JPH0778892B2 - Tracking servo method and tracking servo device - Google Patents

Description

The present invention relates to an apparatus for optically reproducing recorded information recorded on a disc, such as a compact disc (CD) player and a video disc player, so-called optical recorded information. The present invention relates to a tracking servo method for a reproducing apparatus and the apparatus thereof.

2. Description of the Related Art First, an outline of an optical recording information reproducing apparatus will be described below with reference to the drawings.

FIG. 6 is a plan view of the recorded information surface of the disc on which the information signal is recorded. In FIG. 6, 610 is a pit called a pit, 620 is the spot of the main beam of laser light, 630 is the spot of the sub-beam of laser light, and 640 is the disc moving relative to the pickup lens for rotation of the disc. It is in the direction of being. The recorded information surface of the disk is a mirror surface and reflects the laser light. The elliptical pit is dented so that the amount of reflected light when there is a spot of laser light in the vicinity is weakened by the interference effect of the reflected light here and the reflected light around the pit. direction
The pits are lined up along the 640. Each of the pit rows is called a track, the direction in which the pits are lined is called the track direction, and the direction perpendicular to the track is called the tracking direction. The information signal is modulated on the pit length and the interval between the pits and recorded on the disc. The main beam is used to read an information signal, and the sub beam is used to generate a tracking error signal which is a servo error of a tracking servo. Tracking servo is control for driving the pickup lens in the tracking direction so that the main beam spot is always on the track.

FIG. 7 is a configuration diagram of a pickup of the optical recording information reproducing apparatus. In FIG. 7, 710 is a pickup lens, 711 is a half prism, 712 is a diffraction grating, 713 is a collimator lens, 714 is a semiconductor laser, 715 is a light receiving lens,
716 is a cylindrical lens, 717 is a 6-division photodiode, 718 is a focus actuator and a tracking actuator, 719 is a turntable motor, and 720 is a disk. Wavelength emitted from semiconductor laser 714 is about 0.8 μm
The divergent laser light enters the collimator lens 713, is converted into parallel light here, is then divided into three beams by the diffraction grating 712, is transmitted through the half prism 711, and is in the direction perpendicular to the disk surface, that is, the focus direction. It is focused by a pickup lens 710 equipped with a focus actuator which is a driving mechanism that moves in the tracking direction and a tracking actuator 718 which is a driving mechanism which moves in the tracking direction, and each forms three spots of about 1 μm on the disk surface. When the three spots are reflected on the disc surface, the main beam is diffracted by the pits engraved on the disc surface to change the amount of light collected by the pickup lens 710, and the two sub-beams are tracked. Control information is given. The reflected laser light from the disk 720 goes backwards through the pickup lens 710, and the half prism 7
The light is reflected by 11 and goes to the light receiving lens 715 as shown in FIG. 7, and the reflected light is narrowed down by the light receiving lens 715, passes through the cylindrical lens 716, and reaches the 6-division photodiode 717. The pickup lens 710 is supported on the pickup housing by a spring called a pickup spring.

FIG. 8 is a block diagram of the main part of the recorded information reproducing apparatus. In FIG. 8, reference numeral 810 is a disk, 820 is a laser beam, 830 is a pickup including the pickup lens 710 shown in FIG. 7, 840 is a traverse stand, 850 is a housing of the recorded information reproducing apparatus, and 860 is a turntable motor. . The focus error signal is a signal indicating how much the distance between the disc and the pickup lens deviates from the focal length of the pickup lens, and is used as a servo error signal for focus servo. The tracking error signal is a signal indicating how much the position of the main beam spot (hereinafter referred to as the position of the pickup lens) deviates in the tracking direction with respect to the track, and is used as a servo error signal for tracking servo. The focus drive signal is a signal that drives the pickup lens in the direction perpendicular to the disc, the tracking drive signal is a signal that drives the pickup lens in the tracking direction, and the traverse drive signal is the traverse table in the tracking direction (the disc radial direction). Is a signal to drive to. Disc 8 by turntable motor 860
10 rotates almost along the track (in the track direction).

FIG. 9 is a waveform diagram of the tracking error signal and the on-track signal, and the horizontal axis represents the position of the pickup lens in the tracking direction with respect to the track. The tracking error signal is generated by converting the reflected light amounts of the two sub-beams into electric quantities by the photodiodes and taking the difference between the two. The off-track signal is a logical binary signal that distinguishes whether the main beam (pickup lens) is near the track or between the tracks. When the main beam is near the track, the reflected light amount of the main beam becomes small. It is generated by utilizing the phenomenon that the reflected light amount of the main beam is always large when the main beam is between the tracks. When the main beam is near the track, the reflected light amount of the main beam increases or decreases because when the main spot includes the pit, the reflected light at the pit and the reflected light around the pit interfere with each other. The amount of light reflected from the main spot becomes smaller,
This is because when the main spot does not include a pit, the reflected lights do not interfere with each other and the reflected light amount of the main spot increases. Below, when the main spot is near the track, the pickup lens is said to be in the on-track state. The on-track signal is at high level "1", and when the main spot is between tracks, the pickup lens is in the off-track state. Yes, the on-track signal is low level “0”. Moving the main spot (pickup lens) to another track (target track) is called track jump. The track jump is performed by changing the extension amount of the pickup spring in the tracking direction when the moving distance is short. When the distance is long, the traverse table is moved in the tracking direction. The movement distance of the pickup lens during a track jump is often measured by the number of sign inversions (zero crosses) of the tracking error signal when the pickup lens is in the on-track state. As the number of people passing between pits increases,
The tracking error signal becomes incorrect and it becomes difficult to measure the moving distance of the pickup lens. Therefore, the movement speed of the pickup lens during the track jump must be prevented from becoming too high.

An example of the conventional tracking servo device described above will be described below with reference to the drawings.

FIG. 3 is a block diagram of a conventional tracking servo device. In FIG. 3, 310 is a low-pass filter that compensates the low-pass gain of the tracking servo open-loop gain, and 320 is the phase compensation so that the phase near the gain intersection point of the tracking servo open-loop gain is not delayed by 180 ° or more. A high-pass filter, 330 is an adder that adds the signals on the two input terminals and outputs the result on the output terminal, and 340 is a high-level "1" signal on the input terminal 343.
Is a selector that outputs the signal on the input terminal 341 to the output terminal, and outputs the signal on the input terminal 342 to the output terminal when the signal on the input terminal 343 is low level “0”. When the upper signal is high level "1", the signal on input terminal 351 is output to the output terminal, and when the signal on input terminal 353 is low level "0", input terminal 3
The selector that outputs the signal on 52 to the output terminal, JPC is high level "1" when tracking servo is applied.
Is a logic binary signal which is set to low level "0" during track jump.

A detailed block diagram of an example of the low pass filter 310 of FIG. 3 is shown in FIG. In FIG. 4, 410 and 420 are operational amplifiers, 412, 421 and 422 are resistors having a resistance value R, and 411 is a capacitance C.
Is the capacitor. A detailed block diagram of an example of the high pass filter 320 of FIG. 3 is shown in FIG. In FIG. 5, 510 is a delay device, 520 is a coefficient device having a coefficient value C ₀ , 530 is a coefficient device having a coefficient value −C ₁ , and 540 is an addition for outputting the sum of the signals on the two input terminals to the output terminals. It is a container, and 0 <C ₀ and 0 <C ₁ .

The operation of the tracking servo device configured as described above will be described below.

If JPC = "1", the output of the selector 340 becomes the tracking error signal, and the output of the selector 350 becomes the output signal of the high-pass filter 320, so the tracking servo loop is closed and the low-pass gain of the open loop gain. And the phase at the gain intersection point are compensated, and tracking servo is applied. When doing a track jump
JPC = "0", the pickup lens is accelerated and decelerated by the track jump signal, and the pickup lens is moved to the target track. Acceleration / deceleration at this time is performed so that the relative speed between the track and the pickup lens is within an appropriate range. When JPC = "0", the input terminal of the low-pass filter 310 becomes 0 (ground), and the output of the selector 350 becomes a track jump signal. Therefore, during the track jump, the signal of the sum of the output of the low-pass filter 310 with the input terminal set to 0 and the track jump signal becomes the tracking drive signal, but the output of the low-pass filter 310 immediately before the start of the track jump. It becomes a force for holding the extension of the pickup spring in the tracking direction, and the track jump signal becomes a driving force for moving the pickup lens to the target track at an appropriate speed.

However, in the conventional configuration as described above, only 0 is input to the input terminal of the low-pass filter 310 during the track jump, so that the track jump operation or the eccentricity of the disk causes a problem. When the pickup lens moves and the extension amount of the pickup spring changes significantly, the force due to the output of the low-pass filter 310 is significantly different from the force that must be applied to the pickup lens to hold the extension amount of the pickup spring. There is a problem in that the track jump operation becomes unstable, or the tracking servo pull-in becomes unstable when the track jump operation ends and the tracking servo is applied.

The above problems will be described in more detail below with reference to the drawings.

FIG. 10 is a waveform diagram showing the operation of the above-mentioned conventional example. First
In Fig. 10, the horizontal axis represents time and the vertical axis represents amplitude.
A is a tracking error signal, B is a drive signal for driving the tracking actuator, and C is the extension amount of the pickup spring in the tracking direction. Time t ₀ is the time immediately before the start of the track jump, and the tracking servo is closed until time t ₀ for all of A, B, and C (jpc.
= 1), and a state (jpc = 0) in which a track jump is performed after the time t ₀ . In FIG. 10B, a is the output of the low-pass filter 310, b is the output of the high-pass filter 320, and V is the track jump signal for extending the pickup spring. In the state where the tracking servo is closed, Low pass filter 310
Output a of the high pass filter 320 and the output b of the high pass filter 320 are added to drive the tracking actuator, and when the track jump is performed, the output a of the low pass filter 310 and the track jump signal V are added to operate the tracking actuator. To drive.

Here, in general, the following relationship is established between the spring extension amount X and the restoring force F.

F = −k × X (k is a spring constant) That is, in order to keep the extension amount of the pickup spring at X, a driving force −F (= k) that balances the restoring force F with the opposite polarity.
XX) must be applied to the actuator.

When the tracking servo is closed, the pickup spring needs to be held in a state of being extended to some extent in the tracking direction in order to compensate the influence of the tracking error of the traverse servo and the eccentricity of the disk. Now, assuming that the amount of elongation required at the time t ₀ is X ₀ , the corresponding restoring force −k × X ₀ works, but the driving force k balanced with this is the reverse polarity.
By being supplied from the output of the × X ₀ low-pass filter 310, the required extension amount of the pickup spring is maintained.

When performing a track jump, the output a of the low pass filter 310 is first held at k × X ₀ . As a result, the extension amount of the pickup spring is also held at X ₀ . Here, if a track jump is performed in the direction in which the spring is extended, the track jump signal V is added to the output a of the low pass filter 310 as shown in B of FIG. As a result, in the case of a few track jumps, the pickup lens can be slightly moved in the tracking direction to perform a stable track jump operation. However, as the number of jumps increases, the amount of movement of the pickup lens in the tracking direction increases, and the amount of expansion of the pickup spring also increases significantly as shown in C of FIG. When the track pitch is 1.6 μm, the extension amount X ₁ of the pickup spring when N track jumps are expressed as follows.

X ₁ = X ₀ + ΔX (ΔX = N × 1.6 μm) The driving force required to hold the extension amount X ₁ of the pickup spring at this time is expressed as follows.

F = k × X ₁ = k × (X ₀ + ΔX) = k × X ₀ + k × ΔX Here, since the output a of the low-pass filter 310 holds k × X ₀ , the change in the amount of spring extension is changed. The driving force balanced with the restoring force k × ΔX corresponding to the amount ΔX is insufficient, and the force acts in the direction in which the pickup spring contracts as a total. This will help reduce the track jump speed. That is, as the number of track jumps increases, the restoring force k × ΔX of the pickup spring increases, and even if the track jump signal V is added, the pickup lens becomes difficult to move in the tracking direction, and the stability of the operation deteriorates. At the same time, the stability of the servo pull-in operation when the track jump ends and the tracking servo is closed also deteriorates.

In view of the above problems, the present invention does not make the track jump operation unstable even if the extension amount of the pickup spring changes due to the track jump operation or the eccentricity of the disk.
Further, the present invention provides a tracking servo method and an apparatus thereof in which pulling of the tracking servo does not become unstable when the track jump operation is terminated and the tracking servo is started.

Means for Solving the Problems In order to solve the above problems, the present invention, when performing a track jump, outputs a signal proportional to the track jump signal to a low pass filter that compensates for a low pass gain in a tracking servo loop. The tracking actuator is driven by the sum of the track jump signal and the output signal of the low-pass filter that is input.

Effect In the present invention, since a signal proportional to the track jump signal is input to the low-pass filter, even if the extension amount of the pickup spring changes due to the track jump operation or the eccentricity of the disk, the low-pass filter responds to the change. The output of the filter becomes an appropriate value, the track jump operation is not unstable, and the tracking servo pull-in after the track jump operation is not unstable.

Embodiment A tracking servo device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a tracking servo device according to an embodiment of the present invention. In FIG.
110 is a low-pass filter that compensates the low-pass gain of the tracking servo open loop gain, and 120 is a high-pass filter that compensates the phase so that the phase near the gain intersection point of the tracking servo open loop gain is not delayed by 180 ° or more. 130 is an adder that adds the signals on the two input terminals and outputs the result on the output terminal. 140 is the signal on the input terminal 141 on the output terminal when the signal on the input terminal 143 is at high level H "1". And a signal on the input terminal 143 is low level L “0”, the signal on the input terminal 142 is output on the output terminal. Sometimes the signal on the input terminal 151 is output on the output terminal, and the signal on the input terminal 153 is low level L.
A selector that outputs the signal on the input terminal 152 to the output terminal when it is "0", a coefficient unit 160, a high level "1" when the JPC is tracking servo, and a low level when the track jump is performed It is a logical binary signal that makes it "0". FIG. 2 is a waveform diagram of the tracking error signal, the on-track signal and the track jump signal during the track jump.

In FIG. 2, the horizontal axis represents time, and the pickup lens is in the process of moving toward the target track in the outer peripheral direction of the disc. The pickup lens sets the time interval from the time when the tracking error signal changes from positive to negative in the on-track state to the time when the tracking error signal changes from positive to negative in the next on-track state.
It is assumed that the time required to move the truck is T, and this time interval is T.

If T ₂ <T, the track jump signal is set to V and the pickup lens is accelerated toward the outer periphery of the disk for a time τ immediately after the measurement of T is completed.

If T <T ₁ , immediately after the measurement of T is completed, the pickup lens is decelerated toward the outer circumference of the disk (accelerated toward the inner circumference of the disk) by setting the track jump signal to −V for a time τ.

If T ₁ <T <T ₂ , immediately after the measurement of T is finished, the track jump signal is set to 0 for a time τ and the pickup lens is not accelerated or decelerated toward the outer circumference. After a lapse of time τ from immediately after T is measured, the track jump signal is set to 0 and the pickup lens is not accelerated or decelerated until the next measurement of T is completed.

Note that T ₁ and T ₂ are times, T ₁ is set to a time longer than the time required to measure the pickup lens moving distance by the tracking error signal and the on-track signal, and T ₂ is set to be slightly larger than T _1. There is.

The operation of the tracking servo device configured as described above will be described below with reference to FIGS. 1 and 2.

Since JPC is at the high level when the track jump operation is not performed, the output of the selector 140 becomes the tracking error signal and the output of the selector 150 becomes the output signal of the high pass filter. Therefore, at this time, the tracking servo loop is closed, the low pass gain of the servo loop is compensated by the low pass filter 110, the phase compensation is performed at the gain intersection point of the servo loop by the high pass filter 120, and the tracking servo is stably applied. .

Since JPC is at the low level during the track jump operation, the output of the selector 140 becomes the output signal of the coefficient unit 160, and the output of the selector 150 becomes the track jump signal. At this time, the tracking drive signal is the sum of the output signal of the low-pass filter 110 and the track jump signal, but the output signal of the low-pass filter 110 becomes a component that holds the extension amount of the pickup spring in the tracking direction, and the track jump The signal becomes a component that moves the pickup lens toward the target track at a speed within a predetermined range. When the pickup lens is the speed of moving toward the target track in which the time for one track movement is T, it is the rate at which satisfy T ₁ <T <T _2. By the movement of the pickup lens and the movement of the track due to the eccentricity of the disc, every moment,
The expansion amount of the pickup spring changes, but since the signal proportional to the track jump signal is input to the low-pass filter 110, the output of the low-pass filter 110 also changes according to the change in the expansion amount of the pickup spring. To do. That is, as a result of the speed control of the pickup, when the frequency of accelerating and decelerating the pickup lens toward the target track is different, the output of the low-pass filter 110 is automatically adjusted so that the frequencies of both are equal, As a result, the output of the low-pass filter 110 becomes suitable for the extension amount of the pickup spring.

The operation of this embodiment will be described below in more detail with reference to the drawings.

FIG. 11 is a second waveform diagram showing the operation of this embodiment. First
In FIG. 11, the horizontal axis represents time and the vertical axis represents amplitude.
A, B, C, and t ₀ are the same as those described in FIG. 10 of the waveform diagram showing the operation of the conventional example, and therefore the description thereof will be omitted.

In FIG. 11B, a is the output of the low-pass filter 110, b is the output of the high-pass filter 120, V is the track jump signal for extending the pickup spring, and -V.
Is a track jump signal in the direction of contracting the pickup spring, and τ is a predetermined time for adding the track jump signals V and -V. When the tracking servo is closed, the output a of the low-pass filter 110 and the output b of the high-pass filter 120 are added to drive the tracking actuator, and when the track jump is performed, the output of the low-pass filter 110. A is added to the track jump signal V or -V to drive the tracking actuator. In A of FIG. 11, each of T _{01 to} T ₀₅ is a time interval of rising 0 cross points of the tracking error signal, and shows a time required to move a distance of 1 track.

The operation when the tracking servo is closed is the same as that of the conventional example described with reference to FIG.

When performing the track jump, the output a of the low pass filter 110 is first held at k × X ₀ . As a result, the extension amount of the pickup spring is also held at X ₀ . The operation up to this point is similar to that of the conventional example.

Here, assuming that the track jump operation is performed in the direction in which the pickup spring extends, first, the low-pass filter 110
The track jump signal V is added to the output a of the above for a predetermined time τ. Next, the time interval (T _{01 to} T ₀₆ ) of the rising 0 cross point of the tracking error signal is measured. In FIG. 11B, since T ₀₁ > T ₂ and T ₀₂ > ₂ , the track jump signal V is added for a predetermined time τ immediately after the measurement of T ₀₁ and T ₀₂ is finished. At this time, since the lens moves in the direction in which the pickup spring expands every time one track jumps, the restoring force of the pickup spring increases accordingly. However, every time the track jump signal V is added, a value proportional to the track jump signal V is added to the input of the low pass filter 110, so that the output a of the held low pass filter 110 gradually increases. . As a result, it is possible to generate a driving force having a polarity opposite to that of the increased restoring force and hold the amount of extension of the spring.

At this time, when the absolute value of the output a of the low-pass filter 110 is smaller than the absolute value of the restoring force of the spring, a force acts in the direction in which the pickup spring contracts as a whole, so that the track jump speed decreases. Then, since it takes a long time to move the distance of one track, T ₀₁ > T ₂ , T ₀₂ > ₂ , T ₀₃ > T ₂ as shown in B of FIG. Since a value proportional to the track jump signal V is added to the input of the low pass filter 110, the output a of the low pass filter 110 automatically increases until it is balanced with the restoring force of the spring.

When the absolute value of the output a of the low-pass filter 110 is larger than the absolute value of the restoring force of the spring, the force acts in the direction in which the pickup is extended as a whole, so that the track jump speed is increased. Then, since the time required to move the distance of one track becomes short, T ₀₄ <T ₁ as shown in FIG. 11B, and each track jump is proportional to the negative track jump signal −V. Since the value is added to the low pass filter input, the output a of the low pass filter 110 will automatically decrease until it balances the restoring force of the spring.

When the absolute value of the restoring force of the spring is equal to the absolute value of the output a of the low-pass filter 110, that is, when the driving force of the output a of the low-pass filter 110 is balanced with the restoring force of the spring, the pickup spring is Since it is properly held in that position, the track jump speed is almost constant. Then, since the time required to move the distance of one track is almost constant, T ₁ <T ₀₅ <T ₂ as shown in B of FIG. 11, and the value proportional to the track jump signal is low. Since it is not added to the input of the low pass filter, the output a of the low pass filter 110 is held in that state.

That is, during the track jump operation, the driving force that always balances with the restoring force of the pickup spring is supplied by the output a of the low-pass filter 110. This is not limited to the movement of the pickup lens due to the track jump operation, and the same operation is guaranteed when the extension amount of the pickup spring changes due to the movement of the track due to the eccentricity of the disk.

As described above, according to this embodiment, during the track jump, the proportional component of the track jump signal is passed through the low pass filter 11
By inputting 0, the output signal of the low pass filter 110 becomes an appropriate value even during the track jump, and when the moving distance of the track jump is long, the eccentricity of the disk is large and the track vibrates greatly in the tracking direction. Even in this case, the track jump can be performed stably.

EFFECTS OF THE INVENTION As described above, by slightly modifying the conventional method, the present invention is stable even when reproducing a disc having a large eccentric amount and performing a track jump having a large moving distance. It can perform track jumps and is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a block diagram of a tracking servo device according to an embodiment of the present invention, and FIG. 2 is a waveform of a tracking error signal, an on-track signal, and a track jump signal during a track jump for explaining the operation of the tracking servo device. FIG. 3 is a block diagram of a conventional tracking servo device, FIG. 4 is a block diagram of a low-pass filter which is a component of FIG. 3, and FIG. 5 is a high-pass filter which is a component of FIG. FIG. 6 is a block diagram of a filter, FIG. 6 is a plan view of a disc, FIG. 7 is a configuration diagram of a pickup of an optical recording information reproducing apparatus, FIG. 8 is a configuration diagram of a main part of the optical recording information reproducing apparatus, and FIG. Is a waveform diagram of a tracking error signal and an on-track signal, FIG. 10 is a waveform diagram for explaining the operation of a conventional tracking servo device, and FIG. 11 is an operation of one embodiment of the present invention. It is a 2nd waveform diagram for explaining. 110 …… Low-pass filter, 120 …… High-pass filter,
130 …… adder, 140,150 …… selector, 160 …… coefficient multiplier, 710 …… pickup lens, 711 …… half prism, 712 …… diffraction grating, 713 …… collimator lens, 714
...... Semiconductor laser, 715 …… Receiving lens, 716 …… Cylindrical lens, 717 …… 6-division photodiode, 718…
… Drive system, 719 …… Turntable motor, 720 …… Disk, 810 …… Disk, 820 …… Laser light, 830 …… Pickup, 840 …… Traverse stand, 850 …… Recording information reproducing device housing, 860… … A turntable motor.

Claims (4)

[Claims] 1. A low-pass filter for compensating the open loop low-pass gain of a tracking servo, and a high-pass filter for compensating the phase so that the phase near the gain intersection of the open-loop gain is not delayed by 180 degrees or more. A tracking error signal is input to the low-pass filter and the high-pass filter when the tracking servo is applied, and a signal of the sum of the output signal of the low-pass filter and the output signal of the high-pass filter When the tracking actuator is driven by and the track jump is performed, a signal proportional to the track jump signal is input to the low pass filter, and tracking is performed by the sum signal of the track jump signal and the output signal of the low pass filter. Tracking servo method to drive the actuator. 2. The tracking servo method according to claim 1, wherein the track jump signal is generated so that the relative speed between the track and the pickup lens is within a predetermined range. 3. When T ₁ and T ₂ are set to predetermined times, and when the time required for the pickup lens to move a distance of one track is T ₂ or more, the pickup lens is accelerated toward a target track, 2. The tracking servo method according to claim 1, wherein a track jump signal is generated so as to decelerate the pickup lens toward a target track when the time required for the pickup lens to move a distance of one track is T ₁ or less. 4. A low pass filter for compensating a low band gain of an open loop gain of a tracking servo, and a high pass filter for compensating a phase of the open loop gain in the vicinity of a gain intersection point by 180 degrees or more. When,
First selecting means for selecting either the track jump signal or the output signal of the high-pass filter, a coefficient multiplier for multiplying the track jump signal by a predetermined coefficient, a tracking error signal or the coefficient multiplier. Select
A second selecting means for outputting to the low pass filter; and an adder for adding the output of the low pass filter and the output of the first selecting means, and when the track jump is performed, the first selecting means The tracking servo device configured to output the track jump signal to the adder, and the second selection means to output the output of the coefficient unit to the adder.