JP4272363B2 - Magnetic disk unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic disk device capable of optimally correcting read waveform distortion.
[0002]
[Prior art]
Conventionally, when writing magnetization transition information to a hard disk, which is a magnetic disk device, if a certain transition point and a previous transition point are close to each other, the waveform is distorted due to mutual interference and deviates from the target transition point. This shift is called NLTS (Non Linear Transition Shift), and writing is performed by shifting the transition point in advance in consideration of this shift. This technique is called light pre-compensation.
[0003]
FIG. 5 is an explanatory diagram of waveform correction by conventional write pre-compensation, FIG. 5 (a) is a description of a write current (no correction) waveform, and FIG. 5 (b) is an explanation of a read waveform (no correction). It is. In FIG. 5A, when writing is performed on the magnetic disk with the write current having the waveform shown in the figure, and then reading from the magnetic disk is performed, the waveform shown in FIG. 5B is obtained. The maximum and minimum peaks of the read waveform are shifted from the rising and falling points (transition points) of the target write current by α1 and α2.
[0004]
FIG. 5C illustrates the write current (with correction) waveform, and FIG. 5D illustrates the read waveform (with correction). In order to correct the waveform of FIG. 5B, in FIG. 5C, writing is performed with a waveform that rises behind the target transition point by .beta.1 and falls earlier by .beta.2 from the target transition point. Pre-compensation). Thereafter, when reading from the magnetic disk, the waveform shown in FIG. The maximum and minimum peaks of the read waveform coincide with the target transition points (the rising and falling points of the write current) in FIG.
[0005]
In the write pre-compensation in FIG. 5C, writing was performed with a waveform that rises by β1 later than the target transition point and falls by β2 earlier, but the head, magnetic disk (medium), etc. Depending on the characteristics, writing may be performed with a waveform that rises earlier than the target transition point and falls later.
[0006]
6A and 6B are explanatory diagrams of NLTS correction by conventional write pre-compensation. FIG. 6A is a description of write current, FIG. 6B is a description of medium magnetization state, and FIG. • Explanation of pre-compensation write current.
[0007]
When writing is performed on the medium (magnetic disk) with the write current having the waveform shown in FIG. 6A, the medium magnetization state shown in FIG. 6B is magnetized by shifting by α from the target transition point (NLTS). Each arrow on the upper side of FIG. 6B indicates the magnetization direction of the medium. In this case, the write pre-compensation is such that the falling of the write current is shifted (delayed) by β from the target falling point (FIG. 6A) as shown in FIG.
[0008]
Conventionally, in order to determine the amount of light pre-compensation, a table is prepared in advance and a method corresponding to an actual measurement result (see Japanese Patent Laid-Open No. 5-266687) or a reference amount is determined. Means (see Japanese Patent Application Laid-Open No. 9-180373) and the like for changing the value minutely and determining an optimum value from the actual measurement result have been used.
[0009]
[Problems to be solved by the invention]
The conventional device has the following problems.
[0010]
(1): Regarding a method of preparing a table in advance and making write pre-compensation correspond to an actual measurement value, since the actually measured waveform is distorted due to various factors, means simply using a numerical table such as a peak shift amount According to the above, there is a possibility that proper correction cannot be performed in a case where a deviation from the condition assumed when the table is created occurs.
[0011]
(2): Correcting this defect is a method of obtaining an actual measurement value while changing the amount of light pre-compensation itself within a certain range from a reference value, and obtaining an optimum solution. If the range was too wide or too many sample points were taken, the efficiency would be poor and processing time would be required.
[0012]
An object of the present invention is to solve such a problem and to use a pattern matching technique to appropriately and efficiently determine the amount of write pre-compensation.
[0013]
[Means for Solving the Problems]
FIG. 1 is an explanatory diagram of a magnetic disk device according to an embodiment of the present invention. In FIG. 1, 10 is a medium (magnetic disk), 11 is a magnetic head, 12 is an R / W control unit, 13 is control means, 14 is a decoder, 15 is storage means (waveform table), and 16 is pattern matching means. .
[0014]
The present invention has the following means in order to solve the conventional problems.
[0015]
(1): pre-Write precomp amount written to the reference model medium by a plurality of write waveform with varying, the write pre-compensation amount of-compensation for a plurality of distorted waveform and the strain waveform read out from the medium 10 A storage unit 15 for storing a table; and a control unit 13 for controlling pattern matching. The control unit 13 includes a signal waveform read from the medium 10 for correcting waveform distortion, and a distortion waveform of the table. Pattern matching is performed, the most similar distortion waveform in the table is determined, and the corresponding write pre-compensation amount is determined from the determined distortion waveform . For this reason, it is possible to determine the amount of write pre-compensation with high accuracy even for a waveform including various distortion factors, in which similarity is determined from the entire waveform.
[0016]
(2): In the magnetic disk apparatus of (1), the control means 13 calculates a normal correlation value and performs pattern matching. Therefore, pattern matching can be performed with high accuracy by digital image processing.
[0017]
(3): In the magnetic disk device of (1) or (2), the control means 13 reads the signal waveform from the medium 10 a plurality of times and determines the amount of write pre-compensation. For this reason, the amount of light pre-compensation can be finely adjusted to a more optimal value.
[0018]
(4): In the magnetic disk apparatus of (1) to (3), the control means 13 performs write pre-compensation based on the peak shift amount of the waveform when the similarity by pattern matching is less than a certain value. Make an amount determination. For this reason, even when the waveforms are greatly different and are not suitable for pattern matching, the amount of write pre-compensation can be determined.
[0019]
(5): In the magnetic disk apparatus of (1) to (4), the control means 13 accumulates the similarity by pattern matching and issues a warning when the similarity below a certain value continues. To do. For this reason, it is possible to determine whether or not the waveform in the table is appropriate and re-create the table.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a distortion waveform with respect to the write pre-compensation amount is measured, and a table of the waveform is created and stored in the signal processing software (on the memory). Then, if the most similar waveform is determined by comparing with the actually measured waveform by the pattern matching method, the transition width is also determined, and the amount of write pre-compensation is also determined therefrom. As a result, even a waveform having various distortion factors can be determined using information of the entire waveform, and the write pre-compensation amount can be determined with high accuracy. In addition, in order to further improve the accuracy, it is possible to acquire the actually measured waveform again and make the same determination. Also in this case, the number of times of actual measurement value acquisition is less than that of the conventional method, so that the efficiency can be improved and the processing time can be shortened.
[0021]
(1): Description of Magnetic Disk Device In FIG. 1, the magnetic disk device includes a magnetic disk (medium) 10, a magnetic head 11, a read / write (R / W) control unit 12, a control means 13, a decoder 14, and a waveform. A table 15 and pattern matching means 16 are provided.
[0022]
The magnetic disk 10 records information magnetically. The magnetic head 11 reads / writes information by moving on the surface of the magnetic disk 10. The R / W control unit 12 performs read / write control. The control means 13 performs control of information transfer with the host and the R / W control unit 12, control of write / precompensation, and the like. The decoder 14 converts the read waveform read by the magnetic head 11 into digital information. The decoder 14 can also be provided in the R / W control unit 12. The waveform table 15 is storage means for storing the correspondence between the write pre-compensation amount and the waveform distortion. The pattern matching means 16 performs pattern matching between the waveform in the waveform table 15 and the actually measured waveform.
[0023]
(2): Explanation of the waveform table A distortion waveform with respect to the write pre-compensation amount (set in plural) is measured in advance, and the waveform table is created and stored in storage means such as a memory. It is.
[0024]
FIG. 2 is an explanatory diagram of a waveform table. In FIG. 2, for example, the distortion waveform (1) for the write pre-compensation amounts a1 and b1 is measured as in the upper stage, and the waveform (1) is stored in a storage means such as a memory. Further, the distortion waveform (2) for the write pre-compensation amounts a2 and b2 is measured, and the waveform (2) is stored in a storage means such as a memory. Further, a distortion waveform (3) for the write pre-compensation amounts a3 and b3 is measured, and the waveform (3) is stored in a storage means such as a memory. As described above, a plurality of write pre-compensation amounts are set in advance by the control means 13, and the waveform table 15 of the corresponding distortion waveform is created.
[0025]
In the determination by pattern matching, the signal written to the magnetic disk 10 by the R / W control unit 12 and the magnetic head 11 from the control means 13 is read again via the magnetic head 11 and the R / W control unit 12, and the read actual measurement is performed. Pattern matching is performed with the waveform and the waveform of the waveform table 15. The most similar waveform is determined by this pattern matching, and the write pre-compensation amount corresponding to the waveform is determined.
[0026]
(3): Explanation of Readout Waveform Distortion Correction Method Readout waveform distortion correction is performed by first writing and precompensation amount to waveform distortion correspondence table (predetermined waveform) by experiment and measurement on a magnetic disk device of one model medium. (For example, one waveform table for one model medium). Then, a normal correlation between the waveform in the table and the actually measured waveform of the symmetric device (targeting all one magnetic disk device) is calculated to determine the optimum write / precompensation amount. Instead of calculating the normal correlation in consideration of the calculation time, it is also possible to perform a difference calculation with a quick calculation time.
[0027]
FIG. 3 is a flowchart of read waveform distortion correction processing. Hereinafter, a description will be given according to the processes S1 to S7 in FIG.
[0028]
S1: When the process starts, the control means 13 sets the write pre-compensation amount and writes it to the magnetic disk, and proceeds to process S2.
[0029]
S2: The control means 13 measures the waveform read from the reference magnetic disk, and proceeds to processing S3.
[0030]
S3: The control means 13 stores the waveform measured in the previous period S2 in the nth position of the table, and proceeds to processing S4.
[0031]
S4: The control means 13 determines whether the stored table has a predetermined number of waveforms. If it is determined that the number of waveforms is predetermined, the process proceeds to step S5. If the number of waveforms is not the predetermined number, the process returns to step S1. The table creation in the processes S1 to S3 is performed using the reference model medium while shifting the write waveform little by little.
[0032]
S5: The control means 13 measures the read waveform of the target device, and proceeds to processing S6.
[0033]
S6: The control means 13 performs pattern matching between the read waveform of the target device and the waveform of the table, and proceeds to processing S7. This pattern matching is performed by normal correlation or difference calculation. Further, when there are a plurality of magnetic heads, pattern matching is performed by reading for each head.
[0034]
S7: The control means 13 determines the write pre-compensation amount corresponding to the waveform with the most matched pattern, and ends this process.
[0035]
(4): Explanation of fine adjustment of write pre-compensation Considering the actual operation of read waveform distortion correction, the above processing S5 to S7 are not finished once, but the measured waveform is acquired again as follows. Then, the light pre-compensation amount is determined repeatedly and finely adjusted to obtain a more optimal value. The reason for acquiring the actually measured waveform a plurality of times in this way is that it may happen to hit a medium or the like, and it is dangerous to decide by one measurement. Further, when acquiring the measured waveform again, it is desirable to change the reading position of the medium.
[0036]
FIG. 4 is a flowchart of fine adjustment processing for write pre-compensation. Hereinafter, a description will be given according to the processes S11 to S15 of FIG.
[0037]
S11: When the process starts, the control means 13 measures the read waveform of the target device, and proceeds to process S12.
[0038]
S12: The control means 13 determines whether or not a predetermined fine adjustment is necessary (a predetermined number of times). If fine adjustment is still necessary in this determination, the process proceeds to step S13, and if predetermined fine adjustment is completed, this process ends.
[0039]
S13: The control means 13 performs pattern matching between the read waveform of the target device and the waveform of the table, and proceeds to processing S14.
[0040]
S14: The control means 13 determines the write pre-compensation amount corresponding to the waveform with the most matched pattern, and proceeds to processing S15.
[0041]
S15: The control unit 13 changes the parameter of the target device (sets the determined write / precompensation amount in a waveform correction unit (not shown) such as an encoder of the R / W control unit 12), and returns to the process S11. .
[0042]
As described above, in the method in which the amount of write pre-compensation performed to correct waveform distortion caused by NLTS or waveform interference when reading a signal from a magnetic disk device such as a hard disk device is controlled by software in advance. Create a distortion waveform table, calculate the normal correlation with the actually measured waveform, perform pattern matching, determine the optimal amount of light pre-compensation based on the result, and optimize the correction Can be done.
[0043]
Further, instead of calculating the normal correlation, a difference with a quick calculation time (subtraction by overlapping waveforms) can be performed.
[0044]
Furthermore, once the amount of write pre-compensation is determined, the read waveform is measured again, and fine adjustment is performed by determining the amount of second write pre-compensation using the same method. It is possible to adjust to an optimal value (it is set to the larger value when the value of the write pre-compensation amount is different) than the repetition.
[0045]
Further, when the value of the normal correlation is too low (the waveforms are greatly different), the amount of write pre-compensation can be determined based on the value of the peak shift amount as in the conventional example.
[0046]
Furthermore, a function is provided for accumulating read waveform and normal correlation value data, determining whether the waveform in the distortion waveform table is appropriate based on the accumulated data, and issuing a warning if necessary. You can also. In other words, when a low normal correlation value continues (for example, the head has been changed), the table needs to be recreated. Therefore, the control means 13 displays a warning or notifies the host (personal computer) of the warning. is there.
[0047]
【The invention's effect】
As described above, the present invention has the following effects.
[0048]
(1): The control means performs pattern matching between the signal waveform actually read from the medium and the distortion waveform of the table, determines the most similar distortion waveform in the table, and determines the amount of write pre-compensation. Therefore, the similarity is determined from the entire waveform, and the amount of write pre-compensation can be determined with high accuracy even for a waveform including various distortion factors.
[0049]
(2): Since the control means calculates the normal correlation value and performs pattern matching, pattern matching can be performed with high accuracy by digital image processing.
[0050]
(3): Since the control means determines the amount of write pre-compensation multiple times, the amount of write pre-compensation can be finely adjusted to a more optimal value.
[0051]
(4): When the similarity by pattern matching is below a certain value in the control means, the waveform is greatly different because the amount of write pre-compensation is determined based on the peak shift amount of the waveform. Even if it is not suitable for pattern matching, the amount of light pre-compensation can be determined.
[0052]
(5): The control means accumulates the similarity by pattern matching, and determines whether the waveform in the table is valid in order to issue a warning when the similarity below a certain value continues. The table can be remade.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a magnetic disk device according to an embodiment.
FIG. 2 is an explanatory diagram of a waveform table in the embodiment.
FIG. 3 is a flowchart of a read waveform distortion correction process in the embodiment.
FIG. 4 is a flowchart of fine adjustment processing of write pre-compensation in the embodiment.
FIG. 5 is an explanatory diagram of waveform correction by conventional write pre-compensation.
FIG. 6 is an explanatory diagram of NLTS correction by conventional write pre-compensation.
[Explanation of symbols]
10 Medium (magnetic disk)
11 Magnetic Head 12 R / W Control Unit 13 Control Unit 14 Decoder 15 Storage Unit (Waveform Table)
16 Pattern matching means

Claims (5)

Storage for storing a table of the amount of Write precomp for advance Write precomp amount written to the reference model medium by a plurality of write waveform with varying multiple distorted waveform and the strain waveform read out from the medium Means,
Control means for controlling pattern matching,
The control means performs pattern matching between the signal waveform read from the medium for correcting waveform distortion and the distortion waveform of the table, determines the most similar distortion waveform in the table, and determines the determined distortion waveform. A magnetic disk drive characterized in that the amount of corresponding write pre-compensation is determined. The control means, a magnetic disk device according to claim 1, wherein characterized in that intends row pattern matching by calculating the normalized correlation value.   3. The information processing apparatus according to claim 1, wherein the control means reads a signal waveform from the medium a plurality of times and determines the amount of write pre-compensation.   4. The control unit according to claim 1, wherein when the degree of similarity by pattern matching is equal to or less than a predetermined value, the amount of write pre-compensation is determined based on a peak shift amount of the waveform. The magnetic disk device described.   5. The magnetic disk apparatus according to claim 1, wherein the control means accumulates the similarity by pattern matching and issues a warning when the similarity of a certain value or less continues.

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