JPH0192929A - Automatic focus leading-in device - Google Patents

Abstract

PURPOSE:To lead in a condenser lens to a focal point automatically and stably for an optional recording medium and laser output by varying a threshold level for deciding the focal position corresponding to a change in a sum voltage signal of a differential sensor output. CONSTITUTION:A sample-and-hold device 15 sampling and holding a sum voltage signal obtained at the zero cross of a difference voltage signal and a threshold level deciding device 16 deciding a threshold level from a maximum value of the signal subject to sample and hold are provided. Then a level discriminating device 10a is provided, which outputs an ON signal when it is decided that the sampled sum voltage signal exceeds the threshold level. Thus, stable focus automatic leading-in is attained independently of the kind of recording medium or the intensity of laser power and a condenser lens drive voltage is held even after the focusing to improve the accuracy of focus servo.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic focus retrieval device, particularly an automatic focus retractor in a focus chivo circuit that drives an objective lens of an optical disk device to focus a light beam on a recording surface. This relates to a retraction device.

[-Conventional technology]

3 to 6 show a conventional automatic focus retrieval device disclosed in, for example, Japanese Patent Application No. 116989/1982, and FIG. 3 shows the sum voltage signal value from the differential sensor near the in-focus point. FIG. 4 is a block diagram showing the configuration of a conventional automatic focus pull-in device used in CD players, etc. FIG. 5 is a signal waveform diagram showing the relationship between the sum voltage signal and the threshold level in the conventional device. FIG. 6 is a time chart diagram for explaining the operation of each part of the conventional device. In Figure 4,
(1) is a differential sensor, for example, four seven! 1l
- (not shown), and corresponding output terminals (al) and (al).

(a3) and (a4) are provided. (2a) is the first
With the current-voltage (X - V) converter (hereinafter referred to as the first converter), one cover is placed so that the output of the differential sensor (1) can be taken out diagonally. Terminal (a
l) and (a3). Similarly, (2b) is a second current-voltage converter (hereinafter referred to as a second converter) connected to the output terminals (al) and (a4). (3
) is a differential amplifier, the negative terminal of which is connected to the first converter (2b), and the positive terminal connected to the second converter (2b).
4) is the first converter (2a) and the second converter (2b: connected adder, (5) is the gain regulator (hereinafter referred to as AGO)
It is connected to the output sides of the differential amplifier (3) and the adder (4), and is used to adjust the gains of these.

(6) is connected to this AGO (5) and is a phase gain compensator for compensating the phase gain, (7) is a servo switch (
This switch (hereinafter referred to as a switch) is used to turn on and off the focus servo system formed on the AGO (5) and phase gain compensator (6) sides. (8) is a power amplifier connected to this switch (7) and a pull-in controller (described later), (9) is a zero cross detector, and a differential amplifier (6)
It is connected to the output side of the circuit and detects the zero crossing of the differential voltage signal that is the output. (10) is a level discriminator, which is connected to the output side of the adder (4) and compares and discriminates the separately set threshold level and the value of the sum voltage signal that is the output of the adder (4). .

(11) is a switch controller, and zero cross detector (9)
The on/off state of the switch (7) is controlled by the signal from the level discriminator (10). (12) is a pull-in controller, which is connected to a level discriminator (10), a switch controller (11), and a pull-in command unit to be described later, and controls the operation of the actuator (13) via a power amplifier (8). There it is. (1) is a pull-in command unit that gives a pull-in operation start command to this pull-in controller (12).

The conventional automatic focus retrieval device is configured as described above, and its operation will be explained below. First, Figure 6 (a
): 2. A start signal corresponding to the retraction command is sent to the retraction controller (12). This causes the retraction controller (
12) operates, the sum voltage signal which is the output of the adder (4) is transmitted to the level discriminator (10) and the pull-in controller (12).
) to the power amplifier (8) and thereby the actuator (13) by a driving voltage signal for driving a condensing lens (not shown), which corresponds to this sum voltage signal.
is activated. - A physical quantity, such as the amount of light, detected from a disk (not shown) is converted into an electric current by the differential sensor (1). This current flows through the differential sensor (1)
output terminal (att.

(a3) and the output terminal (azt + (a4t) respectively through the first converter (2a) and the second converter (2b)
l:: Therefore, it is converted to voltage. Next, these voltages are input to a differential amplifier (5) and an adder (4), respectively, to generate a difference voltage signal and a sum voltage signal, respectively.

When the condensing lens is slowly moved, for example, from below to a hill at the start of the focus pull-in operation, the difference voltage signal and the sum voltage signal change as shown by solid lines and broken lines in FIG. 6, respectively. That is, the sum voltage signal reaches its maximum near the focal point, but its change is relatively gentle, and the differential voltage signal crosses zero at the focal point position (indicated by X in FIG. 6). Therefore,
A level discriminator (10) detects the range in which the sum voltage signal exceeds a certain threshold level (indicated by y in Figure 6), and within this range, a zero-cross detector (9) detects the difference 'voltage signal. If the zero-cross output detection signal is detected, the in-focus position can be determined. At this time, the switch controller (November double) switch (7) is closed, and the servo loop is closed, so that the AGC (5)
The gain is adjusted by y4. The phase gain of the error in the obtained light amount is compensated by a phase gain compensator (6) and sent to a power amplifier (8) through a switch (7). At the same time, the power amplifier (8) is activated, which corrects the above-mentioned sum voltage signal by the error in the amount of light sent from the switch (7) and outputs it.
) is driven, thereby completing the automatic focus pull-in operation.

[Problem that the invention seeks to solve]

In the conventional automatic focus retraction device as described above, the CD
It works effectively when the reflectance of the disc used is almost constant and the output of the readout laser is always constant, as in the case of a player, but when the laser When recording, reproducing, and erasing outputs are significantly different, or when recording media with different reflectances are used, the sum voltage signal changes depending on the laser output or medium reflectance, as shown in Figure 5. When determining the in-focus point based on a fixed threshold level as shown in Figure 6(b), for a disk with high reflectance, the servo is pulled in at a position different from the original in-focus point position, as shown in Figure 6(b). Furthermore, there is a problem in that a disc with a low reflectance makes it impossible to detect a focused point as shown in FIG. 6(C).

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide an automatic focus retrieval device that can perform focus retraction on a disk made of any recording medium and can perform focus retraction at any laser power. With the goal.

[Means for solving problems]

The automatic focus pull-in device according to the present invention includes a sample-and-hold device that samples and holds a sum voltage signal at a zero-crossing point of a differential voltage signal, and a threshold level determined from the maximum value of the sum voltage signal upon receiving the output of the sample-and-hold device. A threshold level determiner and a level discriminator that outputs an on signal when it is determined that the sampled and held sum voltage signal exceeds the threshold level are provided.

[For production]

In this invention, the threshold level for determining the focal point position is varied in response to changes in the sum voltage signal of the differential sensor output due to changes in laser output and medium reflectance, so that arbitrary It is possible to automatically and stably draw the condenser lens to the in-focus position for the recording medium and laser output.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of the automatic focus retraction device of the present invention, and FIG. 2 is a time chart diagram for explaining the operation of each part of the embodiment shown in FIG. In the $1 diagram, (1), (2a), (zb).

(6) to (9), (117 to (14) are the same as in the conventional device, so their explanation will be omitted. (15) is an adder (
4) and a sample hold device connected to the output side of the zero cross detector (9), (16) a threshold level determiner connected to the output side of this sample hold device (15), and (10A) this threshold level. This is a level discriminator connected to the output side of the decider (16) and adder (4).

The basic operation between the automatic focusing bags configured as described above is the same as that of the conventional device, and the sum voltage signal and differential voltage signal shown in FIG. 6 are obtained. Writing instruction device (
A start signal is issued from 14), and while the condensing lens moves from bottom to -E due to the driving voltage, the zero crossing of the differential voltage signal when the condensing lens is at the focused position is detected, and the sum voltage signal at that time is detected. is held by the sample and hold device (15).

Since the sample value is maximum at the original focused position of the condenser lens, the threshold level of the sum voltage signal (indicated by 2 in Figure 2) is determined by the threshold level determiner (16) based on this hold value. determined by Therefore, when using a recordable optical disk device or a recordable/erasable optical disk device where the laser output differs significantly between recording, playback, and erasing, or when using recording media with different reflectances, the laser output or the medium Even if the sum voltage signal changes depending on the reflectance, the threshold level can be appropriately set accordingly.

However, the pull-in operation is not performed during the first objective lens scan. After the threshold level is set, the in-focus position can be determined based on the fact that the sample-and-hold value of the sum voltage signal at the zero-crossing point of the differential voltage signal exceeds the threshold level, and the sample-and-hold sum voltage signal When the level discriminator (10A) exceeds the threshold level, the switch (7) is turned on with the level discrimination output signal outputted from the level discriminator (10A), and the devolve is closed, thereby completing the automatic focus pull-in operation. Here, the pull-in controller (12) is configured with, for example, a counter and a D/A converter (both not shown) to generate a stepped triangular wave voltage, and when the in-focus point is detected, the counting of the counter is stopped and the in-focus point is positioned. By maintaining the condensing lens drive voltage signal, it is possible to extremely reduce the deviation of the focus servo, and even if the condensing lens deviates from the in-focus position due to some disturbance, the condensing lens can be immediately returned to the in-focus position. Can be done.

〔Effect of the invention〕

The present invention includes a sample-and-hold device that samples and holds a sum voltage signal when a differential voltage signal crosses zero, a threshold level determiner that determines a threshold level from the maximum value of this sample-and-held signal, and a subsequent number controller for the sum voltage signal. Equipped with a level discriminator that outputs an ON signal when it determines that the value exceeds this threshold level, automatic focus retraction is possible regardless of the type of recording medium or the strength of the laser power. This has the effect of maintaining the condensing lens drive voltage even after the focus is focused, allowing the focus servo to be accurately controlled.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of each part of the embodiment, FIGS. 3 to 6 show a conventional device, and FIG. The figure is a signal waveform diagram showing the relationship between the sum voltage signal and the difference voltage signal near the in-focus point, Figure 4 is a block diagram showing a conventional automatic focus pull-in device, and Figure 5 is a diagram showing the relationship between the sum voltage signal and the threshold level in the conventional device. FIG. 6 is a signal waveform diagram showing the relationship between the two operating stations of each part of the conventional device. In the figure, (1) is a differential centimeter, (3) is a differential amplifier, (4) is an adder, (10A) is a level discriminator, and (15) is a differential amplifier.
) is a sample hole l, and (16) is a threshold level determiner. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A sum voltage signal and a difference voltage signal are extracted from the output of a differential sensor that detects the focal point of a condensing lens provided in an optical disk device, an error signal is extracted from these sum voltage signal and difference voltage signal, and the error signal is extracted from the sum voltage signal and the difference voltage signal. In the automatic focus pull-in device that corrects the sum voltage signal by the error signal and controls the condensing lens with this correction value, the sample-hold device samples and holds the sum voltage signal at the zero-crossing point of the difference voltage signal; a threshold level determiner that determines a threshold level from the maximum value of the signal sampled and held by the device, and outputs an on signal when it is determined that the sampled and held sum voltage signal value exceeds the threshold level. The automatic focusing system comprises a level discriminator, and when an ON signal is output from the level discriminator, a focus servo system is operated, and the focus servo system is controlled by the correction value to automatically pull in the focus. retraction device. (2) The automatic focus pull-in device according to claim 1, wherein the condenser lens driving voltage corresponding to the correction value is maintained even after the automatic focus pull-in is completed.