JP2003272182A - Optical disk drive and focus searching method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive and the focus searching method thereof for preventing the collision between the optical disk and an objective lens at the focus position searching, even when the working distance which is the distance between the optical disk and the objective lens, is the degree of the face wobbling amplitude of the optical disk or smaller. <P>SOLUTION: In the optical disk drive furnished with the objective lens for converging beams of a semiconductor laser diode on a recording layer of the optical disk, a lens actuator moving this objective lens in the direction perpendicular to a surface of the optical disk, and a focus control circuit for controlling to drive this lens actuator, by controlling so that the objective lens approaches to the optical disk while making the lens oscillate with a prescribed amplitude by the focus control circuit at the focus position searching of the objective lens, the number of passing times of the objective lens through the focused position is increased, and the number of generating times of the focus pull-in timing is increased, then the probability of failure in the focus servo pull-in is reduced. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for reproducing information from an optical disk and a focus search method therefor.

[0002]

2. Description of the Related Art An optical disc apparatus records new information at a predetermined position on an optical disc, which is an information storage medium, or rewrites / erases information by using a converging spot, and at the same time, the information is already recorded at a predetermined position on the optical disc. Plays back the recorded information.

The focused spot is generated by focusing the laser light emitted from the optical pickup head onto the optical disc by an objective lens driven by a lens actuator.

Before the recording / reproducing operation of the optical disk device is started, the focus of the objective lens is not on the recording layer of the optical disk.
Therefore, prior to the start of the recording / reproducing operation, the optical disk device performs a focus servo pull-in operation for adjusting the focus of the objective lens to the recording layer of the optical disk to adjust the focus on the optical disk.

As disclosed in Japanese Unexamined Patent Publication No. 3-29118, in the conventional focus servo pull-in, the focus position is searched by moving the position of the objective lens in a triangular wave shape. If the objective lens is driven by an amplitude including the surface deviation of the optical disk centering on the standard focus position and the mounting error existing between the optical disk and the optical pickup head, the focus position will be found within that range. To be

[0006]

In the conventional optical disk device, the distance between the surface of the optical disk and the objective lens (hereinafter referred to as the working distance) is larger than the surface wobbling amplitude of the optical disk. Therefore, in the focus servo pull-in operation for searching the focus of the recording / reproducing light on the recording layer of the optical disk, the operation of searching the position where the focus is achieved is performed while the objective lens is swung to the same extent as the surface wobbling amplitude of the optical disk. However, there was no risk that the objective lens would come into contact with the optical disc.

However, in the recently developed high recording density optical disk apparatus, the working distance is about the same as the surface deviation amplitude of the disk, and the objective lens is the same as the surface deviation of the optical disk in the focus servo pull-in operation. When the in-focus position is searched by oscillating with a certain amplitude, there is a problem that the optical disk and the objective lens may collide.

Further, a method is conceivable in which the objective lens is gradually approached from a position sufficiently distant from the optical disk to search the in-focus position. In this method, the objective lens always passes near the in-focus position, so that the in-focus position can be detected.

However, in this method, there is a problem when the speed at which the objective lens approaches the optical disk is set to be higher than the speed at which the focus servo pull-in range is passed in one rotation of the optical disk.

In other words, considering the surface deviation of the optical disc, when the objective lens is rapidly brought close to the optical disc, it may be considered that the focal point is first passed on the concave side of the optical disc as seen from the objective lens. Here, due to various reasons such as scratches on the surface of the information storage medium and vibration from the outside,
It is assumed that the focus cannot be pulled in at this in-focus position. Then, this time, the convex side of the optical disc as seen from the objective lens comes closer due to the rotation of the optical disc due to the surface wobbling, so that it is no longer in focus. If the surface wobbling amplitude and the working distance are approximately the same, the closest distance of the objective lens to the optical disc becomes the upper limit of the surface wobbling amplitude, and in this case, the possibility that the objective lens and the optical disc come into contact increases.

As described above, if the objective lens is simply brought closer to the optical disc from the side distant from one side, the objective lens and the optical disc come into contact with each other when the approaching speed of the objective lens is made high with emphasis on the high speed of the pulling. Increased risk.

On the other hand, if the objective lens is approached at such a speed that the optical disk makes several revolutions while moving the distance corresponding to the focus servo pull-in range so as to pass through the focus servo pull-in range many times, there is a risk of collision. However, the time required to pull in the focus servo increases.

An increase in the time required for pulling in the focus servo leads to an increase in the time from when the user issues a reproduction or recording command until the actual reproduction or recording starts, leading to a decrease in the operating speed of the optical disk device. There was a problem.

In view of the above problems, the present invention prevents an optical disk from colliding with the objective lens when searching for a focal position even when the working distance, which is the distance between the optical disk and the objective lens, is less than the surface wobbling amplitude of the optical disk. An object is to provide an apparatus and a focus search method thereof.

[0015]

SUMMARY OF THE INVENTION An optical disk device of the present invention comprises an objective lens for focusing the light of a semiconductor laser diode on a recording layer of the optical disk, and the objective lens in a direction perpendicular to the surface of the optical disk. A moving lens actuator and a focus control circuit for driving and controlling the lens actuator are provided to control the objective lens so that the objective lens vibrates at a predetermined amplitude and approaches the optical disc when the focus position of the objective lens is searched.

Further, in the focus searching method in the optical disk device of the present invention, the objective lens for focusing the semiconductor laser diode light on the recording layer of the optical disk is positioned at a predetermined position with a predetermined distance from the optical disk, and this predetermined position is set. The objective lens positioned at is brought close to the optical disk while vibrating with a predetermined amplitude.

According to the present invention, the number of times the objective lens passes through the in-focus position can be increased, so that the number of times of focus pull-in timing is increased, the probability of failing to pull in the focus servo is reduced, and the collision between the objective lens and the optical disk is reduced. It becomes possible to prevent.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the arrangement of an optical disc device which is an information recording / reproducing device according to this embodiment.

The optical disk device 10 records new information at a predetermined position on the optical disk 11 which is an information storage medium by using a converging spot, or rewrites / erases information, and from the predetermined position on the optical disk 11. The information already recorded is reproduced.

The spindle motor 13 drives the optical disk 11 to rotate. The spindle motor 13 is driven by a spindle motor drive circuit 14. The optical pickup head 15 irradiates the optical disc 11 with laser light to record information on the optical disc 11, rewrite / erase information on the optical disc 11, or detect a reproduction signal that is reflected light from the optical disc 11 to reproduce information. The focus control circuit 17 receives a focus error signal from the optical pickup head 15 and sends a focus control signal to the optical pickup head 15 to control the focus of the optical pickup head 15.

The recording / reproducing circuit 19 receives the reproduction signal (RF signal) detected by the optical pickup head 15 during the reproduction operation of the optical disk device 10, and demodulates / decodes the reproduction signal to reproduce information. The recording / reproducing circuit 19 also performs modulation / encoding processing of information supplied from the outside during the recording operation of the optical disk device 10. The signal subjected to the modulation / encoding processing by the recording / reproducing device 19 is a recording signal (RF signal).
Is supplied to the optical pickup head 15. The optical pickup head 15 modulates the laser irradiation light quantity from the recording signal supplied from the recording / reproducing circuit 19 and
Information is recorded in 1.

Next, the optical pickup head 15 shown in FIG. 1 will be described. FIG. 2 shows the optical pickup head 1 of FIG.
It is a figure for demonstrating the structure of FIG. In FIG. 2, the same parts as those in FIG.

The optical pickup head 15 is the objective lens 2
1, a lens actuator 23, a polarization beam splitter 25, a collimator lens 27, a semiconductor laser diode 29, a laser drive circuit 31, a condenser lens 33, and a photodetector 35.

The objective lens 21 is driven and controlled by the lens actuator 23 in a direction perpendicular to the recording surface of the optical disc 11 in order to generate a focused spot of the laser light emitted from the optical pickup head 15 on the optical disc 11. It A semiconductor laser diode (LD) 29 is arranged at a position facing the objective lens 23. The laser light emitted from the semiconductor laser diode 29 is converted into a parallel light flux by the collimator lens 27 and then incident on the polarization beam splitter 25. The laser light that has passed through the polarization beam splitter 25 is narrowed down by the objective lens 21 and irradiated onto the optical disc 11.

The laser light applied to the optical disk 11 through the objective lens 21 is focused on the optical disk 11 as a minute focused spot. The reflected light from the optical disk 11 passes through the objective lens 21 in the direction opposite to the incident light, and then is reflected by the polarization beam splitter 25, and the condenser lens 3
The light enters the photodetector 35 through the detection optical system such as 3.
The photodetector 35 supplies the reflected light from the optical disk 11 to the recording / reproducing circuit 19 as a reproducing signal. Also, the photodetector 3
Reference numeral 5 supplies the reflected light from the optical disk 11 to the focus control circuit 17 as a focus error signal.

At the time of recording / reproducing, the focus of the objective lens 21 is changed by the drive signal from the focus control circuit 17 to the optical disk 1.
Maintained above 1. The lens actuator 23 is configured to use, for example, a permanent magnet around the objective lens 21 and an electromagnetic coil on the optical pickup 15 side so as to surround the permanent magnet. The lens actuator 23 drives the objective lens 21 when a current according to the drive signal from the focus control circuit 17 flows in the electromagnetic coil.

Before the start of recording / reproduction, the objective lens 21
Is not focused on the optical disk 11. Therefore, the focus servo pull-in for focusing the objective lens 21 on the optical disk 11 is performed, and the focus servo is applied so as to focus on the optical disk 11 and maintain it.

The focus servo pull-in will now be described.

In FIG. 3, the working distance, which is the distance between the optical disk 11 and the objective lens 21, is the optical disk 1.
FIG. 3 is a diagram schematically showing a distance relationship between the optical disc 11 and an objective lens 21 in the case where it is not sufficiently larger than the surface wobbling amplitude of 1. Note that FIG. 3 is a view of the optical disc as viewed from the cross-sectional direction along the rotation axis, and shows a state in which the optical disc is rotated once from a viewpoint stopped at a certain point. The working distance is 130 μm to 150 μm, and the surface deviation is The case where the amplitude width is 100 μm at maximum is shown.

The pull-in of the focus servo is to turn on the focus servo by detecting that the objective lens 21 has entered the focusing position within the pull-in range of the focus servo shown in FIG. If the objective lens 21 is within the focus servo pull-in range, a focus error signal that is substantially proportional to the deviation from the in-focus position is obtained. The focus control circuit 17 receives the focus error signal, performs a calculation, and supplies a drive signal for the objective lens 21 to the lens actuator 23, thereby holding the focus position of the objective lens 21.

As shown in FIG. 3, when the working distance is approximately the same as the surface wobbling amplitude, the position of the objective lens 21 is moved in a triangular wave shape with an amplitude that sufficiently covers the surface wobbling amplitude as in the prior art, or an optical disk. When the focus servo pull-in point is searched for by linearly moving from a position away from, when the optical disc 11 is tilted due to the installation state of the optical disc 11, the objective lens 21 and the optical disc 11 are separated before the focus servo pulls in. There is a possibility of collision.

Next, the objective lens 21 in the present embodiment.
I will explain the movement.

FIG. 4 shows an objective lens 21 for the optical disk 11 by the focus control circuit 17 in this embodiment.
It is a figure explaining the operation of.

In this embodiment, as shown in FIG.
The in-focus position is searched for by the proximity locus of the objective lens 21 that brings the distance from the optical disk 11 closer while applying a minute vibration. This is, for example, a triangular wave superimposed on a locus that linearly moves the objective lens 21, and the amplitude of the triangular wave is set to an amplitude within the range of the focus servo pull-in. As a result, even when the in-focus position is found on the concave side of the optical disk 11 for the first time as viewed from the objective lens 21, the overlapping waves repeatedly pass through the in-focus position, so that the timing for pulling the focus increases and the focus servo pull-in fails. You can reduce the probability of doing. Further, as another embodiment, it is conceivable to operate the objective lens 21 with a proximity locus in which a sinusoidal wave is superimposed on a curved proximity locus as shown in FIG.

In the present embodiment, assuming that the amplitude of the wave superimposed on the near trajectory is the width of the focus servo pull-in range, the maximum period of the superimposed component when the objective lens 21 is brought closer to the optical disk 11 is 1 of the superimposed wave. It is the time for passing through the focus servo pull-in range width in a period of time. In this embodiment, the objective lens 21
The approaching speed is such that the time required to pass the focus servo pull-in range width is within a half cycle of the surface wobbling of the optical disk 11. When the approaching speed is slow such that the time required to pass through the focus servo pull-in range width is equal to or more than the half cycle of the surface deviation of the optical disk 11, the surface deviation of the optical disk 11 also causes the in-focus position to pass. However, such a slow approaching speed is not practical because it takes time to pull in the focus servo.

When shaken in a range larger than the focus servo pull-in range width, it means that the search is performed up to a portion where the focus servo pull-in should not occur.
If the amplitude is large, the possibility that the optical disk 11 and the objective lens 21 collide increases. By the way, when the focus servo pull-in is performed and the state is shifted from the in-focus position search to the servo-on state, the moving speed of the objective lens 21 immediately after the search is different from the surface wobbling speed of the optical disk 11 in the focus axis direction. , The speed at which the objective lens 21 follows the surface wobbling of the optical disc 11 by the drive signal output from the focus control circuit 17 (the fact that the objective lens is focused is equivalent to the surface wobbling of the objective lens becoming 0).
A larger acceleration is required to achieve Due to the transfer function from the focus difference signal to the drive signal that the focus control circuit 17 has and the effect of saturation existing in the circuit that drives the lens actuator 23, the acceleration that can be applied until after the focus servo pull-in range is reached after the focus position is detected. There is a limit. Further, when the amplitude of the wave superimposed on the near trajectory of the objective lens 21 is increased, the velocity becomes higher as the amplitude becomes larger even in the same cycle. Therefore, the superimposed amplitude cannot be unnecessarily large.

For example, the lens actuator 23 and the focus control circuit 17 are 400 m away from the objective lens 21.
It is assumed that the maximum acceleration of / s2 can be generated. Here, since the focus servo pull-in range is about 1 to 20 μm,
Assuming that the in-focus position is at the center of the focus servo pull-in range, it is necessary for the objective lens 21 to have a speed (relative speed 0) that follows surface deviation while moving by 0.5 μm. Here, the maximum acceleration that can be generated in the objective lens 21 is a, and the surface shake of the optical disk 11 in the focus axis direction and the focus position have been passed (focus servo is started).
When the relative speed to the objective lens 21 at this time is v, and the distance from when the focus servo starts to be applied at the in-focus position to when the focus servo pulls out of the range is l, the relationship in which the focus servo pull-in is successful is expressed by Equation (1). To be done.

[Equation 1]

Therefore, the optical disc 1 in the focus axis direction
Considering the surface wobbling velocity of 1, it is necessary to determine the amplitude and period of the wave superimposed on the near trajectory of the objective lens 21 so that the relative velocity v is equal to or less than that which satisfies the expression (1). For example, suppose that the objective lens 21 is a close-up trajectory in which a wave represented by h · sin ω · t (h is an amplitude, ω is a period, and t is time) is superimposed at a maximum relative velocity vl with respect to the optical disc 11.
The relationship of Expression (2) is established.

[Equation 2]

On the other hand, when the amplitude of the wave superimposed on the near path of the objective lens 21 is small, the risk of collision is reduced, and the amplitude is small even if the cycle of the wave superimposed on the near path of the objective lens 21 is shortened. The speed of the objective lens 21 becomes smaller as the distance increases. However, as described above, since the maximum velocity excluding the superposition component when approaching the optical disc 11 depends on the amplitude of the superimposed wave, reducing the amplitude means that when approaching the optical disc 11. This causes a decrease in the maximum speed excluding the superimposed component of, and it takes time to pull in the focus servo. Therefore, it is preferable to select the amplitude of the wave superimposed on the near trajectory as the focus servo pull-in range width, and the period as a relative velocity with respect to the optical disc 11 that satisfies the expression (1).

According to the present embodiment, in the optical disc device in which the working distance is not sufficiently larger than the surface wobbling amplitude of the optical disc 11, the focus servo pull-in is performed in the movement pattern when the objective lens 21 approaches the optical disc during the focus servo pull-in. The following effects can be expected by superimposing waves with a small amplitude in the range.

Since the number of times of passing through the in-focus position can be increased as compared with the case of not superimposing a minute wave, the number of times of focus pull-in timing is increased, the probability of focus servo pull-in failure is reduced, and the objective lens and the optical disk are reduced. Reduce the risk of collisions.

Since the number of times the focus pull-in timing is generated largely depends on the period of the superimposed minute amplitude waveform, the focus pull-in timing is generated depending on the relationship between the number of rotations of the optical disc, the surface deviation position, and the focus servo pull-in range. It is possible to expect a stable focus servo pull-in operation, as the number of times of movement does not change significantly.

Since it does not depend on the focus servo pull-in timing generated by surface wobbling, it is also necessary to bring the objective lens close to the objective lens at a slow speed such that the disk makes several revolutions while moving the distance for the focus servo pull-in range. Instead, a high-speed objective lens that moves a distance corresponding to the surface wobbling amplitude during one rotation of the disk can be brought close.

[0045]

According to the present invention, even when the working distance, which is the distance between the optical disk and the objective lens, is not more than the surface wobbling amplitude of the optical disk, the collision between the optical disk and the objective lens can be prevented when searching the focus position. Will be possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical disc device which is an information recording / reproducing device according to an embodiment.

FIG. 2 is a diagram for explaining the configuration of an optical pickup head.

FIG. 3 is a diagram schematically showing a distance relationship between an optical disc and an objective lens.

FIG. 4 is a diagram for explaining the operation of the objective lens with respect to the optical disc in the present embodiment.

[Explanation of symbols]

11 optical disc 13 Spindle motor 14 Motor drive circuit 15 Optical pickup head 17 Focus control circuit 19 Recording / playback circuit 21 Objective lens 23 Lens Actuator 25 Polarizing beam splitter 27 Collimating lens 29 Semiconductor laser diode 31 Laser drive circuit 33 Condensing lens 35 photo detector

Claims (8)

[Claims] 1. In an optical disk device for recording and reproducing from an optical disk, an objective lens for focusing a semiconductor laser diode light on a recording layer of the optical disk, and a direction perpendicular to the surface of the optical disk. And a focus control circuit for driving and controlling the lens actuator, the focus control circuit controlling the objective lens to approach the optical disc while vibrating the objective lens at a predetermined amplitude when searching for a focal position of the objective lens. An optical disk device comprising: 2. The optical disc apparatus according to claim 1, wherein the focus control circuit controls the objective lens so as to approach the optical disc while oscillating the objective lens in a triangular wave shape during the focus search. 3. The optical disk device according to claim 1, wherein the focus control circuit controls the objective lens so as to approach the optical disk while vibrating in a sinusoidal manner during the focus search. 4. The optical disk device according to claim 1, wherein the focus control circuit controls the objective lens so that the objective lens is oscillated by a focus servo pull-in range width to approach the optical disk during the focus search. 5. A focus search method for an optical disk device for reproducing recording from an optical disk, comprising: an objective lens for focusing semiconductor laser diode light on a recording layer of the optical disk, the objective lens having a predetermined distance from the optical disk. A focus searching method for an optical disk device, wherein the objective lens located at a predetermined position is brought close to the optical disk while vibrating the objective lens at the predetermined position with a predetermined amplitude. 6. A focus search method for an optical disk device for reproducing recording from an optical disk, wherein an objective lens for focusing semiconductor laser diode light on a recording layer of the optical disk is a predetermined distance from the optical disk. A focus search method for an optical disk device, wherein the objective lens positioned at a predetermined position is brought closer to the optical disk while vibrating the objective lens at a predetermined width of the focus servo pull-in range. 7. The focus search method for an optical disk device according to claim 5, wherein the objective lens is vibrated in a triangular wave shape when the objective lens is brought close to the optical disk. 8. A focus search method for an optical disk apparatus according to claim 5, wherein the objective lens is vibrated in a sine wave shape when the objective lens is brought close to the optical disk.