JPS61271631A - Tracking servo circuit - Google Patents

Abstract

PURPOSE:To attain tracking stable against various external disturbances without complicated operation by adding a signal corresponding to the polarity of an external disturbance and an error signal to the same amplifier in the same system so as to adjust automatically unstable operation of a servo system due to the external disturbance. CONSTITUTION:When an external disturbance is applied, a selection circuit 26 selects a contact (c) of a switch 20 by using an output signal of a bottom detector 27, a tracking error and a polarity signal to apply a signal pulse of the same polarity as that of the tracking error signal to a summing amplifier 19. If any flaw exists, the circuit 26 selects a contact (b) of the switch 20 by using the output signal of a peak detector 29, the tracking error signal and a polarity signal to apply the tracking error signal and a signal pulse of opposite polarity to the amplifier 19. Thus, the tracking error signal level is changed depending on the type of the external disturbance and the servo loop gain is adjusted automatically to an optimum value so as to attain stable tracking against various external disturbance without complicated operation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a tracking servo circuit for a disc playback device, and in particular, to a tracking servo circuit that can automatically adjust its servo characteristics to an optimal value that minimizes track deviation. be.

[Prior Art] Conventionally, in an information recording disk reproducing device using a pickup reproducing element using a light beam, tracking control of the pickup reproducing element is performed using a tracking error signal, so that the pickup reproducing element accurately follows a recording track. I'm trying to scan. The loop gain adjustment circuit in such a tracking servo circuit detects level fluctuations in the tracking error signal that occur due to disturbances applied to the pickup playback element and its playback device, and sets the loop gain of the tracking servo circuit to a large value. It is known that this was done.

A conventional example of such a tracking servo circuit is shown in FIG. In the figure, (1) is a light emitter such as a laser diode, (2) is a light beam emitted from the light emitter (1),
(3) is a lens, (4) is a beam splitter for distributing the laser beam into a main spot and an auxiliary spot, (
5) is a prism, (6) is a λ/4 plate, (7) is a tracking mirror, and (8) and (11) are lenses. In addition, (9) is a transparent resin that covers the disc recording surface, (10)
are protruding pits forming tracks.

Further, (12) is a photodetector that outputs a current of a magnitude according to the amount of incident light, and (33) and (34) are the photodetectors (12) and (33) and (34).
) a preamplifier for converting the output current of ) into voltage, (3
5) is a summing amplifier that adds the outputs of both advance amplifiers (33) and (34) to form an information signal (31) recorded on the disk.

('13) and (14) are preamplifiers for tracking control, which adjust the amount of incident light output from the photodetector (12) to the photodetector elements A and D of the photodetector (12), respectively. It converts the corresponding current into voltage. (15
) is a differential amplifier that receives the outputs of these amplifiers (13) and (14) and outputs a tracking error signal;
8).

(181) is a low-pass filter attached to the servo amplifier (16) for gain adjustment, and (17) is the servo amplifier (1
This is a drive circuit that receives the output of (6) and drives the tracking mirror (7). In addition, (24) is the differential amplifier (
15) is a level detector that detects level fluctuations in the tracking error signal outputted from the device, and (26) is a selection circuit that controls the switch (20) for switching the loop gain according to the output of the level detector (24). It is.

Next, the tracking control operation of the above device will be explained.

The laser beam (2) emitted from the light emitter (1) passes through a lens (3), a beam splitter (4), and a prism (5).
The light is irradiated onto the information recording disk surface through an optical system such as . The reflected light then passes through the lens (8) and the tracking mirror (
7), guided to a photodetector (12) via a prism (5) and a lens (11). Tracking control is performed according to the intensity of the light incident on portions A and D of the light incident on the photodetector (12). That is, the photodetector (12) outputs a current whose size corresponds to the intensity of the incident light, but among these, the current whose size corresponds to the intensity of the incident light to the A part and D part is output. Preamplifier (13)
, (14), where each laminar flow is converted to a voltage. The outputs of these amplifiers (13) and (14) are computed by a differential amplifier (15) and become a tracking error signal representing the deviation from the track center. In normal tracking without disturbance, switch (20)
is connected to contact a, and the loop gain of the control loop is set to an optimal value for tracking control by a low-pass filter (18) and a servo amplifier (16). In this way, the tracking error signal is filtered through the low-pass filter (18
) and a servo amplifier (16), the signal is amplified and phase compensated optimally for tracking control, and then applied to the drive circuit (17). The tracking mirror (7) is driven by this drive circuit (17), and the spot of the light beam on the disk is controlled to follow and scan on the track.

In such a circuit, when a disturbance is added and the beam spot on the disk starts to deviate from the track, the tracking error signal that is the output of the differential amplifier (15) increases, and the level fluctuation of this tracking error signal is detected by the level detector. (24), the selection circuit (26) connects the switch (20) to the contact, and the low-pass filter (1
81) and a servo amplifier (16), the loop gain is set to be large and operates to prevent the beam spot on the disk from deviating from the track.

[Problems to be Solved by the Invention] As mentioned above, the disk has a structure in which the recording surface is covered with a transparent resin (9), and it is possible for air bubbles or opaque foreign matter to get mixed in therein. Sometimes. In such a case, the bubble causes a kind of lens effect, and the refractive index in the bubble part of the disk is different from that in the transparent part, so the light beam appears to have moved. For this reason, the tracking error signal becomes large, the loop gain is set to a large value, and the beam spot works to follow the track. However, in the case of opaque foreign objects, a phenomenon occurs that distorts the light intensity distribution, so even though the spot is not off track, the tracking error signal becomes large, and therefore the loop gain also becomes large, and the circuit moves the spot on track. I'm working to bring it back. However, since the spot was not actually off the track, the spot is moved off the track by the above operation, and the reproduction characteristics are significantly degraded.

Therefore, the loop gain adjustment circuit of this tracking servo circuit increases the loop gain when the spot actually deviates from the track and the tracking error signal increases, causing disturbances that can be detected, such as vibrations and air bubbles on the disk. However, for disturbances that increase the tracking error but do not actually cause the spot to deviate from the track, i.e., scratches and opaque foreign objects on the disk, the loop gain is set to normal tracking control without disturbances. Even though it is preferable to lower the loop gain than
There was a problem in that it encouraged disturbances.

The present invention has been made in view of the above points, and can automatically adjust the loop gain of the tracking servo circuit to an appropriate amount for various disturbances, and overcomes the drawbacks of the conventional loop gain adjustment circuit as described above. It is an object of the present invention to provide a tracking servo circuit for an information recording disk reproducing device that eliminates the problem and prevents malfunctions.

[Means for Solving the Problems] A tracking servo circuit for a disc playback device according to the present invention includes a disturbance detection means for detecting the type of disturbance, a tracking error polarity identification means for detecting the polarity of a tracking error signal, and a tracking servo circuit for a disc playback device according to the present invention. a signal generating means for generating signals of the same polarity and opposite polarity as the error signal; and a signal generating means for supplying a signal of an optimum value according to the disturbance to an amplifier in the tracking servo loop based on the outputs of the disturbance detecting means and the discriminating means. This is provided with an addition means for adding more.

[Operation] The type of disturbance, that is, whether the disturbance causes the pickup element to deviate from the track or not, is detected, and based on the detection result, an appropriate signal is sent from the signal generator to the amplifier in the tracking servo loop. The servo characteristics are automatically adjusted.

[Embodiments of the invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram schematically showing an information recording disk reproducing apparatus equipped with a tracking servo circuit according to an embodiment of the present invention, and the same parts as in FIG. 4 are given the same reference numerals. Here, to summarize this embodiment, the type of disturbance is detected for one amplifier in the tracking servo loop, and the disturbance is of a nature that causes the beam spot to deviate from the track and increases the tracking error signal. A signal of an appropriate polarity is added from a signal generator based on the identification result, and comfortable servo operation can be obtained by the added signal. A bottom detector (27) that detects the lower envelope of the reproduced information signal to be output, a peak detector (29) that detects the upper envelope of the reproduced information signal, a bottom detector (27), and a peak detector It is composed of level detectors (28) and (30) that respectively detect fluctuations in the output level of the detector (29).

(25) is a polarity discrimination circuit that discriminates the polarity of the tracking error signal, and (26) controls the switch (20) by the output from the @/vibration discrimination circuit (32) and the output of the polarity discrimination circuit (25). A selection circuit that selects either the same polarity or the opposite polarity signal, (21>, (22>) is a signal generator that generates the same polarity pulse or the opposite polarity signal pulse from the output of the tracking error signal level detector (23). If the beam spot deviates from the track and the tracking error signal becomes large, i.e. if there is vibration or bubbles on the disc, apply a pulse with the same polarity as the tracking error signal. If a tracking error signal occurs even though the beam spot is on the track, i.e. if there is a scratch or an opaque foreign object on the disk, add a pulse to cancel the tracking error signal. The servo gain is weakened to obtain optimal servo operation.

Next, the operation will be explained.

The operation of the control loop is almost the same as the conventional operation, so a detailed explanation will be omitted here.
The operation of stabilizing the servo loop by adding same-polarity and opposite-polarity pulses of 22> to the servo loop will be described.

The operation from the time when the laser beam emitted from the light emitter (1) is irradiated onto the disk until the reflected light reaches the photodetector (12) is the same as the conventional one. and a photodetector (12)
The current output with a size corresponding to the intensity of the light incident on the 8th part and the C part is converted into a voltage signal by preamplifiers (33) and (34). These amplifiers (33), (34)
The outputs of are summed by a summing amplifier (35) to form the information signal (31) recorded on the disc.

Here, the amount of light incident on the photodetector (12) is small because the light beam is diffusely reflected on the protruding bits (10) forming the track, and most of the amount of light exits on the other mirror surfaces of the disk. This is mostly because the light is reflected back to you.

Figure 2 (a) shows the light reflection intensity with respect to the spot position, and when the main spot β shown in Figure 2 (b) follows the track center, the amount of incident light is at two points, and the amount of incident light is at two points. It increases on both sides, ie as the spot goes off track. Note that α and γ in FIG. 2(b) indicate auxiliary spots. Also, in the same figure, bit (10) is indicated by a two-dot chain line;
) are formed intermittently within the range shown by the two-dot chain line.

When the light beam is following the track, the minimum amount of incident light when the main spot β is on the bit and the maximum amount of incident light when the main spot β is on the mirror surface do not change. That is, the waveform of the information signal and its envelope,
Further, the level of the tracking error signal becomes as shown in FIG. 3(a).

However, in the case of disturbances, here vibrations and air bubbles on the disk, the maximum incident light intensity when the spot is on a mirror surface does not change, but when the spot goes off track, for example as shown in Fig. 2(b). When the spot β moves in the direction of arrow Become. In this case, the level of the tracking error signal also fluctuates as shown in the figure.

On the other hand, when there are scratches and opaque foreign matter on the disk, the scratches and opaque foreign matter distort the light intensity distribution and the amount of light incident on the photodetector (12) decreases. The reduction ratio is the same whether the spot β is on the bit (10) or on the mirror surface.

Therefore, since the amount of change changes in proportion to the absolute amount of incident light, the minimum amount of incident light does not change when spot β is on bit (10), but the maximum amount of incident light when spot β is on the mirror surface. is significantly reduced, and the information signal envelope has a missing upper part as shown in FIG. 3(C). Furthermore, the level of the tracking error signal also changes as shown in the figure.

Vibrations, scratches, etc. are discriminated by detecting the fluctuations in the envelope of the information signal that changes depending on the type of disturbance as described above. In this case, it is generally thought that increasing the servo characteristics will result in stability against vibrations, while weakening the servo characteristics will result in stability against scratches, so contradictory operations are required.

Now, with the above circuit configuration, it is possible to distinguish between vibrations and scratches, so stable operation can be achieved by using these signals to strengthen or weaken the servo.

In this embodiment, this operation can be performed without changing the low-pass filter as in the conventional case, and complicated constant calculation of the low-pass filter is not required.

First, to explain from the normal state, the switch (20) is
It is connected to the contact point, that is, the state when there is no disturbance, and is given a loop gain suitable for the spot to follow and scan on the track.

Next, when the spot tries to deviate from the track due to vibrations and air bubbles on the disk, a large tracking error signal is generated, and the output of the servo drive circuit corresponding to this error signal is applied in the opposite direction to the direction in which the spot is deviating from the track. , operates to prevent the spot from going off track. Therefore, when a signal of the same polarity as the error signal is added, the output of the servo drive circuit increases accordingly to the extent that the error signal increases, and force is applied in the opposite direction to prevent the spot from moving normally on the track. Follow-up scanning begins.

Next, in the case of a disturbance caused by a scratch or an opaque foreign substance on the disk, the error signal becomes large even though the spot is on the track, and the spot appears to be off the track, causing the spot to deviate from the track. Therefore, when the error signal and a signal of opposite polarity are added, the error signal is canceled out, and a state close to normal operation is achieved, so that the spot does not suddenly deviate from the track.

The above is the movement of the servo system in response to each disturbance.

Therefore, when a disturbance is applied, the selection circuit (26) selects the contact C of the switch (20) using both the output signal of the bottom detector (27) and the tracking error and polarity signals, so that the output signal is the same as the tracking error signal. A signal pulse of polarity is applied to the summing amplifier (19). If there is a flaw, the selection circuit (26) selects the contact point of the switch (20) using both the output signal of the peak detector (29) and the tracking error and polarity signals to output the tracking error signal and the polarity signal. A signal pulse of opposite polarity is applied to the summing amplifier (19).

In this way, by changing the level of the tracking error signal according to the type of disturbance, the servo loop gain is automatically adjusted to the optimal value, so it can be constantly adjusted against various disturbances without complicated operations. Stable tracking is possible.

In the above embodiment, the size and length of the signal pulse due to vibration and scratches are fixed, but the size may be changed depending on each type, and the signal pulse can be generated according to the error signal. You may. Further, the signal pulses to be added may be any amplifier in the servo loop. In that case, it goes without saying that attention should be paid to the level of the signal pulse.

[Effects of the Invention] As described above, according to the present invention, unstable operation of the servo system that occurs in response to disturbance can be corrected by adding a signal corresponding to the polarity of the disturbance and error signal to one amplifier in the servo loop. Since automatic adjustment is performed without the need to calculate complicated constants such as a low-pass filter, there is an effect that stable tracking can always be performed against various disturbances without complicated operations.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram of a tracking servo circuit of a disc playback device according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining changes in the amount of incident light due to movement of a light beam.
FIG. 3 is a waveform diagram for explaining the disturbance detecting means of the present invention, and FIG. 10 is a block diagram of a tracking servo circuit of a conventional disk reproducing apparatus. (9)...Disk transparent resin, (10)...Pit, (16)...Servo amplifier, (18)...Low pass filter, (20)...Switch, (21)...
・Signal generator, (22)...Signal generator, (25)・
...Polarity identification circuit, (26)...Selection circuit, (32)
...Flaw/vibration discrimination circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] In a tracking servo circuit that controls the position in the track direction of a pickup reproducing element that reproduces an information signal using a tracking error signal obtained from an information recording surface, the type of disturbance is detected based on a change in the envelope level of the information signal. Disturbance detection means, identification means for identifying the polarity of the tracking error signal, signal generation means for generating signals of the same polarity and opposite polarity as the tracking error signal, and detecting the signal based on the outputs of the disturbance detection means and identification means. A tracking servo circuit comprising: adding means for selecting a signal generated from the generating means and adding and inputting the signal to an amplifier in a tracking servo loop.