A servo control method based on low-frequency periodic similarity

Abstract

This invention discloses a servo control method based on low-frequency period similarity. First, through digital sampling, the servo adjustment deviation at each sampling moment within the -1th optical disc rotation cycle is obtained. Then, based on the servo controller, the servo drive quantity at each moment within the -1th cycle is obtained. Based on the servo adjustment deviation and servo drive quantity at adjacent moments within the -1th cycle, the incremental value of the low-frequency jitter of the optical disc at each moment within the 1st cycle is obtained through a low-pass filter. This is then combined with the 1st... n cycle t The servo drive quantity at time t, obtain the t period. t The actual servo drive quantity at each moment, thus obtaining the first... n cycle t The servo drive adjusts the position at time +1, and then repeatedly executes servo control based on low-frequency periodicity similarity within the optical disc rotation cycle, eventually causing the servo drive to adjust the position to reach the target position.

Description

Technical Field

[0001] This invention relates to the field of optical storage servo control technology, and in particular to a servo control method based on low-frequency period similarity. Background Technology

[0002] Servo control technology is the core technology of optical disc systems. In actual use, the optical disc is driven to rotate at high speed by the spindle motor. Due to disc and mounting errors, multi-directional jitter occurs, including surface vibration, eccentricity, and tilt, causing changes in the distance and angle between the disc track and the objective lens. During the reading and writing of information on the optical disc, the system automatically detects positional deviations in each direction and uses high-speed, high-precision servo control technology to perform gain and phase compensation at different frequencies. Simultaneously, the drive unit drives the objective lens to perform high-speed position adjustments, ensuring that the focused spot always tracks the target track of the optical disc, achieving high-precision reading and writing of information. The aforementioned jitter includes large-amplitude low-frequency periodic fluctuations and small-amplitude non-periodic medium-to-high-frequency fluctuations. Traditional servo PID control does not distinguish between input fluctuations; it only calculates the drive output based on the input servo error signal and controls the drive unit to adjust the position or speed accordingly, enabling the servo to track the target position. Therefore, traditional PID control algorithms require high gain K values, resulting in increased system cutoff frequencies and affecting the system's anti-interference and stability. Summary of the Invention

[0003] This invention discloses a servo control method based on low-frequency periodic similarity to overcome the above-mentioned technical problems.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows: A servo control method based on low-frequency period similarity includes the following steps: S1: Obtain the first... through digital sampling Servo adjustment deviation at each sampling moment within the optical disc rotation cycle That is, the first Within the period The deviation between the actual position of the objective lens and the target position at any given time; where, An index representing the period of jitter during the operation of an optical disc; Indicates the time within the period; This represents the number of times the servo adjustment deviation signal is sampled within one optical disc rotation cycle, i.e., the total number of sampling moments. S2: According to the first Servo adjustment deviation at each sampling moment within the optical disc rotation cycle Based on the servo controller, obtain the first Within the period servo drive quantity at any moment And pre-record; S3: According to the... Sampling time during the optical disc rotation cycle Servo adjustment deviation and the Sampling time during the optical disc rotation cycle Servo adjustment deviation and the -1 cycle servo drive quantity at any moment By using a low-pass filter, the first... Within the period The increment value of low-frequency jitter of the optical disc at any given time And pre-record; S4: Obtain the... Sampling time during the optical disc rotation cycle Servo adjustment deviation Based on the servo controller, obtain the first cycle servo drive quantity at any moment ; S5: According to the... Within the period The increment value of low-frequency jitter of the optical disc at any given time and the cycle servo drive quantity at any moment , obtain the cycle The actual servo drive quantity at any given moment ; S6: According to the... cycle The actual servo drive quantity at any given moment , obtain the cycle The position of the servo drive after adjustment at any time is used to adjust the position of the servo drive; S7: In the S4~S6 are executed repeatedly within each optical disc rotation cycle to achieve the goal of... Servo control based on low-frequency periodic similarity within a cycle; S8: In the subsequent optical disc rotation cycle, S1~S7 are repeated in each cycle to achieve servo control based on low-frequency periodic similarity in each cycle.

[0005] Furthermore, in S1, the first... Servo adjustment deviation at each sampling moment within the optical disc rotation cycle The formula used is as follows:

[0006]

[0007]

[0008] In the formula: An index representing the period of jitter during the operation of an optical disc; Indicates the time within the period; Indicates the first Servo adjustment deviation at each sampling moment within the optical disc rotation cycle. Indicates the first Within the period The actual position of the servo at any given moment. Indicates the first Within the period Real-time jitter data from optical disc vibration and eccentricity; For the first Within the period Low-frequency jitter data at any given moment; Indicates the first Within the period High-frequency jitter data at any given moment; It is a low-pass filter.

[0009] Furthermore, in step S3, the first... Within the period The increment value of low-frequency jitter of the optical disc at any given time The formula used is as follows:

[0010] In the formula: For low-pass filters: Indicates the first Within the period Time's up The increment value of low-frequency jitter on the optical disc at any given moment; Indicates the first Within the period Low-frequency jitter of the optical disc at any given moment; Indicates the first Within the period The amount of low-frequency jitter on the optical disc at any given moment.

[0011] Furthermore, in S5, the first... cycle The formula used for the actual servo drive quantity at any given time is as follows:

[0012] In the formula: Indicates the first cycle Adjusting deviation based on servo timing Calculated servo drive quantity; Indicates the first cycle Actual servo drive quantity at any given moment; Indicates the first Within the period The increment value of low-frequency jitter of the optical disc at any given time.

[0013] Furthermore, in S6, the first... cycle The formula used to determine the adjusted position of the servo drive at any given time is as follows: ; In the formula: Indicates the first cycle The position adjusted by the servo drive at any given moment.

[0014] Beneficial effects: The servo control method based on low-frequency period similarity of the present invention first obtains the first... -1 Servo adjustment deviation at each sampling moment within the optical disc rotation cycle That is, the first -1 cycle The deviation between the actual position of the objective lens and the target position at time t; according to the first -1 cycle Servo adjustment deviation at any time Based on the servo controller, obtain the first -1 cycle servo drive quantity at any moment And pre-record it. According to the first -1 cycle Servo adjustment deviation at any time Obtain the first by using a low-pass filter. Within the period The increment value of low-frequency jitter of the optical disc at any given time And pre-record it. Combined with the first n cycle t The servo drive quantity at time 1, obtain the servo drive quantity at time 2. cycle t The actual servo drive quantity at each moment, thus obtaining the first... n cycle t The position adjusted by the servo drive at time +1. In the... S4~S6 are executed repeatedly within each optical disc rotation cycle to achieve the goal of... Servo control based on low-frequency periodic similarity within a cycle. In subsequent optical disc rotation cycles, S1~S7 are repeated in each cycle to achieve servo control based on low-frequency periodic similarity in each cycle, ultimately ensuring that the adjusted position of the servo drive reaches the target position. This invention addresses the problems of traditional PID control technology by utilizing the periodic similarity of low-frequency jitter to eliminate it. This prevents the servo drive adjustment from corresponding to the low-frequency portion of the optical disc jitter, effectively suppressing servo tracking errors caused by periodic interference. It also effectively reduces the servo tracking frequency and the high gain K value of the servo PID control, significantly reducing the system cutoff frequency, improving system phase stability, and enhancing the servo tracking performance of the driver in the optical storage system. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the servo control method based on low-frequency periodic similarity of the present invention; Figure 2a This is a Bode diagram of the controller loop in an embodiment of the present invention; Figure 2b This is a Bode diagram after adding the controlled object in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This embodiment introduces a servo control method based on low-frequency periodic similarity, including the following steps, such as... Figure 1 As shown: S1: Obtain the first... through digital sampling Servo adjustment deviation at each sampling moment within the optical disc rotation cycle That is, the first Within the period The deviation between the actual position of the objective lens and the target position at any given time; where, An index representing the period of jitter during the operation of an optical disc; Indicates the time within the period; This represents the number of times the servo adjustment deviation signal is sampled within one optical disc rotation cycle, i.e., the total number of sampling moments. Preferably, in step S1, the first... Servo adjustment deviation at each sampling moment within the optical disc rotation cycle The formula used is as follows:

[0019]

[0020]

[0021] In the formula: An index representing the period of jitter during the operation of an optical disc; Indicates the time within the period; Indicates the first Servo adjustment deviation at each sampling moment within the optical disc rotation cycle. Indicates the first Within the period The actual position of the servo at any given moment. Indicates the first Within the period Real-time jitter data from optical disc vibration and eccentricity; For the first Within the period Low-frequency jitter data at any given moment; Indicates the first Within the period High-frequency jitter data at any given moment; It is a low-pass filter.

[0022] Specifically, when an optical disc is spinning at high speed, vibration and eccentricity will cause the disc to jitter, and the servo error signal will show a sinusoidal shape. Therefore, the jitter often has low-frequency periodic fluctuations. The low-frequency components in the optical disc servo jitter show periodic similarity, and the servo deviation signal can be detected through the servo error signal.

[0023] Specifically, the jitter caused by optical disc vibration and eccentricity is modeled as low-frequency and high-frequency jitter components, and the model is as follows:

[0024] in, For the first Within the period Low-frequency jitter data at any given moment; express Within the period High-frequency jitter data at any given moment.

[0025] However, the jitter modeled above cannot be directly detected and obtained; it requires the detection and acquisition of servo deviation and servo drive. Specifically, the formulas used to utilize servo deviation and servo drive are as follows:

[0026]

[0027]

[0028]

[0029]

[0030] In the formula: Indicates the first Within the period Real-time jitter data from optical disc vibration and eccentricity; No. Within the period Real-time jitter data from optical disc vibration and eccentricity; Indicates the first The actual position of the servo at the initial moment within the cycle; i An index representing a moment within a period; S2: According to the first Servo adjustment deviation at each sampling moment within the optical disc rotation cycle Based on the servo controller, obtain the first Within the period servo drive quantity at any moment And pre-record; Specifically, the servo controller is represented as follows:

[0031] In the formula: Indicates a servo controller; Indicates the first Within the period The servo drive quantity at any given moment.

[0032] Specifically, in this embodiment, it is necessary to The relevant values ​​at all sampling times within the period are acquired and recorded. The optical disc rotates to the [number]th [time]. After the cycle, it is no longer possible to return to real-time. For periodic data, only pre-recorded values ​​can be retrieved; S3: According to the... Servo adjustment deviation at sampling time t within the optical disc rotation cycle and the Sampling time during the optical disc rotation cycle Servo adjustment deviation and the Within the period servo drive quantity at any moment By using a low-pass filter, the first... Within the period The increment value of low-frequency jitter of the optical disc at any given time And pre-record; Preferably, in step S3, the first... Within the period The increment value of low-frequency jitter of the optical disc at any given time The formula used is as follows:

[0033]

[0034]

[0035] In the formula: For low-pass filters: Indicates the first Within the period Time's up The increment value of low-frequency jitter on the optical disc at any given moment; Indicates the first Within the period Low-frequency jitter of the optical disc at any given moment; Indicates the first Within the period The amount of low-frequency jitter on the optical disc at any given moment.

[0036] S4: Obtain the... Within the period Servo adjustment deviation at any time That is, the first Within the period The deviation between the actual position and the target position at a given time is obtained based on the servo controller. cycle servo drive quantity at any moment ; Specifically, this embodiment uses a PDIC (photodetector) to detect the deviation between the actual servo position and the target position in real time during the current cycle. Based on the servo deviation, the servo drive quantity is updated. To compensate for the output deviation, the torque converter of the drive unit applies an operation opposite to the direction of the deviation, thereby eliminating the deviation between the servo adjustment position and the target.

[0037] Specifically, the first is obtained through the servo controller. cycle servo drive quantity at any moment The formula used is as follows:

[0038] In the formula: This indicates a servo controller, where the servo drive is in the opposite direction to the deviation. Indicates the first Within the period The servo drive quantity at any given moment; Indicates the first Within the period Servo deviation at any given moment.

[0039] S5: According to the... Within the period The increment value of low-frequency jitter of the optical disc at any given time and the cycle servo drive quantity at any moment , obtain the cycle The actual servo drive quantity at any given moment ; Specifically, the low-frequency increment value of the previous period Servo drive quantity in the current cycle Superimposed to generate the actual servo drive quantity. To compensate for servo deviation, the drive unit torque converter performs an operation opposite to the deviation direction, while simultaneously storing the incremental value of the low-frequency jitter in this cycle. Specifically, the deviation direction is detected by the PDIC, and the servo error detection includes the focus error signal and the tracking error signal. For example, if the magnitude of the focus error signal FE changes from positive to negative after passing through 0, and then from negative to positive after passing through 0 again, it indicates that the distance between the objective lens and the optical disc changes from far to near, and then from near to far. Therefore, the deviation direction and magnitude are the current servo adjustment deviation detected in real time by the servo error detection system.

[0040] Preferably, in step S5, the first... cycle The actual servo drive quantity at any given moment as follows: Specifically, the first cycle The actual driving quantity of the time servo is determined by cycle Superposition of driving forces at each moment cycle Acquisition of low-frequency jitter increment at any given time: Combine the low-frequency jitter increment of the servo in the previous cycle with... The driving values ​​at each moment are summed up as the current value for the first time. Within the period The actual driving value at time t. The calculation of the actual driving value is as follows:

[0041] In the formula: Indicates the first cycle The servo drive quantity at any given time is obtained through servo PID calculation; Indicates the first cycle Actual servo drive quantity at any given moment; Indicates the first Within the period The increment value of low-frequency jitter of the optical disc at any given time.

[0042] S6: According to the... cycle The actual servo drive quantity at any given moment , obtain the cycle The position of the servo drive after adjustment at any time is used to adjust the position of the servo drive; Preferably, the first cycle The formula used to determine the adjusted position of the servo drive at any given time is as follows: ; In the formula: Indicates the first Within the period The position adjusted by the servo drive at any given moment; S7: In the S4~S6 are executed repeatedly within each optical disc rotation cycle to achieve the goal of... Servo control based on low-frequency periodic similarity within a cycle.

[0043] S8: In the subsequent optical disc rotation cycle, S1~S7 are repeated in each cycle to achieve servo control based on low-frequency periodic similarity in each cycle.

[0044] Specifically, the goal of the focusing servo system is to ensure that the laser beam can be correctly focused on the information layer of the optical disc. In this embodiment, the deviation of the servo tracking the target position needs to be within ±45nm.

[0045] Specifically, by utilizing the periodic similarity of the low-frequency signal in the servo error signal, the low-frequency component of the servo error signal... and Since they are approximately equal, their impact on servo error does not need to be considered. Therefore, when adjusting the servo drive, it is not necessary to consider the corresponding low-frequency part. Periodic The time deviation consists of the following:

[0046] Specifically, Figure 2a In the simulation, the Bode plot of the controller was performed. In the figure, the orange curve represents the gain and phase of a traditional PID controller without increments, while the blue curve represents the gain and phase comparison after adding increments. The figure shows that the controller introduces both high-gain and low-gain curves, before the controlled object (torque generator) is introduced. Figure 2a For comparison and reference. Figure 2b The orange curve represents the effect of incorporating the low-frequency cycle similarity proposed in this embodiment. As can be seen from the graph, it achieves amplitude-frequency characteristics essentially the same as a traditional PID high-gain K-value controller. Traditional servo PID control does not differentiate between input fluctuations; it only calculates the drive output based on the input servo error signal and adjusts the position or speed of the drive unit accordingly to enable the servo to track the target position. However, the servo control method based on low-frequency cycle similarity in this embodiment can significantly reduce the servo gain K value. In summary, this embodiment improves the controller gain by adding incremental bias; therefore, the performance of the low-frequency cycle similarity method in this embodiment can significantly reduce the servo gain K value.

[0047] This embodiment of a servo control method based on low-frequency periodic similarity first obtains the servo adjustment deviation at each sampling moment within the previous optical disc rotation cycle through digital sampling. Then, it uses the servo adjustment deviation within the previous cycle... The servo adjustment deviation at any given time is obtained from the servo controller within the previous cycle. The servo drive quantity at each moment is recorded in advance. Based on the servo adjustment deviation at adjacent moments in the previous cycle and the servo adjustment deviation at the previous cycle... The servo drive quantity at any given moment is obtained by passing it through a low-pass filter to capture the value from the previous cycle. The incremental value of low-frequency jitter of the optical disc at any given time is pre-recorded; based on the servo adjustment deviation of the current cycle, the servo drive quantity of the current cycle is obtained from the servo controller, and the previous cycle's value is used as the basis for further calculation. The incremental value of low-frequency jitter of the optical disc at any given moment is superimposed on the servo drive quantity of the current cycle to obtain the current actual servo drive quantity. This allows for the determination of the adjusted position of the servo drive. Servo control based on the similarity of low-frequency periodicity is repeatedly executed within the optical disc rotation cycle, ultimately ensuring that the adjusted position reaches the target position. This embodiment is particularly applicable to situations where low-frequency periodic jitter is caused by vibration, eccentricity, and tilt due to disc warping and spindle installation errors during high-speed optical disc rotation. Addressing the problems of traditional PID control technology, the periodic similarity of low-frequency jitter is utilized to eliminate it. This ensures that the servo drive adjustment quantity does not correspond to the low-frequency portion of the optical disc jitter, effectively suppressing servo tracking errors caused by periodic interference. This effectively reduces the servo tracking frequency and the high gain K value of the servo PID control, significantly reducing the system cutoff frequency, improving system phase stability, and enhancing the servo tracking performance of the driver in the optical storage system.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A servo control method based on low-frequency periodic similarity, characterized in that, Includes the following steps: S1: Obtain the first... through digital sampling Servo adjustment deviation at each sampling moment within the optical disc rotation cycle That is, the first Within the period The deviation between the actual position of the objective lens and the target position at any given time; where, An index representing the period of jitter during the operation of an optical disc; Indicates the time within the period; This represents the number of times the servo adjustment deviation signal is sampled within one optical disc rotation cycle, i.e., the total number of sampling moments. S2: According to the first Servo adjustment deviation at each sampling moment within the optical disc rotation cycle Based on the servo controller, obtain the first Within the period servo drive quantity at any moment And pre-record; S3: According to the... Sampling time during the optical disc rotation cycle Servo adjustment deviation and the Sampling time during the optical disc rotation cycle Servo adjustment deviation and the -1 cycle servo drive quantity at any moment By using a low-pass filter, the first... Within the period The increment value of low-frequency jitter of the optical disc at any given time And pre-record; S4: Obtain the... Sampling time during the optical disc rotation cycle Servo adjustment deviation Based on the servo controller, obtain the first cycle servo drive quantity at any moment ; S5: According to the... Within the period The increment value of low-frequency jitter of the optical disc at any given time and the cycle servo drive quantity at any moment , obtain the cycle The actual servo drive quantity at any given moment ; S6: According to the... cycle The actual servo drive quantity at any given moment , obtain the cycle The position of the servo drive after adjustment at any time is used to adjust the position of the servo drive; S7: In the S4~S6 are executed repeatedly within each optical disc rotation cycle to achieve the goal of... Servo control based on low-frequency periodic similarity within a cycle; S8: In the subsequent optical disc rotation cycle, S1~S7 are repeated in each cycle to achieve servo control based on low-frequency periodic similarity in each cycle.

2. The servo control method based on low-frequency periodic similarity according to claim 1, characterized in that, In S1, the first... Servo adjustment deviation at each sampling moment within the optical disc rotation cycle The formula used is as follows: In the formula: An index representing the period of jitter during the operation of an optical disc; Indicates the time within the period; Indicates the first Servo adjustment deviation at each sampling moment within the optical disc rotation cycle. Indicates the first Within the period The actual position of the servo at any given moment. Indicates the first Within the period Real-time jitter data from optical disc vibration and eccentricity; For the first Within the period Low-frequency jitter data at any given moment; Indicates the first Within the period High-frequency jitter data at any given moment; It is a low-pass filter.

3. The servo control method based on low-frequency periodic similarity according to claim 1, characterized in that, In step S3, the first step is obtained through a low-pass filter. Within the period The increment value of low-frequency jitter of the optical disc at any given time The formula used is as follows: In the formula: For low-pass filters: Indicates the first Within the period Time's up The increment value of low-frequency jitter on the optical disc at any given moment; Indicates the first Within the period Low-frequency jitter of the optical disc at any given moment; Indicates the first Within the period The amount of low-frequency jitter on the optical disc at any given moment.

4. The servo control method based on low-frequency periodic similarity according to claim 1, characterized in that, In S5, the first... cycle The formula used for the actual servo drive quantity at any given time is as follows: In the formula: Indicates the first cycle Adjusting deviation based on servo timing Calculated servo drive quantity; Indicates the first cycle Actual servo drive quantity at any given moment; Indicates the first Within the period The increment value of low-frequency jitter of the optical disc at any given time.

5. The servo control method based on low-frequency periodic similarity according to claim 1, characterized in that, In S6, the first... cycle The formula used to determine the adjusted position of the servo drive at any given time is as follows: ； In the formula: Indicates the first cycle The position adjusted by the servo drive at any given moment.

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