CN100587816C - Method and device for compensating astigmatic difference of optical drive - Google Patents

Abstract

The invention discloses a method and a device for compensating the astigmatic difference of an optical drive. First make the optical drive to focus on a disc and then perform track crossing. Continuously adjust the compensation value of the astigmatism difference compensator and measure the peak-to-peak value of a focus error signal or a push-pull cross-track error signal during track crossing. Finally, the optimal compensation value of the astigmatism difference compensator is calculated according to the peak-to-peak measurement results of the focus error signal or the cross-track error signal of the push-pull method. The invention can effectively solve the problem that the known fixed astigmatism difference compensation value is not the best astigmatism difference compensation value, so as to reduce the optical signal distortion of the known optical drive system and improve the read/write quality of the optical drive system.

Description

Method and device for compensating astigmatic difference of optical drive

technical field

The invention relates to a method and a device for compensating the astigmatic difference of an optical drive, and in particular to a method and a device for compensating the astigmatic difference of the AS45 and AS0 of the optical drive.

Background technique

The performance of an optical drive is closely related to the optical quality of its internal system, and astigmatism is one of the important factors that cause the optical quality of the internal system to deteriorate. When the optical quality of the internal system of the optical drive is affected by astigmatism, the focus error signal (focus error signal, FE signal) and cross-track error signal (tracking error signal, TE signal) generated by the optical drive are easily distorted, resulting in difficulties in servo control. It is easy to cause the optical drive to be unfocused or off-track. In addition, the astigmatism caused by the optical disc drive’s read/write laser spot deformation will not only cause more errors in the data reproduction signal (radio frequency signal, RF signal) when reading the disc, but also reduce the writing quality of the optical drive. Difference.

Please refer to FIG. 1 , which is a schematic diagram of astigmatism difference. The phenomenon of astigmatism is mainly caused by the fact that after the laser beam passes through the objective lens, the focus of the horizontal meridian plane and the focus of the vertical sagittal plane cannot be focused on the same focus, and the light spot on the focal plane will become an ellipse. Usually, when the long axis of the elliptical light spot is clamped at 45 degrees to the optical disc track (track) read/write by the optical drive, it is called AS45 astigmatism; Clipping 0 degrees is called AS0 astigmatism.

Taking AS45 astigmatism as an example, when the light spot of the optical pickup head has AS45 astigmatism, it introduces a feedback (feedthough) phenomenon, so that when the elliptical light spot crosses the track, the focus signal (FE) unexpectedly Behavior is similar to the cross-track error signal (filtered: ripple) when crossing the track. This phenomenon is especially evident on optical discs (such as DVD±R) with lands and grooves. When the AS45 astigmatism is more serious, the difference between the major axis and the minor axis of the elliptical light spot is greater. The asymmetry of the light spot imaged on the photodetector in the optical pickup head will be more obvious, which will cause the jitter of the focus signal (FE) to increase when crossing tracks, and eventually even lead to the out-of-control of the focus servo. Therefore, when the optical pickup head has AS45 astigmatism, it must be corrected to increase the stability of the focus servo control.

Therefore, usually the optical pickup head manufacturers will compensate for the above-mentioned AS45 and AS0 astigmatism, so that the impact of the above-mentioned AS45 astigmatism and AS0 astigmatism on the read/write quality of the optical drive is minimized. Please refer to FIG. 2 , which is a known optical drive system. The optical drive system includes a Blue-ray (BD) laser light source 21 , a DVD laser light source 22 and a CD laser light source 23 for reading different discs. The blue laser light source 21, the DVD laser light source 22 or the CD laser light source 23 are focused on the data layer of the optical disc 25 after passing through the objective lens 24, and the reflected laser light will be projected on the photodetector 26 to convert the optical signal into an electrical signal, The electrical signal is processed by the digital signal processor (DSP) 28 of the control unit 27 to obtain a focus error signal (FE) and a push-pull cross-track error signal (mainpush-pull, MPP). Wherein the control unit 27 decides to turn on the BD laser light source 21, the DVD laser light source 22 or the CD laser light source 23, and fills the astigmatism compensation value into the astigmatism compensator (astigmatism compensator) 29, to compensate for focusing on the optical disc 25. Optical aberration of the dot to improve the read/write quality of the optical drive system. The astigmatism compensator 29 is usually made of liquid crystal material. When its pressurized voltage changes, the refractive index of the astigmatism difference compensator 29 also changes along with the applied voltage, to compensate the laser beam passing through the astigmatism difference compensator 29, so that the light spot that makes it reach the optical disc 25 is a circle shape. In this way, the read/write quality of the optical drive can be maintained at its best.

In the known technology, the recommended compensation values of the two kinds of astigmatism AS45 and AS0 are provided by the optical pickup head manufacturer. The suggested compensation values of AS45 and AS0 astigmatism are fixed without any flexibility. However, the recommended compensation value provided by the optical pickup manufacturer is usually not the optimal compensation value required by the optical drive system, because the optimal compensation value may be affected by changes in the environment, aging of the optical pickup, differences in playing discs, and even usage Changes in habits (upright or horizontal play) and other factors. And because the development of optical drives has entered the blue-ray (blue-ray) era, there are more stringent requirements for the optical quality of the optical pickup head. Therefore, if we only refer to the recommended value provided by the optical pickup head manufacturer, when the two kinds of astigmatism AS45 and AS0 appear, the optical signal distortion of the optical drive system will still occur, and in severe cases, the optical drive will fail to read/write.

Contents of the invention

Therefore, how to effectively compensate the astigmatism difference AS45 and AS0 will be the focus of the present invention. In view of this, the object of the present invention is to provide a method and device for compensating the astigmatic difference of the optical drive. The problem that the known fixed astigmatism difference compensation value is not the best astigmatism difference compensation value is effectively improved, so as to reduce the optical signal distortion of the known optical drive system, thereby improving the read/write quality of the optical drive system.

Secondly, the present invention proposes a method for compensating the astigmatism of the optical drive. Firstly, the optical drive focuses on an optical disc and then crosses tracks. Continuously adjust the compensation value of the astigmatism difference compensator and measure a focus error signal or a peak-to-peak value of a push-pull cross-track error signal during track crossing. Finally, the optimal compensation value of the astigmatism difference compensator is calculated according to the peak-to-peak measurement results of the focus error signal or the cross-track error signal of the push-pull method.

Again, the present invention proposes a device for compensating optical drive astigmatism, comprising: an optical pick-up head, which contains a photodetector, a computing unit and a peak-to-peak detector, and it calculates according to the detection signal of the photodetector A focus error signal or a peak-to-peak value of a push-pull method cross-track error signal; a logic comparison unit and a memory, and the logic comparison unit combines the peak-to-peak value of the focus error signal or the push-pull method cross-track error signal with The existing peak-to-peak signal comparison in the memory calculates the best astigmatism difference compensation value; and, a control unit and an astigmatism difference compensator, wherein the control unit outputs a value according to the best astigmatism difference compensation value The control signal is sent to the astigmatic difference compensator.

In order to enable your examiner to further understand the features and technical content of the present invention, please refer to the following detailed description and accompanying drawings of the present invention. However, the accompanying drawings are for reference and illustration only, and are not intended to limit the present invention.

Description of drawings

Figure 1 is a schematic diagram of astigmatic difference.

Fig. 2 is a known optical drive system.

3A, 3B, 3C, 3D, and 3E are schematic diagrams of light spots imaged on a photodetector (PDIC) when the optical drive system is affected by AS45 astigmatism.

4A, 4B, and 4C are schematic diagrams showing the relative relationship between the cross-track error signal and the focus error signal when the optical drive system affected by AS45 astigmatism is cross-track.

Fig. 5 is a flow chart of the method for compensating the astigmatic difference of the optical drive AS45 according to the present invention.

6A, 6B, 6C, 6D, and 6E are schematic diagrams of light spots imaged on a photodetector (PDIC) when the optical drive system is affected by ASO astigmatism.

7A, 7B, and 7C are schematic diagrams of cross-track error signals of the push-pull method when the optical drive system is affected by AS0 astigmatism.

FIG. 8 is a flow chart of the method for compensating the astigmatic difference of the optical drive AS0 according to the present invention.

FIG. 9 is a system diagram for compensating AS45 astigmatism and AS0 astigmatism in the present invention.

Fig. 10 is a detailed structure diagram of the astigmatism difference compensator of the present invention.

And, each reference numeral in the above-mentioned drawings is explained as follows:

21BD laser light source 22DVD laser light source

23CD laser light source 24 objective lenses

25 discs 26 light detectors

27 control unit 28 digital signal processor

29 astigmatism difference compensator 41 light detector

71 photodetectors 100AS45 astigmatism difference compensator

110AS0 astigmatism compensator 910 optical read head

920 computing unit 930 peak-to-peak detector

940 logic comparison unit 950 memory

960 Control Unit 970 Astigmatism Compensator

Detailed ways

Please refer to FIGS. 3A, 3B, 3C, 3D, and 3E, which are schematic diagrams of light spots imaged on the photodetector (PDIC) when the optical drive system is affected by AS45 astigmatism. When the optical drive system has no AS45 astigmatism (ie AS45=0), the light spot is circularly symmetrical as shown in FIG. 3A . However, when the optical drive system is affected by a slight AS45 astigmatism (ie AS45=0.1λ), the light spot is elliptical and forms an angle of 45 degrees with the track on the optical disc, as shown in FIG. 3B and FIG. 3C . Fig. 3B is the light point imaging of the read/write laser reaching the platform (land) on the optical disc and then reflecting back to the photodetector 41; while Fig. 3C is the reflection of the read/write laser reaching the groove (groove) on the optical disc The light spot of the light detector 41 is imaged. Because the depths of the lands and grooves on the optical disc are different, the optical path difference after the laser passes through the lands and the grooves is different. Therefore, when the optical drive system is affected by the slight AS45 astigmatism, the direction of the image on the photodetector 41 is different when the light spot reads/writes the platform and when the light spot reads/writes the groove, and thus causes a focus error signal (FE) behave differently. In addition, the photodetector 41 includes photodetectors of four parts A, B, C and D, and the focus error signal FE is (A+C)-(B+D). Therefore, when the light spot with slight AS45 astigmatism is on the platform, its corresponding focus error signal is positive (ie FE>0); and when the light spot with slight AS45 astigmatism is on the groove When , the corresponding focus error signal is a negative value (ie FE<0).

In the same way, it can be proved that when the optical drive system is affected by the serious AS45 astigmatism (ie AS45=0.2λ), the light spot is elliptical and forms an angle of 45 degrees with the track on the optical disc, as shown in Figure 3D and Figure 3E . Fig. 3D is the light point imaging of the read/write laser reaching the platform (land) on the optical disc and then reflecting back to the photodetector 41; while Fig. 3E is the reflection of the read/write laser reaching the groove (groove) on the optical disc The light spot of the light detector 41 is imaged. Affected by the more severe AS45 astigmatism, the difference between the long and short axes of the light spot will be greater. In addition, when the light spot with severe AS45 astigmatism is on the platform, its corresponding focus error signal is a large positive value (ie FE>>0); When the light spot is on the groove, its corresponding focus error signal is a relatively large negative value (ie FE<<0).

From the above description, we can know the influence of AS45 astigmatic difference on the light spot shape and focus error signal. Please refer to FIGS. 4A , 4B and 4C again, which are schematic diagrams of the relative relationship between the cross-track error signal and the focus error signal when the optical drive system affected by AS45 astigmatism is cross-track.

FIG. 4A is a schematic diagram of cross-track error signals and focus error signals when the optical drive system is not affected by AS45 astigmatism (ie AS45=0). Generally speaking, when the optical drive system crosses the track to move the light spot through the platform (land) and groove (groove) structure of the optical disc, when the cross-track error signal (TE) generates a sine wave, it can be confirmed that the light spot has crossed a The track is from the platform (land) across the groove (groove) to the next platform (land). It can be seen from FIG. 4A that due to the good focus, the focus error signal (FE) does not change much when the light spot crosses the land and the groove.

Please refer to FIG. 4B and FIG. 4C again, which are schematic diagrams of the read/write light spot and corresponding focus error signal (FE) and cross-track error signal (TE) generated when the optical drive system is affected by AS45 astigmatism. When the optical drive system produces a light spot with AS45 astigmatism difference, because the light spot is just at a 45-degree angle with the track, when using the astigmatism method to generate the focus error signal FE, it will be affected by this elliptical light spot, making the light When the dot crosses the land and the groove, the amplitude of the focus error signal (FE) changes as shown in FIG. 4B and FIG. 4C . When the astigmatism is more severe (from AS=0.1λ to AS=0.2λ), the difference between the long and short axes of the light spot will be greater, resulting in a more serious change in the amplitude of the focus signal (FE).

Therefore, the degree of AS45 astigmatism can be judged and compensated by using the peak-to-peak value of the focus error signal (FE) when the light spot crosses tracks. Please refer to FIG. 5 , which is a flow chart of the method for compensating the astigmatism of the optical drive AS45 according to the present invention. Wherein, the process of the method is carried out when the optical drive system performs a cross-track action so that the light spot moves through the platform (land) and groove (groove) structure of the optical disc, and steps 310 to 340 will be executed multiple times and will find The optimal compensation value of AS45 astigmatism AS45_OPT.

Step 310: Complete the action of judging and focusing on the disc.

Step 320: Adjust the compensation value AS_T of the AS45 astigmatism difference compensator, measure the peak-to-peak value FEpp of the focus error signal and record it as FEpp_T.

Step 330: Determine whether FEpp_Min is greater than FEpp_T. If yes, go to step 340; if not, end the method flow.

Step 340 : Set AS45 AS45 astigmatism optimal compensation value AS45_OPT to AS_T, and replace FEpp_Min with FEpp_T.

Therefore, as shown in FIG. 4A, when the astigmatism difference AS45=0, the focus error signal FE will not produce amplitude changes when passing through the lands and grooves on the optical disc, and the peak-to-peak value FEpp of the focus error signal FE is zero (FEpp= 0). When the astigmatism difference AS45=0.1λ, the amplitude of the focus error signal FE passing through the platform and the groove on the optical disc will change, resulting in a focus error signal as shown in Figure 4B and its peak-to-peak value FEpp is greater than zero (FEpp>0); when When the astigmatism difference AS45=0.2λ, the amplitude change will be more serious, and the focus error signal FE will have a greater amplitude change when passing through the platform and groove on the optical disc, resulting in a focus error signal FE as shown in Figure 4C and its peak-to-peak value FEpp is much greater than zero (FEpp>>0).

Therefore, the inventors use the above optical characteristics to find out the best AS45 astigmatism compensation value. That is, during the track-crossing process of the optical drive system, the compensation value of the AS45 astigmatism difference compensator is changed, and the peak-to-peak value FEpp of the focus error signal FE is measured. The adjustment is continued until the peak-to-peak value FEpp of the measured focus error signal is a minimum. In this way, the light spot at this time is the closest to a symmetrical circle, and the AS45 astigmatism is also the minimum value, achieving the purpose of compensating for the AS45 astigmatism.

Therefore, when the optical drive system focuses on the disc (step 310), before the track is locked (on track), the light spot will cross the track, adjust the compensation value AS_T of the AS45 astigmatism compensator, and measure the focus error at this time The peak-to-peak value FEpp of the signal is recorded as FEpp_T (step 320). FEpp_T is compared with FEpp_Min in the memory (as shown in FIG. 9 ) (step 330 ) to obtain the AS45 astigmatism difference compensation value AS45_OPT when FEpp is the minimum value. AS45_OPT is the optimal compensation value of AS45 astigmatism (step 340). That is to say, after steps 310 to 340 are executed multiple times, the optimal compensation value AS45_OPT for AS45 astigmatism difference can be found.

Please refer to FIGS. 6A , 6B, 6C, 6D, and 6E, which are schematic diagrams of light spots imaged on the photodetector (PDIC) when the optical drive system is affected by ASO astigmatism. When the optical drive system has no AS0 astigmatism (ie AS0=0), the light spot is circularly symmetrical as shown in FIG. 6A . However, when the optical drive system is affected by slight AS0 astigmatism difference (i.e. AS0=0.1λ), the light point imaging of the read/write laser light reaching the platform on the optical disc and reflected back to the photodetector 71 presents an ellipse and is consistent with the track on the optical disc. 0 degree angle, as shown in Figure 6B; while the read/write laser reaches the groove (groove) on the optical disc and then reflects back to the photodetector 71. As shown in Figure 6C. This is because the lands and grooves on the optical disk have different depths, resulting in different optical path differences after the laser passes through the lands and grooves, resulting in different imaging angles at which light spots appear on the photodetector. Therefore, when the optical drive system is affected by a slight AS0 astigmatism, the change of the shape of the light spot makes the light spot and the track pitch of the optical disc have a slight mismatch. Therefore, when the optical drive system crosses tracks, it is difficult for the optical drive system to effectively sense Output the push-pull cross-track error signal MPP.

In the same way, it can be proved that when the optical drive system is affected by the serious AS0 astigmatism difference (i.e. AS0=0.2λ), the image of the spot on which the read/write laser reaches the platform on the optical disc and is reflected back to the photodetector 71 presents an elliptical shape and The 0-degree angle with the track on the optical disc is shown in Figure 6D; while the light point image of the read/write laser reaching the groove (groove) on the optical disc and then reflected back to the photodetector 71 presents an ellipse and is clamped with the track on the optical disc. The 90 degree angle is shown in Figure 6E. Therefore, when the optical drive system is affected by serious AS0 astigmatism, the change of the shape of the light spot makes the light spot and the track pitch of the optical disc more mismatched, and therefore when the optical drive system crosses tracks, it is more difficult for the optical drive system to effectively sense Push-pull cross-track error signal.

From the above description, we can know the influence of AS0 astigmatism on the light spot shape and the cross-track error signal of the push-pull method. Please refer to FIGS. Schematic diagram of the cross-track error signal of the push-pull method.

7A is a schematic diagram of the cross-track error signal MPP of the push-pull method when the optical drive system is not affected by the astigmatism difference AS0 (ie, the astigmatism difference AS0=0). The optical drive system crosses tracks so that the light spot moves through the optical disc's platform (land) and groove (groove) structure. Due to the close relationship between the light spot size and the track pitch, the push-pull cross-track error signal MPP is easy to detect and its peak-to-peak value MPPpp is the maximum value.

Please refer to FIG. 7B and FIG. 7C again, which are schematic diagrams of the read/write light spot and the corresponding push-pull cross-track error signal MPP generated when the optical drive system is affected by AS0 astigmatism. When AS0 astigmatism (AS0=0.1λ) occurs, the diameter of the light spot perpendicular to the track direction will change, making the light spot not match the track pitch, and therefore it is difficult for the optical drive system to effectively sense the cross-track error signal of the push-pull method MPP. The peak-to-peak signal MPPpp of the cross-track error signal MPP of the push-pull method will be attenuated as shown in FIG. 7B . When the AS0 astigmatism difference is more severe (AS0=0.2λ), the cross-track error signal MPP of the push-pull method will be severely distorted during cross-track, resulting in a smaller peak-to-peak MPPpp, as shown in FIG. 7C .

Therefore, the degree of AS0 astigmatism can be judged and compensated by using the peak-to-peak value of the cross-track error signal (TE) when the light spot crosses the track. Please refer to FIG. 8 , which is a flow chart of the method for compensating the astigmatic difference of the optical drive AS0 according to the present invention. Wherein, the process of the method is carried out when the optical drive system performs a cross-track action so that the light spot moves through the platform (land) and groove (groove) structure of the optical disc, and steps 610 to 640 will be executed multiple times and will find The optimal compensation value of AS0 astigmatism AS0_OPT.

Step 610: Complete the action of judging and focusing on the disc.

Step 620: Adjust the compensation value AS0_T of the AS0 astigmatism difference compensator, measure the peak-to-peak value MPPpp of the push-pull cross-track error signal and record it as MPPpp_T.

Step 630: Determine whether MPPpp_Max is smaller than MPPpp_T. If yes, go to step 640; if not, end the process of the method.

Step 640: Set the AS0 astigmatism optimal compensation value AS0_OPT to AS0_T, and replace MPPpp_Max with MPPpp_T.

Therefore, the inventor utilizes the cross-track error signal MPP of the push-pull method to sense the degree of AS0 astigmatism difference of the optical drive system, and continuously adjusts the compensation value of the AS0 astigmatism difference until the detected push-pull method cross-track error signal MPP Its peak-to-peak signal MPPpp is the maximum value. In this way, the AS0 astigmatism at this time is the minimum value, and the optical drive system obtains the best AS0 astigmatism compensation.

Therefore, when the optical drive system focuses on the disc (step 610), before the track is locked, the light spot will cross the track, adjust the compensation value AS0_T of the AS0 astigmatism difference compensator, and measure the cross-track error signal of the push-pull method at this time The peak-to-peak value of MPPpp, recorded as MPPpp_T (step 620). Compare MPPpp_T with MPPpp_Max in the memory (as shown in FIG. 9 ) (step 630 ) to obtain the AS0 astigmatism difference compensation value AS0_OPT when MPPpp is the maximum value. AS0_OPT is the optimal compensation value of AS0 astigmatism difference (step 640).

It should be noted that the above method of compensating AS45 astigmatism and AS0 astigmatism can be executed during the startup of the optical drive system, so there is no need to waste extra time to optimize astigmatism when the optical drive system is reading/writing Correction of compensation values.

Please refer to FIG. 9 , which is a structural diagram of a system for compensating AS45 astigmatism and AS0 astigmatism in the present invention. When the photodetector (not shown) in the optical pickup head 910 generates detector signals A, B, C, and D, the arithmetic unit 920 performs operations on the detector signals A, B, C, and D to calculate the focus The error signal FE((A+C)-(B+D)) or the push-pull cross-track error signal MPP((A+D)-(B+C)). After the focus error signal FE or the push-pull cross-track error signal MPP is input to the peak-to-peak detector 930, the peak-to-peak value FEpp of the focus error signal FE or the peak-to-peak value MPPpp of the push-pull cross-track error signal MPP can be obtained. Next, the logical comparison unit 940 compares the existing peak-to-peak signals in the memory 950 to calculate the optimal astigmatism compensation value. The control unit 960 outputs a control signal to the astigmatism compensator 970 to compensate AS45 astigmatism and AS0 astigmatism of the optical drive system.

In addition, the astigmatic difference compensator 970 is a liquid crystal structure, and the refractive index of light in the astigmatic difference compensator 970 is changed by changing the voltage applied to the liquid crystal structure, thereby achieving the purpose of compensating the AS45 astigmatism and AS0 astigmatism. The detailed structure of the astigmatism difference compensator 970 is shown in FIG. 10 , which is subdivided into 8 blocks. When wanting to compensate AS45 astigmatism difference, add voltage to 1, 2, 5, 6 blocks of AS45 astigmatism difference compensator 100, namely change the refractive index of 1, 2, 5, 6 blocks, and 3, 4 , 7, and 8 remain unchanged. In this way, the AS45 astigmatism of the light spot can be improved. Similarly, when the AS0 astigmatism difference is to be compensated, voltages are applied to blocks 1, 8, 4, and 5 of the AS0 astigmatism difference compensator 110, that is, the refractive indices of blocks 1, 8, 4, and 5 are changed, and The refractive indices of blocks 2, 3, 6, and 7 remain unchanged, so that the AS0 astigmatism of the light spot can be improved.

Therefore, when the present invention mainly utilizes cross-track, the peak-to-peak value FEpp of focus error signal is used as the discrimination signal of compensating AS45 astigmatism difference, and utilizes the peak-to-peak value MPPpp of cross-track error signal of push-pull method as the discrimination signal of AS0 astigmatism difference . The above two signals are the most discriminative signals of AS45 astigmatism and AS0 astigmatism, but these two signals can be used interchangeably depending on the situation, and the peak-to-peak value FEpp of the focus error signal can also be used as the signal to compensate for AS0 The identification signal, and the peak-to-peak value MPPpp of the cross-track error signal of the push-pull method can also be used as the identification signal of AS45 astigmatic difference. In addition to these two kinds of signals for identification signals, other signals collected by the photodetector are sent to the peak-to-peak detector of the signal through the operation of the control unit, and can also be used as compensation identification signals for astigmatic difference. For example, the data restoration signal RF can also be used as a discrimination signal of AS45 or AS0 astigmatism, or the differential push-pull cross-track signal DPPTE can also be used as a discrimination signal of AS0 or AS45 astigmatism.

Therefore, the advantage of the present invention is to find the best compensation value for compensating the AS45 astigmatism difference and the AS0 astigmatism difference when the optical drive system is started. Compared with the known technology, the optimal compensation value is provided by the optical pickup head manufacturer, and the user has no way to correct it. However, the present invention can adjust the astigmatism compensator to the optimum value according to the discrimination signal of AS45 astigmatism difference and the discrimination signal of AS0 astigmatism difference when the optical drive system is crossing tracks. In this way, even if the astigmatism changes due to factors such as changes in the environment, aging of the optical pickup head, differences in playing discs, and even changes in usage habits (upright or horizontal playback), the present invention can correct and obtain the best Astigmatism compensation value. Therefore, the optical signal distortion of the optical drive system is reduced, and the read/write quality of the optical drive system is improved.

In summary, although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall prevail as defined by the appended claims.

Claims (8)

1. A method for compensating optical drive astigmatism, which comprises an astigmatism compensator, comprising the following steps: Make the optical drive focus on a disc and perform track crossing; continuously adjusting the compensation value of the astigmatic difference compensator and measuring a peak-to-peak value of a focus error signal or a push-pull cross-track error signal; and The optimal compensation value of the astigmatism difference compensator is calculated according to the peak-to-peak value measurement results of the focus error signal or the cross-track error signal of the push-pull method. 2. The method as claimed in claim 1, wherein the astigmatism difference compensator comprises an AS45 astigmatism difference compensator and an ASO astigmatism difference compensator. 3. The method as claimed in claim 2, wherein the compensation value of the AS0 astigmatism difference compensator when the peak-to-peak value of the push-pull cross-track error signal is selected as the maximum value is the best value of the AS0 astigmatism difference compensator compensation value. 4. The method according to claim 2, wherein the compensation value of the AS45 astigmatism difference compensator when the peak-to-peak value of the focus error signal is the minimum value is selected as the optimal compensation value of the AS45 astigmatism difference compensator. 5. A device for compensating astigmatic difference of optical drive, comprising: An optical pickup head having a photodetector that generates a detection signal; a computing unit connected to the optical pickup head to receive the detection signal; A peak-to-peak detector is connected to the arithmetic unit, and calculates a focus error signal or a peak-to-peak value of a push-pull method cross-track error signal according to the detection signal of the photodetector; a memory having a pre-stored peak-to-peak signal; A logical comparison unit, comparing the peak-to-peak value of the focus error signal or the push-pull cross-track error signal with the peak-to-peak signal pre-stored in the memory to calculate the best astigmatism compensation value; and An astigmatism difference compensator is connected with a control unit, wherein the control unit outputs a control signal to the astigmatism difference compensator according to the optimal astigmatism difference compensation value to compensate the astigmatism difference. 6. The device as claimed in claim 5, wherein the astigmatism difference compensator comprises an AS45 astigmatism difference compensator and an ASO astigmatism difference compensator. 7. The device according to claim 6, wherein the logic comparison unit compares the peak-to-peak value of the focus error signal with the existing peak-to-peak signal in the memory, and selects the AS45 astigmatism difference compensation whose peak-to-peak value is the smallest. The compensation value of the compensator is used as the optimal compensation value of the AS45 astigmatism difference compensator. 8. The device as claimed in claim 6, wherein the logic comparison unit compares the peak-to-peak value of the push-pull cross-track error signal with the peak-to-peak signal prestored in the memory, and selects the AS0 of the maximum peak-to-peak value. The compensation value of the astigmatism difference compensator is used as the best compensation value of the AS0 astigmatism difference compensator.

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