JP2644126B2 - Optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for optically recording or reproducing information, and more particularly to detecting a tracking error of an information recording medium in which an information track is wobbled in advance.

[0002]

2. Description of the Related Art FIG.
l. 44 No. 1 is a perspective view showing a conventional optical recording / reproducing device shown in 10 pp 1403 to 1409, particularly using a compact disk (hereinafter, referred to as a CD) on which recording can be performed as a medium. In FIG. 1, reference numeral 1 denotes a semiconductor laser, in which a collimator lens 3 and a compound prism 4 are arranged in the emission direction of the laser beam 2. The compound prism 4 deflects the laser beam 2 in the direction of the objective lens 5 for forming a focused spot on the information recording medium. Reference numeral 6 denotes a quarter-wave plate, which is provided between the compound prism 4 and the objective lens 5. Reference numeral 7 denotes a cylindrical lens for giving astigmatism to the laser beam 2 reflected by the information recording medium, and reference numeral 8 denotes a converging lens for converging the laser beam 2. 9 is a photodetector for detecting the laser beam 2 reflected by the information recording medium,
It consists of at least four light receiving surfaces. 10 is the above code 1
Numeral 11 denotes a box for holding optical components, numeral 11 denotes a tracking coil attached to the box 10, and numeral 12 denotes a rotation axis of the box 10.

Next, the characteristic points of the information recording medium used in this conventional example will be explained. First, in this type of medium, a guide groove is provided in advance for tracking during recording. The guide groove contains information for controlling the rotation speed of the information recording medium and absolute address information in the form of wobbling of the guide groove (hereinafter referred to as wobbling). To elaborate further,
The guide groove is wobbled with an amplitude of about 4% of the groove interval, and its frequency is defined as 22.05 ± 1 kHz. The number of rotations of the medium in a recordable CD is controlled so that the linear velocity becomes a constant value within a range of 1.2 to 1.4 meters per second, and the wobbling frequency is always centered. This is done by controlling the number of revolutions to reproduce at the value of 22.05 kHz.
Further, the absolute address information is included in a form where the frequency is modulated with a deviation of 1 kHz for 22.05 kHz.

Next, the operation will be described. For tracking error detection in the conventional optical recording / reproducing apparatus shown in FIG. 3, a well-known push-pull method is used. FIG.
FIG. 2 is a plan view of an optical system for explaining a detection principle in a push-pull method, and shows only a part necessary for explanation of the principle. 13 is a condensed spot formed by the objective lens 5, 14 is an information recording medium, and 15 is a guide groove. FIG. 7A shows that the objective lens 5 is displaced by the same amount as the amount of the tracking, which is the deviation between the condensing spot 13 and the guide groove 15, so that the track is followed. Such follow-up methods are generally FIG (a)
As shown in FIG.
Despite the fact that 3 is exactly at the center of the guide groove 15, a parallel shift occurs in the optical axis of the laser beam incident on the photodetector 9. Therefore, an offset occurs in the tracking error signal which is a subtraction signal of the outputs from the two light receiving surfaces.
FIG. 5 is a graph showing the amount of offset generation with respect to the track following amount of the objective lens 5. For example, when the track following amount is 200 microns, a tracking offset is generated by about 0.16 microns. Usually, the allowable value of the tracking offset is about 0.05 to 0.1 micron, so that it is understood that the track following amount is limited to about 120 microns.

By the way, in the conventional example shown in FIG.
Instead of displacing the objective lens 5 and following the track, the optical system held in the box 10 is
The track following is performed by rotating about the track. FIG. 4 ( b ) shows an example in which the entire optical system is displaced to follow the track as described above, and no relative displacement occurs between the objective lens 5 and the photodetector 9, so that the light There is no parallel displacement of the optical axis of the laser beam incident on the detector 9, and no offset occurs in the tracking error signal. Therefore, stable tracking can be performed regardless of the track following amount.

[0006]

Since the conventional optical recording / reproducing apparatus is configured as described above, there are the following problems. First, since the entire optical system is displaced to follow the guide groove, a large driving force is required. Further, the influence of the tracking offset generated due to the inclination of the information recording medium was inevitable. This problem will be described next with reference to the drawings. FIG. 6 is a plan view of the optical system in the push-pull method when the information recording medium is tilted, and shows only a part necessary for explaining the principle. When the information recording medium 14 is tilted, a parallel shift occurs in the optical axis of the laser beam incident on the photodetector 9 even though the condensing spot 13 is located exactly at the center of the guide groove 15, An offset occurs in the tracking error signal. FIG. 7 is a graph showing an offset generation amount with respect to the inclination of the information recording medium 14. For example, when the inclination angle is 1 degree, a tracking offset is generated by about 0.1 μm. Therefore, from the above-mentioned allowable value, the inclination angle is 1
It turns out that the degree is the limit.

As a countermeasure against the above-mentioned problem, there is a method in which an additional sensor for detecting the inclination of the information recording medium is provided, and the inclination of the box is corrected based on the sensor signal. In addition, track following by displacement of the objective lens
Oite, similarly additional sensor for detecting a displacement amount of the objective lens provided in, there is doing the removal of the offset. However, these countermeasures require an additional sensor, making it impossible to reduce the size and cost of the box, and furthermore, even if the tilt of the information recording medium and the displacement of the objective lens can be accurately detected. However, since the amount of offset with respect to the inclination of the information recording medium and the amount of offset with respect to the displacement of the objective lens differ depending on the shape of the guide groove of the information recording medium, a new problem that the amount of offset cannot be completely removed. A point had occurred.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and detects a tracking error of an information recording medium having a guide groove which has been wobbled in advance by using a so-called push-pull detection method. It is an object of the present invention to obtain an optical recording / reproducing apparatus free from occurrence of offset.

[0009]

Means for Solving the Problems] engagement Ru optical recording reproducing apparatus in the present invention, have a guide groove formed by meandering at a constant cycle
Laser beam from the light source on the information recording medium
To record, play, and erase information,
Using the Sprue method, the guide groove
Tracking to follow the beam spot of Xavim
In an optical recording / reproducing apparatus for generating a Guerra signal,
In the information recording medium, the guide groove is
It has a meandering structure.
The first wobbling signal component for the guide groove is
From the signal obtained by the Sshupuru method,
A first electric circuit for extracting a second wobbling signal component
Means and the first and second wobbling signal components
Then, by synchronous detection of these signal components,
Errors due to the following error of the above-mentioned condensed spot with respect to the reference line
Second electric circuit means for generating a difference signal;
The gain is adjusted and the gain-adjusted error signal is pushed.
The tracking error is subtracted from the signal obtained by the pull method.
Third electrical circuit means for generating a signal . The present invention relates to an optical recording / reproducing apparatus according to claim 1.
And the first electric circuit means is a bandpass filter.
Alternatively, it is a low-pass filter. This departure
The optical recording and reproducing apparatus according to claim 1, wherein
The second electric circuit means is a multiplier.

[0010]

[Action] Oite to the present invention, Warwickshire from the reproduction signal of information
First wobbling signal component extracted by the bling method
And the push-pull signal obtained by the above push-pull method.
Synchronous detection with the second wobbling signal component extracted from the signal
Wavy, the condensing spot with respect to the reference line of the guide groove
Generates an error signal corresponding to the tracking error of
The gain is adjusted for the push-pull signal to
Generate tracking error signal by signal subtraction
Information in the tracking signal.
Offset component due to tilt of recording medium or displacement of objective lens
Can be reliably removed, and the inclination and
Accurate tracking accuracy regardless of the displacement of the object lens
Can be improved step by step. That is, the first and second wobble
Focusing spot is actually obtained by synchronous detection of the
For small steady tracking deviations that cannot be tracked by
The signal that does not include the offset component
The error signal is generated, and the error signal is
Gain adjustment for the push-pull signal containing set components
And subtract from this push-pull signal to trigger
Since the racking error signal is generated, the offset
A push that removes components and enables accurate tracking
It is possible to obtain a double signal as a tracking error signal.
it can.

[0011]

【Example】

Embodiment 1 FIG. FIG. 1 is a plan view of an optical system and a circuit connection diagram of an optical recording / reproducing apparatus showing an embodiment of the present invention. In the figure, reference numerals 1 to 5 and 9 correspond to FIG.
Is the same as FIG. Reference numerals 6 to 8 are omitted because they are not essential to the present invention. A differential amplifier 16 is connected to the two light receiving surfaces 9A and 9B of the photodetector 9, and generates a tracking error signal TE by a push-pull method. A numeral 17 is connected to the two light receiving surfaces 9A and 9B. This is an adder for generating the reproduced signal RF. Reference numeral 18 denotes a band-pass filter to which the output signal TE of the differential amplifier 16 is input. The cut-off frequency is set to, for example, about 10 kHz in the low frequency side and about 30 kHz in the high frequency side, and outputs a signal D. . Reference numeral 19 denotes a low-pass filter to which the output signal RF of the adder 17 is input, and the cutoff frequency is set to, for example, about 30 kHz.
Reference numeral 20 denotes an amplifier having a gain G1 to which the output signal RF of the low-pass filter 19 is inputted, and outputs a signal S. 2
Reference numeral 1 denotes a multiplier to which the output signal D of the band-pass filter 18 and the output signal S of the amplifier 20 are input.
Is output. Reference numeral 22 denotes a low-pass filter to which the output signal M0 of the multiplier 21 is input. The cut-off frequency is set to, for example, less than 20 kHz, and the signal M1 is output. 23 is an output signal M of the low-pass filter 22
1 is an amplifier having a gain of G2 and a signal OFS
Is output. 24 is an output signal TE of the differential amplifier 16;
This is a differential amplifier to which the output signal OFS of the amplifier 23 is input, and outputs a signal CTE.

Next, the operation will be described. FIG. 2 is a plan view showing the information recording medium 14 having the wobbled guide grooves 15. 25 is the wobbled guide groove 15
, P is the pitch of the guide groove 15, and W is the maximum value of the wobbling amplitude with respect to the center line 25. X is the displacement of the condensing spot 13 from the center line 25. The displacement U of the guide groove 15 from the center line 25 is represented by the following equation, where f is the wobbling frequency (22.05 ± 1 kHz). U = W · sin (2πft) (1) The output signal TE of the differential amplifier 16 is a normal push-pull signal, and is represented by the following equation. TE = A · sin {2π (X−U) / P} + B (2) where A is the amplitude of the push-pull signal, and B is the offset component generated by the inclination of the information recording medium, the displacement of the objective lens, and the like. is there. Since only the wobbling frequency component of the signal TE is extracted by the band-pass filter 18, the output signal D of the band-pass filter 18 is represented by the following equation. D = A · sin (−2πU / P) = − 2πA · U / P = −2πA · W / P · sin (2πft) (3) In the above equation, the wobbling amplitude W is the guide groove 15.
Approximate calculation is performed assuming that the pitch P is sufficiently small. The output signal S of the amplifier 20 is a signal obtained by passing only a signal component equal to or lower than the wobbling frequency in the low-pass filter 19 out of the RF signal which is a reproduction signal of information, and is expressed by the following equation. S = E0 + E1 · cos {2π (X−U) / P} (4) In the above equation, E0 is the DC component of the RF signal, and E1 is the amplitude of the wobbling signal component. Since the multiplier 21 multiplies the signals S and D, the multiplied signal M0 is calculated from the equations (3) and (4) as follows. Note that the approximation is performed in the middle of the calculation, assuming that U is sufficiently smaller than P, as in equation (3). M0 = D · S = D · [E0 + E1 · cos {2π (X−U) / P}] = D · {E0 + E1 · cos (2πX / P) · cos (2πU / P) + E1 · sin (2πX / P) Sin (2πU / P)｝ = D ｛{E0 + E1 ・ cos (2πX / P) + E1 ・ (2πU / P) ・ sin (2πX / P)｝ = D ・ E0 + D ・ E1 ・ cos (2πX / P)-( 2πA · W / P) · (2πW / P) · E1 · sin (2πft) · sin (2πft) · sin (2πX / P) = D · E0 + D · E1 · cos (2πX / P) − (2πW / P)・ (2πW / P) ・ A ・ E1 ・ sin (2πX / P) ・ {1-cos (4πft)} / 2 (5) The low-pass filter -22 has a cut-off frequency lower than the wobbling frequency f. Therefore, the output signal M1 is (5) From the equation, M1 = K · sin (2πX / P) (6) where K = − (2πW / P) · (2πW / P) · A · E1 / 2 (7) Since K is a constant, the output signal M1 is focused spot
It is expressed as a sine function only for the displacement X from the center line 25 of the unit 13 . Therefore, equation (6) itself can be a tracking error signal, but since the constant K is extremely small, it cannot be said that the tracking error signal is highly accurate. However, there is no occurrence of an offset component depending on the tilt of the information recording medium and the displacement of the objective lens.

The normal push-pull signal TE expressed by the equation (2) includes an offset component B depending on the tilt of the information recording medium and the displacement of the objective lens. When you follow the track,
As a matter of course, due to the offset component B, the condensing spot 13 does not correctly follow the guide groove 15. At this time, in equation (6), a non-zero signal M1 corresponding to the tracking error amount X is output, and this signal M1 corresponds to the offset component B. Therefore, the magnitude of the signal M1 is amplified by the amplifier 23 so as to be the same as the offset component B, and the amplified signal OFS is subtracted from the push-pull signal TE by using the differential amplifier 24, whereby the push-pull signal TE Is the signal C-TE from which the offset component has been removed. As described above, the equation (6) itself has a very small value of the constant K, so that the accuracy as a tracking error signal is low, but it is sufficient to know the approximate offset component, and the correction as described above is performed. By using the obtained signal CTE, the tracking follow-up accuracy can be remarkably improved.

Embodiment 2 FIG. In FIG. 1, the low-pass filter 19 is used to extract the wobbling frequency component from the RF signal, but may be the same as the band-pass filter 18.

[0015]

As described above, according to the present invention, the first cue extracted from the reproduced signal of the information by the wobbling method.
Wobbling signal component and the push-pull method
Second wobbling extracted from the push-pull signal
Synchronous detection of the signal component and the reference
Generates an error signal corresponding to the tracking error of the focused spot
This error signal is gained with respect to the push-pull signal.
Adjust and track by subtracting these signals
Since the error signal is generated, there is an effect that the tracking follow-up accuracy can be remarkably improved regardless of the inclination of the information recording medium and the displacement of the objective lens.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical system and a circuit connection diagram of an optical recording / reproducing apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a plan view of an information recording medium having wobbled guide grooves according to the present invention.

FIG. 3 is a perspective view showing a conventional optical recording / reproducing apparatus.

FIG. 4 is a plan view of an optical system illustrating a detection principle of the push-pull method.

FIG. 5 is a graph showing an offset generation amount with respect to a track following amount of an objective lens.

FIG. 6 is a plan view of an optical system showing occurrence of offset when the information recording medium is inclined in the push-pull method.

FIG. 7 is a graph showing an offset generation amount with respect to a tilt of an information recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 5 Objective lens 9 Photodetector 13 Focused spot 14 Information recording medium 15 Guide groove 16, 24 Differential amplifier 17 Adder 18 Bandpass filter 19, 22 Lowpass filter 20, 23 Amplifier 21 Multiplier

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshiya Toshizaki 1 Baba Zhoujo, Nagaokakyo-shi, Kyoto, Japan Inside Mitsubishi Electric Corporation R & D Laboratory (72) Inventor Takeyuki Ito 1 Baba Zhou, Nagaokakyo-shi, Kyoto Mitsubishi Electric Corporation Electronic Products Development Laboratory (72) Inventor Kenjiro Kimome 1 Baba Zoshosho, Nagaokakyo-shi, Kyoto Prefecture Mitsubishi Electric Corporation Electronic Products Development Laboratory (56) References JP-A-4-243028 (JP) , A)

Claims (3)

(57) [Claims] 1. A record from a light source on an information recording medium having a guide groove formed by meandering at a constant cycle - Zabi - a beam is irradiated condensing, recording of information, reproduction, co the erased ,
Using flop Sshupuru method, with respect to the reference line of the guide groove
In an optical recording / reproducing apparatus for generating a tracking error signal for following a converging spot of a laser beam, said information recording medium is formed by meandering said guide groove in advance at a predetermined period. And a first wobble from the information reproduction signal to the guide groove.
Signal obtained by the above push-pull method
A first electrical circuit means for extracting a second wobbling signal component for the guide groove from the first and second wobbling signal components.
The synchronous detection of the signal component of
Error signal corresponding to the following error of the focused spot
A second electrical circuit means for forming, the error signal to gain adjustment, the gain adjusted error signal <br/> the push-pull method and subtracted from the signal obtained from the by Tiger <br/> Kkinguera - a signal An optical recording / reproducing apparatus comprising: a third electric circuit unit for generating the electric signal. Wherein said first electrical circuit means, the band-pass filter - or B - pass filter - an optical recording reproducing apparatus according to claim 1, wherein the a. Wherein said second electrical circuit means, optical recording and reproducing apparatus according to claim 1, characterized in that it is a multiplier.