JP3261915B2 - Tracking control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk as an information recording medium and an apparatus for recording and reproducing information signals using the optical disk. More particularly, the present invention relates to an optical disk by improving the pull-in characteristics and control characteristics of a tracking servo of an optical disk. This is to enable stable and accurate recording and reproduction.

[0002]

2. Description of the Related Art An optical disk has many features such as a high recording density, a long life of a medium for non-contact recording / reproduction, and random access is much faster than a medium such as a tape. Numerous application proposals have been made for compact discs, video discs, and image files, data files, and document files as recording / playback machines. In the field of reproduction-only machines, a fairly large market has already been formed, and a very large market scale is expected with the practical use of recording / reproduction machines.

In such a recording / reproducing method using an optical disk, a beam spot of a laser or the like having a diameter of about 1 μm is usually formed using a laser, and a local spot is formed on a recording film provided on a track of the optical disk. This is a so-called thermal recording in which a temperature rise is caused to cause a physical change such as a reflectivity and a magnetization polarity on a recording film, and an information signal is recorded in a minute range.

[0004] The present invention relates to an improvement in a tracking servo which causes an optical beam to accurately follow a track in the above apparatus. Hereinafter, an example of a conventional tracking servo will be described with reference to the drawings.

FIG. 15 is a block diagram of a conventional tracking servo. In FIG. 15, 100 is an optical disk,
101 is a pre-groove, 102 is a laser as a light source,
103 is a collimator lens, 104 is a beam splitter, 105 is an objective lens, 106 is a tracking actuator, 107 and 108 are detectors, 109 is a differential amplifier, 110 is an equalizer A for tracking servo, 1
11 is a drive amplifier A for tracking, 112 is a switch A for tracking servo, 113 is an equalizer B for feed control, 114 is a command device, 115 is a D / A converter, 116 is a switch B for feed control, and 117 is a switch B for feed control. Access switches C and 118 are drive amplifiers B for feed control, 119 is a linear actuator, and 120 is an optical head.

The operation based on the above configuration will be briefly described below. A pre-groove 101 is provided on the optical disc 100. In the figure, the pregroove is enlarged to help understanding, but the actual width is about 0.6 μm,
The height of the groove is about 0.1 μm, and extremely fine tracks are accurately recorded in advance in a spiral or concentric manner over the entire circumference of the disk. This is to ensure compatibility between unrecorded disks, and recording and reproduction can be easily realized by accurately following the pregroove. Although not shown, a signal indicating a radial position of a track usually called an address and rotational angle position information called a sector are recorded on the pre-groove in a form such as intermittent of the pre-groove. By performing the reproduction, it is possible to obtain information on the position currently being reproduced.

Reference numeral 102 denotes a laser as a light source. Light emitted from the laser is converted into parallel light by a collimator lens 103, reflected by a beam splitter 104 toward the optical disk, and pre-glued by an objective lens 105. −
The light is focused on the substrate 101. The light reflected by the pre-groove 101 passes through the beam splitter 104 via the objective lens 105, and is guided to the photodetectors 107 and 108. A λ / 4 plate may be inserted between the beam splitter and the objective lens as needed to improve the accuracy of the amount of transmitted light, but this is omitted here. 107, 10
The photodetector 8 receives the light diffracted and reflected by the pre-groove, and the light flux condensed by the interference between the 0-order light and the primary light shows the amount of deviation from the center of the pre-groove. The state is reflected, and the difference between the output of each photodetector is detected by the differential amplifier 109, whereby a tracking error signal is obtained. The method of obtaining a tracking error signal in a far-field state where the spot is relatively large by the reflected and diffracted light of the pre-groove is called a far-field method or a push-pull method. The output signal of the differential amplifier 109 passes through an equalizer 110 and a drive amplifier 111, and the tracking actuator 106 outputs the objective lens 1
05 in the radial direction (arrow L direction) of the optical disc.
A tracking servo that accurately displaces the pregroove by displacing a minute amount corresponding to the eccentricity of the disk is realized. Reference numeral 112 denotes a switch A which opens and closes a tracking servo, and is normally in an off state except when reproducing with a light beam following a pregroove. Numeral 113 denotes an equalizer B for feed control, which adjusts frequency characteristics so that the DC component of the tracking servo circuit is stably absorbed by the linear motor 119. 11
Reference numeral 6 denotes a switch B which is turned on when forming a feed control loop substantially in conjunction with the tracking switch 112 described above. Reference numeral 117 denotes an access switch C, which is a D / A whose target position and speed information is 115 from the command device 114.
Provided to the feed control loop via the converter. 11
An eight-drive amplifier is used to amplify the signal of one of the switches 116 and 117 and supply and control the signal to the linear motor 119. By this operation, the optical head 120 becomes 1 μm.
It can accurately follow tracks with a track pitch of a little over m,
The address and the sector at an arbitrary radial position can be searched by being largely displaced in the radial direction (arrow 121) by the linear motor.

For example, when accessing an arbitrary sector of an optical disk having a pre-groove and an address signal at a high speed, a linear motor 11 mounted with an optical head is required.
9 by moving the optical head by the feed control device. For this reason, a current is supplied to a linear motor for controlling the movement of the optical head, and the optical head is moved to the vicinity of the designated sector (hereinafter referred to as a coarse search). At the end of the coarse search, the tracking servo is operated again. The search is performed after a procedure of searching for a sector specified by a track jump or the like (hereinafter referred to as a fine search). During this time, the above address,
The read information after demodulation of the sector and the information on the number of tracks crossing the track are input to the command device, and the difference between the current position and the target position is always managed, thereby realizing quick access to the target track.

[0009]

In the conventional tracking servo described above, when the objective lens 105 is displaced by the tracking actuator 106 in the direction of arrow L, the output of the differential amplifier 109 becomes the pre-groove 101.
Undesirable disturbances other than the tracking error signal caused by the above-mentioned cause a problem that the pull-in of the tracking servo becomes unstable.

This will be described with reference to FIGS. The differential amplifier 109 when the switch 112 is now opened
Is shown in FIG. 16 (a). At this time, when the tracking actuator 106 shown in FIG. 15 is driven to give a displacement shown in FIG. 16C, a fluctuation of the tracking error signal as shown in FIG. 16B is observed. That is, it can be seen that disturbance occurs in the tracking error signal output from the differential amplifier 109 due to the light beam irradiated on the 100 optical disks due to the vibration of the objective lens 105.

This disturbance is caused by the fact that the spot of light on the photodetectors 107 and 108 moves by the above-mentioned vibration of the objective lens 105 and the distribution fluctuates (hereinafter referred to as spot movement disturbance), and the objective lens of 105 Deviates from the center of the incident light entering the objective lens (hereinafter referred to as incident distribution disturbance).

In a spot movement disturbance, the light detector 1
The light spot projected on 07, 108 typically has a diameter of 4
When the objective lens is moved by about 100 μm and moves by 100 μm, the tracking error signal has a difference of 50% or more between the plus side and the minus side, and the DC component is imbalanced by 1 or more. The disturbance due to the movement of the spot on the photodetector has the vibration frequency and the phase of the objective lens substantially coincident with each other, and the amplitude is almost proportional to the moving amount of the objective lens. This situation will be described with reference to FIG. 17, which is a schematic diagram of a detection portion when the tracking servo is operating. FIG. 17 (b) shows that the eccentricity is zero, the center of the objective lens 105,
This shows a state in which the division centers of the photodetectors 107 and 108 match. In this state, ideally, the first-order diffracted lights P1 and P2 at both ends of the pre-groove 101 and the zero-order light P0 limited by the aperture of the objective lens are accommodated in the respective photodetectors, and the pre-groove is interfered by the phase difference. A tracking error signal indicating the positional relationship between the groove 101 and the incident light in the track direction is detected. The signal is transmitted to the tracking actuator 10 through each element of the tracking servo described above.
The objective lens follows the pre-groove accurately according to the eccentricity of the disk. On the other hand, in FIGS. 17A and 17C, as a result of the above-described eccentricity follow-up, the objective lens moves in the direction corresponding to △ x1 and △ x2 in the disk with large eccentricity. P1 leaks into the photodetector 108 as shown in the stage (a) or P2 leaks into the photodetector 107 as shown in (c).
Of the tracking error signal. Here, since the phases of P1 and P2 are inverted, mixing occurs on the detector, and it becomes impossible to separate them after detection. If this amount becomes too large while following the eccentricity of the disk, the tracking servo will not be able to operate normally and will be disengaged. The maximum amount depends on the configuration of the detection system,
The value is around +/− 200 μm without correction or the like. As described above, in FIG. 17, the state where the relationship between the pre-groove and the objective lens is constant is easier to understand. Therefore, the state where the tracking servo is operated has been described. 107, 1
08 and the objective lens 105 are the same, and when the objective lens is vibrated by a disturbance as shown in FIG. 16C, the tracking error signal is added and modulated according to the disturbance as shown in FIG. Will receive.

In order to reduce the occurrence of the incident distribution disturbance, the diameter of the incident light beam is generally set to be larger than the diameter of the objective lens, the light intensity distribution is made as flat as possible, and the occurrence of the disturbance is reduced. The influence on the tracking error signal appears at a frequency that is twice the vibration frequency of the objective lens, and the amplitude is relatively small as compared with the spot movement disturbance because the distribution of the incident light beam is suppressed relatively flat. However, if the displacement of the objective lens exceeds a specified range at the time of the above-described search or the like, the incident distribution disturbance appears relatively large. In particular, in recent devices according to the present invention in which the optical head is required to be smaller, lighter, and faster in access, together with the simplification of the support mechanism of the objective lens,
In many cases, it is difficult to perform the tracking servo pull-in operation again after the search due to the disturbance to the two types of tracking error signals, and the disturbance occurs when the switch 112 is closed and the tracking servo is operated. Is still generated, especially when tracking is performed on an optical disk with large eccentricity.
There is a problem that stability is lost when the bob is operated again.

[0014]

In order to solve the above problems, a tracking servo device according to the present invention uses an optical beam on an optical disk to record and reproduce information signals on the optical disk.
A tracking actuator for detecting a tracking error signal from the optical disk and displacing the objective lens with respect to the light beam in the radial direction of the optical disk by using the tracking error signal; and substantially controlling the light beam and the tracking actuator. And a linear actuator which moves in the radial direction of the optical disk. When the optical head is moved at a high speed, a third position is used so that the positions of the actuator, the light beam and the photodetector do not change by using a tracking error signal.
Is provided.

The third servo has extraction means for extracting a tracking error signal at a specific position in a direction orthogonal to the track, and outputs the light beam and the objective lens by inputting the output of the extraction means to the objective lens driving means. A control system is configured to control the relative positions of the two to be substantially constant. Further, the extracting means includes a track center detecting means obtained from the sum output of the photodetector, and a holding means for extracting the output of the tracking error signal detecting means by the output of the center detecting means.

Here, the center detecting means is different between a read-only disc and a recording / reproducing disc. In the case of a read-only disc on which information pits have been recorded in advance, the information reproduction of the pit train when crossing a track is performed based on the sum output of the photodetector. Level detection means for detecting a signal and detecting that its level has become equal to or more than a certain value or less than a certain value, or extreme value detection for detecting the maximum value or the minimum value of the output detection means of the envelope detection means of the reproduced signal of the pit train. Means can be used.

In the case of a recording / reproducing disc, since the information pit string has only an address portion in an initial stage before information is recorded, the center detecting means determines that the level of the groove signal is equal to or more than a certain value from the sum output of the photodetector. Alternatively, it can be realized by a configuration using a level detecting means for detecting a fixed value or less, or a polarity detecting means for detecting a change in polarity of the change rate polarity of the output of the sum output of the photodetector.

Further, as a configuration that can be used in a read-only disc and a recording / reproducing type, an oscillating means for generating a signal having a frequency higher than the primary resonance frequency of an objective lens driving means (tracking actuator); The objective lens is oscillated with a small amplitude so that the track crossing frequency is always at a somewhat high frequency, and the tracking error signal is applied to the tracking actuator through a low-pass filter. .

As another configuration, first and second information amplitude detecting means for detecting the information signal amplitude of each output of the tracking photodetector divided into two, and the first and second information amplitude detecting means.
An amplitude difference detector for detecting a difference between the information amplitude detectors is input to the objective lens driving unit, and the AC amplitudes of the two photodetectors are controlled to be substantially the same. It has a configuration of:

Further, each of the above-described components is provided with a detector for detecting the displacement of the tracking actuator in the tracking direction, and only the AC component of the output of the detector is fed back to the tracking servo, and the respective components are supplied via a low-pass filter or the like. The signal and the band of the extracting means are divided, added and synthesized, and then input to the tracking actuator.

[0021]

According to the present invention, the track center signal in the tracking error signal can be extracted by the above-described structure, and unnecessary vibration of the objective lens which generates the spot movement disturbance and the incident distribution disturbance can be accurately detected. Since a third servo loop for supplying to the driving means is constituted and unnecessary vibration can be suppressed efficiently, the displacement of the light beam incident on the objective lens is suppressed within a specified range, so that the tracking servo system is desirably used. A stable tracking servo was realized by suppressing oscillation and improving the pull-in characteristics of the tracking servo. Furthermore, when the tracking servo is pulled in, the high-speed movement by the linear actuator ends, so that the track traversing frequency decreases, and the detection frequency characteristic of the extracting means decreases, so that the stability of the third servo system decreases. Therefore, the AC component of the movement of the objective lens is fed back to play the role of frequency compensation, and the stability of the third servo system can be improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A tracking servo device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. In the figure, 1 is an optical disk, 2 is a disk motor, 3 is an optical head, 4 is a laser, 5 is a collimator lens, 6 is a beam splitter, 7 is a λ / 4 plate, 8 is an objective lens, 9 Are tracking actuators, 10,
11 is a photodetector, 12 is an incident light beam, 13 is a reflected light beam, 1
4 is a linear actuator, 15 is a differential amplifier, 16 is an equalizer a, 17 is a tracking switch a, 18
Is a drive amplifier a, 19 is an equalizer b, 20 is a feed switch b, 21 is a drive amplifier b, 22 is a command device such as a microcomputer, 23 is a D / A converter, 24
Is an access switch c, 25 is an adder, 26 is a center detector, and 27 is a third servo switch d.

The operation of the tracking servo system configured as described above will be described. In the case of a recording / reproducing type disc, a pre-groove described in the conventional example is provided on the optical disc 1,
The read-only disc is provided with a pit row of information pits, and is rotated at a predetermined rotation speed by the disc motor 2 and the turntable 2a.

Reference numeral 4 denotes a laser as a light source. Light emitted from the laser is converted into parallel light by a collimator lens 5, reflected by a beam splitter 6 toward the optical disk, and λ / 4 of 7 is output. The light is accurately focused on the information recording surface of the optical disk 1 by the objective lens 8 via the plate. The beam splitter 6 often uses a polarization beam splitter to reduce the amount of light returning to the laser. Optical disk 1
Is reflected by the beam splitter 6 through the objective lens 8 and the .lambda. / 4 plate 7, and the photodetectors 10, 11
It is led to. At this time, if necessary, a convex lens for narrowing down is often inserted between the beam splitter and the photodetector, but is not shown here. The incident light flux 12 has a diameter larger than the effective diameter of the objective lens 8 and makes the distribution as flat as possible in order to reduce the occurrence of the incident distribution disturbance. Further, the optical head 3 includes a focus photodetector for detecting a focus error of the light spot, a focus actuator for moving the objective lens in the direction of the surface deflection of the disk, and the like. There is a detection system and a drive system of a focus control loop that accurately follows the above, but the description is omitted because it is not directly related to the present invention. Similarly, as for the entire apparatus, a circuit for a focus servo loop combining them and a modulation / demodulation circuit for recording / reproducing a signal are not directly related except for ON / OFF timing, so that illustration and description are omitted. I do.

The differential amplifier 1 which is a tracking error signal
The output signal of No. 5 is adjusted in frequency characteristics by 16 equalizers a which are phase compensators, the response characteristics of the tracking servo are optimized, and the tracking signals of 9 are passed through the switches a and 18 of the drive amplifier a. The tracking is supplied to the actuator, and the objective lens 8 is displaced by a very small amount corresponding to the eccentric amount of the disk by about 100 μm in the radial direction (the direction of the arrow 1) of the optical disk to accurately follow the track of the pre-groove or the track of the information pit row. It constitutes a servo. The switch a 17 is for opening and closing the tracking servo, and is normally in an off state except when reproducing with a light beam following a pre-groove. When jumping to an adjacent track, the switch is in an off state only for the jump period. . Reference numeral 19 denotes a feed control equalizer b, which adjusts and stabilizes the frequency characteristic so that the DC component of the tracking servo circuit is stably absorbed by the linear actuator 14 and stabilizes the frequency characteristic.
This is to optimize the response of the voltage. The switch b at 20 is substantially in cooperation with the switch a for tracking, except when jumping, and is turned on when a feed control loop is formed. The 24 access switches c are
The target position and speed information is output from the command device 22 to the D / A converter 23 via a bus 22d, applied to the feed control loop, and passed through the drive amplifier b 21 to the switches 20 and 24 of the switch c. Among them, any one of the signals is amplified and supplied to the linear actuator 14 for driving control. The optical disk can be moved at a high speed in the radial direction (the direction of the arrow x) by passing a current through the 14 linear actuators using the above signals. Linear actuator
Although not shown, the motor comprises a coil and a magnetic circuit. With the above configuration, the optical head 3 follows a track having a pitch of slightly more than 1 μm with a high accuracy of +/− 0.1 μm or less, or is largely displaced in the radial direction (arrow x) by a linear motor and at an arbitrary radial position. The address, sector and information recorded therein can be searched.

Regarding the center detector which is a feature of the present invention,
A first embodiment in which information pits such as a compact disk are recorded in advance will be described with reference to FIGS. FIG. 2 is a block diagram showing a configuration of the center detector, and FIG. 3 is an operation explanatory diagram showing main waveforms.

In FIG. 2, 31 is a detector, 32 is a level detector, 33 is a sample hold, and 34 is an equalizer c.
It is. In the output of the adder 25 in FIG. 1, the recorded information appears as a high-frequency signal. This is due to the effects of pits such as phase difference and scattering of light, and the pitted portion has a small amount of reflected light, and the non-pitted portion has a large amount of reflected light because it is close to a mirror surface.
This is because it is detected as the strength of the electric signal. At this time, if the switch a17 of the tracking servo loop is in the off state, the light spot does not follow the track, and the information pits as shown in FIG. Rows 51a, 51b ... 51
e, 51f are replaced with 52a, 52a ', 52b, 52b'.
・ Being crossed like 52e, 52e ', 52f,
The output of the adder 25 becomes a burst signal for discretely reproducing a high-frequency signal as shown in FIG. 3 (b). As described above, the amount of reflected light is small and the signal level is low in the portion where the information pit is present. FIG. 3 (a) shows a representation in which only one information pit crosses one track for convenience of illustration, but in reality each burst signal contains a number of high-frequency signals determined by the relationship between the rotation speed and the track crossing speed. I have. FIG. 3C shows a signal obtained by removing a direct current component of this signal. When the signal passes through a detector for detecting the envelope of 31, an envelope signal shown in FIG. 3D is obtained. Fig. 3
The track center pulse signal of (e) is obtained. This signal means that the information pits are included most, and the pulse portion is a signal that substantially represents the center of the track. FIG. 3F shows a tracking error signal of the output of the differential amplifier 15. When this tracking error signal (f) is extracted by means of the sample hold 33 or the like at the output of the level detector 32, the center position of the tracking error signal caused by spot movement disturbance due to the vibration of the objective lens shown in FIG. , The center correction signal indicating the deviation amount is detected. Originally, when the tracking servo is off, the center point of the track is the zero point of the tracking error signal when the tracking servo is off. A signal proportional to the vibration is detected. Therefore, the output of the center detector 26 is supplied to the tracking actuator 9 via the equalizer c of 34, the switch b of 27, and the drive amplifier of 18 to form a control system for suppressing the vibration. Even when the tracking servo loop is not operating, unnecessary vibration of the objective lens 8 is minimized, the tracking error signal is kept normal, and even when the random access is severe, such as at the end of random access, the vibration is large. Vibration can be suppressed efficiently, and stable tracking servo pull-in can be realized instantaneously. The loop gain of the vibration suppression control loop as the third tracking servo is about 1/10 of the gain of the tracking servo loop, which is sufficient.
Since the tracking servo loop gain is about 60 dB, a sufficient effect can be obtained when the gain of the vibration suppression control loop is about 40 dB and the cutoff frequency is about 300 Hz.

In this case, the maximum value of the envelope signal shown in FIG. 3D is detected to detect the center of the track such as 52a, 52b. On the other hand, the minimum value of the envelope signal is detected and 52a ', The same effect can be obtained even if the center between adjacent tracks such as 52b 'is detected, and if both signals are combined, the sampling frequency for detection can be doubled and more stable detection characteristics can be obtained. It is.

The detection of the track center pulse has been described by using the level detector such as the comparator to detect the vicinity of the maximum value and the minimum value. Detected levels can be made relative, such as floating slice technology that generates and uses levels and can respond to changes in the level of high-frequency signals. Maximum value detection circuits and minimum value detection circuits that detect signal polarity changes The accuracy of center detection may be increased by using the method described above.

Next, a second embodiment of the center detector 26 will be described with reference to FIGS. This embodiment shows a case of a recording / reproducing type disc having a pre-groove,
As described above, even if the information pit does not exist except for the address portion, it is configured to be detected. FIG. 4 is a block diagram of a center detector 26b that replaces the center detector 26 of FIG. 1. Components having the same functions as those of FIG. 2 are denoted by the same reference numerals. FIG. 5 is a waveform diagram showing main detected waveforms.

In FIG. 4, 35 is a filter, 36 is a level detector, 33 is a sample and hold, and 34 is an equalizer c. The filter 35 is a combination of a low-pass filter that removes a high-frequency signal and a DC cut filter that removes a DC component when there is a recording signal 55 as shown in FIG. As shown in FIG. 5 (b), in a normal recording / reproducing type disc, the output of the adder 25 has different reflectivities between the upper pre-groove 54a and the adjacent pre-groove 54a '. , Duty ratio, depth and the like.
Here, a case will be described in which the reflectivity is higher on the pre-groove, and when information is recorded, the reflectivity of that portion decreases. FIG. 5A shows pre-grooves 53a and 53b.
Shows the positional relationship between the light spots 54a, 54a ', etc., and (b) shows the output of the adder 25, which is a high-level signal on a pre-groove having a high reflectivity. An existing pregroove contains a high frequency component such as 55b. Here, the frequency of the signal b is a frequency crossing the track, and the maximum speed at the time of high-speed access is about 500 KHz, and the frequency of 55b is about 10 times that of 5 to 10 MHz, so that it is sufficiently separated by a low-pass filter in 35. It is possible, and it becomes a waveform close to a sine wave as shown in (c). Here, the pulse at the maximum reflectivity in (d) is detected as the track center pulse using the level detector 36, and the pulse portion becomes a signal representing the approximate center of the track. (E) is a tracking error signal of the output of the differential amplifier 15 in FIG. When the tracking error signal (e) is extracted by means of the sample hold 33 or the like at the output of the level detector 36, the tracking error signal from the center position of the tracking error signal caused by spot movement disturbance due to the vibration of the objective lens shown in (f) is obtained. A center correction signal indicating the amount of deviation is detected. The output of the center detector 26b is
In the same manner as in the embodiment, the control system supplies the signal to the tracking actuator 9 via the drive amplifier of the 34 equalizers c and 27 and the switches b and 18 to suppress the vibration. When the camera is not operating, unnecessary vibration of the objective lens 8 is minimized, the tracking error signal is kept normal, and efficient movement is performed even in a state of high vibration due to rapid movement such as at the end of random access. Suppressed and stable tracking servo pull-in can be realized instantaneously. Since the purpose of this loop is to suppress vibration, the gain of the DC component may be lowered, and the level of the DC component may vary depending on the accuracy of the detection system such as the pulse width of the sample and hold level detector 36. Although different, it is desirable that the center of the incident light beam 12 and the center of the objective lens and the center of the tracking photodetectors 10 and 11 are completely in an ideal state, and it is desirable that the DC component of the detection signal be zero. However, there is no problem in suppressing vibration. This is the same in the first embodiment. Therefore, the role of the center detectors 26 and 26b is stable if the tracking error signal at almost the same position on the track can be extracted even if the center of the track cannot be accurately detected. Vibration suppression control can be realized.

Next, an embodiment of the level detector 36 of the second embodiment will be described with reference to FIG. FIG. 6A is a circuit configuration diagram, and FIGS. 6B to 6E are waveform examples of main parts. FIG.
In (a), 41 is a comparator, 42 is an exclusive OR (hereinafter referred to as EXOR) 43, 44, 46 and 47 are resistors, and 45 and 48 are capacitors. (A) input terminal i
Is a signal (b) close to a sine wave, which is the output of the filter 35 of FIG. A signal having the same phase as i is input to the negative input of the comparator 41, and a signal (c) whose phase is slightly delayed by the resistor 44 and the capacitor 45 is input to the positive input, and voltage comparison is performed. A pulse waveform (d) that switches at the point where the change polarity changes is output. This pulse
The signal is switched near the point indicating the maximum value and the minimum value of the signal (b). When this pulse is input to the EXOR 42 with one of them slightly delayed by the resistor 47 and the capacitor 48, the maximum value of the output of the adder 25 corresponding to the center of the pre-groove and the center between adjacent pre-grooves as shown in (e). , A level detector capable of outputting a pulse with both the minimum value and the minimum value can be configured, and the sampling frequency can be increased, which is effective in stabilizing the vibration suppression control system of the present invention.

In this embodiment, an example is shown in which the reflectance on the pre-groove is high. However, in the case where the relationship between the reflectance on the pre-groove and the relationship between the pre-groove and the pre-groove are opposite in relation to the depth of the pre-groove. However, since recording is not performed by a change in reflectance as in magneto-optical recording, it can be used sufficiently even when there is no change in the signal of the adder between a recorded portion and an unrecorded portion.

Next, a third embodiment of the center detector will be described with reference to FIGS. In the present embodiment, the center of the track is detected from the tracking error signal itself regardless of the presence or absence of the information pit or the pre-groove. FIG. 7 is a block diagram of a center detector 26c to be replaced with the center detector 26 of FIG. 1. Components having the same functions as those of FIG. 2 are denoted by the same reference numerals. FIG. 8 is a waveform diagram showing main detected waveforms of the present embodiment.

In FIG. 7, reference numeral 61 denotes a positive peak position detector of the tracking error signal, 62 denotes a negative peak position detector, 6
Reference numerals 3 and 64 denote a sample and hold, 65 denotes a synthesizer, and 34 denotes an equalizer c.

The operation will be described below with reference to the waveform diagram of FIG. FIG. 8A shows a tracking error signal, and FIG.
Of the differential amplifier 15 of FIG. Positive peak position detector 6
1 outputs a signal (b) obtained by pulsing the maximum value portion of the comparator 41 in FIG. This is EXOR42 of FIG.
Can be easily obtained by replacing with a logical product circuit or by pulsing one edge with a monomultivibrator. Similarly, the negative peak position detector outputs a signal (c) in which the minimum value portion of the comparator 41 in FIG. 6 is pulsed by replacing the EXOR 42 with a logical sum or using a multivibrator. Sample hold 63, 64
Samples and holds the tracking error signal at the outputs of the positive peak position detector 61 and the negative peak position detector 62, and outputs signals having substantially the same waveforms as those shown in FIGS. Output. The two signals are subjected to voltage division combining such as resistance division by the combiner 65, and a signal is generated in which the DC component is removed while leaving the amount of deviation from the optical axis center of the objective lens. The output of the center detector 26c is output to 34 equalizers c and 27 switches b and 18 in the same manner as in the first embodiment.
Is supplied to the tracking actuator 9 via a drive amplifier of the above, the control system for suppressing the vibration is minimized, unnecessary vibration of the objective lens 8 is minimized, the tracking error signal is kept normal, and the random access is completed. Vibration can be suppressed efficiently even in a state where there is a lot of vibration due to strong movements such as time, and stable tracking servo pull-in can be realized.

Next, a fourth embodiment of the center detector will be described with reference to FIGS. In this embodiment, similarly to the third embodiment, the center of the track is detected from the tracking error signal itself regardless of the presence or absence of information pits and pre-grooves. FIG. 9 is a block diagram of a center detector 26d to be replaced with the center detector 26 of FIG. 1. Components having the same functions as those of FIG. FIG. 10 is a waveform diagram showing main detected waveforms of the present embodiment.

In FIG. 9, 66 is a low-pass filter,
67 is an oscillator, 68 is an adder, and 34 is an equalizer c having the same characteristics as in the first embodiment.

The operation will be described below with reference to the waveform diagram of FIG. FIG. 10A shows a tracking error signal which is an output of the differential amplifier. This embodiment is most different from the other embodiments in that the frequency of the tracking error signal is kept high when the vibration suppression control loop is operating. It amplitude is small but finely vibrating the objective lens is added to the output of the oscillator 67 of the relatively high frequency of about 10～50KHz <br/> as (b) to the adder 68, the track 2 to three Is always crossed at the addition frequency. For this reason, the frequency of the tracking error signal is high as a carrier of disturbance such as spot movement, and simply removing the tracking error signal by the low-pass filter 66 results in the amount of displacement from the optical axis center of the objective lens as shown in FIG. To generate a signal. The output of the center detector 26d is supplied to the tracking actuator 9 via the equalizer c of 34, the switch b of 27, and the drive amplifier of the switch 18 as in the other embodiments, to constitute a control system for suppressing the vibration. As a result, unnecessary vibration of the objective lens 8 is minimized, the tracking error signal is kept normal, and vibration is efficiently suppressed even in a state of high vibration due to rapid movement such as at the end of random access. The servo pull-in can be realized.

The present embodiment has the advantage that the configuration can be extremely simplified, but it is not possible to perform a coarse search by counting the track crossing signals normally used during high-speed access, so a radial position detector such as a linear encoder is used. This is an extremely effective configuration in the device. In addition, even when counting the track crossing frequency, it can be used together by a method such as using it for a short time from the end of the rough search until the track is pulled in. Further, by using in combination with the above-described first to third embodiments, a solution to the case where the eccentricity is extremely small, the number of samples is small, and the sample frequency is too low, and the frequency characteristics of the detection system cannot be obtained. Applicable as

In the above embodiment, the oscillator 67 is separately provided. However, the apparatus of the present invention is usually provided with a crystal oscillator such as for a microcomputer and for detecting synchronization, and in most cases, it is necessary to newly provide a crystal oscillator. However, the purpose can be sufficiently achieved by using them together.

Next, the operation of the fifth embodiment of the present invention will be described with reference to the drawings. FIG. 11 is a block diagram of the center detector 26e of the present embodiment, and FIG. 12 is a main waveform diagram.

In FIG. 11, 71 and 72 are high frequency amplitude detectors, 71a and 72a are DC cut filters,
b and 72b are pedestal clamps, 71c and 72c are peak holds, 73 is a differential amplifier, and 34 is an equalizer c.

The operation of this embodiment will be described below with reference to the waveform example of FIG. FIGS. 7A and 7D show detection waveforms of the photodetectors 10 and 11 for detecting a tracking error signal. In the present embodiment, a description will be given by treating a high-frequency signal generated by information pits as a target AC signal. However, a similar effect can be obtained by using an information signal recorded on a pre-groove or an address signal recorded on 20 to 30 in one track as a target signal. Can be obtained. FIGS. 7A and 7D include DC components V1 and V4 corresponding to the reflectivity of the disk, AC components V2 and V5 corresponding to track traversal, and high-frequency signals V3 and V6 based on information pits. The AC component is subtracted by the differential amplifier 15 to remove the DC component corresponding to the reflectivity of the disk, and becomes a tracking error signal as described above. The high-frequency signal generated by the information pits appears as a discrete burst waveform at a low level of V2 and V5 where the reflectivity decreases due to the information pit train.
At the time of normal reproduction, in order for the tracking servo system to accurately follow the track, the V2 and V5 AC components disappear, and a DC signal of only a low level portion and a high-frequency signal of uniform amplitude appear continuously. do not do. here,
The tracking error signal has the opposite polarity on each photodetector,
High frequency signals are of the same polarity. This is because, as shown in FIG. 17, the tracking error signal has the opposite polarity because the tracking error signal is detected by the interference between the first-order diffracted light and the zero-order reflected light due to both edges in the tangential direction of the information pit. Is configured. Therefore, FIG.
When the center line is greatly displaced due to spot movement disturbance as in (c), synthesis occurs in the photodetector, and even if the difference is taken, an accurate spot movement amount on the photodetector is detected. Can not do. This embodiment utilizes the fact that the high-frequency signal is in the same phase in each photodetector because the intensity of the 0th-order light generated by scattering, phase difference, and diffraction due to the information pit is modulated as described above. Things. FIGS. 12B and 12E show signals obtained by extracting only a high-frequency signal with a diode and a capacitor and performing pedestal clamping. FIGS. 8C and 8F show the detection of the peak of the pedestal clamp signal, which can be easily realized by using a peak hold circuit or a sample hold. (G) is a signal obtained by taking the difference between (c) and (f) with the differential amplifier 73, and it is possible to detect a signal substantially similar to the signals of the first to fourth embodiments. The feature of this embodiment is that it can be used together with a tracking servo system. However, in the case of the combined use, the gain of the tracking servo system is reduced due to the polarity of suppressing the movement of the spot on the photodetector. Therefore, for example, the gain of a sufficiently low frequency of a low frequency component of one rotation or less is increased. By switching between the normal tracking servo and the vibration suppression servo of the frequency characteristic, it can also be used for stabilizing the detection operation of the normal tracking servo system. When used in combination, an equalizer and an amplifier can be added separately from the equalizer c, and the configuration can be realized by adding a configuration such as adding an input between the equalizer a16 and the switch a17 of the tracking servo system.

In the above description, the loop in which the amplitude of the high-frequency component is the same between the two photodetectors is configured. However, a configuration in which the DC level of the mirror surface portion where the information pit does not exist can be made uniform. The simplest configuration in that case is 71a, 7
Except for the DC cut of 2a and the pedestal clamps of 71b and 72b, it is possible to use only the peak hold.

In each waveform diagram, FIG. 3 (g), FIG.
(F), FIG. 8 (f), FIG. 10 (c), and FIG. 12 (g) show relatively large error signals indicating the center position. However, this control system is a negative feedback control system, and the control loop Is composed,
During normal operation, the error signal amplitude is naturally suppressed to about 1 / loop gain, and the amplitude is sufficiently small, but the figure is large for easy understanding of the description. This is indicated by an error signal.

Next, a sixth embodiment will be described with reference to FIGS.
4 will be described. The sixth embodiment is obtained by adding a tracking position detector loop as a compensation loop of the first embodiment. In FIG. 13, the same components as those in the first embodiment are denoted by the same reference numerals, and the operation is the same, so that the detailed description is omitted here.

In FIG. 13, reference numeral 75 denotes a tracking position detector, 76 denotes a differentiator, 77 denotes an equalizer d, and 78 denotes an adder. The operation will be described below. The 75 tracking position detector is like a photocoupler in which an LED and a photodetector are paired, and is configured so that the LED light is reflected by the support of the objective lens, and the amount of reflected light changes according to the amount of displacement. Since it is often difficult to use strictly DC at the center of the dynamic range of the tracking servo system, the output is cut by the differentiator 76 to remove the DC component. It is a signal that handles only As a result, the characteristic of the differential output becomes a signal for speed control. After the frequency characteristic is adjusted by the equalizer d at 77 and combined with the output of the center detector 26 at the adder at 78, the driving circuit is switched through the switch d. 18 and input to the objective lens. 14A shows the frequency characteristic of the center position detector of the first to fifth embodiments, and FIG. 14B shows the frequency characteristic of the combination of the tracking position detector and the differentiator. Differential characteristics are exhibited in the band of the signal, and thereafter, unnecessary high frequencies are attenuated like a band-pass filter. Here, although each frequency differs depending on the system, f1 = 10 Hz, f2 = 50 Hz, f
3 = approximately 500 Hz. With this configuration, when the tracking servo is pulled in, the high-speed movement by the linear actuator ends, so that the track traversing frequency is lowered, and the detection frequency characteristic of the extracting unit is lowered, so that the stability of the vibration suppression servo system is reduced. Therefore, the AC component of the movement of the objective lens is fed back, and the stability of the system can be improved as frequency compensation.

The tracking position detector has been described using a photocoupler as an example. However, the present invention is not limited to this, and any method can be used as long as the amount of movement of the objective lens in the tracking direction can be detected.

The configuration of the circuit and the like is not limited to this embodiment, and does not ask analog signal processing or digital signal processing.

Although the present embodiment has been described using an optical disk, an optical card having the same configuration, an optical tape, or the like may be used.
It is obvious that the technique is effective for an apparatus that performs optical recording and reproduction.

[0053]

As described above, according to the tracking control apparatus of the present invention, the tracking position detector for detecting the movement of the objective lens in the tracking direction, the differentiator for cutting the DC component of the tracking position detector, and An extracting means for combining the output of the extracting means with the output of the combining means, inputting the output of the synthesizing means to the objective lens driving means, and extracting a tracking error signal at a specific position with respect to the track in a direction orthogonal to the track; And a third control means for inputting an output of the extraction means to the objective lens driving means so as to control the relative position between the light flux and the objective lens to be substantially constant. In the case where there is an information pit, the level of the information reproduction signal of the pit row is equal to or more than a certain value from the sum output of the photodetector or Level detection means for detecting that the value has become below a predetermined value, or extreme value detection means for detecting the maximum value or the minimum value of the output of the envelope detection means, and in the case of a pregroove, the center detection means is the sum of the photodetectors. Level detecting means for detecting the level of the groove signal from the output to be equal to or more than a fixed value or less than the fixed value, or polarity detecting means for supplying the sum output of the photodetector to the filter and detecting switching of the change rate polarity of the output of the filter. In order to add a simple configuration, or to keep the frequency of the tracking error signal high, the output of the oscillator having a relatively low frequency of about 10 to 50 KHz is added to the adder, and the objective lens is slightly vibrated. , So as to always cross two or three tracks at the addition frequency, to artificially increase the frequency of the tracking error signal, By simply adding a configuration that generates a signal corresponding to the amount of deviation from the center of the optical axis of the objective lens by simply removing the signal with a low-pass filter, vibration during high-speed access is suppressed, stabilizing track pull-in, and high-speed access. It has a great effect on the formation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a main block diagram of a center detector according to the first embodiment.

FIG. 3 is a main waveform diagram of the first embodiment.

FIG. 4 is a main block diagram of a center detector according to a second embodiment.

FIG. 5 is a main waveform diagram of the second embodiment.

FIG. 6 is a circuit diagram and a waveform diagram of an embodiment of peak position detection.

FIG. 7 is a main block diagram of a center detector according to a third embodiment.

FIG. 8 is a main waveform diagram of the third embodiment.

FIG. 9 is a main block diagram of a center detector according to a fourth embodiment.

FIG. 10 is a main waveform diagram of the fourth embodiment.

FIG. 11 is a main block diagram of a center detector according to a fifth embodiment.

FIG. 12 is a main waveform diagram of the fifth embodiment.

FIG. 13 is a block diagram of a sixth embodiment.

FIG. 14 is a frequency characteristic diagram of the sixth embodiment.

FIG. 15 is a block diagram of a conventional example.

FIG. 16 is a main waveform diagram of a conventional example.

FIG. 17 is a schematic diagram of tracking error signal detection.

[Explanation of symbols]

 Reference Signs List 1 optical disk 2 disk motor 3 optical head 4 laser 5 collimator lens 6 beam splitter 7 λ / 4 plate 8 objective lens 9 tracking actuator 10 photodetector 11 photodetector 12 incident light flux 13 reflected light flux 14 linear actuator Reference Signs List 14 linear actuator 15 differential amplifier 16 equalizer a 17 tracking switch a 18 drive amplifier a 19 equalizer b 20 feed switch b 21 drive amplifier b 22 command device 23 D / A converter 24 access switch c 25 adder 26 center detection Device 27 Third servo switch d 31 Detector 32 Level detector 33 Sample hold 34 Equalizer c 35 Filter 36 Level detector 61 Positive peak position detector 62 Negative peak position detector 63, 64 Sump Hold 65 Synthesizer 71, 72 High frequency amplitude detector 71a, 72a DC cut filter 71b, 72b Pedestal clamp 71c, 72c Peak hold 73 Differential amplifier 75 Tracking position detector 76 Differentiator 77 Equalizer d 78 Adder 100 Optical disk 101 Priggle 102 Laser 102 as a light source 105 Objective lens 106 Tracking actuator 107, 108 Detector 109 Differential amplifier 110 Equalizer A for tracking 111 Drive amplifier A 112 for tracking Tracking switch A 113 Equalizer B for feed control 119 Linear motor

Continuation of front page (56) References JP-A-6-28681 (JP, A) JP-A-5-101419 (JP, A) JP-A-61-283038 (JP, A) JP-A-6-314435 (JP, A) , A) JP-A-7-14184 (JP, A) JP-A-6-2697094 (JP, A) JP-A-3-124326 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB (Name) G11B 7/09-7/095

Claims (6)

(57) [Claims] 1. A method for recording and reproducing signals on an optical recording medium having an information track, irradiating and condensing a light beam on the optical recording medium via an objective lens, and obtaining a tracking error signal from reflected light from the optical recording medium. At least two divided photodetectors, tracking error signal detecting means for detecting a tracking error signal from an output of the photodetector, and an output of the tracking error signal detecting means via a tracking control means. Objective lens driving means for driving the lens in a direction perpendicular to the information track of the optical recording medium with respect to the light beam so that the light beam follows the information track; and integrating the light beam and the objective lens driving means with the information of the optical recording medium. Transport means for moving in a direction perpendicular to the track; and a tracking error signal for moving the information track in a direction perpendicular to the track. Extracting means for extracting a tracking error signal at a fixed position; and the extracting means detects a substantially center in a width direction of an information track or an inter-track area sandwiched between adjacent information tracks, so that the level of the sum output of the photodetector is reduced. Holding means for extracting the output of the tracking error signal detecting means by the pulse of the center detecting means, using level detecting means for detecting that the value has become equal to or more than a certain value or less than a certain value and generating a pulse; By inputting the output of the means to the objective lens driving means, the relative positions of the light flux, the objective lens, and the photodetector are controlled to be substantially constant, and the tracking for detecting the movement of the objective lens in the tracking direction is performed. Position detector, differentiator for cutting DC component of tracking position detector, and output of said extracting means Has a synthesizing means for synthesizing, tracking control apparatus characterized by inputting the output of said combining means to said objective lens driving means. 2. The information track has information recorded in advance as a pit string, the photodetector has at least two or more light detection areas, and the center detection means outputs a sum output of the photodetector. 2. The tracking control device according to claim 1, wherein the tracking control device comprises an extreme value detecting unit that supplies the maximum value or the minimum value of the output of the envelope detecting unit to the envelope detecting unit. 3. The information track is a continuous groove for recording information pits called a pregroove later, the photodetector has at least two or more light detection areas, and the center detection means is 2. The tracking control device according to claim 1, further comprising a polarity detection unit that supplies a sum output of the photodetector to a filter and detects a change in polarity of a change rate of the output of the filter. 4. A method for recording and reproducing signals on an optical recording medium having an information track, irradiating and condensing a light beam on the optical recording medium via an objective lens, and obtaining a tracking error signal from reflected light from the optical recording medium. At least two divided photodetectors, tracking error signal detecting means for detecting a tracking error signal from an output of the photodetector, and an output of the tracking error signal detecting means via a tracking control means. Objective lens driving means for driving the lens in a direction perpendicular to the information track of the optical recording medium with respect to the light beam so that the light beam follows the information track; and integrating the light beam and the objective lens driving means with the information of the optical recording medium. Transport means for moving in a direction perpendicular to the track; and a tracking error signal for moving the information track in a direction perpendicular to the track. Extracting means for extracting a tracking error signal at a fixed position; the extracting means for generating a signal having a frequency higher than the primary resonance frequency of the objective lens driving means; and an oscillating means for oscillating the objective lens by a fixed amount. Means for adding the output of the means to the objective lens driving means at a constant level, and a low-pass filter for attenuating the output of the tracking detection means at a certain frequency or higher. A tracking position detector for detecting the movement of the objective lens in the tracking direction; a differentiator for cutting a DC component of the tracking position detector; and a combining unit for combining with an output of the extracting unit. Wherein the output of the combining means is input to the objective lens driving means. The control device. 5. The apparatus according to claim 1, wherein said extraction means is supplied to an objective lens driving means via a switch means, and said switch means is connected only when said tracking control means is not operating. A tracking control device according to any one of the above. 6. The extraction means is supplied to an objective lens driving means via a switch means, and the switch means is connected even when the tracking control means is operating and not operating, and the switching means is connected when the tracking control means is operating. The tracking control device according to any one of claims 1 to 4, wherein the switching is performed such that the gain of the output of the extraction means is equal to or lower than a tracking basic frequency corresponding to one rotation of the medium and the gain is reduced.