JP2640202B2 - Tracking servo circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo circuit for controlling an objective lens through which light reflected from an optical disk passes to a predetermined track of a rotating optical disk.

[0002]

2. Description of the Related Art FIG. 1 is a block diagram showing a configuration of a conventional tracking servo circuit. In this tracking servo circuit, a laser beam emitted from a laser diode 1 is converted into a parallel beam by a convex lens 2, passes through a half mirror 3, passes through an objective lens 4, and is projected onto a surface of an optical disk 6 rotated by a motor 5. You. The laser light reflected by the optical disk 6 passes through the objective lens 4, the half mirror 3 and the lens 8 and is condensed on the two-divided photodetector 9. The output of the split photodetector 9 is amplified by the amplifiers 10 and 11, and the output signal of the amplifier 10 is input to the positive input terminal 12a of the differential amplifier 12 and one positive input terminal 13a of the addition amplifier 13. The output signal of the amplifier 11 is input to the negative input terminal 12b of the differential amplifier 12 and the other positive input terminal 13b of the addition amplifier 13. As a result, the differential amplifier 12 outputs a difference signal X which is the difference between the output signals of the amplifiers 10 and 11, and the summing amplifier 13 outputs the difference signal X.
And outputs a sum signal Y which is the sum of the respective output signals.

[0003] The difference signal X and the sum signal Y are divided by a divider 14.
The divider 14 normalizes the difference signal X by dividing the difference signal X by the sum signal Y in order to remove a level change of the difference signal X due to a change in light reflectance of the optical disk 6 or a change in the amount of laser light.
The normalized tracking error signal X 'is output. The tracking error signal X 'is input to an amplifier 17 through a phase compensation circuit 16 for stabilizing the servo system, and the amplifier 17 amplifies the input tracking error signal to generate a drive signal capable of driving the tracking actuator 7. None, the drive signal is supplied to the tracking actuator 7 to move the objective lens 4 in a direction perpendicular to the optical axis of the laser light, that is, in a radial direction of the optical disk 6, and a tracking servo for causing the laser light to follow the track of the optical disk 6 is performed. Do.

The optical disk 6 rotated by the motor 5 is generally eccentric. Therefore, when the optical disk 6 is rotated and a laser beam is projected on the optical disk 6 from a fixed position, the laser beam projected on the optical disk 6 becomes
The optical disc reciprocates within a predetermined distance between the outer circumference and the inner circumference to repeatedly traverse a plurality of tracks. Therefore, when the optical head operates the focus servo and does not perform the tracking servo operation, the sine wave-like difference signal shown in FIG. 2A crosses zero at the positions of the land (recording portion) and the groove (groove) of the track. X is obtained by the differential amplifier 12. Also, the sum signal Y cos wave shown in a maximum FIG. 2 (b) is obtained by summing amplifier 13 at the position of the land or groove.

When the optical head seeks the target track, control is performed so that the optical head is drawn into the tracking servo at the time of the zero cross of the difference signal X corresponding to the land or groove of the target track. In that case, it is desirable that the optical head is once accelerated to the middle of the target track and then decelerated, so that the moving speed of the optical head (objective lens) on the target track is reduced to zero. However, at present, the moving speed (rush speed) of the optical head when shifting from the seek operation to the tracking servo operation cannot be made zero due to a speed detection error or the like during the movement of the optical head. Therefore, even if the tracking servo operation is performed at the time of the zero crossing of the difference signal X, it is difficult to settle the light spot immediately to the land center of the target track, and the light spot is pulled back to the track center after passing a small distance from the land center. become. Generally, the difference signal X
Is a sin wave signal with a track pitch of one cycle,
As the distance from the center of the sensor (zero crossing point) increases, the slope of the waveform decreases and the sensor sensitivity decreases. Also 1 /
If it goes over 4 tracks or more, the inclination of the sensor will be reversed and the polarity will be reversed. Therefore, when the rush speed of the optical head is high, the amount of overshoot from the target track is large, and the sensor sensitivity may be reduced or the region of the opposite polarity may be reached, so that the pull-in of the tracking servo may fail. In other words, after overrunning the target track, it is possible for the next track to be pulled into the tracking servo, and it is difficult to move the optical head (objective lens) to the target track without overrunning, and it takes a long time to seek the target track. Needs time.

[0006] In order to solve such inconvenience, FIG.
with respect to the sum signal cos wave becomes maximum at a track position as shown in _(a) v a, to obtain a difference signal v _b of sin wave becomes minimum at the track position as shown in FIG. 3 (b), the difference Signal v
tan removal signal by the sum signal v _{a where b} was removed DC component
^-1 calculated, 'to give the signal v _x of the sawtooth' 3 (c) signal v _x of the sawtooth wave shown in by its calculated value 3 by adding an offset in the predetermined area (d ) to obtain a linear signal v _x between one track as shown, the tracking servo system is shown in JP-a-63-181179, which was retracted so the tracking servo by the signal v _x.

[0007]

However, as described above, a sensor signal whose sensor sensitivity is constant for one track can be obtained. However, at this sensor sensitivity, the optical head enters beyond the pull-in capability of the tracking servo. When the speed is reached, the pull-in fails even though linearization is performed between tracks to improve the pull-in capability. In addition, it is necessary to increase the dynamic range of the servo system along with linearization between tracks, but if the dynamic range cannot be increased due to hardware limitations, the linearized signal will be saturated on the way. If the pull-in capability of the tracking servo is reduced due to the saturation, there is a problem that the pull-in of the tracking servo may fail. Meanwhile, in order to obtain a linearized signal between one track, the difference signal shown in FIG. 3 (b), DC formed
Tan ^-1 of the signal divided by the sum signal with the minute removed
An offset is added to the calculated value as shown in FIG. 3 (c) to obtain a saw-tooth wave sensor signal shown in FIG. 3 (d). The information of the sum signal is used to determine the time when this offset is added. ing. However, the continuous servo method has a problem that the information of the sum signal is disturbed since the header portion is detected, and a linearized sensor signal cannot be obtained.

In view of the above problem, the present invention provides a tracking servo system which does not fail to pull in the tracking servo even when the optical head rush speed is high and the dynamic range of the servo system cannot be sufficiently secured. A second invention provides a tracking servo circuit that linearizes a sensor signal without using information of a sum signal and does not fail to pull in a tracking servo even in a continuous servo method. The purpose is to do.

[0009]

According to a first aspect of the present invention, a tracking error signal obtained by normalizing a difference signal between output signals of two photodetectors for receiving reflected light from an optical disk by a sum signal is obtained. A means for calculating the sin ^-1 of the signal, and a positive or negative value from the average level of the sum signal .
A correction tracking error signal having a linear region where the inclination angle of the linear region is different is obtained based on the position information and the calculated value, and the objective lens is drawn into the tracking servo based on the corrected tracking error signal.

According to a second aspect of the present invention, there is provided an arithmetic means for calculating sin- ¹ of a tracking error signal related to a difference signal between output signals of two photodetectors for receiving reflected light from an optical disk, and the arithmetic means performs tracking. Error signal sin
A correction tracking error signal of a triangular wave obtained by calculating ^-1 is obtained, and the objective lens is pulled into the tracking servo by the correction tracking error signal.

[0011]

According to the first aspect of the invention, the difference signal obtained from the output signals of the two photodetectors is normalized by the sum signal to obtain a tracking error signal. Sin of the obtained tracking error signal
^{Operate -1} . Positive or negative position from average level of sum signal
A corrected tracking error signal consisting of a linear region having a different inclination angle depending on the position information and the calculated value is obtained. The objective lens is pulled into the tracking servo by the corrected tracking error signal. Accordingly, when the tracking servo is drawn, the tracking servo capability is changed, and the tracking servo is reliably drawn.

In the second invention, sin- ^{1 of} the difference signal obtained from the output signals of the two photodetectors is calculated. A corrected tracking error signal of a triangular wave synchronized with the difference signal is obtained from the calculated value. The objective lens is pulled into the tracking servo by the corrected tracking error signal. Thus, the land and the groove can be determined based on the inclination direction of the triangular wave, and can be reliably drawn into the tracking servo. The header part is detected by the continuous servo method, and the average level of the sum signal is detected.
Even if the positive or negative position information from the camera is inverted, the linear region of the triangular wave is not inverted and the objective lens does not run away.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 4 is a schematic configuration diagram of the tracking servo circuit according to the first invention. Laser light emitted from a laser diode 1 provided in the optical head passes through a convex lens 2, a half mirror 3, and an objective lens 4 and is projected onto the surface of an optical disk 6 rotated by a motor 5.

The laser beam reflected by the optical disk 6 passes through the objective lens 4, is reflected by the half mirror 3, passes through the lens 8, and is incident on the two-divided photodetector 9. Each signal output by photoelectric conversion by the two-segment photodetector 9 is separately input to amplifiers 10 and 11, and the output signal of the amplifier 10 is connected to the positive input terminal 12 a of the differential amplifier 12 and one positive input terminal of the addition amplifier 13. Input to terminal 13a. The output signal of amplifier 11 is the negative input terminal of differential amplifier 12.
12b and the other positive input terminal 13b of the summing amplifier 13 are input. The difference signal X output from the differential amplifier 12 is input to the divider 14, and the sum signal Y output from the addition amplifier 13 is input to the divider 14 and the gain control unit 19.

The divider 14 divides the difference signal X by the sum signal Y and normalizes the tracking error in order to remove a change in the level of the difference signal X due to a change in light reflectance of the optical disk 6 or a change in the amount of laser light. It outputs a signal X '. The tracking error signal X 'output from the divider 14 is input to the operation control circuit 30. Arithmetic control circuit 30
Is s of the tracking error signal X ′ input thereto.
A calculation unit (not shown) for calculating in ^-1 is provided. The arithmetic control circuit 30 includes, for example, a comparator (not shown) for determining whether the sum signal Y has a positive polarity or a negative polarity.
It has a position information detector for detecting the sum signal average level .
The sum signal Y is a track traversing signal, and has a positive polarity above the average level and a negative polarity below the average level when focusing on the AC component.

Further, when the sum signal Y becomes negative, the correction tracking in which the positive and negative signs of the calculated value obtained by calculating sin ^-1 of the tracking error signal X 'are inverted to extend the linear region is obtained. A correction tracking error signal generator (not shown) for generating an error signal X _O and adding an offset thereto is provided. The corrected tracking error signal X _O output from the arithmetic and control circuit 30 is input to the tracking actuator driving amplifier 17 via the phase compensation circuit 16 for stabilizing the servo system. The tracking actuator driving amplifier 17 has a correction tracking error signal X for driving the tracking actuator 7 described later.
_O is amplified and its drive signal is output. The drive signal of the tracking actuator driving amplifier 17 is given to the tracking actuator 7 for moving the objective lens 4 in a direction (arrow direction) orthogonal to the optical axis of the laser light.

Next, the operation of the tracking servo circuit thus configured will be described with reference to FIG. When the laser diode 1 emits laser light, the laser light becomes parallel light by the convex lens 2, passes through the half mirror 3, passes through the objective lens 4, is condensed by the objective lens 4, and is rotated by the motor 5. The light is projected on the surface of the optical disk 6 which is being used.

The laser light reflected by the optical disk 6 is
The light is condensed on a two-part photodetector 9 through a lens 8. The split photodetector 9 outputs each signal obtained by photoelectrically converting the light incident thereon, and amplifies the output signal by the amplifiers 10 and 11. Each amplified signal is input to a differential amplifier 12 to obtain a difference signal X, which is input to a divider 14,
The sum signal Y is input to 13 and is input to the divider 14.

The divider 14 normalizes the difference signal X by dividing it by the sum signal Y, and inputs the normalized tracking error signal X 'to the arithmetic control circuit 30.

The arithmetic control circuit 30 calculates sin- ¹ of the tracking error signal X '. Here, the tracking error signal X 'is represented by X' = A sin {(2π / P) x} (1) with respect to the radial distance x from the track (land), the amplitude A, and the track pitch P. Then, the tracking error signal X '
The triangular wave L ₁ (TG) shown by the solid line in FIG. 5A obtained by calculating sin ^-1 is given by TG = A sin ^-1 (X '/ A) = A (2π / P) x (2) Is obtained based on

Here, assuming that the radial distance between the tracks is x, between track 0 and -1/4 (1/4) track, the calculation is performed according to the equation (2) , and -1/4 (1 / 4) -1 /
Between two (1/2) tracks, as shown in FIG. 5 (b), based on the information that the sum signal Y is detected to be negative, (1)
The equation is multiplied by a constant α (α> 1) to obtain a straight line L ₂ indicated by a broken line. Then, the positive and negative signs of the calculated value indicating the straight line L ₂ are inverted, and the straight line L ₂ is folded symmetrically on the x-axis to obtain a straight line L ₃ indicated by a broken line. Then, the offset απA + πA
To obtain a straight line L ₄ indicated by a dashed line. This gives-
The sensor sensitivity between the 1/4 (1/4) track and the -1/2 (1/2) track is increased. Also, the corrected tracking error signal X _O has a linear region on the negative side based on the calculated value of sin ^{−1 of the} tracking error signal, similarly to the positive side.

In this way, a corrected tracking error signal X _O indicated by a solid line in FIG. 6 is obtained. The corrected tracking error signal X _O thus obtained is phase-compensated by the phase compensating circuit 16 and amplified by the tracking actuator drive amplifier 17, and then supplied to the tracking actuator 7 to drive the tracking actuator 7.

According to the corrected tracking error signal X _O , the slope of the straight line L ₄ is large between the −1/4 (1/4) track and the −1/2 (1/2) track, thereby increasing the sensor sensitivity. ing,
In other words, since the gain of the servo system is increased, even if the inrush speed of the objective lens 4 occurs that the tracking servo pull-in is limited by the sensor sensitivity indicated by the broken line, the tracking servo pull-in may fail. In addition, the tracking servo pull-in performance can be improved.

FIG. 7 is a waveform diagram showing another embodiment of the corrected tracking error signal X _O. The corrected tracking error signal X _O is calculated by the above equation (1) between the 0th track and the −1/4 (1/4) track to obtain a straight line L ₁ shown by a solid line, and −1/4 (1/4) ) Track to the -1/2 (1/2) track, as shown in FIG. 7 (b), the constant .alpha. ( α <1)
To obtain a straight line L ₄ indicated by a solid line.

By the same arithmetic control as described with reference to FIG. 5 (a), as shown in FIG. 7 (a), between the -1/4 (1/4) track and the -1/2 (1/2) track. To obtain a corrected tracking error signal X _O with reduced sensor sensitivity. Then, the tracking actuator 7 is driven by the corrected tracking error signal X _O in the same manner as described above. According to the corrected tracking error signal X _O , the sensor sensitivity decreases and the pull-in capability decreases between the −1/4 (1/4) track and the −1/2 (1/2) track. As shown in the figure, the linearity between one track does not saturate due to the relationship of the dynamic range of the servo circuit, so that the optical head pulls back to the target track until it passes through the target track and reaches the next track. Can work. Therefore, the retraction capability is substantially improved.

That is, by linearizing one track, if the dynamic range of the servo circuit is exceeded, the sensor sensitivity is substantially reduced due to the saturation. Therefore, the saturation of the corrected tracking error signal X _O is prevented. It is possible to prevent a drop in the tracking servo pull-in capability due to the saturation. Although sin- ¹ of the tracking error signal X 'is calculated, the same effect can be obtained by calculating sin- ^{1 of the} difference signal X input to the divider 14.

FIG. 8 is a waveform chart of the corrected tracking error signal X 'according to the second embodiment of the present invention. In the tracking servo circuit shown in FIG. 4, the arithmetic control circuit 30 calculates the sin ^-1 of the tracking error signal X 'input thereto as described above.
When the calculation is performed by the equation (2) , a triangular wave having a maximum value in a − / 4 track is obtained from the calculated value as shown in FIG.
This triangular wave is obtained in synchronization with the tracking error signal X '(difference signal X), as is apparent from FIG. 8, and the distinction between the land and the groove can be made clear by the inclination direction of the triangular wave. This corrected tracking error signal X _O
Is given to the tracking actuator 7 in the same manner as described above, and the tracking actuator 7 is driven. The track position or glue
The tracking servo can be reliably pulled into the servo position .

It should be noted that the corrected tracking error signal X _O obtained by such a triangular wave has a sin ^{− of the} tracking error signal X ′ even when it is detected that the sum signal Y is negative as shown in FIG. ¹ folded straight L ₂ by the calculated operation value to -1 / 4 (1/4) -1/2 from the track (1 /
2) A straight line based on the calculated value of sin- ¹ of the tracking error signal X 'is not extended in the track . Therefore continuous servo system in a by header portion is detected occurs drop H _D of the signal level of the sum signal Y as shown in FIG. 9 (b), -1 even when the negative sum signal Y as described above Since the straight line of the calculated value obtained by calculating the sin ^-1 of the tracking error signal X 'between the / 2 track and the -1/4 track is not folded, during the period when the sum signal Y should be positive, if the average level of the correction tracking error signal X _O as shown in be level drop accidentally sum signal FIG 9 (a)
The positive or negative position information does not change, the tracking actuator is not erroneously driven, and runaway of the objective lens can be prevented.

Therefore, when the tracking servo is pulled in by such a triangular wave corrected tracking error signal X _O , the continuous servo method is used. Does not run away, and the objective lens can be reliably pulled into the tracking servo. In this case, s
The signal to be calculated in- ¹ may be a difference signal X other than the tracking error signal X '.

FIG. 10 shows a tracking servo circuit for obtaining a corrected tracking error signal X _O without dividing the difference signal X by the sum signal Y. In this tracking servo circuit, the difference signal X is input to the gain control unit 19. In the gain controller 19, a gain for a specific light reflectance of the optical disk 6 or a specific light intensity of the laser diode 1 is set in advance. Difference signal X output from the gain control unit 19 is inputted to the arithmetic control circuit 30, the correction tracking error signal X ₀ which is output from the operation control circuit 30 is input to the phase compensation circuit 16. The sum signal Y is input to another circuit (not shown). Other configurations are the same as those of the tracking servo circuit shown in FIG. 3 with the divider 14 removed, and the same parts are denoted by the same reference numerals.

This tracking servo circuit controls the difference signal X output from the differential amplifier 12 to a predetermined level by the gain control unit 19. The sin ^-1 of the predetermined level difference signal by calculating the arithmetic control circuit 30 in the same manner as described above, and outputs the corrected tracking error signal X ₀ obtained by the calculated value, the correction tracking error in the same manner as previously described Signal X ₀
With this, the tracking servo is pulled in. In this way, if the light reflectivity of the optical disk 6 or the light intensity of the light emitted from the laser diode 1 is known in advance, the tracking servo can be performed without using the divider 14 for normalizing the difference signal X. It can be reliably pulled into the truck.

[0032]

As described above in detail, in the first invention, the correction tracking error signal is provided with a linear region having a different inclination angle. Therefore, even when the off-track amount is large and the inrush speed of the objective lens is high, the objective lens is not required. Can be reliably drawn into the tracking servo. In the second invention, since the correction tracking error signal is a triangular wave, the land and the groove can be distinguished, and the objective lens can be reliably pulled into the tracking servo.

Further, even if the polarity of the level of the sum signal is inverted in the header portion by the continuous servo, the objective lens does not run away. Therefore, according to the present invention, there is an excellent effect that a tracking servo circuit having high tracking servo pull-in performance can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a conventional tracking servo circuit.

FIG. 2 is a waveform diagram of a sum signal and a difference signal.

FIG. 3 is a waveform diagram of a process of obtaining a correction tracking error signal from a difference signal.

FIG. 4 is a schematic configuration diagram of a tracking servo circuit according to the present invention.

FIG. 5 is a waveform diagram illustrating a process of obtaining a corrected tracking error signal based on a tracking signal and a sum signal.

FIG. 6 is a diagram of a corrected tracking error signal according to the first invention based on a calculated value obtained by calculating sin- ¹ of the tracking error signal.

FIG. 7 is a diagram of another corrected tracking error signal obtained based on the tracking error signal and the sum signal.

FIG. 8 is a diagram of a corrected tracking error signal according to the second invention obtained based on the tracking error signal.

FIG. 9 is an explanatory diagram showing a level change of a sum signal and a correction tracking error signal when a header portion is detected in the continuous servo method.

FIG. 10 is a schematic configuration diagram illustrating another configuration example of the tracking servo circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 3 Half mirror 4 Objective lens 6 Optical disk 7 Tracking actuator 9 Two-segment photodetector 10, 11 amplifier 12 Differential amplifier 13 Addition amplifier 19 Gain control part 30 Operation control circuit

Claims (2)

(57) [Claims] 1. A difference signal and a sum signal of output signals of two photodetectors that receive reflected light from an optical disk passing through an objective lens, and a tracking actuator is driven by a tracking error signal related to the difference signal. do it,
A tracking servo circuit for performing a tracking servo pull-in operation to move the objective lens to a predetermined track, comprising: arithmetic means for calculating sin ^-1 of the tracking error signal, wherein the arithmetic means calculates sin ^-1 of the tracking error signal. And the average level of the sum signal
Obtain a corrected tracking error signal comprising a linear region having a different inclination angle obtained based on the positive or negative position information from, and drive the tracking actuator based on the corrected tracking error signal to move the objective lens to a predetermined track. A tracking servo circuit characterized in that it is configured to move to (1). 2. A tracking actuator is driven by a tracking error signal related to a difference signal between output signals of two photodetectors receiving reflected light from an optical disk passing through an objective lens to move the objective lens to a predetermined track. In a tracking servo circuit that performs a tracking servo pull-in operation to move, a calculating means for calculating sin- ^{1 of the} tracking error signal is provided, and a corrected tracking error signal is calculated by a calculated value obtained by calculating sin- ¹ of the tracking error signal. Get,
A tracking servo circuit configured to drive the tracking actuator by the corrected tracking error signal to move the objective lens to a predetermined track.