JPH0479032A - Disk reproducing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a disc playback device such as a compact disc player.

[Summary of the invention]

The present invention performs a focus search operation to position a focus actuator within the control range of a focus servo in a disc playback device such as a compact disc, and determines that there is no disc if a focus OK signal is not detected during the focus search operation. This shortens the time required to detect the presence or absence of a disc in a compact disc player that does not have a disc detection mechanism.

[Conventional technology]

Conventionally, in a low-cost compact disc player that does not have a disc presence detection mechanism, a focus search is performed and the presence or absence of a disc is determined based on whether the focus search is completed.

That is, in a compact disc player, when a disc is loaded, the focus search operation state is set in order to position the focus actuator within the control range of the focus servo.

The focus search operation is an operation in which the focus servo loop is turned off, the focus actuator is moved, a window is opened in response to a FOK (focus OK) signal, and an FZC (focus zero cross) signal is detected. When the FZC signal is detected in this focus search operation, it is assumed that the pick amplifier has entered the control range of the focus servo, and the focus servo loop is closed.

If a disk is mounted, the focus actuator can be driven into the control range of the focus servo by the focus search operation described above. However, if the disc is not mounted, the focus position cannot be found during the focus search operation, and the focus search is not completed. Therefore, if the focus search is not completed, it is determined that there is no disc.

Control during this focus search will be described in detail with reference to a flowchart. FIG. 5 is a flowchart of focus search in a conventional compact disc player.

In the focus search operation state, first, the focus actuator is lowered to the initial position (step 201).
).

Then, the focus actuator is raised from the initial position (step 202).

Then, while raising the focus actuator, it is determined whether the FOK signal is detected (step 203).

The FOK signal is a window signal for detecting an FE (focus error) signal, and the 20FOK signal is output when the sum signal of the 4-division photodetector exceeds a predetermined value. The total sum of reflected light from the disk increases as it approaches the focus position. Therefore, when the focus position is far from the focus position, the addition signal of the 4-division photodetector is less than a predetermined value, and no FOK signal is output.

When approaching the focus position, the addition signal of the 4-part photodetector exceeds a predetermined value, and an FOK signal is output.

If no FOK signal is detected, it is determined whether the focus actuator has been raised to the final position (step 204). If the focus actuator has not reached the final position, the process goes to step 203 and the detection of the FOK signal is continued.

When a disk is mounted, as the focus actuator is raised, it approaches the focus position and an FOK signal is output. Once the FOK signal is detected, it is determined whether the FZC signal is detected (step 205).

The FZC signal is a signal indicating the zero crossing of the FE (focus error) signal. The timing at which the FZC signal is output is the focus position.

If the FZC signal is not detected in step 205, the process proceeds to step 204, where it is determined whether the focus actuator has been raised to the final position. If the focus actuator has not risen to the final position, F
Detects the OK signal and opens the window (step 203)
), the process of detecting the FZC signal (step 205) continues.

When the FZC signal is detected in step 205, the focus servo loop is closed (step 206), and the focus search operation is ended.

In this way, if the FZC signal can be detected, the focus search operation can be completed, but if the disc is scratched or dirty, the FE multiplied signal will be disturbed and the FZC signal will be disturbed.
Sometimes the signal cannot be detected.

No FZC signal is detected in step 205, and step 2
If it is determined in step 04 that the focus actuator has risen to the final position, the focus actuator is lowered to the initial position (step 207).

Then, it is determined whether the focus search operation has been repeated three times (step 20).

If the focus search operation is 3 times or less, step 202
The focus search operation continues.

When a disk is loaded, the FZC signal is detected after three focus search operations or less, and focus servo is applied. However, if no disc is installed, even after three focus search operations are completed,
Focus search is not completed.

If it is determined that the focus search operation has been performed three times or more in step 20B, the focus servo is turned off (step 20B).
09), it is determined that there is no disc.

[Problem to be solved by the invention]

However, as described above, conventional compact disc players that determine that there is no disc if the focus search is not completed have a problem in that it takes a long time to determine the presence or absence of a disc.

That is, as shown in the flowchart of FIG. 5, conventionally, after three focus search operations are completed, it is determined that there is no disc. During this time, the focus actuator is lowered to the initial value once in step 201, the focus actuator is raised three times in step 202, and the focus actuator is lowered to the initial value three times in step 207. The operating time in step 201 is a O(a .

= 200m5ec), the operation time in step 202 is bo (bo = 1sec), and the operation time in step 207 is 00 (c0 = 700fflsec), it will take 7 orcus searches until it is determined that there is no disk. , at least ao + ((bo + co) x 3) -5,3m5ec
It just takes time.

Therefore, an object of the present invention is to provide a disc playback device that can shorten the time required to detect the presence or absence of a disc.

[Means to solve the problem]

The present invention is a disc playback device that is set to a focus search operation state and determines that there is no disc if a focus OK signal is not detected during the focus search operation.

[Effect]

If a focus OK signal is not detected in one focus search operation, it is determined that there is no disc, so the presence or absence of a disc can be detected without repeating the focus search operation multiple times, and the time required to detect the presence or absence of a disc is shortened.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a focus search circuit in a compact disc player to which the present invention is applied. The pickup of this compact disc player has four-segment photodetectors IA and IB as shown in Figure 2.
, IC, and ID are arranged. Photodetector IA~I
Focus servo can be performed using the output of D. That is, when the reflected light from the disk is imaged on the four-part photodetectors IA to ID through the cylindrical lens, if the objective lens is too far away, an elliptical image as shown in FIG. If the lens is too close, see Figure 2C.
The result is an elliptical image as shown in . At the focus position,
The result will be a circular image as shown in the second diagram. Therefore, a focus error can be detected by obtaining a difference signal between the sum signal of the output of the photodetector 1A and the output of the photodetector IC, and the sum signal of the output of the photodetector IB and the output of the photodetector ID.

In FIG. 1, the output current of photodetector IA and
The sum current with the output current of the photodetector IC is supplied to the IV conversion circuit 2 and converted into a voltage value. The sum current of the output current of the photodetector IB and the output current of the photodetector ID is supplied to the I-■ conversion circuit 3 and converted into a voltage value.

The output of the 1-V conversion circuit 2 is supplied to an addition circuit 4 and also to a subtraction circuit 5. The output of the IV conversion circuit 3 is supplied to an addition circuit 4 and also to a subtraction circuit 5.

An adder circuit 4 adds the output of the IV conversion circuit 2 and the output of the IV conversion circuit 3. The output of the adder circuit 4 is supplied to a comparator 7 via an FOK amplifier 6. When the output of the FOK amplifier 6 exceeds a predetermined value, the comparator 7 outputs an FOK (focus OK) signal. 20 FOK signal is taken out from output terminal 8.

A subtraction circuit 5 subtracts the output of the IV conversion circuit 2 and the output of the I-■ conversion circuit 3. An FE (focus error) signal can be obtained from the output of the subtraction circuit 5.

The output of this subtraction circuit 5 is supplied to a zero cross detection circuit 9. The zero cross detection circuit 9 detects the FE from the subtraction circuit 5.
Double signal zero crossing point is detected. At the zero-crossing point of the FE multiplied signal, the zero-crossing detection circuit 9 outputs an FZC (focus zero-crossing) signal. This FZC signal is taken out from the output terminal 10.

As the focus position approaches, the total amount of reflected light from the disk increases, so as shown in Figure 3A,
The output of the adder circuit 4 increases as it approaches the focus position. The output of this adder circuit 4 is the FOK amplifier 6
is supplied to the comparator 7 via. When the output of the adder circuit 4 exceeds a predetermined value, as shown in FIG. 3B, the FO
The K signal becomes high level.

On the other hand, from the subtraction circuit 5, as shown in FIG.
A double signal is output. At this FE multiplied signal zero cross point, the third
As shown in the figure, the FZC signal is output. This FZ
The timing of the C signal corresponds to the just focus position.

In one embodiment of the present invention, if no FOK signal is detected in one focus search operation, it is immediately determined that there is no disc. Since the FOK signal is output when the sum signal of photodetectors IA to ID exceeds a predetermined value, it can be detected without fail if a disk is loaded. If there is no disk, no FOK signal is output.

In this way, by determining the presence or absence of a disc based on the presence or absence of the FOK signal, the presence or absence of a disc can be determined with a single focus search operation, thereby reducing the time required to determine the presence or absence of a disc.

FIG. 4 shows a flowchart of a compact disc focus search to which the present invention is applied.

First, the flag indicating whether or not an FOK signal is detected is set to °“0°
It is initialized to (step 101).

The focus actuator is lowered to the initial position (
Step 102).

Then, the focus actuator is raised from the initial position (step 103).

Then, while raising the focus actuator, it is determined whether an FOK signal is detected (step 104).

If no FOK signal is detected, it is determined whether the focus actuator has risen to the final position (step 105). If the focus actuator has not been raised to the final position, the process goes to step 104 and continues detecting the FOK signal.

If the FOK signal is detected in step 104, a flag is set to 1'' (step 106).

Then, it is determined whether the FZC signal is detected (step E07).

If the FZC signal is not detected, the process goes to step 105, where it is determined whether the focus actuator has been raised to the final position; if the focus actuator has not been raised to the final position, the process goes to step 104;
Detection of the FOK signal continues.

When the FZC signal is detected in step 107, the focus servo loop is closed (step 108), and the focus search operation is ended.

When it is determined in step 105 that the focus actuator has risen to the final position, the flag is set to "0".
°” is detected (step 109).

Here, if the flag is 0, it is determined that there is no disc.

If the flag is "1", the focus actuator is lowered to the initial position (step 110).

Then, it is determined whether the focus search operation has been repeated three times (step 111).

If the focus search operation is 3 times or less, step 103
The focus search operation continues.

If it is determined in step 111 that the focus search operation has been performed three times or more, the focus search is turned off (step 112), and it is determined that there is no disc.

Thus, in one embodiment of the invention, if a FOK signal is detected, a flag is raised at step 106. When one focus search operation is completed, it is determined in step 109 whether the flag is 0", and if the flag is 0", it is determined that there is no disc, and if the flag is 1", the focus search is started. can continue.

Therefore, the time required to detect the presence or absence of a disc can be shortened.

For example, the operating time in step 102 is a I(a l
= 200m5ec), the operation time at step 103 is bl (b+=1sec), and the operation time at step 110 is c + (c I=70On+5ec),
The time it takes to detect the absence of a disc is a + + b = 1.2 sec, which is significantly shorter than the 5.3 sec of the conventional case.

〔Effect of the invention〕

According to this invention, if no FOK signal is detected, it is determined that there is no disc, so it is possible to determine the presence or absence of a disc without waiting for the completion of focus search. Therefore, the time required to detect the presence or absence of a disc is shortened.

[Brief explanation of the drawing]

FIG. 1 is a block diagram used to explain an embodiment of this invention, FIG. 2 is a route diagram used to explain focus search, FIG. 3 is a waveform diagram used to explain an embodiment of this invention, and FIG.
The figure is a flowchart used to explain one embodiment of the present invention, and FIG. 5 is a flowchart used to explain a conventional disc playback device. Explanation of main symbols in the drawings IA to ID: Photodetector, 4: Adder circuit, 5
: Subtraction circuit, 6: Comparator, 8: FOK signal output terminal, 9: Zero cross detection circuit, 10: FZC signal output terminal.

Claims (1)

[Claims] A disc playback device that is set to a focus search operation state and determines that there is no disc if a focus OK signal is not detected during the focus search operation.