JPH0512683A - Focus pull-in device - Google Patents

Abstract

PURPOSE:To perform focus pull-in even in the case of using an optical disk with face wobbling in an optical disk player. CONSTITUTION:This device is provided with an S-shape detector 11 detecting the S-shape area of a focus error signal, a detecting period measuring instrument 12 detecting the presence period of the S-shape, a signal generator 13 outputting voltage and a switch changing over signal in accordance with this output and a switch changeover device 14 switching a servo mode and a search mode. When a relative speed between the focal position of a lens at the time of detecting the S-shape and a disk face is fast, the lens is driven to a direction away from the disk face so as to decease the relative speed. When decreased speed, a servo loop is closed. Thus, the focus pull-in is performed even in the case of using the optical dusk with the face wobbling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus pull-in device in an optical disc player.

[0002]

2. Description of the Related Art In recent years, a high-speed rotating laser disk has attracted attention as an optical disk. Here, there is a need for a focus pull-in device that can pull the focus out of focus.

As a conventional focus pull-in device,
For example, it is shown in Japanese Patent Publication No. 63-13261.

A conventional focus pull-in device will be described below. FIG. 8 shows the principle of this conventional focus pull-in device. In FIG. 8, (A)
Is the focus error signal and threshold voltage,
(B) is the output of both comparators, (C) is the output of the differentiating circuit of (B), (D) is the extracted positive polarity signal of (C), and (E) is the signal of (D) is triggered. Is a signal for closing the servo loop.

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

First, the focus lens is driven so as to approach from a position away from the disc. Then, an S-shaped curve appears in the focus error signal. Differentiate the comparison output with the threshold voltage and close the servo loop with the output closer to the in-focus position as a trigger. As a result, servo is applied near the center of the S curve.

[0007]

However, in the above-mentioned conventional structure, when the relative velocity between the lens and the disk surface is large in the initial state like a surface wobbling disk, it is impossible to pull in even if the servo loop is closed. Had.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a focus pull-in device which can pull in even a surface wobbling disk.

[0009]

To achieve this object, a focus pull-in device according to the present invention comprises an S-shaped detector for detecting an S-shaped region of a focus error signal, and a detection period for detecting an S-shaped existence period. A measuring instrument, a signal generator that outputs a search voltage and a switch switching signal according to the output of the detection period measuring instrument, a servo mode that controls according to the focus error signal, and a search that controls according to the search voltage. It is composed of a switch selector that switches between modes.

[0010]

According to the present invention, with the above structure, the relative speed between the lens and the disk surface when the S-shape is detected is measured, and the lens is driven until this value becomes equal to or less than the pull-in threshold value. Close the servo loop when:
This allows stable focus pull-in.

[0011]

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

First, the configuration centering on the focus control system of the optical disk player will be described with reference to FIG. 51 is a control signal generator, 52 is an actuator driver, 53 is a focus error signal generator, 54 is an optical pickup,
Reference numeral 55 is a spindle motor, and 56 is an optical disk. Here, the purpose of the focus control system is to match the in-focus position of the optical pickup 54 with the disk surface of the optical disk 56.

The configuration of the control signal generator 51 according to the first embodiment of the present invention is shown in FIG. 11 is an S-shaped detector, 111 is a positive value detector, 112 is a negative value detector, 1
Reference numeral 13 is a 0-value detector, 12 is a detection period measuring device, 13 is a signal generator, 14 is a switch selector, 15 is a switch A, 16 is a switch B, 17 is a differentiating circuit, and 18 is an integrating circuit. When the focus error signal is input, the S-shaped detector 11 detects that the error signal is in the middle of S-shaped or has passed. Operation principle of the S-shaped detector 11
Will be explained. In this example, the S-shape outputs a positive value when it is far from the in-focus position and a negative value when it is close. The positive value detector 111 outputs when the value of the error signal is above a certain positive threshold value. The negative value detector 112 outputs when it is below a certain negative threshold value. The zero value detector 113 outputs when it is between the positive threshold value and the negative threshold value.
The detection period measuring device 12 measures the period of three outputs of the S-shaped detector 11, and counts the number of clocks within this period, for example. Then, if the period during which the positive value detector 111 output is present is less than or equal to a certain threshold value period (a), if it is greater than or equal to (b), the certain threshold value period during which the negative value detector 112 output is present is some threshold value. If the period is less than or equal to the period (c), if it is greater than or equal to the period (d), and if the zero-value detector 113 output is present, then five types of signals (e) are output. The signal generator 13 does not output the search voltage (positive voltage) in the direction of approaching the disk, the search voltage (negative voltage) in the direction of moving away from the disk, or the output according to the order of outputting the above five kinds of signals. When the detection period is long, that is, the relative speed is slow, as in (b) and (c), the switch selector 1
4 is instructed to switch the switch A15 and the switch B16 from the search mode to the servo mode. The differentiating circuit 17 and the integrating circuit 18 are components of the servo loop filter. In particular, the integrating circuit 18 is used to update the low frequency component even in the search mode. The focus drive signal is obtained as the sum of the output of switch A15 and the output of switch B16.

Next, the operation of the signal generator 13 will be described with reference to FIG.
Described in. Initially, assume that the lens is well away from the disc. So switch A15, switch B1
A signal for switching to the search mode of No. 6 is output. Then, a positive voltage is output. Here, if (b) is detected, it is determined that the relative speed is sufficiently slow, and the switch A15 and the switch B16 are
The signal for switching to the servo mode of is output. If (a) is detected, (e), (c), (e) are detected, that is, after passing through the S-shaped region at a high relative speed,
Output a negative voltage. This causes the lens to gradually move away from the disc. Then it intersects the disk surface again. Here, if (d) is detected, it is determined that the relative speed is sufficiently slow, and a signal for switching the switches A15 and B16 to the servo mode is output. If (c) is detected (e),
No output is generated after detecting (a) and (e). And
It is again checked whether or not (b) is detected in S-shape detection. Thus, after the S-shape is detected by approaching the disc, the disc is gradually separated from the disc. Then, the speed of surface wobbling becomes slow. Close the servo loop when it becomes slow enough while checking the relative speed. As a result, it is possible to stably pull in the focus even on a disk having a large surface wobbling. FIG. 3 shows how the focal point positions of the disk surface and the lens change with time. In this example, the case where the disk is gradually separated from the disk as shown by the solid line has been described. On the other hand, as indicated by the dotted line, the relative velocity becomes small even when the disc is gradually approached, so that focus pull-in is possible.

As described above, according to this embodiment, the S-shaped detector 11, the detection period measuring device 12, the signal generator 13, the switch selector 14, the switch A15, and the switch B16 are provided, and the focus position of the focus lens is adjusted. It is possible to slow down the relative speed between the in-focus position and the disk surface by gradually separating or moving the disk from the disk, and it is possible to close the servo loop and perform stable focus pull-in.

Next, the operation of the signal generator 13 according to the second embodiment of the present invention will be described with reference to FIG. Initially, assume that the lens is well away from the disc.
Therefore, a signal for switching the switches A15 and B16 to the search mode is output. Then, a positive voltage is output. Here, if (b) is detected, the relative speed is determined to be sufficiently slow, and a switch signal for switching the switches A15 and B16 to the servo mode is output. When (a) is detected, (e), (c), (e) are detected, and then a negative voltage is output. Here, if (d) is detected, it is determined that the relative speed is sufficiently slow, and a signal for switching the switches A15 and B16 to the servo mode is output. If (c) is detected, (e), (a), and (e) are detected, and then a positive voltage is output again. After the S-shape is detected by approaching the disk with a positive voltage, the lens is accelerated with a negative voltage to follow the disk surface. After detecting the S-shape again, the lens is accelerated with a positive voltage to follow the disk surface. In this way, the positive and negative voltages are alternately output to check the relative speed while following the disk surface. The servo loop is closed when the relative speed becomes sufficiently slow. As a result, it is possible to stably pull in the focus even on a disk having a large surface wobbling. FIG. 7 shows how the focal point positions of the disk surface and the lens change with time.

As described above, according to this embodiment, the S-shaped detector 11, the detection period measuring device 12, the signal generator 13, the switch selector 14, the switch A15 and the switch B16 are provided, and the focus position of the focus lens is provided. Positive and negative voltages are alternately output so as to follow the disk surface, and when the relative speed between the in-focus position and the disk surface slows down, the servo loop can be closed here to perform stable focus pull-in. it can.

[0018]

As described above, the focus pull-in device of the present invention includes an S-shaped detector for detecting the S-shaped region of the focus error signal, a detection period measuring device for detecting the S-shaped existence period, and a detection period measurement. A signal generator that outputs a voltage and a switch switching signal according to the output of the device, and a switch selector that switches between servo mode and search mode are provided, and the relative speed between the focal point of the lens and the disk surface is slow. By closing the servo loop at that time, stable focus pull-in can be performed even on the surface wobbling disk.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a control signal generator 51 according to an embodiment of the present invention.

FIG. 2 is a signal generator 13 according to the first embodiment of the present invention.
Flowchart for explaining the operation of

FIG. 3 is a waveform diagram showing a change over time of the focal point positions of the disk surface and the lens in the first embodiment of the present invention.

4 is a waveform diagram for explaining the operation of the S-shaped detector 11 in FIG.

FIG. 5 is a block diagram showing the configuration of a focus control system of an optical disc player.

FIG. 6 is a signal generator 13 according to a second embodiment of the present invention.
Flowchart for explaining the operation of

FIG. 7 is a waveform chart showing the change over time of the in-focus position of the disk surface and the lens in the second embodiment of the present invention.

FIG. 8 is a waveform diagram for explaining the operation principle of a conventional focus pull-in device.

[Explanation of symbols]

11 S-shaped detector 12 Detection period measuring instrument 13 Signal generator 14 Switch changer 15 Switch A 16 Switch B 17 Differentiating circuit 18 Integrator circuit 111 Positive value detector 112 Negative value detector 113 0 value detector

Claims (5)

[Claims] 1. An S-shaped detector for detecting an S-shaped region of a focus error signal, a detection period measuring device for detecting an S-shaped existence period, and a search voltage and a switch switching according to the output of the detection period measuring device. A focus pull-in device including: a signal generator that outputs a signal; a switch selector that switches between a servo mode that controls according to the focus error signal and a search mode that controls according to the search voltage. 2. A signal generator sets a selector switch to a search mode and outputs a positive voltage with the focus lens of the focus lens away from the disc surface to bring the lens close to the disc for S-shaped detection. The focus retraction device according to claim 1, wherein the selector switch is set to the servo mode when the relative speed between the focus position of the lens and the disk surface at the time of S-character detection is slow. 3. The signal generator outputs a negative voltage and waits for S-character detection when the relative speed at the time of S-character detection is high, and the relative speed at the time of S-character detection falls below a threshold value. The focus pull-in device according to claim 2, wherein this is repeated until the threshold value is reached, and when the threshold value is equal to or less than the threshold value, the selector switch is set to the servo mode. 4. The signal generator outputs a positive voltage and waits for S-shaped detection when the relative speed at the time of S-shaped detection is high, and the relative speed at the time of S-shaped detection is below a threshold value. The focus pull-in device according to claim 2, wherein this is repeated until the threshold value is reached, and when the threshold value is equal to or less than the threshold value, the selector switch is set to the servo mode. 5. The signal generator outputs a negative voltage and waits for S-curve detection when the relative speed at the time of detecting the S-curve is high,
Check whether the relative speed at the time of character detection is below the threshold value, if it is below the threshold value, set the changeover switch to servo mode, and if it is larger than the threshold value, output a positive voltage. The focus retracting device according to claim 2, wherein the voltage is alternately output, and the changeover switch is set to the servo mode when the relative speed at the time of detecting the S-shape becomes equal to or less than a threshold value.