JP3846590B2 - Optical disk drive and focus control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc driving apparatus and a focus control method, and more particularly to an optical disc driving apparatus and a focus control method that enable quick and reliable focus control for an optical disc having two or more recording layers.
[0002]
[Prior art]
An optical disc typified by a compact disc has only one information recording layer. In recent years, there has been a demand for a larger recording capacity. This increase in capacity can be answered by, for example, reducing the track pitch or reducing the size of the pits. In order to further increase the capacity, an optical disc in which a plurality of recording layers is formed has been proposed.
[0003]
FIG. 21 shows a configuration example of such an optical disc. In this optical disc, a recording layer A is formed on a disc substrate 101, and further a recording layer B is formed thereon. A protective film 102 is further formed on the recording layer B.
[0004]
The disk substrate 101 is made of a transparent material such as polycarbonate, the recording layer A is made of a semi-transparent film, and the recording layer B is made of a total reflection film such as aluminum.
[0005]
When reproducing information from the recording layer A, the code L₁As shown, the laser beam is focused on the recording layer A, and the reflected light from the recording layer A is received.
[0006]
On the other hand, when the information recorded in the recording layer B is reproduced, the code L₂As shown, the laser beam is focused on the recording layer B through the recording layer A composed of a translucent film. Then, the reflected light is received through the recording layer A. Thus, since the recording layer A is composed of a semi-transparent film, information on the recording layer B can be read through the recording layer A.
[0007]
[Problems to be solved by the invention]
When the recording layer to be reproduced is changed to the recording layer B (or recording layer A) while the laser beam is focused on the recording layer A (or recording layer B), a jump pulse is applied to the focus servo loop. Then, after jumping the optical head in the direction of the new recording layer, the focus servo may be applied so that the focus error signal is reduced on the new recording layer.
[0008]
However, due to variations in optical heads and disks, the position where the focus error signal is minimum is not necessarily the correct focus position. For this reason, usually, an offset signal is added to the focus error signal to obtain an optimum focus state.
[0009]
However, in the conventional apparatus, the offset value is constant even when information is reproduced from any recording layer. Accordingly, there is a problem that it is difficult to stably reproduce information from a plurality of recording layers.
[0010]
The present invention has been made in view of such a situation, and enables information to be recorded or reproduced accurately on any of a plurality of recording layers quickly and reliably.
[0013]
[Means for Solving the Problems]
  Of the present inventionFirstThe optical disk drive device on the side includes an irradiation unit that irradiates light for recording or reproducing information on the optical disc, a focus control unit that controls a focus state of light irradiated by the irradiation unit in response to a focus error signal, Generating means for generating an offset signal to be added to the focus error signal, and when the offset signal is generated by the generating means, the amplitude of the tracking error signal corresponding to the tracking state of the light irradiated by the irradiating means, on the recording layer of the optical disc Detection means for detecting the amplitude of the RF signal corresponding to the recorded information or the jitter of the signal reproduced from the optical disc, and the tracking error signal for the increase in the offset signal when the offset signal is sequentially increased from the minimum value The absolute value of the rate of change of the amplitude is a predetermined first threshold value A first intermediate value or offset that is an intermediate value between the value of the first offset signal that is less than the first threshold from the top and the value of the second offset signal that is less than the first threshold and greater than or equal to the first threshold. The absolute value of the rate of change in the amplitude of the RF signal with respect to the increase in signal is a value of the third offset signal in which the absolute value of the RF signal is greater than or equal to a predetermined second threshold value and less than the second threshold value. The second intermediate value, which is an intermediate value with respect to the value of the fourth offset signal, or the absolute value of the rate of change in jitter with respect to the increase in the offset signal is less than the predetermined third threshold value and greater than or equal to the third threshold value. The generation means uses the third intermediate value, which is an intermediate value between the value of the fifth offset signal and the value of the sixth offset signal that is greater than or equal to the third threshold and less than the third threshold, as the optimum value of the offset signal. The generated offset signal is set to its optimum value. Gosuru characterized in that it comprises an offset control unit.
  Of the present inventionSecondThe side focus control method searches for the optimum focus offset position of the light for recording or reproducing information on the optical disc by changing the value of the offset signal to be added to the focus error signal, and When the amplitude of the tracking error signal corresponding to the tracking state, the amplitude of the RF signal corresponding to the information recorded on the recording layer of the optical disc, or the jitter of the signal reproduced from the optical disc is detected and the recording layer is changed, The first offset signal in which the absolute value of the change rate of the amplitude of the tracking error signal with respect to the increase in the offset signal is less than the first threshold value when the offset signal is sequentially increased from the minimum value. And the value of the second offset signal that is less than the first threshold and greater than or equal to the first threshold. A first intermediate value that is a value, a value of a third offset signal in which the absolute value of the rate of change of the amplitude of the RF signal with respect to an increase in the offset signal is less than the second threshold value and the second threshold value A second intermediate value that is an intermediate value between the value of the fourth offset signal that is less than the threshold value and greater than or equal to the second threshold value, or the absolute value of the rate of change in jitter with respect to the increase in the offset signal is a predetermined third value. A third intermediate value, which is an intermediate value between the value of the fifth offset signal that becomes less than the third threshold and less than the third threshold and the value of the sixth offset signal that becomes less than the third threshold and less than the third threshold, As an optimum value of the offset signal corresponding to the recording layer, the offset signal is controlled to an optimum value corresponding to the recording layer.
[0014]
  Of the present inventionFirstIn the aspect, when the offset signal to be added to the focus error signal is generated, the amplitude of the tracking error signal corresponding to the light tracking state, the amplitude of the RF signal corresponding to the information recorded on the recording layer of the optical disc, or When the jitter of the signal reproduced from the optical disc is detected and the offset signal is sequentially increased from the minimum value, the absolute value of the change rate of the amplitude of the tracking error signal with respect to the increase of the offset signal is greater than or equal to a predetermined first threshold value. A first intermediate value that is an intermediate value between a value of the first offset signal that is less than the first threshold value and a value of the second offset signal that is less than the first threshold value and greater than or equal to the first threshold value; A third offset at which the absolute value of the rate of change of the amplitude of the RF signal with respect to the increase is greater than or equal to a predetermined second threshold and less than the second threshold The second intermediate value that is an intermediate value between the value of the signal and the value of the fourth offset signal that is less than the second threshold and greater than or equal to the second threshold, or the absolute value of the change rate of jitter with respect to the increase of the offset signal Is an intermediate value between the value of the fifth offset signal that becomes less than or equal to the third threshold and less than the third threshold and the value of the sixth offset signal that becomes less than the third threshold and more than the third threshold. The third intermediate value is the optimum value of the offset signal, and the offset signal is controlled to the optimum value.
  Of the present inventionSecondIn the aspect, the optimum focus offset position of the light for recording or reproducing information on the optical disc is searched by changing the value of the offset signal added to the focus error signal, and the tracking state of the light irradiated on the optical disc is set. When the amplitude of the corresponding tracking error signal, the amplitude of the RF signal corresponding to the information recorded on the recording layer of the optical disc, or the jitter of the signal reproduced from the optical disc is detected and the recording layer is changed, the offset signal is A value of the first offset signal in which the absolute value of the rate of change in the amplitude of the tracking error signal with respect to the increase of the offset signal when the value is sequentially increased from the minimum value becomes less than the first threshold value from a predetermined first threshold value; It is an intermediate value between the value of the second offset signal that is less than the first threshold and greater than or equal to the first threshold. The first intermediate value, the value of the third offset signal in which the absolute value of the rate of change of the amplitude of the RF signal with respect to the increase in the offset signal is less than the second threshold and less than the second threshold is less than the second threshold. From the second intermediate value, which is an intermediate value with the value of the fourth offset signal that is greater than or equal to the second threshold, or from the absolute value of the rate of change in jitter with respect to the increase in the offset signal is less than the predetermined third threshold A third intermediate value that is an intermediate value between the value of the fifth offset signal that is equal to or greater than the third threshold value and the value of the sixth offset signal that is equal to or greater than the third threshold value and less than the third threshold value is the recording layer. As the optimum value of the offset signal corresponding to the offset signal, the offset signal is controlled to the optimum value corresponding to the recording layer.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of the configuration of an optical disk reproducing apparatus to which the optical disk driving apparatus of the present invention is applied. In FIG. 1, an optical disc 1 has a plurality of (two or more) recording layers. For example, in the case of two layers, the optical disc 1 is configured as shown in FIG.
[0016]
The optical disk 1 is rotated by a spindle motor 2 at a predetermined speed. The optical head 3 is configured to irradiate the optical disc 1 with laser light and receive reflected light from the optical disc 1.
[0017]
The PLL circuit 5 binarizes the RF signal output by the optical head 3 reproducing the signal recorded on the optical disc 1 to generate a binarized RF signal, and extracts a clock included in the RF signal. Generate a synchronous clock signal. The CLV circuit 6 receives the binarized RF signal output from the PLL circuit 5 and the synchronous clock signal, and outputs an error signal of both phases. The switch 8 is controlled by the control circuit 17 and selects one of the output of the CLV circuit 6 or the output of the initial drive circuit 7 and outputs it to the spindle motor 2.
[0018]
The data decoder 4 receives the binary RF signal output from the PLL circuit 5 and the synchronous clock signal, and decodes the binary RF signal with reference to the synchronous clock signal.
[0019]
The optical head 3 generates a focus error signal according to the principle of the astigmatism method, for example, and generates a tracking error signal according to the principle of the push-pull method, for example. The focus servo circuit 9 receives a focus error signal output from the optical head 3, drives the focus coil 12 in response to the focus error signal, and focuses the optical head 3 in a direction perpendicular to the optical disk 1. It is made to control. The tracking servo circuit 10 receives the tracking error signal output from the optical head 3, drives the tracking coil 13 in response to the tracking error signal, and controls the optical head 3 in a direction perpendicular to the track of the optical disk 1. It is made to do.
[0020]
A signal output from the tracking servo circuit 10 is supplied to the sled servo circuit 15, and the sled servo circuit 15 drives the sled motor 16 in response to the signal to move the optical head 3 in the radial direction of the optical disc 1. Has been made. The control circuit 17 controls the switch 8 in addition to the focus servo circuit 9, the tracking servo circuit 10, and the thread servo circuit 15.
[0021]
In this embodiment, a tracking error signal maximum amplitude search circuit 31 is also provided. This tracking error signal maximum amplitude search circuit 31 has a level detection circuit 41, which detects the level of the tracking error signal output from the optical head 3 and outputs the detection result to the control circuit 42. It is made like that. The control circuit 42 detects the optimum focus position of the optical head 3 from the output of the level detection circuit 41.
[0022]
When the focus offset position of the optical head 3 with respect to the recording layer of the optical disk 1 is changed, the tracking error signal changes as shown in FIG. In other words, when the position of the optical head 3 is adjusted to the optimum focus offset position (optimum point), the amplitude of the tracking error signal becomes maximum, and when it deviates from the optimum point, the amplitude of the tracking error signal becomes small. The control circuit 42 obtains the optimum point according to this principle.
[0023]
Then, the control circuit 42 controls the offset generation circuit 43 in order to obtain the optimum point, and generates an offset signal having a predetermined value. The offset signal is added to the focus error signal output from the optical head 3 in the adder 32, and the output of the adder 32 is output to the focus servo circuit 9.
[0024]
An optimum focus offset position storage circuit 33 is connected to the control circuit 42 of the tracking error signal maximum amplitude search circuit 31. The optimum focus offset position storage circuit 33 stores data of the optimum focus offset position obtained as a result of the search by the tracking error signal amplitude maximum search circuit 31.
[0025]
Next, the operation will be described with reference to the flowchart of FIG. First, in step S1, a disk activation process is executed. That is, when the optical disc 1 is mounted on the playback device, the control circuit 17 controls the sled servo circuit 15 and drives the sled motor 16 to move the optical head 3 to a predetermined reference position of the optical disc 1, for example, the innermost circumference. Move to the track position. Further, the control circuit 17 switches the switch 8 to the initial drive circuit 7 side and supplies the initial drive signal output from the initial drive circuit 7 to the spindle motor 2 via the switch 8. As a result, the spindle motor 2 is driven and rotated.
[0026]
Further, the control circuit 17 controls the focus servo circuit 9 to execute focus servo. The optical head 3 irradiates a default recording layer (for example, recording layer A in FIG. 21) of the optical disc 1 with laser light, receives the reflected light, and generates a focus error signal and a tracking error signal. The focus error signal is supplied to the focus servo circuit 9 via the adder 32, and the focus servo circuit 9 drives the focus coil 12 in response to the focus error signal to determine the position of the optical head 3 in the focus direction. Control.
[0027]
The PLL circuit 5 receives an RF signal input from the optical head 3 that reproduces and outputs a signal recorded on the recording layer A of the optical disc 1, and binarizes the RF signal to generate a binarized RF signal. At the same time, a synchronous clock signal synchronized with the synchronous signal included in the RF signal is generated. The CLV circuit 6 compares the phases of the synchronous clock signal and the binarized RF signal and outputs an error signal thereof. The control circuit 17 switches the switch 8 to the CLV circuit 6 side when a predetermined time elapses after the spindle motor 2 is activated or when the rotation of the spindle motor 2 reaches a predetermined rotation speed. As a result, the error signal output from the CLV circuit 6 is supplied to the spindle motor 2 and the CLV servo is executed. Thereby, the optical disk 1 is driven so that the linear velocity is constant.
[0028]
Next, it progresses to step S2 and an optimal focus search process is performed. The optimum focus search process will be described later. The control circuit 42 of the tracking error signal maximum amplitude search circuit 31 controls the offset generation circuit 43 to add a predetermined offset signal to the focus error signal via the adder 32. . When the focus state is not appropriate, the amplitude of the tracking error signal output from the optical head 3 is small, and when the focus state is in an optimum state, the amplitude of the tracking error signal is maximum. Therefore, the amplitude of the tracking error signal is detected by the level detection circuit 41, and the control circuit 42 determines whether or not the tracking error signal having the maximum amplitude is obtained. When it is determined that a tracking error signal having the maximum amplitude is obtained, the offset value generated by the offset generation circuit 43 at that time is obtained.
[0029]
Then, the process proceeds to step S3, and the optimum focus offset value obtained in step S2 is stored in the optimum focus offset position storage circuit 33.
[0030]
When the optimum focus offset position is obtained in one recording layer (for example, recording layer A in FIG. 21), the process proceeds to step S4, where a similar search has been performed for all recording layers of the optical disc 1. If it is determined that the search has not been performed for all the recording layers, the process proceeds to step S5, and the recording layer changing process is executed. That is, the control circuit 17 controls the focus servo circuit 9 to add a jump pulse to the focus error signal (or generate a jump pulse instead of the focus error signal). As a result, the focus coil 12 drives the optical head 3 in the focus direction in response to this jump pulse, and the laser beam focused on the recording layer A until now is focused on the recording layer B. When the supply of the jump pulse is stopped, the normal focus servo loop is closed again, and the laser generated by the optical head 3 in the recording layer B is applied by applying servo so that the focus error signal is minimized. The light is focused.
[0031]
Then, the process returns to step S2, and the optimum focus search process is executed in the recording layer B. Then, the obtained optimum focus offset value is stored in the storage circuit 33 in step S3.
[0032]
As described above, when N recording layers are formed on the optical disc 1, N optimum focus offset values are stored in the optimum focus offset position storage circuit 33.
[0033]
When the optimum focus offset values (positions) of all the recording layers of the optical disc 1 are stored, the process proceeds from step S4 to step S6, and the focus position is changed to a preset default recording layer. For example, the control circuit 17 controls the focus servo circuit 9 to generate a necessary number of jump pulses to focus the laser beam on the recording layer A closest to the disk substrate 101.
[0034]
At this time, in step S 7, the control circuit 42 of the tracking error signal maximum amplitude search circuit 31 reads the focus offset value of the recording layer A stored in the optimum focus offset position storage circuit 33 and supplies it to the offset generation circuit 43. . The offset generation circuit 43 generates an offset signal corresponding to the offset value, and the offset signal is added to the focus error signal in the adder 32 and supplied to the focus servo circuit 9. Since the focus coil 12 is driven by a focus error signal to which an optimum offset value is added by the focus servo circuit 9, an optimum focus state is realized in the recording layer A.
[0035]
Next, the process proceeds to step S8 and waits until a change of the recording layer to be reproduced is instructed. When the change of the recording layer is instructed, the process proceeds to step S9 and the focus position is changed to the designated recording layer. To do. That is, at this time, the control circuit 17 controls the focus servo circuit 9, generates a predetermined jump pulse, and changes the focus position from the recording layer A to the recording layer B, for example.
[0036]
Next, in step S10, an optimum offset value reading process for the designated recording layer is executed. That is, the control circuit 42 of the tracking error signal maximum amplitude search circuit 31 reads the offset value of the recording layer B stored in the optimum focus offset position storage circuit 33 and outputs it to the offset generation circuit 43. The offset generation circuit 43 generates an offset signal corresponding to the offset value, and the adder 32 adds the offset signal to the focus error signal. Since the focus servo circuit 9 drives the focus coil 12 in response to the output of the adder 32, an optimum focus state is realized in the recording layer B (a focus that maximizes the tracking error signal amplitude). State is realized).
[0037]
Thereafter, the process returns to step S8, and the subsequent processing is repeatedly executed.
[0038]
Next, the optimum focus search will be described. As described above, at the time of this search, tracking servo has not been started yet. As a result, the optical head 3 is in a state of periodically traversing a plurality of tracks of the optical disc 1. That is, since the rotation centers of the optical disk 1 and the spindle motor 2 are deviated due to eccentricity, the information reproduction point (light spot by the laser beam) of the optical head 3 periodically crosses a plurality of tracks unless tracking servo is applied. It will be. As a result, the optical head 3 outputs a tracking error signal as shown in FIG. 4, for example. As shown in the figure, the tracking error signal changes periodically.
[0039]
The level detection circuit 41 of the tracking error signal amplitude maximum search circuit 31 detects the peak hold value and the bottom hold value of the tracking error signal, and detects the difference between them as the amplitude of the tracking error signal. The amplitude detection signal is supplied to the control circuit 42. The amplitude of the tracking error signal changes corresponding to the focus offset value of the optical head 3 as shown in FIG. The control circuit 42 detects the optimum point of the focus offset at which the maximum amplitude of the tracking error signal is obtained by a so-called hill climbing method.
[0040]
That is, as shown in FIG. 5, the offset signal output from the offset generation circuit 43 is expressed as S₀, S₁, S₂, ... and α are sequentially increased. And three consecutive sampling points S_i-1, S_i, S_{i + 1}Amplitude value R of tracking error signal at_i-1, R_i, R_{i + 1}And R_iIs maximized (R_i-1<R_i> R_{i + 1}The sampling point S_iIs the optimum point. Therefore, the control circuit 42 controls the offset generation circuit 43 to output a predetermined initial value and an offset signal that changes by α thereafter, add it to the focus error signal in the adder 32, and output it to the focus servo circuit 9.
[0041]
FIG. 6 shows a processing example when the focus offset position is adjusted by this hill climbing method. First, in step S21, the initial value S is added to Sn.₀Set. Then, set the focus offset position to Sn (in this case, Sn = S₀), The amplitude value of the tracking error signal in that case is measured, and the measurement result is Rn (in this case, Rn = R₀).
[0042]
That is, the control circuit 42 sends an offset signal S to the offset generation circuit 43.₀Is generated. The focus servo circuit 9 receives the offset signal S by the adder 32.₀The focus coil 12 is controlled in response to the focus error signal to which is added, and the focus offset of the optical head 3 is adjusted.
[0043]
At this time, the level detection circuit 41 detects the amplitude of the tracking error signal output from the optical head 3 and outputs it to the control circuit 42. The control circuit 42 sets the amplitude value of the tracking error signal detected at this time to Rn (in this case, Rn = R₀).
[0044]
Next, proceeding to step S22, Sn +₀And add the value of α. That is, the following equation is calculated.
Sn + = S₀+ Α
[0045]
Then, the offset signal Sn + (= S₁). That is, the offset generation circuit 43 generates an offset value that is larger than the offset signal Sn generated in step S21 by α. Since the focus servo circuit 9 controls the focus coil 12 in response to the focus error signal to which the offset value is added, the optical head 3 further changes the focus offset of the optical head 3 by the offset value α. .
[0046]
At this time, the level detection circuit 41 detects the amplitude of the tracking error signal output from the optical head 3. The control circuit 42 determines the amplitude of the tracking error signal detected by the level detection circuit 41 at this time as Rn + (in this case, R₀+ = R₁).
[0047]
Next, the process proceeds to step S23, where Sn-₀Set a value smaller by α. That is, the following equation is calculated.
Sn- = S₀-Α
[0048]
That is, the control circuit 42 controls the offset generation circuit 43, and the offset signal Sn generated in step S21 (in this case, Sn = S₀) Is generated by a value smaller than α. Since the focus error signal to which the offset signal Sn− is added is supplied to the focus coil 12 via the focus servo circuit 9, the optical head 3 has an offset value S.₀The focus offset is changed by the offset value −α from the case where the error occurs.
[0049]
At this time, the level detection circuit 41 detects the amplitude of the tracking error signal output from the optical head 3 and outputs it to the control circuit 42. The control circuit 42 sets the amplitude value of the tracking error signal at this time to Rn− (in this case, Rn− = R₀Set to-).
[0050]
As a result of the processing in steps S21 to S23 described above, the offset value added to the focus error signal is changed to the initial value S as shown in FIG.₀Amplitude value Rn (= R) of the tracking error signal when set to₀) And the amplitude value Rn + (= R of the tracking error signal when the offset signal is increased by α.₀+ = R₁) And the amplitude value Rn − (= R of the tracking error signal when the offset signal is reduced by α.₀-) Is obtained.
[0051]
Therefore, the process proceeds to step S24, where it is determined whether Rn is equal to or greater than Rn + and whether Rn is equal to or greater than Rn−. That is, it is determined whether Rn is larger than Rn− and Rn + (whether Rn is the maximum value).
[0052]
Usually, as shown in FIG.₀The amplitude Rn (= R of the tracking error signal when₀) Is an amplitude value Rn − (= R when the offset signal is small by α.₀The amplitude Rn + (= R) of the tracking error signal when the offset signal is larger by α than₀+ = R₁) Is smaller. Therefore, in this case, the process proceeds to step S25, and it is determined whether or not Rn + is larger than Rn−. In this case, Rn + (= R₀+ = R₁) Is Rn-(= R₀Since it is larger than −) (because it is a section rising to the right in FIG. 5), the process proceeds to step S26.
[0053]
In step S26, Sn− is replaced with Sn (= S₀) Is set. Then, to the new Sn, Sn + (= S₁) And set Rn− to the previous Rn (= R₀) And Rn + (= R)₁) Is set. Further, a new Sn (= S₀+ Α = S₁) Plus α (= S₀+ 2α = S₂) Is set. That is, the following equation is calculated.
Sn + = Sn + α
[0054]
The control circuit 42 controls the offset generation circuit 43 and uses Sn + (= S₂). That is, Sn + (= S generated in step S22₀Offset Sn + (= S larger than + α) by α₀+ 2α = S₂). Then, the amplitude of the tracking error signal detected at that time is set to Rn + (= R₁+ = R₂).
[0055]
That is, as a result, in the state shown in FIG. 5, three sampling points S moved to the right side by α from the previous case.₀, S₁, S₂The amplitude value of the tracking error signal at Rn − (= R₀), Rn (= R₁) And Rn + (= R₂) Is set.
[0056]
Then, it returns to step S24 and it is determined whether Rn is larger than Rn- and Rn +. If Rn is not the maximum value, the process proceeds to step S25, and it is determined again whether Rn + is greater than Rn−. When Rn + is larger than Rn−, the process proceeds to step S26, and the same processing is repeated.
[0057]
Then, when the section to be sampled moves to the right in FIG. 5 and Sn reaches the optimum point, the amplitude value Rn obtained at that time is larger than Rn− and larger than Rn +. That is, Rn becomes the maximum value. Therefore, in this case, the process proceeds from step S24 to step S28, and the value of Sn at that time is set as an optimum value that maximizes the amplitude Rn of the tracking error signal. That is, the control circuit 42 subsequently generates the offset signal Sn as the optimum value from the offset generation circuit 43 thereafter.
[0058]
On the other hand, when sampling is performed in the lower right section in FIG. 5, the value of Rn + is smaller than Rn−. Accordingly, in this case, the process proceeds from step S25 to step S27, Sn is set as Sn +, Sn is set as Sn−, Rn + is set as Rn, and Rn is set as Rn +. , Rn- until then is set. Then, a value smaller by α than the new Sn is set to Sn−. That is, the following equation is calculated.
Sn- = Sn-α
[0059]
That is, in FIG. 5, the sampling point on the left side is sampled by Sn-. Then, the amplitude value of the tracking error signal when the offset signal Sn− is generated from the offset generation circuit 43 is detected, and the detected amplitude value is set to Rn−.
[0060]
Then, the process returns to step S24, and it is determined whether Rn is larger than Rn− and Rn +. In FIG. 5, in the downward-sloping section, Rn is still smaller than Rn−, so the process proceeds to step S25, further proceeds from step S25 to step S27, and the same processing is repeated. Then, when the sampling point sequentially advances to the left (in the direction of the optimum point) in FIG. 5 and Sn reaches the optimum point, Rn is larger than Rn + and larger than Rn−. At this time, the process proceeds from step S24 to step S28, and the value of the offset signal Sn at that time is set to the optimum value. Thereafter, the control circuit 42 causes the offset generation circuit 43 to continuously generate the optimum value.
[0061]
In the above, the optimum point (maximum value) is detected by the so-called hill-climbing method, but the optimum point can be obtained as shown in FIG. 7, for example. That is, in the embodiment of FIG. 7, the offset signal is sequentially changed by α, and S₀First, all of the interval from to Sn is sampled. At that time, the offset signal corresponding to the sudden rising change point of the tracking error signal obtained by sampling is expressed as Sm.₁The offset signal corresponding to the sudden downward change point of the tracking error signal is detected as Sm₂Detect as. And change point Sm₁And Sm₂The middle point of is the optimum point (adjustment point).
[0062]
FIG. 8 shows a processing example in the case of obtaining the optimum point by the method shown in FIG. In this embodiment, first, in step S31, 0 is initially set to the variable n, and the following equation is calculated in step S32.
S [n] = SMIN + α × n
[0063]
Here, SMIN represents a minimum value of the offset adjustment value, and α represents a width for changing the offset signal on the step.
[0064]
In this case, since n = 0, S [0] is set to SMIN.
[0065]
The control circuit 42 controls the offset generation circuit 43 to generate this S [n] (in this case, S [0] = SMIN). Then, the amplitude of the tracking error signal at this time is detected by the level detection circuit 41, and the value is set to R [n] (= R [0]).
[0066]
In step S33, the variable n is incremented by 1 (n = 1). It is determined whether or not the variable n incremented in step S34 is smaller than NUM. This NUM is a value obtained by (SMAX−SMIN) / α, where SMAX is the maximum offset value. That is, it represents the sampling number of the offset scan range.
[0067]
If n is smaller than NUM, not all sampling points have been sampled yet, so the process returns to step S32 and the following equation is calculated.
S [n] = SMIN + α × n
[0068]
That is, in this case, a value larger by α than SMIN is set as the offset signal S [1]. Then, the amplitude of the tracking error signal when the offset signal S [1] is generated is measured, and the value is set as R [1].
[0069]
Thereafter, the process proceeds to step S33, where the variable n is incremented by 1, and in this case, n = 2. If it is determined in step S34 that the variable n (= 2) is smaller than NUM, the process returns to step S32 and the same process is repeatedly executed. In this way, S shown in FIG.₀Amplitude value R of the tracking error signal at sampling points from 1 to Sn₀To Rn are obtained.
[0070]
As described above, when the sampling of the search range is completed, the variable n becomes equal to NUM. Therefore, the process proceeds from step S34 to step S35, and the variable n is initialized to 1. In step S36, whether or not the difference between the amplitude value R [n] at the current reference point and the previous amplitude value R [n-1] is larger than a preset reference value Th. Determined. In this case, it is determined whether or not the value of R [1] -R [0] is greater than Th. As shown in FIG. 7, since the first period of the sampling range has an upward characteristic, R [1] is sufficiently larger than R [0] (the difference (R [1] −R [0 ]) Is greater than Th). Then, it progresses to step S37 and changes point Sm₁As described above, a value between sampling points S [n] and S [n−1] is set. That is, the following equation is calculated.
Sm₁= (S [n] + S [n-1]) / 2
[0071]
In this case, the point between S [1] and S [0] is Sm₁Set to
[0072]
In step S38, the variable n is incremented by 1 (n = 2). In step S39, it is determined whether the variable n is smaller than NUM. When the variable n is smaller than NUM, the process returns to step S36, and it is determined whether or not the value of R [2] -R [1] is larger than Th. As shown in FIG. 7, during the period in which the tracking error signal changes greatly, the difference between the two sampling values is larger than the reference value Th. Therefore, the process proceeds to step S37 again, and Sm₁To (S [2] + S [1]) / 2. That is, the value on the right side by α is Sm₁Will be set to.
[0073]
In step S38, the variable n is incremented by 1 again to set n = 3, the process returns from step S39 to step S36, and the same process is repeated.
[0074]
Then, as the sampling point moves to the right side in FIG. 7, the change rate of the tracking error signal gradually decreases. When it is determined that the value of R [n] −R [n−1] is smaller than Th, the process proceeds from step S36 to step S40. That is, at this time, Sm₁Includes a change point (abrupt upward change point) from a section where the change rate of the amplitude of the tracking error signal is large to a section where the amplitude is small.₁Will be set as
[0075]
In step S40 and subsequent steps, from a period in which the rate of change in the amplitude of the tracking error signal gradually decreases, a change point that decreases suddenly becomes a steep downward change point Sm.₂To ask for.
[0076]
For this reason, in step S40, it is determined whether or not the value of R [n−1] −R [n] is smaller than the reference value Th. As shown in FIG. 7, the left sampling value R [n-1] is smaller than the right sampling value R [n] (upward period) and the right sampling value R [n]. However, even if it is smaller than the left sampling value R [n−1], the value of R [n−1] −R [n] is smaller than the reference value Th in a period in which the difference is small. Therefore, the process proceeds from step S40 to step S41, where Sm₂Is set to a value between S [n] and S [n−1]. That is, the following equation is calculated.
Sm₂= (S [n] + S [n-1]) / 2
[0077]
In step S42, n is incremented by 1. In step S43, it is determined whether the variable n is smaller than NUM-1 (whether the search range has not yet reached the right end in FIG. 7). When the variable n is smaller than NUM-1, the process returns to step S40, and the same processing is repeated for two sample values on the right side by one sample in FIG. If the difference between the two sample values is smaller than the reference value Th, the process proceeds again to step S41, where Sm₂Is set to an intermediate value between the two sampling points.
[0078]
In this way, when the sampling point sequentially moves in the right direction in FIG. 7 and the sampling value R [n] on the right side in the drawing becomes smaller than the sampling value R [n−1] on the left side, the difference between the two ( R [n−1] −R [n]) is equal to or larger than the reference value Th. At this time, Sm₂Is set to an intermediate value between sampling points S [n−1] and S [n−2]. And the value at this time is a steep downward change point Sm₂It is said.
[0079]
As described above, the sudden change point Sm at step S37.₁In step S41, sudden change point Sm₂Is obtained, the process proceeds to step S44, where the change point Sm₁And Sm₂The intermediate point is obtained as the optimum point. That is, (Sm₁+ Sm₂) / 2 is set as the optimum point.
[0080]
When it is determined in step S39 that the variable n is equal to or greater than NUM, the process proceeds from step S39 to step S40. If it is determined in step S43 that the variable n is equal to or greater than NUM-1, the process proceeds from step S43 to step S44.
[0081]
In the embodiment shown in FIG. 3, when the optical disc 1 is mounted on a playback device, the optimum focus offset position in all the recording layers of the optical disc 1 is searched in advance and stored. It is also possible to search for the optimum focus offset position each time it is changed.
[0082]
The flowchart of FIG. 9 represents a processing example in this case. That is, first, in step S51, the process waits until a change of the recording layer for focusing light is commanded. When the change is commanded, the process proceeds to step S52, and a jump pulse to be focused on the designated recording layer is detected. Generated in the focus servo circuit 9. As a result, the optical head 3 jumps in the focus direction to a position where it can focus on the designated recording layer.
[0083]
In step S53, a process for searching for the optimum focus position in the recording layer that has just jumped is executed. This optimum focus search process is the same as the process in step S2 in FIG.
[0084]
When the optimum focus search process is completed in step S53, the process returns to step S51, and the same process is repeatedly executed. That is, such processing is performed every time the recording layer is changed.
[0085]
Therefore, in this case, as shown in FIG. 10, the control circuit 42 of the tracking error signal amplitude maximum search circuit 31 of the reproducing apparatus of the optical disc 1 is an offset signal that maximizes the amplitude of the tracking error signal detected by the level detection circuit 41. Is generated in the offset generation circuit 43, and thereafter, the offset signal is continuously generated in the offset generation circuit 43. As a result, the maximum focus offset position storage circuit 33 shown in FIG. 1 is not necessary in this embodiment.
[0086]
FIG. 11 shows still another operation example. In the embodiment of FIG. 9, the optimum focus search process is executed every time the recording layer is changed. However, if the recording layer is changed, data can be actually reproduced every time the recording layer is changed. It takes time to be able to do it. The embodiment of FIG. 11 makes it possible to shorten this time.
[0087]
That is, first, in step S61, the process waits until the recording layer change is instructed. When the recording layer change is instructed, the process proceeds to step S62 to generate a jump pulse in the focus servo circuit 9, and the optical head. 3 is moved toward the recording layer.
[0088]
Next, it progresses to step S63 and the process which detects the amplitude of the tracking error signal at that time is performed. That is, the control circuit 42 of the tracking error signal amplitude maximum search circuit 31 reads the amplitude value of the tracking error signal output from the level detection circuit 41 at that time, and sets the read value to Rn.
[0089]
In the case of this embodiment, the reproducing apparatus is configured as shown in FIG. The detected value Rn is supplied to and stored in the optimum focus offset position storage circuit 33. In the optimum focus offset position storage circuit 33, the amplitude of the tracking error signal detected when the immediately preceding recording layer is reproduced is also R._PIs remembered as Therefore, in step S64, R_PIt is determined whether the value of −Rn is greater than a preset reference value T.
[0090]
That is, the currently obtained amplitude Rn is the previous obtained amplitude Rn._PIf the difference is smaller than the reference value T, even if it is larger or smaller, it is possible to reproduce the data sufficiently stably without changing the focus offset value. Do not do. That is, the same offset value as that in the previous recording layer reproduction is generated as it is. Then, the process returns to step S61, and the subsequent processing is repeatedly executed.
[0091]
On the other hand, the current amplitude Rn is the previous amplitude R._PIf it is smaller and the difference is larger than the reference value T, the process proceeds from step S64 to step S65, and the optimum focus search process is executed. This optimum focus search process is the same as the process in step S2 of FIG. 3 or step S53 of FIG. When the optimum focus search process is completed, the process returns to step S61, and the subsequent processes are repeatedly executed.
[0092]
That is, in this embodiment, the focus search process is executed only when the amplitude of the tracking error signal does not become sufficiently large due to the shift of the focus offset, so that compared to the case of the embodiment shown in FIG. The number of times the focus search process is executed can be reduced, and the reproduction of data from the recording layer can be started as quickly as that much.
[0093]
FIG. 12 shows another embodiment of an optical disk reproducing apparatus to which the disk drive apparatus of the present invention is applied. In this embodiment, an RF signal amplitude maximum search circuit 51 is provided instead of the tracking error signal amplitude maximum search circuit 31 of FIG. The RF signal output from the optical head 3 is input to the RF signal amplitude maximum search circuit 51.
[0094]
The RF signal amplitude maximum search circuit 51 includes a level detection circuit, a control circuit, and an offset generation circuit, like the tracking error signal amplitude maximum search circuit 31 shown in FIG. Other configurations are the same as those in FIG.
[0095]
That is, in the embodiment of FIG. 12, when the start of the reproduction operation is instructed, the control circuit 17 transfers the optical head 3 to the innermost track position of the optical disc 1 as in the embodiment of FIG. After that, the spindle motor 2 is driven to rotate the optical disc 1. Thereafter, both the focus servo circuit 9 and the tracking servo circuit 10 are set in an operating state. That is, the focus servo and tracking servo are applied.
[0096]
In this state, the relationship between the focus offset and the amplitude of the RF signal is shown in graphs as shown in FIGS. That is, when the focus offset of the optical head 3 with respect to the recording layer of the optical disk 1 is set to an optimum value, the amplitude of the RF signal becomes maximum. Therefore, the optimum point can be searched and set by obtaining the maximum value of the amplitude of the RF signal in the RF signal amplitude maximum search circuit 51, as in the case of obtaining the maximum value of the amplitude of the tracking error signal. . Since the process is the same as that in the embodiment of FIG. 1, the description thereof is omitted.
[0097]
Also, as shown in FIG. 9, when the optimum focus search process is executed using the RF signal every time the recording layer is changed, the optimum focus offset position storage circuit 33 shown in FIG. As shown in FIG. 13, the apparatus has a configuration in which the optimum focus offset position storage circuit 33 is omitted.
[0098]
In addition, when performing the maximum amplitude search using the RF signal, when performing the processing shown in FIG. 3 or FIG. 11, the playback apparatus requires the optimum focus offset position storage circuit 33 as shown in FIG. .
[0099]
FIG. 14 shows still another embodiment. In this embodiment, a minimum jitter search circuit 61 is provided instead of the tracking error signal amplitude maximum search circuit 31 in the embodiment of FIG. Then, the jitter measuring circuit 62 detects jitter from the output of the PLL circuit 5 and outputs the detected jitter to the jitter minimum search circuit 61. Similar to the tracking error signal maximum amplitude search circuit 31 shown in FIG. 1, the minimum jitter search circuit 61 includes a level detection circuit, a control circuit, and an offset generation circuit.
[0100]
Other configurations are the same as those in FIG.
[0101]
The jitter measuring circuit 62 detects the absolute value of the phase difference between the binarized RF signal output from the PLL circuit 5 and the synchronous clock signal, and outputs this as jitter to the jitter minimum search circuit 61. The relationship between the jitter and the focus offset is as shown in FIG.
[0102]
That is, as shown in FIG. 15, when the focus offset of the optical head 3 with respect to the optical disc 1 is optimum, the jitter is minimized, and when the optical head 3 is deviated from this optimum position, the jitter increases. Therefore, by obtaining the minimum value of this jitter, it is possible to obtain the optimum focus offset point of the optical head 3 with respect to the optical disc 1.
[0103]
As shown in FIG. 16, the minimum value of jitter can be obtained by a hill climbing method. That is, the sampling points are sequentially increased by α, and when the central sample value becomes smaller than the left and right sample values, the sample point at which the central sample value is obtained is set as the optimum point.
[0104]
FIG. 17 shows an example of processing for obtaining the minimum value of jitter by the hill-climbing method.
[0105]
First, in step S71, the initial value S is added to Sn.₀Set. Then, set the focus offset position to Sn (in this case, Sn = S₀), The jitter amplitude value (magnitude) in that case is measured, and the measurement result is expressed as Rn (in this case, Rn = R).₀).
[0106]
That is, the control circuit 42 sends an offset signal S to the offset generation circuit 43.₀Is generated. The focus servo circuit 9 receives the offset signal S by the adder 32.₀The focus coil 12 is controlled in response to the focus error signal to which is added, and the focus offset position of the optical head 3 is adjusted.
[0107]
At this time, the level detection circuit 41 detects the amplitude of the jitter output from the jitter measurement circuit 62 and outputs it to the control circuit 42. The control circuit 42 sets the amplitude value of the jitter detected at this time to Rn (in this case, Rn = R₀).
[0108]
Next, the process proceeds to step S72, where Sn + is changed to S.₀And add the value of α. That is, the following equation is calculated.
Sn + = S₀+ Α
[0109]
Then, the offset signal Sn + (= S₁). That is, the offset generation circuit 43 generates an offset value that is larger than the offset signal Sn generated in Step S71 by α. Since the focus servo circuit 9 controls the focus coil 12 in response to the focus error signal to which the offset value is added, the optical head 3 further changes the focus offset position of the optical head 3 by the offset value α. Let
[0110]
At this time, the level detection circuit 41 detects the amplitude of the jitter output from the jitter measurement circuit 62. The control circuit 42 sets the amplitude of the jitter detected by the level detection circuit 41 to Rn + (in this case R₀+ = R₁).
[0111]
Next, the process proceeds to step S73, where Sn-₀Set a value smaller by α. That is, the following equation is calculated.
Sn- = S₀-Α
[0112]
That is, the control circuit 42 controls the offset generation circuit 43, and the offset signal Sn generated in step S71 (in this case, Sn = S₀) Is generated by a value smaller than α. Since the focus error signal to which the offset signal Sn− is added is supplied to the focus coil 12 via the focus servo circuit 9, the optical head 3 has an offset value S.₀The focus offset position is changed by the offset value −α from the case where the error occurs.
[0113]
At this time, the level detection circuit 41 detects the amplitude of the jitter output from the jitter measurement circuit 62 and outputs it to the control circuit 42. The control circuit 42 sets the jitter amplitude value at this time to Rn− (in this case, Rn− = R₀Set to-).
[0114]
As a result of the processes in steps S71 to S73, the offset value added to the focus error signal is changed to the initial value S as shown in FIG.₀Jitter amplitude value Rn (= R₀) And an amplitude value Rn + (= R of jitter when the offset signal is increased by α.₀+ = R₁) And an amplitude value Rn − (= R of jitter when the offset signal is reduced by α.₀-) Is obtained.
[0115]
Therefore, the process proceeds to step S74, where it is determined whether Rn is equal to or smaller than Rn + and whether Rn is equal to or smaller than Rn−. That is, it is determined whether Rn is smaller than Rn− and Rn + (whether Rn is the minimum value).
[0116]
Usually, as shown in FIG.₀Jitter amplitude Rn (= R₀) Is an amplitude value Rn − (= R when the offset signal is small by α.₀The amplitude of jitter Rn + (= R when the offset signal is larger than α by less than −)₀+ = R₁Larger) Therefore, in this case, the process proceeds to step S75, and it is determined whether or not Rn + is smaller than Rn−. In this case, Rn + (= R₀+ = R₁) Is Rn-(= R₀Since it is smaller than-) (because it is a downward-sloping section in FIG. 16), the process proceeds to step S76.
[0117]
In step S76, Sn− is replaced with Sn (= S₀) Is set. Then, to the new Sn, Sn + (= S₁) And set Rn− to the previous Rn (= R₀) And Rn + (= R)₁) Is set. Further, a new Sn (= S₀+ Α = S₁) Plus α (= S₀+ 2α = S₂) Is set. That is, the following equation is calculated.
Sn + = Sn + α
[0118]
The control circuit 42 controls the offset generation circuit 43 and uses Sn + (= S₂). That is, Sn + (= S generated in step S72₀Offset Sn + (= S larger than + α) by α₀+ 2α = S₂). Then, the amplitude of the jitter detected at that time is set to Rn + (= R₁+ = R₂).
[0119]
That is, as a result, in the state shown in FIG. 16, three sampling points S moved to the right by α from the previous case.₀, S₁, S₂The jitter amplitude value at Rn − (= R₀), Rn (= R₁) And Rn + (= R₂) Is set.
[0120]
Then, it returns to step S74 and it is determined whether Rn is smaller than Rn- and Rn +. If Rn is not the minimum value, the process proceeds to step S75, and it is determined again whether Rn + is smaller than Rn−. When Rn + is smaller than Rn−, the process proceeds to step S76, and the same processing is repeated.
[0121]
Then, when the section to be sampled moves to the right in FIG. 16 and Sn reaches the optimum point, the amplitude value Rn obtained at that time is smaller than Rn− and smaller than Rn +. That is, Rn becomes the minimum value. Therefore, in this case, the process proceeds from step S74 to step S78, and the value of Sn at that time is set as an optimum value that maximizes the jitter amplitude Rn. That is, the control circuit 42 subsequently generates the offset signal Sn as the optimum value from the offset generation circuit 43 thereafter.
[0122]
On the other hand, when sampling is performed in the upwardly rising section in FIG. 16, the value of Rn + is larger than Rn−. Therefore, in this case, the process proceeds from step S75 to step S77, Sn is set as Sn +, Sn is set as Sn−, Rn + is set as Rn, and Rn is set as Rn. , Rn- until then is set. Then, a value smaller by α than the new Sn is set to Sn−. That is, the following equation is calculated.
Sn- = Sn-α
[0123]
That is, in FIG. 16, the sampling point on the left side is sampled by Sn-. Then, the amplitude value of the jitter when the offset signal Sn− is generated from the offset generation circuit 43 is detected, and the detected amplitude value is set to Rn−.
[0124]
Then, the process returns to step S74, and it is determined whether Rn is smaller than Rn− and Rn +. In FIG. 16, in the section that rises to the right, since Rn is still larger than Rn−, the process proceeds to step S75, and from step S75 to step S77, the same processing is repeated. Then, when the sampling point sequentially advances to the left (in the direction of the optimum point) in FIG. 16 and Sn reaches the optimum point, Rn is smaller than Rn + and smaller than Rn−. At this time, the process proceeds from step S74 to step S78, and the value of the offset signal Sn at that time is set to the optimum value. Thereafter, the control circuit 42 causes the offset generation circuit 43 to continuously generate the optimum value.
[0125]
Further, as in the case shown in FIG. 7, the steep downward change point Sm₂And sudden up change point Sm₁And the midpoint of both can be determined as the optimum point that exhibits the minimum jitter.
[0126]
That is, in this case, as shown in FIG.₀Through Sn, the sampling value R₀To Rn are obtained in advance. And from these sample values, the change point Sm₁And Sm₂And find the midpoint of both.
[0127]
FIG. 19 shows a processing example in this case. In this embodiment, first, in step S91, a variable n is initially set to 0, and in step S92, the following equation is calculated.
S [n] = SMIN + α × n
[0128]
Here, SMIN represents a minimum value of the offset adjustment value, and α represents a width for changing the offset signal on the step.
[0129]
In this case, since n = 0, S [0] is set to SMIN.
[0130]
The control circuit 42 controls the offset generation circuit 43 to generate this S [n] (in this case, S [0] = SMIN). Then, the jitter amplitude at this time is detected by the level detection circuit 41, and the value is set to R [n] (= R [0]).
[0131]
In step S93, the variable n is incremented by 1 (n = 1). It is determined whether or not the variable n incremented in step S94 is smaller than NUM. This NUM is a value obtained by (SMAX−SMIN) / α when the maximum offset value is SMAX, as in the case described above. That is, it represents the sampling number of the focus offset scan range.
[0132]
If n is smaller than NUM, not all sampling points have been sampled yet, so the process returns to step S92 to calculate the following equation.
S [n] = SMIN + α × n
[0133]
That is, in this case, a value larger by α than SMIN is set as the offset signal S [1]. Then, the jitter amplitude when the offset signal S [1] is generated is measured, and the value is set as R [1].
[0134]
Thereafter, the process proceeds to step S93, where the variable n is incremented by 1, and in this case, n = 2. If it is determined in step S94 that the variable n (= 2) is smaller than NUM, the process returns to step S92 and the same processing is repeatedly executed. In this way, S shown in FIG.₀Jitter amplitude value R at sampling points from A to Sn₀To Rn are obtained.
[0135]
As described above, when the sampling of the search range is completed, the variable n becomes equal to NUM. Therefore, the process proceeds from step S94 to step S95, and the variable n is initialized to 1. In step S96, whether or not the difference between the amplitude value R [n] of the current reference point and the previous amplitude value R [n-1] is smaller than a preset reference value Th. Determined. In this case, it is determined whether or not the value of R [0] -R [1] is smaller than Th. As shown in FIG. 18, since the first period of the sampling range has a downward-sloping characteristic, R [0] is sufficiently larger than R [1] (the difference (R [0] −R [1 ]) Is greater than Th). Then, it progresses to step S97 and changes point Sm₂As described above, a value between sampling points S [n] and S [n−1] is set. That is, the following equation is calculated.
Sm₂= (S [n] + S [n-1]) / 2
[0136]
In this case, the point between S [1] and S [0] is Sm₂Set to
[0137]
In step S98, the variable n is incremented by 1 (n = 2). In step S99, it is determined whether the variable n is smaller than NUM. When the variable n is smaller than NUM, the process returns to step S96, and it is determined whether or not the value of R [1] -R [2] is smaller than Th. As shown in FIG. 18, the difference between the two sampling values is larger than the reference value Th during the period in which the jitter changes greatly. Therefore, the process proceeds again to step S97, where Sm₂To (S [2] + S [1]) / 2. That is, the value on the right side by α is Sm₂Will be set to.
[0138]
In step S98, the variable n is incremented by 1 again to set n = 3, the process returns from step S99 to step S96, and the same process is repeated.
[0139]
Then, as the sampling point moves to the right in FIG. 18, the rate of change in jitter gradually decreases. When it is determined that the value of R [n−1] −R [n] is smaller than Th, the process proceeds from step S96 to step S100. That is, at this time, Sm₂Shows the change point (abrupt downward change point) from the interval in which the rate of change of the amplitude of jitter is large to the interval in which it is small.₂Will be set as
[0140]
In step S100 and subsequent steps, from the period in which the rate of change in the amplitude of jitter gradually increases, the change point that suddenly increases is changed to the steep upward change point Sm.₁To ask for.
[0141]
Therefore, in step S100, it is determined whether or not the value of R [n] −R [n−1] is greater than the reference value Th. As shown in FIG. 18, the left sampling value R [n-1] is larger than the right sampling value R [n] (downward period) and the right sampling value R [n]. However, even if it is larger than the sampling value R [n−1] on the left side, the value of R [n] −R [n−1] is smaller than the reference value Th in a period in which the difference is small. Therefore, the process proceeds from step S100 to step S101, where Sm₁Is set to a value between S [n] and S [n−1]. That is, the following equation is calculated.
Sm₁= (S [n] + S [n-1]) / 2
[0142]
In step S102, n is incremented by 1. In step S103, it is determined whether the variable n is smaller than NUM-1 (whether the search range has not yet reached the right end in FIG. 18). When the variable n is smaller than NUM-1, the process returns to step S100, and the same processing is repeated for two sample values on the right side by one sample in FIG. If the difference between the two sample values is smaller than the reference value Th, the process proceeds again to step S101, where Sm₁Is set to an intermediate value between the two sampling points.
[0143]
In this way, when the sampling point sequentially moves in the right direction in FIG. 18 and the sampling value R [n] on the right side in the drawing becomes abruptly larger than the sampling value R [n−1] on the left side, the difference between the two ( R [n] −R [n−1]) is equal to or greater than the reference value Th. At this time, Sm₁Is set to an intermediate value between sampling points S [n−1] and S [n−2]. And the value at this time is a sudden up change point Sm₁It is said.
[0144]
As described above, the sudden downward change point Sm in step S97.₂In step S101, the sudden change point Sm₁Is obtained, the process proceeds to step S104, and the change point Sm₁And Sm₂The intermediate point is obtained as the optimum point. That is, (Sm₁+ Sm₂) / 2 is set as the optimum point.
[0145]
When it is determined in step S99 that the variable n is equal to or greater than NUM, the process proceeds from step S99 to step S100. If it is determined in step S103 that the variable n is equal to or greater than NUM-1, the process proceeds from step S103 to step S104.
[0146]
When the optimum point is obtained by the method shown in FIG. 7 or FIG. 18, even when noise is superimposed on the tracking error signal, RF signal, or jitter, the influence of noise is reduced. Can do.
[0147]
Even when the optimum focus offset position is searched using jitter, the processing shown in FIG. 3 or 9 or the processing shown in FIG. 11 can be performed. When searching for the optimum focus offset position in the process shown in FIG. 3 or FIG. 9, the playback apparatus is configured as shown in FIG. That is, in this case, the optimum focus offset position storage circuit 33 is required. On the other hand, when the processing shown in FIG. 11 is executed, the optimum focus offset position storage circuit 33 is not required as shown in FIG.
[0148]
In the above embodiment, the case where the optical disk drive apparatus of the present invention is applied to an optical disk reproducing apparatus has been described as an example. However, the present invention can also be applied to the case of recording information on an optical disk.
[0149]
【The invention's effect】
  As described above, the present inventionFirstAccording to the aspect, when the offset signal to be added to the focus error signal is generated, the amplitude of the tracking error signal corresponding to the light tracking state, the amplitude of the RF signal corresponding to the information recorded on the recording layer of the optical disc, Alternatively, when the jitter of the signal reproduced from the optical disc is detected and the offset signal is sequentially increased from the minimum value, the absolute value of the rate of change in the amplitude of the tracking error signal with respect to the increase in the offset signal is equal to or greater than a predetermined first threshold value. A first intermediate value that is an intermediate value between a value of the first offset signal that becomes less than the first threshold and a value of the second offset signal that becomes less than the first threshold and greater than or equal to the first threshold. The third offset signal in which the absolute value of the rate of change in the amplitude of the RF signal with respect to the increase in the frequency is greater than or equal to a predetermined second threshold and less than the second threshold A second intermediate value that is an intermediate value between a value and a value of the fourth offset signal that is less than the second threshold and greater than or equal to the second threshold, or an absolute value of the rate of change in jitter with respect to an increase in the offset signal is predetermined. A third value that is an intermediate value between the value of the fifth offset signal that becomes less than the third threshold value and less than the third threshold value and the value of the sixth offset signal that becomes more than the third threshold value and less than the third threshold value. As the optimum value of the intermediate value offset signal, the offset signal is controlled to the optimum value. Therefore, even when information is recorded on or reproduced from any of the plurality of recording layers, there is a variation in the optical disc or the like. It is possible to always realize an optimal focus state regardless of changes over time.
  In addition, the present inventionSecondAccording to the aspect, the optimum focus offset position of the light for recording or reproducing information on the optical disc is searched by changing the value of the offset signal added to the focus error signal, and the tracking state of the light irradiated on the optical disc When the recording layer is changed by detecting the amplitude of the tracking error signal corresponding to, the amplitude of the RF signal corresponding to the information recorded on the recording layer of the optical disc, or the jitter of the signal reproduced from the optical disc, the offset signal The value of the first offset signal in which the absolute value of the rate of change in the amplitude of the tracking error signal with respect to the increase in the offset signal is less than the first threshold value is greater than or equal to a predetermined first threshold value when the value is sequentially increased from the minimum value And a first value that is an intermediate value between a value less than the first threshold value and a second offset signal value that is greater than or equal to the first threshold value The absolute value of the change rate of the amplitude of the RF signal with respect to the increase of the intermediate value and the offset signal is a value of the third offset signal in which the absolute value of the RF signal is greater than or equal to a predetermined second threshold value and less than the second threshold value. A second intermediate value that is an intermediate value with respect to the value of the fourth offset signal that is equal to or greater than the threshold value, or the absolute value of the rate of change in jitter with respect to an increase in the offset signal is less than a predetermined third threshold value to a third value A third intermediate value that is an intermediate value between the value of the fifth offset signal that is greater than or equal to the threshold and the value of the sixth offset signal that is greater than or equal to the third threshold and less than the third threshold corresponds to the recording layer. Since the offset signal is controlled to the optimum value corresponding to the recording layer as the optimum value of the offset signal, even when information is recorded on or reproduced from any one of the plurality of recording layers, an optical disc or the like Noba Regardless of the attached and aging, it is possible to always realize the optimum focus state.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of an optical disk reproducing apparatus to which an optical disk driving apparatus of the present invention is applied.
FIG. 2 is a graph for explaining a relationship between a focus offset and a tracking error signal.
FIG. 3 is a flowchart for explaining the operation of the embodiment of FIG. 1;
FIG. 4 is a diagram showing a waveform of a tracking error signal during an initial operation.
FIG. 5 is a diagram illustrating a principle for obtaining an optimum point of focus offset by a hill-climbing method.
6 is a flowchart showing an example of processing for obtaining an optimum point according to the principle shown in FIG. 5;
FIG. 7 is a diagram for explaining the principle of obtaining an optimum point from a sudden climbing change point and a sudden descending change point.
8 is a flowchart showing an example of processing for obtaining an optimum point according to the principle shown in FIG.
FIG. 9 is a flowchart for explaining the operation of the embodiment of FIG. 10;
10 is a block diagram illustrating a configuration example of an optical disc playback device that executes the process of FIG. 9;
FIG. 11 is a flowchart showing another operation example of the embodiment of FIG. 1;
FIG. 12 is a block diagram showing another configuration example of an optical disc playback apparatus to which the optical disc drive apparatus of the present invention is applied.
FIG. 13 is a block diagram showing another configuration example of an optical disc playback apparatus to which the optical disc drive apparatus of the present invention is applied.
FIG. 14 is a block diagram showing still another configuration example of an optical disc playback apparatus to which the optical disc drive apparatus of the present invention is applied.
FIG. 15 is a graph showing the relationship between focus offset and jitter.
FIG. 16 is a diagram for explaining the principle of obtaining an optimum point by a hill-climbing method.
17 is a flowchart showing an example of processing for obtaining an optimum point according to the principle of FIG. 16;
FIG. 18 is a diagram illustrating a principle for obtaining an optimum point from a sudden down change point and a sudden up change point.
FIG. 19 is a flowchart showing an example of processing for obtaining an optimum point according to the principle shown in FIG. 18;
FIG. 20 is a block diagram showing another configuration example of an optical disc playback apparatus to which the optical disc drive apparatus of the present invention is applied.
FIG. 21 is a cross-sectional view showing a configuration of a two-layer optical disc.
[Explanation of symbols]
1 optical disk, 2 spindle motor, 3 optical head, 9 focus servo circuit, 10 tracking servo circuit, 12 focus coil, 13 tracking coil, 31 tracking error signal amplitude maximum search circuit, 32 adder, 33 optimum focus offset position storage circuit, 41 level detection circuit, 42 control circuit, 43 offset generation circuit

Claims (2)

In an optical disc driving apparatus for recording or reproducing information on a plurality of recording layers of an optical disc,
Irradiating means for irradiating light for recording or reproducing information on the optical disc;
Focus control means for controlling the focus state of the light emitted by the irradiation means in response to a focus error signal;
Generating means for generating an offset signal to be added to the focus error signal;
When the offset signal is generated by the generation means, the amplitude of the tracking error signal corresponding to the tracking state of the light irradiated by the irradiation means, the RF signal corresponding to the information recorded on the recording layer of the optical disc Detecting means for detecting the amplitude of the signal or jitter of the signal reproduced from the optical disc;
When the offset signal is sequentially increased from a minimum value, the absolute value of the rate of change in the amplitude of the tracking error signal with respect to the increase in the offset signal is a predetermined first threshold value or more and less than the first threshold value. A first intermediate value that is an intermediate value between a value of one offset signal and a value of a second offset signal that is less than the first threshold and greater than or equal to the first threshold, and the RF signal with respect to an increase in the offset signal The absolute value of the rate of change in the amplitude of the third offset signal that is less than or equal to a second threshold value and less than the second threshold value, and the fourth value that is less than the second threshold value and greater than or equal to the second threshold value. A second intermediate value, which is an intermediate value with respect to the offset signal value, or an absolute value of the rate of change of the jitter with respect to an increase in the offset signal from less than a predetermined third threshold value to the third threshold value or more The third intermediate value that is an intermediate value between the value of the fifth offset signal and the value of the sixth offset signal that is greater than or equal to the third threshold and less than the third threshold is set as the optimum value of the offset signal. And an offset control means for controlling the offset signal generated by the generating means to the optimum value. In a focus control method of an optical disk drive device for recording or reproducing information on a plurality of recording layers of an optical disk,
Search for the optimum focus offset position of the light for recording or reproducing information on the optical disc by changing the value of the offset signal to be added to the focus error signal,
The amplitude of the tracking error signal corresponding to the tracking state of the light applied to the optical disc, the amplitude of the RF signal corresponding to the information recorded on the recording layer of the optical disc, or the jitter of the signal reproduced from the optical disc Detect
When the recording layer is changed, the absolute value of the rate of change of the amplitude of the tracking error signal with respect to the increase in the offset signal when the offset signal is sequentially increased from the minimum value is greater than or equal to a predetermined first threshold value. A first intermediate value that is an intermediate value between a value of the first offset signal that is less than the first threshold value and a value of the second offset signal that is less than the first threshold value and greater than or equal to the first threshold value; The absolute value of the rate of change of the amplitude of the RF signal with respect to the increase in the offset signal is a value of a third offset signal that is greater than or equal to a predetermined second threshold value and less than the second threshold value, and less than the second threshold value. A second intermediate value that is an intermediate value with respect to a value of the fourth offset signal that is equal to or greater than the second threshold, or an absolute value of the rate of change of the jitter with respect to the increase of the offset signal is a predetermined third threshold. A third intermediate value that is an intermediate value between the value of the fifth offset signal that is less than the third threshold and less than the third threshold and the value of the sixth offset signal that is less than the third threshold and less than the third threshold A focus control method characterized in that the offset signal is controlled to the optimum value corresponding to the recording layer with the value set as the optimum value of the offset signal corresponding to the recording layer.

Images