JP3237237B2 - Optical head device, optical disk device, and tracking error detection method - 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 head device and an optical disk device suitable for application to tracking error detection by the one-beam push-pull method.

[0002]

2. Description of the Related Art In an optical disk system, a push-pull method is one of the tracking servo error detection methods.

FIG. 6 is for explaining the principle of the push-pull method. As shown in FIG.
The reflected light from the disk substrate 30 composed of the pre-groove 31 in which the groove is formed and the other lands 32 is mainly (0th order) and (± 1) in the direction perpendicular to the pre-groove 31.
Next, the light is reflected as diffracted light. Therefore, two-divided photodetectors L and R are arranged, and each of the photodetectors L and R has (0th order) + (+ 1st order) and (0th order) + (− 1st order).
It is known that if the light beams are separately detected, the respective signal intensities are as follows.

I _R = DC + ACos (φ + V) (1) I _L = DC + ACos (φ−V) (2) If the differential signals of equations (1) and (2) are taken, the following is obtained. become _{I P = I R -I L =} -2ASinφSinV DC here is a DC component, the photodetector L,
Area S1, ± 1 where the 0th-order and ± 1st-order diffracted light exist on R
The size of DC is determined by the area S0 where there is no 0th-order diffracted light without the 0th-order diffracted light, the intensity E0 of the 0th-order diffracted light, and the intensity E1 of the ± 1st-order diffracted light. The values of the coefficients A and φ are S0, S1,
It is determined by E0, E1, and the phase difference between the 0th order diffracted light and the ± 1st order diffracted light. V is the distance between the track center Q on the disk and the spot center P.

When there is no tracking error, V = 0
And I _P = 0. If there is a tracking error, V ≠ 0 and I _P ≠ 0. Therefore, a tracking error can be detected depending on whether _IP is 0 or not.

[0006]

In the push-pull method, when the objective lens 4a fluctuates during tracking or the surface of the disk 5 is inclined, the centers of the photodetectors L and R coincide with the centers of the diffracted light. And the difference appears in the DC component DC of the equations (1) and (2) (S0 and S1 differ between I _R and I _L ), and the tracking error signal includes an offset amount. Error occurs.

FIG. 7 shows the deviation between the centers of the two-part photodetectors L and R and the centers of the diffracted light due to the fluctuation of the objective lens 4a.

[0008] As shown in FIG.
The light beam emitted from the lens is converted into parallel light by the collimator lens 2, reflected by the beam splitter 3, and collected on the disk 5 by the objective lens 4a. The light reflected on the disk 5 returns on the outward path, passes through the beam splitter 3, and is detected by the photodetectors L and R. At this time, if the objective lens 4a moves to the position indicated by 4b, the positional relationship between the photodetectors L and R and the objective lens 4a shifts, and the center of the diffracted light and the photodetector as shown in FIG. L and R deviate from the center (hereinafter referred to as tracking error).

As a result, an offset occurs, and even if the objective lens 4a is positioned on the track, the offset becomes an error, so that a tracking error signal is detected even in the case of normal tracking.

FIG. 7B shows the relationship between the amount of fluctuation of the objective lens 4a and the amount of tracking error. FIG.
As shown in (b), the tracking error amount is almost proportional to the fluctuation amount of the objective lens 4a.

FIG. 8A is a diagram showing a shift between the center of the diffracted light and the centers of the photodetectors L and R due to the inclination of the disk 5 surface. As shown in FIG. 8A, a light beam emitted from the semiconductor laser 1 passes through a collimator lens 2 and a beam splitter 3, and is condensed on a disk 5 by an objective lens 4. The light reflected on the disk 5 is transmitted through the beam splitter 3 and detected by the photo detectors L and R. At this time, if the disk surface 5 is inclined as indicated by 5a (shown by a broken line), the centers of the photodetectors L and R deviate from the centers of the diffracted light, causing an offset and causing an error in the tracking error signal.

FIG. 8B is a diagram showing the inclination of the disk surface 5 and the tracking error amount. As shown in FIG. 8B, as the inclination of the disk surface 5 increases, the tracking error amount increases.

It is an object of the present invention to provide an optical head device, an optical disk device, and a tracking error detection method for detecting and removing an offset due to a fluctuation of an objective lens or a tilt of a disk surface in a push-pull method.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is to provide a light emitting means for emitting light, a light from the light emitting means, and a groove and a land in a predetermined area. Light collecting means for collecting light on a recording medium whose boundary meanders at a predetermined cycle; first light receiving means to fourth light receiving means arranged in parallel in a tracking direction of the recording medium and receiving reflected light from the recording medium If, by calculating the output from the first light receiving means through fourth light receiving means, first to obtain a tracking error signal including an offset amount by a push-pull method
A signal processing unit and, by rotating the recording medium, an output from the first to fourth light receiving units with respect to a predetermined frequency component output from the first to fourth light receiving units. A second signal processing means for obtaining an offset signal by calculating, and a third signal processing for removing the offset signal by calculating outputs from the first signal processing means and the second signal processing means. And an optical head device. The object is to provide a light emitting unit that emits light,
The light from said light emitting means and focusing means for and a groove and a land portion in a predetermined region, and the boundary between the groove portion and the land portion are focused onto a recording medium to meander at a predetermined cycle, the Recording medium
The first to fourth light receiving means which are arranged in parallel in the body tracking direction and receive the reflected light from the recording medium, and the outputs from the first to fourth light receiving means are calculated, whereby the push a first signal processing means for obtaining a tracking error signal including an offset amount by pull method, by rotating the recording medium, the first
A second signal processing means for obtaining an offset signal by calculating an output from the first to fourth light receiving means with respect to a predetermined frequency component output from the light receiving means to the fourth light receiving means; An optical disc apparatus comprising: a third signal processing unit for removing an offset signal by calculating an output from the first signal processing unit and the output from the second signal processing unit. . The object is to cause light to be emitted by a light emitting unit, and to condense the light on a recording medium having a groove and a land in a predetermined area, and a boundary between the groove and the land meandering at a predetermined cycle. And the reflected light from the recording medium is
Received by the first light receiving means through fourth light receiving means which is divided into four in the tracking direction, by calculating the output from the first light receiving means through fourth light receiving means, a tracking error signal including an offset amount by a push-pull method And by rotating the recording medium, the first
A predetermined frequency component is output from the light receiving means to the fourth light receiving means, an offset signal is obtained by calculating the output, and a tracking error signal including the offset amount and the offset signal are calculated by calculating the offset signal. The problem is solved by a tracking error detection method characterized by removing the error from the error signal.

[0015] The above object is also achieved by a swing means for swinging an objective lens for condensing light on a recording medium at a predetermined frequency,
The problem is solved by an optical head device and an optical disk device including the first to third signal processing units.

[0016]

According to the present invention, as shown in FIG. 4, the surface of the disk substrate 30 is formed by rotating the disk substrate 30 because the pregroove 31 which is a groove and the land 32 which is a land meander at a predetermined period. Then, predetermined frequency components are output from the photodetectors 10a to 10d, so that the differential amplifiers 13, 14, 16 and the DC cut circuit 22 shown in FIG.
a to 22d and the amplitude value detection circuits 20 and 21 or the differential amplifier 16, the DC cut circuits 22a and 22d, and the amplitude value detection circuits 20 and 21 shown in FIG. Accordingly, a tracking error signal from which the offset amount has been removed can be obtained.

Also, by oscillating the objective lens 4a at a predetermined frequency by a vibrator or the like, a predetermined frequency component is output from the photodetectors 10a to 10d, so that the differential amplifiers 13, 14, 16 and a DC cutoff circuit are provided. 22a
22d and the amplitude value detection circuits 20 and 21, or the differential amplifier 16, the DC cut circuits 22a and 22d, and the amplitude value detection circuits 20 and 21, the offset amount can be calculated. The obtained tracking error signal can be obtained.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention for removing an offset of a push-pull signal.
FIG. 4 is a perspective view of the disk used in this embodiment.

In this embodiment, the optical disk shown in FIG. 4 was used. As shown in FIG. 4, the disk substrate 30 is divided into a pregroove 31 which is a groove portion and a land 32 other than the groove as a header portion, and a boundary between the pregroove 31 and the land 32 has a predetermined period. Meandering (hereinafter called wobble). When the recording density of the optical disk is the same between the inside and the outside, it is necessary to change the number of rotations of the inner and outer circumferences according to the position of the pickup (CLV).
(Constant Linear Velocity)) to control the rotation of the inner and outer circumferences by generating a pilot signal so that the wobble has a predetermined frequency f (for example, 22.05 KHz).

However, when the disk substrate 30 rotates, the wobble causes the center of the spot 33 and the center of the track to be displaced at a period of the frequency f. The displacement amount U is U = U ₀ Sin2πft (t: time). Since U ₀ is a very small amount, U ≒ 2πft. On the other hand, the intensities of the photodetectors L and R at the portion S1 where the ± 1st-order diffracted light and the 0th-order diffracted light intersect each other are represented as follows.

[0022] _{I 'L = (DC)'} + A L Cos (φ + U) ··· (3) I 'R = (DC)' + A R Cos (φ-U) ··· (4) (3) and equation A _L and A _R in equation (4) are the area of S1,
It is determined by the intensity of the ± first-order diffracted light and the phase difference between the zero-order diffracted light and the ± first-order diffracted light. However, the intensity of the ± 1st-order diffracted light and the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light are constants determined by each optical head device, and therefore, from the amplitudes A _L and A _{R in} Expressions (3) and (4), Since the shift amount of the area S1 is obtained by the four-divided photodetector described, the offset amount due to the fluctuation of the objective lens or the inclination of the disk surface can be calculated.

Next, a circuit for calculating an offset amount in the push-pull method according to the first embodiment of the present invention will be described.

As shown in FIG. 1, in this embodiment, photodetectors 10b and 10c having the same size are provided inside, and photodetectors 10a and 10c having the same size are provided inside.
d are arranged at equal intervals so as to be located outside of them, and the outer photodetectors 10a and 10d are larger than the photodetectors 10b and 10c in consideration of the margin due to the tracking error amount.

The photo detectors 10a and 10b are
Input by the arithmetic unit 12 and (DC) ₁+ A₁Cos (φ-
V) is output. Photo detector 1
0c and 10d are input to the adder 11, and (DC)_Two
+ A_TwoA current corresponding to Cos (φ + V) is output.
From the differential amplifier 15 (DC)_Two− (DC)₁-(A_Two+
A₁) A current corresponding to SinφSinV is output.
Where (DC)_Two− (DC)₁Is the offset amount,
V and A₁, A_TwoIs V and V shown in equations (1) and (2).
A.

The photodetectors 10a to 10d are connected to circuits 22a to 22d for removing a direct current component (DC) 'shown in equations (3) and (4), respectively.
From the wobble frequency component, AaSin2πft, A
bSin2πft, -AcSin2πft, -AdSi
n2πft is output.

Here, the coefficients Aa to Ad are expressed by the following equations (3) and (4).
Are values corresponding to A _R × Sin φ and A _L × Sin φ. From the differential amplifier 13, (-Ad-Ab) Sin2
πft, (−Ac−Aa) Sin
A current corresponding to 2πft is output. Differential amplifier 16
From the amplitude value detection circuits 20, 2 such as a peak hold circuit.
The DC component (-Ac-Aa)-(-Ad-Ab) from which the variation of Sin2πft has been removed by passing 1 is output so as to match the offset amount (DC) _2- (DC) ₁ . The tracking error signal from which the offset amount has been removed from the differential amplifier 19− (A ₁ + A ₂ ) Sin φS
inV is output.

Next, a method of detecting the offset amount will be described.

First, the objective lens 4a is servo-tracked to the pre-groove 31 shown in FIG. At this time, the spots reflected by the disk substrate 30 are detected by the photo detectors 10a to 10d and converted into current. The outputs of the photodetectors 10a to 10d are added to an adder 1
Tracking error signals ((DC) ₂ − (DC) ₁ −) calculated by the differential amplifiers 1 and 12 and the differential amplifier 15 and including the offset amount
(A ₁ + A ₂ ) SinφSinV) is obtained.

Next, when the disk substrate 30 is rotated, the wobble frequency component AaSin2πft,
AbSin2πft, -AcSin2πft, -AdS
Since in2πft is output from the DC component cut circuits 22a to 22d, this output is output to the amplitude value detection circuits 20 and 21.
When the signals are processed by the differential amplifiers 13, 14, and 16, an offset amount ((DC) _2- (DC) ₁ ) is obtained as described later.

Next, the outputs of the differential amplifiers 15 and 16 are differentiated by the differential amplifier 19, and the tracking error signal-(A ₁ + A ₂ ) Sin φSin from which the offset amount has been removed.
V is obtained.

Next, the fact that the offset amount can be obtained by the above-described circuit configuration will be described with reference to FIGS.

FIG. 2 is a diagram for explaining a circuit for removing the offset amount when there is no offset amount due to the fluctuation of the objective lens and the inclination of the disk surface.

As shown in FIG. 2, since there is no offset amount, the center of the diffracted light coincides with the center of the photodetectors 10b and 10c. Therefore, Ab = Ac, Aa = Ad, and the differential amplifiers 13, 1
4 (−Ad−Ab) Sin2πft, (−A
a-Ac) Sin2πft matches. Therefore, 0 is output from the differential amplifier 16. On the other hand, the differential amplifier 15
Tracking error signal without offset
Since (A ₁ + A ₂ ) SinφSinV is output, the tracking error signal − (A ₁ + A ₂ ) SinφSinV having no offset amount is also output from the differential amplifier 19.

FIG. 3 shows that a spot is formed by the photodetector 10c due to the fluctuation of the objective lens 4a and the inclination of the disk surface 5.
And 10d side. As shown in FIG. 3, the sum of the spot areas of the photodetectors 10b and 10d is larger than that of the photodetectors 10a and 10c.
Is larger than the sum of the spot areas at Moreover, in the photodetector 10c, the + 1st-order diffracted light and -1
Since both diffracted lights of the second-order diffracted light are located, the photodetector 10c outputs a light quantity proportional to the difference between the spot areas of the + 1st-order diffracted light and the -1st-order diffracted light. Therefore, it is the output of the differential amplifier 14 and its amplitude value (−Ac−
The absolute value of Aa) is the output of the differential amplifier 13 and is smaller than the absolute value of the amplitude value (−Ad−Ab).
Since the difference between the amplitude values corresponds to the displacement amount of the spot, when the difference between the differential amplifiers 13 and 14 is multiplied by a constant and amplified, the differential amplifier 16 outputs a positive offset amount. On the other hand, the spot from the differential amplifier 15 is the photodetector 1
Since the offset amount having a positive sign appears by the amount shifted to the 0c and 10d sides, the offset amount is removed from the tracking error signal by subtracting the positive offset amount from the differential amplifier 16 by the differential amplifier 19. can do.

Similarly, when the spot is the photodetector 10
b and 10c, the differential amplifier 1
6 outputs a negative offset amount, and the differential amplifier 15
Since the negative offset amount is also output from the differential amplifier 19, the offset amount can be removed from the tracking error signal by the differential amplifier 19.

FIG. 5 is a push button showing a second embodiment of the present invention.
FIG. 3 is a configuration diagram of a double signal detection circuit. As shown in FIG.
As in the first embodiment, the photodetectors 10a to 10d
It is arranged. The photo detectors 10a and 10b
It is input to the adder 12, and (DC)₁+ A₁Cos (φ-
V) is output. Photo detector 1
0c and 10d are input to the adder 11, and (DC)_Two+
A_TwoA current corresponding to Cos (φ + V) is output. difference
From the dynamic amplifier 15, (DC)_Two− (DC)₁-(A ₁+
A_Two) A current corresponding to SinφSinV is output.

The photodetectors 10a and 10d are given by the following equations.
Remove the DC component (DC) 'shown in (3) and (4)
22a, 22d, and 22a, 22d
From the wobble frequency component AaSin2πft, Ad
Sin2πft is output. Amplitude value detection circuit
Ad is output from 20 and Aa is output from the amplitude value detection circuit 21.
The differential amplifier 16 changes K × (Ad−Aa) to (D
C)_Two− (DC)₁(K is a constant
Number). Therefore, from the differential amplifier 19,-(A ₁+ A_Two)
The offset amount corresponding to SinφSinV has been removed.
A tracking error signal is output.

In this embodiment, the case where the wobble is provided on the disk substrate has been described. However, the objective lens is moved in the track direction (FIG. 6) by a vibrator such as an electrostrictive element.
(In the direction perpendicular to the plane of the drawing) at a predetermined frequency, the center Q of the track and the center P of the spot are displaced at a predetermined frequency, so that the ± 1st-order diffracted light shown in FIG. In the area where the zero-order diffracted light intersects, the relational expressions shown in Expressions (3) and (4) hold. Accordingly, as described above, the offset amount can be removed from the tracking error signal using the circuit shown in FIG. 1 or FIG.

[0040]

As described above, according to the present invention ,
The recording medium is arranged side by side in the tracking direction of the recording medium.
First to fourth light receiving means for receiving reflected light from
And the outputs from the first to fourth light receiving means.
By calculating the following equation, it is possible to remove the offset amount caused by the fluctuation of the objective lens and the inclination of the disk surface in the push-pull method, so that the accuracy of tracking error signal detection can be improved. Further, by combining the focus error detection by the push-pull method, the differential concentric circle method, and the differential detection method of the magneto-optical signal, a highly accurate photodetector can be realized integrally.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a push-pull signal detection circuit showing a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a push-pull signal detection circuit when there is no offset amount;

FIG. 3 is a diagram for explaining a push-pull signal detection circuit when there is an offset amount;

FIG. 4 is a disk perspective view showing one application example of the present invention.

FIG. 5 is a configuration diagram of a push-pull signal detection circuit showing a second embodiment of the present invention.

FIG. 6 is a diagram for explaining the principle of the push-pull method.

FIG. 7 is a diagram (I) showing a drawback of the push-pull method.

FIG. 8 is a diagram (II) showing a defect of the push-pull method.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser (light emitting means) 2 collimator lens 3 beam splitter 4, 4a, 4b objective lens (light collecting means) 5, 5a disk (recording medium) 10a photo detector (first light receiving means) 10b photo detector (second light receiving means) 10c Photodetector (third light receiving means) 10d Photodetector (fourth light receiving means) 11,12 Adder 13-19 Differential amplifier 20,21 Amplitude value detection circuit (peak hold circuit) 22a-22d DC cut circuit 30 Disk substrate 31 Pregroove (Groove) 32 Land (Land) 33 Spot L, R Photodetector

Claims (8)

(57) [Claims] 1. A light emitting means for emitting light, and a light from the light emitting means has a groove and a land in a predetermined area, and a boundary between the groove and the land meanders at a predetermined cycle. Light collecting means for collecting light on a recording medium, first light receiving means to fourth light receiving means arranged in parallel in the tracking direction of the recording medium and receiving reflected light from the recording medium; by calculating the output from the fourth light receiving means, a first signal processing means for obtaining a free <br/> no tracking error signal offset by a push-pull method, by rotating the recording medium, wherein A second signal processing for obtaining an offset signal by calculating an output from the first to fourth light receiving means with respect to a predetermined frequency component output from the first to fourth light receiving means. Means; An optical head device comprising: a third signal processing unit for removing an offset signal by calculating outputs from the first signal processing unit and the second signal processing unit. [2 claim] light emitting means for emitting light, and a focusing means for focusing the light from said light emitting means on a recording medium, a swing unit for swinging the focusing means at a predetermined frequency, the A first light-receiving means to a fourth light-receiving means, which are arranged side by side in the tracking direction of the recording medium and receive the reflected light from the recording medium, by calculating outputs from the first light-receiving means to the fourth light-receiving means, a first signal processing means for obtaining a free <br/> no tracking error signal offset by a push-pull method, by swinging the swinging means at a predetermined frequency, said first light receiving means to the fourth A second signal processing unit for obtaining an offset signal by calculating outputs from the first to fourth light receiving units with respect to a predetermined frequency component output from the light receiving unit; Processing means and By calculating the output from the signal processing unit, the optical head apparatus characterized in that it comprises a third signal processing means for removing the offset signal. 3. A light emitting means for emitting light; and a light from the light emitting means having a groove and a land in a predetermined area, and a boundary between the groove and the land meandering at a predetermined cycle. Light collecting means for collecting light on a recording medium, first light receiving means to fourth light receiving means arranged in parallel in the tracking direction of the recording medium and receiving reflected light from the recording medium; by calculating the output from the fourth light receiving means, a first signal processing means for obtaining a free <br/> no tracking error signal offset by a push-pull method, by rotating the recording medium, wherein A second signal processing for obtaining an offset signal by calculating an output from the first to fourth light receiving means with respect to a predetermined frequency component output from the first to fourth light receiving means. Means; An optical disc device comprising: a third signal processing unit for removing an offset signal by calculating outputs from the first signal processing unit and the second signal processing unit. 4. A light emitting means for emitting light, and a focusing means for focusing the light from said light emitting means on a recording medium, a swing unit for swinging the focusing means at a predetermined frequency, the A first light-receiving means to a fourth light-receiving means, which are arranged side by side in the tracking direction of the recording medium and receive the reflected light from the recording medium, by calculating outputs from the first light-receiving means to the fourth light-receiving means, a first signal processing means for obtaining a free <br/> no tracking error signal offset by a push-pull method, by swinging the swinging means at a predetermined frequency, said first light receiving means to the fourth A second signal processing unit for obtaining an offset signal by calculating outputs from the first to fourth light receiving units with respect to a predetermined frequency component output from the light receiving unit; Processing means and By calculating the output from the signal processing unit, the optical disk apparatus characterized by comprising comprises a third signal processing means for removing the offset signal. 5. Light is emitted by a light emitting means, and the light is collected on a recording medium having a groove and a land in a predetermined area, and a boundary between the groove and the land meandering at a predetermined cycle. The reflected light from the recording medium to a track on the recording medium.
Received by the first light receiving means through fourth light receiving means which is divided into four ring direction, by calculating the output from the first light receiving means through fourth light receiving means, including the offset amount by a push-pull method <br / Obtaining a tracking error signal, rotating the recording medium, outputting a predetermined frequency component from the first light receiving means to the fourth light receiving means, obtaining an offset signal by calculating this output, A tracking error detection method, comprising: removing an offset amount from a tracking error signal by calculating a tracking error signal including the offset amount and the offset signal. 6. Light is emitted by a light emitting means, light from the light emitting means is focused on a recording medium by a light focusing means, and reflected light from the recording medium is tracked on the recording medium.
Received by the first light receiving means through fourth light receiving means which is divided into four ring direction, by calculating the output from the first light receiving means through fourth light receiving means, including the offset amount by a push-pull method <br / By acquiring a tracking error signal and oscillating the light condensing means at a predetermined frequency, a predetermined frequency component is output from the first to fourth light receiving means, and this output is calculated. A tracking error detection method comprising: obtaining an offset signal; and calculating the tracking error signal including the offset amount and the offset signal to remove the offset amount from the tracking error signal. 7. The second light receiving means for a predetermined frequency component output from the first to fourth light receiving means.
The outputs of the first light receiving means and the third light receiving means disposed therebetween are calculated, and the output provided by the third light receiving means is disposed therebetween.
The second calculates the output of the light receiving unit and the fourth light receiving means, a tracking error detection method according to claim 5 or 6 calculates these operations output, characterized in that to obtain an offset signal. 8. The light receiving device according to claim 6, wherein said second light receiving means and said third light receiving means are interposed therebetween.
The output signal of the first light receiving means and the fourth light receiving means is calculated for a predetermined frequency component output from the first and fourth light receiving means to obtain an offset signal. 7. The tracking error detection method according to 5 or 6.