KR100640627B1 - Method for tuning a MR head skew of HDD using CSM test - Google Patents

Abstract

A skew tuning method of an MR head (magnetic recording head) in a hard disk drive is disclosed. According to an aspect of the present invention, there is provided a method of tuning an MR head skew of a hard disk drive using a CSM test, the method comprising: a) detecting an error count for each off track value by performing a CSM test on a predetermined test track; b) determining whether the number of minimum equivalent offtrack values representing an offtrack value having an error count equal to the minimum error count for a predetermined threshold offtrack range is greater than a threshold number; And c) repeating step a) after reducing the recording density when it is determined in step b) that it is larger than the threshold number. According to the present invention, the reliability of the head tuning method for correcting the off-track phenomenon is improved by detecting the case where the read capability of the head is abnormal.

Description

Method for tuning a MR head skew of HDD using CSM test}

1 is a diagram illustrating the concept of MR head skew.

2 shows a conventional MR head skew tuning method using a correction skew value.

3 shows a CSM graph.

4 is a diagram showing an MR head skewing method according to a first embodiment of the present invention;

5 is a CSM graph when there is a flaw in the performance of the MR head.

6 is a CSM graph for a normal MR head for the same track as in FIG.

7 shows an MR head skewing method according to a second embodiment of the present invention.

8 illustrates an MR head skewing method according to a third embodiment of the present invention.

9 is a diagram illustrating an MR head skewing method according to a fourth embodiment of the present invention.

The present invention relates to a method of skewing an MR head of a hard disk drive, and more particularly, to detect a case in which the read capacity of the head is abnormal, and in this case, by re-adjusting the recording density and performing a CSM test again, The present invention relates to an MR head skewing method for improving the reliability of MR head skewing of a drive.

1 is a diagram illustrating the concept of a skew value.

The hard disk drive includes a disk 110, a head 120 for reading data from the disk, and an arm 130 for supporting and moving the head 120. The disc 110 rotates in a counterclockwise direction and moves in a fan shape around the arm center 132 of the head 122 to move to the track 140 where the data to be read in the disc is located.

The head 120 is composed of a recording head 122 and a reading head 124, and due to the characteristics of the recording and reading operations, the two are positioned to line up in the direction of the arm center.

Since the track in the disc 110 is circular and the direction of movement of the head 122 is also curved in a fan shape, as shown in FIG. 1, the direction and the head of the track 130 are the recording head 122 and the reading head 124. ), The direction of connection is not necessarily identical. That is, when the recording head 122 is located at the track center 142 of the track 140, the read head 124 may not be located at the track center 142, which is called an offset between the recording head and the reading head. .

By the offset of the recording head and the reading head, when the recording and reading operations are performed at the same time, there is a difference between the angle at which the arm 130 is moved during the recording operation and the angle at which the arm 130 is moved during the reading operation. When the recording head 122 is located at the center 134 of the track, the distance away from the track center 142 by the read head 124 is referred to as a skew value. The distance moved in the inner circumferential direction or the outer circumferential direction is referred to as a correction skew value T. The correction skew value differs from track to track.

In Fig. 1, since the recording head 122 and the read head 124 are positioned side by side in the track at position B, the correction skew value T is 0, but at positions A and C the recording head 122 and the read head 124 are Since it is not located side by side on the track, the correction skew value T is not zero. In general, when the arm 130 is moved in the disc circumferential direction, that is, in the case of position A, the correction skew value is defined as a positive value, and when the arm 130 is moved in the disc circumferential direction, that is, the position C is In this case, the correction skew value is defined as a negative value.

The correction skew value T is determined differently for each track and stored in a predetermined storage space in the hard disk drive. The hard disk drive extracts a corrected skew value from this storage location during recording and reading operations, and then corrects the skew value using this corrected off track value and determines the arm travel distance.

2 is a diagram illustrating a conventional MR head skewing method using a correction skew value.

In step 210, the number of errors is detected for each skew value by performing a CSM test on a predetermined test track.

The Channel Statistic Measurement (CSM) test is performed by recording a predetermined write pattern on a predetermined test track, reading the recorded pattern again, and counting the number of errors.

The head center of the recording head is regarded as the skew value = 0, the CSM test is performed while the head is moved in the direction of the disc inner circumference, that is, the skew value is increased by +1, and the head is moved in the direction of the disc circumference. The number of errors is detected by performing a CSM test in increments of one. The range of skew values can be determined differently for each test, and the test is generally performed at 33 points of -16 to +16. Skew values and error counts can be graphed and called CSM graphs. A typical CSM graph is shown in FIG. 3.

3 is a diagram illustrating a CSM graph.

Referring to FIG. 3, the number of errors Y is the smallest at the center position of the track and the shape of the bath tube increases as the number of errors increases toward the edge.

Reference is again made to FIG. 2.

In step 220, the correction skew value Tc is determined by calculating the area center for each point P (X, Y) in the CSM graph.

The off track value Tc is calculated by the following equation.

[Equation 1]

Tc = Sum (X * Y) / Sum (Y)

Here, Tc represents a correction skew value, X represents a skew value, and Y represents the number of errors in each skew value.

In step 230, the correction skew value Tc is stored in a predetermined place in the hard disk drive. In general, the correction skew value Tc is stored by correcting the skew value in a skew table in which a skew value for each zone of a disk is stored.

In operation 240, the hard disk drive extracts the corrected skew value from the skew table when searching the corresponding zone, and determines the moving distance of the arm using the extracted skew value.

However, according to the MR head skewing method described above, accurate correction skew values cannot be generated when the reading capability of the head itself is abnormal. That is, the number of errors determined by the CSM test is generated not only by the track off-track phenomenon but also by the failure of the head itself. The conventional method does not consider the abnormality of the read capability of the head, and only corrects the skew value by using the error count. Because it determines.

Accordingly, the present invention has been made to solve the above-described problem, and detects a case where the read capacity of the head is abnormal, and in this case, readjusts the recording density and performs a CSM test again, whereby MR head skew of the hard disk drive is performed. To provide a MR head skewing method which further improves the reliability of the tuning.

In order to achieve the above object, the present invention, in the head tuning method of the hard disk drive using the CSM test, a) detecting the number of errors per skew value by performing a CSM test on a predetermined test track ; b) determining whether the number of minimum equivalent skew values representing a skew value having an error frequency equal to the minimum error frequency for a predetermined threshold offtrack range is greater than a threshold number; And c) if it is determined in step b) that the number is greater than the threshold number, repeating step a) after reducing the recording density.

Here, the threshold off-track range is determined by extending the predetermined threshold range selected by the user around the skew value having the minimum error count.

In addition, the present invention, after the step b), f1) including the step of checking whether the error count in the leftmost off-track and the error number in the right-most offtrack in the CMS graph is equal to the minimum number of errors, f2 If it is determined that the step is the same in step f1), the method includes reducing the recording density and performing a CSM test again.

The present invention also includes a step of g) checking whether the flag is set to 1 after the steps b) and f1) by using a flag indicating that the recording density has been changed, and when the flag is set to 1, And ending the tuning process without going any further.

In addition, the present invention provides a head tuning method of a hard disk drive using a CSM test, comprising the steps of: a) determining a skew value representing a rough correction skew value by performing a skew calibration on a predetermined test track; b) detecting the number of errors per skew value by performing a CSM test based on the skew value; c) determining whether the number of minimum equivalent skew values representing a skew value having an error frequency equal to the minimum error frequency for a predetermined threshold offtrack range is greater than the threshold number; And d) if it is determined in step c) that the number is greater than the threshold number, repeating step a) after reducing the recording density.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a view showing an MR head skewing method according to a first embodiment of the present invention.

In step 410, the number of errors per skew value is detected by performing a CSM test on a predetermined test track.

The CSM test is performed by recording a predetermined write pattern in a predetermined test track, reading the recorded pattern again, and counting the number of errors.

When the CSM test is performed, a CSM graph as shown in FIG. 3 is generated. In the CSM graph, each point {X, Y} represents {skew value, error frequency at the skew value}.

In step 420, the number N_Tme of the minimum equivalent skew value Tme is counted in the predetermined threshold offtrack range -A + Tmin = <X <= A + Tmin. Here, Tmin is a skew value having a minimum error count, that is, a minimum skew value, and Tme represents a skew value having the same error count as the minimum error count Ymin in the CSM graph. Threshold range A is selectable by the user.

In step 430, it is checked whether the number N_Tme of minimum equivalent skew values is greater than the threshold number N_th. The threshold number N_th is selectable by the user. If so, go to step 440; otherwise, go to step 450.

In step 440, the recording density (Data Rate, DR) is reduced to a predetermined value, and then the flow proceeds to step 410 again.

In step 450, the correction skew value Tc is determined by calculating the area center for each point P (X, Y) in the CSM graph. The off track value Tc is calculated by the above equation (1).

In operation 460, the skew value of the corresponding zone is corrected and stored in the skew table using the correction skew value Tc calculated in operation 450.

According to the method of FIG. 4, in the case of error occurrence due to the defect of the head in steps 420 and 430, and in the case of the error occurrence due to the defect of the head in step 440, after performing readjustment of the recording density, the CSM test is performed again. As a result, the results of the CSM test due to the defect of the head can be readjusted more reliably, and as a result, the reliability of the head tuning method can be improved.

FIG. 5 shows an example of a CSM graph when there is a defect in the performance of the head, and FIG. 6 shows a CSM graph for a normal head for the same track.

In the case of the normal head of FIG. 6, the skew value intervals (-16, +6) have a relatively small error frequency and have a minimum error frequency when -6, whereas in the case of the abnormal head of FIG. +16) With very high error counts in total, we can see that the minimum error counts occur when the skew values are -5 and -3.

According to Equation 1 for obtaining the correction skew value as the area center, the area center obtained from each point in FIG. 5 cannot be regarded as an optimal value for correcting the off-track phenomenon. This is because the area center does not reflect the minimum number of errors in FIG. 5.

According to the present invention, the correction skew value is not calculated from the CSM graph generated when the head is abnormal, but instead, the CSM test is performed after reducing the recording density DR so that a normal CSM graph, that is, a graph as shown in FIG. Then, the correction skew value is calculated by applying Equation 1 to the new CSM graph.

For example, in Fig. 5, the minimum skew values Tmin are -5 and -3, with N_Tme = 2 if the user selects the threshold range A = 3. If the user selects the threshold number A = 1, the method according to FIG. 4 will perform a new CSM test without the CSM graph of FIG. 5 being based on the calculation of the correction skew value. As a result, according to the present invention, the user may exclude the test result of the CSM determined by the user as the CSM test result due to the abnormal head by selecting the threshold range and the threshold number from the calculation of the correction skew value.

7 is a diagram illustrating a head tuning method according to a second embodiment of the present invention.

In step 710, the number of errors per skew value is detected by performing a CSM test on a predetermined test track.

In step 720, the number N_Tme of the minimum equivalent skew value Tme is counted in the predetermined threshold offtrack range -A + Tmin = <X <= A + Tmin.

In step 730, it is checked whether the number N_Tme of minimum equivalent skew values is greater than the threshold number N_th. The threshold number N_th is selectable by the user. If so, go to step 740; otherwise, go to step 735.

In step 735, it is checked whether the error count Y_left in the leftmost offtrack and the error count Y_right in the rightmost offtrack are equal to the minimum error count Ymin. If all are the same proceed to step 740, otherwise proceed to step 850.

Error count at leftmost off track Y_left indicates error count at skew value in the outermost circumferential direction of the disc (i.e., -16, in FIG. 5), and error count at rightmost offtrack Y_right is indicated for innermost disc. The error count at the skew value of (ie, +16 in FIG. 5).

In step 740, the recording density (Data Rate, DR) is reduced to a predetermined value, and then the process proceeds to step 710 again.

In step 750, the correction skew value Tc is determined by calculating the area center for each point P (X, Y) in the CSM graph. The off track value Tc is calculated by the above equation (1).

In operation 760, the skew value of the corresponding zone is corrected and stored in the skew table using the correction skew value Tc calculated in operation 750.

According to the method of FIG. 7, the CSM test result of another case indicating an abnormal case of the head can be excluded from the correction skew value calculation. That is, when the number of errors Y_left at the leftmost skew value and the number of errors Y_right at the rightmost skew value are the same as the minimum number of errors Ymin, even when the number of minimum equivalent skew values N_Tme is smaller than the threshold number N_th, it is not reliable. In this case, it is determined that the recording density needs to be changed again in step 735 of FIG. 7, and the flow proceeds to step 740.

8 is a diagram illustrating a head tuning method according to a third embodiment of the present invention.

In step 810, the number of errors per skew value is detected by performing a CSM test on a predetermined test track.

In step 820, the number N_Tme of the minimum equivalent skew value Tme is counted in the predetermined threshold offtrack range -A + Tmin = <X <= A + Tmin.

In step 830, it is checked whether the number N_Tme of minimum equivalent skew values is greater than the threshold number N_th. The threshold number N_th is selectable by the user. If so, go to step 840; otherwise, go to step 835.

In step 835, it is checked whether the error count Y_left in the leftmost offtrack and the error count Y_right in the rightmost offtrack are both equal to the minimum error count Ymin. If all are the same proceed to step 840, otherwise proceed to step 850.

In step 840, it is checked whether the flag flag indicating that the recording density has been changed is set to one. If flag = 1, go to step 846; otherwise, go to step 842. Flag flag is stored in a table that stores test results for each track, and when the flag is set to 1, it indicates that the recording density has already been changed.

In step 842, the flag flag = 1 is set.

In step 844, the recording density DR is changed to the lowest value and the flow proceeds to step 810 again.

In the case where flag = 1 in step 846, that is, in step 840, it is regarded as a tuning failure and the head tuning process ends.

In step 850, the correction skew value Tc is determined by calculating the area center for each point P (X, Y) in the CSM graph. The off track value Tc is calculated by the above equation (1).

In operation 860, the skew value of the corresponding zone is corrected and stored in the skew table using the correction skew value Tc calculated in operation 850.

According to the method of Fig. 8, a flag indicating whether or not the recording density is changed is stored in a table storing test results for each track, and after the CSM test is performed again after the recording density is changed, the CSM that has already been performed for the changed recording density If it is a test, and if the test result for the changed recording density is not trusted, it is regarded as a tuning failure and the tuning procedure is terminated. This may prevent the CSM test of step 810 from being repeatedly performed without any results.

9 is a diagram illustrating a head tuning method according to a fourth embodiment of the present invention.

In step 905, a skew value S representing a coarse skew value is determined by performing skew calibration for a given test track.

Skew correction is a method of roughly calculating the optimal travel of an arm to seek the corresponding track of the disc using four types of burst signals prerecorded on the disc and is well known to those skilled in the art.

In other words, in the embodiment of FIG. 9, before the correction skew value is calculated using the CSM test, the skew correction is used to generate a rough arm moving distance or skew value for correcting the off-track phenomenon.

In step 910, the number of errors is detected for each skew value by performing a CSM test based on the skew value S determined in step 905.

In step 920, the number N_Tme of the minimum equivalent skew value Tme is counted in the predetermined threshold offtrack range -A + Tmin = <X <= A + Tmin.

In step 930, it is checked whether the number N_Tme of minimum equivalent skew values is greater than the threshold number N_th. The threshold number N_th is selectable by the user. If so, go to step 940; otherwise, go to step 935.

In step 935, it is checked whether the error count Y_left in the leftmost offtrack and the error count Y_right in the rightmost offtrack are both equal to the minimum error count Ymin. If all are the same proceed to step 940, otherwise proceed to step 950.

In step 940, it is checked whether the flag flag indicating that the recording density has been changed is set to one. If flag = 1, go to step 946; otherwise, go to step 942. The flag flag is stored in the zone map for each track, and when the flag is set to 1, it indicates that the recording density has already been changed.

In step 942, the flag flag = 1 is set.

In step 944, the recording density DR is changed to the lowest value and the flow proceeds to step 905 again. Unlike the method of Fig. 8, skew correction is performed again after the change of the recording density.

In the case where flag = 1 in step 946, that is, in step 940, the tuning is considered a failure and the head tuning process ends.

In step 950, the correction skew value Tc is determined by calculating the area center for each point P (X, Y) in the CSM graph. The off track value Tc is calculated by the above equation (1).

In step 955, the final skew value S is generated by adding the skew value S generated in step 950 to the skew value S generated in step 950. The final skew value S 'represents the final distance the arm must travel to seek the track.

In step 960, the skew value of the corresponding zone is corrected and stored in the skew table using the correction skew value Tc calculated in step 850.

In the method of FIG. 9, compared to the method of FIG. 8, steps 905 and 955 have been added. That is, after roughly calculating the moving distance of the arm for correcting the offset of the recording head and the reading head by the skew correction, that is, the skew value, the skew value calculated by the skew correction is added to the correction skew value generated by the CSM test. By this, the moving distance of the arm, that is, the final skew value S 'is generated. In other words, according to the method of FIG. 9, faster head tuning is possible by calculating an approximate movement distance of the arm for correcting the off track phenomenon using the skew correction.

In the head tuning method of FIGS. 4 to 9, the moving distance (skew value or skew value) of the arm for correcting the off track phenomenon is calculated for a predetermined test track. This process is repeated for each head and zone, and for each test track if there are more than one test track for each zone.

On the other hand, the head tuning method according to the present invention can be created by a computer program. Codes and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the program is stored in a computer readable media, and read and executed by a computer to implement the MR head skewing method. The information storage medium includes a magnetic recording medium, an optical recording medium, and a carrier wave medium.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

As described above, according to the present invention, a case in which the read capacity of the head is abnormal is detected, and in this case, the CSM test is performed again after readjusting the recording density, thereby further improving the reliability of the head tuning of the hard disk drive. A head tuning method is provided.

Claims (10)

In the head tuning method of the hard disk drive using the CSM test, a) detecting an error number per skew value by performing a CSM test on a predetermined test track; b) determining whether the number of minimum equivalent skew values representing a skew value having an error count equal to the minimum error count for a predetermined threshold offtrack range is greater than the threshold number; And c) if it is determined in step b) that it is greater than the threshold number, then repeating step a) after reducing the recording density. The method of claim 1, wherein the threshold off-track range is determined by extending a predetermined threshold range selected by a user around a skew value having a minimum number of errors. The method of claim 2, d) determining the correction skew value representing the moving distance of the arm for correcting the off-track phenomenon by calculating the area center for each point P (X, Y) in the CSM graph generated in step c). It further comprises a method. The method of claim 3, wherein e) correcting a skew value of a corresponding zone of the hard disk drive using the corrected skew value, and storing the skew value in a skew table. The method of claim 1, wherein after step b), f1) checking whether the number of errors in the leftmost offtrack and the number of errors in the rightmost offtrack in the CMS graph are equal to the minimum number of errors, and f2)) If it is determined that the same in step f1), the method comprising the step of reducing the recording density and then performing a CSM test again. The method of claim 1, wherein the zone map includes a flag indicating that the recording density has been changed, g) checking whether the flag is set to 1 after the steps b) and f1), and if the flag is set to 1, ending the tuning process without proceeding any further. How to. In the head tuning method of the hard disk drive using the CSM test, a) determining a skew value indicative of a coarse correction skew value by performing a skew calibration on a predetermined test track; b) detecting the number of errors per skew value by performing a CSM test based on the skew value; c) determining whether the number of minimum equivalent skew values representing a skew value having an error frequency equal to the minimum error frequency for a predetermined threshold offtrack range is greater than the threshold number; And d) if it is determined in step c) that the threshold number is greater than the threshold number, then reducing the recording density and repeating step a) again. The method of claim 7, wherein e) By calculating the area center of each point P (X, Y) in the CSM graph generated in step d), a correction skew value representing the moving distance of the arm for correcting the offset of the recording head and the reading head is obtained. The method further comprises the step of determining. The method of claim 8, f) storing a new correction skew value generated by summing the correction skew value to the skew value in a skew table of a hard disk drive. A computer-readable recording medium having recorded thereon a program for executing the method of claim 1 on a computer.

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