition to the reference focus servo gain in a state where the focus control is in a closed loop. As a result, it is possible to suppress the influence of the change in the power of the light beam and the disturbance during recording and reproduction.
[0092]
FIG. 4 shows how the focus error signal (FE signal) 31s output from the differential amplifier circuit 31 changes under the control of the focus drive circuit 33 in a state where the focus control is in an open loop. In the example shown in FIG. 4, it is assumed that the recording medium 1 includes three information layers 226, 227, and 228 as shown in FIG. 2A.
[0093]
As shown in FIG. 4, three S-shaped focus error signals are obtained corresponding to the three information layers 226, 227, and 228, respectively.
[0094]
When the target information layer is the first information layer 226, the S-shaped amplitude detection circuit 35 detects the amplitude value F1 shown in FIG. 4 as the amplitude value of the focus error signal corresponding to the target information layer. . When the target information layer is the second information layer 227, the S-shaped amplitude detection circuit 35 detects the amplitude value F2 shown in FIG. 4 as the amplitude value of the focus error signal corresponding to the target information layer. . When the target information layer is the third information layer 228, the S-shaped amplitude detection circuit 35 detects the amplitude value F3 shown in FIG. 4 as the amplitude value of the focus error signal corresponding to the target information layer. .
[0095]
Note that the focus error signal is an S-shaped signal as shown in FIG. 4 under ideal conditions, but in reality, the S-character is distorted due to surface blurring of the recording medium 1 or reproduction noise. It becomes a signal of the shape. Therefore, in order to reliably detect the target information layer, it is preferable to limit the amplitude and the waveform time width assumed from the fluctuation component due to the focus offset and the surface blur of the recording medium 1.
[0096]
As described above, the signal component generated based on the light beam reflected by the information layer other than the target information layer appears almost equally in both the focus signals F + and F−. For this reason, by performing focus control according to the difference between the focus signal F + and the focus signal F−, it is possible to substantially cancel the signal component. This is true regardless of whether an information layer other than the target information layer is in a recorded state or an unrecorded state. Therefore, when focus control is performed on the target information layer, it is reflected by the information layer other than the target information layer regardless of whether the information layer other than the target information layer is in a recorded state or an unrecorded state. It is possible to substantially cancel the influence of the focused light beam on the focus control. As a result, it is possible to perform focus control with an appropriate gain for the target information layer.
[0097]
FIG. 5 shows an example of the configuration of the tracking control unit 17 (FIG. 1) and an example of the configuration of the gain setting unit 7 (FIG. 1).
[0098]
The tracking control unit 17 receives the tracking signal T + and the tracking signal T−, generates a tracking error signal 51s corresponding to the difference between the tracking signal T + and the tracking signal T−, and a differential amplifier circuit And a tracking drive circuit 53 for driving the voice coil 15 of the optical pickup 3 in accordance with the tracking error signal output from 51 and the tracking servo gain set by the gain setting unit 7.
[0099]
The gain setting unit 7 includes a TE amplitude detection circuit 54, a gain setting circuit 52, and a TE reference value circuit 55.
[0100]
Hereinafter, operations of the tracking control unit 17 and the gain setting unit 7 will be described with reference to FIG. It is assumed that the focus of the light beam is located on the target information layer as a result of executing the focus control by the focus control unit 16.
[0101]
The tracking drive circuit 53 moves the objective lens 12 in the radial direction of the recording medium 1 with tracking control as an open loop. As the objective lens 12 moves, the tracking error signal (TE signal) 51s output from the differential amplifier circuit 51 changes.
[0102]
FIG. 6 shows the waveform of the tracking error signal 51s thus obtained.
[0103]
The TE amplitude detection circuit 54 detects the amplitude value (T2 in the example of FIG. 6) of the tracking error signal 51s. The TE reference value circuit 55 outputs a reference amplitude value obtained in advance by experiments. The gain setting circuit 52 determines the reference tracking servo gain by comparing the detected amplitude value (T2 in the example of FIG. 6) with the reference amplitude value output from the TE reference value circuit 55. The gain setting circuit 52 outputs a tracking servo gain setting signal 70 s indicating the reference tracking servo gain to the tracking drive circuit 53.
[0104]
The tracking drive circuit 53 sets a tracking control gain (tracking servo gain) according to the tracking servo gain setting signal 70s, and sets the tracking control to a closed loop. As a result, tracking control based on the tracking servo gain set according to the tracking servo gain setting signal 70s is started.
[0105]
The control for setting the tracking control to a closed loop / open loop is achieved, for example, by providing a switch in the middle of the feedback loop of the tracking control and switching the switch ON / OFF by the tracking drive circuit 53.
[0106]
The gain setting unit 7 preferably further includes a summing amplifier circuit 56. The summing amplifier circuit 56 receives the tracking signal T + and the tracking signal T−, and generates a tracking sum signal corresponding to the sum of the tracking signal T + and the tracking signal T−. In this case, the gain setting circuit 52 corrects the tracking servo gain based on the tracking sum signal output from the addition amplification circuit 56 in addition to the reference tracking servo gain when the tracking control is in a closed loop state. Thereby, it becomes possible to compensate for the influence of the change in the power of the light beam and the disturbance during recording and reproduction. For example, the gain setting circuit 52 preferably corrects the tracking servo gain so as to be inversely proportional to the level of the tracking sum signal.
[0107]
As described above, the signal component generated based on the light beam reflected by the information layer other than the target information layer appears almost equally in both the tracking signals T + and T−. For this reason, by performing tracking control according to the difference between the tracking signal T + and the tracking signal T−, it is possible to substantially cancel the signal component. This is true regardless of whether an information layer other than the target information layer is in a recorded state or an unrecorded state. Therefore, when tracking control is performed on the target information layer, it is reflected by the information layer other than the target information layer regardless of whether the information layer other than the target information layer is in a recorded state or an unrecorded state. It is possible to almost cancel the influence of the emitted light beam on the tracking control. As a result, it is possible to perform tracking control with an appropriate gain for the target information layer.
[0108]
For each information layer, depending on whether the other layer is in an unrecorded state or a recorded state, the combination is divided into four cases, when there are three information layers, A total of 12 types of servo gains are set. Similarly, in the case of two layers, a total of four types of servo gains are set for each information layer.
[0109]
Further, it is desirable that the area for setting the reference focus servo gain and the reference tracking servo gain and the recording area of the track for recording / reproducing are separated from the unrecorded area and the recording area. That is, when an unrecorded state and a recorded state region are mixed for each track, the influence on the other layer changes stepwise. That is, even if there are two information layers, it is necessary to set more gains depending on the recording patterns of the other layers as well as the above four types. In this case, it is possible to perform good recording and reproduction by executing the above-described process for obtaining the reference focus servo gain and the reference tracking servo gain again every time an error factor occurs. As another method, it is effective to obtain these values in each area of the information layer in advance and switch the servo gain for each area.
[0110]
(Second Embodiment)
Here, as a method for determining the servo gain for the recording medium 1 including a plurality of information layers, a method using a wobble groove meandering at a constant period along the track direction will be described.
[0111]
FIG. 7 shows a plurality of guide tracks 71 formed on one of the plurality of information layers (target information layer). A recording mark 72 indicating that an information signal has been recorded is formed on the guide track 71.
[0112]
The guide track 71 is formed to meander slightly in a direction perpendicular to the track direction at a constant period. The meandering period is set to be higher than the tracking frequency of the tracking servo operation.
[0113]
8 shows an example of the configuration of the tracking control unit 17 (FIG. 1) used in the recording / reproducing apparatus for the recording medium 1 having the wobble groove shown in FIG. 7, and the gain setting unit 7 (FIG. 1). An example of the configuration is shown.
[0114]
The configuration shown in FIG. 8 is basically the same as the configuration shown in FIG. However, the configuration shown in FIG. 8 is when the focus control is in a closed loop state and the tracking control is in a closed loop state (that is, a state where a signal recorded on a specific track is being reproduced). 5 differs from the configuration shown in FIG. 5 in that the focus servo gain and tracking servo gain can be set.
[0115]
Hereinafter, operations of the tracking control unit 17 and the gain setting unit 7 will be described with reference to FIG.
[0116]
The differential amplifier circuit 51 outputs a tracking error signal corresponding to the difference between the tracking signal T + and the tracking signal T−. When the tracking control is in a closed loop state, the tracking error signal output from the differential amplifier circuit 51 includes a signal (wobble signal) corresponding to the wobble of the guide groove as a residual component of the tracking control.
[0117]
The wobble amplitude detection circuit 81 detects the amplitude value of the wobble signal included in the tracking error signal. The wobble amplitude reference value circuit 85 outputs a reference amplitude value obtained in advance by experiments. The gain setting circuit 82 determines the reference tracking servo gain by comparing the detected amplitude value with the reference amplitude value output from the wobble amplitude reference value circuit 85. The gain setting circuit 82 outputs a tracking servo gain setting signal 70 s indicating the reference tracking servo gain to the tracking drive circuit 83.
[0118]
The tracking drive circuit 83 resets the tracking control gain (tracking servo gain) in accordance with the tracking servo gain setting signal 70s. As a result, tracking control based on the tracking servo gain reset according to the tracking servo gain setting signal 70s is started.
[0119]
The gain setting circuit 82 determines the reference focus servo gain by comparing the detected amplitude value with the reference amplitude value output from the wobble amplitude reference value circuit 85, and indicates the reference focus servo gain. The focus servo gain setting signal 7s may be output to the focus drive circuit 33 (FIG. 3). In this case, the focus drive circuit 33 resets the focus control gain (focus servo gain) in accordance with the focus servo gain setting signal 7s. As a result, focus control based on the focus servo gain reset according to the focus servo gain setting signal 7s is started.
[0120]
Note that gain correction based on the amplitude value of the wobble signal detected by the wobble amplitude detection circuit 81 may cause a large control error for a sudden change in disturbance. For this reason, the gain setting circuit 82 finely adjusts the tracking servo gain based on the tracking sum signal output from the addition amplification circuit 86 in addition to the reference tracking servo gain, and changes in the power of the light beam during recording and reproduction It is preferable to compensate for the influence of disturbance.
[0121]
According to the second embodiment, in addition to the effect obtained in the first embodiment, in addition to the effect that the tracking servo gain can be set while the tracking control is in a closed loop state. be able to. This makes it possible to always set an optimum gain even during the recording / reproducing operation.
[0122]
Although the phase of the wobble groove has not been described in detail here, the CLV format in which the linear velocity of recording is constant is advantageous in order to increase the recording capacity of the disk-shaped recording medium. In this case, the wobble groove has different phases between adjacent tracks. The wobble amplitude obtained as a result is a waveform subjected to amplitude modulation in the circumferential direction.
[0123]
As a format for forming the wobble groove of the recording medium, it is desirable that the wobble phase is the same between adjacent tracks. When the recording medium is in the disk form shown in this embodiment, the zone CLV format is applied. In other words, the radial direction of the disk is divided into a plurality of zones, and the same phase is set between adjacent tracks in the zone. In the zone switching region, the number of wobbles is increased stepwise toward the outer periphery. By adopting the wobble groove having the above configuration, the wobble amplitude can be almost constant in any region, and high-speed servo gain setting can be performed.
[0124]
On the other hand, as a method for increasing the recording capacity, there is a CLV format. In this case, the wobble groove has different phases between adjacent tracks. The wobble amplitude thus obtained is different in the radial direction.
(Third embodiment)
Up to this point, the method for correcting the servo gain in the vicinity of the recording / reproducing track has been described, but here, preliminary recording / reproducing is performed in advance in a specific area on the recording medium before recording / reproducing the information signal. A servo gain learning method for determining the correction value of each servo gain will be described.
[0125]
FIG. 9 shows the configuration of the recording medium 1 for learning the servo gain. The recording medium 1 includes an information area 91, a test area 92 in which a test signal indicating a basic pattern in which interlayer crosstalk between information layers can occur, and a management information area 93 for describing servo operation conditions and the like. .
[0126]
The test area 92 is provided in an area close to the information area 91.
[0127]
FIG. 10 shows an example of a cross section of the test area 92 of the recording medium 1. FIG. 10 shows eight basic patterns (a) to (h) on the assumption that two states of an unrecorded state and a recorded state exist at random for each of the three information layers 226, 227, and 228. Is recorded at different positions in the radial direction of the tell area 92.
[0128]
For example, in FIG. 10B, a basic pattern indicating a combination in which the information layer 226 is in an unrecorded state, the information layer 227 is in an unrecorded state, and the information layer 228 is in a recorded state is recorded in the test area 92. Indicates that
[0129]
FIG. 11 shows the procedure of the method for learning the servo gain. This method can be executed by the recording / reproducing apparatus 1000.
[0130]
In the following description, a method of learning the servo gain for the second information layer (for example, the information layer 227 shown in FIG. 10) will be described as a representative example. Needless to say, the servo gain can be learned in the same manner for information layers other than the second information layer (for example, the information layers 226 and 228 shown in FIG. 10).
[0131]
Servo gain learning is started in response to a signal indicating that learning of servo gain output from the system control system 8 is started.
[0132]
In the preliminary servo setting step 101, the gain setting circuit 32 (FIG. 3) sets the initial value of the focus servo gain, and the gain setting circuit 52 (FIG. 5) sets the initial value of the tracking servo gain. These initial values are set to values slightly lower than the servo gain optimum for the recording medium 1 set in advance.
[0133]
In the test area seek step 102, the optical pickup 3 is moved so that the test area 92 shown in FIG. For example, it is assumed that the optical pickup 3 has moved so that the test area 92 in which the basic pattern (a) shown in FIG. 10 is recorded is irradiated with the light beam.
[0134]
In the F offset application step 103, the focus drive circuit 33 (FIG. 3) sets the focus control to an open loop state, and allows a predetermined current provided by the offset circuit 34 (FIG. 3) to flow through the voice coil 15 (FIG. 1). Thus, the objective lens 12 is moved in the direction perpendicular to the recording medium 1.
[0135]
In the S-shaped amplitude detection step 104, the S-shaped amplitude detection circuit 35 (FIG. 3) detects the amplitude value of the focus error signal corresponding to the second information layer.
[0136]
In the S-shaped amplitude comparison step 105, the gain setting circuit 32 (FIG. 3) compares the amplitude value detected by the S-shaped amplitude detection circuit 35 with the reference amplitude value.
[0137]
In the focus servo gain setting step 106, the gain setting circuit 32 (FIG. 3) sets the focus servo gain based on the comparison result between the detected amplitude value and the reference amplitude value.
[0138]
In the focus control ON step 107, the focus drive circuit 33 (FIG. 3) sets the focus control to a closed loop state. As a result, focus control based on the focus servo gain is started.
[0139]
In the TE amplitude detection step 108, the TE amplitude detection circuit 54 (FIG. 5) detects the amplitude value of the tracking error signal.
[0140]
In the TE amplitude comparison step 109, the gain setting circuit 52 (FIG. 5) compares the amplitude value detected by the TE amplitude detection circuit 54 with the reference amplitude value.
[0141]
In the tracking servo gain setting step 110, the gain setting circuit 52 (FIG. 5) sets the tracking servo gain based on the comparison result between the detected amplitude value and the reference amplitude value.
[0142]
In this way, by performing the above-described steps 102 to 110, the optimum focus servo gain and the optimum tracking servo gain are obtained for one basic pattern (for example, the basic pattern (a) shown in FIG. 10). Can be sought.
[0143]
In the recording pattern confirmation step 111, it is confirmed whether there is another basic pattern to be learned for the second information layer. If “Yes” in step 111, steps 102 to 110 are repeated, and if “No” in step 111, the servo gain learning is terminated.
[0144]
For example, when the servo gain is learned for the eight basic patterns (a) to (h) shown in FIG. 10, Steps 102 to 110 are repeated eight times.
[0145]
In this way, the optimum servo gain is learned in advance for the basic pattern recorded in the test area 92, and the pattern recorded in the information area 91 adjacent to the test area 92 is any of the basic patterns. This makes it possible to perform a stable servo operation using a servo gain optimum for the recording pattern.
[0146]
Next, a method for shortening the time for learning the servo gain will be described. In the method described above, when the recording medium 1 includes three information layers and there are eight basic patterns to be learned, 3 × 8 = 24 times are repeated by repeating the steps 102 to 110 shown in FIG. Need to learn servo gain.
[0147]
Here, in order to shorten the time for learning the servo gain, from the information layer closest to the light beam incident side toward the information layer farthest (or closest to the information layer farthest from the light beam incident side) A method of recording information on the recording medium 1 (toward the information layer) is adopted. For example, as shown in FIG. 2A, when the recording medium 1 includes three information layers 226, 227, and 228, and the information layers 226, 227, and 228 are stacked in this order from the light incident side, Information is recorded from the inner circumference side to the outer circumference side of the information layer 226. When there is no empty area in the information area of the information layer 226, recording on the information layer 227 is started. When there is no empty area in the information area of the information layer 227, recording on the information layer 228 is started.
[0148]
When the recording medium 1 is a rewritable type, it is preferable to provide a full-surface recording identifier in a specific area such as a control track of the recording medium 1. When recording on all information layers is completed, a code indicating that recording on all information layers is completed is recorded in the full-surface recording identifier. Before recording information on the recording medium 1, the recording pattern of the recording medium 1 can be specified by checking the code recorded on the full-surface recording identifier. As a result, it is possible to select a servo gain optimum for the recording pattern from the servo gains obtained in advance by learning.
[0149]
According to this method, in a state where recording on all information layers of the recording medium is not completed, the basic patterns that can exist among the eight basic patterns (a) to (h) shown in FIG. These are limited to the four basic patterns (a), (c), (g), and (h) shown in FIG. In this case, it is sufficient to record only four types of basic patterns in the test area 92 of the recording medium 1, and when the recording medium 1 includes three information layers, the number of times required for learning the servo gain is 3 × 4 = 12. Time is enough. In this way, by limiting the recording order in the information layer, the number of times required for learning the servo gain can be halved.
[0150]
Further, recording / reproduction based on the basic pattern (a) shown in FIG. 10 is not important for the information layer 227, and the basic patterns (a) and (c) shown in FIG. Recording and playback based is not important. Therefore, if the learning of the servo gain for these basic patterns is omitted, the number of times required to learn the servo gain can be further reduced by three times. As a result, the number of times required for learning the servo gain is nine.
[0151]
In addition, when a method of providing an identifier indicating the completion of recording for each information layer of the recording medium 1 and confirming the identifier indicating the completion of recording for each information layer before recording information on the recording medium 1, the recording medium If an identifier indicating the completion of recording on one information layer 226 is detected, it is not necessary to consider the unrecorded state of the information layer 226, and the number of times required for learning the servo gain can be set to eight.
[0152]
When an identifier indicating completion of recording in all information layers is detected, it is sufficient to learn the servo gain for the basic pattern (h) shown in FIG. 1 = 3 times.
[0153]
Even when the recording order on the information layer is limited in the direction from the information layer 228 farthest to the light beam incident side to the nearest information layer 226, the basic pattern to be learned is shown in FIG. (A), (b), (f), and (h). As a result, the same effect as described above can be obtained.
[0154]
As described above, by limiting the recording order in the information layer, it is possible to significantly reduce the time required for learning the servo gain.
[0155]
(Fourth embodiment)
Another method for learning the servo gain will be described. The present embodiment relates to a method for efficiently learning servo gain for a recording medium in which a signal is recorded in advance in a target information layer or a read-only medium.
[0156]
Here, it is assumed that only four types of basic patterns (e) to (h) shown in FIG. 10 are recorded in the test area 92 of the recording medium 1.
[0157]
FIG. 12 shows the procedure of the method for learning the servo gain. This method can be executed by the recording / reproducing apparatus 1000.
[0158]
In the following description, a method of learning the servo gain for the second information layer (for example, the information layer 227 shown in FIG. 10) will be described as a representative example. Needless to say, the servo gain can be learned in the same manner for information layers other than the second information layer (for example, the information layers 226 and 228 shown in FIG. 10).
[0159]
Servo gain learning is started in response to a signal indicating that learning of servo gain output from the system control system 8 is started.
[0160]
In the preliminary servo setting step 115, the gain setting circuit 32 (FIG. 3) sets the initial value of the focus servo gain, and the gain setting circuit 52 (FIG. 5) sets the initial value of the tracking servo gain. These initial values are set to values slightly lower than the servo gain optimum for the recording medium 1 set in advance.
[0161]
In the test area seek step 116, the optical pickup 3 is moved so that the test area 92 shown in FIG. For example, it is assumed that the optical pickup 3 has moved so that the test region 92 in which the basic pattern (e) shown in FIG. 10 is recorded is irradiated with the light beam.
[0162]
In the focus servo gain setting step 117, the gain setting circuit 32 (FIG. 3) sets a first focus servo gain among a plurality of focus servo gains prepared in advance. As a result, the focus drive circuit 33 (FIG. 3) performs focus control based on the first focus servo gain.
[0163]
In the error rate measurement step 118, the signal reproduction system 6 (FIG. 1) reproduces the signal recorded on the information layer 227 of the recording medium 1, and measures a demodulation error in the reproduction signal. For example, the decoder 21 (FIG. 1) measures the demodulation error and outputs the measurement result to the gain setting circuit 32 (FIG. 3).
[0164]
In the reproduction condition confirmation step 119, it is confirmed whether or not there is another focus servo gain to be tested for the basic pattern (e) shown in FIG. If “Yes” in step 119, steps 117 to 118 are repeated, and a demodulation error in the reproduction signal is measured for the next focus servo gain among a plurality of focus servo gains prepared in advance. If “No” in step 119, the process proceeds to step 120.
[0165]
In the error rate comparison step 120, the gain setting circuit 32 (FIG. 3) compares a plurality of demodulation errors obtained for a plurality of focus servo gains prepared in advance.
[0166]
In the optimum focus servo gain determination step 121, the gain setting circuit 32 (FIG. 3) determines the focus servo gain that provides the most stable and small error rate as the optimum focus servo gain. As a result, the focus drive circuit 33 (FIG. 3) starts focus control based on the optimum focus servo gain.
[0167]
The optimum tracking servo gain is also determined by a method similar to the method for determining the optimum focus servo gain.
[0168]
In the tracking servo gain setting step 122, the gain setting circuit 52 (FIG. 5) sets a first tracking servo gain among a plurality of tracking servo gains prepared in advance. As a result, the tracking drive circuit 53 (FIG. 5) performs tracking control based on the first tracking servo gain.
[0169]
In the error rate measurement step 123, the signal reproduction system 6 (FIG. 1) reproduces the signal recorded on the information layer 227 of the recording medium 1, and measures a demodulation error in the reproduction signal. For example, the decoder 21 (FIG. 1) measures the demodulation error and outputs the measurement result to the gain setting circuit 52 (FIG. 5).
[0170]
In the reproduction condition confirmation step 124, it is confirmed whether there is another tracking servo gain to be tested for the basic pattern (e) shown in FIG. If “Yes” in step 124, steps 122 to 123 are repeated, and a demodulation error in the reproduction signal is measured for the next tracking servo gain among a plurality of tracking servo gains prepared in advance. If “No” in step 124, the process proceeds to step 125.
[0171]
In the error rate comparison step 125, the gain setting circuit 52 (FIG. 5) compares a plurality of demodulation errors obtained for a plurality of tracking servo gains prepared in advance.
[0172]
In the optimum tracking servo gain determination step 126, the gain setting circuit 52 (FIG. 5) determines the tracking servo gain that provides the smallest and stable error rate as the optimum tracking servo gain. As a result, the tracking drive circuit 53 (FIG. 5) starts tracking control based on the optimum tracking servo gain.
[0173]
As described above, the optimum focus servo gain and the optimum tracking servo gain are obtained for one basic pattern (for example, the basic pattern (e) shown in FIG. 10) by performing the above-described steps 116 to 126. Can be sought.
[0174]
In the recording pattern confirmation step 127, it is confirmed whether there is another basic pattern to be learned for the second information layer. If “Yes” in step 127, steps 116 to 126 are repeated. If “No” in step 127, the servo gain learning is terminated.
[0175]
In this way, the optimum servo gain is learned in advance for the basic pattern recorded in the test area 92, and the pattern recorded in the information area 91 adjacent to the test area 92 is any of the basic patterns. This makes it possible to perform a stable servo operation using a servo gain optimum for the recording pattern.
[0176]
The relationship between the servo gain when the information layer is in the recording state and the servo gain when the information layer is in the unrecorded state is obtained in advance, and the servo gain when the information layer is in the unrecorded state is determined as the information layer. May be obtained from the servo gain in the recording state.
[0177]
Although the method for measuring the error rate of the reproduction signal and learning the servo gain based on the error rate has been described here, the servo gain is based on information other than the error rate (for example, the jitter value of the reproduction signal). May be learned.
[0178]
When the jitter value of the reproduction signal is measured and the servo gain is learned based on the jitter value, the error rate measurement steps 118 and 123 in FIG. 12 are replaced with the jitter value measurement step, and the error rate comparison steps 120 and 125 are performed. Instead of the jitter value comparison process, the servo gain having the smallest jitter value and stable may be determined as the optimum servo gain. Alternatively, a servo gain that can ensure a good value in a fixed focus range may be determined as the optimum servo gain.
[0179]
Further, instead of measuring the error rate, a method of measuring the residual component of each servo signal is also effective. For this purpose, the error rate measuring step 118 in FIG. 12 is used as the residual amplitude measuring step for the focus error signal, the S-shaped amplitude detection circuit 35 (FIG. 3) is used as the focus residual amplitude measuring circuit, and the error rate comparing step 120 is used as the focus residual amplitude. Let it be a comparison process. In the focus servo gain setting step 117, the focus servo gain is changed step by step, and the focus residual measurement circuit measures the amplitude of the residual component of the focus error signal at each level. Obtain the servo gain.
[0180]
Similarly, in the tracking operation, the error rate measurement step 123 in FIG. 12 is a tracking error signal residual amplitude measurement step, the TE amplitude detection circuit 54 (FIG. 5) is a tracking residual amplitude measurement circuit, and the error rate comparison step 125 is tracked. This is a residual amplitude comparison process. In the tracking servo gain setting step 122, the tracking servo gain is changed stepwise, and the tracking residual measurement circuit measures the amplitude of the residual component of the tracking error signal at each level. The servo gain may be obtained.
[0181]
Note that the focus servo gain obtained using the focus servo residual amplitude does not necessarily have to have the minimum residual amplitude depending on the circuit scale and accuracy of the recording / reproducing apparatus. For example, correction for ensuring a certain operation margin, for example, a focus residual component is not minimum, but a condition may be set such that no malfunction occurs even if the focus servo gain fluctuates to some extent. Similarly, the tracking servo gain may be set to a condition that does not cause a malfunction even if the tracking servo gain fluctuates to some extent, although correction for ensuring a certain operating margin, for example, the tracking residual component is not minimum. .
[0182]
As described above, the method of detecting the residual component of the focus servo or tracking servo signal and determining the gain is the state where each servo operation is performed in a closed loop and the influence from other layers is included. This is effective in that the servo operation state can be adjusted.
[0183]
(Fifth embodiment)
Another method for learning the servo gain will be described. This embodiment relates to a method for obtaining a servo gain in two stages.
[0184]
FIG. 13 shows the procedure of the method for learning the servo gain. This method can be executed by the recording / reproducing apparatus 1000. However, the focus control unit 16 and the gain setting unit 7 shown in FIG. 1 have the configuration shown in FIG. 14, and the tracking control unit 17 and the gain setting unit 7 shown in FIG. 1 are shown in FIG. Assuming that
[0185]
In the following description, a method of learning the servo gain for the second information layer (for example, the information layer 227 shown in FIG. 10) will be described as a representative example. Needless to say, the servo gain can be learned in the same manner for information layers other than the second information layer (for example, the information layers 226 and 228 shown in FIG. 10).
[0186]
Servo gain learning is started in response to a signal indicating that learning of servo gain output from the system control system 8 is started.
[0187]
In the test area seek step 130, the optical pickup 3 is moved so that the test area 92 or the information area 91 shown in FIG.
[0188]
In the F offset application step 131, the focus drive circuit 33 (FIG. 14) sets the focus control to an open loop state, and applies the offset voltage provided by the F offset circuit 152 (FIG. 14) to the voice coil 15 (FIG. 1). As a result, the objective lens 12 is moved in a direction perpendicular to the recording medium 1.
[0189]
In the FE amplitude detection step 132, the FE amplitude detection circuit 35 (FIG. 14) generates a focus error signal corresponding to the second information layer from the focus error signal generated based on the light beams reflected by the plurality of information layers. The amplitude value of is detected.
[0190]
In the FE amplitude comparison step 133, the gain setting circuit 150 (FIG. 14) compares the amplitude value detected by the FE amplitude detection circuit 35 with the reference amplitude value.
[0191]
In the focus servo gain setting step 134, the gain setting circuit 150 (FIG. 14) sets the focus servo gain based on the comparison result between the detected amplitude value and the reference amplitude value.
[0192]
In the focus control ON process 135, the focus drive circuit 33 (FIG. 14) sets the focus control to a closed loop state. As a result, focus control based on the focus servo gain is started.
[0193]
In the TE amplitude measurement step 136, the tracking drive circuit 53 (FIG. 15) sets the tracking control to an open loop state, and moves the objective 12 in the radial direction of the recording medium 1. The TE amplitude detection circuit 54 (FIG. 15) detects the amplitude value of the tracking error signal.
[0194]
In the TE amplitude comparison step 137, the gain setting circuit 151 (FIG. 15) compares the amplitude value detected by the TE amplitude detection circuit 54 with the reference amplitude value.
[0195]
In the tracking servo gain setting step 138, the gain setting circuit 151 (FIG. 15) sets the tracking servo gain based on the comparison result between the detected amplitude value and the reference amplitude value.
[0196]
In the tracking control ON process 139, the tracking drive circuit 53 (FIG. 15) sets the tracking control to a closed loop state. As a result, tracking control based on the tracking servo gain is started.
[0197]
In the F offset application process 140, the focus drive circuit 33 (FIG. 14) sets the focus control to a closed loop state, and applies the offset voltage provided by the F offset circuit 152 (FIG. 14) to the voice coil 15 (FIG. 1). Thus, the objective lens 12 is moved in the direction perpendicular to the recording medium 1. However, the offset voltage applied to the voice coil 15 is smaller than the offset voltage applied to the voice coil 15 in the F offset application step 131 so that the focus control operation can maintain a closed loop. As a result, the objective lens 12 moves in a direction perpendicular to the recording medium 1 by a small distance compared to the F offset applying step 131.
[0198]
In the FE offset detection step 141, the FE offset detection circuit 153 (FIG. 14) detects the displacement amount (FE offset voltage) of the FE signal that varies according to the offset voltage applied to the voice coil 15 in the F offset application step 140. To do.
[0199]
In the FE offset voltage comparison step 142, the gain setting circuit 150 (FIG. 14) compares the FE offset voltage detected by the FE offset detection circuit 153 (FIG. 14) with the reference offset voltage. The reference offset voltage is obtained in advance as a displacement amount of the FE signal that varies according to the offset voltage applied to the voice coil 15 when a recording medium including a single information layer is used.
[0200]
In the focus servo gain setting step 143, the gain setting circuit 150 (FIG. 14) sets the focus servo gain based on the comparison result between the detected FE offset voltage and the reference offset voltage.
[0201]
In the T offset application process 144, the T offset circuit 153 (FIG. 15) applies a fixed offset voltage to the output of the tracking drive circuit 53 in a pulsed manner, thereby moving the objective lens 12 minutely in the tracking direction.
[0202]
In the TE offset detection step 145, the TE offset detection circuit 142 (FIG. 15) detects the displacement amount (TE offset voltage) of the TE signal that varies according to the offset voltage applied to the voice coil 15 in the T offset application step 144. To do.
[0203]
In the TE offset voltage comparison step 146, the gain setting circuit 151 (FIG. 15) compares the TE offset voltage detected by the TE offset detection circuit 154 (FIG. 15) with the reference offset voltage. The reference offset voltage is obtained in advance as a displacement amount of the TE signal that varies according to the offset voltage applied to the voice coil 15 when a recording medium including a single information layer is used.
[0204]
In the tracking servo gain setting step 147, the gain setting circuit 151 (FIG. 15) sets the tracking servo gain based on the comparison result between the TE offset voltage and the reference offset voltage.
[0205]
As described above, the focus servo gain is obtained in two stages (that is, the focus servo gain is obtained when the focus control is in the open loop state, and the focus servo gain is obtained when the focus control is in the closed loop state). Gain can be determined more precisely. Similarly, the tracking servo gain is obtained in two stages (that is, the tracking servo gain is obtained when the tracking control is in an open loop state, and the tracking servo gain is obtained when the tracking control is in a closed loop state). It can be determined more precisely.
[0206]
By performing steps 130 to 147 shown in FIG. 13 for the eight basic patterns (a) to (h) shown in FIG. 10, the servo gains corresponding to these basic patterns can be accurately determined. it can. Further, as described in the third embodiment, it is possible to reduce the time required for learning the servo gain by limiting the recording order in the information layer.
[0207]
Although the focus servo gain and tracking servo gain targeted by the present invention have been described here, the best condition of the focus servo gain and the tracking servo gain is obtained in each pattern area, and the focus offset amount and tracking offset amount are obtained. Further, the optimum recording / reproducing conditions may be obtained by performing the same method.
[0208]
The servo conditions corresponding to the respective recording patterns obtained here are stored in the system controller, and the servo conditions are controlled in correspondence with the recording state of the information area. In addition, it is effective to select an intermediate condition of the above-described recording pattern in an area where the recording state is complicatedly mixed.
[0209]
(Sixth embodiment)
In this method, the servo gain information obtained in advance corresponding to the recording state of each information layer is reproduced on the recording medium to guarantee a stable servo operation. The servo gain obtained by the methods of the third, fourth, and fifth embodiments is recorded in a specific area of the recording medium, for example, the management information area 93 in FIG. That is, almost the same parameters can be applied to the servo conditions obtained by the combination of the recording medium and the recording / reproducing apparatus, except when the recording medium or the recording / reproducing apparatus is deteriorated. Therefore, it is effective to write the identifier of the recording / reproducing apparatus and the servo condition in the management information area on the recording medium. According to this method, when the recording medium is mounted on the recording / reproducing apparatus, this management information area is reproduced, and when there is a recording history with the recording / reproducing apparatus, the reference signal is reproduced under the servo conditions described first. If the obtained servo state matches the contents of the management information, recording / reproduction is performed under the servo conditions. On the contrary, when the measurement result under the servo condition is different from the description content, the optimum servo condition is obtained by performing a learning process in which the servo condition is changed stepwise. When the above method is used, the servo condition learning time can be reduced for frequently used recording media.
[0210]
On the other hand, the influence of inter-layer interference between information layers is different for each recording medium, but the structure of the recording medium is the same, and those produced by the same manufacturing process tend to have the same tendency. For this reason, it is effective to learn the servo gain obtained by the methods of Embodiments 3, 4, and 5 in the manufacturing process of the recording medium and record the learning result in the management information area 93. . As a method of recording the learning result in the management information area 93, the first method and the second method can be considered. The first method is a method in which a learning result is formed on a substrate as uneven pit information used in a read-only recording medium. The first method can be said to be a simpler method, because once the servo condition value is obtained for a specific recording medium, it is not necessary to increase the subsequent manufacturing process. The second method is a method of measuring the servo condition for each recording medium at the time of manufacture and recording the result in the management information area 93. In this case, the management information area 93 is configured to be recordable and reproducible in the same manner as the information area 91. As a result, higher accuracy servo conditions can be set in advance, including the characteristic difference for each recording medium. As described above, the servo gain information including the servo gain and the tracking gain corresponding to the unrecorded state and the recorded state of each information layer is obtained in the manufacturing process, and forms of the first method and the second method on the recording medium 1 Is recorded in the management information area 93. As a result, when the user records / reproduces the information signal on the recording medium, the recording medium 1 can be mounted on the recording / reproducing apparatus 1000, and the servo gain information in the management information area 93 can be immediately read and operated. The time required for servo learning of the playback device can be shortened.
[0211]
In the six embodiments described so far, the method for obtaining the servo condition of the second information layer among the three information layers has been described. However, the present invention can be similarly applied to other information layers. And it can be applied to all cases where there are a plurality of information layers.
[0212]
【The invention's effect】
As described above, the present invention uses the focus error signal corresponding to the target information layer with respect to the servo gain fluctuation that occurs depending on the recording state / unrecorded state of the information layer other than the target information layer. The focus servo gain can be compensated, and the tracking servo gain can be compensated using the tracking error signal. This makes it possible to realize a stable servo operation of the multilayer recording medium.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a recording / reproducing apparatus 1000 according to an embodiment of the present invention.
2A is a block diagram showing an example of the configuration of a recording medium 1 and an example of the configuration of an optical system for the recording medium 1. FIG.
FIG. 2B is a block diagram showing an example of the configuration of the photodetector 13 and an example of the configuration of the preamplifier 14;
FIG. 3 is a block diagram showing an example of the configuration of the focus control unit 16 and an example of the configuration of the gain setting unit 7;
FIG. 4 is a diagram showing how a focus error signal (FE signal) 31s changes.
FIG. 5 is a block diagram illustrating an exemplary configuration of the tracking control unit 17 and an exemplary configuration of the gain setting unit 7;
FIG. 6 is a diagram showing a waveform of a tracking error signal 51s
FIG. 7 is a view showing a plurality of guide tracks 71 formed on one of a plurality of information layers (target information layer).
FIG. 8 is a block diagram illustrating an exemplary configuration of the tracking control unit 17 and an exemplary configuration of the gain setting unit 7;
FIG. 9 is a diagram showing a configuration of a recording medium 1 for learning servo gain.
10 is a diagram showing an example of a cross section of a test area 92 of the recording medium 1. FIG.
FIG. 11 is a flowchart showing a procedure of a method for learning a servo gain.
FIG. 12 is a flowchart showing a procedure of a method for learning a servo gain.
FIG. 13 is a flowchart showing a procedure of a method for learning a servo gain.
FIG. 14 is a block diagram showing an example of the configuration of the focus control unit 16 and an example of the configuration of the gain setting unit 7;
FIG. 15 is a block diagram showing an example of the configuration of the tracking control unit 17 and an example of the configuration of the gain setting unit 7;
[Explanation of symbols]
1 Recording medium
7 Gain setting section
12 Objective lens
16 Focus control unit
17 Tracking controller
31 Differential amplifier circuit
32 Gain setting circuit
34 Focus offset circuit
51 Differential amplifier circuit
52 Gain setting circuit

Claims (1)

A recording / reproducing apparatus for a recording medium including a plurality of information layers,
A focus error signal is generated from the light beam reflected by the recording medium, and the light beam applied to the recording medium follows the target information layer among the plurality of information layers according to the focus error signal. A focus control unit that performs focus control to
A tracking error signal is generated from the light beam reflected by the recording medium, and the light beam irradiated to the recording medium is formed on a target information layer among the plurality of information layers according to the tracking error signal. A tracking control unit that performs tracking control so as to follow one of the plurality of tracks,
The plurality of tracks include wobble tracks that meander in a predetermined cycle along the track direction,
A wobble amplitude detection circuit for detecting a wobble amplitude value of a wobble signal included in the tracking error signal in a state where the tracking control is in a closed loop;
A recording / reproducing apparatus , further comprising: a gain setting unit that compares the wobble amplitude value with a reference amplitude value and sets the gain of the focus control according to the comparison result .

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