JPH1125473A - Optical disk device and optical axis correcting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device and an optical axis correcting method capable of performing stable data reading by all lenses for plural optical disks. SOLUTION: This device comprises an optical pickup for recording/ reproducing an optical disk 1 by changing over objective lenses 3, 4 for plural kinds of optical disks 1, a bobbin driving means 6 moving a light spot to a target track, a bobbin control part for servo controlling the bobbin driving means 6, a carriage driving means 14 moving the optical pickup in the radial direction of the optical disk 1 and a carriage control part servo controlling the means 14 based on the low frequency component of a tracking position deviation signal. The servo control is performed so that a signal component generated from the optical pickup becomes maximum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for reproducing information on an optical disk by an optical pickup.
In particular, the present invention relates to an optical disk device for reproducing information of two types of optical disks and an optical axis correction method.

[0002]

2. Description of the Related Art An optical disk device is a device for recording and reproducing signals on a track of an optical disk by focusing light emitted from a light source such as a semiconductor laser on an optical disk surface by an objective lens via an optical prism or the like. It is in the limelight as a memory device. Among them, CD-RO
M drive devices are rapidly becoming popular as inexpensive data playback devices for computers. However, in order to record high-quality moving images such as movies for a long time, an optical disk having a larger recording capacity than a CD is required.
In recent years, DVD has been proposed as a new standard with higher density. The recording density of an optical disc is determined by the size of the light spot focused by the objective lens, but the size of the light spot is proportional to the wavelength and inversely proportional to the numerical aperture. It is necessary to shorten the wavelength of the laser and improve the numerical aperture of the objective lens. However, when the numerical aperture of the objective lens is large, when the optical disc is tilted with respect to the optical axis of the laser beam, coma aberration occurs in the laser beam and the shape of the condensed spot tends to be easily distorted. Since the coma aberration increases in proportion to the cube of the numerical aperture of the objective lens and the thickness of the optical disk, the DVD standard improves the characteristics with respect to the tilt of the optical disk by reducing the thickness of the optical disk to half that of the CD. .

[0003] The DVD has a recording capacity much larger than that of a CD, and is considered to be a medium that will replace the CD in the future. However, a huge number of CD software assets already on the market cannot be ignored. It is indispensable for a next-generation optical disk device and an optical axis correction method to have reproduction compatibility between a CD and a DVD. However, as described above, in order to improve the characteristics with respect to the tilt of the optical disc, D
VD differs from CD in optical disk thickness. This is a major obstacle in terms of optical reproduction compatibility. The objective lens is designed to minimize the light spot that is focused according to the thickness of the optical disk.For optical disks with different thicknesses, the laser beam passing through the center of the lens and the laser beam passing through the periphery of the lens are converged. A shift called a spherical aberration occurs at the position, and signal reading becomes impossible. Therefore, several types of optical systems have been proposed in order to realize reproduction compatibility even for different optical disk thicknesses. Here, a method will be described in which a dedicated objective lens is mounted on each optical disc, and the lens is switched according to the optical disc to collect one light spot.

FIG. 3 is a perspective view of the structure of a conventional shaft-sliding / rotating type actuator of an optical disk device. Referring to FIG. 3, the conventional optical pickup includes a bobbin 21 which slides in a focus direction with respect to a support shaft 22 and rotates in a track direction. The bobbin 21 includes a DVD objective lens 23 and a CD objective. The lens 24 is mounted on the carriage at a position where the amount of eccentricity from the support shaft 22 is equal. A tracking coil 25 and a magnetic piece 26 are adhered and fixed to the side surface of the bobbin 21, and a magnetic circuit is formed by a DVD tracking magnet 27 and a CD tracking magnet 28 provided opposite thereto. Since the magnetic energy is minimized when the magnetic piece 26 is located facing the center of the magnet,
In the configuration shown in FIG. 3, the magnetic circuit for DVD and the magnetic circuit for CD
One bobbin 21 can be provided with a neutral position. Switching of the objective lens is performed by moving the neutral position of the bobbin 21 by applying a kick pulse voltage to the tracking coil 25.

In the optical pickup having the actuator configuration shown in FIG. 3, each objective lens 23 for DVD or CD,
If the center of 24 is displaced from the center of the optical axis, the amount of light incident on the lens decreases, and the signal characteristics deteriorate. The amount of deviation of the center position of the optical axis is determined by the mounting accuracy of the semiconductor laser on the carriage, and the position of the bobbin 21 is neutral at the position where the magnetic energy is minimized.
It is determined by the mounting accuracy of the magnetic piece and the tracking magnet.

In order to ensure this signal characteristic, it is necessary to control the carriage driving means so that the deviation between the center of the optical axis and the lens center is generally within ± 300 μm. The carriage drive gain is set low to reduce power consumption, and the traverse is ± 200 to ±
Follow with a deviation within 300 μm. Therefore, it is necessary to minimize the displacement due to factors other than traverse, but it is very difficult to manage the displacement of the lens center with respect to the optical axis at the time of lens switching with mechanical precision during mass production. A displacement of about ± 100 μm occurs.

Next, the operation of the conventional optical disk apparatus will be described below with an example of a configuration in which an objective lens is switched using an axis sliding / rotating type actuator. FIG. 4 is a block diagram showing a configuration of a track servo control system of a conventional optical disk device. Referring to FIG. 4, a conventional optical disk apparatus includes a carriage 2 which is controlled to move in a radial direction of an optical disk from which information is read / written, and a DVD objective lens 3 and a CD objective lens 4 mounted on the carriage 2. A fixed bobbin 5, a bobbin driving means 6 mounted on the carriage 2 for causing the bobbin 5 to follow a track on the optical disk 1, and a light detection mounted on the carriage 2 and receiving reflected light from the optical disk 1. Device 7, signal generating means 8 for generating a track error signal from the signal of the photodetector 7, servo control means 9 for controlling the positioning of the bobbin driving means 6 via a driver 10 based on the track error signal, A low-pass filter for filtering and passing a low-frequency component of the tracking error signal; Using the low frequency component of the track error signal extracted by filter 11 outputs a control signal for servo-controlling the movement of the radial direction of the optical disk 1 of the carriage 2 servo controller 1
2 and a carriage driving means 14 for moving the carriage 2 in the radial direction of the optical disc 1 via a driver 13 based on this control signal.

The optical disk 1 is mounted on the upper surface of a turntable connected to an optical disk motor (not shown) and is driven to rotate. The tracking of a high frequency band such as eccentricity in the track of the optical disc 1 is performed by driving the bobbin 5, but when the tracing is continued along the track, the position of the objective lens gradually increases because the track is formed in a spiral shape. The track error signal is offset from the moving center of the driving means 6 by a DC component.

In the configuration of the track servo shown in FIG.
Since the servo of the carriage 2 is performed following the magnetic neutral position of the bobbin 5, the bobbin 5 must be assembled so that the center of the optical axis and the magnetic neutral position of the bobbin 5 coincide. In practice, the position of the bobbin 5 is finely adjusted while monitoring the signal characteristics.

[0010]

However, in the above-mentioned conventional optical pickup, since the structure of the actuator is configured as described above, the bobbin 5 has two or more lenses 3, 4 (or 23, 24). Is attached, the fine adjustment of the mounting position of the bobbin 5 can be performed only for one lens 3, 23 (or 4, 24), so that the position of the other lens 4, 24 (or 3, 23) is 5 is determined by the magnetic neutral position. For this reason, there arises a problem that the lens position is deviated from the center of the optical axis and the signal characteristics deteriorate. SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical disk apparatus and an optical axis correction method capable of stably reading data with all lenses even when an objective lens is switched for two or more types of optical disks.

[0011]

In the optical disk apparatus of the present invention, light is emitted in the radial direction of the optical disk so that the signal component of the information signal output from the optical pickup having two types of objective lenses can be extracted as the maximum value. The movement of the pickup is controlled. According to the present invention, it is possible to stably read data from various optical disks by using an optical pickup having a plurality of objective lenses.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is applicable to two or more types of optical discs having different recording densities.
By preparing two or more objective lenses and switching between the objective lenses, an optical pickup for condensing a light spot on the optical disk to record / reproduce data and moving the light spot to a target track on the optical disk surface. A bobbin driving unit, a bobbin control unit that servos the bobbin driving unit based on a track position shift signal generated from an output signal of a photodetector of the optical pickup, and a carriage that moves the optical pickup in a radial direction of the optical disc. A signal of an information signal generated from an output signal of a photodetector of the optical pickup, comprising: a driving unit; and a carriage control unit that servo-controls the carriage driving unit based on a low-frequency component of the track position shift signal. Support the optical pickup in the radial direction of the optical disc so that the component can be output to the maximum. Servo control so that the signal component of the information signal can be output to the maximum of the optical axis shift that occurs when a plurality of objective lenses mounted on the optical pickup are switched. Data can be stably read from various optical disks.

According to a second aspect of the present invention, the carriage driving means is servo-controlled by adding an offset voltage to a low frequency component of a track position shift signal. By performing servo control of the optical pickup in the radial direction of the optical disk with an offset voltage corresponding to the optical axis shift of the lens, data can be stably read from various optical disks.

According to a third aspect of the present invention, an optical pickup is provided in the radial direction of an optical disk so that the jitter or signal error number of an information signal generated from an output signal of a photodetector of the optical pickup is minimized. This is characterized by performing servo control, whereby the signal component of the information signal can be extracted to the maximum, and more stable and reliable reading of information becomes possible.

According to a fourth aspect of the present invention, two or more types of optical discs having different recording densities are used.
By preparing at least two lenses and switching between them, a light spot is focused on the optical disc to record and
An optical pickup for reproducing, a bobbin driving means for moving the light spot to a target track on an optical disk surface, and the bobbin driving means based on a track position shift signal generated from an output signal of a photodetector of the optical pickup. A control unit that servos, a carriage driving unit that moves the optical pickup in a radial direction of the optical disc,
A control unit that servos the carriage driving unit based on a low-frequency component of the track position shift signal, so that a signal component of an information signal generated from an output signal of a photodetector of the optical pickup can be output to a maximum. Servo control of the optical pickup in the radial direction of the optical disk, to correct the optical axis shift when switching the objective lens, when the plurality of objective lenses mounted on the optical pickup is switched By performing servo control so that the signal component of the information signal can output the generated optical axis deviation to the maximum, data can be stably read from various optical disks.

The invention according to claim 5 of the present invention is characterized in that an offset voltage applied to a low frequency component of a track position shift signal is adjusted, and the offset voltage corresponding to the optical axis shift of each objective lens is adjusted. By performing servo control of the optical pickup in the radial direction of the optical disk with the offset voltage, data can be stably read from various optical disks.

According to a sixth aspect of the present invention, there is provided an optical pickup in the radial direction of an optical disk such that jitter or a signal error number of an information signal generated from an output signal of a photodetector of the optical pickup is minimized. This is characterized by performing servo control, whereby the signal component of the information signal can be extracted to the maximum, and more stable and reliable reading of information becomes possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a tracking servo control system of the optical disk device of the present invention.
In FIG. 1, the optical disc device according to the present embodiment
A carriage 2 whose movement is controlled in a radial direction of an optical disk 1 from which information is read / written, a bobbin 5 mounted on the carriage 2 and having an objective lens 3 for DVD and an objective lens 4 for CD bonded and fixed thereto; A bobbin driving means 6 mounted on the carriage 2 for causing the bobbin 5 to follow a track on the optical disk 1; a photodetector 7 mounted on the carriage 2 for receiving reflected light from the optical disk 1; Signal generating means 8 for generating a track error signal and an information signal from the signal of the device 7; servo control means 9 for controlling the positioning of the bobbin driving means 6 via a driver 10 based on the track error signal; Signal amplitude measuring means 15 for measuring the amplitude of the information signal output from the means 8; and the amplitude of the measured information signal is maximized. A CPU 16 for calculating and controlling such an offset voltage, an offset generating means 17 for generating an offset voltage based on the calculation result, and an adder 18 for adding the offset voltage to a low frequency component of the track error signal. .

The track error signal to which the offset voltage has been added by the adder 18 is input to the servo control means 12. The servo control means of the carriage controls the low frequency component of the track error signal extracted by the low-pass filter 11 and the occurrence of offset. Using the carriage control signal to which the offset voltage generated by the means 17 is added, the carriage driving means 14 is driven to be positioned by the driver 13 to control the movement of the carriage 2 in the radial direction of the optical disc 1. The optical disk 1 is mounted on the upper surface of a turntable coupled to an optical disk motor (not shown) and is driven to rotate.

As an example of determining the optimum offset voltage, the track servo is turned off by the servo control means 9.
There is a method in which the CPU 16 obtains an optimum offset voltage by monitoring the average value of the information signal amplitude when a voltage is applied to the bobbin 5 to offset the bobbin 5 in the state described above. FIG. 2 shows the signal amplitude characteristics of the reproduced information signal when the position of the bobbin 5 is offset in the radial direction of the optical disc 1 with respect to the center of the optical axis. The information signal amplitude becomes maximum at the position of the bobbin 5 that coincides with the center of the optical axis, and the signal amplitude value decreases with the displacement of the bobbin 5. Therefore, it is possible to monitor the maximum value of the information signal amplitude by applying an offset voltage to the bobbin 5.

The offset generating means 17 generates an arbitrary predetermined offset voltage value, and the average of the information signal amplitudes for a certain period of time after the servo is turned on by the servo control means 12 becomes the maximum offset value. A similar offset voltage can be obtained by the selection method.
Also, instead of monitoring the maximum point of the amplitude of the information signal, the same effect as in the above embodiment can be obtained by monitoring the minimum point of the jitter value of the information signal or the number of errors occurring in the information signal.

[0022]

As described above, the optical disk apparatus according to the present invention corrects the deviation of the optical axis so that the signal component of the information signal can be output to the maximum according to each objective lens provided corresponding to different optical disks. However, it is possible to perform an optical disk apparatus and an optical axis correction method that can perform carriage servo in a range where the amplitude of the information signal is sufficiently good and has stable data reading characteristics regardless of the type of the optical disk.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a track servo control system of an optical disc device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of a reproduced information signal with respect to a displacement of a bobbin of an optical pickup of the optical disc device according to the embodiment of the present invention.

FIG. 3 is a perspective view of the configuration of a conventional shaft-sliding rotation type actuator of an optical disk device.

FIG. 4 is a block diagram showing a configuration of a track servo control system of a conventional optical disk device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 2 Carriage 3, 23 Objective lens for DVD 4, 24 Objective lens for CD 5, 21 Bobbin 6 Bobbin drive means 7 Photodetector 8 Signal generation means 9, 12 Servo control means 10, 13 Driver 11 Low-pass filter 14 Carriage drive Means 15 Signal amplitude measuring means 16 CPU 17 Offset generating means 18 Adder 22 Support shaft 25 Tracking coil 26 Magnetic piece 27 DVD tracking magnet 28 CD tracking magnet

Claims (6)

[Claims] 1. An optical disk having two or more types of optical disks having different recording densities is provided with two or more objective lenses, and by switching the objective lenses, a light spot is focused on the optical disk to record and reproduce data. An optical pickup,
A bobbin driving unit that moves the light spot to a target track on the optical disk surface; and a bobbin control unit that servos the bobbin driving unit based on a track position shift signal generated from an output signal of a photodetector of the optical pickup. A carriage driving unit that moves the optical pickup in a radial direction of the optical disc; and a carriage control unit that servo-controls the carriage driving unit based on a low-frequency component of the track position shift signal. An optical disc device, wherein an optical pickup is servo-controlled in a radial direction of an optical disc so that a signal component of an information signal generated from an output signal of a detector can be output to a maximum. 2. The optical disk device according to claim 1, wherein an offset voltage is added to a low frequency component of the track position shift signal to servo-control the carriage driving means. 3. The optical pickup according to claim 1, wherein the optical pickup is servo-controlled in a radial direction of the optical disk such that a jitter or a signal error number of an information signal generated from an output signal of a photodetector of the optical pickup is minimized. Item 2. The optical disk device according to item 1. 4. A light for recording and reproducing data by converging a light spot on an optical disk by preparing and switching two or more lenses for each of two or more types of optical disks having different recording densities. A pickup, bobbin driving means for moving the light spot to a target track on the optical disk surface, and control for servoing the bobbin driving means based on a track displacement signal generated from an output signal of a photodetector of the optical pickup. Unit, a carriage driving unit for moving the optical pickup in a radial direction of the optical disk, and a control unit for servoing the carriage driving unit based on a low-frequency component of the track position shift signal, wherein the optical detection of the optical pickup is performed. Optical signal so that the signal component of the information signal generated from the output signal of the Radially optical pickup servos to, optical axis correction method characterized by correcting the optical axis deviation when switching the objective lens. 5. The optical axis correction method according to claim 4, wherein an offset voltage applied to a low frequency component of the track position shift signal is adjusted. 6. The optical pickup according to claim 1, wherein the optical pickup is servo-controlled in a radial direction of the optical disk so that the number of jitters or signal errors of an information signal generated from an output signal of a photodetector of the optical pickup is minimized. Item 5. The optical axis correction method according to Item 4.