JPS6320726A - Optical disk device - Google Patents

Abstract

PURPOSE:To secure the stable control properties of an optical disk device by substituting a sample error signal for the value obtained from the preceding sampled value for a single sampling period if it is decided that said error signal is not appropriate. CONSTITUTION:The signal DELTAX(t) supplied to a protecting circuit 11 is compared with the sampled value preceding by a step. The normal sampled value is confirmed when the difference obtained from said comparison is kept within a fixed range + or -DELTAw1. Then such a sampled value is available. While the wrongly sampled value is decided if said difference of comparison exceeds the range + or -DELTAw1, therefore the sampled value preceding by a step is used instead. A delay circuit 111 which delays the signal DELTAX(t) by a sampling time T is used together with a window comparator 112 having the width + or -DELTAw for comparison performed between the 1-step preceding sampled value and the present sampled value. A track holding circuit 113 holds an input only for a period during which the comparator 112 decides that the present sampled value is wrong and otherwise transmits the signal DELTAX(t) as it is. Thus it is possible to secure the stable control properties for an optical disk device despite a detection error of a servo signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical disk device, and particularly relates to a high-frequency sampling servo system suitable for performing focusing and tracking control of a light spot using a servo signal obtained intermittently. This article relates to the optical disc device used.

[Conventional technology]

Optical disk (Write data to any recording area on the screen,
For optical disc devices that read data from arbitrary areas, it is necessary to correctly control the relationship between the disc surface and the read and write light beam spots, that is, in autofocus control and tracking control, intermittently read data from specific areas on the track. A method has been proposed in which a servo signal area is provided for the above control, and the above control is performed in a sampling manner based on this signal. For example, the Tokuko Sho 5
No. 8-21336, 1984 (Showing 59), 45th Academic Conference of the Japan Society of Applied Physics, 13p-E-8 and 13P
-E-9'''Sector servo type data file optical disk'' Part I, Part 2, etc.

A feature of these methods is that in focusing and tracking servo of an optical disc, servo signals are not detected continuously from the track.

It is obtained intermittently, and based on this, the sampling servo method is adopted. This has the advantage of not being influenced by parts other than the sample points.

For example, when recording data bits, a pulse with an intensity about 10 times that of reading is generally incident on the photodetector.
In the case of continuous control, these pulses may disturb the focus and tracking servo systems;
The sampling servo method does not use signals other than sample points, so it is not affected by recording pulses. In addition, in general, on optical discs, reflectance etc. change before and after data pits are recorded, so in the case of continuous control, the characteristics of the control system may change, but in the sampling servo system,
There is an advantage that the servo system can be stabilized without being affected by such changes.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, the problem of implementing focus and tracking control of an optical disc using a sampling servo method is discussed, but it is based on the premise that the servo signal is detected correctly, and it is assumed that the servo signal is correctly detected. Or, there is no consideration given to errors in detecting servo signals due to some kind of error in the servo system.

Therefore, if there is a detection error in the servo signal, the error will not be corrected at least until the next sampled servo signal, resulting in a problem that the control characteristics will be random and a control system with the specified performance cannot be constructed. .

An object of the present invention is to provide an optical disk device that can minimize the influence of detection errors in servo signals and ensure stable control characteristics.

[Means for solving problems]

The above purpose is based on the fact that servo signal detection errors do not occur very frequently, that is, the occurrence of the above errors in normal control conditions is rare, and The possible deviation range of the servo signal in the control state is estimated from consecutive past -7 or multiple sample values, or by combining this with eccentricity information or adjacent track information, etc., and sampled according to predetermined criteria. This is achieved by determining whether or not the servo signal is erroneous, and in the case of an error, replacing the erroneous sample value with the estimated value. This is achieved by completing the time required to make a determination and send the sample value or alternative data to the servo system within a certain period of time. This is because the time required for these determinations acts as dead time in the servo system, and if this time is taken too long, the phase margin of the servo system decreases, resulting in a decrease in stability.

[Effect]

In the present invention, before the detected servo signal is used as an input signal to the servo system, it is first determined whether or not the signal is erroneous. To do this, the possible range of the servo signal at the next sample point is estimated from the temporally continuous servo signal, and the detected servo signal is determined using a limit value set in consideration of noise, deviation, etc. in normal control conditions. evaluate. In other words, determine whether it is within or outside the above limit, and if it is within the limit, then yes! 1. is treated as new sample data, and if it is outside, this is not used and the above estimated value is used as sample data. Therefore, even if an abnormal servo signal is detected due to a defect in the disk, good control characteristics can be obtained without being affected by this.

Instead of a normal data read/write state, a state in which the data moves between tracks (track jump) occurs during access, seek, or in a state in which the data continuously remains on one track. Naturally, a large deviation signal is added to the tracking signal at this time in response to the above movement. Alternatively, it may happen that the servo signal cannot be found for a certain period in the middle. That is, in such a state, it may become impossible to determine whether the servo signal is incorrect. Therefore, the above-mentioned error determination operation can be applied or not applied depending on the operating state of the device, so that good operation can be obtained in any case.

There may be cases where the above determination is incorrect continuously or extremely frequently. For example, in the case of a large defect. Regarding defects, the maximum defect that can be handled can be estimated in advance based on the performance of the device. Therefore, the control and operation method of the device can be determined based on the continuation of the error state. Further, determination of escape from such an abnormality M (for example, a defective part) can be made by detecting that errors in the determination results have disappeared continuously. Therefore, the limit value for the above determination is not necessarily constant, but can be made variable depending on the state.

Next, a method of setting the time required for the above determination, which is the second point of the present invention, will be explained. ΔX in Figure 4(a)
(t) represents the temporal change in the true amount of deviation from the target point in the focus or tracking servo system. Specifically, it represents the amount of defocus of the light spot in the focus servo system, and the deviation from the track center in the tracking servo system. Indicates the distance between light spots. The servo system operates so that ΔX→0. Now, in a sampling servo system, the obtained error (No. 2) is a stepped waveform represented by ΔX (t) obtained by sampling and holding ΔX (t) at a time interval T. The frequency transfer function Gh of the sample and hold circuit (jw) is −J w T Gh U w) = (1-e) /j w
T (1) denoted by 9, its positional characteristic (ρ
h (w) becomes '#h (w) =-T/=w. Note that here, f = 2 K v , f
s = 1/T. Therefore, the sample and hold element acts as a kind of low-pass filter, and its phase delay amount is linear with respect to frequency, and the sampling frequency (f
s) delayed by π (180”) for a frequency component equal to
A phase delay of 180'' is generated for a frequency component of f=fs/10.

On the other hand, as mentioned above, in the present invention, the sampled data is checked in order to prevent the servo system from being disturbed by a signal due to an erroneous sample entering the servo system. The signal sent to is ΔX (t) as shown in FIG. 4(b), which is a signal obtained by delaying ΔX (t) by Δt. Delaying the signal by Δt means -J in terms of frequency transfer function.
w Δ t Ga (j w) = c (
3), and its phase characteristic 'P, + (w) is (
ρ, s(w)=-w・Δt=−2πf・Δt(4). Therefore sample hold and check time Δ
The total phase delay Cρ(f) caused by t is (
2L From equation (4), ψ(f)=ψ), (w)+ψ, +(w). Here, if the ratio between the sample interval T and Δt is expressed as η, and η=Δt/T (6), then Δt=η·T=η/f s.

Generally, the amount of phase delay in a servo system becomes a problem at the gain crossover frequency (fo) of the servo system, which is defined as the frequency at which the gain of the open loop transfer function of the servo system is 1. The stability condition for the servo system is that the phase of the open loop system at f6 is -π (-180°) or less, and the margin until reaching -180° is the phase containing C
Defined as pm. It is generally said that approximately (ρ□〉45° (8) is required as an index of stability.

On the other hand, in a servo system for focusing and tracking of an optical disk, the gain crossover frequency f. is often below 3KHz. This is because the actuator that has the function of correcting the position of the light spot in the servo loop is a mechanical system and has a harmful resonance point called multiple resonance at a frequency around 20KHz. This is because if the diameter is made thicker, the servo system will have gain at multiple resonance points, making the servo system more likely to become unstable.

Therefore, the optical disk servo system is f, = IK ~ 3K)
It is common to have a phase margin (pc=45° culm degree) at lz.

However, in a sampling servo system, a phase lag as shown in equation (7) is added, so if a sample hold element is simply added to a continuous servo system, the phase margin Cpm decreases and the servo system becomes unstable. be. fs/fc
, Δt/T and phase delay (P) are plotted in FIG.

For example, f s = 30 KHz, f c =
3 KHz.

In the case of Δt/T=0.1, the total phase delay p is −21.6′, which reduces the phase margin by 21.6°, resulting in a decrease in stability.

The decrease in phase margin can be compensated for by a type of differential circuit called a phase advance circuit. However, if the amount of phase advance is increased too much, the gain in the high frequency region increases at the same time, resulting in an increase in fc, and the system becomes unstable due to multiple resonances. Therefore, there is actually a limit to the amount that can be compensated by the phase advance circuit.
According to the applicant's study, the amount of phase advance that can be compensated for is at most 40' without widening the servo band fc too much.
It has been found that in order to secure a degree and phase margin of 40° or more, it is practically desirable to set the angle to about 20°. Therefore, the amount of position lag (p
(fc) is calculated using equation (7) as CP(f c)=-180°(1+2y+)・”>-4
0°(9)s, and practically the left side is 120° culm degree.
Although the above calculations were performed using a zero-order hold as a sample hold, it is possible to make the phase delay caused by the hold circuit smaller than in equation (2) by using, for example, a first-order hold other than a zero-order hold.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a block diagram of an optical disc device according to the present invention. l is a read/write optical head; 10.1
1. The system consisting of ~14 is a focus control system, 20,2
1. 24 indicates a tracking control system. Compared to the block diagram of the prior art based on the sampling servo method, the present invention has a protection function against signal detection errors.
The feature is that protection circuit means 1 and 21 are used. Therefore, the components other than the protection circuit means 11 and 21 are structurally the same as the sampling servo type optical disk apparatus in the prior art. That is, optical head 1
reads servo signals and data signals on the disk, and also performs data write operations. A servo signal area is extracted from the signal on the disk, and a focus and tracking control signal is obtained by a servo signal detection circuit 10.20. For example, the focus signal detection circuit 10 can use an astigmatism method, and the W call detection circuit 20 can use a tracking (pre-wobbled pits) method.These servo signals can be held in areas other than the servo signal area. Read/write data.

Now, if we perform zero-order hold on the sample value of the servo signal mentioned above, and assume that it takes time Δt to check for erroneous samples, the servo system will have a phase lag (ρ(f c)) given by equation (7). Therefore, since Bezo (f c) is added to the continuous control system, in order to compensate for that 89, in addition to the compensation element in the continuous control system, compensation based on the sampling control described above is performed. 12.22 in the figure is a compensation circuit that also performs phase compensation between the two.Driver 13.23 and actuator 14.2
4 controls the light spot by the outputs of the compensation circuits 12 and 22, respectively, and performs focus and tracking control. If there is an error in the detection of the servo signal in the conventional optical disk device using the sampling servo method mentioned above,
Since it is not corrected until at least the next sample, a large control error occurs. For example, in tracking control, only one sample is smaller than the true error signal δ (μm
), the track deviation ΔX at that time exhibits a response as shown in Fig. 2 due to the incorrect sample δ, and its maximum value a (μm) exhibits the characteristics as shown in Fig. 3. The parameter N is the number of samples per track.

The present invention is characterized by a protection means that can set δ→0 when there is a detection error δ. An example of this protection circuit will be explained below.

FIG. 6 is a block diagram showing an example of this protection circuit.

The part surrounded by the broken line indicates the protection circuit 11 (or 22), and this input is the sampled and held signal ΔX (t
), and the output is ΔX', which is the signal that completed the chinch
<t). In this example, ΔX (
t) is compared with the sample value one sample before, and if the difference is within a certain range ±ΔW, it is determined to be a normal value.

That sample value is used, but if the difference exceeds ±ΔW, it is determined that it is an erroneous sample, and the sample value of one library is continued to be used. In order to compare the value one sample ago with the current value, the signal ΔX is
A delay circuit 111 that delays (t) and a window comparator 112 having a window width of ±ΔW are used. The track hold circuit 113 is the window comparator 11
2, only for the period in which the current value is determined to be incorrect.
It has the function of holding the input and passing the signal as is in other cases. In addition, the delay circuit 116 delays the signal by the time Δt required for the above determination, and if there is an error, the erroneous data is transferred to the track hold circuit 28113 during the determination.
For example, if the acceleration as a disturbance that the servo system can tolerate is a, then the displacement ΔY caused by the disturbance during l sample time T is Since it is given by ΔY=-aT2, it may be determined based on this value while considering other factors. Suppose a = 0, 5 G.

If T"30ttscc, ΔY=0.002 μm, and this value is a standard value for ΔW.

Note that in the example shown in FIG. 6, the protection circuit 11 is realized using an analog delay element for comparison with the previous sample value, but a protection circuit with a similar concept can perform A/D conversion, D
It is also possible to perform it digitally using /A conversion and memory elements.

In this case as well, the time required for the determination is Δt.

FIG. 7 shows another example of the protection circuit 11. In this example, using n values from n samples ago to
An estimate of the sample value to be obtained is generated and the estimate is compared with the current value actually obtained. As a result of the comparison, if the difference is within ±ΔW2, it is determined that the value is correct,
That value is adopted, but if the difference exceeds ±ΔW, it is considered an error and that estimated value is used for that period. To create an estimate by values up to n samples ago.

A delay circuit 111 whose time delay is from T to nT.

Using the current value estimating circuit 114, the current value and the estimated value are compared by a comparator 117 with a window width Δw2°. Based on the determination by the window comparator 117, the switch 115 switches between the current value and the estimated value. As with the previous example, the protection circuit in this example can also be realized with a digital circuit configuration, if the function of the current value estimation circuit 114 is to be enhanced.

In some cases, it may be more desirable to digitize.

By devising the estimation circuit 114, the protection circuit shown in FIG.
It becomes possible to have the ability.

Δt of the delay circuit, that is, the time required to check the erroneous sample, is set to η=Δt/T so as to fully satisfy equation (9) when a zero-order hold is used as the hold circuit. If the sampling frequency f5 = 30 KHz and the gain crossover frequency fc = 3 KHz, from Fig. 5, f
Since s/fc: 10, from the graph in Fig. 5, Δt /T=
If it is about 0.1, the phase BtL amount at fc (p(f
c) is approximately 20', which fully satisfies equation (9) and allows a servo-stable system to be constructed. Note that Δt/T=
If it is 0.1, then T=33μ5ec1'.

It is sufficient to design the algorithm and hardware for checking erroneous samples so that Δt<3.3μscc.

Although the current value estimation circuit in this example is configured to calculate the current value from the value up to n samples ago, it is not necessary to use consecutive samples; for example, the error signal at the same position up to n disk rotations ago It is also possible to perform estimation using .

〔Effect of the invention〕

According to the present invention, when performing sampling methods such as focusing and tracking in an optical disc file device, it is possible to check the sampled error signal, so if the correct error signal cannot be detected due to some defects in the disc, the sampled error signal can be checked. However, correct control can be performed without affecting the servo system due to the defect.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the configuration of an embodiment of the present invention, Figure 2 is a diagram explaining the response of the servo system when the servo system makes one sample error, and Figure 3 is a diagram explaining the response of the servo system when the servo system makes one sample error. A graph plotting the maximum response amount a of the servo system when erroneously sampled, Figure 4 shows the sample hold and judgment time Δ
Figure 5 is a graph explaining the amount of phase delay ψ caused by sample hold and delay Δt. Figure F6 is a diagram explaining an embodiment of the protection circuit of the present invention. The figure is a diagram illustrating another embodiment of the protection circuit of the present invention. [Explanation of symbols] 1... Optical head, 10.20... Detection circuit. 11.21... Protection circuit, 12.22... Phase compensation circuit, 13.23... Driver, 14.24... Actuator, a... Maximum track deviation amount, δ...
Amount of incorrect samples, N... Number of samples per disk rotation, T... Sampling period, ΔX (t)... Zero-order hold signal of error signal, fs... Sampling frequency, fc... Gain crossover Frequency, Δt...judgment time, 111...delay circuit, 112, 117...window comparator, 113...trunk hold circuit, 114...current value estimation circuit, 115...changeover switch, 116 ...Δ is a delay circuit. 2nd item Fig. 3 S<,, sail) 4. Prisoner Yukuni js/fc (f, 3・+ji!Otsu no L J 7th

Claims (1)

[Claims] 1. An optical disk device that uses sampling control to control focusing, tracking, etc. has a means for checking whether the sampled error signal value is an appropriate value, and if it is determined that it is not appropriate, the error signal is kept constant. 1. An optical disc device comprising a protection means for substituting a value created using a previous sample value for a period of time.