JPH0138786Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a tracking servo retraction device.
In particular, the present invention relates to a servo retracting device in a tracking servo device for ensuring that recorded information detection points always accurately track recording tracks on a recording medium.

In a recorded information reproducing device, a tracking servo device as described above is indispensable, and uses a so-called tracking error signal corresponding to the deviation between the recording track and the information detection point in the direction perpendicular to the track to move the information detection point in the direction perpendicular to the track. bias control,
Tracking deviations caused by eccentricity of the recording track are corrected.

For example, when considering a so-called scan operation in which a desired recording track is searched, the information detection point is rapidly scanned in the radial direction of the recording disk with the tracking servo loop closed. Since the tracking actuator that controls the deviation of the information detection point has a drive limit, when the drive limit is reached, the tracking servo loop is opened and the information detection point naturally returns to its center of deviation. Then, the servo loop is closed again, and fast-forward scanning is performed while tracking is performed. This operation is repeated until reaching the vicinity of the designated recording track.

When the servo loop is opened and the information detection point returns to its deflection center point, the speed at which the information detection point returns to its center of deviation becomes extremely high, and therefore the speed at which the information detection point traverses the recording track also increases. If the tracking servo loop is closed under such conditions, it will cause a vibration phenomenon of the actuator, and in extreme cases, servo locking will become impossible.

Therefore, the applicant of the present application has proposed a servo retraction device as shown in Fig.
Specification No. 109778 (see Utility Model Application Publication No. 59-17071)). In the figure, reference numeral 1 indicates a part of a recording track, and a light spot 2 is used as an information detection point for detecting information on this recording track. When the center of this light spot 2 is on the center line of the track 1, the other pair of light spots 3 and 4 are positioned on both side edges of the track 1. Therefore, if the information detection light spot 2 is shifted in the direction perpendicular to the track 1, the difference in light intensity between the two light spots 3 and 4 will change accordingly. A signal proportional to the amount of reflected light from the optical spots 3 and 4 is obtained, and the differential amplifier 7
A tracking error signal C is output by generating a difference between the two signals. This error signal C is frequency and phase compensated by the equalizer amplifier 8 and becomes input to the drive amplifier 10 via the loop switch 9. This drive amplifier 1
With the output of 0, the so-called tracking mirror drive coil 1, which is a tracking actuator, is activated.
Drive 1. This rotational movement of the mirror 12 causes the optical spot 2 to be deflected in a direction perpendicular to the track, thereby performing tracking servo. Therefore, the above loop becomes a tracking servo loop.

The tracking error signal C also becomes one input of the comparator 13 and is compared with a reference level, but in this example, a zero level comparison is made. This comparison output E is applied to the edge detector 14, and a pulse F synchronized with the rising and falling timings is output. This edge detector 14 may have a differential circuit configuration. This edge detection output F is the clock (CK) of delayed flip-flop (DFF) 15.
It is used as input.

On the other hand, the light receiving element 1 receives the reflected light from the information detection point 2.
6 receives the light, converts it into a signal, and amplifies it in an amplifier 17. The output B of this amplifier 17 becomes one input of the level comparator 18, and the reference level 19
The level is compared with. This comparison output D is the first
It serves as a data input for the DFF 15, and its Q output G serves as an on/off control signal for the loop switch 9.

FIG. 2 is a diagram for explaining the operation of the apparatus shown in FIG. 1, and FIG. 2 is a diagram showing the relative movement of the information detection point with respect to the recording track when the tracking servo loop is open. Moreover, FIGS. BG are waveform diagrams showing the signals B to G of the apparatus of FIG. 1, respectively.
When the recording disk, which is a recording medium, is rotating at a predetermined rotational speed when the servo loop is open, the eccentricity of the recording track 1 causes the information detection point 2 to move relative to the track in the direction shown by arrow X in Figure A. will be moved. Corresponding to this relative movement, the reproduced signal from the information detection point 2 becomes the envelope of the reproduced RF (high frequency) signal as shown in FIG. B, if the amplifier 17 has an envelope detection function. Further, a similar output can be obtained even if the amplifier 17 is configured to detect the average level of the reproduced signal. Further, the tracking error signal has a waveform having a level and polarity corresponding to the amount and direction of deviation of the information detection point, as shown in FIG. The comparison outputs of both waveforms B and C from the level comparators 18 and 13 become rectangular wave trains as shown in FIGS. D and E.

That is, the output D of the level comparator 18 is a pulse that is low level when the information detection point 2 is on the recording track, and high level when it is not, and the output E of the level comparator 13 is a pulse that is low level when the information detection point 2 is on the recording track, and high level when the information detection point 2 is not on the recording track. The pulse rises when point 2 is on the center line of the tracks and falls when it is on the center line between tracks. The rising and falling edges of the output of the pulse E are detected by the edge detector 14 to obtain the pulse waveform shown in FIG. F. As a result, the Q output of DFF15 becomes as shown in Figure G,
During the low level of this waveform, the switch 9 is on (loop closed), and during the high level of this waveform, the switch 9 is off (loop open).

Now, if we consider the period when the servo loop is closed,
The loop is closed only when the comparison level of the envelope B of the reproduced RF signal by the comparator 18 changes from a low level to a high level between adjacent zero-crossing points of the servo error signal C (that is, the generation point of the signal F). It's becoming like that. This can be done by detecting that recorded information detection point 2 is moving from on track 1 to between tracks (that is, by detecting that the distance between the information detection point 2 and track 1 is increasing). This means opening the loop. During this time, the servo error signal C is a signal that drives the information detection point 2 to move in the Y direction in FIG. This Y direction is opposite to the component in the direction perpendicular to the track of the direction of relative movement indicated by
2 rotates in response to this, and performs an operation to shift the information detection point 2 in the Y direction. This is equivalent to a braking action that reduces the relative speed of the information detection point 2 to the truck. This braking action always occurs during the loop closing period to reduce the relative speed, and when this relative speed falls below a certain value (within the permissible range of loop retraction), the servo loop will be locked.

In this configuration, since the zero-crossing point of the tracking error signal is detected and the servo loop switch is turned on and off, a timing lag occurs before the brake is actually applied to the tracking mirror. As a result, if the on/off period of the servo loop switch is short, there is a drawback that the braking effect is not sufficient.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and the object is to provide a tracking servo retraction device that can perform servo retraction stably by effectively applying a braking effect to the tracking actuator. The purpose is

The tracking servo retraction device according to the present invention opens the tracking servo loop for a predetermined period when the tracking actuator, which shifts the recorded information detection point in a direction substantially orthogonal to the track, reaches its drive limit, and by opening the loop, the information detection point The system detects the return speed when the actuator returns to the deflection center position, applies braking force to the tracking actuator according to this speed, and uses this braking force to stably pull the servo system. do.

The present invention will be explained below using the drawings.

FIG. 3 is a block diagram of one embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals. In this example, equalizer 8 and loop switch 9
A brake force applying circuit 20 for applying a brake to the rotation of the mirror 12 is provided between the mirror 12 and the mirror 12. This brake force applying circuit 20 includes a diode D ₁ that grounds only the negative polarity signal of the tracking error.
and switch S ₁ , and a series circuit of diode D ₂ and switch S ₂ that also ground only the positive polarity signal, and each of these series circuits is connected between the output line of equalizer 8 and the ground. It is connected. Two-input AND gates _G1 and _G2 are provided to control each of these switches _S1 and _S2 , and DFF1 detects the moving direction of the information detection point.
The Q output G of 5 is applied directly to one input of gate G ₁ and is applied directly to one input of gate G ₂ of inverter I _1.
Supplied via.

A frequency detection circuit 21 is provided which detects the frequency of the error signal C from the differential amplifier 7 and generates, for example, a high level detection signal F when the frequency is higher than a predetermined frequency _.
Each of _G2 is used as an input. And coil 1
A comparator 22 is provided to detect the drive signal supplied to the tracking actuator 1, and when the drive signal level exceeds a predetermined range (i.e., when the tracking mirror 12, which is a part of the tracking actuator, rotates) A comparison output is generated when the limit is reached) and the MMV (monostable malachi vibrator)
Trigger 23. Single output A of this MMV23
As a result, the loop switch 9 becomes open, and the servo loop becomes open during that time.

A flip-flop (FF) 24 is provided which is set by this single output A, and this FF2
The frequency detection circuit 21 is activated by the Q output of No. 4. The detection output F of this detection circuit 21 causes FF
24 is designed to be reset. The other configurations are the same as the example shown in FIG. 1, and their explanation will be omitted.

Figures 4A to 4H are signals A for each part of the block in Figure 3.
-H waveforms are shown correspondingly, B is the output of the amplifier 17, C is the output of the amplifier 7, D is the output of the comparator 18, E is the output of the comparator 13, and DFF
15 clock input terminals.
H is the waveform at the output end of the loop switch 9.

When the mirror 12, which is the actuator, reaches its rotation limit, the MMV 23 is triggered and outputs a high-level pulse shown in FIG. A for a certain period of time. As a result, the loop switch 9 is opened, the servo loop is opened, the drive signal is no longer applied to the coil 11, and the mirror 12 begins to return to the center of rotation, so the information detection point 2 is located at the arrow X in FIG. (or the opposite direction). Therefore,
The waveforms of the read RF signal envelope and the tracking error signal change as shown in Figures B and C, respectively. At this time, the FF 24 is set and the frequency detection circuit 21 is activated, and begins to detect the frequency of the error signal (C), that is, the recovery speed of the information detection point 2. When this speed exceeds a certain value, the detection output changes to a high level as shown in Figure F, and gates _G1 and _G2 are controlled to be open.

Now, considering the case where the information detection point 2 is moving in the direction X shown in FIG. 2, the error signal waveform is as shown in FIG.
The respective output waveforms of No. 3 are as shown in Figures D and E.

If DFF 15 is adapted to read data input D on the falling edge of its clock input E, then the Q output of DFF 15 will remain high as shown in Figure G. If the information detection point 2 is moving in the opposite direction to the direction X in Fig. 2, DFF15
The Q output of will remain at a low level.

Now, since the output F of the DFF 15 is at a high level, only the output of the gate _G1 is at a high level, turning on the switch _S1 . Therefore, only the negative polarity signal of the error waveform shown in FIG. C is grounded, and only the positive polarity signal is input to the loop switch 9. At this time, MMV23 is set so that the loop switch is on.
By selecting the time constant , only the positive error signal shown in FIG. H will be applied to the actuator. This positive polarity signal becomes a force that attracts the information detection point 2 in the opposite direction to the direction X (the Y direction component in FIG. 2), and eventually a braking force is applied to the actuator.

When the information detection point ₂ is moving in the opposite direction to the _direction Therefore, a braking force is applied that pulls the information detection point 2 in the direction opposite to the Y direction.

When the return speed of the mirror 12 decreases to a certain speed due to this braking force, the output F of the frequency detection circuit 21 becomes a low level, and the gates G ₁ ,
Let G ₂ be closed. Therefore, the switch S ₁ (or S ₂ ) is turned off and application of the brake force is released. At this time, since the relative velocity between the information detection point 2 and the track 1 is decreasing, the tracking servo system can be stably locked.

FIG. 5 is a block diagram of another embodiment of the present invention, in which parts equivalent to those in FIG. 3 are designated by the same reference numerals and their explanation will be omitted. In this example, an F/V conversion circuit 25 is added that detects the frequency of the tracking error signal and outputs a signal at a level corresponding to the frequency, and this output is applied to the adder ₂₆ via the switch S3 and the inverter. _I2 and switch _S4 to adder 26. The output of the switch 9 is also applied to this adder 26, and the output of this adder 26 serves as the input of the driver 10. Switch S ₃ and
Control of S ₄ is performed by each output of gates G ₁ and G ₂ , respectively.

In this example as well, when the return speed of the mirror 12 exceeds a certain value, the switch S ₃ (or S ₄ ) is turned on and the F/V conversion output corresponding to the contact return speed is applied to increase the brake force. will be granted.

Note that the adder 26 may be provided before the loop switch 9; in this case, as in the example shown in FIG. Granting will be delayed slightly, but this is not a problem. Third
Even in the illustrated example, the brake force applying circuit 20 may be provided at the output stage of the loop switch 9.

As another example, when the return speed exceeds a certain value, a DC component that acts as a brake is externally applied to the output stage of the loop switch, and after the speed has decreased to a certain value, this DC component is applied to the output stage of the loop switch. The application of the components may also be stopped. In short, it is sufficient that the signal applied to the tracking actuator acts as a brake on the return of the mirror to its neutral point.

Furthermore, the DFF 15 is used to apply the brakes while detecting the direction of movement of the information detection point 2, but during so-called scan operation to search for a desired track, the direction of movement is predetermined, so the scan direction is indicated. Switch based on signal
S ₁ , S ₂ (S ₃ , S ₄ ) may be controlled.

As described above, according to the present invention, the speed at which the information detection point returns to the deflection center position is detected and the brake is applied to the tracking actuator accordingly, so that the braking effect is more sufficient. This has the advantage of ensuring servo retraction.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a tracking servo pull-in device currently being proposed, Fig. 2 is a signal waveform diagram showing the operation of the block in Fig. 1, Fig. 3 is a block diagram of one embodiment of the present invention, and Fig. 4 is a block diagram of a tracking servo retraction device currently being proposed. This figure is an operational waveform diagram of the block in FIG. 3, and FIG. 5 is a block diagram of another embodiment of the present invention. Explanation of symbols of main parts, 1...recording track,
2... Information detection point, 9... Loop switch, 11
... Coil, 12 ... Tracking mirror, 15
...DFF, 20...Brake application circuit, 21...
...Frequency detection circuit, 23...MMV.

Claims (1)

[Scope of utility model registration request] A servo retracting device in a tracking servo device that controls the position of a recording track and a recording information detection point in a direction substantially perpendicular to the recording track, the tracking actuator for biasing the recording information detection point in the direction. means for opening a tracking servo loop for a predetermined period when the driving limit is reached, and detecting a return speed at which the recorded information detection point returns to the deviation center position by opening the loop, and detecting the return speed at which the recording information detection point returns to the deviation center position and detecting the return speed according to this speed. and means for applying a braking force to the tracking actuator, and the tracking servo system is stably retracted by the braking force.