JP3975539B2 - Optical disk device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc apparatus having a focusing control system, and more particularly to an apparatus with improved focusing control performance.
[0002]
[Prior art]
In recent years, as interest in multimedia increases, there is a demand for recording a large amount of data such as video data of moving images on an optical disc (for example, a disc-shaped optical recording medium such as a compact disc (CD)). It is growing. In order to satisfy this requirement, it is necessary to further increase the capacity and speed of the optical disk.
[0003]
On the other hand, as represented by a CD, it is important that an optical disk be easy to handle (easy to carry by hand or when attached to or detached from an optical disk device). Therefore, enlarging the recording area in order to realize a large capacity is not so much welcomed because it leads to an increase in the diameter of the disc and impairs ease of handling.
[0004]
Therefore, in the optical disc, it is mainstream to realize a large capacity in the direction of increasing the recording density. As a result, today's optical discs are becoming increasingly dense.
[0005]
Also, among optical discs, the numerical aperture of the objective lens is standardized to 0.45 for CDs, whereas the numerical aperture is standardized to 0.6 for digital video discs (DVDs) that appear thereafter. Yes. This trend of increasing numerical aperture is expected to accelerate further in the future. Since the numerical aperture may be considered to be an angle for narrowing the laser beam, the laser beam is narrowed at a tighter angle as the numerical aperture increases. Further, it is known that an allowable error range of focusing of the objective lens called a depth of focus is inversely proportional to the square of the numerical aperture. Therefore, as the numerical aperture increases, the allowable error range of focusing becomes very small.
[0006]
Against this background, focusing control systems in optical disk devices are required to improve control performance (realize high control accuracy) without sacrificing stability and responsiveness. ing.
[0007]
By the way, in a conventional optical disk apparatus (for example, an optical disk apparatus having a focusing control system designed using a phase compensation method that is well-known in the field of classical control and is a relatively simple method), a focusing error is detected. It is performed at the main spot on the optical disc (that is, a focusing error signal is generated by an astigmatism method or the like based on the return light from the main spot), and focusing control is performed only based on the detection of the focusing error at the main spot. I was doing.
[0008]
The main spot refers to the position on the optical disk where the laser beam is irradiated when the number of laser beams irradiated on the optical disk is one, and on the other hand, for example, detection of a tracking error is 3 When a total of three laser beams of a main beam (0th order diffracted light) and a side beam (+ 1st order diffracted light, −1st order diffracted light) are irradiated to the optical disk by performing the spot method, the main beam is irradiated. The position on the optical disc is called.
[0009]
The reason for detecting the focusing error at the main spot in this way is that the reproduction of the recording data of the optical disc is performed based on the return light from the main spot. Therefore, in order to accurately reproduce the recording data, the focusing error at the main spot is detected. This is because it is necessary to detect.
[0010]
[Problems to be solved by the invention]
However, the conventional optical disc apparatus focusing control method has the following disadvantages.
[0011]
(A) In a digital system that calculates a control command value for a focusing actuator or the like based on a focusing error signal in the focusing control system, a digital operation is performed between the time when the focusing error signal is input and the time when the control command value is output. There is a delay by the time required for processing. Therefore, when the disc rotates during this delay time, the main spot when the control command value is output becomes a position different from the main spot when the focusing error is detected (ie, the current spot). The focusing control at the rotational position is performed based on the detection result of the focusing error at the past rotational position). Since the disturbance that is constantly mixed in the focusing error signal is caused by the surface vibration of the disk synchronized with the rotation, the degree of the detected focusing error changes if the rotational position is different. As a result, the focusing control performance deteriorates due to the time delay in this digital system. Further, when the time delay is excessive, even the stability of the focusing control system is lost.
[0012]
(B) Among the focusing control systems, an analog system (particularly a focusing actuator) has a period from when a control command value is applied to when it starts to exert its effect due to the dead time (phase delay) of the system itself. There is an essential problem that it takes a certain amount of time. Therefore, in order to stabilize the system, the focusing control performance has to be sacrificed to some extent.
[0013]
(C) The amount of operation of the focusing actuator is naturally limited. Therefore, when an excessive focusing error is detected due to a sudden disturbance (unsteady disturbance) caused by a defect such as a scratch on the disk or external vibration, an excessive control command value is output accordingly. The operation amount of the focusing actuator is saturated.
[0014]
(D) Further, when an integral element is included in the focusing control system, when such an excessive control command value is output, a phenomenon called winding occurs and the focusing control performance deteriorates. In winding, when an excessive control command value is limited by the limiter, the actual operation amount of the focusing actuator by the value limited by the limiter is smaller than the operation amount by the original control command value (thus, the original control command value). Therefore, the output side of the control command value misunderstands that the reason why the control effect as expected is that the output value of itself is too small, This is a phenomenon in which an excessive control command value is output even though the limiter is not transmitted to the focusing actuator. When this winding phenomenon occurs, the response of the focusing control system becomes oscillating.
[0015]
As described above, there are various disadvantages in the conventional focusing control method of the optical disc apparatus. Accordingly, an object of the present invention is to provide an optical disc apparatus in which a focusing control system is improved by eliminating these disadvantages.
[0016]
[Means for Solving the Problems]
An optical disc apparatus according to a first aspect of the present invention is an optical disc apparatus having a focusing control system in a position in front of a main spot that is a position for reading recorded data from the optical disc with the direction opposite to the rotation direction of the optical disc as the front. Detect a focusing error First Detection means A second detection means for detecting a focusing error in the main spot, a first filter for extracting a low frequency component of the focusing error signal obtained by the first detection means, and the second detection means And a second filter that extracts a high-frequency component of the focusing error signal obtained by the above-described step, a low-frequency component signal extracted by the first filter and a high-frequency component signal extracted by the second filter Using It is characterized by focusing control.
[0017]
In this optical disk device, By the first detection means, A focusing error is detected at a position ahead of the main spot (that is, a position that should become the main spot due to the rotation of the disk) with the direction opposite to the rotation direction of the optical disk as the front. Therefore, a focusing error when the front position becomes the main spot is detected in advance (to be able to obtain a future focusing error signal).
[0018]
By performing the focusing control based on such a future focusing error signal, the focusing control system cancels the delay time of the focusing control system and performs the focusing control without a time delay (a virtual focusing control system without a time delay is configured. )be able to. As a result, the inconveniences (a) and (b) are eliminated, so that the stability of the focusing control system and the focusing control performance are improved.
[0019]
In this way, when a future focusing error signal is obtained, an excessive focusing error is detected at the position where it will be the main spot from now on due to sudden disturbance caused by a disk defect or external vibration. You can even know that in advance. As a result, measures are taken in advance so that an excessive control command value is not output (for example, a small control command value is output in advance before the position where an excessive focusing error is detected becomes the main spot to perform focusing. It is possible to start driving the actuator), so that the problems (c) and (d) described above are also solved.
[0020]
As specific means for performing in advance such a measure that an excessive control command value is not output, The first Extract low-frequency components from the focusing error signal obtained by the detection means First Further comprising a filter, First Focusing control is performed using the low frequency component signal extracted by the filter. is doing .
[0021]
The reason is as follows. Steady disturbances due to disc surface vibrations are present in the relatively low frequency band of the focusing error signal, whereas sudden disturbances due to disc defects and external vibrations are present in the relatively high frequency band of the focusing error signal. Exists. Therefore, First By performing focusing control using the low-frequency component signal (the signal from which the high-frequency component has been removed) of the focusing error signal obtained by the detection means, the component due to sudden disturbance from the future focusing error signal Since the focusing control is performed using the signal from which the signal is removed, output of an excessive control command value due to sudden disturbance is prevented. As a result, the above disadvantages (c) and (d) are also eliminated. From this point, the stability of the focusing control system and the focusing control performance can be improved.
[0023]
Ma Further, a current focusing error signal is obtained by the second detection means, and a high frequency component of the current focusing error signal is extracted by the second filter, so that a component due to mixing of stationary disturbance is removed. The focusing error signal is obtained. And Low frequency component signal extracted by the first filter and high frequency component signal extracted by the second filter Is used together to perform focusing control.
[0024]
In this way, not only the future focusing error signal from which the component due to sudden disturbance is removed, but also the current focusing error signal that includes the component due to sudden disturbance but has removed the component due to stationary disturbance. By performing focusing control using also, it becomes possible to satisfactorily attenuate the deviation due to the steady disturbance existing in the low frequency band and the deviation due to the sudden disturbance existing in the high frequency band, respectively. Focusing control performance is further improved.
[0025]
In addition, as another example of specific means for performing in advance a measure for not outputting an excessive control command value as described above, the claims of the present invention are provided. 2 As in the optical disc apparatus according to the present invention, first detection means for detecting a focusing error at a position ahead of the main spot, second detection means for detecting a focusing error at the main spot, and detecting external vibration of the optical disc apparatus And a focusing error signal obtained by the first detecting means and a focusing error signal obtained by the second detecting means at a ratio corresponding to the magnitude of the external vibration detected by the vibration detecting means. And weighting means for weighting, and focusing control may be performed using a signal weighted by the weighting means.
[0026]
In this optical disc apparatus, the future focusing error signal obtained by the first detecting means and the current focusing error signal obtained by the second detecting means are detected by the vibration detecting means and the external vibration of the optical disc apparatus is detected. Is weighted by the weighting means at a rate corresponding to the size of the. Then, focusing control is performed using the signal weighted by the weighting means.
[0027]
In this way, by performing the focusing control using the signal obtained by weighting the future focusing error signal and the current focusing error signal at a rate corresponding to the magnitude of the external vibration, the sudden occurrence caused by the external vibration Even when an extraordinary disturbance is mixed in the future focusing error signal, output of an excessive control command value due to the external vibration is prevented.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of an optical path system of an optical pickup of an optical disc apparatus according to the present invention. In this optical pickup, a diffraction grating 2 that splits a laser beam L generated from a semiconductor laser 1 as a light source into a main beam L0 (0th order diffracted light) and side beams L1 and L2 (+ 1st order diffracted light, −1st order diffracted light). These beams L 0, L 1, L 2 are reflected by the half mirror 3, converted into a parallel beam by the collimator lens 4, condensed by the objective lens 5, and irradiated onto the recording surface of the optical disk 6. The
[0031]
The return lights L0 ′, L1 ′, and L2 ′ of the beams L0, L1, and L2 from the recording surface pass through the objective lens 5 and the collimator lens 4 again, and then pass through the half mirror 3 to generate astigmatism. The light is received by a photodetector (photodetector) 8 through a cylindrical lens (not shown).
[0032]
For example, in an optical disk apparatus that employs the three-spot method as a tracking error detection method, a diffraction grating that has already been provided for the three-spot method may be used as it is.
[0033]
Further, as means for dispersing the laser beam L generated from the semiconductor laser 1, a holographic optical element having a function as a diffraction grating, a liquid crystal panel, an electrochemical element, a cylindrical lens instead of the diffraction grating 2 is used. Alternatively, an optically transparent parallel flat plate (for example, a plate glass) inclined at an angle with respect to the optical axis direction of the laser beam L may be provided.
[0034]
FIG. 2 shows an example of the irradiation positions on the recording surface of the optical disk 6 of the beams L0, L1, and L2 of FIG. As shown in the figure, the main spot MS, which is the irradiation position of the main beam L0, and the side spots SS1, SS2, which are the irradiation positions of the side beams L1, L2, are arranged on a line parallel to the track formed by the pits p. In addition, the mounting angle of the diffraction grating 2 is set such that the side spot SS1 is in front of the main spot MS and the side spot SS2 is in the rear of the main spot MS, with the direction opposite to the rotation direction of the optical disc as the front. The positional relationship between the spots MS, SS1, and SS2 is set by the adjustment.
[0035]
Therefore, if a focusing error is detected based on the return light L1 ′ of the side beam L1 from the side spot SS1, a focusing error at a position ahead of the main spot MS by a distance x between the side spot SS1 and the main spot MS is detected. (That is, obtaining a future focusing error signal for a time t determined by the distance x and the number of revolutions n of the disk).
[0036]
Therefore, on the photodetector 8 in FIG. 1, in order to detect a focusing error by the astigmatism method, for example, as shown in FIG. 3, the four-part received light that receives the return light L0 ′ from the main spot MS is received. In addition to the elements (photodiodes) 8A to 8D, four-divided light receiving elements 8E to 8H that receive the return light L1 ′ from the side spot SS1 are provided. (Furthermore, in this example, four divided light receiving elements 8I to 8L for receiving the return light L2 ′ from the side spot SS2 are also provided. The meaning of providing the light receiving elements 8I to 8L will be described later.)
[0037]
The focusing control system of this optical disc apparatus performs focusing control using a signal obtained by any one of the processes listed as [Processing Example 1] to [Processing Example 4].
[0038]
[Processing Example 1]
As shown in FIG. 4, in order to detect a focusing error by the astigmatism method from the output signals E to H of the light receiving elements 8E to 8H that receive the return light L1 ′ from the side spot SS1, FE1 = (E + G) − Calculate (F + H). As is well known, the astigmatism method generates astigmatism in a laser beam so that the light quantity distribution on the four-divided light receiving element becomes a perfect circle in the focused state (the amount of light received by each light receiving element is equal). On the other hand, in the out-of-focus state, this light quantity distribution has an elliptical shape (the amount of light received by the pair of light receiving elements on the diagonal is different from the amount of light received by the other pair of light receiving elements). With regard to the light receiving elements 8E to 8H, this signal FE1 is a focusing error signal. Then, focusing control is performed using the focusing error signal FE1.
[0039]
As described above, the focusing error signal FE1 is a future focusing error signal for a time t determined by the distance x between the side spot SS1 and the main spot MS and the rotational speed n of the disc.
[0040]
The distance x is, for example, in the optical path system of the optical pickup (FIG. 1), the wavelength of the laser generated from the semiconductor laser 1, the distance between the semiconductor laser 1 and the diffraction grating 2, the pitch of the diffraction grating 2, Since the adjustment can be made by changing the focal length of the objective lens 5 or the like, the time t can be set to a desired length by adjusting the distance x.
[0041]
Therefore, for example, by making the time t coincide with the calculation time of the digital circuit of the focusing control system and performing the focusing control using the focusing error signal FE1, the delay time due to this calculation is canceled (virtual calculation It is possible to configure a focusing control system without time delay due to
[0042]
Further, for example, by making the time t coincide with the delay time generated by the focusing actuator of the focusing control system and performing the focusing control using the focusing error signal FE1, a control command is sent to the focusing actuator earlier by the delay time. Since the value can be applied, the delay time of the focusing actuator can be canceled.
[0043]
Further, for example, by performing the focusing control using the focusing error signal FE1 after making the time t coincide with the sum of the delay time of the digital circuit operation and the delay time of the focusing actuator, both of these delay times can be reduced. You will be able to cancel.
[0044]
The focusing error signal FE1 is obtained in this way, and the focusing error signal FE3 (past And a signal FE obtained by adding a signal obtained by multiplying the signal FE1 by a coefficient k (0 ≦ k ≦ 1) and a signal obtained by multiplying the signal FE3 by a coefficient (1-k) as shown in the following equation. The focusing control may be performed using the signal FE, and the coefficient k may be adjusted as appropriate.
[0045]
FE = kFE1 + (1-k) FE3
[0046]
By doing so, focusing control is performed using a signal obtained by weighting a future focusing error signal and a past focusing error signal at an arbitrary ratio for a time t, so that the side spot SS1 and the main spot MS can be controlled. While the distance x is kept constant, it is possible to arbitrarily change how long the focusing control is performed using the future focusing error signal within the time t. (Conversely, when it is not necessary to arbitrarily change the time, the installation of the light receiving elements 8I to 8L in FIG. 3 may be omitted.)
[0047]
[Processing example 2]
As shown in FIG. 5, the low-frequency component of the focusing error signal FE1 obtained in [Processing Example 1] is extracted by a low-pass filter, and focusing control is performed using the low-frequency component signal FE11 extracted by this low-pass filter.
[0048]
This signal FE11 is a signal obtained by removing a high frequency component from the focusing error signal FE1. As mentioned above, steady disturbances due to disc surface fluctuations exist in the relatively low frequency band of the focusing error signal, whereas sudden disturbances due to disc defects and external vibrations are focusing errors. Present in a relatively high frequency band of the signal.
[0049]
Therefore, by using this signal FE11, even if an excessive focusing error is detected at the position where it is supposed to become the main spot from now on due to a sudden disturbance due to a disk defect or external vibration, a future focusing will be performed. Since focusing control is performed using a signal obtained by removing a component due to sudden disturbance from the error signal, output of an excessive control command value due to sudden disturbance is prevented.
[0050]
[Processing Example 3]
As shown in FIG. 6, the same signal FE11 as [Processing Example 2] is obtained. At the same time, a focusing error signal FE2 (current focusing error signal) is obtained by the astigmatism method from the output signals A to D of the light receiving elements 8A to 8D that receive the return light L0 ′ of the main beam L0, and the high-frequency component of this FE2 Is extracted with a high-pass filter. Then, focusing control is performed using both the signal FE11 and the high-frequency component signal FE21 extracted by the high-pass filter.
[0051]
This signal FE21 is a signal including a high frequency component of the current focusing error signal FE2. Therefore, by using the signal FE21 together with the signal FE11, the deviation due to the steady disturbance existing in the low frequency band and the deviation due to the sudden disturbance existing in the high frequency band can be satisfactorily attenuated. .
[0052]
[Processing Example 4]
As shown in FIG. 7, the same focusing error signals FE1 and FE2 as those in [Processing Example 3] are obtained. Then, a signal FE12 obtained by multiplying the signal FE1 by a coefficient k (0 ≦ k ≦ 1) and a signal FE22 obtained by multiplying the signal FE2 by a coefficient (1-k) are obtained, and focusing is performed using these signals FE12 and FE22 in combination. Take control.
[0053]
In this example, an acceleration sensor (not shown) for detecting external vibration applied to the optical disk apparatus is mounted on the optical disk apparatus (however, an appropriate sensor other than the acceleration sensor capable of detecting such external vibration is used. Vibration detection means may be provided). When the external vibration detected by the acceleration sensor is large, the value of k is decreased (for example, less than 0.5). Conversely, when the external vibration is small, the value of k is increased (for example, 0.5 or more). ).
[0054]
As a result, when the external vibration applied to the optical disk apparatus is large, focusing control is performed using a signal obtained by weighting the current focusing error signal FE2 at a larger ratio than the future focusing error signal FE1, and conversely, the external vibration is generated. When the value is smaller, the focusing control is performed using a signal in which the future focusing error signal FE1 is weighted at a larger ratio.
[0055]
Therefore, even when a sudden disturbance due to external vibration is mixed in a future focusing error signal, output of an excessive control command value due to the external vibration is prevented.
[0056]
In the above example, the present invention is applied to an optical disc apparatus that employs the astigmatism method as a focusing error detection method. However, an optical disc that employs another appropriate focusing error detection method (for example, knife edge method). The present invention may be applied to an apparatus.
[0057]
Further, the present invention is not limited to the above example, and it is needless to say that various other configurations can be taken without departing from the gist of the present invention.
[0058]
【The invention's effect】
As described above, according to the optical disc apparatus of the first aspect of the present invention, so-called focusing control based on the future focusing error signal cancels the delay time of the focusing control system, and focusing without time delay is performed. Since the control can be performed, the stability of the focusing control system can be improved and the focusing control performance can be improved.
[0060]
Also, By performing the focusing control using the low-frequency component signal of the future focusing error signal, the focusing control is performed using the signal obtained by removing the component due to sudden disturbance from the future focusing error signal. The This Suddenly It is also possible to prevent the output of an excessive control command value due to incident disturbance. Ru From this point, the stability of the focusing control system and the focusing control performance can be improved.
[0061]
Also, Using not only future focusing error signals from which components due to sudden disturbances have been removed, but also current focusing error signals that have components due to sudden disturbances but have been removed from stationary disturbances By performing focusing control Low There is also an effect that the deviation due to the steady disturbance existing in the frequency band and the deviation due to the sudden disturbance existing in the high frequency band can be attenuated satisfactorily. Ru Thus, the focusing control performance can be further improved.
[0062]
Next, claims of the present invention 2 The optical disc apparatus according to claim 1 performs focusing control using a signal obtained by weighting a future focusing error signal and a current focusing error signal at a rate corresponding to the magnitude of external vibration. In addition to the effect of the optical disk device according to the present invention, when sudden disturbance due to external vibration is mixed in the future focusing error signal, an output of an excessive control command value due to the external vibration is prevented. From this point, the stability of the focusing control system and the focusing control performance can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an optical path system of an optical pickup of an optical disc apparatus according to the present invention.
2 is a diagram showing an example of a beam irradiation position on a recording surface of the optical disc in FIG. 1. FIG.
FIG. 3 is a diagram illustrating an example of arrangement of light receiving elements on the photodetector in FIG. 1;
FIG. 4 is a diagram showing an example of processing in a focusing control system of the optical disc apparatus according to the present invention.
FIG. 5 is a diagram showing another example of processing in the focusing control system of the optical disc apparatus according to the present invention.
FIG. 6 is a diagram showing another example of processing in the focusing control system of the optical disc apparatus according to the present invention.
FIG. 7 is a diagram showing another example of processing in the focusing control system of the optical disc apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor laser, 2 Diffraction grating, 3 Half mirror, 4 Collimator lens, 5 Objective lens, 6 Optical disk, 8 Photo detector, 8A-8H Light receiving element

Claims (2)

In an optical disc apparatus having a focusing control system,
First detection means for detecting a focusing error at a position ahead of a main spot, which is a position for reading recording data from the optical disk, with the direction opposite to the rotation direction of the optical disk as the front;
Second detection means for detecting a focusing error in the main spot;
A first filter for extracting a low frequency component from the focusing error signal obtained by the first detection means;
A second filter for extracting a high frequency component from the focusing error signal obtained by the second detection means;
An optical disc apparatus characterized in that focusing control is performed using a low frequency component signal extracted by the first filter and a high frequency component signal extracted by the second filter. In an optical disc apparatus having a focusing control system,
First detection means for detecting a focusing error at a position ahead of a main spot, which is a position for reading recording data from the optical disk, with the direction opposite to the rotation direction of the optical disk as the front;
Second detection means for detecting a focusing error in the main spot;
Vibration detecting means for detecting external vibration of the optical disc device;
The focusing error signal obtained by the first detecting means and the focusing error signal obtained by the second detecting means are weighted at a rate corresponding to the magnitude of the external vibration detected by the vibration detecting means. With weighting means
An optical disc apparatus characterized in that focusing control is performed using a signal weighted by the weighting means.

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