KR20080017995A - Method for servo calibration in disk which have both cstw pattern area and astw pattern area - Google Patents

Abstract

A servo calibration method in a disk having both a CSTW pattern area and an ASTW pattern area is provided to calculate a PES(position error signal) accurately and to execute read/write operations on a target track accurately by executing the servo calibration operation according to TPI(track per inch). All tracks of a disk are divided into K zones and N-K zones based on the boundary line between a CSTW(conventional servo track write) pattern area and an ASTW(ammonite servo track write) pattern area(S102,S104). A sampling value of parameter necessary for servo control is measured in the sampled positions among the N zones, and an independent servo calibration operation is executed on each pattern area by referring to the measured sampling value(S106,S108).

Description

Method for servo calibration in disk which have both CSTW pattern area and ASTW pattern area}

1 is a diagram illustrating a disc in which a CSTW pattern region and an ASTW pattern region coexist.

FIG. 2 is a diagram for illustrating a difference in track per inch (TPI) between a CSTW pattern region and an ASTW pattern region.

3 is a diagram illustrating a relative position of a servo burst signal with respect to a track.

4A is a diagram illustrating a first position offset to compensate for the head position when the head is offtracked to 5% or less.

4B shows a second position offset to compensate for head position when the head offtracks above 5% and below 45%.

4C is a diagram showing MR skew due to the positional difference between the recording head and the reading head.

5A is a diagram illustrating an error of MR skew in the CSTW pattern region and the ASTW pattern region.

5B is a diagram illustrating PES errors in the CSTW pattern region and the ASTW pattern region.

6 is a flowchart illustrating a servo calibration operation according to an embodiment of the present invention.

7 is a flowchart illustrating a servo calibration operation according to another embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hard disk drive. In particular, when performing a calibration operation of a servo signal recorded on a disk having a CSTW pattern area and an ASTW pattern area, the accuracy thereof is improved, thereby improving data access performance according to accurate PES signal detection. The present invention relates to a servo calibration method that can be improved.

The hard disk drive includes a plurality of magnetic heads connected to a rotating disk. The head magnetizes the disk surface to record information or detects the magnetic field of the disk surface to read the information. Information is typically stored in tracks formed concentrically on the disk, the tracks having a plurality of sectors, each sector having a servo field and a data field.

The tracking servo device of the hard disk drive controls the head to move on the track's centerline. The tracking servo reads the servo burst signals from the disk to calculate the position of the head relative to the track centerline, and controls the voice coil motor (VCM) with reference to the calculated results so that the head follows the track's centerline. To control.

As a method of recording a servo pattern, there is a method of using a servo writer during a hard disk manufacturing process. However, this method has a problem in that the accuracy of recording is lowered due to non-repeatable run out (NRRO), disk flutter and motor vibration.

In addition to the increase in storage density, HDDs are rapidly increasing in track density. In other words, TPI (Track Per Inch) is increasing. As the track density increases, the track width becomes narrower, and thus the accuracy of servo writing that records the servo pattern used for locating the head to disk is approaching its limit.

Therefore, at present, the servo pattern is recorded using a conventional servo track write (CSTW) method and a spiral seed pattern, which is a method of recording a servo pattern using a servo recorder. ASTW (Ammonite Servo Track Write) method is being used simultaneously.

Conventionally, the entire disk is evenly divided into N zones, and the parameters necessary for servo control, for example, MR (Magnetic Registor) offset, are measured at some of the sampled positions and measured on the disk's maintenance cylinder. In the case of Track Seeking, when the head is between the sampled positions, the MR offset of the target track is calculated by interpolation using the MR offsets measured at adjacent sampling positions. The position of the lead head was compensated.

However, this interpolation method assumes that the track width is uniform, and thus does not reflect the position error and the change in the track width due to the difference in the pattern. In particular, in the recording of the servo pattern, when both the CSTW method and the ASTW method are used, a change in the interval between tracks occurs before and after the conventional method, and the conventional method performs a calibration operation based on the measured sampling data without considering this. Was performed.

In particular, using the conventional method, the problem is more prominent in different pattern regions than in the same pattern region. That is, since the track width that changes back and forth between the boundary of the CSTW pattern area and the ASTW pattern area cannot be reflected, when the head performs tracking operation with reference to sampling data existing in different pattern areas, the target track This causes the data to be read and written from outside the center of the.

An object of the present invention is to accurately calculate a position error signal (PES) by performing a servo calibration operation in consideration of a track per inch (TPI) that changes based on a boundary line between a CSTW pattern region and an ASTW pattern region. The present invention provides a servo calibration method that enables accurate and stable read / write operations on a track.

In order to solve the above technical problem, the servo calibration method according to the present invention includes all the tracks of the disc as K and NK zones, respectively, based on a boundary line between the CSTW pattern area and the ASTW pattern area. Dividing and measuring a sampling value of a parameter required for servo control at a sampled position among the N zones, and performing an independent servo calibration operation for each pattern region with reference to the measured sampling value.

In this case, a servo calibration operation is performed between a zone and a zone having the same pattern by using an interpolation method of measured sampling values, and a zone measured between the zones and zones having a different pattern based on a boundary line. It is preferable to perform a servo calibration operation using a method of extrapolating a sampling value.

The parameter includes: MR (Magnetic Resistor) skew caused by the positional difference between the recording head and the reading head, to compensate for the head position when the head mounted on the disc drive is offtracked to 5% or less relative to the center of the track. A first position offset and a second position offset may be included to compensate for the head position when the head mounted to the disc drive is offtracked by more than 5% and less than 45% relative to the center of the track.

The K zones in the CSTW pattern region preferably have a smaller width than the N-K zones in the ASTW pattern region. It is preferable that at least one sampled position exists for each zone.

Servo calibration method according to another embodiment of the present invention for solving the technical problem, K and NK zones (Kone), respectively, based on the boundary of the CSTW pattern area and the ASTW pattern area of the entire track of the disk Dividing into N, measuring a sampling value of a parameter required for servo control at a sampled position among the N zones, classifying the pattern into a pattern area and storing the sampling value in a memory in a lookup table form; and seek as a target track. The method may include determining which pattern region the target track exists in, and receiving a sampling value of a corresponding parameter from the memory to perform a servo calibration operation.

Here, the servo calibration operation is performed between the zones having the same pattern and the zones by interpolating the measured sampling values, and the sampling measured based on the boundary line between the zones having the different patterns and the zones. It is preferable to perform a servo calibration operation by using an extrapolation method.

If the target track exists at the boundary line, the servo calibration operation may be performed at a distance of moving the predetermined track from the target track.

The memory may be a non-volatile memory (Read Only Memory), the first memory for storing the sampling value measured in the CSTW pattern area; And a second memory for storing the sampling value measured in the ASTW pattern region.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, if it is determined that the detailed description of the related well-known configuration or function may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a diagram illustrating a disc in which a CSTW pattern region and an ASTW pattern region coexist.

The portion A recorded by the servo writer occupies a predetermined area (about 3,000 to 4,000 tracks) of the outer area of the disc. After recording servo information in the predetermined area, a spiral seed pattern is recorded in an adjacent track, and a servo pattern B is recorded in an inner area direction through a servo copying of the spiral seed pattern. The spiral seed pattern is a form in which bits of a certain frequency are listed and have sinks arranged at regular intervals.

In the servo copying process, final servo information is recorded in concentric tracks formed by connecting sinks of a predetermined position in each spiral track. As described above, when the servo recording methods are used differently in one disc, a change in the interval between tracks appears before and after the boundary of the area. In general, the use of a spiral seed pattern results in a larger track width.

FIG. 2 is a diagram for illustrating a difference in track per inch (TPI) between a CSTW pattern region and an ASTW pattern region.

Referring to FIG. 2, the Conventional Servo Track Write (CSTW) pattern area recorded on the outer periphery of the disc has a track width of about 470 nm per track, whereas the ASTW (Ammonite Servo Trck Write) pattern area has a track width of about 490 nm per track. Has In other words, the track becomes nonuniform between the CSTW pattern area and the ASTW pattern area. This causes a wrong servo control signal to be generated when performing the servo calibration operation by interpolation.

3 is a diagram illustrating a relative position of a servo burst signal with respect to a track.

Referring to FIG. 3, the A, B, C, and D bursts are servo bursts for obtaining the PES signal. These servo bursts are recorded in a constant order in the track direction and in a constant phase relationship with each other in the radial direction of the disc. There are other E and F bursts (not shown) to compensate for MR skew.

The center line of the target track is the boundary position between the A burst and the B burst, that is, the position where the magnitude of the A burst and the magnitude of the B burst are read by the read head. When the center of the read head is located at the boundary position of the A burst and the B burst (center line of the target track), the area of the A burst and the B burst scanned by the read head is the same. C bursts and D bursts are needed to accurately detect how far the read head is from the center of the track.

By demodulating the A, B, C, and D bursts, the relative position of the head and the track centerline can be determined. In this case, PES is calculated in different ways depending on the degree of head offtrack. For example, when the head is offtracked to 5% or less based on the track center line, the position of the head is compensated by using AB_Slope (hereinafter, referred to as a first position offset) calculated by Equation 1 below.

Also, for example, when the head is offtracked by more than 5% and less than 45% based on the track centerline, the head may be controlled by using NP_Slope or NP_Offset (hereinafter referred to as second position offset) calculated by Equation 2 below. To compensate for the position.

,

,

The first position offset and the second position offset are parameters for head position control in addition to the MR offset. As described above, the MR offset is caused by the difference in position between the recording head and the reading head. The offset is not large in the middle diameter (MD) region, but is large in the inner diameter (ID) region or the outer diameter (OD) region. Seems.

4A is a diagram illustrating a first position offset to compensate for the head position when the head is offtracked to 5% or less. 4B shows a second position offset to compensate for head position when the head offtracks above 5% and below 45%. 4C is a diagram showing MR skew due to the positional difference between the recording head and the reading head.

4A to 4C, it can be seen that the first position offset AB_Slope is the largest in the MD region and the small in the ID or OD region, and the second position offset NP_Offset is the smallest in the MD region. Or it can be seen that the large in the OD region, MR skew is the smallest in the MD region, and the larger toward the ID region or OD region, it can be seen that it changes linearly.

Performing the first and second position offset and MR offset measurements on all tracks of the disc is subject to realistic constraints. Because there are typically 160,000 to 180,000 tracks on a disk, the memory capacity is too much to be stored and used in the disk's maintenance cylinder or non-volatile memory for every offset for each track. to be.

Therefore, the entire disc is divided equally into a plurality of zones each including a sampling position, and interpolation is performed using the sampling values of the parameters measured at the sampled positions of each zone to compensate for the target track. Determine the value. 4A to 4C, the plurality of circles represent the sampling positions. However, this method does not consider the track density difference between the CSTW pattern region and the ASTW pattern region, and a problem occurs when the head tracks within a predetermined range based on the boundary line between the CSTW pattern region and the ASTW pattern region.

FIG. 5A is a diagram showing an error of MR skew in the CSTW pattern region and the ASTW pattern region, and FIG. 5B is a diagram showing the PES error in the CSTW pattern region and the ASTW pattern region.

Conventionally, an entire disc is divided into a plurality of zones having equal intervals (for example, 10 zones), a sampling value is measured at sampled positions of each zone, and calibration using interpolation is performed with reference to this. Thus, assuming that the total tracks of the disc are 200,000, which is divided into 10 zones, one zone occupies 20,000 tracks. In a disc that uses the CSTW system and the ASTW system, the CSTW system by the servo recorder is generally applied to 3,000 to 4,000 tracks. Therefore, at least one sampling position exists in the CSTW pattern region, and may not even exist.

When a sampling position existing in the CSTW pattern region is referred to as a first sampling position, the second sampling position is present in the track 20,000th thereafter, and thus, according to the first sampling value and the second sampling position according to the first sampling position. When the intermediate value of the second sampling value is determined using interpolation, an error occurs at the boundary between the CSTW pattern area and the ASTW pattern area existing between the first and second sampling positions. The probability of occurrence is greatly increased. This is because the two pattern regions have different track densities as described above.

Referring to FIG. 5A, a linear graph for estimating MR skew of tracks existing therebetween is shown with reference to a sampling value measured according to a conventional servo calibration method. This is because the interpolation is based on the sampling values measured in each zone without considering the discontinuity of the track densities of the CSTW pattern region and the ASTW pattern region.

The linear graph which estimates the MR skew of tracks which exist in the meantime with reference to the sampling value measured by the servo calibration method which concerns on this invention is shown by the solid line. This method divides the CSTW pattern region and the ASTW pattern region, divides them into a plurality of zones, and obtains independent sampling data for each pattern region to perform independent calibration. That is, the CSTW pattern region and the ASTW pattern region are divided into K and N-K zones, respectively, and sampling data is measured in each zone to perform calibration through interpolation and extrapolation. Therefore, the accuracy of the calibration can be increased.

Referring to FIG. 5B, the discontinuity of the PES signal calculated through the first position offset AB_Slope and the second position offset NP_Offset according to the conventional scheme is illustrated. When the head follows the track, the PES signal should have linearity over the whole area. However, as described above, when the calibration is performed without considering the track density difference at the boundary line between the CSTW pattern area and the ASTW pattern area, when the head follows the track center line, that is, the offtrack is zero. The PES signal appears discontinuously in the interval. This causes a problem in servo control using PES.

6 is a flowchart illustrating a servo calibration operation according to an embodiment of the present invention.

The boundary line position of the disk where the CSTW pattern region and the ASTW pattern region coexist is searched for (S102). The boundary line usually exists in the OD region and has a track number of 10,000 or less. Since the position of the boundary line is the end of the portion recorded by the servo recorder, the search is easy. Since the spiral seed pattern by the self-servo recording method is recorded on the basis of the boundary line, it is easier to search.

Thereafter, the CSTW pattern region and the ASTW pattern region are divided into K and N-K zones based on the searched boundary line (S104). The reason for setting or dividing a zone for each pattern region as described above is to perform a calibration operation independently for each pattern region. Since the CSTW pattern area occupies a very small area compared to the ASTW pattern area, the section of K zones set in the CSTW pattern area is relatively shorter than the zones NK set in the PSTW pattern area. It is preferable. For example, if 15,000 tracks are allocated to each of the N-K zones, it is preferable to allocate 1,500 tracks to each of the K zones.

In operation S106, a sampling value of a parameter required for servo control is measured at a sampled position among the N zones. One sampled position may exist in each of the N zones. It may also be present in more than that. The sampled position is preferably located at the center of the position occupied by each zone. However, in the case of the K-th zone of the CSTW pattern region and the K + 1-th zone existing in the ASTW pattern region as described above, it is preferable to be handled differently. That is, it is preferable that a point close to the boundary line is selected as the sampling position. In that case, the accuracy of the servo calibration can be further increased. The parameters necessary for the servo control may include the first position offset AB_Slope, the second position offset NP_Offset, and an MR skew.

Finally, an independent servo calibration operation is performed for each pattern region based on the measured value of the measured parameter (S108). As a method of performing a servo calibration operation, it is preferable to perform a calibration operation by interpolating each pattern region using the measured sampling data. That is, when performing a track seeking operation, the parameter value when the target track is between the sampling positions is calculated by interpolating the measured sampling data.

However, when the target track exists near the boundary line, the servo control may be inaccurate when the interpolation method is used. Therefore, the parameter value at the point is extrapolated by the method of extrapolating two sampling data in the same pattern area. Estimate For example, if the target track is at the end of the K-th zone of the CSTW pattern method, by performing extrapolation by referring to the sampling values of the K- 1st zone and the sampling value of the K-th zone, Estimate the parameter value. Servo control is performed using the estimated parameter values.

7 is a flowchart illustrating a servo calibration operation according to another embodiment of the present invention.

The boundary line between the CSTW pattern region and the ASTW pattern region is searched (S202), and the CSTW pattern region is divided into K and N-K zones based on the found boundary line (S204). Thereafter, the sampling value of the parameter required for servo control is measured at the sampled position (S206). Since this has been described above, a detailed description thereof will be omitted.

The sampling values of the parameters measured at the sampled positions are classified for each pattern region and stored in the memory in the form of a lookup table (S208). The memory may be a maintenance cylinder provided in a disk or a separate nonvolatile memory. In addition, since the data is stored for each pattern region, the memory may be classified into a first memory for storing sampling values of parameters measured in the CSTW pattern region and a second memory for storing sampling values of parameters measured in the ASTW pattern region. The reason for separately storing each pattern region as described above is described below. Such steps are preferably performed during the manufacturing process of the disk drive.

After the power of the hard disk drive is turned on and a predetermined ready time has elapsed, when the head performs the Seeking operation by the actuator, the target track is located in a certain pattern area. It is determined whether there exists (S212, S214, S216). If the CSTW pattern area or the ASTW pattern area exists, the sampled data values are received from the corresponding memory (the first memory or the second memory) (S220 and S222).

Thereafter, a calibration operation is performed using the received sampling data (S224). In this case, a method of interpolating the measured sampling values is used between zones having the same pattern and the zones, and between the zones having different patterns and the zones, the sampling values measured based on the boundary line are extrapolated. Use the way.

If it is determined as the CSTW pattern area, a calibration operation is performed by receiving a sampled value from the first memory. In this case, only the first memory in which the sampling value for the CSTW pattern region is stored is used. As a result, only the data related to the CSTW pattern region is transmitted not only when the target track exists between the sampled positions of the same pattern region but also when the pattern region exists between different sampled positions. As a result, a calibration operation by extrapolation can be easily performed.

For example, assuming that the target track is located in the K-th zone of the CSTW pattern region, and that the closest sampling values are located in the K-th zone of the CSTW pattern region and the K + 1th zone of the ASTW pattern region, respectively, the calibration operation. Instead of receiving the K th and K + 1 th sampling values, the K th th and K th sampling values are received. This makes it possible to easily perform the calibration operation by the extrapolation without the need for a separate control operation.

If the target track is located at the boundary between the CSTW pattern area and the ASTW pattern area, the section between the track where the CSTW pattern area ends and the tracks where the ASTW pattern area begins is not used, so that the heads are the tracks. If it is in between, after moving the reference distance by a predetermined distance in consideration of the repeatability of the seek operation (S218), the operation to determine the pattern region as described above is repeatedly performed. The calibration operation is then performed.

As described above, since the servo calibration method according to the present invention performs independent calibration operations in consideration of changes in track density between the CSTW pattern region and the ASTW pattern region, it is possible to accurately measure or estimate parameter values necessary for servo control. In this way, the PES can be detected accurately, so that the head can be controlled to accurately follow the center line of the track. That is, data access performance can be improved.

Claims (12)

In the servo calibration method of a disk in which a CSTW pattern region and an ASTW pattern region coexist, Dividing the entire track of the disc into K and N-K zones, respectively, based on a boundary line between the CSTW pattern region and the ASTW pattern region; And Measuring a sampling value of a parameter required for servo control at a sampled position among the N zones, and performing an independent servo calibration operation for each pattern region with reference to the measured sampling value Calibration method. The method of claim 1, Between the zone and the zone having the same pattern, the servo calibration operation is performed by interpolating the measured sampling values. A servo calibration method is performed between a zone having a different pattern and a zone by using a method of extrapolating a sampling value measured based on a boundary line. The method of claim 1, wherein the parameter, A servo calibration method comprising an MR (Magnetic Resistor) skew that occurs due to a positional difference between the write head and read head. The method of claim 1, wherein the parameter, And a first position offset to compensate for the head position when the head mounted on the disc drive is offtracked to 5% or less relative to the center of the track. The method of claim 1, wherein the parameter, And a second position offset to compensate for the head position when the head mounted on the disc drive is offtracked by more than 5% and less than 45% relative to the center of the track. The method of claim 1, wherein the K zones present in the CSTW pattern region, And a smaller width than the N-K zones existing in the ASTW pattern region. The method of claim 1, wherein the sampled position is, Servo calibration method characterized in that at least one exists for each zone. In the servo calibration method of a disk in which a CSTW pattern region and an ASTW pattern region coexist, Dividing the entire track of the disc into K and N-K zones, respectively, based on a boundary line between the CSTW pattern region and the ASTW pattern region; Measuring a sampling value of a parameter required for servo control at a sampled location among the N zones, classifying the data into a pattern area and storing the sampled value in a memory in a lookup table; And Determining a pattern region in which the target track exists and performing a servo calibration operation by receiving a sampling value of a corresponding parameter from the memory when the seek operation is performed on the target track; Servo calibration method. The method of claim 8, Between the zone and the zone having the same pattern, the servo calibration operation is performed by interpolating the measured sampling values. A servo calibration method is performed between a zone having a different pattern and a zone by using a method of extrapolating a sampling value measured based on a boundary line. The method of claim 8, wherein when the target track is at the boundary line, And performing the servo calibration operation at a distance of moving a predetermined track from the target track. The method of claim 8, The memory is a servo calibration method, characterized in that the non-volatile memory (Read Only Memory). The method of claim 8, wherein the memory, A first memory for storing sampling values measured in the CSTW pattern area; And And a second memory for storing the sampling value measured in the ASTW pattern region.

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