JPH0467693B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking control device for controlling tracking so that a pickup follows a track on a disk.

[Summary of the invention]

The present invention is a tracking control device that performs tracking control so that a pickup follows a track on a disk, and detects a signal corresponding to the position of the track from an output signal of the pickup, and detects a signal corresponding to the position of the track from the output signal of the pickup, and detects a signal corresponding to the position of the track from the output signal of the pickup, The signal is clamped by a clamp circuit, the output of the clamp circuit is waveform-shaped by a waveform shaping circuit, an on-track signal indicating that the pickup is on the track is detected from the output of the waveform shaping circuit, and when the on-track signal is detected, tracking is performed. By closing the servo loop, the tracking servo can be accurately and quickly locked in without being affected by the pick-up position, disc variations, etc.

[Conventional technology]

Video disc players, digital audio disc players, and the like are equipped with tracking control devices that perform tracking control so that a pickup follows a track on the disc. The tracking servo loop of such a tracking control device is designed to be closed when the pickup is positioned on the track so that the lock-in operation can be performed quickly.

FIG. 4 shows a block diagram of a conventional tracking control device for an optical video disc player. In the figure, 1 to 3 are spots of laser light irradiated onto a track on the disk from a pickup (not shown), and when spot 1 for information reproduction is located approximately at the center of the track, spots 2 and 3 for tracking are located at the center of the track. It is located at both ends of the . Reference numeral 5 denotes a comparator as a waveform shaping circuit, and a signal obtained by photoelectrically converting the reflected light from the spot 1 by a light receiving element (not shown) is supplied to its inverting terminal via the amplifier 4, and a signal is supplied to its non-inverting terminal. A reference potential V generated by a reference potential generation circuit 6 is supplied. 7 is an AND gate that outputs the AND of the output of the comparator 5 and a signal from a control circuit such as a microcomputer (not shown); 8 is a loop switch controlled by the output of the AND gate 7; Reference numeral 9 denotes a subtraction circuit that subtracts a signal from a light receiving element (not shown) that receives reflected light from the spots 2 and 3 to generate and output a tracking error signal. The tracking error signal is supplied via an equalizer 10, a loop switch 8, and an amplifier 11 to an actuator 12 that drives a tracking mirror, an objective lens, and the like.

Spot 1 is located at positions A to E as shown in FIG.
As the object moves, the tracking error signal changes as shown in FIG. 6a. That is, the tracking error signal is zero when spot 1 is at position B, has a negative peak when spot 1 is at position A, and has a positive peak when spot 1 is at position C, and has an upward slope to the right during this period. Spot 1 is at position A to C
Corresponding to the tracking error signal supplied via the equalizer 10, loop switch 8, and amplifier 11, the tracking servo is performed when the polarity is negative, in the right direction in FIG. Further, when the value is positive, the actuator 12 moves it to the left. Since the tracking error signal becomes zero at position D and has a negative peak at position E (corresponding to position A), position C
Between E and E, the slope slopes downward to the right. When spot 1 shifts slightly from position D to position E, a negative tracking error signal is generated, and spot 1 is further moved to the right. Further, when spot 1 shifts slightly from position D to position C, a positive tracking error signal is generated, and spot 1 is further moved to the left. Therefore, spot 1 is at position C to E.
It is not stable between these positions and is controlled to be located at positions A to C.

On the other hand, the average level of the signal output by the light receiving element that receives the reflected light from spot 1 (in other words, the average level of the amount of reflected light) is as shown in FIG. 6b.
It is the least amount at position B on the track where pits are formed, and the most amount is at position D where the mirror surface is formed.

For example, the operation when performing a scan operation will be explained with reference to FIG. 7. In the normal playback state, a high level signal is output from the AND gate 7 (FIG. 7b), and the loop switch 8 is closed. ing. Therefore, since tracking control is being performed at this time, the level of the tracking error signal is small (FIG. 7a), and the level of the average signal representing the average amount of light output from the amplifier 4 is approximately constant (FIG. 7a). Figure c). When a low level signal is applied from the control circuit to the AND gate 7 at time _t1 , the AND gate 7 is opened and its output becomes a low level. As a result, the loop switch 8 is opened, and the pickup is transported at high speed in the radial direction of the disk during time _T1 . During this time, since the pickup crosses the track, the level of the tracking error signal changes greatly (FIG. 7a). On the other hand, at this time, the average signal level also increases greatly each time the track is crossed (FIG. 7c). This average signal is compared with a reference potential V in a comparator 5 and shaped into a waveform. Since the reference potential V is set to a value approximately halfway between the high level and low level of the average signal, the comparator 5 outputs an on-track signal that is high level when the pick-up crosses a track, and low level when the pick-up crosses between tracks. (Fig. 7d). Therefore, when a high level signal is applied from the control circuit at time _t2 , the AND gate 7 passes the on-track signal, which is high level when the pickup is on the track and low level when it is between tracks ( Figure 7e). As a result, loop switch 8
is closed only when the pick-up is on the track, and at time t ₃ when time T ₂ has elapsed since time t ₂ .
The tracking servo locks in at .
In this manner, the loop switch 8 is closed only when the pickup is on the track, so that a quick and stable lock-in operation can be performed.

However, in such a tracking control device, since the reference potential V is fixed, changes may occur due to aging of the disk, changes in reflectance on the inner and outer peripheries, or changes in the power of the laser beam, etc.
As shown in FIG. 8, when the level of the average signal changes above or below the reference potential V, it becomes impossible to detect the on-track signal.

Therefore, for example, as shown in FIG. 9, it is conceivable to add the signals from spots 2 and 3 by an adder circuit 21 and adjust the output by a potentiometer 22 to use it as a reference potential for the comparator 5. In this way, the reference potential changes in accordance with the reflectance of the disk or the intensity of light, so that the influence thereof can be eliminated.

[Problem that the invention seeks to solve]

However, in the apparatus shown in FIG. 9, it is necessary to adjust the balance between the signal from spot 1 and the added signals of spots 2 and 3, which is a troublesome task. For example, actuator 1
2, when the mirror, lens, etc. are largely displaced, this balance is disrupted, resulting in the drawback that the on-track signal cannot be detected accurately. Furthermore, since this device adds the signals from spots 2 and 3, it cannot be applied to a device that generates a tracking error signal using a so-called one-beam system.

[Means for solving problems]

FIG. 1 is a block diagram of a tracking control device according to the present invention, and parts corresponding to those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the present invention, the average signal from spot 1 is supplied to clamp circuit 31 via amplifier 4. The clamp circuit 31 includes a coupling capacitor 32, a buffer amplifier 33 with a gain of 1, for example, a resistor 34, and a switch 35. 36 is an inverter that controls on/off of the switch 35. The other configurations are the same as in FIG. 4.

[Effect]

The operation will be explained with reference to FIG. The signals from spots 2 and 3 are supplied to the subtraction circuit 9 to generate a tracking error signal, which is supplied to the actuator 12 via the equalizer 10, loop switch 8, and amplifier 11 to perform tracking control as described above. Same as in case.

It is now assumed that a high level signal and a low level signal are repeatedly applied from the control circuit to the AND gate 7, and a scan operation is being performed. This loop control signal to the AND gate 7 (FIG. 2b) is inverted by the inverter 36, so the switch 3
5 is open when the loop switch 8 is closed, and closed when it is open. That is, when the tracking servo loop is opened, the switch 35 is closed, and the reference potential V output from the reference potential generation circuit 6 is applied to the connection point between the capacitor 32 and the buffer amplifier 33 via the resistor 34. Since the input impedance of the buffer amplifier 33 is set to be sufficiently larger than the output impedance of the amplifier 4 connected to the input side of the capacitor 32, the capacitor 32 is connected to the reference potential generation circuit 6, the switch 35, the resistor 34,
It is charged through the path of capacitor 32 and amplifier 4.
Since the impedance of the resistor 34 and the output impedance of the amplifier 4 are small, this charging is performed relatively quickly. At the time when charging is completed, the DC potential at the connection point between the capacitor 32 and the buffer amplifier 33 is clamped to the reference potential V. Since the buffer amplifier 33 has a gain of 1, the DC potential at its output terminal also becomes the reference potential V. Since the tracking servo loop is now open, the signal input to the capacitor 32 is a signal in which an AC component (corresponding to the position of the track) generated each time the track is crossed is superimposed on a predetermined DC component _E2 . (Figure 2a). Of these, the DC component E ₂ is blocked by the capacitor 32, so the AC component is superimposed on the clamped DC potential (reference potential V) and input to the inverting terminal of the comparator 5 via the buffer amplifier 33 (second Figure c). Therefore, the center value of the AC component (value of the DC component) is always the reference potential V,
The comparator 5, whose non-inverting terminal is supplied with the reference potential V, generates and outputs an on-track signal whose waveform has been accurately shaped (FIG. 2d). Since a low-level loop control signal is currently input to the other end of AND gate 7, this on-track signal is not output from AND gate 7.

When the pickup is moved for a predetermined time or to a predetermined position and a loop control signal (high level signal) for closing the tracking servo loop is input to the AND gate 7, the switch 35 is opened. Since the input impedance of the buffer amplifier 33 is sufficiently large and there is no discharge path, the electric charge charged in the capacitor 32 is held almost unchanged. As a result, the DC potential at the connection point between the capacitor 32 and the buffer amplifier 33 is higher than the DC potential (E ₂ ) at the other end of the capacitor 32 by the potential difference (V - E ₂ ) due to the charged charge, that is, equal to the reference potential V. It becomes electric potential. Even if a signal to close the tracking servo loop is issued, the tracking servo loop has not yet locked in, so the level change in the average signal is large. Therefore, the signal in which the AC component is superimposed on this DC potential is the reference potential V.
, an on-track signal is generated (second
Figure d). Now, a high-level loop control signal is input to the other input of AND gate 7, so
This on-track signal passes through AND gate 7 and closes loop switch 8. The loop switch 8 repeats closing and opening until the relative speed between the pick-up and the track becomes small and the pick-up can follow the track, and when the relative speed becomes sufficiently small, the tracking servo loop closes in. Therefore, the level E ₁ of the average signal input to the capacitor 32 thereafter becomes smaller (E ₁ <E ₂ ). At this time, the DC potential on the output side of the capacitor 32, and therefore the DC potential output from the buffer 33, becomes V-(E ₂ - E ₁ ), which is smaller than the reference potential V, so the loop switch 8 remains closed from then on. . If the clamp circuit 31 is kept in the clamp state even after the tracking servo loop locks in, the DC potential of the output of the clamp circuit 31 will remain equal to the reference potential V, and a slight change in the polarity of the average signal will cause the loop switch to 8 is closed or opened, making the tracking state unstable.

Since the average signal is clamped just before the tracking servo loop is closed, the on-track signal can always be detected immediately after the tracking servo loop is closed.

Note that charging of the capacitor 32 does not necessarily need to be performed during the entire period when the loop switch 8 is open. Furthermore, although it is difficult to completely suppress the discharging of the charged charges, the time from when the loop control signal becomes high level until it locks in is about 1 second at most, so it is not practical. It's not really a problem.

Of course, the reference potential V may be zero. In this case, the clamp circuit 31 includes an npn transistor as a switch 35, its base resistor 41, and a capacitor 32, as shown in FIG.
If the input impedance of the comparator 5 is sufficiently large, the buffer amplifier 33 can be omitted.

Although the present invention has been described above in a case where it is applied to a tracking control device for an optical video disk player, the present invention can also be applied to a tracking control device for a non-optical disk recording/reproducing device.

〔effect〕

As described above, in the present invention, in a tracking control device that performs tracking control so that a pickup follows a track on a disk, a signal corresponding to the position of the track is detected from the output signal of the pickup, and the tracking servo loop is opened. The signal is clamped by a clamp circuit for a predetermined period of time, the output of the clamp circuit is waveform-shaped by a waveform shaping circuit, an on-track signal indicating that the pickup is on the track is detected from the output of the waveform shaping circuit, and the on-track signal is Since the tracking servo loop is closed when the detection is made, the tracking servo can be accurately and quickly locked in without being affected by the positions of the inner and outer circumferences of the pickup disk, unevenness of the disk, etc.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a tracking control device of the present invention, Fig. 2 is a waveform diagram thereof, Fig. 3 is a circuit diagram of another embodiment, Fig. 4 is a block diagram of a conventional tracking control device, and Fig. 5 is a schematic plan view showing the positional relationship between the spot and the track;
7 and 8 are waveform diagrams thereof, and FIG. 9 is a circuit diagram of another embodiment. 1, 2, 3... Spot, 4, 11... Amplifier, 5
... Comparator, 6... Reference potential generation circuit, 7... AND gate, 8... Loop switch, 9... Subtraction circuit, 10
... Equalizer, 12 ... Actuator, 21 ... Adder circuit, 22 ... Potentiometer, 31 ... Clamp circuit, 32 ... Capacitor, 33 ... Buffer amplifier, 35 ... Switch, 36 ... Inverter.

Claims (1)

[Scope of Claims] 1. In a tracking control device that performs tracking control so that a pick-up follows a track on a disk, a signal corresponding to the position of the track is detected from an output signal of the pick-up, and a tracking servo loop is opened. The signal is clamped by a clamp circuit for a predetermined period during which the pickup is on the track, the output of the clamp circuit is waveform-shaped by a waveform shaping circuit, and an on-track signal indicating that the pickup is on the track is generated from the output of the waveform shaping circuit. detect,
A tracking control device characterized in that a tracking servo loop is closed when the on-track signal is detected.