JP4048060B2 - Optical disc apparatus and optical disc reproducing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc reproduction technique for reproducing information on an optical disc using an optical pickup.
[0002]
[Prior art]
As peripheral devices for personal computers, optical disk devices such as CD-ROMs, CD-R / RW drives, DVD-ROMs, and DVD-RAM drives are widely used. An optical disc device rotates an optical disc on which an information signal is recorded by a spindle motor, irradiates a signal recording surface with a light beam, converts reflected light from the signal recording surface into an electrical signal by a detector, and uses a signal processing circuit. An optical disk recording information signal is obtained. At this time, the actuator for driving the objective lens is driven in a direction perpendicular to the optical disk (focus direction) and in a radial direction (tracking direction) with respect to the disk.
[0003]
In an optical disk apparatus, it is necessary to control an actuator in a focus direction and a tracking direction with high accuracy with respect to a disk recording surface in order to read data recorded on the disk. Therefore, a focus error signal and tracking error signal are generated from the output signal of the optical pickup by a signal processing circuit, an actuator control signal is output by a servo circuit having a phase compensation filter for stabilizing servo operation, and an actuator is driven by a power amplifier. A servo loop is formed by generating a signal.
[0004]
In the servo loop, the servo gain adjustment circuit provided in the servo circuit absorbs the optical variation of the optical pickup, the variation of the output signal of the optical pickup by various discs, and the sensitivity variation of the actuator, so that the servo loop becomes a stable servo loop. Adjust the gain.
The necessary gain of this servo loop is calculated based on the disc standard, spindle motor axis deviation, turntable runout and other mechanical variations, disc rotation frequency, etc. If it is a focus servo loop, the disc runout, disc In consideration of the maximum standard amount of warpage and the maximum turntable shake amount, the servo loop gain is set at the disk rotation frequency so as to suppress the variation in the focus direction within the defocus that allows data reading. Also in the tracking servo loop, the servo loop is configured by setting the servo gain that suppresses within the required deviation at the disk rotation frequency in consideration of the maximum eccentricity of the disk and the maximum eccentricity of the turntable.
[0005]
[Problems to be solved by the invention]
By the way, when the optical disk is rotated at a high speed, the actuator control signal waveform may be a signal in which a high-frequency signal is superimposed on a normal error signal (hereinafter, this high-frequency signal is referred to as actuator signal distortion). This actuator control signal distortion is schematically shown in FIG.
FIG. 5 is a characteristic diagram showing actuator signal distortion, FIG. 5 (a) is a characteristic chart showing a state in which actuator control signal distortion is superimposed on an error signal, and FIGS. 5 (b) to 5 (f) are spindle motors. It is a characteristic view which shows the actuator signal distortion superimposed on the error signal for every rotation speed.
[0006]
In FIG. 5A, reference numeral 501 denotes an error signal, and reference numeral 502 denotes an actuator control signal distortion superimposed on the error signal. Reference numeral 503 denotes the maximum error signal value, and reference numeral 504 denotes the minimum error signal value. FIG. 5B shows a case where the rotation speed of the spindle motor is 1500 r / m, and the actuator control signal distortion is not superimposed on the error signal 501a. FIG. 5C shows a case where the rotation speed of the spindle motor is 2500 r / m, and the actuator control signal distortion is not superimposed on the error signal 501b. FIG. 5D shows a case where the rotational speed of the spindle motor is 5000 r / m, and an actuator control signal distortion 502c having a small amplitude is superimposed on the error signal 501c. FIG. 5E shows a case where the rotation speed of the spindle motor is 7500 r / m, and an actuator control signal distortion 502d having a large amplitude is superimposed on the error signal 501d. FIG. 5F shows a case where the rotation speed of the spindle motor is 10,000 r / m, and an actuator control signal distortion 502e having a large amplitude is superimposed on the error signal 501e. Note that 503a to 503e indicate maximum error signal values, and 504a to 504e indicate minimum error signal values.
[0007]
As shown in FIG. 5, the actuator control signal distortion 502 increases the frequency of superimposition and the signal level as the rotation of the optical disk increases. This actuator control signal distortion 502 occurs in a high frequency band that cannot be suppressed by the servo loop set as described above, destabilizes the actuator operation, deteriorates the error rate of the optical disk read data, and further causes the servo to shift. There is a problem and the data reading speed is deteriorated.
[0008]
Therefore, in order to suppress the actuator control signal distortion by the servo loop, it is necessary to set the servo loop gain excessively and to set the servo loop gain up to a high frequency. However, depending on the sensitivity of the actuator and the dynamic range of the servo processing circuit, there is a limit to setting a stable servo loop setting up to a high frequency band. Further, setting the servo loop gain excessively leads to an increase in power consumption of the actuator control system, and raises the temperature of the entire optical disc apparatus.
[0009]
Actuator control signal distortion caused by high-speed rotation of the optical disk may cause servo misalignment. As a result, refocus processing, retracking processing, and read retry processing are performed, which significantly reduces the data reading speed. There is a problem that.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disc reproduction technique that enables stable reading of optical disc information by monitoring actuator servo control signal distortion and performing processing so as to reduce the actuator servo control signal distortion. is there.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, a high-frequency signal (actuator control signal distortion) superimposed on an actuator control signal is monitored, and based on the result, the rotational speed or servo loop characteristics of the optical disk are controlled.
[0012]
The actuator signal distortion can be monitored by detecting the amplitude of the actuator control signal and comparing whether the amplitude is larger or smaller than a predetermined amplitude value. Alternatively, it can be implemented by counting the number of signal components larger than a predetermined amplitude value.
[0013]
Further, according to the present invention, the optical disc reproducing method includes a step of detecting a focus error signal and a tracking error signal, and when the focus error signal or the tracking error signal exceeds a predetermined value, the rotation speed of the spindle motor is decreased. Steps.
[0014]
Alternatively, the optical disc reproducing method includes a step of detecting a focus error signal and a tracking error signal, and a step of reducing a rotation speed of a spindle motor when the focus error signal or the tracking error signal exceeds a first detection value. And increasing the rotation of the spindle motor when the focus error signal or the tracking error signal is lower than a second detection value lower than the first detection value.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings using examples.
FIG. 1 is a block diagram showing an embodiment of an optical disk apparatus according to the present invention. In the figure, reference numeral 101 denotes an optical disk on which information signals are recorded at a constant linear velocity. A spindle motor 102 generates a driving force for rotating the optical disc 101. Reference numeral 103 denotes a rotation detector that outputs a pulse signal according to the rotation speed of the spindle motor 102 using a Hall element. Reference numeral 104 denotes a rotation control circuit, which controls the rotation of the spindle motor to a desired number of rotations based on output signal pulses from the rotation detector and information read from the optical disk. Further, the rotational speed of the spindle motor 102 is controlled by signals from the focus error signal level detector 113 and the tracking error signal level detector 114. Reference numeral 105 denotes an objective lens that focuses a light beam from a semiconductor laser on the signal recording surface of the disk 101. An actuator 106 drives the objective lens 105 in a direction perpendicular to the disk (focus direction) or in a radial direction (tracking direction) with respect to the disk. An optical pickup 107 is composed of various prisms including a semiconductor laser, a signal detection detector, and the like. A slider 108 moves the actuator 106 and the optical pickup 107 to arbitrary radial positions on the optical disk 101. A signal processing circuit 109 generates a focus error signal and a tracking error signal, which are control error signals of the actuator 106, based on an output signal from the optical pickup 107, and generates a focus error signal level detector 113 and a tracking error signal level. Output to the detector 114 and the servo circuit 110. The servo circuit 110 includes a servo loop gain amplifier and a phase compensation filter, performs phase compensation based on the focus error signal and tracking error signal from the signal processing circuit 109, and outputs the focus drive signal and tracking drive signal to the power amplifier 111. To do. The power amplifier 111 drives the actuator 106 based on the output signal of the servo circuit 110. A control unit 112 controls the entire apparatus. A focus error signal level detector 113 determines whether or not the focus error signal level during focus servo control is equal to or higher than a predetermined detection level, and outputs the determination result to the rotation control circuit 104.
[0016]
In the optical pickup 107, the detection distance range between the focusing light of the objective lens in the focus direction and the signal recording surface of the optical disc is determined (usually 6 μm with the focal point in the CD), and servo control is possible only within the detection range. It becomes.
FIG. 2 is a characteristic diagram for explaining the relationship between the focus error signal and the detection level. In the figure, the horizontal axis represents the distance d1 between the objective lens and the signal recording surface of the optical disc, and the vertical axis represents the focus error signal FE. In the figure, a curve 201 is a focus error signal, and draws an S-shaped curve having an extreme value with reference to the in-focus position. 202 is the maximum value of the focus error signal, and 203 is the minimum value of the focus error signal. Here, the predetermined first detection level of the focus error signal is a threshold value determined at the time of design, and is set within the maximum value 202 and the minimum value 203 of the focus error signal curve 201 and can be servo controlled. A value that does not exceed the range (detection distance range).
Further, two values in the positive direction and the negative direction centering on the focus error signal average operating point are set as the second detection level. Alternatively, either one may be set. As a means for setting, a fixed value may be set in advance, a value designated by the control unit, or a percentage of the amplitude of the focus signal 201. This signal level detector An electric circuit using a comparator circuit or a digital circuit that makes a determination based on a digital value after A / D conversion may be used.
[0017]
When the focus error signal level is small, the following effects can be obtained by reducing the threshold level as in the second detection level.
(1) The rotational speed of the disc can be increased.
(2) Power consumption can be reduced.
(3) The servo stability can be increased.
(4) Further, the servo gain can be lowered.
[0018]
In FIG. 1, the tracking error signal level detector 114 determines whether or not the tracking error signal level during tracking servo control is equal to or higher than a predetermined detection level, and outputs the determination result to the rotation control circuit 104.
FIG. 3 is a characteristic diagram for explaining the relationship between the tracking error signal and the detection level. In the figure, the horizontal axis indicates the distance d2 between the light spot by the objective lens and the track of the optical disk, and the vertical axis indicates the tracking error TE. In the figure, a curve 301 is a tracking error signal. 302 is the maximum value of the tracking error signal, and 303 is the minimum value of the tracking error signal. A tracking error signal as shown in Figure 3, the signal level changes and composed track portion at a pit on the optical disc, depending on whether a mirror portion which is between tracks, the curve 301 having an extreme value It becomes. In order to read data on the optical disc, it is necessary to perform servo control on the track portion, and the track portion becomes the servo control range.
[0019]
Here, the predetermined first detection level of the tracking error signal is set within the maximum value 302 and the minimum value 303 of the tracking error signal and is a value that does not exceed the servo control range (track portion). Further, a second detection level is set between two values in the positive direction and the negative direction around the tracking error signal average operating point. Alternatively, either one is set as the second detection level. As a means for setting, a predetermined fixed value may be set in advance, or a value specified by the control unit may be any percentage of the maximum tracking signal amplitude. Even an electric circuit using a circuit may be a digital circuit that is determined by a digital value after A / D conversion.
When the tracking error signal level is small, if the threshold level is reduced as in detection level 2, the same effect as in the case of focus error control can be obtained.
[0020]
As described above, by setting the detection level, in the optical disc apparatus of the present embodiment, the error signal when the actuator servo is performed is monitored by the signal level detector as in the control flow shown in FIG. By detecting the actuator control signal distortion that occurs when the optical disk rotates at high speed, the rotational speed of the spindle motor can be lowered before the servo shift occurs, and a stable optical disk reading speed can be realized.
[0021]
FIG. 4 is a flowchart showing an embodiment of the processing operation of the optical disk apparatus according to the present invention. In this embodiment, a predetermined detection level is determined, and the magnitude of the focus error signal level value is determined with respect to this, and the rotation of the spindle motor 102 is controlled based on the result.
In the figure, if the focus error signal level value is greater than or equal to a predetermined value in step 401, and if the tracking error signal level value is greater than or equal to a predetermined value in step 402, the rotational speed of the spindle motor 102 is decelerated in step 403. If the focus error signal level value or the tracking error signal level value is lower than a predetermined value in either step 401 or step 402, the process directly returns to step 401.
[0022]
Next, a second embodiment of the present invention will be described.
FIG. 6 is a flowchart showing another embodiment of the processing operation of the optical disk apparatus according to the present invention. The error signal level detectors 113 and 114 can detect an error signal level peak value within a certain period of time. Further, by setting the first detection level and the second detection level with the detection level of two values in the plus direction and the minus direction or one of the two values in the plus direction around the error signal average operating point, for example, When the first detection level is detected as in the first embodiment, it is detected that there is actuator control signal distortion that occurs during high-speed rotation of the optical disk, and the rotational speed of the spindle motor before the servo shift occurs. And lower than the second detection level set closer to the in-focus level than the first detection level, it is detected that there is no actuator control signal distortion that occurs during high-speed rotation of the optical disk, and the spindle It is possible to operate with the maximum performance according to the reading position of the optical disk, such as increasing the rotational speed of the motor.
[0023]
In the figure, in step 601, it is determined whether or not the focus error signal level value is equal to or higher than the first detection level. If it is equal to or higher than the first detection level (in the case of Yes), step 602 shifts to the spindle motor 102 in FIG. 1 and controls to reduce the rotational speed of the spindle motor 102. In step 601, when it is lower than the first detection level (in the case of No), the process proceeds to step 603 to determine whether or not the tracking error signal level is equal to or higher than the first detection level. If it is equal to or higher than the first detection level (Yes), the rotation of the spindle motor 102 is controlled to be decelerated at step 602. If it is determined in step 603 that the tracking error signal level value is lower than the first detection level (in the case of No), step 604 is also transferred. In step 604, it is determined whether or not the focus error signal level value is equal to or lower than the second detection level. If not, the process returns to step 601 without doing anything. If the focus error signal is less than or equal to the second detection level in step 604 (Yes), the process moves to step 605 to determine whether or not the tracking error signal level value is less than or equal to the second detection level. If it is above the second detection level (in the case of No), the processing returns to step 601 as it is. In step 605, when the tracking error signal level value is less than or equal to the second detection level, the process proceeds to step 606, where control is performed to accelerate the rotation speed of the spindle motor.
[0024]
Next, a third embodiment will be described with reference to FIG.
FIG. 7 is a block diagram showing a second embodiment of the optical disk apparatus according to the present invention, and FIG. 8 is a flowchart showing a third embodiment of the processing operation of the optical disk apparatus shown in FIG. In FIG. 7, the output of the focus error signal level detector 113 and the output of the tracking error signal level detector 114 are supplied to the servo circuit 110, and the servo loop characteristic, that is, the gain of the servo circuit is changed. Different from the device.
[0025]
As in the second embodiment, the first detection level and the second detection level are set in the focus and tracking error signal level detectors 113 and 114. When the error signal level detects the first detection level, it is detected that there is an actuator control signal distortion that occurs during high-speed rotation of the optical disc, and the servo loop gain setting of the servo circuit is controlled to increase by a certain value. Actuator control signal distortion is reduced by servo loop characteristics.
When the second detection level or lower is detected, it is detected that there is no distortion of the actuator control signal that occurs during high-speed rotation of the optical disc, and the servo loop gain setting of the servo circuit is controlled to be lowered by a certain value, and excessive servo Prevents loop characteristics and reduces power consumption.
[0026]
However, when changing the servo loop gain, there is a limit to maintaining stable servo loop characteristics, so the maximum and minimum amounts of servo loop gain should be set, and the actuator servo control signal distortion will be reduced even when the servo loop gain is maximum. If it is detected, control is performed to reduce the rotation speed of the spindle motor before the servo deviation occurs.
[0027]
This will be described more specifically with reference to FIG. In the figure, in step 801, it is determined whether or not the focus error signal level is equal to or higher than the first detection level. If it is equal to or higher than the first detection level, the process proceeds to step 802 to determine whether the focus loop gain is maximum. If the gain is the maximum, this is controlled in step 803 so that the rotational speed of the spindle motor 102 is reduced. If the focus loop gain is maximum in step 802, the focus loop gain is increased in step 804. If it is determined in step 801 that the focus error signal level is lower than the first detection level (No), it is further determined in step 805 whether the focus error signal level is equal to or lower than the second detection level. If it is equal to or lower than the second detection level (Yes), it is determined in Step 806 whether or not the focus loop gain is minimum. If the focus loop gain is not the minimum in step 806, the focus soup gain is decreased in step 807 and the process proceeds to step 808. If the focus error signal level is higher than the second detection level in step 805, the process proceeds to step 808.
[0028]
In step 808, it is determined whether the tracking error signal level is equal to or higher than the first detection level. If it is equal to or higher than the first detection level (Yes), the process proceeds to step 809, where it is determined whether or not the tracking loop gain is maximum. If the loop gain is maximum, in step 803, the rotation of the spindle motor 102 is decelerated and controlled. If the loop gain is not the maximum in step 809 (No), control is performed to increase the tracking loop gain in step 810. If it is lower than the first detection level in step 808, it is determined in step 811 whether the tracking error signal level is equal to or lower than the second detection level. If it is below the second detection level (Yes), it is determined in step 812 whether the tracking loop gain is maximum,
If it is the maximum (Yes), the process returns to Step 801. If the tracking loop gain is not the minimum (No), the tracking loop gain is decreased in step 813 and the process returns to step 801.
[0029]
As described above, in this embodiment, the servo unstable operation caused by the actuator servo control signal distortion is reduced by the servo loop characteristic, the optimum servo loop characteristic can be set, and a stable optical disc reading speed can be realized.
[0030]
Next, a fourth embodiment will be described. The error signal level detectors 113 and 114 detect the error signal level peak value within a certain fixed time, and calculate the difference from a predetermined error signal level to be set, thereby setting the servo loop gain of the servo circuit. Thus, a stable servo loop characteristic can be obtained instantaneously. Also, as in the third embodiment, when the servo gain maximum amount and the minimum amount are set and the actuator servo control signal distortion is detected even with the servo loop gain maximum amount, the spindle motor Control to reduce the rotation speed.
As described above, by controlling the servo loop characteristics according to the actuator servo control signal distortion level, the servo unstable operation caused by the actuator servo control signal distortion is reduced, and the stable servo optical disk with the optimum servo loop characteristics. Reading speed can be realized.
[0031]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent servo deviation due to actuator control signal distortion generated when the optical disk operates at high speed rotation, and to perform stable actuator control.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention.
FIG. 2 is a characteristic diagram for explaining a relationship between a focus error signal and a detection level.
FIG. 3 is a characteristic diagram for explaining a relationship between a tracking error signal and a detection level.
FIG. 4 is a flowchart showing an embodiment of the processing operation of the optical disc apparatus according to the present invention.
FIG. 5 is a characteristic diagram showing actuator signal distortion.
FIG. 6 is a flowchart showing another embodiment of the processing operation of the optical disc apparatus according to the present invention.
FIG. 7 is a block diagram showing a second embodiment of the optical disc apparatus according to the present invention.
FIG. 8 is a flowchart showing a third embodiment of the processing operation of the optical disc apparatus shown in FIG. 7;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Optical disk, 102 ... Spindle motor, 103 ... Rotation detector, 104 ... Rotation control circuit, 105 ... Objective lens, 106 ... Actuator, 107 ... Optical pick-up, 108 ... Slider, 109 ... Signal processing circuit, 110 ... Servo circuit, DESCRIPTION OF SYMBOLS 111 ... Power amplifier, 112 ... Control part, 113 ... Focus error signal level detector, 114 ... Tracking error signal level detector

Claims (2)

A spindle motor that rotates the optical disc, an information reading unit that irradiates a signal recording surface of the optical disc through an objective lens and reads an information signal on the signal recording surface, and an output signal from the information reading unit A signal level detection unit that generates and outputs a focus error signal and a tracking error signal; a detection value detected by the signal level detection unit; and a spindle according to a loop gain of the focus error signal or the tracking error signal Control means for controlling the rotational speed of the motor or controlling the loop gain, wherein the control means is a case where the focus error signal or the tracking error signal exceeds a first detection value, and the focus error signal Signal or loop of the tracking error signal When the in has not reached the maximum value, the loop gain is increased, and when the loop gain of the focus error signal or the tracking error signal has reached the maximum value, the rotational speed of the spindle motor is decreased, and When the focus error signal or the tracking error signal is lower than the second detection value lower than the first detection value, and the loop gain of the focus error signal or the tracking error signal does not reach the minimum value An optical disc apparatus characterized in that when the loop gain of the focus error signal or the tracking error signal reaches a minimum value, the loop gain is left as it is . The full Okasuera signal or in a case where tracking error signal exceeds the first detection value, if the loop gain of the focus error signal or the tracking error signal does not reach the maximum value, the loop gain thereof When the loop gain of the focus error signal or the tracking error signal reaches the maximum value, the rotation speed of the spindle motor is decreased, and the focus error signal or the tracking error signal is detected by the first detection. a lower than lower than the value second detection value, if the loop gain has not reached the minimum value of the focus error signal or the tracking error signal, it lowers the loop gain, the focus error signal or The loop gain of the tracking error signal has reached the minimum value If an optical disk reproducing method, characterized by the loop gain and it is.

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