JPH01279426A - Focus servo pull-in device - Google Patents

Abstract

PURPOSE:To attain focus servo pull-in in a short time by detecting a moving direction of a lens, applying a brake signal to interfere the movement and starting the focus servo as soon as the free vibration of the lens is decreased. CONSTITUTION:An RF signal detector 4 detects the amplitude of an RF signal from an optical pickup 2. When the amplitude is small, it is judged as out of focus servo to allow a changeover device 7 to open a focus servo loop filter 6. In this case, when a lens free vibration detector 11 detects a free vibration with a large amplitude, a lens moving direction detector 12 uses a focus error signal to detect the moving direction of the lens and a brake signal generator 13 generates a brake signal in a direction interfering with the movement of the lens. This is repeated till a large amplitude is not detected. Then an output of a search waveform generator 9 is used to start focus search. When a just focus detector detects the presence of focus, the changeover device 7 closes the loop filter 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a focus servo pull-in device for servoing an optical disk.

2. Description of the Related Art In recent years, optical disc playback devices such as compact discs have become popular. Here, servo characteristics, especially the pull-in time in the focus servo pull-in device, are one of the important things.

An example of the conventional focus servo pull-in device described above will be described below with reference to the drawings.

FIG. 3 shows a processing block configuration of a conventional focus servo pull-in device, and FIG. 4 shows a processing flow. First, regarding Fig. 3, 1 is an optical disk, 2 is an optical pickup, 3 is an actuator driver, and 4 is an RF
A signal detector, 6 is a Chanut focus detector, 6 is a focus servo loop filter, 7 is a first switch, 8 is a second switch, 9 is a search waveform generator, and 31 is a fixed period signal generator. .

The operation of the focus servo pull-in device configured as described above will be described below.

The optical pickup 2 converts the reflected light from the optical disk 1 into a focus servo signal and an RF multiplied signal.The actuator driver 3 drives the optical pickup 2 in the focusing direction in accordance with the output of the second switching unit 8. The RF signal detector 4 detects whether the amplitude of the RF multiplied signal from the optical pickup 2 is large or not. The just focus detector 6 follows the figure 8 curve of the focus error signal from the optical pickup 2 and detects when the focus is achieved. This becomes operational when the signal generator 31 finishes generating a signal for a certain period of time. The focus servo loop filter 6 is a filter having a closed servo loop and a frequency characteristic and gain necessary for voice. 1st
The cutter 7 opens the loop filter when the RF signal reverse generator 4 detects that the RF multiplied signal amplitude has become small. The loop filter is closed when the just-focus detector 5 detects that the focus is still correct. The second switch 8 outputs the waveform of the search waveform generator 9 when the signal for a certain period ends in the signal generator 31 for a certain period. Further, when the just focus detector 5 detects that the focus is achieved, the loop filter is closed. The constant +yr signal generator 31 generates a signal for a certain period when the RF signal detector 4 detects that the RF multiplied signal amplitude has become small.

Next, FIG. 4 shows the flow of focus servo pull-in processing. First, the RF multiplied signal amplitude is detected. Repeat if the amplitude is large. If the amplitude is small, it is determined that the focus servo is off, and the servo loop is opened. At this time, there is a possibility that the lens is undergoing free vibration with a large amplitude. Therefore, the system waits for a certain period of time during which it can be expected that this vibration has become sufficiently small. Then, a focus search is started using a search waveform such as a triangular wave. Then, the point in time when the just focus value reaches the open position near 1b of the 8 characters is detected. Then close the servo loop.

Problems to be Solved by the Invention However, in the above configuration, it is necessary to use the maximum period that can accommodate various vibration states as a fixed period, so it takes a very long time from opening the servo loop to starting focus search. The problem was that it took a long time.

In view of the above problems, the present invention provides a focus servo pull-in device that takes a short time from opening the servo loop to starting focus search.

Means for Solving the Problems In order to solve the above problems, the focus servo retraction device of the present invention includes a lens free vibration detector that detects whether the free vibration of the lens has a large amplitude, and a lens movement direction detection device. If the free vibration of the lens is detected to have a large amplitude, it detects the direction of movement of the lens and generates a brake signal in the opposite direction to attenuate the amplitude. The focus search is configured such that the amplitude is reduced to a small amplitude, and then the focus search is immediately started.

Function The present invention uses the above-described configuration to detect the moving direction of the lens, applies a brake signal to prevent this movement, and starts focus search as soon as the free vibration of the lens becomes small, so that the focus servo can be activated in a short time. can be drawn in.

EXAMPLE Hereinafter, a focus servo pull-in device according to an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the processing block configuration of the focus servo pull-in device of the present invention, and FIG. 2 shows the flow of the processing. First, regarding Fig. 1, 1 is an optical disk, 2 is an optical pickup, 3 is an actuator driver, 4 is an RF signal detector, 6 is a just focus detector, 6 is a focus servo loop fill, and 7 is a first switch. , 8 is a second switch, 9 is a search waveform generator, 11 is a lens free vibration detector, 12 is a lens movement direction detector,
13 is a brake signal generator.

The operation of the focus servo pull-in device configured as described above will be described below.

The optical pickup 2 converts the reflected light from the optical disc 1 into a focus error signal and an RF multiplied signal. The actuator driver 3 drives the optical pickup 2 in the focus direction according to the output of the second switch 8. The RF signal detector 4 detects whether the amplitude of the RF multiplied signal from the optical pickup 2 is large. The just focus detector 5 detects the point in time when focus is achieved based on the figure 8 curve of the focus error signal from the optical pickup 2. This becomes operational when the lens free vibration detector 11 detects that the amplitude of free vibration has become small. The four force null servo lube filter 6 is a filter that has the necessary frequency characteristics and gain when the servo loop is closed.

When the RF signal detector 4 detects that the RF multiplied signal amplitude has become small, the first switch 7 opens the loop fill and outputs the signal from the brake signal generator 13. Further, when the just focus detector 5 detects that the focus is achieved, the loop filter is closed. Second switch 8
outputs the waveform of the search waveform generator 9 when the lens free vibration detector 11 detects that the amplitude of free vibration has become small. The loop filter is closed when the just focus detector 5 detects that focus is achieved. The lens free vibration detector 11 is an RF signal detector 4
After detecting that the double signal amplitude has become small, a focus error signal is used to start an operation for detecting that the amplitude of free vibration has become small. The lens movement direction detector 12 is R
After the F signal detector 4 detects that the RF multiplied signal amplitude has become small, the direction of movement of the lens is detected using the focus error signal. A brake signal generator 13 generates a brake signal in a direction that prevents movement of the lens.

Next, FIG. 2 shows the flow of focus servo pull-in processing. First, the RF multiplied signal amplitude is detected. Repeat if the amplitude is large. If the amplitude is small, it is determined that the focus servo is off, and the servo loop is opened. At this time, there is a possibility that the lens is performing self-11 vibrations with large amplitude. Therefore, it is detected whether or not large-amplitude free vibration is occurring. If the amplitude is large, the direction of movement of the lens is detected from the focus error signal, and a brake signal is generated in a direction that prevents this movement. Then, large-amplitude free vibrations are detected again and repeated until large amplitudes are no longer detected. Then, a focus search is started using a search waveform such as a triangular wave. Then, the point in time when the camera reaches the Chanut focus range near the center of the figure 8 is detected. Then close the servo loop.

Next, a first example of the operating principle of the lens free vibration detector 11 will be explained with reference to FIG. FIG. 5a shows the relationship between the focus position of the optical pickup and the position of the DEINUK recording surface. Further, FIG. 6 shows the movement of the focus error signal. It is assumed that the focus position is oscillating with a large amplitude due to free vibration. It is also assumed that the recording surface of the Deinuk is also shaking due to vibrations. The free vibration frequency of a typical lens is about 30 Hz. on the other hand,
The frequency of surface runout is approximately 4 Hz. A figure 8 appears at the intersection of these curves. Check the period between S-curves with the same appearance using the focus error signal. This can be obtained, for example, by the method shown in FIG. In Fig. 6a, the period when the focus error signal is higher than TH1 is A, and the period lower than TH2 is B.
shall be. This is shown in Figure 6. At this time, 8 as shown in Figure 5.
When letters appear consecutively, they can be detected in the order of ABBAABBA...

At this time, the repetition period t1, t2, 13 is approximately 33m8
So, it is almost constant. Therefore, it can be determined that the amplitude is large if the repetition period of the 8-characters in which the polarities appear in the same order is within a certain range including the free vibration period of the lens. On the other hand, when the amplitude becomes small, the figure 8 does not appear at all or appears at every period of surface runout, that is, about every 260 ms.

Next, a second example of the operating principle of the lens free vibration detector 11 will be explained. Check the time intervals of 8 characters in which the order of polarity is different in the focus error signal. This can be obtained, for example, by the method shown in FIG.

In a, the period higher than TH1 in the focus error signal is designated as A, and the period lower than TH2 is designated as B. This is shown in b. At this time, if 8 characters appear in succession as shown in Figure 6, ABBAAB
It can be detected around 1 of BA...

At this time, the interval from the time of change from A to B to the time of change from B to A, or the interval from the time of change from B to A to the time of change from A to B, T1°T2.・・・・・・
..., T7 will be 33m5 or less. Therefore, if the appearance interval of eight characters whose polarities appear in different orders is within a certain range, it can be determined that the amplitude is large. On the other hand, when the amplitude becomes smaller, 8
Either the characters do not appear at all, or the intervals are longer than a certain range due to the period of surface runout.

The principle of the lens movement direction detector 12 can be determined by knowing whether the order of the 8 characters in FIG. 6 is AB or BA.

For example, AB is detected as upward, and BA is detected as downward.

As shown in FIG. 6C, the brake signal generator 13 generates a drive signal to cause the brake to move downward in the case of AB, and to move upward in the case of BA.

Alternatively, it may be generated only in one direction.

As an example of the principle of the just focus detector 5, the sixth
In the diagram, until A appears and then B appears, or B
This can be achieved by detecting the period between the appearance of A and the next appearance of A.

As described above, according to this example, it is detected whether the free vibration of the lens has a large amplitude or not, and if the amplitude is not large, the focus search is immediately started, and if the amplitude is large, the brake is applied in a direction that prevents the movement of the lens. Focus servo pull-in can be performed in a shorter time than before by providing a means to apply a signal to the actuator, detect whether the signal has attenuated to a small amplitude, and start focus search as soon as the amplitude becomes small. .

Effects of the Invention As described above, the present invention can perform focus servo pull-in in a short time by providing a lens free vibration detector, a lens movement direction detector, and a brake signal generator.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a focus servo pull-in device according to an embodiment of the present invention, FIG. 2 is a flowchart of the processing in FIG. 1, FIG. 3 is a processing block diagram of a conventional focus servo pull-in device, and FIG. Flowchart of the processing in Figure 3, Figure 6 is a waveform diagram showing the operating principle of the lens free vibration detector in Figure 451, Figure 6 is the operation of the lens free vibration detector, lens movement direction detector, and just focus detector. It is a waveform diagram for the sake of explanation. 1... Optical disc, 2... Optical pickup, 3... Actuator driver, 4
...RF signal detector, 6...Just focus detector, 6...Focus servo loop filter, 7...First switch, 8...・・・
...Second switch, 9...Search waveform generator, 1
1... Lens free vibration detector, 12...
- Lens movement direction detector, 13...Brake signal generator. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 4 Figure 5 (CLT

Claims (2)

[Claims] (1) A lens free vibration detector that detects whether the free vibration of the lens has a large amplitude, a lens movement direction detector that detects the movement direction of the lens, and a brake signal that prevents the movement of the lens. a generator, and when the free vibration of the lens is detected to have a large amplitude, a focus servo pull-in device generates a brake signal, attenuates the amplitude to a small amplitude, and then starts a focus search. (2) The focus servo pull-in device according to claim 1, wherein the lens free vibration detector determines that the amplitude is large when the time interval of the S-shaped lines in which the polarities appear in different orders in the focus error signal is within a certain range.