JPH0689444A - Focus searching circuit - Google Patents

Abstract

PURPOSE:To shorten the time required for focus searching by searching the focus while making an objective lens gradually descend after abruptly displacing the objective lens toward an optical disk by means of a focusing coil. CONSTITUTION:A pre-processing circuit 5 performs adding and subtracting processing of a reproducing output signal of an optical disk 2 from an optical pickup 4 so as to generate a focusing error signal FE and a reproducing signal, etc., and outputs these signals through an amplifier circuit 6. A servo circuit 7 controls the focusing coil 9 of the pickup 4 through an amplifier 8 based on the signal FE and outputs a zero crossing signal FZC for focusing risen when the signal FE crosses a zero level. After stopping the drive of the coil 9 of the circuit 7 by means of the signal FZC, a system control circuit 10 abruptly moves the objective lens toward the disk by means of a prescribed focus searching signal DI then generated and, after then, moves the lens with a prescribed speed so as to search a focus. Consequently, the time for focus searching is shortened.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology (FIG. 5) Problem to be Solved by the Invention (FIG. 5) Means for Solving the Problem (FIGS. 1 and 2) Action (FIGS. 1 and 2) Example (1) Configuration of Embodiment (FIGS. 1 to 4) (2) Effect of Embodiment (3) Other Embodiment Effect of Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus search circuit, and is suitable for application to an optical disc device for recording or reproducing desired information by using, for example, a magneto-optical disc.

[0003]

2. Description of the Related Art Conventionally, in this type of optical disk device, a focus search process is executed to detect a control target of the fork control, and the focus control is performed with the control target as a reference. This focus search processing is performed by monitoring the focus error signal while moving the objective lens with a predetermined drive signal, and in this kind of optical disc device, the focus error signal is recorded on the surface of the recording layer of the magneto-optical disc. It is designed to collect the beam correctly.

By the way, in the magneto-optical disk, the surface of the recording layer is protected by a transparent member such as polycarbonate, and reflected light can be obtained not only from the surface of the recording layer but also from the surface of this transparent protective member. Furthermore, the magneto-optical disk has a characteristic that the reflectance of the recording layer surface is low, and the control target is set to the surface of the transparent protective member by erroneously detecting the reflected light from the surface of the transparent protective member and the reflected light from the surface of the recording layer. May be set.

For this reason, in this type of optical disc device, the objective lens is first moved closer to the magneto-optical disc side and then gradually moved away, and when the distance is increased, the timing at which the focus error signal crosses 0 level is detected. Therefore, the control target can be correctly detected.

That is, as shown in FIG. 5, in the optical disc device, the focus search signal DV is set so that the objective lens approaches the magneto-optical disc from the holding position when the object lens is not energized.
After raising the signal level of, the signal level is gradually lowered (FIG. 5 (A)). Along with this, in the focus error signal FE, when the focus search signal DV rises, the light beam first focuses on the surface of the transparent protective member, so that the signal level changes to a small S shape, and then the recording layer. When the light beam is focused on the surface, the signal level changes in an S shape (Fig. 5).
(B)).

On the other hand, when the focus search signal DV falls, in the focus error signal FE,
First, the light beam is focused on the surface of the recording layer to change the signal level into an S shape, and subsequently, the light beam is focused to the surface of the transparent protective member to change the signal level to a small S shape. . As a result, in the optical disc device, a focus zero-cross signal FZC (FIG. 5C) in which the signal level rises at the timing when the focus error signal FE crosses 0 level is generated, and at the fall of the focus search signal DV By detecting the rising edge of the focus zero-cross signal FZC, the focus search processing can be executed to correctly detect the control target.

[0008]

By the way, in the focus search in this manner, if the objective lens is moved at a high speed, the vibration of the objective lens cannot be prevented, so that the focus error signal FE is generated. It becomes impossible to reliably detect the timing of crossing the 0 level.

Therefore, in this type of magneto-optical disk device, the focus search signal D takes about 1 second.
After raising V, the focus search signal DV is lowered in the following 1 second period. Therefore, in the conventional optical disk device, there is a problem that the focus search takes time.

Further, as described above, the focus search signal D
When the focus search is performed by gradually lowering V, if the magneto-optical disk has a surface deviation, the rise of the signal level of the focus error signal FE is outside the frequency band of the focus servo circuit, and in this case, the control target is eventually set. It cannot be detected correctly.

In this case, in the conventional optical disk device, the focus search processing is repeated, and eventually the focus search processing requires more time.

The present invention has been made in consideration of the above points, and an object of the present invention is to propose a focus search circuit capable of shortening the time required for focus search.

[0013]

In order to solve such a problem, in the present invention, a light beam emitted from a predetermined light source is condensed on a disk-shaped recording medium 2 through an objective lens 28, and the disk-shaped recording medium is recorded. In the optical disc device 1 for recording desired information on the optical disc 2 or reproducing the recorded information on the disc-shaped recording medium 2, a focus error for receiving the reflected light of the light beam and generating a focus error signal FE of the light beam. The signal detecting means 7, the objective lens changing means 9 for changing the position of the objective lens 28, and the focus error signal FE.
And a predetermined reference level are obtained, and comparing means 7 for generating a focus zero-cross signal FZC in which the signal level of the focus error signal FE rises when the signal level of the focus error signal FE crosses the reference level, and a focus search signal D1 are generated. When the objective lens variable means 9 is driven by the focus search signal generating means 10 and the focus search signal D1 and the signal level of the focus zero cross signal FZC rises, the focus error signal FE instead of the focus search signal D1. And a focus control means 10 for driving the objective lens varying means 9 on the basis of the reference value, and the focus search signal generating means rapidly moves the objective lens 28 in a direction from the holding position in the non-energized state toward the disk-shaped recording medium 2. After the objective lens 28 is held at the search start position by moving the From the search start position away from the disc-shaped recording medium 2 to the movable objective lens 28 at a predetermined speed, to generate a Fuo Kas search signal D1.

Further, in the present invention, the focus search signal generating means 10 causes the focus search signal D to hold the objective lens 28 at the T1 search start position for a predetermined period.
By generating 1, the vibration of the objective lens 28 that occurs when the objective lens 28 is moved is suppressed.

Further, in the present invention, the focus search signal generating means 10 is arranged so that the objective lens 2 is at the search start position.
The objective lens 28 is attached to the contact member 24 that limits the movable range of
Occurs when the objective lens 28 is moved by generating a focus search signal D1 so that the object lens 28 is moved, and generating the focus search signal D1 so as to hold the objective lens 28 at the T1 search start position for a predetermined period. The vibration of the objective lens 28 is suppressed.

Further, in the present invention, the focus control means 10 drives the objective lens varying means 9 by switching the gain higher by a predetermined gain during the period in which the objective lens varying means 9 is driven by the focus search signal D1.

[0017]

In the disk-shaped recording medium, the objective lens 28 is rapidly moved in the direction of approaching the disk-shaped recording medium 2 from the non-energized holding position to hold the objective lens 28 at the search start position. By moving the objective lens 28 at a predetermined speed from the search start position so as to move away from 2, it is possible to shorten the time required for the focus search by the amount that the objective lens 28 is rapidly moved.

Further, at this time, the objective lens 28 is held at the search start position for a predetermined period T1.
By damping the vibration of the objective lens 28 by abutting the objective lens 28 against the contact member 24, the focus search can be reliably performed.

Further, the focus can be surely searched for by driving the objective lens variable means 9 by switching the gain higher by a predetermined gain.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Configuration of Embodiment In FIG. 1, reference numeral 1 denotes an optical disk device as a whole,
The desired information is recorded / reproduced using the magneto-optical disk 2.

That is, in the optical disc device 1, the spindle motor 3 is driven to rotate the magneto-optical disc 2 at a predetermined rotation speed, and in this state, the optical pickup 4 is driven to record and reproduce desired information. At this time, in the optical disc device 1, the output signal of the optical pickup 4 is added / subtracted by the preprocessing circuit 5 to generate a focus error signal FE, a reproduction signal, a tracking error signal, etc., and these signals are amplified. It is amplified by the circuit 6.

Further, in the optical disc device 1, the reproduction signal is output from a signal processing circuit to a predetermined signal processing circuit to process the reproduced signal, thereby reproducing the recorded information on the magneto-optical disk 2, whereas the focus error signal FE is reproduced. , A tracking error signal or the like is output to the servo circuit 7.

Based on the focus error signal FE, the servo circuit 7 drives the focus coil 9 of the optical pickup via the amplifier circuit 8 so that the focus control can be performed. In No. 1, desired information can be surely recorded / reproduced. Further, the servo circuit 7 generates a focus zero cross signal FZC which rises at the timing when the signal level of the focus error signal FE crosses 0 level, and outputs it to the system control circuit 10.

On the other hand, in the system control circuit 10, the entire operation mode is controlled to the focus search mode when the operation of the entire optical disk device 1 is controlled and the magneto-optical disk 2 is loaded and when the power is turned on. By switching, the control target of the focus servo is detected.

That is, in the focus search mode, the system control circuit 10 outputs a control signal to the servo circuit 7 to stop driving the focus coil 9 based on the focus error signal. Subsequently, the system control circuit 10 outputs a predetermined focus search signal D1 to the servo circuit 7, and the focus servo circuit 7 drives the focus coil 9 with this focus search signal D1.

At this time, the system control circuit 10 generates the focus search signal D1 by sequentially reading out the focus search data stored in a predetermined memory circuit and converting it into an analog signal.

Here, as shown in FIG. 2, in the system control circuit 10, after the signal level of the focus search signal D1 is rapidly raised, it is held at this signal level for the period T1 (see FIG. 2 ( A)).

Here, as shown in FIG. 3, in the optical pickup 4, the light beam emitted from the laser diode is reflected by the mirror 26 and guided to the objective lens 28, and the light transmitted through this objective lens 28 is magneto-optical disc. It is designed to irradiate 2. The objective lens 28 is held by a focus coil 9 having a yoke 30 and a magnet 32 arranged at both ends, so that the focus coil 9 can be driven to move up and down.

Accordingly, in the optical disc device 1,
When the objective lens 28 is gradually moved in the direction of the magneto-optical disc 2, the light beam can be first focused on the surface of the transparent protective member 20, and then the light beam can be focused on the recording layer surface 22. ing. The entire optical pickup 4 is protected by the cover 24, and the system control circuit 10 rapidly raises and holds the signal level of the focus search signal D1 to hold the objective lens as shown by the broken line in FIG. 28 is abutted against the cover 24.

Accordingly, in the optical disc device 1,
After the objective lens 28 is suddenly brought close to the magneto-optical disk 2, a focus search is performed so as to gradually move away from the magneto-optical disk 2, whereby the control target can be reliably detected.

At this time, in the optical disc device 1, by rapidly raising the signal level of the focus search signal D1, the time required for the focus search can be shortened accordingly. Further, in the optical disc device 1, during the period T1, the focus search signal D
By holding the signal level of 1 at a constant value, the objective lens 28 is kept pressed against the cover 24 during this period T1, and thus the objective generated when the objective lens 28 is rapidly moved. The vibration of the lens 28 is damped.

Accordingly, in the optical disc device 1,
Even when the objective lens 28 is rapidly moved to perform the focus search as described above, when the objective lens 28 is continuously moved,
Vibration of the objective lens 28 can be prevented, and the focus search can be performed reliably and promptly.

That is, in the system control circuit 10, when the signal level of the focus search signal D1 is raised and the period T1 has elapsed, the signal level is gradually lowered during the period T2. When the focus zero-cross signal FZC does not rise during the period T2, the system control circuit 10 successively raises the signal level during the period T3, and the changes in the periods T2 and T3 are repeated a predetermined number of times. It is done like this.

As a result, in the servo circuit 7, the signal level changes into an S-shape at the timing when the light beam is focused on the surface of the recording layer and the surface of the transparent protective member in accordance with the change of the focus search signal D1. A focus error signal FE can be obtained (FIG. 2 (B)).

In the system control circuit 10, while moving the objective lens 28 with the focus search signal D1, the focus zero cross signal FZC output from the servo circuit 7 is monitored, and the focus search signal D1 is gradually raised. Focus zero cross signal F while lowering
When the signal level of ZC rises, a control signal for operation switching is output to the servo circuit 7. In response to this control signal, in the servo circuit 7, the focus search signal D1
Instead, the focus coil 9 is driven by the focus error signal FE.

As a result, in the servo circuit 7, the position of the objective lens 28 determined by the signal level of the focus search signal D1 at this time is set as a control target, and the signal level of the focus error signal FE becomes 0 level. Then, the focus coil 9 is driven.

That is, as shown in FIG. 4, in the optical disc device 1, the focus search signal D1 (see FIG.
(A)) and outputs the focus error signal F.
The signal level of E (FIG. 4 (B)) falls, and then 0
When crossing the level, the focus zero-cross signal FZC
As the signal level in (Fig. 4 (C)) rises,
The focus search processing ends. As a result, in the optical disc device 1, the surface of the recording layer can be reliably set as a control target for focus control.

During the focus search period, the system control circuit 10 raises the control signal SEL (FIG. 4D) output to the amplifier circuit 6 to improve the gain of the amplifier circuit 6 by 6 [dB]. To do. That is, even when the signal level of the focus search signal D1 is rapidly raised and then gradually lowered, if the magneto-optical disc 2 has a surface deviation, the objective lens 28 vibrates similarly to the case where the objective lens 28 vibrates. A focus error signal FE in which the signal level changes in an S-shape in a short cycle is obtained, and when this surface deviation is severe, the S-shape change is out of the band of the servo circuit 7.

Further, when the objective lens 28 is moved downward, the moving speed is increased due to the weight of the objective lens 28, and in this case, the focus zero cross signal may not rise. For this reason, in this embodiment, during the focus search, the band of the servo circuit is held as it is and the gain of the amplifier circuit 6 is improved by 6 [dB] instead, which causes surface deviation or the like. Even if it does, the control target can be surely detected.

In practice, it has been found from experiments that the control target can be detected with certainty even if the period T2 is set to about 0.75 seconds, which is shorter than the conventional one.

(2) Effects of the Embodiments According to the above construction, the objective lens is rapidly displaced toward the magneto-optical disk side, pressed against the cover to suppress the vibration, and then the objective lens is gradually lowered. At the same time, by improving the gain of the amplifier circuit and performing the focus search, the time required for the focus search can be shortened.

(3) Other Embodiments In the above-described embodiments, the case where the objective lens is pressed against the cover to suppress the vibration of the objective lens has been described, but the present invention is not limited to this, and is separately applied. Place contact members,
You may press against this.

Further, in the above-mentioned embodiment, the case where the desired information is recorded and reproduced by using the magneto-optical disk has been described, but the present invention is not limited to this, and is widely applied to the optical disk device such as a compact disk player. can do.

[0045]

As described above, according to the present invention, after the objective lens is abruptly displaced to the magneto-optical disk side, the objective lens is gradually lowered to perform the focus search, which is required for the focus search. A focus search circuit that can reduce the time can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optical disk device according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the focus search signal.

FIG. 3 is a sectional view for explaining the operation.

FIG. 4 is a signal waveform diagram for explaining the overall operation.

FIG. 5 is a signal waveform diagram for explaining a conventional focus search process.

[Explanation of symbols]

1 ... Optical disk device, 2 ... Magneto-optical disk, 4 ...
Optical pickup, 6 ... Amplifying circuit, 7 ... Servo circuit,
9 ... Focus coil, 10 ... System control circuit,
28 ... Objective lens.

Claims (4)

[Claims] 1. A light beam emitted from a predetermined light source is condensed on a disk-shaped recording medium via an objective lens to record desired information on the disk-shaped recording medium, or recording on the disk-shaped recording medium. In an optical disk device for reproducing information, a focus error signal detecting means for receiving a reflected light of the light beam to generate a focus error signal of the light beam, and an objective lens changing means for changing a position of the objective lens. And a comparison means for obtaining a comparison result between the focus error signal and a predetermined reference level, and generating a focus zero-cross signal in which the signal level rises when the signal level of the focus error signal crosses the reference level. Focus search signal generating means for generating a focus search signal, and the objective lens variable by the focus search signal. Driving a stage, and when the signal level of the focus zero-cross signal rises, a focus control means for driving the objective lens varying means on the basis of the focus error signal instead of the focus search signal, and a focus control means, The focus search signal generating means abruptly moves the objective lens from the holding position in the non-energized state toward the disk-shaped recording medium to hold the objective lens at the search start position, and then at predetermined intervals. A focus search circuit for generating the focus search signal so as to move the objective lens at a predetermined speed from the search start position so as to move away from the disk-shaped recording medium. 2. The focus search signal generating means generates the focus search signal so as to hold the objective lens at the search start position for a predetermined period, thereby moving the objective lens. The focus search circuit according to claim 1, wherein the vibration of the objective lens generated in the above is suppressed. 3. The focus search signal generating means generates the focus search signal so that the objective lens abuts a contact member that limits a movable range of the objective lens at the search start position, By generating the focus search signal so as to hold the objective lens at the search start position for a predetermined period, vibration of the objective lens generated when the objective lens is moved can be suppressed. Claim 1 characterized by
The focus search circuit described in. 4. The focus control means drives the objective lens varying means by switching the gain high by a predetermined gain during a period in which the objective lens varying means is driven by the focus search signal. The focus search circuit according to claim 1, claim 2, or claim 3.