JP2007317254A - Optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive which has a means for discriminating kinds of disks correctly in a short time without measuring their cover layer thickness or difference of reflectivity on the recording surface. <P>SOLUTION: This optical disk drive has a first sample and hold means for setting the spherical aberration correction lens to the first correcting position in advance, and holding the maximum amplitude of the focus error signal formed by motion controlling the focusing point of the objective lens to pass the cover layer and the recording surface, a second sample and hold means for setting the spherical aberration correction lens to the second correcting position set adjoining the first correcting position in advance, and holding the maximum amplitude of the focus error signal formed by motion controlling the focusing point of the objective lens to pass the cover layer and the recording surface, and a discriminator to specify the kind of the optical disk from the maximum amplitudes of the focus error signal obtained by the first and second sample and hold means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus, and more particularly to an optical disc apparatus provided with a means for discriminating a plurality of types of optical discs.

  In recent years, various types of optical discs can be used in one optical disc apparatus. As types of optical disks, DVD (Digital Versatile Disc) -based discs are a single-layer and double-layer discs for reproduction only, DVD-R (DVD-Recordable) that can be recorded only once, DVD-RW (DVD that can be rewritten many times) -Rewritable), rewritable DVD-RAM (DVD-Random Access Memory), etc., CD (Compact Disc), BD (Blu-Ray) using a blue laser, HD DVD ( There are optical discs of High Definition DVD), each of which has a plurality of types, and these can be selectively used.

In such an optical disc apparatus that performs recording and reproduction using various optical discs, it is required to quickly determine which type of optical disc is loaded and quickly switch to a setting according to the specifications of the optical disc. ing.
The optical disc can be discriminated by reading the type signal recorded at a specific location on the disc, but the optical pickup position adjustment operation must be repeated until the type signal can be read. Another method is taken because it has a problem of taking time. As an example, many techniques have been proposed in which an optical disk is irradiated with a light beam and the light beam reflected from the disk is detected as an electrical signal by a photodetector, and the characteristics of the disk are extracted from the detected signal to determine the type. (For example, refer to Patent Document 1).

Here, an outline of a conventional optical disc discrimination method will be described.
An optical disc has a recording surface (also referred to as a reflective layer) for recording information and a cover layer (also referred to as a transparent substrate layer) formed on the recording surface. The thickness of the cover layer and the recording surface It is classified into various types according to physical characteristics.
The method of discriminating the type of the optical disc from the difference in the thickness of the cover layer and the physical characteristics of the recording surface is to move the objective lens for condensing the light beam toward the optical disc surface in the optical axis direction. This is performed by discriminating the detection signal of the reflected light obtained.

First, in order to determine the thickness of the cover layer, the objective lens is moved toward the disc at a constant speed in the optical axis direction, and the singular point of the detection signal generated when the focal point is located on the cover layer surface is discriminated. Further, the singular point of the detection signal generated when the objective lens is further advanced and the focal point is located on the recording surface is discriminated, and the thickness of the cover layer is calculated from the moving time of the objective lens in the meantime. Further, physical characteristics such as reflectance of the recording surface are discriminated from the level of the detection signal generated when the focal point is located on the recording surface, and the type of the optical disc is specified from these discrimination results.
JP 2005-327422 A

When identifying the type of the loaded optical disc, it is possible to calculate the thickness of the cover layer from the singular point that appears in the detection signal by moving the objective lens, or to make use of the difference in reflectivity of the recording surface Since the method is easily affected by scratches, dirt, surface blurring, eccentricity, and the like on the disk surface, it has become more difficult to discriminate as the number of types of optical disks using a short wavelength blue laser increases.
The present invention has been made in view of the above-described problems, and does not measure the thickness of the cover layer and the reflectance of the recording surface, which has been conventionally performed, and accurately discriminates the types of a plurality of optical discs in a short time. The present invention provides an optical disc apparatus having means capable of performing the above.

The present invention has the following configuration as means for solving the above problems. That is,
An objective lens capable of adjusting the focal point on the recording surface of the mounted optical disc, and a position adjustment for suppressing the spread of the focal point due to spherical aberration on the optical path of the laser beam that irradiates the recording surface of the optical disc Optical disc apparatus comprising: a spherical aberration correction lens capable of performing the same; and a focus error generating means for generating a focus error signal based on the reflected light of the laser beam reflected by the recording surface of the optical disc, and for determining the type of the optical disc The spherical aberration correction lens is moved to a first spherical aberration correction position stored in advance so that the focal point of the objective lens passes through the recording surface of the optical disc and the cover layer protecting the recording surface. The focal point generated by the objective lens is positioned on the recording surface of the optical disc. First sample-holding means for holding the maximum amplitude value of the cas error signal and the spherical aberration correction lens are moved to a second spherical aberration correction position stored in advance, and the focal point of the objective lens is recorded on the optical disc. A second sample-and-hold means for holding the maximum amplitude value of the focus error signal generated by the movement, passing through the surface and the cover layer protecting the recording surface, and the first and second There is provided an optical disc apparatus comprising: a discriminating unit that compares the magnitude of the maximum amplitude value of the focus error signal obtained by the sample hold unit and discriminates the type of the optical disc according to the comparison result.

According to the configuration of the first aspect of the present invention, the spherical aberration correction lens is moved to the optimum spherical aberration correction position of the type of the optical disk stored in advance, and the in-focus position of the objective lens is varied within a predetermined range at that position, and the objective is changed. Measure the maximum amplitude of the focus error signal generated when the focal point of the lens is positioned on the recording surface of the optical disc, and compare the measurement results at multiple positions. The type of the optical disc can be specified.
As a result, it is possible to provide an optical disc apparatus having means capable of accurately discriminating the types of a plurality of optical discs in a short time without measuring the difference in the thickness of the cover layer and the reflectance of the recording surface that has been conventionally performed. .

Hereinafter, an optical disk device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of an optical disk apparatus according to the present invention, and FIG. 2 is a characteristic diagram showing a correction position of a spherical aberration correction lens and an amplitude change of a focus error signal due to a difference in the optical disk. First, the configuration of the optical disc apparatus according to the present invention will be described with reference to FIG. In FIG. 1, functional blocks that are not directly related to the discrimination of the optical disc are omitted for the sake of clarity.

  In FIG. 1, an optical disk 26 as an information recording medium is provided with a recording surface 1 on which information is recorded and a transparent cover layer 2 that protects the recording surface 1. An objective lens 4 is disposed below the cover layer 2, and the position of the objective lens 4 can be moved in the optical axis direction by a focus actuator 3 as indicated by a dotted line in the figure. The moving range of the objective lens 4 at the time of disc discrimination is appropriately controlled by the ramp signal generated by the ramp signal generation circuit 18 and the actuator driver 19 that amplifies the ramp signal and supplies the ramp signal to the actuator 3. Reciprocating drive is performed to pass through the layer 2 and the recording surface 1.

The laser beam emitted from the laser diode 5 travels straight through the beam splitter 13, passes through the fixed spherical aberration correction lens 6 and the movable spherical aberration correction lens 7, passes through the rising mirror 11 and the objective lens 4, and enters the recording surface 1. Irradiated towards. The laser beam applied to the recording surface 1 is reflected at this position and returns to the beam splitter 13 along the same path as before. The path of the laser beam returned to the beam splitter 13 is changed here and guided to the photodetector 12. The photodetector 12 is composed of a photodiode, converts the input laser beam into an electrical signal, and supplies the electrical signal to the focus error detection circuit 14.
The spherical aberration correction lens 7 is attached to a transfer mechanism 9 fitted with a lead screw 8, and is moved in the direction of the optical axis when the stepping motor 10 is rotated to irradiate the recording surface 1 with the laser beam. It works to correct the spherical aberration. The motor driver 21 drives the rotation direction and the number of steps of the stepping motor 10 for determining the correction position.

The focus error detection circuit 14 generates a focus error signal whose amplitude varies depending on the focal position of the objective lens 4 from the signal supplied from the photodetector 12, and the generated focus error signal is then sent to the focus error amplitude measurement circuit 15. Where the maximum amplitude of the focus error signal is measured. Note that the maximum amplitude of the focus error signal is the focus error signal generated when the focal point of the objective lens is positioned on the recording surface of the optical disk, that is, when the laser beam diameter becomes the smallest on the recording surface. It indicates the amplitude of.
A sample hold circuit 16 and 17 are connected to the output side of the focus error amplitude measurement circuit 15, and the sample hold timing of both sample hold circuits is controlled by pulses supplied from the hold timing generation circuit 23 and 24, respectively. Then, the respective hold potentials 17 as in the sample hold circuit 16 are supplied to the next discrimination circuit 25, respectively.
Separately from the hold timing generation circuits 23 and 24, signals indicating the end of the sample hold are supplied to the AND circuit 20, respectively. The AND output of the AND circuit 20 is connected to the determination circuit 25 and used for the determination start timing of the optical disc type.

  The actuator driver 19 and the motor driver 21 are supplied with a control signal from a lens position control circuit 22 that controls each lens position. A timing pulse is supplied from the lens position control circuit 22 to the same timing 24 as the hold timing generation circuit 23 in order to control the timing of the sample hold.

Next, the disc discrimination operation of the optical disc apparatus according to the present invention will be described.
When disc discrimination is performed, an unknown optical disc is first loaded, and a focus error occurs when the spherical aberration correction lens 7 is moved on a predetermined optical disc (for example, a BD disc) under the control of the lens position control circuit 22. The spherical aberration correction lens 7 is moved to the correction position where the signal amplitude becomes maximum. The position where the amplitude of the focus error signal of the specific optical disc is maximized is measured in advance, and data is stored in the lens position control circuit 22.

In this state, the focus actuator 3 reciprocates the objective lens 4 so that the focal point of the laser beam passes through the cover layer 2 and the recording surface 1, and the focus error amplitude measurement circuit 15 and the focus error detection circuit 14 The maximum amplitude of the generated focus error signal is detected and stored in the sample and hold circuit 16.
A signal for storing the maximum amplitude of the focus error signal in the sample-and-hold circuit 16 is obtained by moving the spherical aberration correction lens 7 to a position where the amplitude of the focus error signal is maximum on a specific optical disk by the hold timing generation circuit 23. Thus, after the amplitude measurement is performed by the focus error amplitude measurement circuit 15 for a certain period, it is supplied. The hold timing generation circuit 23 supplies a signal indicating that the amplitude measurement has been completed to the AND circuit 20.

  Next, based on the data stored in the lens position control circuit 22, the second specific optical disk having a value adjacent to the position of the spherical aberration correction lens 7 where the amplitude of the focus error signal of the specific optical disk is maximized. The spherical aberration correction lens 7 is selected and moved to the optimum correction position of the optical disk stored in the data. Thereafter, similarly, the objective lens 4 is reciprocally driven by the focus actuator 3 so that the focal point of the laser beam passes through the cover layer 2 and the recording surface 1, and the focus error amplitude measurement circuit 15 generates the focus error detection circuit 14. The maximum amplitude is detected from the focus error signal and stored in the sample and hold circuit 17 this time.

A signal for storing the maximum amplitude of the focus error signal in the sample hold circuit 17 is sent to the spherical aberration correction lens 7 by the hold timing generation circuit 24 at a position where the amplitude of the focus error signal is maximum in the second specific optical disc. Are supplied after the amplitude is measured by the focus error amplitude measuring circuit 15 for a certain period.
A signal indicating that the measurement is completed is supplied from the hold timing generation circuit 24 to the AND circuit 20, and the output of the AND circuit 20 connected to the determination circuit 25 becomes a high level to determine the unknown optical disc. Is started. A discrimination result is output from the discrimination circuit 25 to the outside and is also supplied to the lens position control circuit 22 at the same time.

Next, the determination operation of the determination circuit 25 will be described with reference to FIG.
FIG. 2 is a diagram showing a change in focus error amplitude due to a difference in the optical disk when the spherical aberration correction lens 7 is moved. Usually, even if the same laser beam and optical system are used, the physical properties of the disk depend on the type of the optical disk. Since the target formats are different, the spherical aberration correction lens positions at which the focus error amplitude has the maximum value are different as shown in the figure.
Such spherical aberration is a phenomenon in which the focal point of the laser beam is not focused at one point on the optical axis but is shifted in the depth direction, and is mainly strongly influenced by the thickness of the cover layer. As a result, the focal point spreads on the recording surface, which causes a problem of reducing information reading sensitivity and information recording accuracy. Such spherical aberration can be reduced by providing a spherical aberration correction lens in the optical path of the laser beam and moving the position of the correction lens in accordance with the type of the optical disk.

In FIG. 2, the disk type of the specific optical disk is disk A, the disk type of the second specific disk is disk B, and the spherical aberration correction lens position at which the focus error amplitude of the disk A has the maximum value is LP # A, A spherical aberration correction lens position at which the focus error amplitude of the disk B has the maximum value is LP # B.
When the spherical aberration correction lens 7 is moved to a position where the focus error amplitude of the disk A shows the maximum value, if the unknown optical disk is the disk A, the focus error amplitude is fa # max, and if the disk A is the disk B, the focus error amplitude is fa. It becomes.
On the other hand, when the spherical aberration correction lens 7 is moved to a position where the focus error amplitude of the disk B reaches the maximum value, the focus error amplitude is fb # max if the unknown optical disk is the disk B, and the focus error amplitude if the disk A is the disk A. Becomes fb.

  From FIG. 2, the focus error amplitude of the unknown optical disc measured by moving the spherical aberration correction lens 7 to the position LP # A where the focus error amplitude of the disc A shows the maximum value, and the focus error amplitude of the disc B reaches the maximum value. If it is larger than the focus error amplitude measured by moving the spherical aberration correction lens 7 to the indicated position LP # B (measured value at LP # B <measured value at LP # A), the disc is the disc A or the focus error It can be determined that the spherical aberration correction lens position at which the signal amplitude is maximized is on the right side of the position of LP # A (state a).

  Conversely, the focus error amplitude of the unknown optical disk measured by moving the spherical aberration correction lens 7 to the position LP # A where the focus error amplitude of the disk A shows the maximum value, and the position where the focus error amplitude of the disk B shows the maximum value. If it is smaller than the focus error amplitude measured by moving the spherical aberration correction lens 7 to LP # B (measured value at LP # B> measured value at LP # A), the disc is the disc B or the focus error signal. It can be determined that the spherical aberration correction lens position at which the amplitude is maximum is located on the left side of the position of LP # B (state b).

Next, the spherical aberration correction lens position where the amplitude of the focus error signal is maximized by the control of the lens position control circuit 22 is on the right side of the LP # A position (when the measurement is in the state a) or the LP # B position. Assuming a third specific optical disk located on the left side (when the measurement is in the state b), the spherical aberration correction lens 7 is set at a position where the amplitude of the focus error signal of the optical disk stored in advance is maximized. Then, the same measurement is performed again, and the focus error maximum amplitude at that time is LP # C.
As a result of the measurement again, the previous comparison result is “measurement value at LP # B <measurement value at LP # A”, and the current measurement result is “measurement value at LP # A> measurement at LP # C”. If the value is “value”, the type of the unknown disk is specified as disk A. If the current measurement result is “measurement value at LP # A <measurement value at LP # C”, the correction position of the spherical aberration correction lens 7 is changed again and the measurement is repeated.
In other words, when the magnitude relation between the two focus error amplitudes measured repeatedly is reversed, the unknown optical disk is identified as the type of the specific optical disk used for setting the spherical aberration correction lens position one before. is there.

As described above in detail, in the optical disc apparatus according to the present invention, the focus error amplitude of an unknown optical disc at the optimum spherical aberration correction lens position of two types of discs adjacent to each other where the spherical aberration correction lens position where the focus error amplitude has the maximum value is adjacent. Optical disc discriminating means that can identify an unknown optical disc type by repeating the measurement and discrimination of the focus error error amplitude by changing the position of the spherical aberration correction lens again and then discriminating the magnitudes of the two measured amplitudes. It is what has.
The optical disc discriminating means according to the present invention makes it possible to discriminate the types of a plurality of optical discs accurately in a short time without measuring the difference in the thickness of the cover layer and the reflectance of the recording surface that has been conventionally performed.

1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. FIG. 6 is a characteristic diagram showing a correction position of a spherical aberration correction lens and an amplitude change of a focus error signal due to a difference in optical discs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Recording surface 2 ... Cover layer 3 ... Focus actuator 4 ... Objective lens 5 ... Laser diode 6 ... Fixed spherical aberration correction lens 7 ... Movable spherical aberration correction lens 8 ... Lead screw 9 ... Transfer mechanism 10 ... Stepping motor 11 ... Raising mirror 12 ... photodetector 13 ... beam splitter 14 ... focus error detection circuit 15 ... focus error amplitude measurement circuit 16 ... sample hold circuit (first sample hold means)
17 ... Sample hold circuit (second sample hold means)
DESCRIPTION OF SYMBOLS 18 ... Lamp signal generation circuit 19 ... Actuator driver 20 ... AND circuit 21 ... Motor driver 22 ... Lens position control circuit 23, 24 ... Hold timing generation circuit 25 ... Discrimination circuit (discrimination means)
26 ... Optical disc

Claims (1)

An objective lens capable of adjusting the focal point on the recording surface of the mounted optical disc, and a position adjustment for suppressing the spread of the focal point due to spherical aberration on the optical path of the laser beam that irradiates the recording surface of the optical disc Optical disc apparatus comprising: a spherical aberration correction lens capable of performing the same; and a focus error generating means for generating a focus error signal based on the reflected light of the laser beam reflected by the recording surface of the optical disc, and for determining the type of the optical disc In
The spherical aberration correction lens is moved to a first spherical aberration correction position stored in advance, and the focal point of the objective lens is moved so as to pass through the recording surface of the optical disc and the cover layer protecting the recording surface. A first sample hold means for holding a maximum amplitude value of the focus error signal generated when the focal point of the objective lens is positioned on the recording surface of the optical disc by this movement;
The spherical aberration correction lens is moved to a second spherical aberration correction position stored in advance, and the focal point of the objective lens is moved so as to pass through the recording surface of the optical disc and the cover layer protecting the recording surface. Second sample and hold means for holding the maximum amplitude value of the focus error signal generated by this movement;
Discriminating means for comparing the magnitude of the maximum amplitude value of the focus error signal obtained by the first and second sample and hold means and discriminating the type of the optical disc according to the comparison result;
An optical disc apparatus comprising:

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