JPH0690797B2 - Tracking servo method - 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 device.

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. 27 is a surface view of the recorded information surface side of the disc on which the information signal is recorded. In FIG. 27, 201 is a dent called a pit, 202 is a spot of a main beam of laser light, 203 is a spot of a sub-beam of laser light, 2
04 is the direction in which the disc is moving with respect to the spot due to the rotation of the disc. The recorded information surface of the disk is a mirror surface and reflects the laser light. When the spot is on the pit, the reflected light at the pit portion and the reflected light around the pit interfere with each other to weaken the reflected light amount.
The pits are lined up along the direction 204, but each one of this pit row is called a track, and the direction in which the pits are lined up
204 is called the track direction, and the direction perpendicular to the track on the disk surface is called the tracking direction. The information signal is converted into the pit length P and the pit interval q 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 signal of a tracking servo. The tracking servo means that the spot of the main beam is always on the track, and specifically, it is a control for driving the pickup lens in the tracking direction by the tracking actuator. Hereinafter, simply, the spot means the spot of the main beam.

FIG. 28 is a configuration diagram of a pickup of the optical recording information reproducing apparatus. In FIG. 28, 205 is a pickup lens, 206 is a half prism, 207 is a diffraction grating, 208 is a collimator lens, 209 is a semiconductor laser, 210 is a light receiving lens, and 211 is a cylindrical lens. A lens, 212 is a 6-division photodiode, 2
Reference numeral 13 is a focus actuator and a tracking actuator, 214 is a disk, and 215 is a spindle motor. The wavelength emitted from the semiconductor laser 209 is about 0.8μ
The divergent laser beam of m enters the collimator lens 208,
Here, after being converted into parallel light, it is divided into three beams by the diffraction grating 207, transmitted through the half prism 206, and is a drive mechanism that moves in a direction perpendicular to the disk surface. A focus actuator and a drive mechanism that moves in the tracking direction. It is focused by a pickup lens 205 equipped with a tracking actuator 213 which is 1 μm each on the disc surface.
Connect the spots. When the three spots are reflected on the disc surface, the main beam is diffracted by the pits engraved on the disc surface, and the pickup lens 20
The amount of light collected at 5 is changed, and tracking control information is given to the two sub-beams. The reflected laser light from the disk 214 goes backward through the pickup lens 205, is reflected by the half prism 206, faces right as shown in FIG. 28, is narrowed down by the light receiving lens 210, passes through the cylindrical lens 211, and is divided into six photodiodes 212. Reach

The pickup lens 205 is supported on the pickup housing by a spring called a pickup spring.

FIG. 29 is a waveform diagram of the tracking error signal and the on-track signal. In FIG. 29, the horizontal axis is the position of the spot in the tracking direction, "1" is the high level, "0" is the low level, and the right side is the outer peripheral direction of the disc. 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 on-track signal goes high when the spot is near the track, and when the spot is not near the track,
That is, logic 2 that goes low when it is between tracks
This is a value signal, and when the spot is near the track, the reflected light amount of the spot increases or decreases depending on whether the spot hits the pit or not, and when the spot is between the tracks, the reflected light amount of the spot changes. It is generated by using the phenomenon that it is always large. The polarity of the tracking error signal is correct when the on-track signal is high level, and the polarity of the tracking error signal is inverted when the on-track signal is low level. Moving a spot from the currently playing track to another track is called a track jump.
If the spot is moved too fast in the tracking direction for a track jump, the spot will pass through between the pits more often, and the spot error may occur due to changes in the tracking error signal level or changes in the on-track signal value. It becomes difficult to measure the moving distance in the tracking direction. Therefore, the moving speed of the spot during the track jump must be set so as not to become too high.

FIG. 30 is a waveform diagram of a tracking error signal and an on-track signal. In FIG. 30, the horizontal axis represents time, and the spot moves in the tracking direction toward the outer circumference of the disc with respect to the track. FIG. 31 is a waveform diagram of the tracking error signal and the on-track signal. In FIG. 31, the horizontal axis represents time, and the spot moves in the tracking direction toward the center of the disc. The polarity of the tracking error signal is the same as in Fig. 23 below.The polarity of the signal that drives the tracking actuator, that is, the tracking drive signal, is positive when the spot moves to the outer circumference of the disc, and when the drive is negative, the spot moves. Move to the inner circumference of the disc.

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

FIG. 26 is a block diagram of a conventional tracking servo device. In FIG. 26, 100 is a selector that outputs a signal on the input terminal 101 when the input terminal 103 is at a high level and outputs a signal on the input terminal 102 when the input terminal 103 is at a low level, and 104 is a tracking servo. Reference numeral 105 denotes a tracking actuator, which is a filter for compensating the phase at the gain intersection of the open loop gain and the gain of the servo band.

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

When the on-track signal is high level, the tracking error signal is input to the compensation filter 104 and the tracking servo loop is closed. When the on-track signal is low level, the input of the compensation filter 104 becomes 0, and the tracking servo loop is opened. The tracking error signal shows the correct polarity when the on-track signal is at the high level, but the tracking error shows the opposite polarity when the on-track signal is at the low level. Even if the spot deviates from the track due to eccentricity or the like, the tracking servo is pulled in by the above operation.

Problems to be Solved by the Invention However, in the above-mentioned configuration, since the target track cannot be set, it is not possible to know which track the tracking servo pulls in to match the spot, or when the on-track signal is at a low level. Since the actuator is not driven, there is a problem that the tracking servo pull-in time becomes long.

In order to solve such a point, the present invention provides a tracking servo method in which a tracking servo pulls in a short time so that a spot coincides with a target track.

Means for Solving the Problems In order to solve the above problems, the tracking servo method of the present invention uses a tracking servo loop when optically reproducing a spot on a track showing recording information formed on a recording medium and reproducing the track. The closed state is the 0th state, the state in which the spot is accelerated toward the target track is the 1st state, and the spot is set to the target track so that the relative speed between the spot and the track is within a predetermined range. The second state is a state of accelerating toward the spot, the third state is a state of accelerating the spot to move away from the target track, and the spot is away from the target track by a predetermined distance or more in the zero state. If it detects that the spot is approaching the target track, the first state is set. If it is output, the second state is set. In the second state, if it is detected that the spot is approaching the target track at a predetermined speed or more, the third state is set. In the third state, If it is detected that the spot is moving away from the target track, the first state is set. In the second state, if it is detected that the spot is moving away from the target track, the first state is set. If it is detected that the spot is within a predetermined distance from the target track, and if the relative speed between the spot and the target track is 0, the state is set to the 0th state.

Effect The present invention uses the above method so that the spot moves toward the target track when the spot is about to deviate from the target track, and the relative speed between the spot and the target track becomes appropriate when the spot is moving toward the target track. The tracking servo loop is closed when the spot is near the target track and the relative speed between the target track and the spot is sufficiently small. Therefore, the tracking servo does not pull in so that the spot coincides with other than the target track, and the tracking actuator pulling time is always driven because the tracking actuator that moves the spot toward the target track is driven. It will be short.

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

FIG. 2 is a block diagram of a tracking servo device embodying the tracking servo method in the embodiment of the present invention. In FIG. 2, 1 is an analog-digital converter for converting a tracking error signal into a digital signal, 2 is a servo processor, 3 is a digital-analog converter, and 4 is a tracking actuator.

Figure 1 is a state transition diagram showing the tracking servo method.
In the figure, 5 is the 0th state in which the tracking servo loop is closed, 6 is the first state in which the spot is accelerated to the target track, and 7 is the second state in which the spot is accelerated toward the target track at an appropriate speed. Reference numeral 8 indicates a third state in which the spot is accelerated in the direction opposite to the target track. A program for processing performed by the tracking servo device is included in the servo processor 2, and FIG. 3 is a block diagram showing a part of processing performed by the servo processor 2.

In FIG. 3, reference numeral 9 denotes an input terminal, and a selector for outputting a tracking error signal input to the input terminal 10 when 12 is at a high level, and a signal on the input terminal 11 when the input terminal 12 is at a low level, 13 Is a gain compensation filter that compensates the gain in the servo band of the open loop gain of the tracking servo, 14 is an adder that adds the output of the gain compensation filter 13 and the output of the selector 16 and outputs the tracking drive signal, and 15 is the tracking servo Phase compensation filter that compensates for the phase at the open loop gain intersection point of, 16 is input terminal 17 when input terminal 19 is high level
The selector 20 which outputs the above signal and outputs the brake pulse signal which is input to the input terminal 18 when the input terminal 19 is at the low level is a coefficient unit.

FIG. 4 shows the relationship between the waveform of the tracking error signal, the waveform of the on-track signal, and the measured value of the position counter when the spot is moving in the tracking direction toward the outer circumference of the disc with respect to the track on the disc surface. Is shown. FIG. 5 shows the relationship between the waveform of the tracking error signal, the waveform of the on-track signal, and the measured value of the position counter when the spot is moving in the tracking direction toward the center of the disc with respect to the track on the disc surface. It is shown. 6 to 17 are waveform diagrams of the tracking error signal and the brake pulse signal when the state of the tracking servo device is the second state. First
18 to 25 are waveform diagrams of the tracking error signal and the on-track signal when the spot is moving on the disk surface in the tracking direction. In FIGS. 4 to 25, the horizontal axis represents time, “1” is high level, and “0” is low level. The position counter is a counter that measures how much the spot deviates from the target track, and the brake pulse signal is a signal used to accelerate or decelerate the spot in the tracking direction.

The processing performed by the servo processor will be described below. When the state of the tracking servo device is the 0th state, the spot is pulled into the target track, the tracking servo ON signal is at high level, and the tracking servo loop is closed. When the tracking servo device is in a state other than the 0th state, the tracking servo ON signal is at a low level and the tracking servo loop is open. The position counter is set to 0 when the tracking error signal is negative when the tracking servo device is in the 0th state, and is set to 0 when the tracking error signal is positive when the tracking servo device is in the 0th state. Is set to -1, otherwise, the position counter is incremented by 1 when the sign of the tracking error signal and the on-track signal change as shown in FIG. 18, FIG. 19, FIG. 20 or FIG. When the sign of the tracking error signal and the on-track signal change as shown in FIG. 22, 23, 24, 25, the position counter is decremented by one.

When the state of the tracking servo device is the first state, the brake pulse signal is -B when the measured value of the position counter is 0 or more, and the brake pulse signal is B when the measured value of the position counter is -1 or less. However, B is a sufficiently large positive driving force. Therefore, at this time, the spot is accelerated by a large drive in the tracking direction toward the target track.

When the tracking servo device is in the second state, the time T during which the tracking error signals have the same sign
The following processing is performed according to the length of the.

(1) When T ₂ <T and the measured value of the position counter is 0 or more, as shown in FIGS. 6 and 7, the brake pulse signal is set to −B for time t every time time T ₂ elapses. Otherwise, the brake pulse signal is set to 0, and if the measured value of the position counter is -1 or less, the brake is applied for the time t every time T ₂ elapses as shown in FIGS. 12 and 13. The pulse signal is set to zero.

(2) Figure 8 when the T ₁ <T <T _2, Fig. 9, Figure 14,
The brake pulse signal is set to 0 as shown in FIG.

(3) When T <T ₁ and the measured value of the position counter is 0 or more, immediately after the sign of the tracking error signal is inverted as shown in FIGS. 10 and 11, the brake pulse signal changes to B for the time t. If the measured value of the position counter is set to -1 or less, the brake pulse signal is set to -B for a time t immediately after the sign of the tracking error signal is inverted as shown in Figs. Otherwise, the brake pulse signal is set to 0. However, T ₁ , T ₂
Is a time set so that the relative speed between the spot and the track has an appropriate value, and t is an appropriately set time. Therefore, when the state of the tracking servo device is in the second state, the spot is driven under speed control toward the target track so that T ₁ <T <T ₂ in the tracking direction.

When the tracking servo device is in the third state and the measured value of the position counter is 0 or more, the brake pulse signal is B, and the measured value of the position counter is-.
If it is 1 or less, the brake pulse signal is -B. Therefore, at this time, the spot is accelerated by a large driving force in the tracking direction so as to move away from the target track.

If the on-track signal becomes low level when the state of the tracking servo device is the 0th state, the state of the tracking servo device transits to the first state. When the tracking servo device is in the first state and the measured value of the position counter is 1 or more, the sign of the tracking error signal and the on-track signal are as shown in FIG. 22, FIG. 23, FIG. 24, FIG. If so, the tracking servo device transits to the second state. When the tracking servo device is in the first state and the measured value of the position counter is −2 or less, the sign of the tracking error signal and the on-track signal are shown in FIG. 18, FIG. 19, FIG. 20, FIG. If such a change occurs, the state of the tracking servo device transits to the second state.

If the time during which the tracking error signal has the same sign when the state of the tracking servo device is the second state is shorter than the time T ₀ , the state of the tracking servo device transits to the third state. However, T ₀ <T ₁ <T ₂ .

When the tracking servo device is in the second state or the third state and the measured value of the position counter is 0 or more, the sign of the tracking error signal and the on-track signal are shown in FIG. 18, FIG. 19 or FIG. If it changes as shown in FIG. 21 or FIG. 21, the state of the tracking servo device transits to the first state. If the state of the tracking servo device is the second state or the third state and the sign of the tracking error signal and the on-track signal change as shown in FIG. 22, FIG. 23, FIG. 24, or FIG. The state of the servo device transits to the first state.

If the tracking error signal is increasing when the state of the tracking servo device is the first state and the measured value of the position counter is 0, the state of the tracking servo device transits to the 0th state. If the tracking error signal has decreased when the state of the tracking servo device is the first state and the measured value of the position counter is -1, the state of the tracking servo device transits to the zero state. When the tracking servo device is in the second state or the third state, the measured value of the position counter is −
When changing from 1 to 0 or 0 to -1, the state of the tracking servo device transits to the first state.

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

When the spot starts to move away from the currently reproducing track, that is, the target track in the tracking direction due to vibration of the housing of the optical recording information reproducing apparatus and shock or eccentricity of the disk (disturbance), the state of the tracking servo apparatus becomes first.
Then, the tracking servo loop is opened, and the spot is accelerated toward the target track with a large driving force in the tracking direction. When the acceleration force at that time is larger than the disturbance or when the disturbance disappears, the spot starts to approach the target track in the tracking direction, and the state of the tracking servo device becomes the second state. When the tracking servo device is in the second state, speed control is performed such that the time T during which the tracking error signals have the same sign is T ₁ <T <T ₂ , and the spot is accelerated in the tracking direction toward the target track. . At that time, when the spot is excessively accelerated in the tracking direction toward the target track due to the influence of the disturbance, and the time T when the tracking error signals have the same sign becomes T <T ₀ , the state of the tracking servo device becomes the third state. . When the tracking servo device is in the third state, it is accelerated by a large driving force so as to move away from the target track in the tracking direction. When the acceleration force at that time is larger than the disturbance or when the disturbance disappears, the spot begins to move away from the target track in the tracking direction, and the state of the tracking servo device becomes the first state. The state of the tracking servo device becomes the first state when the spot passes the target track when the state of the tracking servo device is the second state. When the tracking servo device is in the first state and the spot is in the vicinity of the target track and the spot begins to approach the target track in the tracking direction, the tracking servo device is in the zero state and the tracking servo The loop is closed and the tracking servo pulls in.

The position counter measures how much the spot deviates from the target track, and whether the spot moves in the tracking direction relative to the track depends on whether the measured value of the position counter is increasing or decreasing. It is judged by whether it is.

To describe the above operation more simply, when the spot is moving away from the target track, the spot is accelerated by a large drive so that it approaches the target track, and when the spot is approaching the target track, the approach speed is an appropriate speed. That is, the spot is accelerated and decelerated so that the tracking servo loop is closed when the spot is near the target track and the relative speed between the spot and the target track is small. A brake pulse signal is input to the gain compensation filter 13 when the tracking servo loop is opened so that the gain compensation filter 13 has an appropriate value when the tracking servo loop is closed. As the tracking servo device operates as described above, the tracking servo stably pulls into the target track in an extremely short time.

In the above description, the sign of the tracking error signal and the on-track signal are assumed to change only one by one, but when both change at the same time, the purpose depends on how much one of the two has changed before the change occurs. The direction in which the spot is moving relative to the track shall be determined and the position counter shall be updated accordingly.

EFFECTS OF THE INVENTION As described above, according to the present invention, even if the spot deviates from the target track due to the vibration of the optical recording information reproducing apparatus housing, shock, eccentricity of the disk, etc., the spot does not deviate one track stably in a short time. Can be pulled into the target track, and a so-called track jump for moving the spot from the currently playing track to another track can be realized very easily by changing the target track, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a state transition diagram of a tracking servo device according to an embodiment of the present invention, FIG. 2 is a block diagram of the tracking servo device, and FIG. 3 shows a part of contents processed by the servo processor of FIG. A block diagram expressed, FIG. 4 is a relationship diagram showing the waveform of the tracking error signal, the waveform of the on-track signal, and the measurement value of the position counter, and FIG. 5 is the waveform of the tracking error signal, the waveform of the on-track signal, and the position counter. 6 to 17 are waveform diagrams of the tracking error signal and the brake pulse signal, and FIGS. 18 to 25 are waveform diagrams of the tracking error signal and the on-track signal, FIG. 26. Is a block diagram of a conventional tracking servo device, FIG. 27 is a disk surface view of an optical recording / reproducing device, and FIG. 28 is a pitch of the optical recording / reproducing device. Diagram of the up, Figure 29, the 30
FIG. 31 is a waveform diagram of the tracking error signal and the on-track signal. 1 ... Analog-digital converter, 2 ... servo processor, 3 ... digital-analog converter, 4 ... tracking actuator, 5 ... 0 state, 6 ... first state, 7 ... second State, 8 ... third state, 9 ... selector, 13 ... gain compensation filter, 14 ... adder, 15 ...
… Phase compensation filter, 16 …… Selector, 20 …… Coefficient unit,
100 …… selector, 201 …… pit, 202 …… main spot, 203 …… sub spot, 204 …… disc rotation direction, 205 …… pickup lens, 206 …… half prism, 207 …… diffraction grating plate, 208 ...... Collimator lens, 20
9 …… Semiconductor laser, 210 …… Light receiving lens, 211 …… Cylindrical lens, 212 …… Six-half photo diode, 213
...... Focus and tracking actuator, 214 ...
… Disk, 215… Spindle motor.

Claims (5)

[Claims] 1. When optically reproducing a spot by irradiating a track showing recording information formed on a recording medium, a state in which a tracking servo loop is closed is defined as a 0th state, and the spot is directed toward a target track. A state of accelerating is referred to as a first state, a state of accelerating the spot toward the target track is set as a second state so that a relative speed between the spot and the track is within a predetermined range, and the spot is the target track. When the third state is a state of accelerating so as to move away from the target track, in the 0th state, when it is detected that the spot is more than a predetermined distance from the target track, the first state is set and the first state is set. At this time, if it is detected that the spot is approaching the target track, the second state is set. In the second state, the spot is moved to the target track. If it is detected that the spot is approaching the target track at a predetermined speed or more, the third state is set. In the third state, if it is detected that the spot is moving away from the target track, the first state is set. In the state of 1), if it is detected that the spot is moving away from the target track, it is set to the 1st state. In the 1st state, it is detected that the spot is within a predetermined distance from the target track. A tracking servo method in which the state is set to the 0th state when it is detected that the relative speed between the target track and the target track is 0. 2. A counter having a value that increases or decreases according to a change in the sign of the tracking error signal and a change in the signal value of the on-track signal, which determines the position of the spot in the tracking direction on the disk and increases the value. The direction of movement of the spot in the tracking direction on the disc is determined by whether the tracking error signal is increasing or decreasing, or when the tracking error signal changes from decreasing to increasing or decreasing to increasing. A tracking servo method that determines that the relative speed with respect to is 0. 3. A filter for generating a low-frequency component of a tracking drive signal, wherein a signal for accelerating and decelerating a spot in a tracking direction with respect to a target track is input to the filter when the state is not the 0th state. Item 2. The tracking servo method according to Item 1. 4. The tracking servo method according to claim 1, wherein the relative speed between the spot and the track is detected by measuring the time from when the sign of the tracking error signal is inverted to when the sign is next inverted. 5. When the sign change of the tracking error signal and the change of the signal value of the on-track signal occur at the same time, how much time past the sign change of the tracking error signal or the change of the signal value of the on-track signal before the change occurs The direction of movement of the spot in the tracking direction on the disc is determined depending on whether it has occurred.
The tracking servo method described.