KR100262958B1 - Method for servo control of optical disk - Google Patents

Abstract

The present invention relates to a servo control method for an optical disc having a high speed of arithmetic processing.

The servo control method of the optical disk of the present invention comprises the steps of initializing to a frequency and performing servo; Lowering the reference sampling frequency and performing arithmetic processing at a variable and variable sampling frequency when the operation time needs to be secured; When the calculation process ends, reducing the changed sampling frequency to the reference sampling frequency, and performing servo on the reduced reference sampling frequency.

The servo control method of the optical disc of the present invention can perform a time-consuming operation such as automatic gain adjustment using a conventional digital servo controller.

Description

Servo control method of optical disc.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing apparatus for an optical disc, and more particularly, to a servo control method for an optical disc having a high computational processing speed.

In an optical disc system, in order to read data recorded on a disc and reproduce data, a process of irradiating a light beam to a signal track of the disc and converting the reflected signal into an electrical signal by a photodetector is required. This requires focusing, tracking, and spindle control. In particular, focusing and tracking servos require different servo bands depending on the type of disc and the disc's double speed playback. It is necessary to change the gain by automatically detecting its characteristics according to the type and speed of the disc, which is called automatic gain adjustment. However, if the automatic gain adjustment is performed during normal playback, the algorithm processing for the automatic gain adjustment causes a lot of computational processing to be performed in a limited time. Therefore, high speed hardware (especially a digital servo controller; DSP) is inevitably required to perform all the computations within a limited specific time. Since this results in an increase in the cost of the system, a system control method that does not result in an additional increase in cost is required.

A control circuit of an optical disc using a conventional digital servo controller will be described with reference to FIG.

FIG. 1 is a block diagram showing a control circuit of an optical disc according to the prior art. In the configuration of FIG. 1, the control circuit of the optical disc according to the prior art is connected to the LD output control unit 14 and under the control of the LD output control unit 14. An optical pickup 2 for irradiating a light beam to the signal track of the optical disc 1 and converting the light beam reflected from the signal track into an electrical signal, a preamplifier unit 3 connected in series to the output terminal of the optical pickup 2; Common connection to the signal processing section 4 connected to the output terminal of the preamplifier section 3, the analog / digital converter 5 and the microcomputer 8 connected to the preamplifier section 3 and the signal processing section 4 in common. Connected to the digital servo controller 6 controlled by the microcomputer 8, the digital / analog converter 7 connected to the output terminal of the digital servo controller 6, and the output terminal of the digital / analog converter 7; Focusing / tracking driver (9) and sled The driver 10 and the spindle driver 11, the feeder 12 connected in common to the sled driver 10 and the optical pickup 2, and the optical disc 1 are seated on the output end of the spindle driver 11. The motor 13 connected in series is provided.

The light source from the laser diode is condensed on the signal track of the optical disc 1 by the objective lens OL, and the light is reflected on the signal track and passes through the objective lens OL. Photodiode (PD). In the photodiode PD, the received optical signal is converted into an electrical signal and supplied to the preamplifier 3. The preamplifier 3 detects a focus error signal, a tracking error signal, and a high frequency signal RF from the signals from the optical pickup 2 and supplies them to the signal processor 4 and the analog / digital converter 5. In this case, the high frequency signal RF is processed by the signal processor 4 to undergo error correction, decoding, and the like.

The analog / digital converter 5 samples the focus error signal, the tracking error signal, the high frequency signal RF, and the like from the preamplifier 3 at a sampling frequency and converts the analog signal into a digital signal. The digital form signal from the analog / digital converter 5 is supplied to the digital servo bearer 6. The digital server controller 6 then supplies a digital form signal from the analog-to-digital converter 5 to the digital servo controller 6 under the control of the microcomputer 8. The digital verso controller 6 then processes the signal from the analog-to-digital converter 5 under the control of the microcomputer 8 and performs signal processing such as filter operation and supplies it to the digital-to-analog converter 7. The digital / analog converter 7 converts a signal from the digital servo controller 6 into an analog signal and supplies it to the focusing / tracking driver 9, the sled driver 10, and the spindle driver 11 in common. do. By the signal supplied to the focusing / tracking driver 9, the focusing / tracking driver 9 causes the light beam from the objective lens OL to fall within the depth of focus in the signal track of the optical disc 1. And a tracking servo for causing the light beam from the objective lens OL to follow the center of the signal track of the optical disc 1. In response to the signal input to the sled driver 10, the sled driver 10 drives the feeder to remove the direct current (DC) component of the tracking error to move the optical pickup 2 in the radial direction of the optical disc 1. Control to move linearly. By the signal supplied to the spindle driver 11, the spindle driver 11 controls to make the rotation speed of the motor 13 which mounted the optical disc 1 constant.

The control circuit for controlling the optical disc 1 using the digital servo controller 6 depends on the processing speed of the digital servo controller 6. The frequency of disturbance changes according to the increase in the speed of the optical disk 1 or the type of the optical disk 1, and it requires more execution time to automatically adjust the gain of the servo system corresponding to the frequency of the disturbance. Digital servo controller is required. However, since the digital servo controller having such a high speed of operation is usually manufactured at high cost, the recording / reproducing apparatus of the optical disc employing the same has a low price competitiveness. Therefore, it is desirable to have a method capable of performing a large amount of time-consuming computation processing in a limited time using a conventional digital virso controller without increasing the cost.

Accordingly, it is an object of the present invention to provide a servo control method of an optical disc capable of performing many time-consuming computational processes such as automatic gain adjustment using a conventional digital servo controller.

1 is a block diagram showing a control circuit of a conventional optical disc.

2 is a characteristic diagram showing a relationship between a sampling frequency and a gain or phase when the sampling frequency is stored by dividing by "a" in the servo control method of the optical disc according to the embodiment of the present invention.

3 is a characteristic diagram showing a relationship between a sampling frequency and a gain or phase when the gain value is lowered in FIG.

4 is a sampling frequency waveform diagram of a digital servo controller in a servo control method of an optical disc according to an embodiment of the present invention.

5 is a flowchart showing the processing procedure of the servo control method of the optical disk according to the embodiment of the present invention step by step.

* Explanation of symbols for main parts of the drawings

1: optical disc 2: optical pickup

3: preamplifier section 4: signal processing section

5: analog to digital converter 6: digital servo controller

7: digital to analog converter 8: microcomputer

9: Focusing / Tracking Driver 10: Sled Driver

11: spindle driver 12: feeder

13: motor 14: LD output processing unit

In order to achieve the above object, the servo control method of the optical disk of the present invention comprises the steps of initializing the sampling frequency to be the reference sampling frequency to perform the servo to correspond to the reference double speed; When it is necessary to secure the calculation time, lowering the reference sampling frequency to perform arithmetic processing at a variable and variable sampling frequency. 'When the computation processing is completed, the variable sampling frequency is reduced to the reference sampling frequency, and the servo is performed at the reduced reference sampling frequency. Characterized in that it comprises a step.

Other objects and features of the present invention in addition to the above objects will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 2 to 5.

2 and 3 also show the change in the servo band and the gain compensation method according to the sampling frequency decrease through simulation in the servo control method of the optical disk according to an embodiment of the present invention.

In Figs. 2 and 3, the horizontal axis represents a change in frequency (Hz), and the vertical axis in Figs. 2 (a), 3 (a), 2 (b) and 3 (b) is shown. Are the gain (dB) and the phase (deg) changes, respectively.

The first graph 1 is indicated by a solid line in the drawing, and is a servo transmission characteristic when the digital servo controller 6 is configured with a sampling frequency of fs. The second graph 2 is indicated by a dotted line, and in the case where the sampling frequency fs is lowered to 1 / a (a = 2 in the example of the figure), that is, when the digital servo controller 6 is configured with 1/2 x fs. Servo transmission characteristic.

Referring to the first and second graphs (1, 2), lowering the sampling frequency 1 / a increases the gain frequency at 0 (dB) (in FIG. 2 (a), the phase is 180 (deg)). Notice how the frequency is lowered, the important thing is how much of the phase margin is when the sampling frequency is lowered.

For this purpose, when the sampling frequency is lowered to 1 / a as shown in the second graph 2 in FIG. 3 and the loop gain is lowered in proportion to the decreasing rate, the phase margin is reduced to one servo. Decrease to a value that cannot affect.

Therefore, operation processing that takes a long time that is difficult to calculate with the basic sampling frequency fs lowers the sampling frequency and also reduces the loop gain in proportion to this sampling frequency. There is no difference except to give a little.

Here, this region in which the DC gain is reduced at low frequencies by lowering the loop gain does not have a great influence on the servo band, so it does not need to be considered. At this time, a method of reducing the sampling time variably (by changing the value of a at 1 / a × fs) may be effectively applied to obtain more accurate characteristics, although there is no significant effect according to the DC gain reduction.

4 is a timing diagram showing an interrupt cycle of a sampling frequency of a digital servo controller in the servo control method of the optical disc of the present invention.

4 (a) shows an interrupt period when the sampling frequency is a basic sampling frequency of fs. Here, the normal arithmetic processing time t _normal of the digital servo controller is an absolutely necessary time for performing normal arithmetic processing, for example, arithmetic processing for focusing servo and tracking servo. However, if a separate calculation process such as automatic gain adjustment other than the normal arithmetic processing such as focusing servo or tracking servo is required, in order to perform a normal arithmetic processing and a separate arithmetic processing, the sampling frequency is lowered so that the interrupt cycle must be a normal arithmetic processing. The interval t _normal and in addition to the separate operation processing time t _auto such as automatic gain adjustment should be greater than or equal to.

Importantly, as described in FIGS. 2 and 3, gain selection is performed to secure phase margin (stable stability), and automatic gain adjustment is performed to determine an optimal gain for the current disk and system.

5 is a flowchart showing the processing procedure of the servo control method of the optical disc of the present invention step by step, which is controlled by the microcomputer 8 shown in FIG. 1 and is performed by the digital servo controller 6.

In the first stage, when the power supply is turned on or the optical disc is loaded, the system including the digital servo controller 6 is initialized (first stage). The sampling frequency is initialized to the basic sampling frequency fs to correspond to the 1x speed, and the loop gain is also initialized to the basic loop gain value G to correspond to the 1x speed (step 2) and then in the normal mode state. The first to third tasks, which perform arithmetic processing to perform various servos, are performed. At this time, the focusing servo for controlling the light beam from the objective lens to fall within the depth of focus of the signal track and the actuator of the optical pickup 2, unless the automatic gain adjustment mode is used in the first task, which is an operation for focusing servo and tracking servo. A tracking servo is driven to control the objective lens to follow the center of the signal track by driving an actuator. Tracking auto gain adjustment is performed after focusing tracking servo is performed. When the automatic gain adjustment mode is performed, the computation time is inevitably increased compared to the normal mode, and thus it cannot be calculated using the basic sampling frequency fs.

Therefore, as described in FIGS. 2 and 3, when setting the autofocus gain adjustment mode, the sampling frequency is divided by the basic focus sampling frequency fs by an arbitrary value a, and " fs / a (converted focus sampling frequency fs'). Lowers to the frequency of). In addition, in proportion to the focus sampling frequency fs' converted to ensure phase margin, the loop gain value is divided by an arbitrary value a by dividing the default focus loop gain value / a (converted focus loop gain value G). Adjust to ")" (step 4).

After performing the fourth step, it is determined whether the focus auto gain adjustment has been completed. (Step 5) If it is determined that the focus auto gain adjustment has been completed, it is reset to the basic focus sampling frequency fs and the basic focus loop gain value G. . The resetting of the basic focus sampling frequency fs is reset by adjusting to "converted focus sampling frequency fs' x a" using an arbitrary value a in the fourth step. And reset to the basic focus loop gain value G '× a. And the reset of the basic focus loop gain value G is "converted focus loop gain value G using an arbitrary value a in the fourth step." (6th step) On the other hand, if it is determined in step 5 that the automatic adjustment of the focus automatic gain has not been completed, step 5 is repeated.

After performing the sixth step, the tracking automatic gain adjustment mode is set. At this time, the basic tracking sampling frequency fs is divided by an arbitrary value a, and the conversion tracking sampling frequency fs' = fs'a is adjusted, and the loop gain value is changed by dividing the basic tracking loop gain value G by an arbitrary value a. Adjust by decreasing the tracking loop gain value G '= basic loop gain value / a "(step 7).

After performing the seventh step, it is determined whether the tracking auto gain adjustment has been completed. (Step 8) If it is determined that the tracking auto gain adjustment has been completed, the sampling frequency is determined by using " a " With the converted tracking sampling frequency fs '× a, the loop gain value is reset to the default tracking sampling frequency and the default tracking loop gain value, respectively, with the converted tracking loop gain value G' × a. In the eighth step, if it is determined that the focus auto gain adjustment is not completed, the eighth step is repeated.

After all of these automatic gain adjustments are completed, the control signal is supplied from the microcomputer 8 to perform the next command from the microcomputer 8, and is interpreted. (Step 10) As a result of the analysis, the command is an arbitrary servo. If the command is for the first to third tasks corresponding thereto. Then, the digital servo controller 6 performs the tenth step. (Eleventh step)

The arithmetic processing performed by the digital servo controller 6 under the control of the microcomputer 8 is performed as the first task to the third task according to the performance of each servo. In step 11 may be optionally performed in the automatic gain adjustment mode.

Looking at the processing sequence of each task step by step, the first task is performed arithmetic processing for the focus and tracking servo performed in the third or eleventh step. First, the focus servo performs (step 12), and determines whether the focus auto gain adjustment mode has been set (step 13). As a result, if the focus auto gain adjustment mode is set, focus auto gain adjustment is performed. Step 14) Next, it is determined whether the focus auto gain adjustment has ended. (Step 15) When it is determined that the focus auto gain adjustment has been completed, the focus auto gain adjustment completion is set (step 16). The tracking servo is performed. (Step 17) Meanwhile, when the focus auto gain adjustment mode is not set in step 13 and the focus auto gain adjustment is not completed in step 15, step 17 is performed.

Tracking tracking is performed, and it is determined whether all of the present are in the tracking auto gain adjustment mode. (Step 18) If the tracking auto gain adjustment mode is determined, tracking auto gain adjustment is performed (step 19). If the automatic tracking adjustment is determined to have been completed, the setting returns to the completion of the tracking automatic gain adjustment (step 21). If it is determined that the information is not determined or the tracking auto gain adjustment is not completed in step 20, the method returns without performing the tracking auto gain mode.

The second task is a processing procedure for performing and returning a spindle servo (step 22) for controlling the rotational speed of the motor 13 on which the disk 1 is seated, and the third task is an optical process in the radial direction of the disk 1. The processing procedure for performing and returning a sled servo for controlling the pickup 2 to linearly move (step 23) is shown.

As described above, the servo control method of the optical disk of the present invention can perform a time-consuming operation such as automatic gain adjustment using a conventional digital servo controller.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (5)

Initializing the sampling frequency to be the reference sampling frequency so as to correspond to the reference double speed and performing servo; Lowering the reference sampling frequency and performing arithmetic processing at a variable and variable sampling frequency when it is necessary to secure a calculation time; And reducing the sampling frequency, which has been changed, to a reference sampling frequency when the calculation process is completed, and performing servo at the reduced reference sampling frequency. The method of claim 1, The lowering and varying the sampling frequency may include dividing the sampling frequency by an arbitrary value. The method of claim 2, And the reducing step of the sampling frequency causes the sampling frequency to be multiplied by the arbitrary value. The method of claim 1, And the step of performing arithmetic processing includes varying a loop gain so as to be proportional to a variable sampling frequency and using the same in arithmetic processing. The method of claim 1, And wherein said calculating processing is an arithmetic processing for automatic gain adjustment.

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