JP2640529B2 - Optical disk player - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical information recording disk (hereinafter, simply referred to as a disk) player, and more particularly to a focus servo device for an optical disk player.

2. Description of the Related Art In an optical disk player, a light beam converged by an objective lens is irradiated onto a recording surface of a disk, and recorded information is read using reflected light (or transmitted light). Therefore, it is necessary to always converge the light beam accurately, so that a focus servo device for controlling the position of the objective lens in the optical axis direction is indispensable.

In such a servo device, if the distance between the objective lens and the recording surface when the light beam is accurately converged on the recording surface of the disk is D ₀ , the objective lens is located at that position (in-focus position). reference level the signal level of the focus error signal is the (e.g., zero level), when the distance between the objective lens and the recording surface becomes large or small relative to D _0, the signal level of the focus error signal thereof spaced Is generated based on the light beam that has passed through the recording surface as a signal that changes in accordance with the degree and has different polarities. Therefore, the characteristics of the focus error signal with respect to the distance between the objective lens and the recording surface, so-called S-curve characteristic centered on the distance D _0. By controlling an actuator for driving the objective lens in the direction of its optical axis in accordance with the signal level of the focus error signal, the objective lens is moved up and down with respect to the recording surface so that the disk is always warped against warpage of the disk. The light beam can be accurately focused on the recording surface.

By the way, if the disk has a large surface warpage, or if there is an obstacle such as a scratch or a bubble on the disk, when the light beam passes over such a portion, the focus error signal is out of the pull-in range of the S-curve characteristic. Errors such as out-of-focus and a decrease in the amount of reflected light may occur. At this time, if the focus servo pull-in range is narrow, the objective lens cannot follow the swing of the disk surface, and the specified information reading spot diameter is not formed on the disk surface. Failures that cannot be made occur.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an optical disk player having a large pull-in range in a focus servo device.

In order to achieve the above object, a light beam passing through an objective lens of a pickup is converged as a reading spot on an information recording disk, and a focus error signal indicating a distance from an in-focus position of the objective lens is obtained to obtain a focus error signal. A focus servo device that performs positioning in the optical axis direction; and a tracking servo device that obtains a tracking error signal indicating a deviation of the read spot from a target track on the information recording disk and causes the read spot to follow the target track. An optical disc player, wherein the focus servo device detects that the objective lens is not within a predetermined distance range from an in-focus position, and generates an out-focus signal; and the out-focus signal. At the time of occurrence A compensation error signal generating means for generating a predetermined level compensation error signal is a and larger than that level in the same polarity of the focus error signal,
Signal selection relay means for supplying the compensation error signal to the objective lens driving means in preference to the focus error signal when the out-of-focus signal is present, wherein the tracking servo device receives a beam spot for reading information. A light intensity obtained from the pair of second photoelectric conversion elements, which is provided on both sides of the first photoelectric conversion element and includes a pair of second photoelectric conversion elements for receiving a pair of beam spots for tracking error detection. The difference between the signals is used as the tracking error signal,
The pair of second photoelectric conversion elements are provided so as to receive the beam spot for information reading when the objective lens is out of the predetermined distance range from the in-focus position, and the out-of-focus detection means , The pair of second
The out-of-focus signal is generated when a sum signal of light intensity signals obtained from a photoelectric conversion element exceeds a predetermined level which is equal to or higher than the level of the sum signal of the light intensity signals at the in-focus position of the objective lens. And

Embodiment In the present invention, in order to extend the pull-in range of the focus servo, for example, the level of a portion of the S-curve characteristic of the focus error signal outside the pull-in range is increased. Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

Figure 1 shows a focus servo apparatus for an optical disc player, the three beam spots obtained by allowed to focus the laser beam, i.e., relative to the spot S ₁ for reading recorded information, the disk of the spots S ₁ manner respectively preceding and subsequent ones tracking information detecting spots S ₂ and S ₃ is irradiated to the recording track T of the disk from a pickup (not shown) during the movement. The reflected light from the disk due to these beam spots is converted into photoelectric conversion elements 1 to 3 built in the pickup.
Incident on.

The photoelectric conversion element 1 is arranged so that each light receiving surface is divided into four by two straight lines orthogonal to each other, and is constituted by four light receiving elements independent of each other. Then, the adders 4 and 5 obtain the two output sums of the elements facing each other with respect to the center of the light receiving surface. The sum of the two outputs is supplied to a subtractor 6, and the difference output between them is used as a focus error signal. The focus error signal is supplied to one input terminal of the sample hold circuit 9 and one input terminal of the spot circuit 10. Further, the respective output sums are supplied to the adder 7 to detect the sum of the two output sums, and the detected output becomes a focus sum signal.

On the other hand, the respective outputs of the photoelectric conversion elements 2 and 3 are supplied to an adder 8, where the sum of the two outputs is detected, and this sum signal becomes a tracking sum signal. The tracking sum signal is supplied to a comparison input terminal of the level comparator 11 and a high-pass filter (hereinafter referred to as HP
F) 12. When the amplitude of the tracking sum signal exceeds the comparison reference voltage V _TH1 , the level comparator 11 supplies a high level signal to one input terminal of the AND gate 13.
After removing the low-frequency component from the tracking sum signal, the HPF 12 supplies the signal to the phase adjustment circuit 14. The phase adjustment circuit 14 is, for example, a low-pass filter (hereinafter, referred to as LPF)
And compensates for the output of the HPF 12 by the amount of phase change of the signal in the HPF 12 and supplies it to the comparison input terminal of the level comparator 15. The level comparator 15 supplies a high level signal to the holding operation terminal of the sample and hold circuit 9 and the other input terminal of the AND gate 13 when the output of the phase adjustment circuit 14 exceeds the comparison reference level V _TH2 . The HPF 12, the phase adjustment circuit 14, and the level comparator 15 constitute an out-of-focus detection unit 30.

The sample hold circuit 9 holds the instantaneous value of the focus error signal in accordance with the output of the level comparator 15, and supplies the instantaneous value of the focus error signal to the zero cross detector 16 via a capacitor for removing the DC component of the held level.

Zero crossing detector 16, the retention level of the positive voltage level V ₁ when positive, selectively causing a negative voltage level -V ₁ for a negative level selection circuit 17. | V ₁ | is selected to be equal to or greater than the amplitude value of the S-characteristic of the focus error signal, for example. The level selection circuit 17 supplies the selected voltage to the other input terminal of the signal selection circuit 10.

The signal selection circuit 10 relays the focus error signal when the output of the AND gate 13 is low, and relays the output of the level selection circuit 17 to the equalizer amplifier 18 when the output is high. The sample-and-hold circuit 9, the AND gate 13, the zero-cross detector 16, the level selection circuit 17, and the signal selection circuit 10 constitute a waveform conversion unit 21.

The equalizer amplifier 18 performs predetermined phase compensation on the output of the signal selection circuit 10 and supplies the output to the driver 19. driver
The power amplifier 19 amplifies the output of the equalizer amplifier 18 and supplies it to the drive coil 20 of the focus actuator. The drive coil 20 is provided with an objective lens (not shown) built in the pickup in a direction and an amount corresponding to the polarity and level of the focus error signal supplied via the driver 19.
Is moved in the direction of the optical axis. In addition, in the optical disk player, a spindle servo and a tracking servo are indispensable, and a well-known one is used.

Next, the servo pull-in operation in the focus servo device having such a configuration will be described with reference to the waveform diagram of FIG.

First, changes in the output levels of the focus error signal and the tracking sum signal when the objective lens is moved in a direction away from the position close to the recording surface of the disk are respectively described in the second.
These are shown in FIGS. In the focus error signal, the level of the S-characteristic becomes 0 at the in-focus position, and the level before and after the S-character characteristic changes symmetrically in accordance with the separation distance. This portion is a pull-in range for stably performing the focus servo operation. Furthermore, the light spot diameter irradiates the entire light-receiving element 1 is divided into four parts become larger away from the focus position D _0, the error output is 0. On the other hand, the tracking sum signal shows a peak-like characteristic that rises and falls before and after the separation distance at which the S-curve characteristic occurs in the focus error signal. This peak-like characteristic exhibits two peaks sandwiching the S-shaped curve characteristic. Reason for showing such characteristics, but at the focus position D ₀ is the main beam of the light spot is in the minimum diameter, the light receiving elements adjacent expanded light spot diameter as becomes out-of-focus 2
And to reach 3. When the main beam having a relatively high level irradiates the light receiving elements 2 and 3, the output levels of both light receiving elements increase, and peak characteristics occur.

FIG. 8A shows the level characteristics of the tracking sum signal when the distance between the light receiving element 1 and the light receiving elements 2 and 3 is relatively small. FIG. 8B shows a tracking level characteristic when the distance between the light receiving element 1 and the light receiving elements 2 and 3 is relatively large. Further, it shows a level characteristic with respect to a separation distance of a focus sum signal described later. The reason why the polarity of the S-shaped characteristic beak is different in FIGS. 8A to 8C is that the direction of separation from the disk surface is different.

As described above, the focus error signal and the tracking sum signal exhibit certain level characteristics according to the distance of the objective lens from the disk recording surface.

From the characteristics of the tracking sum signal, the level comparator
A portion exceeding the threshold voltage V _TH1 is detected by 11 so that it can be determined that the objective lens exists in the separation distance range where the S-curve characteristic of the focus error signal exists.

In addition, the peak portion of the tracking sum signal is generated corresponding to a portion outside the pull-in range of the S-shaped curve, and this peak portion is extracted by the HPF 12 as shown in FIG. As can be seen from FIGS. 8A and 8B, the peak characteristics can be selected by selecting the positions of the light receiving elements 2 and 3 or the shape of the light receiving surface.

The phase change by the HPF 12 is compensated by the phase adjusting circuit 14 as shown in FIG. Of the phase-compensated output of the HPF 12, the threshold voltage V is set by the level comparator 15.
_The portion exceeding _TH2 is detected as shown in FIG. 2 (F), and the peak portion is determined.

The output of this level comparator 15 indicates that the objective lens
Is supplied to the sample hold circuit 9 and the AND gate 13 as the out-of-focus signal representing the absence of D ₀ within a predetermined distance range. When the sampler hold circuit 9 samples the level of the focus error signal in response to the out-focus signal, the zero-cross detector 16
But to determine the polarity of the sampled instantaneous values, positive or negative voltages V ₁ in accordance with the polarity is selected to the level selection circuit 17, to supply it to the signal selection circuit 10.

When the out-focus signal is supplied in the presence of the output of the level comparator 11, the AND gate 13 relays the output of the level selection circuit 17 to the equalizer amplifier 18 prior to the focus error signal.

Accordingly, the separation distance characteristic of the original focus error signal as shown in FIG. 2A is a characteristic in which the amplitude of the out-of-focus portion is increased as shown in FIG. 2G. Such a level-compensated focus error signal (hereinafter, referred to as a compensated focus error signal) has a focus servo with a wider range of pull-in than the original focus error signal as shown in FIG. 2 (G), and the dynamic range of the focus servo becomes larger. I have. When such a compensated focus error signal is supplied to the focus drive system, the focus servo follows over a wide range of vertical movement of the disk surface. In addition, even if disturbance occurs due to scratches on the disk, etc., the focus will be quickly returned to the focused state due to the strong pull-in force of the focus servo. There is less maneuvering to lock the servo and less interruptions in performance.

Next, another configuration example of the waveform conversion unit 21 is shown in FIGS.

In the configuration example shown in FIG. 3, the sample-and-hold circuit 9 responds to an out-focus signal as shown in FIG. The instantaneous value of the fluctuating focus error signal is sampled and held, and thereafter, the charge of the capacitor holding the level is gradually discharged through the resistor. A triangular output is obtained by amplifying the level of the attenuated output of the sample and hold circuit 9 as shown in FIG. When this is selected by the signal selection circuit 10, a compensated focus error signal with level compensation as shown in FIG. 5D is obtained.

In the configuration example shown in FIG. 4, when the focus error signal goes out of focus, the sample hold circuit 9 holds the instantaneous value of the focus error signal, and the signal selection circuit 10 outputs this. . Therefore, in the original focus error signal, the portion where the level is reduced by out-focus is maintained at a constant value as shown in FIG. 5 (E).

In the above embodiment, the case where the signal processing is performed by hardware by the waveform conversion unit 21 has been described. However, the configuration may be performed by software using a signal processor as shown in FIG.

In the waveform converter shown in FIG. 6, the focus error signal is sampled by the sample and hold circuit 81, digitized by the A / D converter 82, and supplied to the signal processor 83 as, for example, 8-bit data. The signal processor 83 is controlled by the microprocessor 84, thereby compensating the frequency characteristic for the focus error signal and performing processing such as equalizer characteristic and gain switching control. The 8-bit data output from the signal processor 83 is converted into an analog signal by the D / A converter 87 and is used as a drive input for the drive circuit 19. The signal processor 83 sends a sample timing pulse to the sample / hold circuit 81, an A / D timing pulse to the A / D converter 82, and a D / A to the D / A converter 87.
Timing pulses are supplied respectively. Predetermined data is stored in the ROM 86 in advance. The RAM 85 temporarily stores data obtained in the signal processing process.

Next, the waveform conversion process of the focus error signal when the signal processor 83 is used will be described with reference to the flowchart of FIG. 7 while referring to the waveform diagram of FIG.

First, the signal processor 83 is a microprocessor
In response to the focus error signal processing command from 84, the process proceeds to this subroutine, and the output data FE of the A / D converter 82 is read (step S1). It is determined whether or not the out-of-focus signal is supplied via the microprocessor 84. Also, in order to ensure more operation, a level comparator
It is also determined whether 11 outputs are supplied (step S
2). If the out-focus signal has been supplied, it is determined whether the value of the data FE is positive or negative (step S3). The value of the data FE is positive when to replace the value of the data FE to the value V ₁ (step S4). The value of the data FE is when negative replaces the value of the data FE to the value -V ₁ (step S5). data
If the value of FE is 0, the process proceeds to step S6 (step S6).
S3). When the out-focus signal is not supplied (step S2), the value of the data FE remains unchanged. Next, the data FE is subjected to data processing of F = f (FE) by an arithmetic processing routine that performs an equalizer operation according to the equalizer function F = f (χ) (step S6). The processed output data F is supplied to the D / A converter 87 (step S
7). When steps S1 to S7 are repeated to perform waveform processing of the focus error signal, a compensated focus error signal as shown in FIG. 2 (G) is obtained.

As described above, in the present invention, the focus error signal is supplied to the focus drive system after performing the waveform conversion processing for expanding the pull-in range of the S-shaped characteristic of the original focus error signal. The dynamic range is expanding.

The circuit configuration of each of the out-of-focus detection unit 30 and the waveform conversion unit 21 is not limited to the embodiment, and various types can be selected and combined.

Effect of the Invention As described above, in the optical disk player of the present invention, when the objective lens of the pickup is not within a predetermined distance range from the in-focus position, the amplitude of the focus error signal in the focus servo device is made smaller than the original signal level. Increase the dynamic range of the focus servo loop to generate a strong pull-in force, so the pull-in operation is quick, and the objective lens follows even when the disk surface moves up and down relatively large, which is preferable. . Further, as a means for detecting out-of-focus, a pair of second photoelectric conversion elements for generating a tracking error signal provided on both sides of the first photoelectric conversion element for reading information is used, which leads to cost reduction. Also,
There is an effect that adjustment of the out-of-focus detection position can be easily performed by adjusting the distance between the first photoelectric conversion element and the second photoelectric conversion element.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment, FIG. 2 is a signal waveform diagram for explaining the operation of the first embodiment, and FIGS. FIG. 5 is a block diagram showing an example, and FIG. 5 is a waveform converter shown in FIGS. 3 and 4.
FIG. 6 is a block diagram showing an example in which the waveform converter 21 is constituted by a digital circuit, and FIG. 7 is a signal waveform diagram for explaining the operation of the signal processor of FIG. FIGS. 8 (A) to 8 (C) are flow charts for explanation, and signal waveform diagrams showing waveform examples of the tracking sum signal and the focus sum signal. Explanation of Signs of Main Parts 11, 15… Level comparator 21… Waveform converter 30… Out-focus detector

Claims (2)

(57) [Claims] An optical axis of the objective lens is obtained by converging a light beam having passed through an objective lens of a pickup as a reading spot on an information recording disk and obtaining a focus error signal indicating a distance from an in-focus position of the objective lens. An optical disc including a focus servo device for positioning in a direction, and a tracking servo device for obtaining a tracking error signal indicating a deviation of the read spot from a target track on the information recording disk and causing the read spot to follow the target track. A focus servo device, wherein the focus servo device detects that the objective lens is not within a predetermined distance range from a focus position, and generates an out-focus signal; and the generation of the out-focus signal. The four at the time A compensating error signal generating means for generating a compensating error signal of a predetermined level having the same polarity as the polarity of the cas error signal and greater than the level thereof; And a signal selection relay unit for supplying the signal to the objective lens driving unit. The tracking servo device is provided on both sides of the first photoelectric conversion element that receives a beam spot for reading information, and includes a pair of tracking errors. Including a pair of second photoelectric conversion elements for receiving a beam spot for detection,
The difference between the light intensity signals obtained from the pair of second photoelectric conversion elements is used as the tracking error signal, and the pair of second photoelectric conversion elements are arranged so that the objective lens is at the predetermined distance from a focus position. The out-of-focus detection means is provided so as to receive the beam spot for information reading when deviated from the range, wherein the sum signal of the light intensity signals obtained from the pair of second photoelectric conversion elements is used for the objective lens. An optical disc player, wherein the out-of-focus signal is generated when a predetermined level which is equal to or higher than a level of a sum signal of the light intensity signals at a focus position is exceeded. 2. The focus servo apparatus according to claim 1, wherein the light receiving surface includes the first photoelectric conversion element divided into four by two orthogonal lines, and a sum of intensity signals obtained from light receiving surfaces located at one diagonal position. 2. The optical disc player according to claim 1, wherein a difference from a sum of intensity signals obtained from light receiving surfaces located at the other diagonal positions is used as the focus error signal.