KR100736406B1 - Method and record readable medium, and hard disk drive for tuning the mr skew between read head and write head - Google Patents

Abstract

A skew tuning method between a read head and a write head of an HDD(Hard Disk Drive), a recording medium, and the HDD are provided to detect when an optimum offtrack value is incorrectly calculated, and to determine whether to finely tune skew between the read head and the write head based on the detected results, thereby preventing the skew from being compensated with an incorrect offtrack value. Data is recorded on a sector of a predetermined track, and the data recorded on the sector is read from each of plural offtrack values(S410-S430). The recorded data is compared with the read data, and error generation frequency is counted based on the compared results(S440). Minimum error generation frequency, intermediate error generation frequency which adds a predetermined value to the minimum error generation frequency, the first offtrack value whose error generation frequency is the same as the intermediate error generation frequency, and the second offtrack value having a larger value than the first offtrack value are calculated(S450,S460). The number of offtrack values, of which error generation frequency which individually corresponds to offtrack values having a larger value than the second offtrack value and having a smaller value than the first offtrack value is smaller than the intermediate error generation frequency, is detected(S470). If the detected number is larger than a reference value, a default value is maintained without compensating skew(S480-S483).

Description

Method and Record readable medium, and Hard Disk Drive for Tuning the MR Skew between read head and write head}

The detailed description of each drawing is provided in order to provide a thorough understanding of the drawings cited in the detailed description of the invention.

1 is a schematic diagram showing an MR skew between a read head and a write head of a hard disk drive.

2 is a flowchart of a conventional test for tuning MR skew between a read head and a write head of a normal hard disk drive.

3A is a graph of the test results shown in FIG. 2.

3B is a graph of MR skew tuning test results for a bad magnetic head.

4 is a flowchart illustrating an MR skew tuning method of a magnetic head of a hard disk drive according to an exemplary embodiment of the present invention.

5 is a block diagram of a hard disk drive driving circuit capable of MR skew tuning of a magnetic head of a hard disk drive according to an exemplary embodiment of the present invention.

The present invention relates to a method and apparatus for an MR skew tuning test, and more particularly, by using a head count of a hard disk drive having a bad head using an error count curve drawn for each offtrack value. It is possible to detect a case of calculating a wrong optimal offtrack value and to calculate an optimal offtrack value based on this, a recording medium recording a program for executing the method, and an optimal offtrack value. It's about a hard disk drive.

1 is a schematic diagram showing an MR skew between a write head 21 and a read head 22 of a hard disk drive. Referring to FIG. 1, a physical offset (Magneto Resistive head Skew, hereinafter referred to as 'MR Skew') exists between the write head 21 and the read head 22 of the magnetic head 20. As a result, when the write head 21 writes data in predetermined sectors of one track Track1 on the disc 10, the write head 21 finds the track track1 to be written and then writes the data. The head 21 writes data at a distance MR Skew away from the read head 21.

When the read head 22 tries to read the recorded data after the write head 21 writes data to predetermined sectors of the track track1, the read head 22 reads the MR skew. Since the recorded data must be read by moving Skew), a read error occurs when the MR skew value is not correct. Therefore, offset compensation is required to reduce the read error due to the MR skew.

In the hard disk manufacturing process, there are Servo Calibration Test and MR Skew Fine Tuning Test as a method for compensating the MR skew. The servo measurement test determines the first optimal offset compensation value (or off-track value) for compensating the MR skew using the servo information of the track.

The MR skew fine tuning test obtains the data obtained from the servo measurement test using an error occurrence number generated when reading the predetermined track with a plurality of different off-track values after recording data on the predetermined track. In order to further reduce the error present in the first order optimal offset compensation value.

2 is a flowchart of a conventional test for tuning MR skew between a read head and a write head of a normal hard disk drive. Referring to FIG. 2, first, a head number to be tested and a track track1 to be tested are determined. Predetermined data is recorded in sectors of a predetermined track 1 of the hard disk drive (S210). A predetermined offtrack value X is set (S220), and at least one time is read based on the set offtrack value X (S230). The number of error occurrences Y is recorded by comparing the data written in the sectors with the read data (S240). The steps S210 to S240 are repeated by changing the offtrack value X (S250). The offtrack value X may be changed by a predetermined amount (eg, 1%) in the left direction (up to + 50%) and the right direction (up to -50%) with respect to the center of the track track1.

If the quality of the disc is poor, the servo information will be defective, and the track width will be non-uniform. Therefore, in order to reduce the test error caused by the deviation of the track widths, the N (N> 1) adjacent to the track to be tested (e.g., track1) is reduced. , Repeating the steps (S210 to S240) for the tracks (e.g., track1-20, track1-10, track1, track1 + 10, and track1 + 20) to calculate the average value of the number of error occurrences. The calculated average value can be used for the MR skew microtuning test.

A plurality of error occurrence times (eg, Y1 to Yn) corresponding to each of the plurality of offtrack values (eg, X1 to Xn) are obtained, and an optimal offtrack value t1 is calculated based on these values. Obtained by (S260)

The tracks to be tested are changed to calculate the optimal off track values for each track by repeating the steps S210 to S260 (S270).

FIG. 3A is a graph f1 (x) of the test results shown in FIG. 2. Referring to FIG. 3A, the graph shows a bath tube curve f1 (x) of an error monitoring value provided by an off-track channel chip in the case of a normal head. The minimum error occurrence count indicates a channel error monitoring value when the read error occurrence count is minimum. The number of intermediate error occurrences is a value that is obtained experimentally to obtain a negative offtrack value and a positive offtrack value. The N off track value is an off track value corresponding to the number of intermediate error occurrences in a negative (−) off track direction from an off track value corresponding to the minimum number of error occurrences, and the P off track value is the minimum error occurrence. The off-track value corresponding to the number of times of occurrence of the intermediate error in the positive off-track direction from the off-track value corresponding to the number of times.

In the graph, the area center point of the hatched portion of which the number of error occurrences is smaller than the number of middle error occurrences is obtained by Equation 1, and the off-track value at the area center point is set as an optimal off track value t1.

3B is a graph f2 (x) of the MR skew tuning test result of the defective magnetic head. Referring to FIG. 3B, in the case of a bad magnetic head, the graph of the test result shows an abnormal curve f2 (x). When the optimal off track value based on the abnormal curve f2 (x) is obtained by Equation 1, the wrong optimal off track value t2 is not the optimal off track value t1 of the normal magnetic head. It is selected as the off track value. Therefore, in the case of MR skew microtuning with the wrong optimal offtrack value (t2), the offtracked data signal is written when data is written, and a lot of errors occur during data readout, resulting in a process failure. .

Therefore, the technical problem to be achieved by the present invention is to detect the case of calculating the wrong optimal off-track value by the head characteristics of the hard disk drive having a defective head, and to determine the optimal off-track value based on the detected result The purpose of this study is to improve hard disk process yield and quality.

According to an aspect of the present invention, a method for tuning a skew between a read head and a write head of a hard disk drive includes a data read step, an error count count step, an operation step, a detection step, and a skew tuning step. . The data reading step records data in at least one sector of a predetermined track and reads data recorded in the at least one sector from each of a plurality of different off-track values.

The counting error counting step compares the recorded data with the read data, and counts the number of error occurrences based on the comparison result.

The calculating step may include a minimum number of error occurrences, an intermediate number of error occurrences obtained by adding a predetermined value to the minimum number of occurrences of errors, based on the number of error occurrences corresponding to each of the plurality of different off-track values, and the plurality of operations. A first offtrack value and a second offtrack value selected from the offtrack values are calculated. An error occurrence frequency corresponding to each of the first offtrack value and the second offtrack value is the same as the intermediate error occurrence frequency.

The first off track value is an off track value that is smaller than the second off track value and the off track value corresponding to the minimum error occurrence frequency and has a minimum difference between the minimum error occurrence frequency. The second off-track value is an off-track value that is greater than the off-track value corresponding to the minimum number of occurrences of the error and has a minimum difference from the off-track value corresponding to the minimum number of occurrences of the error.

The detecting step detects the number of off-track values belonging to a range smaller than the first off-track value and larger than the second off-track value among the off track values having the number of error occurrences smaller than the number of intermediate error occurrences. do.

The skew tuning step includes a default value holding step and a skew fine tuning step. The default value maintaining step maintains a default value without compensation for skew when the detected number is larger than a predetermined reference value. In the skew fine tuning step, when the detected number is less than or equal to the predetermined reference value, multiply the error occurrence times corresponding to each of the off-track values of the first group by each of the off-track values of the first group. The value obtained by dividing the sum by the sum of the error occurrence times corresponding to each of the off-track values of the first group is obtained, and the optimal off track value is obtained. The off-track values of the first group are off-track values existing between the first off-track value and the second off-track value among the plurality of off-track values.

BRIEF DESCRIPTION OF THE DRAWINGS In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings. You must do it. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

4 is a flowchart illustrating an MR skew tuning method of a magnetic head of a hard disk drive according to an exemplary embodiment of the present invention. Referring to FIG. 4, first, a head number to be tested and predetermined tracks (eg, track1) are determined, and data is recorded in predetermined sectors of the predetermined track 1 (S410). A predetermined offtrack value (eg, -18%) is set (S420), and data is read using the set offtrack value (S430). The number of reads here is variable. The read data is compared with the recorded data (for example, may be recorded in a predetermined data storage device). The error occurrence count Y is counted and recorded (S440). After changing the set offtrack value (eg -18%), the steps S410 to S440 are repeated with the changed value (eg -17%) (S450).

If the quality of the disc is poor, poor Servo information will result, and the width of the track will be non-uniform. Therefore, in order to reduce the test error caused by the deviation of the track widths, the adjacent N ( After the steps S410 to S450 are repeated for N> 1 tracks, an average value calculated by calculating an average value of the number of error occurrences may be used for the MR skew microtuning test.

On the basis of the number of error occurrences (or an average value of the number of error occurrences) corresponding to each of a plurality of different off-track values according to the result of step S450, the minimum number of error occurrences, the number of intermediate error occurrences, and the first off-track value (x1) and the second off-track value x2 are calculated (S460).

The number of intermediate error occurrences is a value that is experimentally determined to obtain the first off track value x1 and the second off track value x2.

An error occurrence frequency corresponding to each of the first offtrack value x1 and the second offtrack value x2 is the same as the intermediate error occurrence frequency. The first offtrack value x1 is less than the offtrack value t2 corresponding to the second offtrack value x2 and the minimum number of occurrences of an error, and the offtrack value t2 corresponding to the minimum number of occurrences of an error. ) Is the minimum off-track value. The second off track value (x2) is greater than the off track value (t2) corresponding to the minimum number of occurrences of an error, and the off track value having a minimum difference from the off track value (t2) corresponding to the minimum number of occurrences of an error. to be.

Among the plurality of different offtrack values, an error occurrence frequency corresponding to offtrack values existing in an area smaller than the first offtrack value x1 and greater than the second offtrack value x2 is the intermediate error occurrence number. The number N of smaller off-track values is detected (S470).

When the detected number N is larger than a predetermined reference value K (N> K), error detection information about the tested head and the track track1 is stored in a maintenance cylinder of the disc. After storing (S481) and performing the above steps (S410 to S481) at least once more and the same result (if N> K) is obtained (S482), it is kept at the default value (Default) without compensation for skew ( S483). In this case, the default value is a value obtained as a result of a Servo Calibration Test in which the MR skew is compensated primarily by using the servo information of the track.

If the detected number N is less than or equal to the predetermined reference value K, an error corresponding to each of the off-track values of the first group and each of the off-track values of the first group, as shown by Equation 1 The sum of the number of occurrences and the sum of the sum values is obtained (SUM (XY)), and the sum of the error occurrences corresponding to each of the first group of off-track values is obtained (SUM (Y)). Based on this, an optimal offtrack value t1 is obtained (SUM (XY) / SUM (Y)). The off-track values of the first group are off-track values existing between the first off-track value (X1) and the second off-track value (X2) among the plurality of off-track values (S490). The steps S410 to S490 are repeated by changing the track to be tested.

5 is a block diagram of a driving circuit of the hard disk drive 500 capable of MR skew tuning of the magnetic head 521 according to an embodiment of the present invention. Referring to FIG. 5, the hard disk drive 500 may include a disk 510, a head stack assembly 520, a voice coil motor driving circuit 530, a nonvolatile memory 540 that may be implemented as a flash memory, and a controller. 550. The disk 510 stores data. The head stack assembly 520 has a magnetic head 521 and an actuator 522. The magnetic head 521 includes a write head 523 and a read head 524. The actuator 522 allows the magnetic head 521 to access data on the disk 510. The voice coil motor driving circuit 530 rotates the actuator 522.

The flash memory 540 stores a plurality of instructions for the MR skew tuning test of the magnetic head 521. The controller 550 calculates an optimal off-track value by performing a plurality of commands for the MR skew tuning test patched from the flash memory 540, and based on this, the voice coil motor driving circuit 530. To generate a control signal for controlling

The controller 550 writes data in predetermined sectors of a predetermined track, reads data stored in the predetermined sectors at least once in a plurality of different off-track values, and reads the recorded data and the read data. The number of error occurrences is counted based on the result of comparing the data.

The controller 550 may generate a minimum number of error occurrences, an intermediate number of error occurrences obtained by adding a predetermined value to the minimum number of occurrences of errors, based on the number of error occurrences corresponding to each of the plurality of different off-track values, and the plurality of errors. A first offtrack value and a second offtrack value selected from the offtrack values of are calculated.

The number of intermediate error occurrences is a value that is experimentally determined to obtain the first offtrack value and the second offtrack value.

An error occurrence frequency corresponding to each of the first offtrack value and the second offtrack value is the same as the intermediate error occurrence frequency. The first off track value is an off track value smaller than the second off track value and an off track value corresponding to the minimum number of error occurrences, and having a minimum difference between the off track values corresponding to the minimum number of error occurrences. The second off-track value is an off-track value that is greater than the off-track value corresponding to the minimum number of occurrences of the error and has a minimum difference from the off-track value corresponding to the minimum number of occurrences of the error.

The controller 550 may generate an error frequency corresponding to the off-track values existing in an area smaller than the first off-track value and larger than the second off-track value among the plurality of different off-track values. Detect the number N of offtrack values less than the number of times

The controller 550 maintains a default value without compensating for skew when the detected number N is greater than a predetermined reference value K. FIG. When the detected number N is less than or equal to the predetermined reference value K, the controller 550 may include an error corresponding to each of the off-track values of the first group and each of the off-track values of the first group. A value obtained by dividing the number of occurrences by the sum of the multiplication values and the sum of the error occurrence times corresponding to each of the first group of offtrack values is obtained, and the optimal offtrack value is obtained. The off-track values of the first group are off-track values existing between the first off-track value and the second off-track value among the plurality of off-track values.

The present invention can be embodied as computer readable codes on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, optical data storage, and the like. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. And functional programs, codes and code segments for implementing the present invention can be easily inferred by programmers in the art to which the present invention belongs.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, the method for tuning the skew between the read head and the write head of the hard disk drive according to the present invention detects a case where a wrong optimal offtrack value is calculated by the head characteristics of a hard disk drive having a bad head. Determining whether to fine tune the skew between the read head and the write head based on the detected result has an effect of preventing the skew from being compensated with an incorrect off-track value.

Claims (9)

A first step of recording data in a sector of a predetermined track and reading data recorded in the sector at each of a plurality of offtrack values; A second step of comparing the recorded data with the read data and counting the number of occurrences of an error based on the comparison result; Based on the number of error occurrences corresponding to each of the plurality of offtrack values, the minimum number of error occurrences, the intermediate number of error occurrences plus a predetermined value plus the minimum number of error occurrences, and each of the plurality of offtrack values A third step of calculating a second off track value having a first off track value having a corresponding error occurrence number equal to the intermediate error occurrence number and a value greater than the first off track value; Among the plurality of off-track values, the number of off-track values corresponding to each of the off-track values smaller than the first off-track value and having a value larger than the second off-track value is smaller than the intermediate error number is determined. Detecting a fourth step; And And a fifth step of maintaining a default value without compensating for skew when the detected number is greater than a predetermined reference value. The method of claim 1, The first off track value is, An off-track value smaller than the off-track value corresponding to the minimum number of error occurrences and having a minimum difference from the minimum number of error occurrences, The second off track value is, And an off track value greater than the off track value corresponding to the minimum number of error occurrences and having a minimum difference between the minimum number of error occurrences and the minimum number of error occurrences. The method of claim 2, When the detected number is less than or equal to the predetermined reference value, the sum of the error occurrence times corresponding to each of the off-track values of the first group and each of the off-track values of the first group is obtained by adding up the sum values. And a value obtained by dividing the sum of the number of error occurrences corresponding to each of the group off track values as an optimal off track value, Off-track values of the first group, And off-track values between the first off-track value and the second off-track value among the plurality of off-track values. The method of claim 2, The different plurality of off track values of the first step are And a skew between a read head and a write head of a hard disk drive, characterized in that it belongs to a predetermined range in a lateral direction based on the center of the predetermined track. The method of claim 2, The fifth step, And storing the test head and the error detection information about the track in a maintenance cylinder of the disk when the detected number is larger than a predetermined number. How to tune skew between write heads. The method of claim 2, The fifth step, Read head of a hard disk drive, characterized in that if the first step is performed at least once before the fifth step before maintaining the default value without compensation for skew, and if the same result as before To tune the skew between data and the write head. A recording medium having recorded thereon a program for performing a method of tuning a skew between a read head and a write head of a hard disk drive according to any one of claims 1 to 6. In the hard disk drive, A disk for storing data; A magnetic head having a read head and a write head; An actuator for flying the magnetic head to access data on the disk; A voice coil motor driving circuit for rotating the actuator; A flash memory storing a plurality of instructions for performing a tuning test of the magnetic head; And And a controller configured to perform a plurality of instructions for the tuning test patched from the flash memory to calculate an optimal offtrack value, and generate a control signal for controlling the voice coil motor driving circuit based on the same. , The controller, Data is recorded in a sector of a predetermined track, data stored in the sector is read based on each of a plurality of off-track values, and the number of error occurrences is counted based on a result of comparing the recorded data with the read data. and, A minimum number of error occurrences based on the number of error occurrences corresponding to each of the plurality of offtrack values, an intermediate number of occurrences of the minimum number of error occurrences plus a predetermined value, and a corresponding one of the plurality of offtrack values Calculates a first off track value having an error occurrence frequency equal to the intermediate error occurrence frequency and a second off track value having a value greater than the first off track value; Among the plurality of offtrack values, the number of offtrack values corresponding to offtrack values smaller than the first offtrack value and larger than the second offtrack value and smaller than the intermediate error occurrence count is determined. Detect, And a default value without compensation for skew when the detected number is larger than a predetermined reference value. The method of claim 8, The controller, When the detected number is less than or equal to the predetermined reference value, a value obtained by adding up a value obtained by multiplying an error occurrence number corresponding to each of the off-track values of the first group and each of the off-track values of the first group is added to the first value. The optimal off track value is obtained by dividing the sum of the number of error occurrences corresponding to each of the group off track values. Off-track values of the first group, And among the plurality of offtrack values, offtrack values existing between the first offtrack value and the second offtrack value.

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